Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

The operation of a diaphragm shock tube of 5 cm inside diameter in which the driver gas is heated by the discharge of electrical energy ( ~ 10³ joules) is analyzed in detail. A technique is described for the measurement of the heated driver gas pressure and empirical relations are obtained which enable the shock speed to be calculated from a knowledge of the discharge voltage and test gas pressure. Using helium driver gas initially at atmospheric pressure, shock Mach numbers of about 20 are obtained in argon at an initial pressure of about 1 Torr. The separation of shock front and contact surface is analyzed by means of a convenient shock reflection technique using a smear camera. The properties of the shock-heated gas are shown to agree with the predictions of standard shock wave theory, which yields a temperature of about 1.3•10⁴°K and an electron density of about I0¹⁷ cm⁻³ for the case of a Mach 20 shock in argon at 0.5 Torr. In this case the shock-heated gas sample is observed to be about 5 cm in length at a position 1.2 meters from the diaphragm. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The stability of converging waves was analysed with theory and by experiment. A computer code was written in FORTRAN language for the calculation of wavefront positions of plane shock waves and cylindrical converging shock waves in ideal gas. The criteria for stability were defined and the limit of stability of imploding shock waves was obtained using the code. In order to test the model, an experiment was set up to generate shock waves in an electrothermal shock tube. These shock waves were made to propagate into a wedged channel, and the variations of the shapes of the waves front were measured from high speed framing camera pictures. Good agreement was found between the experimentally observed velocity and the model calculation, indicating that the computer procedure is a valid method to analyse the stability of converging waves. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johanneaburg, in fulfilment of the requirerments for the degree of Doctor of Philosophy. / In this work a new high speed metal forming process is experimentally and theoretically investigated and discussed. The high speed metal forming is carried out in a liquid shock tube. The pressure energy of a liquid shock wave, which is generated non-explosively is used to form the metal workpiece.(abbreviation abstract) / Andrew Chakane 2019

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering, 2017. / The cardinal aspects of supersonic and hypersonic propulsion intake design involve understanding the internal shock wave structures forming therein. A study was conducted to explore the effects of internal surface curvature and entry deflection angle on steady axisymmetric shock waves. Very little is known about these influences with only Curved Shock Theory, produced by M¨ older, providing analytical insight directly after a curved shock wave. The shock waves and accompanying flow fields which were generated were studied via experimental and numerical means. Radius normalised internal radii of curvature of 1, 1.5 and 2 with entry deflection angles of 0◦, 4◦ and 8◦ were investigated between a Mach number range of Mach 2.4 and 3.6. Experimental results were produced using a blow down supersonic wind tunnel facility and were captured via shadowgraph and schlieren flow visualisation techniques. The numerical simulations were validated using the experimental results. A self similar curved shock wave shape equation was presented with an empirical model which uses flow Mach number and internal radius of curvature in order to produce the resulting curved shock shape. Curved Shock Theory streamlines were used to try predict the internal surfaces that produced the curved shocks but results did not correlate. This was due to extreme streamline curvature curving the streamlines when the shock angle approached the Mach angle. Very good agreement was however found between the theoretical and numerical streamlines at lower curvatures. The higher the internal surface curvature and entry deflection angle, the greater the flow fields were impacted. Steeper characteristics formed as a result, curving the shock wave more noticeably. Both the internal surface curvature and entry deflection angle were found to have an effect on the trailing edge expansion fans which then altered the shape of downstream shock wave structures. The highest curvature models produced steady double reflection patterns due the flow being turned in onto itself by the imposed internal surface curvature. The effects of conical and curved internal surfaces were explored for additional insight into the presence of flow-normal curvature and the curving of the attached shock waves. / XL2018

