Aerodynamic Damping Measurements From Ambient Excitation of a Slender Model in Mach 5 Flow

Aerothermoelastic dynamic stability involves the coupling of the aerodynamics with rigid body modes and structural modes of the vehicle in hypersonic flight. This experimental study characterizes the aerodynamic damping of a structurally compliant single degree-of-freedom (SDOF) model in the UT Mach 5 blowdown wind tunnel. Free-stream turbulence is shown to induce broadband frequency forcing and structurally excite the SDOF model. The ambient excitation method coupled with different output-only system identification algorithms was used to measure both aerodynamic stiffness and aerodynamic damping. Experimental measurements from optically tracking the structure's motion were compared with predicted structural behavior using steady-state computational fluid dynamic (CFD) results and Newtonian theory. The aerodynamic stiffness results show good agreement between CFD, Newtonian theory, and experimental measurements in the quasi-steady regime. Aerodynamic pitch damping in the Mach 5 flow is shown to be measurable, and the results lie close to the expected values.