Shock Wave Diffraction Research Articles

Propagation characteristics of pulverized coal and gas two-phase flow during an outburst.

Coal and gas outbursts are dynamic failures that can involve the ejection of thousands tons of pulverized coal, as well as considerable volumes of gas, into a limited working space within a short period. The two-phase flow of gas and pulverized coal that occurs during an outburst can lead to fatalities and destroy underground equipment. This article examines the interaction mechanism between pulverized coal and gas flow. Based on the role of gas expansion energy in the development stage of outbursts, a numerical simulation method is proposed for investigating the propagation characteristics of the two-phase flow. This simulation method was verified by a shock tube experiment involving pulverized coal and gas flow. The experimental and simulated results both demonstrate that the instantaneous ejection of pulverized coal and gas flow can form outburst shock waves. These are attenuated along the propagation direction, and the volume fraction of pulverized coal in the two-phase flow has significant influence on attenuation of the outburst shock wave. As a whole, pulverized coal flow has a negative impact on gas flow, which makes a great loss of large amounts of initial energy, blocking the propagation of gas flow. According to comparison of numerical results for different roadway types, the attenuation effect of T-type roadways is best. In the propagation of shock wave, reflection and diffraction of shock wave interact through the complex roadway types.

Three-dimensional shock wave diffraction off a discontinuous edge

The interaction of three-dimensional vortex flows was investigated through vortex shedding off a discontinuous edge. Two wedges of $$14.5^\circ $$ wedge angle (up and downstream edges) were separated by an offset. The size of the offset (5, 10, and 20 mm) and the Mach number (Mach 1.32, 1.42, and 1.6) were the key parameters investigated. Experimental images were taken and computational simulations were run; a close relation was found between the two. This enabled the three-dimensional effects of the flow to be studied and analysed. It was found, as the offset increased in size, the vortices shed off the up and downstream edges took a longer time to merge and the strength of the interaction was weaker. The vortex topology changed with a larger offset; the downstream vortex was thinner (in terms of cross-sectional diameter) adjacent to the offset, which is an indication of a change in density, than the rest of the vortex along the downstream diffraction edge. This particular feature was more prevalent at lower Mach numbers. The effect of a higher Mach number was to increase the rate of dissipation of the vortices, lengthen the shear layer due to the higher upstream velocity, and make the vortex profile elliptical.

Shock wave processes in collisional gas particle mixtures

Structures and propagation of shock waves in high density particle suspensions in gas are investigated theoretically and numerically. A physical and mathematical model which takes into account integral collisions between the particles on the basis of molecular-kinetic approaches of theory of granular materials is applied. The possibility of different types of shock waves, including double front structures is revealed. The role of particle collisions in the dynamics of particle dense layer expansion under an influence of divergent shock wave and in processes of shock wave diffraction past a backward-facing step is analyzed.

Numerical and experimental study of shock waves emanating from an open-ended rectangular tube

We examine the dynamics of a high-speed shock-induced flow near the open end of a shock tube using the particle image velocimetry (PIV) and the background oriented schlieren (BOS) methods along with two- and three-dimensional numerical simulations. In experiments, planar shock waves (\(M=1.3\)–1.6) are discharged from a rectangular (\(24\,\hbox {mm} \times 48\,\hbox {mm}\)) low-pressure section of a shock tube open to the atmosphere. Due to the rectangular exit geometry, the resulting flow is highly three-dimensional and, thus, more complicated, compared to well-studied circular/axisymmetric geometries. The study focuses on the spatio-temporal flow structure up to 1 ms after the shock wave diffraction. PIV and BOS visualization techniques share the same post-processing principle, and the iterative multi-step cross-correlation algorithm applied in the PIV software is adapted here for the calculation of background pattern displacement on the BOS images. Particular attention is given to the resolution of flow regions where sharp gradients are present, such as a diffracted shock front or embedded shocks. Computational fluid dynamic simulations of the problem are also conducted to validate the experimental results and methods and to gain more insight into the three-dimensional flow dynamics. PIV and BOS images are found to be consistent with the corresponding numerical flow visualizations.

Shock wave interactions between slender bodies

A complex interference flowfield consisting of multiple shocks and expansion waves is produced when high-speed slender bodies are placed in close proximity. The disturbances originating from a generator body impinge onto the adjacent receiver body, modifying the local flow conditions over the receiver. This paper aims to uncover the basic gas dynamics produced by two closely spaced slender bodies in a supersonic freestream. Experiments and numerical simulations were used to interpret the flowfield, where good agreement between the predictions and measurements was observed. The numerical data were then used to characterise the attenuation associated with shock wave diffraction, which was found to be interdependent with the bow shock contact perimeter over the receiver bodies. Shock-induced boundary layer separation was observed over the conical and hemispherical receiver bodies. These strong viscous-shock interactions result in double-reflected, as well as double-diffracted shock wave geometries in the interference region, and the diffracting waves progress over the conical and hemispherical receivers’ surfaces in “lambda” type configurations. This gives evidence that viscous effects can have a substantial influence on the local bow shock structure surrounding high-speed slender bodies in close proximity.

