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  • 1
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    Implosion of a spherical shock wave reflected from a spherical wall (2005)
    Cambridge University Press
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    Publication Date: 2005-05-10
    Description: The paper describes results of experiments of a converging spherical shock wave reflected from a spherical wall. In order to visualize the motion and the flow field behind the shock waves, an aspheric lens-shaped transparent test section made of acrylic PMMA (polymethyl methacrylate) with an inner spherical cavity was designed and constructed. This test section made optical flow visualization with collimated object beams possible. Spherical shock waves were produced at the centre of the spherical cavity by explosion of silver azide pellets ranging from 1.0 to 10.0 mg with corresponding energies of 1.9 to 19 J. The charges were ignited by irradiation of a pulsed Nd:YAG laser beam. Pressures were also measured at two points with pressure transducers mounted flush at the inner wall of the test section. The pellet was simultaneously ignited on two sides or was shaped to produce a uniform diverging spherical shock wave. This spherically diverging shock wave was reflected from the spherical inner wall of the test section to form a converging spherical shock wave. We visualized the shock-wave motion by using double exposure holographic interferometry and time-resolved high-speed video recording. The sequence of diverging and converging spherical shock-wave propagations and their interaction with gaseous explosion products were observed. The convergence, acceleration and stability of the imploding shock wave in the test section were studied. © 2005 Cambridge University Press.
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    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 2
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    The persistence of regular reflection during strong shock diffraction over rigid ramps (2001)
    Cambridge University Press
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    Publication Date: 2001-03-25
    Description: We report on calculations and experiments with strong shocks diffracting over rigid ramps in argon. The numerical results were obtained by integrating the conservation equations that included the Navier-Stokes equations. The results predict that if the ramp angle θ is less than the angle θe that corresponds to the detachment of a shock, θ 〈 θe, then the onset of Mach reflection (MR) will be delayed by the initial appearance of a precursor regular reflection (PRR). The PRR is subsequently swept away by an overtaking corner signal (cs) that forces the eruption of the MR which then rapidly evolves into a self-similar state. An objective was to make an experimental test of the predictions. These were confirmed by twice photographing the diffracting shock as it travelled along the ramp. We could get a PRR with the first exposure and an MR with the second. According to the von Neumann perfect gas theory, a PRR does not exist when θ 〈 θe. A viscous length scale Xint is a measure of the position on the ramp where the dynamic transition PRR → MR takes place. It is significantly larger in the experiments than in the calculations. This is attributed to the fact that fluctuations from turbulence and surface roughness were not modelled in the calculations. It was found that Xint → ∞ as θ → θe. Experiments were done to find out how Xint depended on the initial shock tube pressure Po. The dependence was strong but could be greatly reduced by forming a Reynolds number based on Xint. Finally by definition, regular reflection (RR) never interacts with a boundary layer, while PRR always interacts; so they are different phenomena.
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  • 3
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    Vorticity production in shock diffraction (2003)
    Cambridge University Press
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    Publication Date: 2003-03-10
    Description: The production of vorticity or circulation production in shock wave diffraction over sharp convex corners has been numerically simulated and quantified. The corner angle is varied from 5° to 180°. Total vorticity is represented by the circulation, which is evaluated by integrating the velocity along a path enclosing the perturbed region behind a diffracting shock wave. The increase of circulation in unit time, or the rate of circulation production, depends on the shock strength and wall angle if the effects of viscosity and heat conductivity are neglected. The rate of vorticity production is determined by using a solution-adaptive code, which solves the Euler equations. It is shown that the rate of vorticity production is independent of the computational mesh and numerical scheme by comparing solutions from two different codes. It is found that larger wall angles always enhance the vorticity production. The vorticity production increases sharply when the corner angle is varied from 15° to 45°. However, for corner angles over 90°, the rate of vorticity production hardly increases and reaches to a constant value. Strong shock waves produce vorticity faster in general, except when the slipstream originating from the shallow corner attaches to the downstream wall. It is found that the vorticity produced by the slipstream represents a large proportion of the total vorticity. The slipstream is therefore a more important source of vorticity than baroclinic effects in shock diffraction.
