A modular RANS approach for modeling hypersonic flow transition on a scramjet-forebody configuration

In this study, the laminar-turbulent flow transition scenario on a 20%-scale X-51A forebody configuration, is simulated with a recently proposed RANS (Reynolds-Averaged Navier–Stokes) transition/turbulence model, which takes into account of the rational effects of compressibility, crossflow and flow-separation characteristics on different instability modes in 3-D boundary-layer flows (Fu and Wang 2013). First, we perform model validation with a number of available experiments on boundary layer transition including hypersonic flows past sharp leading-edge flat plates and cones, nose blunted cones and double ramps. Moreover, a new formula is established to convert measured free-stream noise level to FSTI (free-stream turbulence intensity) that is more adopted by engineering transition approaches. The results show generally good agreement with experimental data, proving that the present model responds accurately to both FSTI and leading edge radii. Then, a simplified analysis is proposed to characterize the present model behavior in pre-transitional flow regions. The results identify the model capability of the transition onset prediction with regard to the influences of nose bluntness as well as roughness elements. Finally, the success in its application to the forebody configuration (with/without trips) under both quiet and noisy conditions, indicates that the mixed-mode transition scenario indeed benefits from such a modular prediction approach, which embodies current conceptual understanding of the transition process.