AdvancedTraining_4_Boundary_Layers_and_Heat.pdf
Boundary Layers and Heat Transfer

Velocity Boundary Layer
Along the solid surface, the fluid velocity varies from V∞ to zero at the wall -velocity boundary layer δ

Near Wall Treatments
-The boundary layer is a very complex region of high velocity gradient and diffusion dominated development.
-To model it precisely would necessitate an extremely fine grid.
-An empirical relationship is therefore used to describe the shape of the boundary layer so that only one grid cell near the wall is required

Modelling
-Fine grid to resolve thermal and velocity gradients
-Not too fine
-For KE turbulence model, first cell centre MUST be outside laminar sublayer

Heat Transfer
-For smooth walls, heat transfer rate per unit area is related to the ‘Stanton number’:

Heat Transfer
-Stanton number is determined depending on y+ in the near wall cell
-Heat transfer rate is then determined based on temperature difference
-This heat is transferred from solid cell to fluid cell

Friction
-Rer =‘roughness Reynolds number’
-If Rer < 3.3 treat as smooth, otherwise

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