On the Application of Transition Correlations in Turbomachinery Flow Calculation

Prediction of boundary-layer transition is important to turbomachine design. Various experimental correlations are still the most practical models used in engineering calculations. In an acceleration or deceleration flow field, however, the predictions depend on the free-stream turbulence intensity incorporated in the correlations. A numerical analysis is therefore presented in this paper to investigate how much the different implementations of the turbulence levels can affect the numerical results. The main emphasis is on the importance of such influence in engineering calculations in comparison with the importance of correlation and grid resolution effects. The analysis is performed using an industrial Reynolds-averaged Navier-Stokes solver with different transition correlations and models of free-stream turbulence intensity. Eight benchmark test cases, including basic incompressible flat-plate cases and more realistic transonic cascade cases, have been calculated. The study reveals that the effects of grid resolution and the choice of correlations on the transition results are relatively small. But a proper presentation of free-stream turbulence intensity in the correlations plays a vital role in this sort of calculation. The use of a computed local turbulence level with the correlations appears to be the most flexible choice among the approaches considered.