Magnetohydrodynamic Drag Force Measurements in an Expansion Tube

The use of a magnetic field to manipulate the shock layer for a re-entry vehicle has been proposed as a possible method for increasing drag of planetary entry vehicles. Whilst the field of magnetohydrodynamics (MHD) is well established, the application of this field to planetary entry vehicles is not well understood. The current state of the literature uses analytical, numerical, and experimental means to investigate the feasibility of this technology. However, the validity of the analytical and numerical methods used thus far have not been well validated due to limited experimental data in realistic flow regimes. For this reason, the current paper presents some of the first measurements in this field done in an expansion tube-a type of facility which seems uniquely suited for this type of study. The unique advantage of the expansion tube is that it can generate high enthalpy flows representative of true flight conditions with a non-ionised freestream. This is one of the critical areas for uncertainty in existing experimental data for magnetohydrodynamic aerobraking, which have been predominantly done in arc jet tunnels. Therefore, the focus of the current paper has been on proving that the magnetohydrodynamic force is present and can be measured in an expansion tube. Two different methods have been investigated to achieve this aim. These are accelerometer measurements and strain measurements. Drag force measurements have been taken with several conditions with the accelerometer technique, however issues have arisen with the strain measurements which have prevented data to have been taken. Issues encountered for both methods have been discussed here, and possible solutions are provided. The acceleration measurements have shown that an MHD force can be measured, but further analysis is required to understand these measurements.