Contribution of DLR to the Aerodynamic Data Base of the X-38 Vehicle

Kurzfassung

Numerical results for the X-38 vehicle, shape 3.1 and 8.3 are presented and discussed. For shape 3.1 the present report is a continuation of previous numerical studies carried out at DLR and therefore dedicated to explain and/or clarify specific problems found during those investigations. Flap and aileron efficiency are analyzed with respect to the geometry adopted for the flap, at several Mach numbers and under flight as well as wind tunnel flow conditions. For shape 8.3 the goal of the present study is to demonstrate the ability of CFD to rebuild the experimental investigation carried out for this shape in the S-3 Modane wind tunnel. Aerodynamic coefficients, flap and aileron efficiencies as well as a flow documentation are presented for M=6 and alpha=40°. The results of the present investigation could not explain the differences found between data obtained from CFD and data obtained for the shape 3.1 in the Langley wind tunnel. However, a good agreement between the numerical results and the aerodynamic data base (ADB) is found for both, flap and aileron efficiency, at the investigated flow conditions even though ADB was defined for flight Reynolds number with turbulent boundary layer. Also, the CFD results for shape 8.3 are in good agreement with the data obtained for this shape in the Modane wind tunnel. The present investigation clearly demonstrates that for viscous dominated problems a good experimental/numerical correlation is achieved when not only the same physics but also the same degree of geometrical representation of the configuration is employed for both simulations. In most cases the numerical experimental discrepancies arising by the geometrical simplifications of the CFD configurations are larger than the discrepancies found due to CFD numerical accuracy and/or lack of physical modeling.