Prediction of Transition Effects on Flap Heating at Hypersonic Speeds

Kurzfassung

Computations of aerodynamic heating along deflected control surfaces of re-entry vehicles fall traditionally short in cases where peak heating is governed by laminar-turbulent transition within the interaction zone of shock and boundary layer. Current practise is to perform fully turbulent computations and to use a special uncertainty factor that accounts for the local overheating due to transition. Besides the drawback that this uncertainty factor must be chosen rather large to cover certain ranges of flow condition and control deflection angles this approach leads to false local distributions of the heat flux since these distributions differ between fully turbulent and transitional flows. Application of traditional transition prediction tools for these problems is difficult because often flow separation is introduced by the interaction and therefore one cannot use boundary layer theory in order to evaluate transition criteria. Here we present the results obtained with the approach to couple an accurate Navier-Stokes solver with an empirical transition correlation and further correlations for the behaviour of turbulence model within the transition region. The Navier-Stokes solver CEVCATS-N [1] is used to compute the laminar and turbulent flow regions over the complete 3D configuration. The laminar part of the flow is analyzed for characteristic boundary layer parameters such as Re*. The turbulence model used in the present work is the Spalart Allmaras model. This model is analysed for compressible flows with heat transfer. It is found that the model needs an extension in the near-wall region in order to predict heat transfer accurately. This extension of the Spalart Allmaras model is described in Section 3. The engineering transition criterion based on the parameter Re*/M* is used in the present work to determine transition location. This correlation yields engineering accuracy for transition processes of the Tollmien-Schlichting type on blunt hypersonic forebodies, according to Ref. tion. AIAA Paper 97-0275, 1997. [2] Finally, the turbulence model within the Navier-Stokes solver is extended by functions that model the desired transitional behaviour of the flow. For general 3D flow computations these functions should be carefully defined because they should not impair the performance of the turbulence model for fully turbulent boundary layers. The detailed formulations are discussed in Section 4. The performance of the coupled procedure is checked for hypersonic transition problems of 3D flows over deflected control surfaces with transition within the interaction region of shock and boundary layer around the hinge line. The results contain a large body of numerical and experimental data that address sensitivities to numerical and experimental flow parameters. It is found that the effect of transition on heating levels and heating distribution is reasonably well reproduced by the computations.