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Turbine Fundamentals

Choong KW, profile picture
Choong KW

This document provides an overview of gas turbine design fundamentals and concepts. It discusses the key components of gas turbines, including compressors, burners, and turbines. It covers centrifugal and axial flow designs. The document also presents examples calculations for gas turbine power and efficiency. Overall, the document aims to provide students with an understanding of gas turbine theory, design, practical considerations, and comparisons between different gas turbine types and cycles.

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12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Learning goals • This unit is dedicated to gas turbines and students are expected to gain knowledge and understanding of: Gas turbine theory, Design fundamentals; Practical considerations of gas turbines; Gas turbine comparison.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • Gas turbines have been gradually evolved on the dominant main propulsion and ship-service prime movers for destroyers, frigates, cruisers as well as the foil-borne engines for hydrofoil crafts.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • A gas turbine is a rotodynamic machine which uses a gas compression – combustion – expansion cycle. It differs from a reciprocating internal combustion engine in that: 1 - The compression and expansion is performed using rotodynamic components 2 - The combustion takes place at constant pressure
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • GT are characterised by: – High power to weigth ratios; – Lower thermal efficiency; – High output shaft speed; – Better quality fuels; – High air to fuel ratios; – High power to volume ratios; – High availability; – Lower exhaust gas emissions;
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Centrifugal Turbine and centrifugal compressor
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • The Centrifugal Compressor The centrifugal compressor consists of an impeller enclosed in a casing which contains the diffuser.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle (Illustration © Rolls-Royce Ltd., 1969)
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS compressors (Reprinted with permission of copyright owner, United Technologies Corporation)
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS compressors
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Burners About 15-20% of the air from the compressor passes over swirl vanes as it enters the primary zone of the burner. Here also the fuel is introduced through nozzles as a fine spray of droplets. The swirling air causes the good mixing necessary to support rapid, high temperature combustion.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Burners
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Burners
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Burners • The annular burner is well-suited for an axial flow compressor. It is shown in the air distribution pattern in this type may involve introduction of the compressor air in only the first two zones. The tertiary zone may involve final mixing only. The advantage of this type of burner is that it minimizes size and weight with a sound aerodynamic design.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbines • There are two basic types of turbines, comparable to the two types of compressors. Due to the sizable stresses involved, the radial turbine is generally not suitable for the high temperatures necessary in a gas turbine engine. Therefore, the axial flow turbine is the only type that will be discussed here. (See slide nº7)
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbines
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbines
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbines • Turbines may be of the impulse or reaction type depending on rotor blade design.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbines (a) Impulse turbine rotor blades - The flow passages are of constant cross--sectional area resulting in essentially no flow speed, pressure, or temperature change. Those changes occur in the stationary blades (nozzles). The turning of the flow causes the rotor to move. (b) Reaction turbine rotor blades - The blades act as nozzles to accelerate the flow as pressure and temperature decrease. These processes take place in both the stationary and moving blades.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS GT PTO
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS complex power system
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Calculations exercises Example 1
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle Example 1 A gas turbine unit has a pressure ratio of 10:1 and a maximum cycle temperature of 700ºC. The isentropic efficiencies of the compressor and turbine are 0.82 and 0.85 respectively. Calculate the power output of an electric alternator geared to the gas turbine when the air enters the compressor at 15ºC at a rate of 15kg/s. Take Cp=1.005 kJ/kgK and = 1.4 for the compression Take Cp=1.110 kJ/kgK and = 1.333 for expansion γ γ
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS 2 2 0 v hh += 02,23,2301 hWQh ININ =++ ( )12010212 TTChhW p −=−= ( )2323 TTCQ p −= ( ) ( ) ( )23 1243 23 3412 )( inputheat net work TTC TTCTTC Q WW p pp − −−− = +− ==η The steady flow energy equation applies to each component of the turbine. Defining stagnation enthalpy one can analyse the compressor, for instance, using: In the idealised cycle there is no heat transfer during compression and expansion so (for instance) the specific work (per kg of fluid) Similarly there is no work done in the combustion chamber so The efficiency can then be calculated using
