Transient Dynamics Research on the Force-Measurement System for Hypersonic Impulse Combustion Wind Tunnel Based on Inertia Compensation

The signal detected by a force-measurement system (FMS) is transient in an impulse combustion wind tunnel, and the transient property of the FMS will affect the measurement result significantly. This study presents a method to improve the measurement accuracy of aerodynamic loads and achieve the goal of transient measurement. First, the dynamics equation of the FMS is established. Second, the virtual static calibration and modal analysis are conducted to acquire its coefficient matrix, lower-order natural frequencies, and modes. Third, transient analysis is conducted to obtain its output responses. Results show that the mean value of the test signal can be treated as the output of the aerodynamic loads to a certain degree, and that the measurement accuracy can be improved by an order of magnitude after the inertia compensation. The measurement error rates of the drag, lift load, and pitching moment are lower than 8%, 10%, and 7%, respectively, when the frequency of the input load or moment is far from the natural frequency. However, not only can the balance easily be damaged, but the measurement errors also increase sharply when the frequency of the sine load is equal or close to the natural frequency. The results of a force measurement test show that the inertia compensation method can suppress the disturbance of the inertial loads to the output.