Stress wave force balance sting design for magnetohydrodynamic drag force measurements in expansion tubes

This paper discusses the existence of noise observed in measurements taken using a stress wave force balance for magnetohydrodynamic drag measurements in an ionised argon expansion tube test flow. There is compelling evidence to suggest that the noise appearing in the strain gauge signal is a result of electrical interference generated by the ionised test flow. Since the magnetohydrodynamic drag force will generate a signal on a similar order of magnitude to this electrical noise, extracting accurate drag estimations is impractical. This paper analyses a set of new sting designs which aim to increase the signal to noise ratio by reducing axial stiffness of the bar. The materials tested include brass, aluminium, nylon and poly-carbonate. Results indicate that the signal to noise ratio can be improved by a factor of 90 when comparing the signal from the original solid brass design to a new hollow poly-carbonate design