Large Shock Tube Research Articles

Very weak shock wave reflection off curved surfaces

There is a dearth of information on the reflection of very weak shock waves on curved surfaces; and particularly a distinct lack of experimental data at Mach numbers below 1.03. A previous study at Mach numbers between 1.03 and 1.05 showed that there are variations in the accepted reflection evolution on curved surfaces. That work indicated the existence of an apparent regular refection pattern in the curved shock wave reflection evolution which is also predicted for very much weaker waves in acoustic studies. To improve spatial resolution, the current study is performed in a large shock tube with a test section height of 450 mm using a 520 mm radius curved test piece with zero initial ramp angle. Imaging is primarily using shadowgraphy and high-speed photography. Experiments concentrated on tests in a range of $$1.007 \le M \le 1.09$$ with some tests at higher values. No shear layer is evident at the lower Mach numbers as for von Neumann and weak Mach reflection patterns. Transitioned regular reflection appears to cease at incident Mach numbers below 1.07. A reflection pattern resembling a regular reflection exists in the transition between the three-shock patterns and transitioned regular reflection.

Study of the Effect of Electron Cooling: Overview of the Current State

Investigation results of the effect of electron cooling are considered. The current state-of-the-art is analyzed. The possibilities are discussed for the experimental study of the electron cooling phenomenon using a large shock tube and plasma-gas-dynamic stand at the Ioffe Institute.

Исследование эффекта электронного охлаждения. Обзор современного состояния работ

AbstractInvestigation results of the effect of electron cooling are considered. The current state-of-the-art is analyzed. The possibilities are discussed for the experimental study of the electron cooling phenomenon using a large shock tube and plasma-gas-dynamic stand at the Ioffe Institute.

Study on shock resistance of steel plate reinforced with polyurea–woven fiberglass mesh composite under shock wave

To study the dynamic mechanical properties of polyurea–woven fiberglass mesh composite material as a reinforcing layer, the shock resistance tests on plain steel plate, polyurea-reinforced steel plate, and polyurea–woven fiberglass mesh composite–reinforced steel plate were carried out using the large shock tube device. Finite element method simulation was also carried out. The results of experimental and numerical simulation show that the deformation of polyurea–woven fiberglass mesh composite reinforcing layer is smaller than that of pure polyurea reinforcing layer, and the overall deformation of steel plate reinforced by polyurea–woven fiberglass mesh composite is minimal among all the three specimens. With the same polyurea consumption in reinforcing layer, the mass of the 3.5-mm-thick polyurea–woven fiberglass mesh composite–reinforced steel plate is only 2.92% larger than that of the 3.2-mm-thick pure polyurea–reinforced steel plate, but it can reduce the residual displacement of steel plate center by additional 13.03%. The work in this article has some reference value to improve the shock resistance of polyurea-reinforced structure in engineering.

Test Gas Slug Characterization for Large-Scale Shock Tube Facility

An experimental methodology for characterizing the available test gas slug is presented for a gas-driven shock tube. The method employs simple models for theoretical and experimental estimates of the available test gas slug at the time of interaction of the contact surface with the reflected shock wave, avoiding any direct measurement of driver gas in the tube. The measure of this interaction length is estimated against the primary shock Mach number over the entire operating range of a large-diameter shock tube. The trends of driver gas mixing show a strong relation to the theoretical predictions. The trends also suggest that mixing of the contact surface gases in the large shock tube is independent of driver gas composition and could depend largely on diaphragm opening times. The same analysis is also used on a smaller-diameter shock tube, in which resulting trends are readily explained by the known behavior of the contact surface from previous studies. The larger tube data also indicate a laminar boundary layer growth proportionality which can be used to reduce data further. This leads to available test gas slug quantification as a function of the produced shock Mach number alone. The experimental measurement requirements for this method are that of a regular shock tube calibration setup with wall-mounted pressure sensors, which makes it very convenient to implement in any shock tube for preliminary analysis.

Experiments on Guderley Mach reflection

Experiments have been conducted in a large shock tube to examine the four-wave shock reflection pattern, now known as Guderley reflection (GR). The fourth wave, an expansion, is clearly identified, as is the supersonic patch behind the reflected wave. A shocklet terminating the supersonic patch behind the reflected wave is identified, which forms a second triple point further down the Mach stem. Evidence is presented showing the presence of more than one expansion wave and more than one shocklet, thus indicating the existence of more than one supersonic patch. In order to distinguish between cases with a single patch without the shocklet as originally proposed by Guderley and found in some computations, and the indications of a multi-patch geometry found here, and also in other computations, this latter case is designated Guderley Mach reflection (GMR). Multi-exposure images of the shock propagation superimposed on a single image frame enable estimates to be made of the strength of the major waves, and it is shown that the reflected wave is very weak.