Numerical simulation of shock wave diffraction over right angle on unstructured meshes

Numerical simulation of shock wave diffraction over right angle on unstructured meshes

Experimental investigation of shock wave diffraction over a single- or double-sphere model

In this study, the unsteady drag produced by the interaction of a shock wave with a single- and a double-sphere model is measured using imbedded accelerometers. The shock wave is generated in a horizontal circular shock tube with an inner diameter of 200 mm. The effect of the shock Mach number and the dimensionless distance between spheres is investigated. The time-history of the drag coefficient is obtained based on Fast Fourier Transformation (FFT) band-block filtering and polynomial fitting of the measured acceleration. The measured peak values of the drag coefficient, with the associated uncertainty, are reported.

Shock wave diffraction in the presence of a supersonic co-flow jet

The interaction between a diffracting shock wave and a uniform jet is a case that so far has only been partially investigated. This interaction is extremely important for the control of noise generation and improvement of combustor performance. To fill this knowledge gap, three geometries of the diffracting corner, namely a straight ramp, a serrated ramp, and a rounded corner, have been tested experimentally to study the interaction of shock diffraction with a supersonic co-flow jet at incident Mach numbers of 1.31 and 1.59, with Reynolds numbers of $$1.08\times 10^{6}$$ and $$1.68\times 10^{6}$$ , respectively. Schlieren photography was employed to analyse the evolution of the flow phenomena. The aim is to provide a qualitative understanding of the interaction between the diffracting shock wave and the uniform jet relevant to future high-speed transport. The results show that the flow field evolves more rapidly and develops stronger structures for a higher shock Mach number. The diffraction around a rounded splitter develops a periodical vortical structure which continues after the disturbance introduced by the passage of the shock wave is removed.

Numerical Investigation of Shock Wave Diffraction over a Sphere Placed in a Shock Tube

For evaluating the motion of a solid body in a gaseous medium, one has to know the drag constant of the body. It is therefore not surprising that this subject was extensively investigated in the past. While accurate knowledge is available for the drag coefficient of a sphere in a steady flow condition, the case where the flow is time dependent is still under investigation. In the present work the drag coefficient of a sphere placed in a shock tube is evaluated numerically. For checking the validity of the used flow model and its numerical solution, the present numerical results are compared with available experimental findings. The good agreement between present simulations and experimental findings allows usage of the present scheme in nonstationary flows.

A Study of the Complex Flow Features Behind a Diffracted Shock Wave on a Convex Curved Wall

The complex flow features behind a diffracted shock wave on a convex curved wall is investigated using large scale experimentation complemented by numerical computation. The study aimed at explaining the global flow behavior within the perturbed region behind the diffracted shock wave. Experiments were conducted in a purpose built shock tube that is capable of generating a range of incident shock Mach numbers Mn ≤ 1.6. Analysis of higher Mach number shocks on different wall geometries were carried out using numerical code that has been validated by earlier authors. Many flow features that were only distinct at high Mach numbers are clearly identified at low Mach numbers in the present investigation. The separation point moves upstream at incident shock Mach number Mn = 1.5 but moves downstream at higher Mach numbers and is nearly stationary at Mn = 1.6. At incident shock Mach number 3.0 the movement of the separation point tends to be independent of the wall curvature as the wall radius approaches infinity. The present investigation is important in the design of high speed flow devices and in the estimation of flow resistance on supersonic devices and space vehicles.

Shock Wave Diffraction Phenomena around Slotted Splitters

In the field of aerospace engineering, the study of the characteristics of vortical flows and their unsteady phenomena finds numerous engineering applications related to improvements in the design of tip devices, enhancement of combustor performance, and control of noise generation. A large amount of work has been carried out in the analysis of the shock wave diffraction around conventional geometries such as sharp and rounded corners, but the employment of splitters with lateral variation has hardly attracted the attention of researchers. The investigation of this phenomenon around two-dimensional wedges has allowed the understanding of the basic physical principles of the flow features. On the other hand, important aspects that appear in the third dimension due to the turbulent nature of the vortices are omitted. The lack of studies that use three-dimensional geometries has motivated the current work to experimentally investigate the evolution of the shock wave diffraction around two splitters with spike-shaped structures for Mach numbers of 1.31 and 1.59. Schlieren photography was used to obtain an insight into the sequential diffraction processes that take place in different planes. Interacting among them, these phenomena generate a complicated turbulent cloud with a vortical arrangement.

