Measurement of a bluff body aerodynamic yaw moment magnification and damping using a dynamic wind tunnel facility

This paper describes a technique for determining the dynamic aerodynamic yaw moment derivative based on the time response data using an oscillating model rig. The aerodynamic yaw moment derivatives are initially estimated using oscillation frequency and amplitude decay. The results from the dynamic measurement are compared with conventional static test and presented in the form of aerodynamic magnification. The yaw moment derivative exceeds that determined statically across reduced frequency range measured. The yaw damping derivative was found to be a function of freestream speed; at low velocities it is negative but progressively increases to a positive value. With further increases in speed, a self-sustained oscillation is observed with almost constant frequency and amplitude. This result is attributed to coupling between the model wake and the model stability; however, the exact behavior of the interaction is not fully understood; this phenomenon is under further investigation.