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The unsteady flowfield around the Stratospheric Observatory for Infrared Astronomy, a reflecting telescope carried inside an open port of a Boeing 747SP, has been simulated by means of detached eddy simulations and unsteady Reynolds-averaged Navier--Stokes simulations. Vortex generators have been placed upstream of the cavity to control the shear layer spanning the opening. The influence of baffles and displacement bodies placed inside the telescope port on the frequencies of acoustic resonant modes was investigated by acoustic simulations, based on the solution of the homogenous Helmholtz equation. The objective of this study is to improve the telescope's performance by mitigating the amplitudes and changing the characteristic frequencies of the pressure fluctuations inside the cavity. The present simulations show that the investigated measures have a high potential to increase the telescope's pointing stability. DOI: 10.2514/1.40777

Numerical and experimental studies have been performed to show the potential for drag reductions of an array of discrete three-dimensional shock control bumps. The bump contour investigated was specifically designed by means of computational-fluid-dynamics-based numerical optimization for wind-tunnel testing on a modern transonic airfoil. The experimental investigations focused on turbulent flow at a Reynolds number of 5 million and were carried out at the Transonic Wind Tunnel Gottingen. Drag reductions of around 10% in the drag-rise region were found in the experiment even though the results were influenced by wind-tunnel interference effects. A detailed numerical study of the wind-tunnel environment reproduced the influence of the wind-tunnel walls on the bump performance and gave good agreement to the experimental results.

This paper presents a method to improve the tip vortex conservation in a computational fluid dynamics simulation of a helicopter main rotor. Our approach uses vortex-adapted Chimera child grids to achieve a local refinement of the grid in the vicinity of the vortex and thus reduce the numerical dissipation of the vortex. The method is applied to the higher-harmonic-control aeroacoustic rotor lest case to evaluate its potential with respect to the prediction of bladevortex interaction airloads. To allow a meaningful comparison with the experimental data, the rotor is trimmed for thrust, as well as for longitudinal and lateral mast moments, using weak fluid-structure coupling with a flight mechanics code. We obtained a good overall agreement with the experimental data for both aerodynamics and blade dynamics. The effect of the improvement in tip vortex conservation is demonstrated by comparison with simulations without Chimera refinement and with the experimental results. It turned out that a very fine grid resolution in the vicinity of the vortex is necessary to capture the blade-vortex interaction airloads. The required grid resolution was provided by a refinement of the vortex-adapted grids, allowing for a very good reproduction of the blade-vortex interaction airloads, especially on the retreating blade side.