Computational Fluid Dynamics (CFD) - Approach to study Incompressible Boundary Layer flows with Turbulence Models

International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2163
Issue 04, Volume 4 (April 2017) (SPECIAL ISSUE) www.ijirae.com
___________________________________________________________________________________________________
IJIRAE: Impact Factor Value – SJIF: Innospace, Morocco (2016): 3.916 | PIF: 2.469 | Jour Info: 4.085 |
ISRAJIF (2016): 3.715 | Indexcopernicus: (ICV 2015): 47.91
IJIRAE © 2014- 17, All Rights Reserved Page -164
Computational Fluid Dynamics (CFD) - Approach to study
Incompressible Boundary Layer flows with Turbulence
Models
1
Darshan, 2
Jagadeesh.Y.J,
3rd
semester M.Tech1
, Associate Professor2
,
BMSITM, Bengaluru,
Abstract- In turbulence models we create mathematical models that describe the flow properties of a flowing fluid. A
turbulence model is a computational procedure to close the system of mean flow equations and so that a more or less
wide variety of flow problems can be calculated. However, far less precision has been achieved in creating a
mathematical model that approximates the physical behavior of turbulent flows. Reynolds stress model is used to get the
flow behavior and compared with the theoretical solution and the inferences are drawn.
I. INTRODUCTION
Due to the development in the Computer Aided Design / Computer Aided Engineering technology, now it is possible to
analysis the fluid flow problem, in general any engineering problems. The CFD approach has come in this way, when
compared to the theoretical and wind tunnel approach. In the present work of flow analysis over cylinder is made for
turbulence models and postprocessor velocity contour. Initially the geometry is created and then the fluid domain is
discritized by mesh. In the solver and postprocessor its solutions and result are obtained. Basically a theory of CFD-
turbulence models and new software tool are applied. This technique may be used for designing of any fluid equipment by
using the advantage of CAE. Because of the chaotic-like and apparently random behavior of turbulence, we will need
statistical techniques for most of our study of turbulence. CFD is a tool that helps solve a wide range of problems in Fluid
Dynamics and Heat transfer. These phenomena are governed by sets of partial differential equations which in most cases
have no analytical solution. In addition to the governing equations, we also need the boundary and initial conditions,
material properties, and geometrical details in order to completely describe the problem.
II. GOVERNING EQUATIONS AND NUMERICAL PROCEDURE
2.1 CONTINUITY EQUATION
Physical principle:- Law of conservation of mass.
t 


 
d + S

VdS =0
2.2 DISCRETISATION METHODS
The discretisation methods i.e. the numerical methods for solving Partial Differential Equations include the Finite
Difference Methods (FDM), the Finite Volume Method (FVM-also known as control volume method), and the Finite
Element Method (FEM). Other methods, such as spectral schemes, boundary element methods and the cellular automata
are used in CFD but their use is limited to special classes of problems. Each type of method yields the same solution if the
grid is fine enough.
2.3 BOUNDARY CONDITIONS
The present problem has three types of boundaries. They are inlet, outlet and wall boundary. The way these boundary
condition are prescribed are:
a) Dirichlet Condition: Inlet---free stream Velocity boundary condition.
b) Outlet – pressure outlet boundary conditions require the specification of static pressure at the outlet boundary-gauge
pressure-atmospheric.
c) Neymann Condition: Wall – In the present case wall temperature with no slip condition.

___________________________________________________________________________________________________
2.4. TURBULENCE MODELS
REYNOLDS STRESS EQUATION MODEL
The most complex classical turbulence model is the Reynolds Stress Equation Model (RSM), also called the second order
or second moment closure model. Several major drawbacks of the k-ε model emerge when it is attempted to predict flows
with complex strain fields or significant body forces. Under such condition the individual Reynolds stresses are poorly
represented even if the turbulent kinetic energy is computed to reasonable accuracy. The exact Reynolds stress transport
equation on the other hand can account for the directional effects of the Reynolds stress field.
The exact equation for the transport of Rij takes the following form:
ijijijijij
ij
DP
Dt
DR
 