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS 3 4 2 1 1 2 1 T T T T P P k ==⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ = − γ γ ( ) ( ) ( )( ) ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − − −=−= − −− = − −−− = γ γ η 1 23 23 23 23 11 111 rk TT kTT TT kTkT 1 2 P P r = 1 3 T T t = ( ) ( )1243 TTCTTCW pp −−−= ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ −− ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ −= ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − − 11 11 1 γ γ γ γ rrt TC W p Let us assume the compressor and turbine are 100% efficient (no entropy rise) and define the temperature ratio using isentropic formulae as Substituting in equation 4.3 we have (4.4) where r is the pressure ratio, The specific work output can be calculated as a function of pressure ratio r and the non-dimensional peak temperature, i.e. turbine inlet to compressor inlet temperature. (4.5) so (4.6)
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Plotting these efficiency and work relationships with pressure ratio from equations 4.4 and 4.6, we see that efficiency rises with pressure ratio (figure 4.4) for any given peak temperature t there will be some pressure ratio that produces the peak specific power (figure 4.5). At any given pressure ratio, increasing the peak temperature (by injecting more fuel) increases the work output.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • In practice only the simplest gas turbines, driving electrical generators at constant speed, extract power directly from the gas generator shaft as in Figure 4.2. When driving any other load a separate power turbine is desirable: – Increases in load do not slow down the compressor and cause a drop in pressure ratio – The speed:torque characteristic, for a given fuel flow, is much more stable (see figure 4.6) – The starter can rotate the gas generator spool without turning the load
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Calculations exercises Example 2
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle Example 2 A gas turbine takes air at 17ºC and 1.01bar and has a compression ratio of 8:1. The compressor is driven by the HP turbine and the LP turbine drives a CPP via a gear box. The isentropic efficiencies of the compressor and turbines are respectively 0.80, 0.85 and 0.83. Determine the pressure and temperature of the gases entering the power turbine, the net power developed by the unit per kg/s mass flow rate, the net work ratio and the cycle efficiency of the unit. The maximum cycle temperature is 650ºC For the compression process take Cp= 1.005 kJ/kgK and gamma=1.4 For the expansion process take Cp=1.15 kJ/kgK and gamma=1.333 Neglect the fuel mass flow rate.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • The efficiency of an ideal simple cycle gas turbine is purely a function of its pressure ratio. This has two implications: – Efficiency is poor at part-load, when the shaft speed and pressure ratio is lower and one is closer to the self-sustaining point where all the fuel is used purely to overcome component losses – When the effect of component losses is considered, we find that for any peak temperature there is some pressure ratio at which the efficiency peaks: adding further compressor stages will then reduce rather than increase the efficiency.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • The heat exchange cycle overcomes some of these difficulties. The main result of inefficiency in a simple cycle is that the exhaust is hot. Providing it is hotter than the compressor exit temperature one can use a heat exchanger to transfer heat from the exhaust to the air before it enters the combustion chamber: a given turbine entry temperature can thus be achieved with a lower fuel flow than in the equivalent simple cycle
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS recuperated cycle
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Efficiency increases with temperature ratio so the provision of sophisticated turbine cooling systems is beneficial. Efficiency also rises as pressure ratio is reduced but this is at the expense of a drop in specific work so some compromise must be found. Typically heat exchange cycles operate with a pressure ratio of 4 to 5 (compared with 11 to 30 for a large simple cycle engine). 1 3 T T t = The ideal cycle efficiency is then a function of both pressure ratio and the temperature ratio
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS As a further refinement the WR-21 includes an intercooler to cool the air between the LP and HP compressor stages. This leads to a rise in specific power, since less turbine work is required to drive the HP compressor. By itself the intercooler would lead to a drop in efficiency (heat is being wasted); in a recuperated cycle, however, the lower HP compressor exit temperature means that the exhaust gases passing through the recuperator can be cooled further and there is a corresponding rise in efficiency.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS The final WR-21 novelty is that the power turbine has variable throat area nozzle guide vanes. At low powers in a conventional engine the combustor exit temperature must be reduced to limit the power; with a variable area nozzle the power can be reduced by lowering the mass flow whilst maintaining the temperature. Compressor surge is avoided because the gas generator turbine, seeing a higher back pressure, generates less power so the shaft speed and compressor pressure ratio are reduced (which does not have a severe adverse effect on the efficiency since this is a recuperated cycle).
