Open channel hydraulics
- 2. Open Channel flow is also called as – free Surface flow / gravity flow. EXAMPLES : - is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids 19-07-2020 LMT 2
- 3. Hydraulic Parameters • Depth(d) of the channel, Width(w) of the banks and Velocity(v) of the water. 19-07-2020 LMT 3
- 4. • It can be measured by various methods: • Current meters • Various Floats (light weight wooden block or ball) • By empirical formulae, etc. • It is a ratio of width(w) and area (A)of a cross section. d = A/w Hydraulic Parameters • Depth(d) of the channel, Width(w) of the banks and Velocity(v) of the water. • The width of the river is the distance between the two points on your side of the river times the tangent of the angle. This can also be solved by using any two points on your bank of the river. • Velocity(v) will change along the course of any river, and is determined by factors such as the gradient the volume of water, the shape of the river channel and the amount of friction created by the bed, rocks and plants. • To measure the velocity : Stream Discharge The flow of water through a stream channel is called stream discharge. In most countries, it is measured in cubic meters per second. The following equation defines stream discharge mathematically: Q = V x W x D 19-07-2020 LMT 4
- 5. Results according to Mannings equation obtain from each will be different 19-07-2020 LMT 5
- 6. Laminar/ uniform Turbulent non-uniformTo know whether flow is Laminar or Turbulent: REYNOLD’s NUMBER EQUATION It is a ratio between the products of average velocity (v) and depth (d) to the kinematic viscosity (द्रव्याचा चचकटपणा (विरघळेल पदार्थ जसे salt, minerals in river). = rho – density of water = mew – viscocity Constants 19-07-2020 LMT 6
- 7. Types of flows in Fluvial -hydraulics Types of flows Laminar/ uniform Turbulent non- uniform Streaming Flow/ Sub-critical flow/ Low flow regime Shooting flow/ super-critical/ High Flow regime 19-07-2020 LMT 7
- 8. • Laminar flow - water flow in the stream is not altered in its direction. Water flows as parallel molecular streams. (Such type of flow is very rare in nature.) • Turbulent flow - water flows as discrete eddies and whirls. Caused by channel topography and friction with the river bed Other type of flow (given by engineers) • Helical flow - spiral flow in a stream. Caused by channel shape. Meandering channels cause this type of flow. Helical flow has an important role in sediment transport and deposition, and in the creation of point bars.19-07-2020 LMT 8
- 9. The open channel hydraulics is categorized as critical or sub-critical or super- critical based on the Froude number Fe. Froude number is given by the relation: Froude’s number Fe or Fr. Or Fr = v2 / g.D Ratio between the square of mean velocity to the product of acceleration due to gravity and depth of the water is called as Froude number . Fr < 1 = Streaming (stable flow) = Sub –critical = Low flow regime Fr > 1 = Shooting (turbulent flow) = Super –critical = high flow regime Fr = 1 = Critical flow (ideal condition) = Critical flow Shooting flow/ super-critical/ High Flow regime 19-07-2020 LMT 9
- 10. Shear Stress And Stream Power • Shear Stress (t) is a measure of the force of friction from a fluid acting on a river bed during the flow. In the case of open channel flow, it is the force of moving water against the bed of the channel. • Stream Power is a combination of velocity and shear stress • Hence the stream power is a basis of many sediment transport formulae applied for modeling of sediment deposition and erosion in rivers and reservoirs. 19-07-2020 LMT 10
- 11. Shear Stress • Shear stress in fluids- Rivers shear stress required to mobilize sediments delivered to the channel. When the shear stress equals the critical shear stress, the channel will likely be in equilibrium. 19-07-2020 LMT 11
- 12. Stream power Stream power is the rate of energy dissipation against the bed and banks of a river or stream per unit downstream length. It is given by the equation: where Ω is the stream power, ρ is the density of water (1000 kg/m3), g is acceleration due to gravity (9.8 m/s2), Q is discharge (m3/s), and S is the channel slope. 19-07-2020 LMT 12
- 13. Assignment: Different types of cross sections observed in nature Which type will form turbulent flow? Which type has lowest depth? Which type has maximum velocity? Which type shows meandering cross section? Which type of section must be hilly areas?19-07-2020 LMT 13
- 14. Thank you 19-07-2020 LMT 14