Fomichev V.   Yadrenkin M.  

Assessment of the MHD-interaction parameters using shadow pictures in pulse tests

Reporter: Yadrenkin M.

Measurement of some parameters under pulse test conditions is rather difficult problem when the characteristic time of experiment less than 1 ms. Definition of the MHD-parameter by Stuart (S) is necessary for simulations and studies of the magnetohydrodynamic (MHD) flow control. The most reliable way to define the geometry of MHD-interaction area is the analysis of photos obtained using shadow technique during the process.

To study the MHD flow control the hypersonic air flow have been obtained using MHD-test rig based on a shock tube. The test rig allows simulating the hypersonic air flow with the parameters corresponding to the flight conditions at the altitude of 30 to 50 km with Mach numbers 6–12. The magnet system generates B-field with induction up to 2.2 T. High voltage electrical discharge has been used as a flow ionizer. Time of the MHD-interaction is about 100 μs. Use of the pulse discharge to ionize the flow in B-field (B = 0.1–0.34 T) allows to realize mid-intensity MHD-interaction with value of S parameter of 0.05. It has been seen that the increasing of the shock wave slope angle generated by the thin plate occur. In more intensive MHD-interaction with B = 0.6–0.8 T and S ≈ 0.15-0.2 the attached shock wave transforms to the detached bow shock.

To assess S parameter is necessary to know the geometry of plasma area that is defined by the isoline with minimum of effective electrical conductivity of the flow. Shadow technique allows obtaining photos of the shockwave structure as well as plasma glow. Characteristics of the hypersonic flow can be as-sessed using standard gas-dynamic functions are valid to the process in the shock tube.

On the assumption of that the discharge plasma in the MHD-interaction area exists under conditions of the local thermodynamic equilibrium and that the discharge radiates according to the model of a black body radiation, it has been managed to estimate the relative temperature distribution in the normal direction to the flow integrally. The temperature distribution allows to estimate the equilibrium conductivity of the flow. The discretization of brightness of the flow picture allowed to measure characteristic geometry of the interaction area with effective electrical conductivity.

It has been shown experimentally that the pulse electrical discharge can be used effectively for realization of MHD-interaction in a hypersonic flow. In this case the MHD-interaction allows controlling the shock-wave structure of the flow. The Stuart number can be estimated by the flow visualization and by the measurement of full current in the area of MHD-interaction.

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