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Compressor theory
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Compressor theory There are basically two ways to analyse how turbomachinery (compressors or turbines) works. 1 - Trace the changes in temperature and pressure from one blade row to the next using velocity triangles, in which we consider flow within each frame of reference (stationary or rotating) to have constant total temperature and pressure along a streamline 2 - By consideration of the overall power input (Euler equation) resulting from the change in angular momentum across the rotor.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Compressor theory ( ) 2 2 1 1 01, 01 01 1 12 tan 2 2 2 rel a p p p C V U T T T U C C C C α= − + = + − 1 01 ,01 01 ,01 − ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ = γ γ T T P P relrel The “rel” suffix indicates that this is a stagnation quantity in the rotating frame. (The total temperature as measured by a thermocouple mounted on the rotor would be different to that measured by a stationary one).
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Compressor theory relrel TT ,01,02 = ( ) 2 2 2 2 02 02, 02, 2 22 tan 2 2 2 rel rel a p p p V C U T T T U C C C C β= − + = + − ( )02 01 1 1 2 2tan tana a p U T T U C C C α β= + − − relrel PP ,01,02 = 1 02 02 01 01 P T P T γ γ −⎛ ⎞ = ⎜ ⎟ ⎝ ⎠ In the absence of heat transfer . (4.8) If we neglect frictional losses and changes in radius and we can apply an isentropic relationship across the whole stage:
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Compressor theory V1 Air relative velocity Ca1Axial velocity component C1Axial velocity component U Blade velocity α, β fluid angles
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Compressor theory
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Combustor • The calculation is based on the following assumptions (figure 4.19): – No pressure drop takes place across the combustor i.e. burner pressure ratio P4/P5. – Heat addition takes place under constant pressure with no work output – The specific heat capacity of flue gas leaving the combustor is equal to that of hot air at the exit temperature. – Fuel used has got a calorific value of 42.7 MJ/kg – Use of the steady flow energy equation with no heat loss to the surrounding and neglecting velocity and potential heads.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Combustor
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Combustor ) 2 () 2 ( 5 2 5 55 ... 4 2 4 44 . z v hmWQz v hm ++=++++ 55 .. 44 . hmQhm =+ 05055 . 04044 . TCmhmTCm pffbp =+η 05054 . 404044 . )1( TCmfhmfTCm pfbp +=+η 05050404 )1( TCfhfTC pfbp +=+η Based on the following assumptions the general steady flow energy equation Can be re-written as ⇒ ⇒ ⇒
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Combustor 04 05 0404 04 05 )1( 1 p p p fb C C f TC hf T T + + = η Burner temperature ratio Nomenclature: T04 = Stagnation temperature at inlet to combustor T05 = Stagnation temperature at outlet from the combustor ηb= Adiabatic efficiency hf= Calorific value of fuel Cp04= Specific stagnation heat capacity at inlet Cp05= Specific stagnation heat capacity at outlet f = Fuel air ratio
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Combustor Graph for estimating the gases temperature at the combustor outlet for a variety of fuels
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbines
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbine • As with the compressor, we can trace the variation of temperature through the turbine using velocity triangles. ( )202 2 2 2 2 02,02 tan2 222 αax ppp rel CU C U T C V C C TT −+=+−= 1 02 ,02 02 ,02 − ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ = γ γ T T P P relrel relrel TT ,02,03 =if uncooled
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbine ( )3,03 2 3 2 3 ,0303 tan2 222 βax p rel pp rel CU C U T C C C V TT −+=+−= ( )320103 tantan βα axax p CCU C U TT −−+=∴ Neglecting frictional losses and changes in radius relrel PP ,02,03 = and we can apply an isentropic relationship across the whole stage: 1 01 03 01 03 − ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ = γ γ T T P P 02 01 , 02 01 is T isen s T TW W T T η − = = − The turbine isentropic efficiency:
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • Raising the pressure ratio by adding more compressor stages increases the efficiency but also raises the combustor inlet temperature: for a given metallurgical limit for the turbine entry temperature (TET) or (TIT) turbine inlet temperature, this implies a reduction in fuel: air ratio and hence on the specific work.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Leading particulars "leading particulars" characterize the engine so that potential customers can tell at a glance whether the engine might suit their needs. Additional factors can then be considered if the engine seems appropriate.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbine blade cooling Cooling is provided by: 1 - convection inside the blade 2 - impingement of air jets inside the NGV 3 - convection within film cooling holes 4 - an insulating “film” of air around the outside the aerofoils.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbine inlet temperature can be an indicator of certain design features of the engine. Higher inlet temperatures necessitate more sophisticated blade and vane cooling mechanisms and more heat resistant metal components. With present technology, 980ºC – 1100ºC is commonly the maximum for continuous use; The engine rotor speed is of importance for applications which require gearing to electric generators, compressors, pumps, or other direct-drive components; The type and number of compressor and turbine stages, pressure ratio, and air flow are mainly of informational interest. These are rarely a determining factor in selection of an engine. Heat Rate (HR) and/or Specific Fuel Consumption (SFC) are often included in the engine description as a measure of engine efficiency.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GT alternator pack GT tandem alternator pack GT compressor pack GT marine propulsion pack
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle Main components of a gas turbine
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GT maintenance
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GT main performance curves
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GT main performance curves
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS COMPRESSOR CHARACTERISTICS • The most important compressor performance characteristics are the pressure ratio, air flow, and rotational speed. The like-new unit has certain physical capabilities which usually represent a maximum for that design. • To characterize the compressor overall operating conditions would involve an unrealistic number of tables and/or graphs.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS axial flow compressor map
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS centrifuge flow compressor map
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • The absolute pressure ratio across the compressor is plotted versus the equivalent flow∗ for several equivalent speeds. The dotted lines indicate efficiency levels. • The equivalent speed and flow (sometimes called corrected speed and flow) refer to the rotational speed and air flow corrected for inlet temperature and pressure. ∗ Several terms, including "referred," "corrected" and "equivalent" flow and speed are in general use. Equivalent flow and speed are the terms used in this course.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • Surge is a damaging process which should be avoided if at all possible, and choke (maximum) flow represents a condition of lowered efficiency as concerns the compressor.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • The following generalizations should be kept in mind when evaluating compressor performance (at a given speed) with the aid of a map: An increase in pressure ratio moves the compressor closer to surge. A decrease in pressure ratio moves the compressor toward maximum flow (choke). For ambient temperature below 15°C, the equivalent speed is greater than actual, and above 15ºC, it is less than actual. An increase in pressure ratio is accompanied by a decrease in mass flow.
12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • Considering the fact that under full load conditions, approximately 2/3 of the turbine power goes toward running the compressor. For this reason, a 5% loss in compressor efficiency can cause as much as 10% loss in overall efficiency! • Another possible source of inefficiency is the air filter. Inlet air filters are generally used in non-aircraft gas turbines.

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Turbine Fundamentals

  • 1. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS
  • 2. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Learning goals • This unit is dedicated to gas turbines and students are expected to gain knowledge and understanding of: Gas turbine theory, Design fundamentals; Practical considerations of gas turbines; Gas turbine comparison.
  • 3. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • Gas turbines have been gradually evolved on the dominant main propulsion and ship-service prime movers for destroyers, frigates, cruisers as well as the foil-borne engines for hydrofoil crafts.
