Showing papers on "Shock tube published in 1992"

Performance data of the new free-piston shock tunnel T5 at GALCIT

Abstract: A new free piston shock tunnel has been constructed at the Graduate Aeronautical Laboratories at Caltec. Compression tube length is 30 m and diameter 300 mm. Shock tube length is 12 m and diameter 90 mm. Piston mass is 150 kg and maximum diaphragm burst pressure is 130 MPa. Special features of this facility are that the pressure in the driver gas is monitered throughout the compression process until well after diaphragm rupture, and that the diaphragm burst pressure can be measured dynamically. An analysis of initial performance data including transient behavior of the flow over models is presented.

Shock tube study of the drag coefficient of a sphere in a non-stationary flow

Abstract: A shock tube facility was used for inducing relatively high acceleration on small spheres laid on the shock tube floor. The acceleration resulted from the drag force imposed by the post shock wave flow. Using double exposure holography, the sphere trajectory could be constructed accurately. Based upon such trajectories, the sphere drag coefficient was evaluated for a relatively wide range of Reynolds numbers (6000≤ Re ≤ 101000). It was found that the value obtained for the sphere drag coefficient were significantly larger than those obtained in a similar steady flow case.

Test flow disturbances in an expansion tube

Abstract: The operation of an expansion tube is investigated theoretically with emphasis on the factors that have limited the utility of the expansion tube in the past. It is shown why the window of steady test conditions is narrow and how this window can be expanded so that these facilities can be used in a variety of hypersonic research. The theoretical predictions are supported by centerline Pitot pressure measurements using air as the test gas.

Planar fluorescence imaging of a transverse jet in a supersonic crossflow

Abstract: Planar laser-induced fluorescence (PLIF) imaging has been used to examine the mixing and combustion of a sonic jet of gas injected transversely into a supersonic freestream flowing within a shock tube. Single-shot and frame-averaged fluorescence images have been acquired for nonreacting and reacting flows in side-view and end-view orientations. In the nonreacting experiments, nitric oxide seeded within the jet fluid was used to examine the penetration and mixing of the jet with the freestream, without the influence of chemical reaction and heat release. In the reacting experiments, the hydroxyl radical (OH), formed by the combustion of a hydrogen jet injected into an oxidizing freestream, was used to locate the reaction zones. The OH images indicate that combustion takes place primarily in the shear layer formed by the jet and the freestream, and in the boundary layer adjacent to the wall. For both the nonreacting and reacting results, the single-shot images show the presence of large-scale turbulent structures not apparent in the frame-averaged images. These results demonstrate the importance of examining and understanding the instantaneous flowfield, because it is the instantaneous, rather than mean state, of the flow that ultimately determines the extent to combustion.

An Analysis of Combustion Studies in Shock Expansion Tunnels and Reflected Shock Tunnels

Abstract: The effect of initial nonequilibrium dissociated air constituents on the combustion of hydrogen in high-speed flows for a simulated Mach 17 flight condition was investigated by analyzing the results of comparative combustion experiments performed in a reflected shock tunnel test gas and in a shock expansion tunnel test gas. The results were analyzed and interpreted with a one-dimensional quasi-three-stream combustor code that includes finite rate combustion chemistry. The results of this study indicate that the combustion process is kinetically controlled in the experiments in both tunnels and that the presence of the nonequilibrium partially dissociated oxygen in the reflected shock tunnel enhances the combustion. Methods of compensating for the effect of dissociated oxygen are discussed.

Multiple Normal Shock Wave/Turbulent Boundary-Layer Interactions

Abstract: A multiple normal shock/turbulent boundary-layer interaction in a rectangular duct has been investigated experimentally using a two-component laser Doppler velocimeter (LDV). Just upstream of the normal shock system the Mach number was 1.61, the unit Reynolds number was 30 x 106 m ', and the confinement level as characterized by the ratio of the boundary-layer thickness to the duct half height was 0.32. The results presented here identify the fluid dynamic mechanisms involved in the reacceleration process following each shock in the multiple shock system. Two distinct expansion processes occur following each shock in the system: acceleration through a supersonic expansion fan originating near the wall and acceleration through an aerodynamic converging-diverging nozzle in the core flow.

Shock tube and modeling study of propene pyrolysis

Abstract: The thermal decomposition of propene behind reflected shock waves with 1200

Rapid compression of grid‐generated turbulence by a moving shock wave

Abstract: Most of the previous work on turbulence amplification by shock wave interaction is limited to shock wave/boundary layer types of interactions where additional effects due to shock wave oscillation, streamline curvature, and flow separation complicate the understanding of the physics involved in this phenomenon. The present experimental study has focused on interactions of a normal shock with grid‐generated turbulence in a shock tube. The decaying turbulence behind the grid is characterized by a variation of length scales with downstream distance and is subjected to an interaction with the reflected shock traveling in the opposite direction. Considerable amplification of turbulence has been found after the interaction which depends on the length scale of the incoming flow. Spectral analysis has also indicated that large eddies are amplified more than small eddies during interactions with shock waves of the same strength.

