|
|
By Thomas Scheidegger, Fluent Inc Fluent participated in a Drag Prediction Workshop sponsored by the AIAA Applied Aerodynamics Technical Committee in the summer of 2001 1 . This workshop focused on CFD analyses of a wing/ body aircraft configuration tested in three different wind tunnels. FLUENT 5.5 results were presented that made use of a non overlapping multiblock hex mesh of 3.4M cells provided by the Technical Committee. The results were recently recomputed on this mesh and on a different mesh of 1.8M cells provided by Lockheed Martin. Much better agreement with experiment was achieved on both meshes. The Technical Committee specified that the 3.4M cell mesh must resolve the turbulent boundary layer all the way through the viscous sublayer to the surface of the model. Hence, the original calculations were performed with the two layer near wall modeling approach in conjunction with the realizable k-e turbulence model. The flow was assumed to be fully turbulent over the entire surface. While FLUENT was one of the few commercial codes capable of computing converged solutions on the supplied mesh, the predicted drag was too large by about 150 drag counts. Fluent has continued to study this case with the goal of improving the accuracy of the results.
Pressure contours obtained with the Lockheed Martin mesh and the FLUENT 6.0 segregated solver; M= 0.75, a= 2°With the release of FLUENT 6.0, two features were introduced that have dramatically improved the accuracy of the drag polar:
With second order accurate reconstruction of the density, the segregated solver now produces a drag polar virtually identical to that predicted by the coupled solver on the 3.4M cell mesh. Furthermore, with the revision to the wall normal distance calculation, the drag polar predicted by the two solvers on the 3.4M cell mesh is much closer to experimental values. At Mach = 0.75 and lift coefficient C L = 0.7, the drag coefficient C D is now within 20 counts of the mean experimental value, and within the statistical dispersion (21 counts) of the computational results submitted to the Technical Committee, as analyzed by Michael Hemsch 1 . Even better results have been obtained using a slightly modified version of the 1.8M cell wall function mesh supplied to the Technical Committee by Lockheed Martin after the workshop. The importance of the grid is made evident in these calculations, as the improvements to the accuracy of the drag computed by the coupled solver can be attributed solely to the use of the Lockheed Martin mesh. Reference:1. http://aaac.larc.nasa.gov/tsab/cfdlarc/aiaa-dpw/Workshop1/workshop1.html |
FluentNEWS |
||
 |
|
|
|