  • 4. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle
  • 5. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • A gas turbine is a rotodynamic machine which uses a gas compression – combustion – expansion cycle. It differs from a reciprocating internal combustion engine in that: 1 - The compression and expansion is performed using rotodynamic components 2 - The combustion takes place at constant pressure
  • 6. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • GT are characterised by: – High power to weigth ratios; – Lower thermal efficiency; – High output shaft speed; – Better quality fuels; – High air to fuel ratios; – High power to volume ratios; – High availability; – Lower exhaust gas emissions;
  • 7. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Centrifugal Turbine and centrifugal compressor
  • 8. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • The Centrifugal Compressor The centrifugal compressor consists of an impeller enclosed in a casing which contains the diffuser.
  • 9. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle (Illustration © Rolls-Royce Ltd., 1969)
  • 10. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS compressors (Reprinted with permission of copyright owner, United Technologies Corporation)
  • 11. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS compressors
  • 12. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Burners About 15-20% of the air from the compressor passes over swirl vanes as it enters the primary zone of the burner. Here also the fuel is introduced through nozzles as a fine spray of droplets. The swirling air causes the good mixing necessary to support rapid, high temperature combustion.
  • 13. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle
  • 14. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Burners
  • 15. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle
  • 16. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Burners
  • 17. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Burners • The annular burner is well-suited for an axial flow compressor. It is shown in the air distribution pattern in this type may involve introduction of the compressor air in only the first two zones. The tertiary zone may involve final mixing only. The advantage of this type of burner is that it minimizes size and weight with a sound aerodynamic design.
  • 18. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbines • There are two basic types of turbines, comparable to the two types of compressors. Due to the sizable stresses involved, the radial turbine is generally not suitable for the high temperatures necessary in a gas turbine engine. Therefore, the axial flow turbine is the only type that will be discussed here. (See slide nº7)
  • 19. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbines
  • 20. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbines
  • 21. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbines • Turbines may be of the impulse or reaction type depending on rotor blade design.
  • 22. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbines (a) Impulse turbine rotor blades - The flow passages are of constant cross--sectional area resulting in essentially no flow speed, pressure, or temperature change. Those changes occur in the stationary blades (nozzles). The turning of the flow causes the rotor to move. (b) Reaction turbine rotor blades - The blades act as nozzles to accelerate the flow as pressure and temperature decrease. These processes take place in both the stationary and moving blades.
  • 23. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS GT PTO
  • 24. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS
  • 25. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS
  • 26. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS complex power system
  • 27. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS
  • 28. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS
  • 29. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Calculations exercises Example 1
  • 30. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle Example 1 A gas turbine unit has a pressure ratio of 10:1 and a maximum cycle temperature of 700ºC. The isentropic efficiencies of the compressor and turbine are 0.82 and 0.85 respectively. Calculate the power output of an electric alternator geared to the gas turbine when the air enters the compressor at 15ºC at a rate of 15kg/s. Take Cp=1.005 kJ/kgK and = 1.4 for the compression Take Cp=1.110 kJ/kgK and = 1.333 for expansion γ γ
  • 31. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS 2 2 0 v hh += 02,23,2301 hWQh ININ =++ ( )12010212 TTChhW p −=−= ( )2323 TTCQ p −= ( ) ( ) ( )23 1243 23 3412 )( inputheat net work TTC TTCTTC Q WW p pp − −−− = +− ==η The steady flow energy equation applies to each component of the turbine. Defining stagnation enthalpy one can analyse the compressor, for instance, using: In the idealised cycle there is no heat transfer during compression and expansion so (for instance) the specific work (per kg of fluid) Similarly there is no work done in the combustion chamber so The efficiency can then be calculated using
  • 32. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS 3 4 2 1 1 2 1 T T T T P P k ==⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ = − γ γ ( ) ( ) ( )( ) ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − − −=−= − −− = − −−− = γ γ η 1 23 23 23 23 11 111 rk TT kTT TT kTkT 1 2 P P r = 1 3 T T t = ( ) ( )1243 TTCTTCW pp −−−= ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ −− ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ −= ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − − 11 11 1 γ γ γ γ rrt TC W p Let us assume the compressor and turbine are 100% efficient (no entropy rise) and define the temperature ratio using isentropic formulae as Substituting in equation 4.3 we have (4.4) where r is the pressure ratio, The specific work output can be calculated as a function of pressure ratio r and the non-dimensional peak temperature, i.e. turbine inlet to compressor inlet temperature. (4.5) so (4.6)
  • 33. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Plotting these efficiency and work relationships with pressure ratio from equations 4.4 and 4.6, we see that efficiency rises with pressure ratio (figure 4.4) for any given peak temperature t there will be some pressure ratio that produces the peak specific power (figure 4.5). At any given pressure ratio, increasing the peak temperature (by injecting more fuel) increases the work output.