The late-time development of the Richtmyer–Meshkov instability

Measurements have been made of the growth by the Richtmyer–Meshkov instability of nominally single-scale perturbations on an air/sulfur hexafluoride (SF6) interface in a large shock tube. An approximately sinusoidal shape is given to the interface by a wire mesh which supports a polymeric membrane separating the air from the SF6. A single shock wave incident on the interface induces motion by the baroclinic mechanism of vorticity generation. The visual thickness δ of the interface is measured from schlieren photographs obtained singly in each run and in high-speed motion pictures. Data are presented for δ at times considerably larger than previously reported, and they are tested for self-similarity including independence of initial conditions. Four different initial amplitude/wavelength combinations at one incident shock strength are used to determine the scaling of the data. It is found that the growth rate decreases rapidly with time, dδ/dt∝t−p (i.e., δ∝t1−p), where 0.67≲p≲0.74 and that a small dependence on the initial wavelength λ0 persists to large time. The larger value of the power law exponent agrees with the result of the late-time-decay similarity law of Huang and Leonard [Phys. Fluids 6, 3765–3775 (1994)]. The influence of the wire mesh and membrane on the mixing process is assessed.

Shock Tube as a Device for Testing Transonic Airfoils at High Reynolds Numbers

A performance analysis of gas-driven shock tubes shows that transonic airfoil flows with chord Reynolds numbers in the range of 100 million can be generated behind the primary shock in a large shock tube. A study of flow over simple airfoils has been carried out at low and intermediate Reynolds numbers to assess the testing technique. Results obtained from schlieren photos and airfoil pressure measurements show that steady transonic flows similar to those observed for the airfoils in wind tunnels can be generated within the available testing time in a shock tube with either properly-contoured test section walls or a properly-designed slotted-wall test section. The study indicates that the shock tube is a useful facility for studying two-dimensional high Reynolds number transonic airfoil flows.

Interaction of weak shock waves with random media

Recent studies of the scattering of weak shock waves by continuous and discrete scatterers in random media, and of the flow generated in the scattering medium by shock propagation are described. Consideration of the coupling between shock propagation and vorticity and/or entropy fluctuations in a fluid is particularly difficult if the wave is of finite amplitude, for basic nonlinearities of fluid mechanics become important both in the wave propagation and in the turbulent motion. In one experiment, wave propagation through a cubical volume of incompletely and randomly mixed gases at the end of a large shock tube has been studied. In a second, interaction with a random array of discrete scatterers (small helium-filled soap bubbles) is studied in a smaller facility. Both of these flows are visualized by schlieren and shadowgraph photography. The scattered pressure field behind the initial disturbance is measured. Methods for measuring the characteristics of the “turbulence” before and after passage of the wave using laser scattering in the random medium have been developed; the laser speckle pattern at the focal plane of the schlieren system has been recorded photographically and has been analyzed with a computer-controlled photodensitometer to yield information about the scale and intensity of the inhomogeneities in the scattering medium. [Work supported by NSF.]

The focusing of weak shock waves

This paper reports an experimental investigation, using shadowgraphs and pressure measurements, of the detailed behaviour of converging weak shock waves near three different kinds of focus. Shocks are brought to a focus by reflecting initially plane fronts from concave end walls in a large shock tube. The reflectors are shaped to generate perfect foci, arêtes and caustics. It is found that, near the focus of a shock discontinuity, a complex wave field develops, which always has the same basic character, and which is always essentially nonlinear. A diffracted wave field forms behind the non-uniform converging shock; its compressive portions steepen to form diffraction shocks, while diffracted expansion waves overtake and weaken the diffraction shocks. The diffraction shocks participate in a Mach reflexion process near the focus, whose development is determined by competition between the convergence of the sides of the focusing front and acceleration of its central portion. In fact, depending on the aperture of the convergence and the strength of the initial wave, the three-shock intersections of the Mach reflexions either cross on a surface of symmetry or remain uncrossed. In the former case, which is observed if the shock wave is relatively weak, the wavefronts emerge from focus crossed and folded, in accordance with the predictions of geometrical acoustics theory. In the latter, the strong-shock case, the fronts beyond focus are uncrossed, as predicted by the theory of shock dynamics. It is emphasized that in both cases the behaviour at the focus is nonlinear. The overtaking of the diffraction shocks by the diffracted expansions limits the amplitude of the converging wave near focus, and is the mechanism by which the maximum amplification factor observed at focus is determined. In all cases, maximum pressures are limited to rather low values.