MHD Flow Control and Power Generation in Low-Temperature Supersonic Flows

摘要

Report developed under STTR contract for topic AFO5-T016. Results of cold MHD flow deceleration and MHD power-generation experiments conducted at The Ohio State University are presented. MHD effect on the flow is detected from flow static-pressure measurements. The observed static-pressure change is due to the MHD interaction and not Joule heating of the flow in the crossed discharge. Comparison of experimental results with modeling calculations shows that the retarding Lorentz force increases the static-pressure rise produced by Joule heating of the flow, while the accelerating Lorentz force reduces the pressure rise. The experiments show that at the present conditions, the electric current in the MHD power-generation regime is very low, on the order of 1 mA. This is entirely due to the bottleneck effect of the discharge cathode layer at conditions where the MHD open voltage is significantly lower than the cathode-voltage fall. Modeling calculations demonstrate that (1) at the flow conductivities currently achieved in low-temperature MHD flows (sigma approx. 0.1 mho/m), low open voltages reduce the MHD currents by more than two orders of magnitude, and (2) this effect cannot be circumvented by seeding the flow at feasible levels (approx. 0.1% or using electrodes with a high secondary-emission coefficient).