The effect of discrete contour bumps on reducing the transonic drag at off-design conditions on an airfoil have been examined. The research focused on fully-turbulent flow conditions, at a realistic flight chord Reynolds number of 30 million. State-of-the-art computational fluid dynamics methods were used to design a new baseline airfoil, and a family of fixed contour bumps. The new configurations were experimentally evaluated in the 0.3-m Transonic Cryogenic Tunnel at the NASA Langley Research center, which utilizes an adaptive wall test section to minimize wall interference. The computational study showed that transonic drag reduction, on the order of 12% -15%, was possible using a surface contour bump to spread a normal shock wave. The computational study also indicated that the divergence drag Mach number was increased for the contour bump applications. Preliminary analysis of the experimental data showed a similar contour bump effect, but this data needed to be further analyzed for residual wall interference corrections.

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A second international AIAA Drag Prediction Workshop (DPW-II) was organized and held in Orlando Florida on June [21][22] 2003. The primary purpose was to investigate the code-to-code uncertainty, address the sensitivity of the drag prediction to grid size and quantify the uncertainty in predicting nacelle/pylon drag increments at a transonic cruise condition. This paper presents an in-depth analysis of the DPW-II computational results from three state-of-the-art unstructured grid NavierStokes flow solvers exercised on similar families of tetrahedral grids. The flow solvers are USM3D -a tetrahedral cell-centered upwind solver, FUN3D -a tetrahedral node-centered upwind solver, and NSU3D -a general element node-centered central-differenced solver.For the wing/body, the total drag predicted for a constant-lift transonic cruise condition showed a decrease in code-to-code variation with grid refinement as expected.For the same flight condition, the wing/body/nacelle/pylon total drag and the nacelle/pylon drag increment predicted showed an increase in codeto-code variation with grid refinement. Although the range in total drag for the wing/body fine grids was only 5 counts, a code-to-code comparison of surface pressures and surface restricted streamlines indicated that the three solvers were not all converging to the same flow solutions-different shock locations and separation patterns were evident. Similarly, the wing/body/nacelle/pylon solutions did not appear to be converging to the same flow solutions.

A 5~cond international AIAA Drag Predictioii \Voikshop (DPW-II) was organized and held in Orlando Florida on June 21-22. 2003. The primary purpose was to investigate the code-to-code uncertainty. address the sensitivity of the drag prediction to grid size and quantify the uncertainty in predicting nacelle/pylon drag increments at a transonic cruise condition. This paper presents an in-depth analysis of the DPW-II computational results from three state-of-the-art unstructured grid NavierStokes flow solvers exercised on similar families of tetrahedral grids. The flow solvers are USM3D -a tetrahedral cell-centered upwind solver. FUN3D -a tetrahedral node-centered upwind solver. and NSU3D -a general element node-centered central-differenced solver.For the wing/body. the total drag predicted for a constant-lift transonic cruise condition showed a decrease in code-to-code variation with grid refinement as expected.For the same flight condition. the wing/body/nacelle/pylon total drag and the nacelle/pylon drag increment predicted showed an increase in codeto-code variation with grid refinement. Although the range in total drag for the wing/body fine grids was only 5 counts. a code-to-code comparison of surface pressures and surface restricted streamlines indicated that the three solvers were not all converging to the same flow solutions-different shock locations and separation patterns were evident. Similarly, the wing/body/nacelle/pylon solutions did not appear to be converging to the same flow solutions.

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