Near-Field Pressure Signature Prediction of NASA X-59 using JAXA’s Unstructured Grid Solver FaSTAR

Abstract

This paper presents near-field pressure signature prediction for the 1.62%-scale model of National Aeronautics and Space Administration (NASA) X-59 using Japan Aerospace Exploration Agency (JAXA)'s unstructured grid solver FaSTAR. Simulations were conducted for two cases: model-only and static pressure rail. The chosen pressure rail was the shark fin type rail (Rail7), which was newly designed and developed at the Japan Aerospace Exploration Agency (JAXA) and used in the corresponding tests at the JAXA 1 m × 1 m supersonic wind tunnel. The pressure signatures obtained in simulations were compared with those measured in the wind tunnel test. In particular, the Rail7 simulation showed better prediction accuracy in terms of the position and level of the shocks. A series of analyses demonstrates the advantage of the shark fin type rails in validation between CFD and wind tunnel testing. In addition, parametric studies were conducted to investigate the characteristics of the shark-fin-type rail in further detail. These studies were focused on reducing the deflection and attenuation effects of the model shocks occurring owing to interference with the shocks generated by the rail, as well as reducing the pressure increase observed at the aft end of the waveform. The results revealed that a thinner rail width, smaller edge angle (i.e., sharper rails), and larger swept angle were potential options for reducing the interference effects of rail shocks. Furthermore, it was demonstrated that the pressure increase at the aft-end could be reduced by moving the model sufficiently away from the rail. Based on the parametric study results, the potential improved shape of the shark-fin-type rail was validated. The proposed improvement prescribes to reduce the width and edge angle by half and increase the swept angle to 60°. The results demonstrated that using the improved rail geometry, the floating-rail results were significantly closer to the free-air results. This indicated that the effects of rail shock have been sufficiently reduced, which is a significant advantage in terms of design verification of low-boom waveforms. We are investigating more optimized rail geometries based on these studies and are working on new rail designs.