  • 34. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • In practice only the simplest gas turbines, driving electrical generators at constant speed, extract power directly from the gas generator shaft as in Figure 4.2. When driving any other load a separate power turbine is desirable: – Increases in load do not slow down the compressor and cause a drop in pressure ratio – The speed:torque characteristic, for a given fuel flow, is much more stable (see figure 4.6) – The starter can rotate the gas generator spool without turning the load
  • 35. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Calculations exercises Example 2
  • 36. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle Example 2 A gas turbine takes air at 17ºC and 1.01bar and has a compression ratio of 8:1. The compressor is driven by the HP turbine and the LP turbine drives a CPP via a gear box. The isentropic efficiencies of the compressor and turbines are respectively 0.80, 0.85 and 0.83. Determine the pressure and temperature of the gases entering the power turbine, the net power developed by the unit per kg/s mass flow rate, the net work ratio and the cycle efficiency of the unit. The maximum cycle temperature is 650ºC For the compression process take Cp= 1.005 kJ/kgK and gamma=1.4 For the expansion process take Cp=1.15 kJ/kgK and gamma=1.333 Neglect the fuel mass flow rate.
  • 37. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS
  • 38. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • The efficiency of an ideal simple cycle gas turbine is purely a function of its pressure ratio. This has two implications: – Efficiency is poor at part-load, when the shaft speed and pressure ratio is lower and one is closer to the self-sustaining point where all the fuel is used purely to overcome component losses – When the effect of component losses is considered, we find that for any peak temperature there is some pressure ratio at which the efficiency peaks: adding further compressor stages will then reduce rather than increase the efficiency.
  • 39. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • The heat exchange cycle overcomes some of these difficulties. The main result of inefficiency in a simple cycle is that the exhaust is hot. Providing it is hotter than the compressor exit temperature one can use a heat exchanger to transfer heat from the exhaust to the air before it enters the combustion chamber: a given turbine entry temperature can thus be achieved with a lower fuel flow than in the equivalent simple cycle
  • 40. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS recuperated cycle
  • 41. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Efficiency increases with temperature ratio so the provision of sophisticated turbine cooling systems is beneficial. Efficiency also rises as pressure ratio is reduced but this is at the expense of a drop in specific work so some compromise must be found. Typically heat exchange cycles operate with a pressure ratio of 4 to 5 (compared with 11 to 30 for a large simple cycle engine). 1 3 T T t = The ideal cycle efficiency is then a function of both pressure ratio and the temperature ratio
  • 42. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS As a further refinement the WR-21 includes an intercooler to cool the air between the LP and HP compressor stages. This leads to a rise in specific power, since less turbine work is required to drive the HP compressor. By itself the intercooler would lead to a drop in efficiency (heat is being wasted); in a recuperated cycle, however, the lower HP compressor exit temperature means that the exhaust gases passing through the recuperator can be cooled further and there is a corresponding rise in efficiency.
