Laminar-turbulent transition has significant importance in aerodynamics by affecting evolution of losses, appearance of separation and stall. The boundary layer state has dominant effect on the distribution of wall shear stress and surface heat transfer. To predict and manage turbulence in different flow cases is beneficial for optimum advantage, namely, to reduce it when it is harmful (e.g. to decrease the skin friction or heat transfer) and to increase it when it is desirable (to avoid flow separation). The prediction of laminar-turbulent transition at high free-stream turbulence is specifically of great importance in turbomachinery where the boundary layer state defines the blade heat transfer and flow separation margins. However it is well-known that prediction of transition is particularly challenging task for turbulence modelling. A number of turbulence models claim possibility of transition prediction and none of them is proven to be flawless so far. Reynolds-averaged Navier-Stokes equations (RANS) approach fails to predict the location of the point of transition in boundary layers because it requires a priori knowledge of the ”location” of the laminar/turbulent transition.



This work investigates the potency of a two layer or zonal wall model in LES to predict laminar to turbulent flow transition over a NACA0012 airfoil at 1 million Reynolds number. The governing equations for momentum and energy are discretized with a conservative finite-volume formulation using a second-order central (SOC) difference scheme on a non-staggered grid topology. The SOC discretization has minimal dissipation and has been shown to be suitable for LES computations. The two layer wall model is formulated by solving a reduced set of simplified equations in the inner wall region of boundary layer. The inner layer equations are solved on a virtual embedded grid along a normal between the first off-wall grid point (y+ <50) and the wall.



Computational Grid:



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                    Figure 1. C-grid, 10 million cells

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Coherent Structures:



































                                     Figure 3. Iso-surfaces of vorticity





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All the details are not presented on the website due to copyright and proprietary issues.

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