Magnetohydrodynamic drag force measurements in expansion tunnels using an accelerometer-based force balance

An accelerometer-based force balance has been used to measure the magnetohydrodynamic (MHD) drag force which arises when a magnetic field is present in a high-enthalpy ionised flow. This has been conducted using two expansion tunnels, with periods of steady test flow as low as $40\mu \text{s}$. The use of this technique for MHD drag measurements is demonstrated and limitations are discussed. The results show that there is a measurable component of MHD drag in a flow-field where electrodynamic boundary conditions are matched to true flight. Furthermore, it is demonstrated that the measured forces can be attributed exclusively to the MHD effect, with good repeatability. The results indicated that at least $100\mu \text{s}$ of steady flow is required before the MHD force stabilises. Graphic abstract:

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