UFR 301 Evaluation
Boundary layer interacting with wakes under adverse
pressure gradient  NLR 7301 high lift configuration
Underlying Flow Regime 301 © copyright ERCOFTAC 2004
Evaluation
Comparison of CFD calculations with Experiments
Both the EUROVAL and ECARP proceedings [9, 10] include a discussion on the comparison of experimental and CFD results. The figures comparing predictions with measurements, drawn from the ECARP project, are included in Appendix A. More recent results obtained by Godin et al. [14] are included in the discussion, and comparison figures are shown in Appendix B.
Aerodynamic Coefficients
Partner 
Project 
Turbulence Model 
2.6% gap α = 13.1° 
1.3% gap α = 6°  



 
Experiment 
EUROVAL 



 
BAE 
EUROVAL 
Euler Chien kε 




SAAB 
EUROVAL 
Jones Launder k&epsilon + Wolfshtein BaldwinLomax 




HUT 
EUROVAL 
CebeciSmith 




CERFACS 
EUROVAL 
BaldwinLomax JonesLaunder kε 




Dornier 
EUROVAL 
Baldwin Lomax LamBremhorst kε 




CFD Norway 
EUROVAL 
Baldwin Lomax Chien kε 




BAE 
ECARP 
Chien kε +Wolfshtein KalitzinGould 




CASA 
ECARP 
Ganville/Baldwin Lomax 




CFD Norway 
ECARP 
BaldwinLomax Chien kε Chien kε + length scale correction 




Dornier/DASA LM 
ECARP 
Lam  Bremhorst kε 




HUT 
ECARP 
Menter kω (+ SST) 




KTH 
ECARP 
BaldwinLomax Speziale kτ 




ONERA 
ECARP 
Le Balleur 




SAAB 
ECARP 
JonesLaunder kε + Wolfshtein idem + SST ShihLumleyZhuWolfshtein model 




Table 3 lists the experimental and computed lift and drag (not all data were available on the ECARP CDROM, and missing data were taken from a figure in the book). The first six results in Table 3 concern the EUROVAL project, while the others concern the ECARP project. The conclusions of EUROVAL were that the lift coefficient is reasonably well predicted, while the drag coefficient is largely over predicted. This is attributed to grid inadequacy, and a too high artificial dissipation in the boundary layer. The ECARP results show that the lift coefficient is slightly over predicted. The drag coefficients are computed within 10% of the experimental value, and the systematic over prediction found in the EUROVAL project has disappeared. A discussion on the over prediction of the drag coefficient in the EUROVAL project can be found in [13], and is attributed to the influence of numerical dissipation, and the fact that the far field boundary is too close to the airfoil (10 to 15 chords instead of the required 50 chords). The far field circulation correction mentioned before was developed to correct this last point, and was used by several partners in the ECARP project.
Godin et al. [14] did not provide the aerodynamic coefficients.
Pressure distribution plots
Both the EUROVAL and ECARP results contain Cp plots.
EUROVAL: general agreement with experimental data is good, except for the results provided by CERFACS. This is attributed to the StegerWarming flux splitting scheme which seems to produce an excessive amount of dissipation. Cp distributions of Dornier and CFD Norway on the flap for the 2.6% gap case show some differences with the experimental results, which are attributed to the grid and/or turbulence model. A comparison was made between the full Navier Stokes and Thin layer Navier Stokes formulation, and it was concluded that the full Navier Stokes formulation yielded better results. The thin layer formulation seems to yield more diffusive solutions.
ECARP (see Fig. 5): general agreement with experimental data is good, and it is remarked that the BaldwinLomax algebraic model yields good pressure distributions. Some differences are visible on the flap for the 2.6% gap case, where the SST model slightly overpredicts the Cp.
The results of Godin (see Fig. 14) [14] showed a good agreement with experimental data for both the Spalart Allmaras and Menter SST model for the 2.6% gap case. No overprediction of the Cp on the flap was observed for the Menter SST model.
Skin friction distribution plots
EUROVAL: for the 1.3% gap case, the comparison between experimental and computed Cf is reasonable on the wing, except for the results of CERFACS. On the flap, there is only one experimental data point, and none of the computed results comes close to this value. For the 2.6% gap case, only the results of SAAB using the two layer kε model, and of CFD Norway using the BaldwinLomax model are close to the experimental results on the wing. On the flap large differences are apparent between the computed Cf.
ECARP (see Fig. 6): computed Cf results for the 2.6% gap case are close to the experimental values. Skin friction results obtained with algebraic turbulence models are as good as the results obtained with twoequation models. The Menter SST correction did not yield a significant improvement to the results.
The results of Godin (see Fig. 15) [14] showed a good agreement with experimental data for both the Spalart Allmaras and Menter SST model.
Velocity profiles plots
Velocity profiles were measured at different stations on the flap. Comparison with experimental data is made for stations 8, 12, 13, 14 and 16 (see Figure 1 for the locations). The most interesting phenomena is the mixing of the wake from the wing with the boundary layer on the flap.
EUROVAL: only the results for the 2.6% gap case are presented, and they show substantial differences in measured and computed velocity profiles. Results show that for the upstream stations, the Baldwin Lomax model yields better results than the kε model, due to the faster decay of the wing wake predicted by the kε model. However, further downstream (stations 14 and 16), the kε model produces better results.
ECARP (see Figs. 9 and 11): in general a good agreement between computations and experiments was observed. In particular the BAe KalitzinGould model yielded a very good agreement. Two equation models seem to give a better agreement than algebraic turbulence models, and the results using a coupled viscid/inviscid interaction approach. Using a nonlinear approach (SAAB, ShihLumleyZhuWolfshtein model) did not improve agreement with experiment.
The results of Godin (see Fig. 16) [14] showed a good prediction between calculations and experiments, with the Spalart Allmaras model performing slightly better than the Menter SST model. Note that the ECARP results of HUT using Menter appear to be slightly better than the results of Godin.
Reynolds stress profiles plots
Reynolds stress profiles are available for the case with 2.6% gap. The plotted values shown in Figure 10 and Fig. 17 are qr/U_{∞}^{2} with q and r respectively the instantaneous velocity components along the normal to the surface and parallel to the surface.
EUROVAL: only the results by CFD Norway (using both Baldwin Lomax and the Chien kε model) are realistic, and they show that the kε model predicts the Reynolds stresses slightly better. However, the high Reynolds stress levels at stations 12 and 13 (see Figure 1) could not be predicted.
ECARP (see Fig. 10): the results with the BAe KalitzinGould model yield the best agreement with experimental data, followed by the results from the JonesLaunder, Menter SST, and the JonesLaunderWolfshtein models. Results with the LamBremhorst, and the Le Balleur model are worse. The BAe KalitzinGould model is the only model able to predict the high Reynolds stress levels at stations 12 and 13.
The results of Godin [14] showed that the Spalart Allmaras model predicted the Reynolds stresses in closer agreement with experimental data than the Menter SST model. Comparison of the results obtained with the Spalart Allmaras model and the KalitzinGould model showed that the latter results are closer to the experimental values.
© copyright ERCOFTAC 2004
Contributors: Jan Vos  CFS Engineering SA