Visualisation of plane shock wave diffraction from the curved exit of a shock tube

There have been numerous studies of the diffraction of a plane shock wave from the normal exit of a shock tube, including studies of tubes with square, lenticular, or other irregular exit shapes. However, in considering the practical case in which such diffraction may spontaneously occur (e.g. the propagation of a blast wave through climate conditioning ducts or of a shock wave through a tuned motor vehicle exhaust system), the more likely geometric boundary condition would be of a curved exit diffraction surface. The current study explored the diffraction of a plane shock wave from the curved exit of a shock tube with a boundary plate to remove the characteristic length of the shock tube thickness. The cases tested all had: separations between the axis of the curved plate and the shock tube axis of between 0.5 and 2.5 shock tube internal diameters; radius ratios of the exit surface to the shock tube inner diameter of 3 or 5; and Mach numbers ranging between 1.2 and 1.6. The flow field was visualised using a high-speed camera operating at 75 kfps capturing schlieren images. It was found that for the case of the exit surface tangent to the inner surface of the shock tube a vortex loop is not formed but rather a horseshoe vortex which convects downstream bound by the tangent exit plate. For higher Mach numbers it seems that the horseshoe vortex may close into a loop, but this cannot be definitely concluded from the available images. An additional feature was noted which is suspected of being the tangent view of a complex shock wave reflection due to the curved edge diffraction.

Expansion wave diffraction over a 90 degree corner

AbstractThe diffraction of an initially one-dimensional plane expansion wave over a 90° corner was explored using experiment and numerical simulation. Unlike studies of shock diffraction, expansion wave diffraction has hardly been documented previously. The planar expansion wave was produced in a shock tube by bursting a diaphragm. Two independent parameters were identified for study: (i) the initial diaphragm shock tube pressure ratio, which determines the strength (pressure ratio) of the expansion, and (ii) the position of the diaphragm from the apex of the 90° corner, which determines the width of the wave. The experimentation only considered variation in the shock tube pressure ratio whereas the simulation varied both parameters. A Navier–Stokes solver with Menter’s shear stress transport $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}k\mbox{--}\omega $ turbulence model was found to adequately model the overall flow field. A number of major flow features were identified occurring in the vicinity of the corner. These were: a shear layer that originated by flow separation at the apex of the corner; a vortex within a separation bubble that remained attached to the wall, in sharp contrast to what happens in the shock wave diffraction case, where the vortex convects downstream; and a reflected compression wave arising from perturbation signals generated by the diffraction. For a narrow-width expansion wave existing prior to diffraction, the reflected compression wave steepens into an outwardly propagating, weak cylindrical shock wave. Regions of supersonic flow are identified surrounding the bubble and can extend downstream depending on the pressure ratio. Another major flow feature identified in some cases was an oblique shock located near the separation bubble. A large wake region is evident immediately downstream of the bubble and appears to consist of two distinct layers. The experimental results showed large-scale turbulent structures within the separation bubble, and shear layer instability and vortex shedding from the separation bubble were also evident.

Diffraction of Plane Straight Shock Wave Past A Convex Corner

Lighthill's problem on the diffraction of shock wave past a convex corner has been investigated by the application of Ting and Ludloff's method. The nemerical computation for the pressure distribution along the wall has been carried out for P/P0 =3 and P/P0=10. the results agree with those of Lighthill.

Experimental investigation on shock wave diffraction over sharp and curved splitters

Shock wave diffraction occurs when a normal travelling wave passes through a sudden area expansion. Turbulent, compressible, and vortical are the characterising adjectives that describe the flow features, which are slowly smeared out due to the dissipative nature of turbulence. The study of this phenomenon provides insight into several flow structures such as shear layer formation, vortex development, and vortex/shock interaction whose applications include noise control, propulsion or wing aerodynamics. A large amount of research has been carried out in the analysis of shock wave diffraction mainly around sharp wedges, but only few studies have considered rounded corners. This project has the aim to examine and compare the flow features which develop around three different geometries, ramp, symmetric and rounded, with experimental incident shock Mach numbers of 1.31 and 1.59, and Reynolds numbers of 1.08×106 and 1.68×106. Schlieren photography is used to obtain qualitative information about the evolution of the flow field. The results show that ramp and symmetrical wedges with a tip angle of 172° behave in the same manner, which exhibit clear dissimilarities with a curved corner. The flow field evolves more rapidly for a higher incoming Mach number which is also responsible for the development of stronger structures.

