Beric W. Skews

University of the Witwatersrand | wits · School of Mechanical, Industrial and Aeronautical Engineering

Studies of shock-vortex interactions in the past have predominantly been numerical, with a number of idealizations such as assuming an isolated vortex and a plane shock wave. In the present case the vortex is generated from flow separation at a corner. A shear layer results which wraps up into a spiral vortex. The flow is impulsively initiated by t...

Ballistic range experiments were performed for a hemisphere-flare-cylinder model at supersonic Mach numbers in the transitional Reynolds number range at Nagoya University. The free-flight portion was modelled as axisymmetric in ANSYS Fluent® V.19.0. Projectile deceleration was included in the simulation as a function of the drag force over an appro...

Increasingly agile manoeuvre is an advantage in the flight of aircraft, missiles and aerial vehicles, but the principles of accelerating aerodynamics in the transonic regime are only now being fully investigated. This study contributes to the understanding of shock and separation effects on drag during axial acceleration, using a simple geometric c...

Previous work has shown that heat transfer into a plane conducting surface affects shock wave reflection properties. In the more complex reflection case of a curved surface the situation would be different because of the increased number of reflection patterns, with a rapid change in reflection geometry as the wave propagates up the surface. Test p...

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 exi...

The interaction of a plane shock wave in air with concave profiles has been used in the past mainly to understand the nature of shock wave focusing. The current study examines the complex two-dimensional flow field resulting from the interaction of a plane shock wave entering a symmetrical cavity with curved walls. Of particular interest are the de...

Projectile accelerations above \(500~\hbox {ms}^{-2}\) are commonly encountered in aerodynamic applications, but suitable validation data are rare in this regime. Experimental transonic velocity range data for a sphere decelerating under its own drag have been used to validate a numerical model for decelerating objects. The validated model is then...

The experimental visualisation of compressible flows has undergone significant development to the point that a large number of optical techniques exist for extracting both qualitative and quantitative information from these flow fields. However, the visualisation, and importantly, validation, of three-dimensional flows requires further attention. T...

The flow field characteristics that form for a shock wave propagating through a membrane-like termination at the exit of a shock tube are studied. The strength of the shock wave reflected back into the tube, as well as the strength of the shock wave transmitted, is examined. Six different materials are used, ranging from copper and aluminium foils...

A discussion on the diffraction of convex cylindrical shock wave segments is presented. Cylindrical shock waves are considered diffracting around several convex sharp corners with different wall angles (27.5∘,45∘). It is shown that the behaviour of cylindrical shocks is qualitatively similar to that of plane shocks but quantitatively different. The...

In this study, we present the results of an investigation of the propagation of cylindrical shock wave segments in converging–diverging channels. Three planar-symmetric channels were used: two formed from a pair of walls with circular wall profiles (radii 150 mm and 225 mm) and a third following a third-order-polynomial profile. In contrast to the...

The bow shock stand-off distances of a sphere decelerating in air under its own drag were determined through numerical simulations using Fluent. Three cases were investigated with three different initial velocities. These results were then compared to steady-state numerical results obtained from the same CFD code in order to identify differences be...

A computational analysis of expansion wave diffraction was conducted using a large eddy simulation solver. The investigation was aimed at resolving particular flow features following a diffracting expansion wave which were previously identified experimentally through shadowgraph imaging but unresolved in the accompanying RANS computational analysis...

Surface effects resulting from the impact of an underwater shock wave have previously mainly been studied as a consequence of underwater chemical or nuclear explosions. Of the many complex features that occur, one is the development of surface jets or plumes. This particular aspect is examined by applying a shock wave impulse to the bottom of a cir...

The effect of the passage of blast and shock waves over sand on a hard substrate as well as a hard pan was explored. While the initial entrainment by a blast wave is similar to that by a shock wave, there is a reduction in entrainment after the passage of the negative pressure phase which may reduce the overall estimate of entrained mass. Problems...

Understanding the shape of curved axisymmetric shock waves in supersonic intake-type conditions allows one to better design for downstream compression and heating requirements. Numerical results were obtained for ring wedge models with varying internal surface curvatures and wedge entry angles at different flow Mach numbers. Experimental results we...

