Aerodynamic Measurements of Hypersonic Free-Flight via Optical Tracking and Bayesian State Estimation

Optical force and moment measurements of hypersonic free-flight can cover a range of attitudes during a single test and avoid difficulties encountered by alternative measurement techniques. However, the signal to noise ratio of image processing is often low, and results require significant smoothing for meaningful interpretation. This work presents a new method for such measurements in which a sigma-point Kalman filter and Rauch–Tung–Striebel smoother compute a state estimate at each time step using images from two or more high-speed camera images. Markers detected in each image are treated as individual system observations, so cameras need not be synchronized nor be viewing similar features. The benefits of this approach are demonstrated with experiments of a cube in Mach 6 flow in the University of Southern Queensland’s TUSQ wind tunnel. Measured aerodynamic coefficients show strong agreement to CFD simulations also conducted as part of this work; average differences are 1.7% and 7.8% of the maximum measured forces and moments, respectively. A discussion on factors influencing the accuracy, uncertainty, and resolution of the results provides guidance to further improve the method. Moreover, this method can be extended to more complex geometry representing space debris and hypersonic vehicles.