A numerical study of shock wave reflections on low density foam

Abstract: A continuum mixture theory is used to describe shock wave reflections on low density open-cell polyurethane foam. Numerical simulations are compared to the shock tube experiments of Skews (1991) and detailed wave fields are shown of a shock wave interacting with a layer of foam adjacent to a rigid wall boundary. These comparisons demonstrate that a continuum mixture theory describes well the shock interactions with low density foam.

Numerical simulation of Richtmyer–Meshkov instabilities

Abstract: The results of detailed numerical simulations of the Richtmyer–Meshkov instability of the interface between layers of air and either helium or SF6 in a shock tube are reported Two‐ and three‐dimensional simulations based on both the Euler and Navier–Stokes equations were obtained by a finite difference method that employs a front‐tracking technique to keep the interface sharp The nature of the flow patterns induced by the instability is discussed The results of a numerical resolution study and a demonstration of the influence of boundary layers are presented also Agreement with experimental data is found to be satisfactory, with the exception of the initial instability growth rate

Experimental investigation of terminal shock sensors for mixed-compression inlets

Abstract: This paper describes experimental investigations of devices designed for the nonintrusive detection of terminal shock location in mixed-compression inlets at high supersonic flight speeds. Systems based on sensing wall pressures by an array of wall-mounted transducers were selected for detailed study. Pressure signals were processed by three different methods: (1) interpretation of instantaneous pressure distributions, (2) detection of the turbulent intensity amplification occurring at the shock, and (3) determination of the upstream limit to which a search-tone, introduced at the downstream end of the channel, can propagate. The first two of these methods were tested in real time. The third method appeared feasible for weak shocks only; at high shock strengths, propagation upstream of the source could not be detected.

The high enthalpy shock tunnel in Göttingen (HEG)

Abstract: The current status of the new free piston shock tunnel being built in Gottingen is described. The facility is nearing completion with all major components on site and assembled. HEG represents a considerable scale up on existing facilities of this type and consideration of the energies involved must be taken in all aspects of the design. Described are the layout of the facility, calculations of the driving conditions including piston trajectories, expectations for the shock tube flow and calculations for the nozzle flow.

Bifurcation of a reflected shock wave in a shock tube

Abstract: The problem of shock bifurcation observed for a reflected shock interacting with a boundary layer is investigated both experimentally and numerically. The process has been visualized by means of color schlieren photographs that clearly show the characteristic wave pattern. Accompanying pressure measurements hint at the three-dimensional character of the wave system. In a numerical scheme based on the Euler equations the problem has been simulated giving good agreement between the calculated and the observed wave configuration.

Time-dependent quasi-one-dimensional simulations of high enthalpy pulse facilities

Abstract: A numerical methodology is presented for simulating the time-dependent reacting flow inside the entire length of high enthalpy pulse facilities. The methodology is based on a finite-volume TVD scheme for the quasi-1D Euler equations coupled with finite-rate chemistry. A moving mesh and tracking of gas interfaces are used to overcome certain numerical difficulties associated with these types of flows. Simulation results of a helium driven shock tube show that computations can be used to predict the off-tailored behavior of shock tubes and tunnels. Particular attention is given to computations of the flow through the NASA Ames 16-inch combustion driven shock tunnel which show the influence of nonuniformities in the driver section on the reservoir conditions; and the effect of finite secondary diaphragm opening times on the chemical composition of the test flow in the HYPULSE expansion tube.

Waves in partially saturated porous media

Abstract: The propagation of compressional waves in a porous medium is investigated in case the pore liquid contains a small volume fraction of gas. The effect of oscillating gas bubbles is taken into account by introducing a frequency-dependent fluid bulk modulus, which is incorporated in the Biot theory. Using a shock tube technique, new experimental data are obtained for a porous column subjected to a pressure step wave. An oscillatory behaviour is observed, consisting of two distinct frequency bands, which is predicted by the theoretical analysis.

Planar Laser-Induced Fluorescence Imaging of Shock-Tube Flows with Vibrational Nonequilibrium

Abstract: Single-shot planar laser-induced fluorescence images of nitric oxide in shock-heated flows with vibrational nonequilibrium are reported. The results demonstrate that planar laser-induced fluorescence imaging is a promising diagnostic technique for multidimensional high-speed flows because of its ability to examine shock structure and to visualize and measure vibrational nonequilibrium. The flows studied were generated within a shock tube and were composed of dilute mixtures of NO in argon. A narrow-band ArF laser tuned to the D +- X (0,1) R2 (28.5) transition of NO at 193.346 nm was used as the excitation source. The broadband fluorescence was collected at 90 deg to the path of excitation using an intensified, two-dimensional photodiode array. Images presented include a normal incident shock, a normal reflected shock, and a four-image sequence of the development of high-temperat ure supersonic flow over a two-dimensiona l blunt body. The vibrational relaxation in the downstream region of the normal shocks is analyzed and compared with calculations based on known relaxation rates.