This study numerically investigates the compressible flow field near an axisymmetric body that is influenced by constant acceleration at 100 g where the motion is straight and level flight. Selected, instantaneous acceleration and deceleration results are compared to steady-state flow at corresponding projectile Mach numbers. The geometries tested...

Three-dimensional shock wave reflection comprises flow physics that is significantly different from the well-documented two-dimensional cases in a number of aspects. The most important differentiating factor is the sweep of the shock system. In particular, this work examines the nature of flow fields in which there is a transition of shock reflecti...

The reflection of a two-dimensional cylindrical shock wave segment on a concave-cylindrical wall segment was investigated from an experimental and numerical perspective. The images obtained from experiment show no qualitative difference between cylindrical shock behavior and how a plane shock would behave in terms of the features developed. The len...

Shock waves and expansion fans form in supersonic flows as a mechanism to allow fluid to flow conformally over a body. When bodies are in close proximity – such as in the aerospace applications of store carriage and release from aircraft, engine inlet design, and formation flying – these shock waves and expansion fans interact and give rise to an i...

Results are discussed for a slender, 10°cone-cylinder, accelerating at constant 400g along a linear path, while oriented at a fixed, 10° angle of attack, through the transonic Mach number regime 0.75 to 1.20, and with a turbulent free-stream Reynolds number, in the range ∼1×10−6, based on the cylinder diameter. The slender-body was accelerated usin...

The reflection of a two-dimensional cylindrical shock wave segment on a concave-cylindrical wall segment was investigated from an experimental and numerical perspective. Qualitatively, the experimental results show that a cylindrical shock behaves similarly to a plane shock when propagating up a concave-cylindrical wall segment. Thus, whatever diff...

Planar, constant curvature wedge configurations are experimentally and numerically studied in order to determine conditions relating to singly curved shock waves and the effects of varying surface curvatures on shock geometry and downstream flow. Post-shock flow compression is seen to be an important factor in determining conditions on the reflecti...

The use of a Sanderson prism for the visualization of density gradients in a compressible flow is shown to be an inexpensive and versatile substitute for Wollaston prisms in the application of shearing interferometry. Experimentation using the Sanderson prism in a schlieren optical setup was performed to examine the effectiveness of the prism’s use...

Streamlines behind axisymmetric curved shock waves were used to predict the internal surfaces that produced them. Axisymmetric ring wedge models with varying internal radii of curvature and leading-edge angles were used to produce numerical results. Said numerical simulations were validated using experimental shadowgraph results for a series of rin...

This study is a fundamental investigation to demonstrate the effect of significant deceleration on the transonic flow field around a blunt cylindrical projectile through a numerical approach implemented in ANSYS Fluent. The projectile geometry and order of acceleration magnitude is based on a study by Jiang et al. [1], who investigated the near bla...

The propagation of two-dimensional expansion waves over a corner has received very little attention in the past. It can be studied experimentally in a standard shock tube by placing the test section at the end of the high-pressure section rather than the conventional method with placement at the driven section. It is found that reflected compressio...

The diffraction of a cylindrical shock wave segment around convex sharp corners is considered. This investigation is approached from a numerical and analytical perspective. The numerical investigation was carried out using ANSYS Fluent while Whitham’s theory of geometric shock dynamics was used as a basis for the analytical approach. A model based...

The diffraction over a corner normal to the direction of travel of a shock wave has been well documented. This has also been extended to the diffraction of a shock wave over edges with discontinuous profiles in the flow direction. However, these studies have only considered the diffraction of a shock wave travelling over a single, plane surface ini...

The flow field which results from an expansion wave entering a cavity from an upstream tube, and the focusing effect which occurs, is investigated. Different cavity geometries, different expansion wave pressure ratios and different expansion wave widths are explored. As the expansion wave propagates into the cavity it induces flow in the opposite d...

This study is a fundamental investigation to demonstrate the effect of significant deceleration on the transonic flow field around a blunt cylindrical projectile through a numerical approach implemented in ANSYS Fluent. The projectile geometry and order of acceleration magnitude is based on a study by Jiang et al. [1], who investigated the near bla...

