Improvement and verification of γ-Rē_θt transition model

A defect of γ-Rē_θt transition model in outflow transition simulation, i.e., secondary wall friction coefficient up-jump in turbulent zone was investigated and the solution was proposed. The reason of secondary friction coefficient up-jump phenomena was discussed and proved to be the inappropriate solution of transitional momentum thickness Reynolds number that resulted in the failure of boundary layer indicator in the transition model. This problem was addressed by a boundary layer indicator defined by the ratio of shear stress magnitude over vorticity magnitude. When the secondary friction coefficient up-jump was suppressed, friction coefficient value in turbulent zone was lower than expectation. To solve this problem, a viscos sublayer indicator was introduced by Langtry in early time. However, that indicator may be active outside the boundary layer, leading to an incorrect solution of intermittency. To address this problem, a limiter based on viscosity ratio, intermittency and boundary layer indicator was defined upon the viscos sublayer indicator. Finally, the case was validated by flat plate Aerospatiale A-foil and a Reynolds number of 2.1×10⁷ NACA 64₂A015 finite wing. Results show that the modification introduced improves the capture of γ-Rē_{θ t} transition model to boundary layer and viscos sublayer, and friction coefficient distribution is better predicted.