Half a century of continuous shock interaction investigations in the Joint Institute for High Temperatures of Russian Academy of Sciences

This article describes the history of the investigations of shock wave interactions at the Physical Gasdynamic Department, starting from the early 50s of the last century, when the first research related to missile reentry was made. The review focuses on a number of topics studied over more than 50 years and includes the study of strong shock waves, where it is necessary to take into account the physicochemical transformations in gases, shock wave reflection, diffraction, interaction with the boundary layer and with the nozzle, as well as detonation wave formation and interactions. The investigation of shock wave interactions is a current topic at the Joint Institute for High Temperatures of the Russian Academy of Sciences. Some new results are observed: the formation of impulse jets and the self-ignition of a cold hydrogen jet, diffraction of 3D shock waves, and the effect of an impulse jet and diffracted shock wave on an obstacle.

Unsteady flow with separation behind a shock wave diffracting over curved walls

The unsteady separation of the compressible flow field behind a diffracting shock wave was investigated along convex curved walls, using shock tube experimentation at large length and time scales, complemented by numerical computation. Tests were conducted at incident shock Mach numbers of \(M_{\hbox {s}} =\) 1.5 and 1.6 over a 100 mm radius wall over a dimensionless time range up to \(\tau \le \) 6.45. The development of the near wall flow at \(M_{\hbox {s}} =\) 1.5 has been described in detail and is very similar to that observed for slightly lower \(\tau \)’s at \(M_{\hbox {s}} =\) 1.6. Computations were performed at wall radii of 100 and 200 mm and for incident shock Mach numbers from 1.5 up to and including Mach 2.0. Comparing dimensionless times for different size walls shows that for a given value of \(\tau \) the flow field is very similar for the various wall radii published to date and tested in this study. Previously published results that were examined alongside the results from this study had typical values of \(1.6 < \tau < 3.2\). At the later times presented here, flow features were observed that previously had only been observed at higher Mach numbers. The larger length scales allowed for a degree of Reynolds number independence in the results published here. The effect of turbulence on the numerical and experimental results could not be adequately examined due to limitations of the flow imaging system used and a number of questions remain unanswered.

Pressure-Sensitive Paint Measurements of Transient Shock Phenomena

Measurements of the global pressure field created by shock wave diffraction have been captured optically using a porous pressure-sensitive paint. The pressure field created by a diffracting shock wave shows large increases and decreases in pressure and can be reasonably accurately captured using CFD. The substrate, a thin-layer chromatography (TLC) plate, has been dipped in a luminophore solution. TLC plates are readily available and easy to prepare. Illumination comes from two high-intensity broadband Xenon arc light sources with short-pass filters. The sample is imaged at 100 kHz using a Vision Research Phantom V710 in conjunction with a pair of long and short pass filters, creating a band. The PSP results are compared with numerical simulations of the flow using the commercial CFD package Fluent as part of ANSYS 13 for two Mach numbers.

Unsteady relativistic shock-wave diffraction by cylinders and spheres

The unsteady relativistic shock-wave diffraction patterns generated by a relativistic blast wave impinging on a circular cylinder and a sphere are numerically simulated using some high-resolution relativistic kinetic beam schemes in a general coordinate system for solving the relativistic Euler equations of gas dynamics. The diffraction patterns are followed through about 6 radii of travel of the incident shock past the body. The complete diffraction patterns, including regular reflection, transition from regular to Mach reflection, slip lines, and the complex shock-on-shock interaction at the wake region resulting from the Mach shocks collision behind the body are reported in detail. Computational results of several incident shock Mach numbers covering the near ultrarelativistic limit are studied. Various contours of flow properties including the Lorentz factor and velocity streamline plots are also presented to add a better understanding of the complex diffraction phenomena. The three-dimensional relieving effects of the sphere cases are evident and can be quantitatively evaluated as compared with the corresponding cylinder cases.

Unsteady three-dimensional compressible vortex flows generated during shock wave diffraction

The results of an experimental and numerical investigation into the behaviour of the spiral vortex generated by shock wave diffraction over edges yawed to the incident shock wave are presented. Three-dimensional numerical simulations reveal significant distortion and bending of the free vortex in regions near the boundary of the flow domain, so as to meet it at a right angle. The results of numerical simulations were found to mimic the experimentally obtained photographs very well. The numerical results are used to explain the various features of the resultant flow fields, with particular emphasis placed on the behaviour and properties of the spiral vortex, as it evolves with time. The effects of bending on the structure of the vortex are examined. The rate of circulation production for the three-dimensional shock diffraction cases was calculated, and the trends observed correlated with those for the much published two-dimensional diffraction case.