Capturing transition with flow–structure–adaptive KDO RANS model

By extending Bradshaw's assumption from the free shear flows to the wall-bounded flows, the Kinetic energy Dependent Only turbulence model (KDO) established a new Reynolds stress constitution. The Bradshaw function (τ₁₂/k) and the coefficient of the dissipation term are the only two empirical coefficients. They were both calibrated with the turbulent Reynolds number, Re_k=ρk^1/2d/μ which depends on the wall distance. Once the wall distance is replaced with “flow–structure–adaptive” parameters, such as the eddy viscosity ratio, r=μ_t/μ the model could naturally capture various transition phenomena. The improved KDO model is assessed by some test cases including the classic bypass transition of T3A and T3B boundary layers, the natural transition of the T3A boundary layer, and the separation bubble induced transition of Aero-A airfoil. The assessments show that the improved KDO model is not capable of capturing the precise process of the laminar-turbulent flow transition, but the model can accurately predict the transition onset locations. The model does not include specific transition mechanisms; however, for high Reynolds numbers and complex flows with different types of transition, the predictions are reliable.