Shock tube

About: Shock tube is a research topic. Over the lifetime, 6963 publications have been published within this topic receiving 99372 citations.

The influence of the absorption of radiation in shock tube phenomena

Abstract: A theoretical investigation is made of the influence of the absorption of continuum radiation on the gas flow variables behind a strong shock wave advancing into argon at room temperature. A derivation of the emission formula for the total continuum radiation from an ionized gas brings out the need for knowing the amount that the ionization potential is lowered in a plasma. A review of the literature led to the choice of Ecker and Weizel's expression for the ionization potential lowering. Numerical results obtained by combining this expression with the usual shock equations are presented for the equilibrium conditions that are assumed to exist at the plane of maximum luminosity. The absorption at a point behind the plane of maximum luminosity depends on the energy emitted from every element of the luminous region, modified by the absorption along the paths from the emitting elements to this point. The energy emitted from an element depends on the as yet unknown conditions at the element. Thus, the absorption at a point depends on the knowledge of the complete structure of the luminous region that we are seeking to determine. A “relaxation” method for finding the rate of absorption per unit mass is presented. In principle, the method is quite general. Here it is used to find the energy absorped at points in a “shock tube” of finite length and infinite optical cross section, i.e., there is essentially no contribution of radiative energy to a point from points in the same cross section sufficiently far removed. Moreover, the luminous region in this “tube” is assumed to be stratified into plane parallel layers in each of which uniform conditions exist. The absorption term found by this method is introduced into the energy equation. The ionization potential that is present in the energy equation is regarded, of course, as a variable. To obtain an expression for the variation of the degree of ionization with distance, it is necessary to combine the energy equation with the differential forms of the following equations: the equation of state, the Saha equation, the equation for the lowering of the ionization potential, and the conservation equations of mass-flow and momentum. The resulting expression together with similar expressions for the other variables constitute a system of differential equations which were solved (on an IBM computer) both with and without the inclusion in the energy equation of the term for the absorbed energy. Numerical calculations accurate as far as third-order terms showed that the assumptions underlying the “relaxation” method were valid. Results are presented for shock waves of about Mach number 17 advancing into argon at densities of both 1 76 and 1 10 atm, and for a shock wave of Mach number 16 advancing into 1 2 atm of argon. It is found that for a given Mach number the effect of the absorption of energy is to bring the variables to an essentially constant value in a distance which depends on the density ahead of the shock. The greater the density, the shorter is this distance, and the closer is the magnitude of this constant value to the initial value at the plane of maximum luminosity. A method is also presented for finding the absorption energy near the center line of a shock tube of finite optical death. Thus, the influence of the absorption of energy on the flow variables behind the plane of maximum luminosity may be determined for this case, too.

Investigation of strong shock wave interactions with CeO 2 ceramic

Abstract: Strong shock wave interactions with ceramic material ceria (CeO2) in presence of O2 and N2 gases were investigated using free piston driven shock tube (FPST). FPST is used to heat the test gas to very high temperature of about 6800–7700 K (estimated) at pressure of about 6.8–7.2 MPa for short duration (2–4 ms) behind the reflected shock wave. Ceria is subjected to super heating and cooling at the rate of about 106 K/s. Characterization of CeO2 sample was done before and after exposure to shock heated test gases (O2 and N2). The surface composition, crystal structure, electronic structure and surface morphology of CeO2 ceramic were examined using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Results obtained from the experimental investigations show that CeO2 can withstand high pressure accompanied by thermal shock without changing its crystal structure. Reducible CeO2 releases lattice oxygen making it possible to shift between reduced and oxidized states upon the interaction with shock heated gas. Due to such reaction mechanism, CeO2 ceramic undergoes nitrogen doping with decrease in lattice parameter. Investigations reveal that CeO2 retains its crystal structure during strong shock interaction, even at elevated pressure.

Application of underwater shock wave and laser-induced liquid jet to neurosurgery

Abstract: Paper deals with applications of underwater shock waves to medicine. A historical development of underwater shock wave generation by using pulsed Ho:YAG laser beam irradiation in water is briefly described and an overview is given regarding potential applications of shock waves to neuro-surgery. The laser beam irradiation in a liquid-filled catheter produces water vapor bubble and shock waves intermittently produces micro-liquid jets in a controlled fashion from the exit of the catheter. Correlations between shock dynamics and bubble dynamics are emphasized. To optimize the jet motion, results of basic parametric studies are briefly presented. The liquid jet discharged from the catheter exit has an impulse high enough to clearly exhibit effectiveness for various medical purposes. In liquid jets we observed reasonably strong shock waves and hence invented a compact shock generator aiming to apply to microsurgery. We applied it to a rat's bone window and developed an effective method of brain protection against shock loading. The insertion of Gore-Tex® sheet is found to attenuate shock waves drastically even for very short stand off distance and its physical mechanism is clarified. The laser-induced liquid jet (LILJ) is successfully applied to soft tissue dissection. Animal experiments were performed and results of histological observations are presented in details. Results of animal experiments revealed that LILJ can sharply dissect soft tissue with a minimum amount of liquid consumption, while blood vessels larger than 0.2 mm in diameter are preserved. Shock waves and LILJ have a potential to be indispensable tools in neuro-surgery.