Transport-based Transition Prediction for the Common Research Model Natural Laminar Flow Configuration

Kurzfassung

A new, recently published intermittency-based one-equation transition transport model was applied to the NASA Common Research Model Natural Laminar Flow Configuration and the numerical simulation results in terms of the predicted transitions fronts were compared to the results from a two-N-factor strategy based on the eN method and to the transition fronts that were derived from temperature sensitive paint images that were taken during wind tunnel experiments. The new model uses a strongly simplified formulation of the AHD transition criterion and takes compressibility effects into account. The simulation results based on the new model yield transition fronts that agree very well with the transition fronts from the eN-based two-N-factor strategy and the transition fronts derived from temperature sensitive paint images. Because the new model in its current formulation accounts for streamwise transition mechanisms only these findings are a further indication that the design concept of the Common Research Model Natural Laminar Flow Configuration prevents crossflow instabilities to be a relevant transition mechanism at the configuration. This finding confirms the result of the eN-based two-N-factor strategy that does not detect crossflow instabilities of sufficiently high amplification at the transition fronts that were purely due to streamwise transition mechanisms. For the computations that were carried out with the DLR TAU code a reformulation of the sustaining turbulence technique was necessary in order to realize a shielding of all boundary layers (laminar, transitional, and turbulent) at the complete configuration and to make the sustaining turbulence technique work reliably. Effectively, the shielding switches the sustaining terms off inside boundary layers. The current approach is of preliminary character and must be considered as workaround and not as a final formulation of the sustaining terms. A final reliably working und user-friendly new formulation of a modified sustaining turbulence technique has still to be developed.