Studies of radiative emission from the simulated shock layer of the Huygens probe

Abstract: An investigation has been conducted to determine the radiative heating of the Huygens probe. The shock tube facility at Stanford University was used to generate plasma behind strong shocks, which simulates the flow field around the probe. Spectroscopic thchnigues have been used to measure thermophysical quantities of the plasma in the shock tube. A numerical code has been developed using a three temperature model in order to generate one dimensional flow field solutions for comparison with these experimental data. Based on this analysis, the radiative heat transfer at the stagnation point of the prove was approximated.

A shock tube study of reactions of atomic oxygen with isocyanic acid

Abstract: Reactions of atomic oxygen with isocyanic acid (HNCO) have been studied in incident and reflected shock wave experiments using HNCO/N2O/Ar mixtures. Quantitative time-histories of the NH(X3Σ−) and OH(X2Πi) radicals were measured behind the shock waves using cw, narrow-linewidth laser absorption at 336 nm and 307 nm, respectively. The second-order rate coefficients of the reactions: and were determined from early-time NH and OH formation rates, with least-squares two-parameter fits of the results given by: and cm3 mol−1 s−1. The minimum and maximum rate constant factors (ƒ,F) define the lower and upper uncertainty limits, respectively. An upper limit on the rate coefficient of was determined to be: .

Effects of shock wave precursors ahead of hypersonic entry vehicles

Abstract: A model has been developed to predict the magnitude and characteristics of the shock wave precursor ahead of a hypervelocity vehicle. This model includes both chemical and thermal nonequilibrium, utilizes detailed mass production rates for the photodissociation and photoionization reactions, and accounts for the effects of radiative absorption and emission on the individual internal energy modes of both atomic and diatomic species. Comparison of the present results with shock tube data indicates that the model is reasonably accurate. A series of test cases representing earth aerocapture return from Mars indicate that there is significant production of atoms, ions and electrons ahead of the shock front due to radiative absorption and that the precursor is characterized by an enhanced electron/electronic temperature and molecular ionization. However, the precursor has a negligible effect on the shock layer flow field.

Head-On Collision of Normal Shock Waves with a Rubber-Supported Wall

Abstract: The head-on collision between a normal shock wave, propagating into a quiescent gas, and a rubber-supported plate was investigated theoretically and experimentally. In the theoretical part, a physical model was developed for describing the collision process. Three different modes in which the rubber could be loaded, due to its collision with the incident shock wave, were studied. They are: uni-axial stress loading, bi-axial stress loading and uni-axial strain loading. In the first two modes the rubber can expand while carrying the shock-wave induced compressive load, and therefore can be treated as an incompressible medium. This is not the case in a uni-axial strain loading where the rubber cannot expand while carrying the shock-wave-induced load. The model developed was based on both the conservation equations and on an appropriate strain stress relation which describes the rubber behaviour under loading. The model was solved numerically for each of the above-mentioned loading modes. Experiments were conducted in a shock tube; the rubber response to its collision with normal shock wave was studied for the case of bi-axial stress loading. Pressures, in the gas, and stresses, in the rubber, were recorded by using piezoelectric pressure transducers; the shock-wave reflection, in the gas, and the rubber displacement and compression processes were recorded on successive shadowgraphs. Good agreement was found between the experimental and numerical results for the case of bi-axial stress loading. This agreement validates the model developed for the collision process and the reliability of the numerical scheme used for its solution.

Multiple shock-shock interference on a cylindrical leading edge

Abstract: The details of an experimental study of shock wave interference heating on a cylindrical leading edge representative of the cowl of a rectangular hypersonic engine inlet are presented. This Mach 8 study has provided the first detailed pressure and heat transfer rate distributions on a cylinder resulting from a two-dimensional shockwave interference pattern created by two incident oblique shock waves intersecting the cylinder bow shock wave. The peak heat transfer rate was 38 times the undisturbed flow stagnation point level and occurred when the two oblique shock waves coalesced prior to intersecting the cylinder bow shock wave. Development of pressure deflection diagrams identified a new interference pattern consisting of concomitant supersonic jets separated from each other by a shear layer and submerged in the subsonic region between the bow shock wave and body.