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  • 4
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    Flow through a perforated surface due to shock-wave impact (1996)
    Cambridge University Press
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    Publication Date: 1996-05-10
    Description: The factor which is of prime importance in influencing the shock reflection geometry, and resulting pressures, following impingement of a shock wave on a porous surface is the velocity of the flow into the surface. A set of experiments has been conducted, using holographic inferometry in a shock tube, on the impingement of a shock wave on a surface covered with slits, over the full range of shock incidence angles from 0 to 90°. Inverse shock pressure ratios of 0.4, 0.5 and 0.7 were used, and detailed characterization of the flow fields determined. A number of methods are used to infer the inflow into the surface, and measurements are also conducted on the downstream side of the slit plate in order to establish the pressure ratio across the plate. The tests include choking of the flow through the slits. Shock reflection angles are found to be depressed compared to reflection from an impervious wall for cases of regular reflection, but are similar in the case of Mach reflection with the incident wave near glancing incidence. Contrary to assumptions made in previous work it is shown that for wall angles from zero up to approximately 60° the inflow to the plate is inclined to the surface at about 17° and then tends to straighten out until, for normal shock reflection, the flow is also normal to the plate. It appears that this behaviour is linked to the separation of the flow at the inlet to the pores of the model, due to shock wave diffraction. The maximum value of the absolute inflow velocity occurs in the region of transition from regular to Mach reflection. A series of starting vortices is shed on the underside of the slit and is found to follow a path nearly normal to the plate. These vortices lie along a contact surface whose motion is compatible with the strength of the shock wave transmitted through the plate.
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  • 5
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    Analytical prediction of the transition from Mach to regular reflection over cylindrical concave wedges (1985)
    Cambridge University Press
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    Publication Date: 1985-09-01
    Description: Two formulas, based on analytical considerations, which are capable of predicting the wedge angle of transition from Mach to regular reflection over cylindrical concave wedges, are developed. They are derived using Hornung, Oertel & Sandeman’s (1979) conclusion that a Mach reflection can exist only if the corner-generated signals can catch up with the incident shock wave. The good agreement between the present models and the experimental results confirm Hornung et al.’s (1979) concept. The predictions of these models are in better agreement with experimental results than the predictions of Itoh, Okazaki & Itaya’s (1981) model. The present models are very simple to use and apply but, like Itoh et al.’s (1981) model, they also lack the ability to account for the dependence of the transition angle on the radius of curvature of the cylindrical wedge. © 1985, Cambridge University Press. All rights reserved.
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  • 6
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    Experimental and theoretical study of shock wave propagation through double-bend ducts (2001)
    Cambridge University Press
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    Publication Date: 2001-06-22
    Description: The complex flow and wave pattern following an initially planar shock wave transmitted through a double-bend duct is studied experimentally and theoretically/numerically. Several different double-bend duct geometries are investigated in order to assess their effects on the accompanying flow and shock wave attenuation while passing through these ducts. The effect of the duct wall roughness on the shock wave attenuation is also studied. The main flow diagnostic used in the experimental part is either an interferometric study or alternating shadow-schlieren diagnostics. The photos obtained provide a detailed description of the flow evolution inside the ducts investigated. Pressure measurements were also taken in some of the experiments. In the theoretical/numerical part the conservation equations for an inviscid, perfect gas were solved numerically. It is shown that the proposed physical model (Euler equations), which is solved by using the second-order-accurate, high-resolution GRP (generalized Riemann problem) scheme, can simulate such a complex, time-dependent process very accurately. Specifically, all wave patterns are numerically simulated throughout the entire interaction process. Excellent agreement is found between the numerical simulation and the experimental results. The efficiency of a double-bend duct in providing a shock wave attenuation is clearly demonstrated.