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering, 2017. / In traditional two-dimensional shock wave theory the reflection of a shock wave off a surface is treated as an adiabatic process and that the reflection surface is perfectly rigid and smooth with an inviscid flow of the fluid. In reality it has been found that these assumptions are not entirely accurate, and that although they are a good indication in the regular and irregular reflection domains of shock waves over the surface, viscous and thermal effects are present within the flow field. It has been experimentally shown that the transition of regular reflection to irregular reflection exceeds the theoretical limit, which is known as the von Neumann paradox. This paradox has largely been accounted for in the formation of a viscous boundary layer behind the reflected shock wave, based on numerous experimental and computational studies. However, the thermal effects in the reflection process have largely been neglected as the assumption of heat transfer between the post-shock wave gas and the reflection surfaces is assumed to be invalid. These thermal effects were investigated by testing materials with a varying range of thermal conductivities (1.13 to 401 W/mK) and similar surface roughness’s below the suggested limit for hydraulic smoothness. Each experiment placed two test pieces at the same incidence angle, symmetrically in the shock tube. This allowed flow properties to be exactly the same for the two materials being tested with a single plane shock wave. Test Mach numbers ranged from 1.2790 to 1.3986, with tests conducted at shock wave incidence angles of 36◦, 40◦, 60◦ and 70◦. This allowed both the regular and irregular reflection domains to be tested. Shadowgraph images were created using a z-configuration optical set up. These shadowgraph images were analysed quantitatively based on the angles measured as well as qualitatively based on flow features and symmetry. Both the quantitative and qualitative tests indicated that there was a difference in the angles between the reflected shock waves and surfaces based on the material thermal conductivity. In the quantitative tests the value of this angle was larger for materials with a lower thermal conductivity, and smaller for ones with a higher thermal conductivity for the regular reflection cases. In the irregular reflection cases the angle between the reflected and incident shock waves was larger for materials with a higher thermal conductivity. The materials with midrange thermal conductivities had reflection angles that lay within the bounds of the glass and copper angle values. The qualitative images supported these findings showing asymmetry in materials with different thermal conductivities with the intersection of reflected shock waves lying closer to the material with a higher thermal conductivity. Control experiments using test pieces made from an identical material showed no bias due to the location of the test piece in the shock tube / XL2018

Two aspects of detonation dynamics are addressed in this thesis by articles. The first part of the thesis investigates shock reflection phenomena believed to be responsible for enhancing reaction rates in detonations, namely Kelvin-Helmholtz instability and Mach stem bifurcation caused by forward jetting. Three papers are presented. The first numerically investigates shock reflections from a wedge under detonation-like conditions. A state of the art solver of the Euler equations is used. The shock reflection configuration is shown to depend on solver type, wedge implementation, and resolution. The type of reflection (i.e. regular or irregular) is found to depend on corner geometry, even far from the corner, showing initial conditions can play important roles in shock reflections. These complications are addressed with shock-resolved viscous simulations and a new initial condition: the triple point reflection. The numerical method is demonstrated in the second paper, and the presence of Kelvin-Helmholtz instability is investigated. Viscosity is found to play an important role in delaying the instability, which is found not to be a likely source of reaction acceleration on time scales commensurate with autoignition behind the Mach stem, but may become important on scales associated with the detonation cell. Mach stem bifurcations are investigated experimentally and numerically in the third paper. Experimental shock reflections are performed from a free-slip boundary in gases with differing isentropic exponents. Bifurcations are found in experiments, viscous and inviscid simulations. Viscosity is found to delay bifurcations. Inviscid simulations are used to approximate the limits of Mach stem bifurcation in the phase space of Mach number, isentropic exponent, and reflection angle. A maximum isentropic exponent is found beyond which bifurcations do not occur, matching the irregular/regular boundary of the detonation cellular structure. Flow field instability is found in experiments at high Mach number and low isentropic exponent. The second part of the thesis, comprised of one paper, investigates the dynamics of detonations with multiple thermicity peaks using Fickett's detonation analogue. Steady state analysis predicts multiple possible steady states, but only the fastest is singularity-free. Simulations show other solutions develop shock waves that eventually establish a detonation travelling at the fastest velocity allowed by the generalized Chapman-Jouguet criterion. Characteristic and linear stability analysis shows these shocks are found to arise due to instability at the sonic points.