  • 43. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS The final WR-21 novelty is that the power turbine has variable throat area nozzle guide vanes. At low powers in a conventional engine the combustor exit temperature must be reduced to limit the power; with a variable area nozzle the power can be reduced by lowering the mass flow whilst maintaining the temperature. Compressor surge is avoided because the gas generator turbine, seeing a higher back pressure, generates less power so the shaft speed and compressor pressure ratio are reduced (which does not have a severe adverse effect on the efficiency since this is a recuperated cycle).
  • 44. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Compressor theory
  • 45. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Compressor theory There are basically two ways to analyse how turbomachinery (compressors or turbines) works. 1 - Trace the changes in temperature and pressure from one blade row to the next using velocity triangles, in which we consider flow within each frame of reference (stationary or rotating) to have constant total temperature and pressure along a streamline 2 - By consideration of the overall power input (Euler equation) resulting from the change in angular momentum across the rotor.
  • 46. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Compressor theory ( ) 2 2 1 1 01, 01 01 1 12 tan 2 2 2 rel a p p p C V U T T T U C C C C α= − + = + − 1 01 ,01 01 ,01 − ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ = γ γ T T P P relrel The “rel” suffix indicates that this is a stagnation quantity in the rotating frame. (The total temperature as measured by a thermocouple mounted on the rotor would be different to that measured by a stationary one).
  • 47. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Compressor theory relrel TT ,01,02 = ( ) 2 2 2 2 02 02, 02, 2 22 tan 2 2 2 rel rel a p p p V C U T T T U C C C C β= − + = + − ( )02 01 1 1 2 2tan tana a p U T T U C C C α β= + − − relrel PP ,01,02 = 1 02 02 01 01 P T P T γ γ −⎛ ⎞ = ⎜ ⎟ ⎝ ⎠ In the absence of heat transfer . (4.8) If we neglect frictional losses and changes in radius and we can apply an isentropic relationship across the whole stage:
  • 48. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Compressor theory V1 Air relative velocity Ca1Axial velocity component C1Axial velocity component U Blade velocity α, β fluid angles
  • 49. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Compressor theory
  • 50. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Combustor • The calculation is based on the following assumptions (figure 4.19): – No pressure drop takes place across the combustor i.e. burner pressure ratio P4/P5. – Heat addition takes place under constant pressure with no work output – The specific heat capacity of flue gas leaving the combustor is equal to that of hot air at the exit temperature. – Fuel used has got a calorific value of 42.7 MJ/kg – Use of the steady flow energy equation with no heat loss to the surrounding and neglecting velocity and potential heads.
  • 51. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Combustor
  • 52. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Combustor ) 2 () 2 ( 5 2 5 55 ... 4 2 4 44 . z v hmWQz v hm ++=++++ 55 .. 44 . hmQhm =+ 05055 . 04044 . TCmhmTCm pffbp =+η 05054 . 404044 . )1( TCmfhmfTCm pfbp +=+η 05050404 )1( TCfhfTC pfbp +=+η Based on the following assumptions the general steady flow energy equation Can be re-written as ⇒ ⇒ ⇒
  • 53. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Combustor 04 05 0404 04 05 )1( 1 p p p fb C C f TC hf T T + + = η Burner temperature ratio Nomenclature: T04 = Stagnation temperature at inlet to combustor T05 = Stagnation temperature at outlet from the combustor ηb= Adiabatic efficiency hf= Calorific value of fuel Cp04= Specific stagnation heat capacity at inlet Cp05= Specific stagnation heat capacity at outlet f = Fuel air ratio
  • 54. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Combustor Graph for estimating the gases temperature at the combustor outlet for a variety of fuels
  • 55. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbines
  • 56. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbine • As with the compressor, we can trace the variation of temperature through the turbine using velocity triangles. ( )202 2 2 2 2 02,02 tan2 222 αax ppp rel CU C U T C V C C TT −+=+−= 1 02 ,02 02 ,02 − ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ = γ γ T T P P relrel relrel TT ,02,03 =if uncooled
  • 57. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbine ( )3,03 2 3 2 3 ,0303 tan2 222 βax p rel pp rel CU C U T C C C V TT −+=+−= ( )320103 tantan βα axax p CCU C U TT −−+=∴ Neglecting frictional losses and changes in radius relrel PP ,02,03 = and we can apply an isentropic relationship across the whole stage: 1 01 03 01 03 − ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ = γ γ T T P P 02 01 , 02 01 is T isen s T TW W T T η − = = − The turbine isentropic efficiency:
  • 58. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • Raising the pressure ratio by adding more compressor stages increases the efficiency but also raises the combustor inlet temperature: for a given metallurgical limit for the turbine entry temperature (TET) or (TIT) turbine inlet temperature, this implies a reduction in fuel: air ratio and hence on the specific work.
