Aerodynamic Drag Measurement in a High-Enthalpy Shock Tunnel

Shock tunnels create very high temperature and pressure in the nozzle plenum and flight velocities up to Mach 20 can be simulated for aerodynamic testing of chemically reacting flows. However, this application is limited due to milliseconds of its test duration (generally 500 μs–20 ms). For the force test in the conventional hypersonic shock tunnel, because of the instantaneous flowfield and the short test time [1–4], the mechanical vibration of the model-balance-support (MBS) system occurs and cannot be damped during a shock tunnel run. The inertial forces lead to low frequency vibrations of the model and its motion cannot be addressed through digital filtering. This implies restriction on the model’s size and mass as its natural frequencies are inversely proportional the length scale of the model. As to the MBS system, sometimes, the lowest natural frequency of 1 kHz is required for the test time of typically 5 ms in order to get better measurement results [2]. The higher the natural frequencies, the better the justification for the neglected acceleration compensation. However, that is very harsh conditions to design a high-stiffness MBS structure, particularly a drag balance. Therefore, it is very hard to carried out the aerodynamic force test using traditional wind tunnel balances in the shock tunnel, though its test flow state with the high-enthalpy is closer to the real flight condition.