In the research into expansion fan/shock wave interactions, wind tunnel testing is an essential tool allowing controlled freestream conditions and variation of parameters of interest. However, certain considerations must be accounted for in the wind tunnel model design, data collection, and interpretation of the results in order to ensure good qual...

In the conventional von Neumann theoretical treatment of two-dimensional shock wave reflection off a surface, it is assumed that the flow is inviscid and that the reflecting surface is perfectly smooth, rigid, non-porous, and adiabatic. These theoretical predictions have been found to be good predictions of reflection over a significant range where...

An experimental and numerical study was conducted to examine the effects of internal surface curvature and leading-edge angle on the shock waves and steady flow fields produced by axisymmetric ring wedges. Test models with leading-edge-radius-normalised internal radii of curvature of $R_{c}=\{1,1.5,2\}$ and leading-edge angles of $\unicode[STIX]{x1...

When a planar shock wave moving into stationary fluid encounters a straight wedge inclined at some angle, the resulting reflection configuration will be either a regular reflection (RR) or a Mach reflection (MR)(Ben-dor, Shock Wave Reflection Phenomena. Springer, Berlin, 2007). Hornung et al. (J. Fluid Mech. 90:541–560, 1979) note that in order for...

The study of interfering bodies in supersonic airflow is important to the development of a number of flight vehicles, since the aerodynamic loads experienced by the body of interest (the receiver) can be influenced significantly by the interference created when in close proximity to a disturbance generator. Of particular significance is the three-d...

In the past, the Paul Vieille lecture has taken one of two formats: either the exposition on a single topic, such as by Ben-Dor in 2013, or an overview of a range of topics covering work from a single institution or group, such as that by Takayama in 2011. This paper is similar to the latter and will cover a range of experimental studies, some succ...

Although much has been determined about the behavior of two-dimensional instabilities, no experimental evidence has previously been found for three-dimensional forms of this instability. This study demonstrates observations of a conical Kelvin-Helmholtz instability formed by the self-reflection of a conical shock wave. High-speed schlieren images w...

Considering a body in supersonic flow, shock waves and expansion fans develop as a mechanism for the fluid to traverse the contours of the body. In instances where bodies are in close proximity – such as store carriage and release from aircraft, supersonic engine inlets, and formation flying – these shock waves and expansion fans interact, resultin...

Previous research on wave focusing has concentrated on shock wave cavity flows [1]. Expansion wave cavity flows have not been investigated before. This paper looks at the flow resulting from an expansion wave entering a cylindrical cavity. Initially numerical simulations were run with the assumption of a plane diaphragm, however after experimental...

A shear layer exists between two flows of different properties such as velocity or density. A finite thickness exists across a shear layer due to a velocity gradient forming on each side. The associated shear creates a region of mixing that increases in thickness from the point where the fluids first meet. Previous studies on shear layers [1, 2] re...

Research on the application of Geometric Shock Dynamics (GSD) to the propagation of plane shockwaves has shown that GSD and experimental data correlate well for stronger shocks (Ms > 3) but tends to fail for weak shocks. Bryson and Gross [1] investigated the diffraction of plane shocks (Ms ≈ 3) around spheres, cones and cylinders. A comparison of t...

There has been a large amount of work done on the shock wave and boundary layer interaction (SWBLI) as reported by Babinski [1]. In some cases, there is a tendency for the shock to induce separation. In adiabatic and non-reactive flow, the only source of entropy rise is viscosity. The SWBLI is of interest as it establishes a trend. The trend for ex...

The effects of gap width and Mach number variation on shock induced flow through a pipe gap are experimentally and numerically investigated. Both were found to have an effect on the propagation conditions in both pipes as well as the development of the flow features in the gap flow. Mach numbers of 1.34, 1.45 and 1.60 as well as gap widths of 40 to...

This study numerically and experimentally examines the resulting flow field of a shock wave passing through a pipe gap. The effects of gap geometry and shock Mach number variation are investigated. Incident shock Mach numbers of 1.3, 1.4, and 1.5 and gap widths of 25 and 50 mm were used, which correspond to 0.5 and 1.0 pipe inner diameters, respect...

