摘要:

High Mach number shock induced turbulent mixing of two gases of different densities is investigated in a double diaphragm shock tube. The study of shock‐accelerated interfaces between two fluids of different densities is known as the study of shock‐excited Rayleigh‐Taylor or Richtmyer‐Meshkov instability. In the present experiments, the gases are initially separated by a thin plastic membrane materializing the interface. Different measurement techniques have been used to observe the created turbulent mixing zone: infrared absorption of a CO2vibrational‐rotational line which provides average temperature and density profiles in the mixing zone, infrared emission of CO2which gives the evolution of the mixing zone thickness and Schlieren photographs which provide another measurement of the mixing zone thickness as well as qualitative informations on the three‐dimensional nature of the shock and turbulent mixing after interaction. Results are compared to similar experiments at high Mach number conditions.

ISSN:0094-243X    

DOI:10.1063/1.39412

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Numerical simulations of the interaction of Mach 1.3 shock waves and gaseous interfaces between air and helium or SF6 were carried out using EAD, a 2D, second order non‐viscous Eulerian code. The interface, described either by a single sinusoidal wave or a combination of sinusoidal waves of random amplitudes is subjected to Rayleigh‐Taylor instability induced by the incident shock and successive waves reflected from the shock tube end wall. The evolution of the subsequent mixing zone thickness and the kinetic energy of the fluctuating velocity field associated with the mixing are extracted from the simulation and compared with theoretical estimates based on an quasi‐incompressible analysis of the instability.

ISSN:0094-243X    

DOI:10.1063/1.39413

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have observed the interaction between a shock wave and an unsteady jet in shock tube. From the results of the experiment, we have reported that the interaction between the shock wave and the unsteady jet in a shock tube was very strong, and it temporarily generated a hemispherical reflected shock wave. However, we could not clarify the cause of the interaction because of the limits of the experiment. Therefore, we used a numerical computation to clarify it. The computation was carried out by solving axisymmetric viscous flow by means of the MacCormack method. The results obtained from the computations generally supported those expected from the experiment.

ISSN:0094-243X    

DOI:10.1063/1.39415

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A speckle photographic method, which is sensitive to changes of fluid density, is applied for analyzing a compressible turbulent air flow with density fluctuations. Spatial correlation coefficients, turbulent length scales, and energy spectra are determined under the assumption of homogeneous isotropic turbulence. The experiments are performed in a shock tube where the flow is passed through a turbulence grid. Measurements are taken before and after the turbulent regime interacts with the normal shock wave reflected from the tube’s and wall. Amplification of the turbulence intensity by the shock is measured quantitatively and the amplification is shown to be restricted to the lower wave numbers of the spectrum.

ISSN:0094-243X    

DOI:10.1063/1.39416

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A simple approximate analytical theory is developed to predict the rate of decay of a planar shock wave travelling through the gaseous medium blocked by barriers and screens. It involves the following assumptions: (1) the flow is uni‐dimensional; (2) The gas obeys the perfect gas law; (3) heat transfer to confinements is neglected; (4) shock wave velocity is independent of conditions behind it (this is known as Whitham’s approach) and depends only on confinement geometry, distance travelled by the shock wave through the blocked space and its initial Mach number. Experimental data on shock wave attenuation in beds of granular solid material, gas‐solid suspensions, gauzes, porous packings, rough tubes, diaphragms, etc. have been used to varify the theory. It is found the proposed approximate theory gives satisfactory prediction for quenching efficiency in all cases considered, thus allowing to use it for comparative study of various safety measures.

ISSN:0094-243X    

DOI:10.1063/1.39417

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Departing from van Driests theory for compressible turbulent boundary layers, a closed set of general equations containing 3 free parameters is established. The parameters are then determined by fitting the theoretical predictions to reliable experimental data for incompressible boundary layers. By comparing with a great deal of data on two‐dimensional compressible turbulent boundary layers, all received with shock tube experiments, it is shown that this theoretical scheme gives the correct predictions also in the case of high stagnation enthalpy flows up to 2000 K stagnation temperature.

ISSN:0094-243X    

DOI:10.1063/1.39418

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The influence of turbulent boundary layer growth on flow formation in the driven gas of a shock tube with circular cross‐section was investigated theoretically and experimentally.

ISSN:0094-243X    

DOI:10.1063/1.39419

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.39420

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper is a review of different cases when surface laser plasma appears as the result of interaction of laser radiation with the matter. The conditions under which surface laser plasma formation occurs, such as combination of surface material and surrounding gas, intensity and frequency of laser radiation, etc. may vary, and so do the mechanisms of breakdown. This paper offers a system of classification for surface laser plasma states.

ISSN:0094-243X    

DOI:10.1063/1.39421

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In the electrical field of a focused beam of a high‐power Q‐switched CO2laser a so‐called pulsed optical discharge (POD) can be sustained. Applying laser pulses with max. 104pulses/s, peak power 250 kW and pulse length 0.2 &mgr;s, the charge carrier density of a hydrogen plasma at a pressure of several MPa produced during the laser pulse is enhanced up to about the cut‐off density at &lgr;L=10.6 &mgr;m (&bartil;1025m−3) and the electron temperature is increased to about 105K. POD can be sustained very reproducibly by each individual laser pulse, because the optical discharge is ignited in the hot gas of the preceding laser pulse. Time and spatial resolved spectroscopic measurements yield Stark‐broadened Balmer H&bgr;‐line profiles from which, assuming partial local thermal equilibrium, the electron temperature and density can be derived. A numerical model was derived to calculate the time development of the electron density, temperature and plasma radius.

ISSN:0094-243X    

DOI:10.1063/1.39422

出版商:AIP    

年代:1990

数据来源: AIP