Modeling of Natural Transition in Properly Three-Dimensional Flows

The paper describes a method for viscous flow prediction which includes the prediction of transition onset location as an integral part of the calculation. The method is similar to others in that it is based on stability analysis of the boundary layers but acknowledges that solutions of the Reynolds-averaged Navier-Stokes (RANS) equations yield boundary layers of inadequate accuracy when conventional mesh sizes are used. The boundary layers are therefore recomputed to high accuracy by solving the laminar boundary layer equations. Transition onset locations determined by the stability analysis are passed back to the RANS solver for further iterations. The method described in this paper differs from others in that the laminar boundary layer calculation is fully three-dimensional and the stability analysis is through the fully three-dimensional parabolised stability equations for compressible flow. Results are presented to illustrate the capability of the laminar boundary layer method and the effectiveness of the method for solving the parabolised stability equations. In addition, preliminary validation results are presented from calculations of the viscous flow over the AFRL 1303 UCAV concept to demonstrate that the fully three-dimensional laminar boundary layer and stability analysis components can be combined successfully with a RANS method for calculating flows with natural transition