As a converging cylindrical shock wave propagates over a wedge, the shock wave accelerates and the angle between the shock wave and the wedge decreases. This causes the conditions at the reflection point to move from what would be the irregular reflection domain for a straight shock wave into the regular reflection domain. This paper covers a large...

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. Experimen...

Experiments were conducted in a shock tube to determine the effect of planar wedge inlet geometry on the shock wave reflection pattern that occurred on a wedge. High-speed schlieren imaging was used to visualize the experiments conducted in air with a nominal incident shock strength of Mach 1.31. The experimental test pieces consisted of a wedge mo...

Experiments were conducted in a shock tube in order to determine the increases in shock wave strength due to reductions in area. Previous work has shown that if the reduction is too sudden significant wave reflections occur and gains are limited. A variety of curved symmetrical contractions are used, made up of parabolic surfaces with different poi...

The existing nozzle contour profiles of the CSIR's supersonic or High Speed Wind Tunnel (HSWT) produce weak waves in the test section region, which effectively degrades the air flow quality in the test section. This paper describes a calculation method developed to improve the flow quality in the test section region subject to the HSWT's limitation...

The Paleozoic amphibia known as Diplocaulus, of the order Nectridia, are characterized by long tabular horns similar in planform to the wings of a modern jet airliner. Previous research on the hydrodynamics of the head were established from wind tunnel tests but with a fixed body position placed at zero incidence. The current paper examines the hyd...

Most computational fluid dynamics simulations are, at present, performed in a body-fixed frame, for aeronautical purposes. With the advent of sharp manoeuvre, which may lead to transient effects originating in the acceleration of the centre of mass, there is a need to have a consistent formulation of the Navier–Stokes equations in an arbitrarily mo...

A preliminary experimental and numerical investigation into the interaction between two independent shock waves emerging perpendicular to each other into a common space is presented. It is arranged that two shock tubes have a common diffracting edge, so that the two waves arrive at the edge simultaneously. The shock Mach number was 1.31. The mergin...

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 dynam...

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 i...

A study to understand the flow physics produced by two slender bodies in close proximity in high-speed airflow was undertaken. The interference flow field generated by the bodies is dominated by shock and expansion waves, and of particular significance is the complex interaction of the bow-shock wave emanating from the disturbance generator, striki...

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 conditi...

A concept has been developed, and implemented, where the initial shape of a shock wave can, within limits, be arbitrarily set, with a fixed pressure ratio across it, and the duct into which it propagates can also be arbitrarily defined. A narrow slit is positioned on the end wall of a shock tube and is supplied by the essentially constant pressure...

The Kelvin-Helmholtz Instability (KHI) forms along shear layers and takes the form of repeating wave-like structures. Thus the Mach reflection shear layer has the potential to break down into the KHI.

The behaviour of a planar shock wave that encounters an inclined wedge is well known, and Ben-Dor [1] gives a detailed description of the various reflection patterns that form under these circumstances. If the angle of incidence between the shock and the wedge is low enough, then the two shock pattern known as regular reflection (RR) will occur

Shock wave focusing has been of great interest to both researchers and engineers alike. Researchers have concentrated on the fundamental gas dynamics of focus as seen in the studies of Sturtevant and Kulkarny [1] and Skews and Kleine [2]

Vortices resulting from shock wave diffraction have been studied in detail over the last several decades. These studies have concentrated on two dimensional flows. The study of three dimensional vortices as a result of shock wave diffraction is limited

In the past, much attention was given to the diffraction of a shock wave over various geometries; extensively explored through experimentation and simulation [1, 2], and by many others

Transition criteria for the steady case are derived by consideration of local flow conditions at the reflection point and were published by Ben-Dor [1]

The current work presents the results of an experimental study using a conventional diaphragm-constrained, air-driven, circular cross-section shock tube expanding into ambient conditions producing shockMach numbers between 1.25 and 1.64.

