Kyoichi Kuriki

The mechanism of transition in the wake of a thin flat plate placed parallel to a uniform flow

A study was made of the laminar-turbulent transition of a wake behind a thin flat plate which was placed parallel to a uniform flow at subsonic speeds. Experimental results on the nature of the velocity fluctuations have made it possible to classify the transition region into three subregions: the linear region, the non-linear region and the three-dimensional region. In the linear region there is found a sinusoidal velocity fluctuation which is antisymmetrical with respect to the centre-line of the wake. The frequency of fluctuation is proportional to the

Experimental Study of a Plasma Flow in a Magnetic Nozzle

\frac {2}{3}

Transitional Behavior of MPD Arcjet Operation

power of the free-stream velocity, and the amplitude increases exponentially in the direction of flow. The behaviour of small disturbances in the linear region was investigated in detail by inducing velocity fluctuation with an external excitation—actually sound from a loudspeaker. Solutions of the equation of a small disturbance superposed on the laminar flow were obtained numerically and compared with the experimental results. The agreement between the two was satisfactory. When the amplitude of fluctuation exceeds a certain value, the growth rate deviates from being exponential due to non-linear effects. Although velocity fluctuations in the non-linear region are still sinusoidal and two-dimensional, the experimental results on the distributions of amplitude and phase indicate that the flow pattern may be described by the model of a double row of vortices. This configuration lasts until three-dimensional distortion takes place in the final subregion, the three-dimensional region, in which the fluctuation loses regularity and gradually develops into turbulence without being accompanied by abrupt breakdown or turbulent bursts.

Fast Ionization Gauge Studies of Quasisteady Gas Injection into Vacuum

Interaction between an axisymmetric jet of plasma and a magnetic field generated by concentric current loops is studied experimentally. With a large Hall parameter, electrons are confined to the converging‐diverging lines of force. The maximum Hall parameter for electrons is greater than 30. Measurements are made of the electric potential, ion density, electron temperature, and ion velocity. The flow of charged particles is found to be aligned with the magnetic lines of force with a slip relative to neutral atoms. The ion is compressed electromagnetically and is pumped to flow over a potential barrier formed near the center of the coil. The maximum velocity of ions at the exit of the magnetic nozzle is greater than that expected from an isentropic expansion. This extraordinary speed of ions is accounted for in terms of the electrostatic acceleration. In the magnetic channel the energy equation for ions is coupled with the energy equation for electrons.

Super‐Alfvénic flow and collision free shock wave in a plasma wind tunnel

The thrust and discharge voltage of a quasisteady MPD arcjet have been measured, with emphasis on the transitional characteristics from the propellant over-fed to starved condition and from aerodynamic to electromagnetic acceleration. From the anode and cathode potential measurements, the transition into the starved condition was found to be preceded slightly by the transition of acceleration process when the discharge current was increased. At the beginning of the electromagnetic acceleration, the thrust became unstable. This was attributable to radial current expansion toward the outer anode region. At higher discharge current, the flow pattern settled and the quasisteady state was restored.

Current collection by spherical Langmuir probes drifting in a collisionless plasma

Quasisteady gas injection into vacuum has been carried out by using a fast‐acting valve of piston configuration. The pulsed motion of the piston was analyzed from stroboscopic photographs. There is no scatter in valve operation due to O‐ring friction. The pulse width of the jet of several milliseconds and the mass flow rate during steady state can be varied independently. The rise time and the quasisteadiness of the pressure in the transient gas flow were measured by a newly developed fast ionization gauge of triode construction. The guage has a constant sensitivity from 3×10−3 to 2 Torr and a sufficient time resolution, and it introduces little obstruction of the gas flow. The pressure distribution measured in the jet expanding into vacuum agrees well with the rarefied gasdynamic prediction.

Determination of ion temperature by two-probe method.

A super‐Alfvenic and supersonic flow in a plasma wind tunnel were studied experimentally. The wind tunnel was constructed for the studies of the magnetohydrodynamic shock waves and wakes, and has features such as quasisteady flow and low fluctuation level. The Alfven Mach number MA and ion acoustic Mach number M covered in the present experiment are MA = 1−4 and M = 2−6 A standing shock wave was found downstream of the magnetic‐nozzle exit. The shock wave is collision free and the normal of the wavefront is parallel to the magnetic field. Macroscopic features of the shock wave were discussed with reference to the theoretical predictions of the magnetohydrodynamic and collision‐free shock waves.

Modified Poppet Valve for Quasisteady Gas Injection into Vacuum

Current‐voltage characteristics of drifting spherical Langmuir probes have been studied experimentally in collisionless plasmas. In order to single out the effect of probe speed on the ion current collection, the experiment was carried out by a rotating arm facility. With this device the probe speed as well as the properties of the undisturbed plasma were accurately determined. As predicted by the theories of Kanal, Godard, and Laframboise, the ion current at small speed ratios was found to be either increased or decreased as the probe speed increased depending on the ratio of probe radius to Debye length R/λD. As for the absolute magnitude of ion current change by the probe speed, however, discrepancies were found between these theories and the present experiment. The difference is considered to originate from asymmetry in the potential distribution, which is not included in these theories.

Interaction between a Magnetic Field and a Plasma Flow Behind a Shock Wave

A simple method is proposed to estimate the ion temperature of collision-free plasma using a cylindrical and a spherical Langmuir probe. This method is based on the difference in the ion-temperature dependence of the ion-current collection between these probes as predicted theoretically by Laframboise. Curves necessary for the ion-temperature determination are given and are applied to a low-density xenon plasma. Agreement of the probe characteristics with Laframboises theory was also demonstrated.

Establishment of quasi-steady operation in a pulsed MPD arcjet

A fast acting valve has been developed for quasisteady gas injection with a short rise time. The valve has a structure which is a combination of the conventional poppet and piston valves. From gas density measurements by a fast ionization gauge, the rise time was found to be limited by the expansion of the gas front. The minimum rise time is 70 μsec for a specific geometry of gas exit. The design criteria are also discussed.