L1T2 3 element airfoil

Application Challenge 1-08 © copyright ERCOFTAC 2004

Comparison of Test data and CFD

A comparison between the computed and measured surface pressure coefficients for the two incidences is shown in Figure 3. The agreement between the CFD and experimental results is, in general, excellent. There is some small discrepancy at the slat trailing edge for the higher incidence case, where the experimental suction levels are slightly higher and the pressure recovery is a little gentler.

In Figure 4, normal to the surface profiles of total pressure coefficient at four locations for the lower incidence case are presented. It is evident that the CFD calculation is predicting a small, but significant, total pressure deficit due to the wake from the slat. This deficit is still evident at the 50% flap chord location, but has disappeared completely by the flap trailing edge location. By contrast, there is no evidence of a slat wake deficit in the experimental results.

The total pressure deficit due to the wake from the main element is reasonably well predicted by the CFD code. However, there is a small difference in the normal traverse location of the minimum at the 50% flap position. At the flap trailing edge location, the total pressure at the edge of the boundary layer is higher for the CFD prediction. In addition, the CFD simulation predicts a greater spreading of the main element wake at this location than indicated by the experiment.

The total pressure coefficient profiles for the higher incidence test case are shown in Figure 5. By contrast with the lower incidence case, the slat wake deficit is evident in both the CFD and experimental profiles at all locations. The agreement between CFD and experiment for the total pressure deficits for the slat wake at the 35% location and the main-element deficit just downstream of the shroud trailing edge are reasonable. However, further downstream the CFD tends to over predict these deficit levels. In addition, there are differences between CFD and experiment for the normal traverse location of the maximum deficit for the two wakes. It may be further observed that the CFD code tends to under predict the mixing between the slat and main element wakes.

In conclusion, the prediction of surface pressures by RANSMB for the L1T2 test case is in excellent agreement with the experimental measurements over a wide incidence range. This is despite differences in the detail between CFD and experiment for the boundary layer and wake profiles. Therefore, the CFD prediction of lift coefficient by integration of surface pressures can be obtained with a fair degree of accuracy.