A numerical simulation of boundary layer effects in a shock tube

Abstract: SUMMARY A numerical scheme is used to investigate boundary layer effects in a shock tube. The method consists of a mixture of Roe’s approximate Riemann solver and central differences for the convective fluxes and central differences for the viscous fluxes and is implicit in one space dimension. Comparisons are made with experimental data and with solutions obtained via boundary layer equations. Examination of the calculated flow field explains the observed behaviour and highlights the approximate nature of boundary layer solutions. Model experiments are used in the aerospace industry to investigate flow fields around aircraft. The required flow conditions can be generated by connecting a shock tube to a test section containing a model of the aircraft under consideration. Possible conditions range from subsonic to hypersonic, resulting in a wide variation in fluid velocities and temperatures. In addition, shock tubes can be used to study real gas effects such as deviations from ideal gas behaviour. A discussion of some applications can be found in Reference 1. For any application it is necessary to know the flow conditions generated to enable interpretation of the results. If the flow is inviscid and the gas is assumed perfect, then the transient development is well understood (see e.g. Reference 1). In that case the flow can be modelled by the Euler equations in one dimension. However, there are a number of possible effects which can cause departures from the inviscid solution. These include viscosity and heat conduction and so-called real gas effects involving deviations from the ideal equations of state. In this paper we shall be concerned with the first two and shall neglect the last. The departure from inviscid behaviour becomes especially marked when the shock tube is operating at low initial pressures (when the Reynolds number based on the tube radius and the peak velocity is typically about 500). This case is of particular interest fdr the investigation of high-altitude flow over re-entry vehicles. The experimental results of Reference 2 showed dramatic departures from the anticipated inviscid behaviour. One measure of shock tube performance which is of particular interest in experiments is the time interval for which the hightemperature conditions prevail. This time interval, called the test time, is given at some point in the tube by the time difference between the shock and the contact surface passing that point. Inviscid theory predicts that this time interval will increase linearly with distance from the diaphragm. It was reported in Reference 2 that for a fixed shock Mach number the test time

A Shock Tube Study of the Reactions of the Hydroxyl Radical with Several Combustion Species

Abstract: Reactions of the hydroxyl radical, OH, with several organic species of interest in combustion chemistry have been studied near 1200 K and 1 atm in shock tube experiments in which UV absorption was used to monitor the OH concentration. Rate coefficients were measured for the reactions of OH with 2,3-dimethylbutane, isooctane, neooctane, ethylene, propylene, acetylene, formaldehyde, methanol, and ethanol. The values were found to be (in units of 1012 cm3/mol-s): 21, 22, 18, 2.6, 9.6, 0.28, 12, 5.2, and 5.3. These measured values are compared with previous experimental results and, where appropriate, transition-state theory calculations.

Co-extruded shock tube

Abstract: The invention relates to a method of manufacturing a low-energy shock tube by co-extruding two or more layers simultaneously wherein the inner layer has an adhesive affinity for a powdered reactive material and the outer layer(s) provides abrasion, cut and other environmental resistance to the tube. The wall thickness of the inner layer is less than about 0.3 millimeters. The invention also relates to a low-energy shock tube having such configuration and inner layer thickness.

In the footsteps of Ernst Mach — A historical review of shock wave research at the Ernst-Mach-Institut

Abstract: The aim of this paper is to recall some of the historical work on shock waves and to give a brief survey of research activities at the Ernst-Mach-Institut (EMI). Some fundamental results of Ernst Mach (1838 – 1916) are demonstrated and historical remarks are given to the shock tube as an important tool in shock wave research. The activity at EMI in this field was initiated by Prof. H. Schardin (1902 – 1965) in 1955 and has since been continued. Propagation processes of shock and blast waves, blast loading phenomena, shock attenuation, shock reflection at various surfaces, development of new types of blast simulators, electromagnetically driven T-tubes, precursor and decursor phenomena are only a few examples of research topics at EMI that will be discussed.

Crossing shock wave turbulent boundary layer interactions - Variable angle and shock generator length geometry effects at Mach 3

Abstract: By comparing the detailed wall static pressure distributions for 9 inch and 11 inch long fins generating a crossing shock configuration at M = 2.93, the high resolution results of the 9 inch fins are shown to be free of exit effects. Analysis of the static pressure profiles have delineated the limited regions where the single fin results are valid. The characteristics of the complex interaction, with varying shock wave strength, have been described. The data provide a critical test for computational fluid dynamics which, in its initial phase, has performed poorly in predicting the measured wall static pressure distributions.

Initial operation of the UTA shock tunnel

Abstract: Initial experience in operating a small UTA (University of Texas at Arlington) shock tunnel at high Reynolds numbers for perfect gas simulation of hypersonic flow and boundary layer studies is described. Particular attention is given to tradeoffs between various constraints for achieving the test requirements, and methods for obtaining precise control of test conditions and protecting low-range pressure transducers from overpressure damage.