Many complex and fascinating flow features occur when a shock wave impinges on or around a surface. Understanding of these is important in view of the increasing application in a variety of fields, such as medicine and material modification, besides the more conventional fields of blast loading of structures and supersonic aerodynamics. This paper...

In this study both qualitative and quantitative flow visualization techniques are used to examine the complex flow field developed during the interaction of a plane shock wave with a compound profile. Shearing interferometry and direction-indicating colour schlieren are implemented in conjunction with high-speed time-resolved imaging. Comparisons b...

The interaction between an expansion fan and a shock wave and the resulting flow field are of importance both from a research and an applied perspective. Interesting flow phenomena arise from this interaction which are significant in supersonic engine inlet design and aircraft store carriage and release. This paper focuses on the use of various sch...

The diffraction of an initially one-dimensional plane expansion wave over a 900 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 paramete...

The Kelvin-Helmholtz instability (KHI) is an instability that takes the form of repeating wave-like structures which forms on a shear layer where two adjacent fluids are moving at a relative velocity to one another. Such a shear layer forms in the Mach reflection of shock waves. This work focuses on experimentally visualising the presence of the KH...

Experimental testing was conducted for a planar shock wave of incident Mach number \(M_\mathrm{s} = 1.33\) propagating through one of three compound parabolic profiles of 130, 195 or 260 mm in length, all of which exhibit an 80 % reduction in area. Both high-resolution single shot and low-resolution video were used in a schlieren arrangement. Re...

The steady, two-dimensional transition criteria between regular and Mach reflection are well established. Little has been done on the dynamic effect on transition due to a rapidly rotating wedge. Results from experiments and computations done on steady and unsteady shock wave transition from Mach reflection to regular reflection, MR -> RR, are desc...

This work evaluates the potential for producing quantitative data of the density field using a two-dimensional colour schlieren system within the test section of a shock tube. Density gradient components, magnitude and direction, form the basis of the quantitative evaluation. These are encoded onto an imaging plane by means of a colour-coded source...

In the unsteady process of shock reflection off convexly curved surfaces, the Reynolds number can have an influence on the development of the irregular reflection pattern. Time-resolved visualizations of the reflection process and high-resolution numerical simulation are used in this investigation to quantify this influence, which manifests itself...

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_{{s}} = 1.5 and 1.6 over a 100 mm radius wall over a dime...

The reflection of very weak shock waves from concave curved surfaces has not been well documented in the past, and recent studies have shown the possible existence of a variation in the accepted reflection configuration evolution as a shock wave encounters an increasing gradient on the reflecting surface. The current study set out to investigate th...

The aim of this work was to extend a previous investigation of the flow between two parallel disks (one of which was stationary) that have been subjected to a constant energy impact arising from a falling mass onto the upper disk assembly. Whereas the previous work considered the measurement of centreline pressures and distance between the plates o...

In order to examine the transition between regular and Mach reflection in a three-dimensional flow, a range of special geometry test pieces, and inlets, were designed. The concept is to have a geometry consisting of two plane wedges which results in regular reflection between the incident waves off the top and bottom of the inlet capped by two curv...

The transition from so-called regular to irregular shock wave reflection has been the subject of considerable research effort over the last seven decades [1]. The most thoroughly investigated case is that of the straight wedge

This work studied the flow field induced by a blast wave traversing on a circular geometry. This was with a view to explaining the transient development of the complex flow structure that is formed when there is explosion that propagates a shock wave. Tests were conducted in a large scale experimental shock tube on a 200 mm diameter wall using a ra...

Results of numerical and experimental investigations of steady state supersonic viscous corner flows in simplified geometries that resemble typical wing body-fuselage intersections are presented. These flows are numerically calculated using the computational fluid dynamics code of Fluent and include the use of standard turbulence models. Experiment...

The behaviour of conical shock waves imploding axisymmetrically was first studied numerically by Hornung (J Fluid Mech 409:1–12, 2000) and this prompted a limited experimental investigation into these complex flow patterns by Skews et al. (Shock Waves 11:323–326, 2002). Modification of the simulation boundary conditions, resulting in the loss of se...

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...