3 Turbulence zExamples: zWake of a water near the columnn of a bridge. zDispersion of Smoke in the atmosphere.
4 Definition zA Fluid motion in which velocity,pressure, and other flow quantities fluctuate irregularly in time and space. z“Turbulent Fluid motion is an irregular condition of flow in which the various quantities show a random variation with time and space coordinates, so that statistically distinct average values can be obsevered.” - Hinze z“Turbulence is due to the formation of point or line vortice on which some component of the velocity becomes infinite.:” -Jean Leray
13 (a) ZERO-EQUATION MODELS Advantages -Simplest of Models satisfying the requirements. Disadvantages -Some ad hoc assumptions have to be made regarding boundary layer and velocity.
14 (b) ONE-EQUATION MODELS Turbulence Kinetic Energy Dimensionless Turbulent Viscosity Mean Strain Rate
15 (b) ONE-EQUATION MODELS Advantages -Additional assumptions can be avoided. -Break from the equilibrium concepts in a practical consderation. Disadvantages -The length scale is still a algebraic quantity. -Computationally more difficult.
17 (c) TWO-EQUATION MODELS Advantages -Overcomes the short comings of zero and one equation model. Disadvantages -Not appropriate to use in a viscous sublayer. -Still need to make assumptions.
18 3.Reynolds Stress Models Advantages -More General than Eddy-Viscosity Models. -Better Prediction for flow with sudden changes. -Possible Ultimate turbulence models. Disadvantages -None of the equations can be solved exactly. -Computational difficulty because of more no. of PDE.