摘要:

This paper presents a numerical study of strong shock wave diffraction at a convex edge, using an explicit second‐order Godunov‐type Euler scheme based upon the solution of a generalized Riemann problem (GRP). For large diffraction angles the Euler computations produce flow separation at the diffraction edge, without artificial forcing, similar to experimental findings, and salient flow features such as primary and secondary shock waves, contact surfaces and vortex trajectories are well predicted. At smaller diffraction angles the Euler computations show that separation occurs further downstream of the edge than is found experimentally. The preliminary formulation of Navier‐Stokes modelling for this case is considered.

ISSN:0094-243X    

DOI:10.1063/1.39454

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A new generation of spacecraft is currently being designed. Some of the proposed concepts involve the use of air breathing engines during part of the earth to orbit flight phase. In the case of the HOTOL concept studies, the engine intakes will be covered for the re‐entry phase, and will protrude through the windward surface shock layer during re‐entry. An understanding of the complex flow which will occur over the closed intakes during the hypersonic re‐entry is important for at least two reasons. Firstly, the heat transfer on the surfaces has to be estimated to allow for suitable intake cover design. Secondly, the wake of the intakes interacts with the underside of the wings and control surfaces, and could possibly cause handling anomalies.The present paper describes a study in which a simplified model involving a double wedge mounted on a flat plate at incidence (Fig. 1) was tested in the Free Piston Shock Tunnel T3 at the Australian National University. Heat transfer measurements and shock luminosity photographs were recorded at two operating conditions, one with a stagnation enthalpy of 22 MJ/kg and the other with 2.8 MJ/kg. A flow analysis which identified a number of significantly different flow regimes was also performed.Heat transfer measurements indicate that heating rates well in excess of those expected at the stagnation point on the nose of the spacecraft can be expected. The results also highlighted a compromise which is a necessary feature of this type of design. The compromise involves a trade off between intake efficiency during the air breathing phase of operation and the reduction of heat transfer during the re‐entry phase.

ISSN:0094-243X    

DOI:10.1063/1.39514

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.39455

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The problem of an incident planar shock interacting with a downstream obstacle is studied here: half‐diamond and semicircular cylinders are chosen for the obstacles. Experimental data is taken from the UTIAS shock tube facility; in particular; infinite‐fringe inteferograms are analyzed which provides full flowfield data. Numerical results are obtained using a new unsplit version of the second‐order Eulerian Godunov scheme for inviscid gas dynamics which is capable of computing on general, body conforming meshes. Detailed comparisons of the two techniques are offered, and excellent agreement is confirmed.

ISSN:0094-243X    

DOI:10.1063/1.39456

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The diffraction of a plane shock wave at a convex corner with a sharp edge was studied both experimentally and numerically, and the shape of the diffracting shock wave was classified into four different types according to the profiles of wall shocks. The domains and transition boundaries of these four types were shown in an incident shock Mach number‐diffraction angle plane. The flow field behind the diffracting shock wave was also investigated in the present experimental and numerical studies, and the characteristics of the second and the third shock waves which appeared in this perturbed region were discussed.

ISSN:0094-243X    

DOI:10.1063/1.39458

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An experimental and numerical study was made on the shock wave‐induced flows past a circular cylinder in a dusty‐gas shock tube. Air containing fly ashes (mean diameter 5 &mgr;m) was used for dusty‐gas. Flow visualization studies were conducted by a shadowgraph method and an Imacon high speed camera, and a pulsed laser holographic interferometry. The behavior of shock waves past a circular cylinder in a dusty‐gas, the development of dust‐free regions and the formation of vortices behind a circular cylinder were clarified by those flow visualization method. The experimental results of the shock wave‐induced dusty‐gas flow past a circular cylinder were also compared with the numerical simulation using the TVD finite difference scheme applied to the Navier‐Stokes equations. Good agreement was obtained between the interferograms and the numerical simulations.

ISSN:0094-243X    

DOI:10.1063/1.39407

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Detailed distributions of aerodynamic heating were measured in the interaction region caused by a long cylinder on a flat plate in shock tunnel. Oil flow patterns and Schlieren photographs were taken. The results were discussed and approximate methods were given for determining separation shock angle, heating peak values and their locations on both, the cylinder leading edge and the plate.

ISSN:0094-243X    

DOI:10.1063/1.39408

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A planar shock wave, which is discharged from the open end of a circular cross sectional shock tube into free space, is diffracted and results in a spherical shock wave. Behind the spherical shock wave a complicated flow is observable. In this paper this axisymmetric shock wave phenomenon was investigated experimentally and numerically. The experiment was conducted in a 25 mm diameter shock tube equipped with double exposure holographic interferometry. In order to evaluate the axisymmetric interferometric fringes the density profile were obtained numerically by solving the integral equation which relates the density distribution with the three dimensional fringe distributions. To simulate the axisymmetric shock diffraction, the Total Variation Diminishing (TVD) finite difference scheme is applied to the Euler equations. The computational results were compared with the evaluated experimental results. A good agreement was obtained between them.

ISSN:0094-243X    

DOI:10.1063/1.39409

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Liquid helium at temperatures below 2.172 K behaves like a quasi two‐component fluid due to the quantum effects becoming apparent at these low temperatures. The heat which is transported solely by the normal component generates temperature (second sound) shock waves and assists, above certain perturbation levels, the generation of superfluid vortex lines. The mutual friction between these vortex lines, present as a chaotic tangle, and the normal component affects strongly the fluid flow and hence heat transport, leading to a modification of the initially rectangular pulse shape, i.e. the appearance of a second temperature maximum which, close to the heater, can be much stronger than the temperature of the shock front.Experimental investigations of the overshot, made using especially developed temperature probes in the case of plane and axisymmetric heat pulses, will be presented. The results compare favourably with a semi‐phenomenological theoretical model.

ISSN:0094-243X    

DOI:10.1063/1.39410

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The response of a thick, sinusoidally distorted interface between two gases of different density to impulsive acceleration by a sequence of shock waves propagating normal to the plane of the undistorted interface has been studied experimentally and theoretically. A simple analytical model is proposed for the effect of the finite thickness on the linear growth of the disturbances while the amplitude is small. Experiments in a vertical shock tube show that the growth of distortions intially of order 0.1 mm on 1.8 cm thick light‐heavy interfaces induced by weak (1.12<Ms<1.66) shock waves is not measurable, but growth after the first and second reshocks is. The measured growth rates are presented and the initial distortions are inferred from the theory. Several effects of the wall boundary layers are described.

ISSN:0094-243X    

DOI:10.1063/1.39411

出版商:AIP    

年代:1990

数据来源: AIP