Keisuke Udagawa

MHD Boundary Layer Flow Acceleration Experiments

Experiments on boundary layer separation control by Magnetohydrodynamic (MHD) acceleration of a near-wall flow were conducted in M=1.5 supersonic flow. In the test section, the boundary layer separation was produced in front of a forward-facing step installed at the downstream of the test section. 19 pairs of electrodes were flush-mounted on a wall where the step was placed. Magnetic field was applied perpendicularly to the wall to accelerate the flow near the wall by the Lorentz force. Change of the boundary layer separation bubble was observed using a high-speed camera. The size of the separation bubble was reduced about 10% by applying the MHD interaction. Therefore possibility to control the boundary layer separation by the MHD interaction was experimentally demonstrated.

Experimental Study on Supersonic Flow Control by MHD Interaction

This paper presents demonstration experiments on magnetohydrodynamic (MHD) boundary layer control in M=1.5 supersonic flow. In this study, Cs seeded Ar gas was used to operate DC discharge at low voltage to reduce the Joule heating and to obtain high MHD interaction parameter for boundary layer control that was the ratio of the Lorentz force in boundary layer to the skin friction. The effects of the electromotive force have been observed in electrical current distributions along the flow direction, DC voltage dependency of the magnetic field strength, and DC discharge emission distribution in the boundary layer. These results and the plasma potential distribution measurement with floating probes indicated the DC discharge was operated at low loading factor of about 1.5 while the MHD interaction parameter for boundary layer control was in range from 5 to 8. Modification of the supersonic boundary layer was detected by a high speed response Pitot tube as the modification of the Mach number, because the energy input to the supersonic flow was restricted and the MHD interaction was strong enough to modify the boundary layer flow. Because oblique shock-wave in front of a ramp was influenced by upstream boundary layer flow, the oblique shock wave location was investigated by increasing or reducing the momentum of boundary layer flow by the accelerating Lorentz force or the Joule heating. The oblique shock wave location in front of 10 or 20 deg ramp was moved toward downstream by applying the accelerating Lorentz force and moved to upstream by operating DC discharge without the magnetic field.

Production of Wall-Hugging Fast Ionization Waves for Boundary Layer Control

In order to apply the Lorentz force to boundary layer with low Joule heating, sufficient electrical conductivity of about 1 S/m is required in supersonic air flow. In this research, production of Fast Ionization Waves (FIWs) Discharge in supersonic flow has been studied. The FIWs discharge has attractive features, such as feasibility of efficient ionization, flexible electrode location. When steep-rise high voltage pulse was applied to a hot electrode, the FIWs were produced on the discharge cell. Therefore, pulse power supply with three-stage Magnetic Pulse Compression (MPC) was designed and built up to generate the FIWs. The output peak voltage was (+32) kV or (-32) kV with the 50 ns rise-time, and it was possible to operate the pulse power supply up to f = 3 kHz repetition rate. A hot-electrode made of thin cupper tape was exposed in M=3 supersonic test section. To control the ionization volume, in this research, ground tape was pasted on the outside of the test section wall where the boundary layer developed and the hot-electrode was installed. Two capacitive probes, which could detect electrically-charged FIWs’ front propagation and potential amplitude, were embedded in the wall made of acrylic plastic. The FIWs front velocity and reduced electric field were estimated with the two capacitive probes. The charged wave front were observed in M=3 supersonic flow in the both cases of operating positive and negative repetitive pulse discharge. The wave propagation speed was 0.5 cm/ns, when positive 32 kV pulse was applied to electrode under 1 kHz repetition rate. The reduced electric field was estimated from the two capacitive probe was 480 V/cm�� torr.

Analytic Method of the Modified TRV of Circuit Breaker with Circuit Variation by Laplace Transform

When circuit parameters are known, it is easy to calculate the modified transient recovery voltage (TRV) with resister breaking or MOSA (Metal-oxide Surge Arrester) operating by numerical simulations. But, when the TRV is only known, it is very difficult to calculate the modified TRV by numerical simulations. This paper shows the theoretical analytic method of the modified TRV at such a circuit impedance modification as breaking with parallel resister or MOSA operating.A TRV can be calculated by injecting a current from circuit breaker terminals to back impedance. TRV and injected current wave shapes can be expressed with a group of ramp waveforms in Laplace domain. By using our analytic method, the back impedance can be easily derived in the Laplace domain from the TRV and injected current waveforms. As a result, it is shown that the modified TRV at circuit impedance modification can be calculated.