Advantages isVery accurate calculation of mean flow properties and all Reynolds stresses for many simple and more
complex flows including wall jets, asymmetric channel and non-circular duct flows and curved flows.Disadvantages isVery
large computing costs (seven extra PDEs).
III. ANALYSIS-RESULT
A given set up whose theoretical solution was available was modeled in GAMBIT and then subjected to analysis in
FLUENT. A comparative study between Reynolds Stress Model models and theoretical was made, the results of which
have been tabulated below. Five hundred iterations were carried out for each of the analysis in Fluent.
3.1. THE EXPERIMENTAL SET UP CONDITION IS AS FOLLOWS:
Atmospheric air at T = 300 K and a free stream velocity of u = 30 m/s flows across a circular cylinder of diameter 3 cm. the
surface of the cylinder is maintained at 400 K.
Properties of Air: Density = 1.225 kg/m3
, Specific Heat Capacity, Cp = 1006.43 J/Kg-K
Thermal Conductivity (K )= 0.0242 W/m-K, Viscosity( ν) = 1.789e-5 kg/m-s
3.2. VELOCITY CONTOURS
Fig:1. Reynolds Stress Model
3.3. TABULATION OF RESULTS:
AVERAGE HEAT TRANSFER
COEFFICIENT (W/M
2
-K)
ERROR % HEAT TRANSFER
RATE (W/M)
ERROR %
THEORETICAL 119.73 - 1128.46 -
FIVE EQUATION MODEL: REYNOLDS STRESS 78.58 34.37 814.72 27.80

___________________________________________________________________________________________________
INTERPRETATION OF RESULTS:
From the above study of the various models using the FLUENT software it is seen that for the given setup of air flowing
across a cylinder the Reynolds stress model agree with the theoretical value.
IV. CONCLUSION
Turbulence is a phenomenon of great complexity and has puzzled theoreticians for over a hundred years. Its appearance
causes radical changes to the flow which can range from the favorable (efficient mixing) to the detrimental (high energy
losses) depending on one’s point of view. The fluctuations associated with associated with turbulence give rise to the extra
Reynolds stresses on the mean flow. What makes turbulence so difficult to tackle mathematically is the wide range of
length and time scales of motion even in flows with very simple boundary conditions.Although the resulting mathematical
expressions of turbulence models may be quite complicated it should never be forgotten that they all contain adjustable
constants that need to be determined as best–fit values from experimental data that contain experimental uncertainties.
NOTATIONS:
P-pressure
k- turbulent kinetic energy
K-mean kinetic energy
µ - viscosity
η-eddy viscosity
 - viscous stress
U,V,W-free stream mean velocity
u’,v’,w’- instantaneous velocity
ρ – density
e – rate of deformation
E – mean rate of deformation
R- Kinetic Reynold stress
Ω- Rotaion term
 -pressure – strain correlation term
D- diffusion
P- rate of production of R
V. REFERENCES
[1]. Schlichting H. (1979 ), Boundary Layer Theory, Seventh Edition, McGraw Hill
[2]. Cho J.T., Chung M.K. (1992) Intermittency Transport Modeling based on Interactions between intermittency and
mean velocity gradients, Journal of Fluid Mechanics, vol. 237, pp. 301-322
[3]. Suzen Y.B., Huang P.G. (2005) Numerical simulation of unsteady wake/blade interactions in low-pressure turbine
flows using an intermittency transport equation, Journal of Turbomachinery, ASME vol.127, pp. 431- 444
[4]. Majumdar S.,Rajani B.N.,Kulkarni D.,Mohan S.,(2003),RANS computation of low speed turbulent flow in complex
configuration, Proceedings, Symposium on State of the Art and Future Trends of CFD at NAL, NAL SP 03 01
[5]. Patankar S. V. (1980), Numerical Heat Transfer and Fluid flow, McGraw-Hill, New York, N.Y.
[6]. Launder B.E., Spalding D.B.(1974), The numerical computation of turbulent flows, Computer Methods in Applied
Mechanics and Engineering, vol 3, p. 269
[7]. Introduction to CFD by H.K. Versteeg and W. Malala Shekera, LongMan Sc & Tech.
[8]. http://www.tfd.chalmers.se/˜lada, Department of Thermo and Fluid Dynamics. Chalmers University of Technology,
G¨oteborg, Sweden, November 2003 Fluent 6.2 Help Manual
[9]. A κ-ε-r equation turbulence modelby Ji Ryong and Myung kyoon Chung,J.fluid Mechanics 1992.vol.237, pp 301 –
322 www.cfd-online.com

Computational Fluid Dynamics (CFD) - Approach to study Incompressible Boundary Layer flows with Turbulence Models

More Related Content

What's hot (20)

Similar to Computational Fluid Dynamics (CFD) - Approach to study Incompressible Boundary Layer flows with Turbulence Models (20)

More from AM Publications (20)

Recently uploaded (20)

Computational Fluid Dynamics (CFD) - Approach to study Incompressible Boundary Layer flows with Turbulence Models