摘要:

Recent high‐velocity experiments with a ram accelerator are presented. The ram accelerator is a ramjet‐in‐tube projectile accelerator whose principle of operations is similar to that of a supersonic airbreathing ramjet. Different modes of combustion have been explored for accelerating projectiles of nearly identical geometry. Subsonic, thermally choked combustion theoretically allows a projectile to be accelerated to the Chapman‐Jouguet (C‐J) detonation velocity of a particular gas mixture. In the superdetonative regime the same projectile is accelerated while always traveling faster than the detonation velocity, and in the transdetonative regime (85–115% of detonation velocity) the same projectile may transit smoothly from a subsonic to a superdetonative combustion mode. This paper examines operation in these three regimes of flow up to velocities approaching 2500 m/s. Experimental evidence of acceleration in the transdetonative and superdetonative regimes is introduced. A computational fluid dynamics (CFD) code is being developed for studying the flow, combustion, and performance of the ram accelerator, particularly in the superdetonative regime. The code solves the 2D/axisymmetric Euler equations with coupled chemical nonequilibrium processes using a shock‐capturing technique and gives theoretical results showing efficient acceleration of projectiles is possible through velocities as high as 9 km/sec.

ISSN:0094-243X    

DOI:10.1063/1.39414

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The paper discusses the topics of ‘two dimensional’ shock‐induced separation, glancing interaction and hypersonic viscous interaction. Wherever possible both laminar and turbulent boundary layers are considered and reference is made to experimental data and to the results of mathematical modelling.Many quasi‐two dimensional tests have been made to study the flow past a compression corner. The data are reviewed with particular reference to incipient separation and the effects of separation on the pressure and heat transder distributions are described.One of the most important three‐dimensional interactions concerns the way in which a shock wave generated by a fin, pylon, tail‐plane or wing influences the boundary layer growing over the surface to which the shock‐generator is attached. A number of results are examined for a fin mounted on a flat plate or side wall. The sparate and combined effects of incidence, sweep and blutness are described.Even when no separatin occurs the boundary layers at hpersonic speeds can be be thick enough to significantly modify the pressure distribution around a given geometric shape. The example considered here is laminar viscous interaction over a trailing edge control surface and a simple analytical method is used to demonstrate the reductions in control effectiveness.The paper ends with some thoughts on future research topics and the facilities needed to pursue them.

ISSN:0094-243X    

DOI:10.1063/1.39449

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

New approaches to flowfield diagnostics now offer the possibility of generating detailed, multidimensional measurements in high‐speed air. By using a high sensitivity camera and collecting ultraviolet Rayleigh light scattered directly from the air molecules, instantaneous cross sectional images of density can be taken. By vibrationally exciting a line of oxygen molecules in air, a high‐speed flow can be tagged and velocity profiles recorded. These tools are particularly well suited to measurements of shock wave phenomena. Images of structure are recorded by Rayleigh scattering and spatial correlations show regions of correlated motion and the size and shape of turbulent features. Images of velocity profiles give a comprehensible picture of the motion of the flow field. Spatial correlations of the velocity profiles give a measure of coupled motion across the flow or through shocks. Both the velocity profiles and the Rayleigh scattering can be simultaneously recorded. These tools may be extended to measure three components of velocity and vorticity by marking small shaped elements and following them in three dimensions.

ISSN:0094-243X    

DOI:10.1063/1.39457

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.39423

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

It is shown that quasi‐one‐dimensional computational techniques can be successfully used to model the flow in large, geometrically complicated shock tubes. Such shock tubes, or blast simulators, can be used to simulate nuclear or conventional explosions by shaping the pressure history. Results from computations show favorable agreement when compared with data taken in a blast simulator facility in Gramat, France. It is furthermore shown how relatively simple computational tools can be used to design large blast/thermal simulators.

ISSN:0094-243X    

DOI:10.1063/1.39371

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The present study deals with a numerical simulation of shock propagation in chemically reactive two‐phase liquid containing explosive gas bubbles. The mixture ignition due to adiabatic bubble compression by a weak shock wave and the process of the bubble detonation wave formation are analyzed. A series of experimental and theoretic investigations of the dynamics of explosive gas bubbles and their effect on the wave field structure is reviewed.

ISSN:0094-243X    

DOI:10.1063/1.39384

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Recent single pulse shock tube experiments on the mechanisms and rates of reaction of hydrogen atoms with unsaturated compounds are described. Attention is focused on the determination of the rate constants for the abstraction of hydrogen atoms from the resonance weakened bond and the displacement of substituent groups at the site of hydrogen addition. The experimental procedure is demonstrated via measurements of the rate constant for hydrogen atom attack on mesitylene, &agr;,&agr;,&agr;, trifluorotoluene and o‐chlorophenol). The following rate expressions have been determined. k(H+(CH3)3C6H3=H2+(CH3)2C6H3CH2)=3.7×1011exp(−4342/T) l/mol‐s k(H+(CH3)3C6H3=CH3+(CH3)2C6H4)=6.7×1010exp(−3255/T) l/mol‐s k(H+CF3C6H5=CF3+C6H6)=5.2×1010exp(−483l/T) l/mol‐s k(H+o–ClC6H4OH=OH+ClC6H5)=3.2×1010exp(−4307/T) l/mol‐s k(H+o–ClC6H4OH=Cl+C6H5OH)/k(H+o–ClC6H4OH=OH+C6H5Cl) =1.05. Past work is summarized and general trends are noted.

ISSN:0094-243X    

DOI:10.1063/1.39497

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A filmwise non‐equilibrium condensation of vapour consisting of polyatomic molecules, on the endwall of a shock‐tube behind a reflected shock wave, is treated. It is shown that there exists a temporal transition phenomenon on the growth of a liquid film; the film grows approximately in proportion to the time in the early time stages, and after a transition period, it does asymptotically in proportion to the square root of the time. From the comparison between experiment and theory, the condensation parameter and the condensation coefficient of the vapour are deduced. The transition state theory has also shown that the parameter and coefficient are significantly less than those for the complete capture of molecules because of the hindrance of the rotational degrees of freedom of the molecules in the liquid state.

ISSN:0094-243X    

DOI:10.1063/1.39463

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A modified version of the method of strained coordinates is introduced which allows to circumvent the solution of a weakly nonlinear, hyperbolic wave equation by solutions of linear equations. The method is then applied to the analytic description of unsteady reflection of weak shock waves. Here we are especially interested in improving our understanding of the transition from regular reflection to Mach‐reflection which until now has not been dealt with adequately in the literature (von‐Neumann‐paradox).

ISSN:0094-243X    

DOI:10.1063/1.39479

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The history of free piston drivers is reviewed and the free piston facilities established at the Australian National University in the late 1960’s are described, with mention of the sustained and fruitful tradition of research which has been maintained in these facilities. The characteristics of the new free piston shock tunnel, T4, at The University of Queensland are outlined as well as the revival of the expansion tube. Justifications for new, and larger, free piston facilities are discussed, and the construction of new facilities is reported.

ISSN:0094-243X    

DOI:10.1063/1.39406

出版商:AIP    

年代:1990

数据来源: AIP