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  • 7
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    The transition from regular to Mach reflexion and from Mach to regular reflexion in truly non-stationary flows (1980)
    Cambridge University Press
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    Publication Date: 1980-09-01
    Description: An experimental investigation on the IHSM 4 × 8 cm Shock Tube has confirmed the hypothesis of Ben-Dor (1978) and Ben-Dor & Glass (1979) that in truly non-stationary flows the transitions from regular to Mach reflexion (RR → MR) and from Mach to regular reflexion (MR → RR) are different. Consequently it is shown that a hysteresis loop exists in the [formula omitted] transition phenomenon. © 1980, Cambridge University Press. All rights reserved.
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  • 8
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    The reflection of a plane shock wave over a double wedge (1987)
    Cambridge University Press
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    Publication Date: 1987-03-01
    Description: An analysis is presented of the shock wave configurations which will occur when a plane shock is incident on a double wedge for which the second wedge may have a greater (concave case) or a smaller (convex case) inclination than the first wedge. It is shown that seven different reflection processes may be expected depending on the Mach number of the incident shock Mi and the two wedge angles 0^ and 0%,. These processes may be defined by seven regions in the (θ1W θ2W)-plane, for a given value of Mi. Each of the seven processes has been verified by sequences of shadowgraph and schlieren photographs. A shock polar analysis of each of the seven processes has provided information about the pressure changes and the wave structures which develop immediately behind the main reflections along the wedge surfaces. These wave structures have been verified experimentally, and two types have been observed: one normal to the reflecting surface, and the other in the form of a regular reflection. The criteria to determine which of these configurations will occur have not yet been established. It is believed that the present study will be of value in predicting the loading of shock waves on structures, and may lead to a better understanding of shock reflections from concave and convex cylindrical surfaces. © 1987, Cambridge University Press. All rights reserved.
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  • 9
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    Influence of surface roughness on the transition from regular to Mach reflection in pseudo-steady flows (1987)
    Cambridge University Press
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    Publication Date: 1987-03-01
    Description: The effect of surface roughness on the transition from regular (RR) to Mach reflection (MR) over straight wedges in pseudo steady flows was investigated both experimentally and analytically. A model for predicting the RR ⇄ MR transition in the (Miθw)-plane was developed (Miis the incident shock wave Mach number and θwis the reflecting wedge angle). Its validity was checked against experimental results. Since the experimental results are limited to the ranges 1 〈 Mi 〈 2 and surface roughness heights of 0 〈 e ≤ 0.2 cm, the proposed model is applicable to these ranges only. In the proposed model (the boundary layer displacement thickness model), the RR ⇄ MR transition is related to the boundary layer thickness which in turn depends on the surface roughness. © 1987, Cambridge University Press. All rights reserved.
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  • 10
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    Coupled interactions of shock-wave structure with laminar boundary layers in ionizing-argon flows (1980)
    Cambridge University Press
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    Publication Date: 1980-04-01
    Description: Analyses are made of the mutual interactions between shock structure and the sidewall laminar boundary layer and their effects on the quasi-steady flat-plate laminar boundary layer in ionizing-argon shock-tube flows. The mutual interactions are studied using effective quasi-one-dimensional equations derived from an area-averaged-flow concept in a finite-area shock tube. The effects of mass, momentum and energy nonuniformities and the wall dissipations in the ionization and relaxation regions on the argon shock structure are discussed. The new results obtained for shock structure, shock-tube laminar side-wall and quasi-steady flat-plate boundary-layer flows are compared with dual-wavelength interferometric data obtained from the UTIAS 10 × 18 cm Hypervelocity Shock Tube. It is shown that the difference between the results obtained from the present method and those obtained by Enomoto based on Mirels' perfect-gas boundary-layer solutions are significant for lower shock Mach numbers (Ms ∼ 13) where the relaxation lengths are large (∼ 10cm). In general, the present results agree better with our experimental data than our previous results for uncoupled ionizing flows. © 1980, Cambridge University Press. All rights reserved.
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