  • 59. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Leading particulars "leading particulars" characterize the engine so that potential customers can tell at a glance whether the engine might suit their needs. Additional factors can then be considered if the engine seems appropriate.
  • 60. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbine blade cooling Cooling is provided by: 1 - convection inside the blade 2 - impingement of air jets inside the NGV 3 - convection within film cooling holes 4 - an insulating “film” of air around the outside the aerofoils.
  • 61. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle
  • 62. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS
  • 63. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS Turbine inlet temperature can be an indicator of certain design features of the engine. Higher inlet temperatures necessitate more sophisticated blade and vane cooling mechanisms and more heat resistant metal components. With present technology, 980ºC – 1100ºC is commonly the maximum for continuous use; The engine rotor speed is of importance for applications which require gearing to electric generators, compressors, pumps, or other direct-drive components; The type and number of compressor and turbine stages, pressure ratio, and air flow are mainly of informational interest. These are rarely a determining factor in selection of an engine. Heat Rate (HR) and/or Specific Fuel Consumption (SFC) are often included in the engine description as a measure of engine efficiency.
  • 64. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GT alternator pack GT tandem alternator pack GT compressor pack GT marine propulsion pack
  • 65. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle Main components of a gas turbine
  • 66. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GT maintenance
  • 67. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GT main performance curves
  • 68. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GT main performance curves
  • 69. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS COMPRESSOR CHARACTERISTICS • The most important compressor performance characteristics are the pressure ratio, air flow, and rotational speed. The like-new unit has certain physical capabilities which usually represent a maximum for that design. • To characterize the compressor overall operating conditions would involve an unrealistic number of tables and/or graphs.
  • 70. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS axial flow compressor map
  • 71. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS centrifuge flow compressor map
  • 72. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • The absolute pressure ratio across the compressor is plotted versus the equivalent flow∗ for several equivalent speeds. The dotted lines indicate efficiency levels. • The equivalent speed and flow (sometimes called corrected speed and flow) refer to the rotational speed and air flow corrected for inlet temperature and pressure. ∗ Several terms, including "referred," "corrected" and "equivalent" flow and speed are in general use. Equivalent flow and speed are the terms used in this course.
  • 73. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • Surge is a damaging process which should be avoided if at all possible, and choke (maximum) flow represents a condition of lowered efficiency as concerns the compressor.
  • 74. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • The following generalizations should be kept in mind when evaluating compressor performance (at a given speed) with the aid of a map: An increase in pressure ratio moves the compressor closer to surge. A decrease in pressure ratio moves the compressor toward maximum flow (choke). For ambient temperature below 15°C, the equivalent speed is greater than actual, and above 15ºC, it is less than actual. An increase in pressure ratio is accompanied by a decrease in mass flow.
  • 75. 12/2006 School of Marine Science and TechnologySchool of Marine Science and Technology University of NewcastleUniversity of Newcastle GAS TURBINE DESIGN FUNDAMENTALS • Considering the fact that under full load conditions, approximately 2/3 of the turbine power goes toward running the compressor. For this reason, a 5% loss in compressor efficiency can cause as much as 10% loss in overall efficiency! • Another possible source of inefficiency is the air filter. Inlet air filters are generally used in non-aircraft gas turbines.