Shock Mach Number Ms Research Articles

Effects of hydrogen impurities on shock structure and stability in ionizing monatomic gases. Part 1. Argon

At shock Mach numbers Ms ∼ 16 in pure argon with initial pressures p0 ∼ 5 torr and final electron number densities ne ∼ 1017 cm−3, the translational shock front in a 10 x 18 cm hypervelocity shock tube develops sinusoidal instabilities which affect the entire shock structure including the ionization relaxation region, the electron-cascade front and the final quasi-equilibrium state. By adding a small amount of hydrogen (∼ 0·5% of the initial pressure), the entire flow is stabilized. However, the relaxation length for ionization is drastically reduced to about one-third of its pure-gas value. Using the familiar two-step collisional model coupled with radiation-energy loss and the appropriate chemical reactions, it was possible to deduce from dual-wavelength interferometric measurements a precise value for the argon-argon collisional excitation cross-section SAr Ar* = 1·0 x 10−19 cm2/eV with or without the presence of a hydrogen impurity. The reason for the success of hydrogen, and not other gases, in bringing about stabilized shock waves is not clear. It was also found that the electron-cascade front approached the translational-shock front near the shock-tube wall. This effect appears to be independent of the wall material and is not affected by the evolution of adsorbed water vapour from the walls or by water vapour added deliberately to the test gas. The sinusoidal instabilities investigated here may offer some important clues to the abatement of instabilities that lead to detonation and explosions.

衝撃波管管壁における電離境界層の数値解析

A numerical analysis has been made for the ionized reacting, thermal nonequilibrium boundary layer which develops along a shock-tube side-wall, behind an ionizing incident shock wave. The boundary layer flow has been found to change according to the ionization relaxation of the inviscid flow behind the shock wave. It has been shown that the temperature in the boundary layer becomes higher than that outside of the boundary layer in the rapidly ionizing region behind the shock wave.The numerical solutions were obtained for the case of the incident shock Mach number Ms=13, initial pressure p1=10 torr and initial temperature T1=300°K.

Experimental Study of Shocked-Plasma Flows with a Double Search-Coil Conductivity Probe

Distributions of the electrical conductivity of shock-heated argon plasma flows are studied with a conductivity probe. The device has two search coils in order to correct the boundary-layer effect on the conductivity measurements. The boundary-layer effect is found to be small for the following conditions; initial pressure P1=2 Torr, shock Mach number Ms=14 and 17, and P1=5 Torr, Ms=15. Variation of conductivity agrees with theory. However, it is suggested that this effect may not be negligible for lower values of Ms. An discussion is presented for effect of a disturbed flow due to the presence of the coils inside the shock tube on the conductivity measurements. The boundary-layer thickness is also obtained from the measurements and it agrees with that deduced from the calculated structure by Knöös within the oder of magnitude.

Experiments on radiating xenon plasma flows in an arc driven shock tube

The electrical conductivity of xenon plasma in an arc driven shock tube was measured by means of a conductivity probe of magnetic induction type. The decay of continuous emission intensities was also measured at the two wavelengths 4425 Å and 3975Å. The initial xenon pressure (P1) ranged from 1.5 to 10 torr. The shock Mach number (Ms) ranged roughly from 15 to 24. The effect of radiation cooling on the decay of electrical conductivity and that of continuous emission intensity was studied together with our previous measurements in a pressure driven shock tube, (P1= 1-5 torr and Ms = 9-14).For higher. shock Mach numbers, the measured decrease of electrical conductivity and that of continuous emission intensity. could be correlated with continuum radiation loss. For lower shock Mach numbers at P1=1 and 2 torr, however, the decrease is much faster than the calculated value assuming continuum radiation loss alone. To obtain a possible explanation. for this discrepancy, the influence of line radiation loss was briefly discussed.

Experimental Study of the Starting Process in a Reflection Nozzle

The unsteady events occurring during the time after the shock enters the nozzle of a shock tunnel and until a steady flow is established have been investigated for a two-dimensional reflection nozzle by multiple shadowgraphs and interferograms. The influences of different parameters (nozzle half-angle, throat width, and nozzle inlet radius) on the starting process are presented on x-t diagrams for the incident shock Mach number MS = 3. The density along the nozzle axis is presented at several times during the starting process.

Ion Density Profiles behind Shock Waves in Air

Experimental results are reported for the ionization rate behind shock waves of Mach numbers between 7.2 and 9.2. The results were obtained using a hollow, total collector probe in combination with a 38-mm-diam, stainless steel shock tube designed to minimize the impurity level in the test gas. Good agreement was obtained with a theoretical result based on Lin and Teare's rate equations. Equilibrium ion densities in good agreement with theory were measured behind shocks of Mach number 7.2-12.8, with initial pressures between 0.5 and 40-mm Hg. The effects on the measurements of deviations from ideal shock tube flow were determined to be small. Ion densities measured range from 108 to 10 12 cm~3. At the higher ion densities there are large space charge effects inside the probe. Under these circumstances, proper operation of the probe still could be obtained provided the collector potential was not made too high. This implies that the mobility of the NO ions collected must be rather large. ON density profiles behind shock waves in air have been the subject of various recent investigations. Lin, Neal, and Fyfe1 made measurements in a low-density shock tube using microwave techniques and a magnetic induction device, in the range of shock Mach numbers Ms between 14 and 20. A theoretical analysis of their results based on chemical rate equations was given by Lin and Teare.2 Experimental results for even higher shock Mach numbers were reported by Wilson,3 who found that for shock Mach numbers above 27, electron densities become high enough so that electron impact reactions become dominant. At the lower temperature end experimental data have been obtained by Thompson, 4 who used a low-density shock tube in combination with microwave techniques, with infrared emission measurements, and with a hollow, total collector probe described by de Boer.5 The present investigation was undertaken in order to extend the range of measured profiles to still lower temperatures. At these temperatures, both the ion density and the ionization relaxation rate become much smaller, and it is impractical to use a low-density shock tube because the test time required is too long. A 38-mm-diam shock tube was used in combination with the hollow, total collector probe of Ref. 5. This probe has a very high sensitivity and can be used without difficulty in the regime of interest. The main problem to be overcome was the influence of impurities on the ionization rates. This problem could be solved by using great care in the experimental procedures.

Perturbed One-Dimensional Unsteady Flows Including Transverse Magnetic-Field Effects

The effect of small unsteady mass, momentum, and heat addition in a uniform (or piecewise uniform) basic flow is discussed. A general solution is given. A method for obtaining closed-form solutions, in cases where the disturbed flow is self-similar, is also presented. These solutions are applied to find the interaction between a flow, due to a piston starting impulsively from rest, and a transverse magnetic field. It is assumed that Rm « 1 and RmRh « 1, where Rm and Rh are the flow magnetic Reynolds and pressure numbers, respectively. The electrical potential is assumed to be uniform in the channel. Both a narrow (in the streamwise direction) intense magnetic field and a wide, less intense, field are treated. In the latter case it is found that the shock, generated by the motion of the piston, is decelerated by the magnetic field when the shock Mach number Ms is near 1 but is accelerated by the magnetic field when Ms is high. This behavior is due to the electromagnetic body forces dominating at Ms near 1 and the Joule heating dominating at large Ms. These numerical results also apply to the hot-gas region of a shock tube employing strong shocks.