Week 5 - Turbulence modelling challenge
1. Why DNS is not feasible according to Kolmogorov's scale.
Size of the smaller eddies are proportional to 1/Re^(3/4)
In a turbulent flow reynolds number will be high and size of the eddies will be very small. So grid size must be smaller than 1/Re^(3/4) to capture smaller eddies.
In 3D, each dimension of the element must be smaller than the length determined from Kolmogrov scale.
Volume of an element (dV) required to capture an eddy is proportional to 1/Re^(9/4)
Number of elements = V/dV
= Re^(9/4)
Large number of elements is required in DNS which makes it not feasible.
2. AIM: To perform 3D simulation of the given geometry and explain the recirculation region using velocity vectors
Solution procedure:
Geometry model was im ported in the design modeler.
Mesh: Face meshing is applied for the protusions
Nearly 5 lakh elements were generated.
Named selections was provided for inlet, outlet and symmetry.
Solver setting:
Boundary conditions: Velocity inlet: 60m/sec
Pressure Outlet: Atmospheric pressure
Standard Initialization
Results:
Why gof balls have dimples: