Investigation of Error Sources in the Balance and the Standard Dynamic Model in Wind Tunnels

One of the most suitable measurement tools in wind tunnels is the balance, on which strain gauge bridges are installed to suitably measure the applied strains in dynamic and static situations. This article describes a five component dynamic balance and its stimulation system and investigates their error sources when a standard dynamic model is installed on it. It calculates the system frequency response based on the practical tests to select the appropriate sampling frequency for the data acquisition system. In addition, it presents the design of a suitable filter to remove the noise from the original signal. It also presents a signal quality metric based on the minimization of the in-band noise to optimize the filter. This metric is also used to calibrate the system frequency and detect the signal phase and amplitude variations. The practical measurements in 1.5 Mach number on vertical force of the standard dynamic model show significant noise, phase, and amplitude variations, which indicate the side rotations of the model and the instability of the air current on the model during the test.