Low speed longitudinal dynamic stability analysis of a hypersonic waverider using unsteady Reynolds averaged Navier Stokes forced oscillation simulations

Abstract

Hypersonic waveriders have the potential to significantly reduce travel times on long haul civilian transport routes. The design of hypersonic aircraft is heavily influenced by the aerodynamic efficiency at the cruise Mach number, resulting in less than ideal geometries for subsonic flight. Waverider aerodynamics and stability in the low speed regime is rarely investigated and not well understood, but is crucial for horizontal take-offs and landings. To date, low speed analyses of waverider shapes is confined to static investigations, with no studies on the dynamic behaviour ever completed. This paper presents results from unsteady Reynolds Averaged Navier Stokes simulations modelling pitching and plunging forced oscillations of the low speed propelled variant of the Mach 8 HEXAFLY-INT waverider. Tests were conducted at a speed of 20 m/s, which correlates to a Reynolds number of approximately 1.5×106. Pitching and plunging oscillations were at 1 Hz with an angle of attack amplitude of 1 degree. The vehicle was analysed through an angle of attack range from -5 to 15 degrees in 5 degree increments. Results for the HEXAFLY-INT aircraft at the nominal centre of gravity location, 44.4% of the vehicle length, show that the vehicle is positively damped for all cases tested. Static derivative predictions extracted from the dynamic data showed strong agreement with existing static CFD and wind tunnel results. Further dynamic investigations conducted at a centre of gravity location of 53.1% of the vehicle length, the aft static stability limit, also showed positive damping. For these cases, the derivative magnitudes were lower, which indicates decreased damping compared to the nominal centre of gravity location. The vehicle was generally not sensitive to changes in driving frequency, with oscillation rates ranging from 0.5 to 2 Hz tested. However, during plunging tests, the pitching moment derivative was seen to change by as much as 22%. This is attributed to changes in the leading edge vortices with AoA rate. The results from this study, along with previous work looking at the static aerodynamics, stability and control authority, show the feasibility of moving to the flight test phase, but the aircraft dynamic stability in the lateral-directional planes must first be investigated.