UFR 3-05 Evaluation
Shock/boundary-layer interaction (on airplanes)
Underlying Flow Regime 3-05 © copyright ERCOFTAC 2004
Comparison of CFD calculations with Experiments
A detailed comparison of CFD and experimental results can be found in the paper of Hassan and McGuirk . This includes cross plots of surface pressure coefficients and skin frictions together with profiles of the streamwise velocity component, the shear stress, the turbulence kinetic energy and the streamwise and radial normal stress components. The main findings of Hassan and McGuirk with respect to pressure and skin friction coefficients are summarised here and illustrated with cross plots of these coefficients taken from their paper. For more discussion of differences in profiles of flow quantities and their relation to the observed differences in surface pressure and skin friction the reader is referred to . These results can be compared by consulting the CFD data.
Except for the Menter SST model all of the tensorially linear models perform badly. As can be seen from the pressure distribution, the shock is located well downstream of the experimental location and they all fail to predict the pressure plateau in the separation region indicating an insufficiently large recirculation region. The Menter SST model on the other hand gives a very much better prediction of the shock location and pressure plateau. From the skin friction distribution it is seen that the Menter SST model predicts a slightly early separation. The k-ω model gives a separation location close to experiment while the k-ε models give a much delayed separation. This is consistent with the known poor performance of k-ε models under conditions of strong adverse pressure gradient and the improvements that arise from using the ω scale determining equation.
The non-linear models perform much better overall than the linear models (excluding the Menter SST model). Of these models the Speziale model performs least well both in capturing the pressure plateau and in the predicting the separation location. The most significant difference between the Speziale model and the other two models is the lack of any strain dependence in the coefficient Cμ . The Reynolds stress transport models appear to give best overall agreement with experiment as is to be expected although examination of velocity profiles reveals that both these models and the non-linear models lag behind experiment in the flow recovery region.
Figure 1 Cross plots of Cp (left) and Cf (right) for linear models (top row), non-linear models (middle row) and Reynolds stress transport models (bottom row).
© copyright ERCOFTAC 2004
Contributors: Antony Hutton - QinetiQ