JP-10点火延时的激波管研究

JP-10 (exo-tetrahydrodicyclopentadiene, C10H16) ignition delay times were measured in a preheated shock tube. The vapor pressures of the JP-10 were measured directly by using a high-precision vacuum gauge, to remedy the difficulty in determining the gaseous concentrations of heavy hydrocarbon fuel arising from the adsorption on the wall in shock tube experiments. The whole variation of pressure and emission of the OH or CH radicals were observed in the ignition process by a pressure transducer and a photomultiplier with a monochromator. The emission of the OH or CH radicals was used to identify the time to ignition. Experiments were performed over the pressure range of 151-556 kPa, temperature range of 1000-2100 K, fuel concentrations of 0.1%-0.55% mole fraction, and stoichiometric ratios of 0.25, 0.5, 1.0 and 2.0. The experimental results show that for the lower and higher temperature ranges, there are different dependency relationships of the ignition time on the temperature and the concentrations of JP-10 and oxygen.     

COMPUTATION OF NONEQUILIBRIUM HYPERSONIC FLOW OVER CONCAVE CORNERS

1. IntroductionWe consider steady inviscid hyPersonic flow of air about a concave corner including chendcalreaction effects. Computation of nonequllibrium flow is duncult because of the steep gradielltsbehind the shock and an entroPy layer near the body For many cases the time scale of theChemical reactions is 1arger than, or close to, the time scale of the origina1 meChanical problemand the equllibrium chendstry mode1 is not realistic. Therefore, it is necessary to eva1uate thekinetics of c…     

Existence of multidimensional shock waves and phase boundaries

In this paper, a kind of Riemann problem for the Euler equations in a van der Waals fluid is considered. We constructed the weak solution in multidimensional space which contains one shock front and one subsonic phase boundary. We mainly follow the arguments of Majda's [A. Majda, The stability of multi-dimensional shock fronts, Mem. Amer. Math. Soc. 275 (1983) 1-95; A. Majda, The existence of multi-dimensional shock fronts, Mem. Amer. Math. Soc. 281 (1983) 1-93] and Métivier's [G. Métivier, Interaction de deux chocs pour un système de deux lois de conservation, en dimension deux d'espace, Trans. Amer. Math. Soc. 296 (1986) 431-479] work. The linear stability results are based on Majda's [A. Majda, The stability of multi-dimensional shock fronts, Mem. Amer. Math. Soc. 275 (1983) 1-95] work for the single shock front and Wang and Xin's [Y.-G. Wang, Z. Xin, Stability and existence of multidimensional subsonic phase transitions, Acta Math. Appl. Sin. 19 (2003) 529-558] work for the single phase boundary. The initial boundary value problem concerned in this paper is different from the boundary value problem for double shock fronts concerned in [G. Métivier, Interaction de deux chocs pour un système de deux lois de conservation, en dimension deux d'espace, Trans. Amer. Math. Soc. 296 (1986) 431-479], we slightly modified Métivier's frame work to establish the existence for the solution to the nonlinear problem.     

Numerical modelling of shocks in solids with elastic-plastic conditions

Results are presented for a range of one- and two-dimensional shock-wave problems in elastic-plastic and hydrodynamic metals. These problems were solved numerically using the Flux-Corrected Transport (FCT) technique which achieves high resolution without non-physical oscillations, especially at shock fronts, and has not been used before in elastic-plastic solids. The two-dimensional problems were solved using both operator- and non-operator-split techniques to highlight the significant differences between these techniques when solving shock-wave problems in elastic-plastic solids. Comparisons of the elastic-plastic solutions with the hydrodynamic solutions are made and illustrate the importance of including elastic-plastic conditions when modelling the behaviour of solids. Also, the errors in these solutions that are due to the initial conditions are discussed in detail.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Temperatures, pressures and stresses during laser shock processing

Mathematical models are developed to calculate the temperatures, pressures and stresses during laser shock processing for time-modulated (ramp-up, ramp-down and rectangular) laser pulses. Three different shock processing configurations are also considered: non-ablative exposure, ablative exposure and confined ablation with coating. The results for iron show that the plasma pressure reaches an average value of 9 GPa in direct ablation configuration and plays a dominant role for all three types of laser pulses. In the case of confined geometry, the plasma pressure reaches an average value of 20 GPa. All calculated pressures and stresses exceed the yield strength of the workpiece, indicating plastic deformation. It is also shown that pulses with short rise times yield higher plasma pressures.     

A vertex-centred finite volume method with shock detection

This paper introduces a vertex-centred finite volume method for compressible viscous flow incorporating a new shock detection procedure. The discretization is designed to be robust and accurate on the highly stretched and curved meshes necessary for resolving turbulent boundary layers around the leading edge of an aerofoil. Details of the method are described for two-dimensional problems and the natural extension of three-dimensional multiblock meshes is discussed. The shock detection procedure is used to limit the range of the shock-capturing dissipation specifically to regions containing shocks. For transonic turbulent flow this is shown to improve the boundary layer representation significantly.     

Instability of oscillatory shock profile solutions of the generalized Burgers-KdV equation

Oscillatory shock profile solutions of the Burgers-KdV equation are studied in the limit as the viscosity → 0. A rigorous proof of their instability is obtained by showing that the linearized operator about such a solution has many unstable eigenvalues for sufficiently small . The result is obtained by applying a topological method introduced by Alexander, Gardner and Jones to extract spectral information about the perturbed wave with slightly positive viscosity from particular “pieces” of the underlying wave which are approximated by a solitary wave solution of the reduced equation with no viscous dissipation.     

Evaluation of glued-diaphragm fibre optic pressure sensors in a shock tube

Glued-diaphragm fibre optic pressure sensors that utilize standard telecommunications components which are based on Fabry–Perot interferometry are appealing in a number of respects. Principally, they have high spatial and temporal resolution and are low in cost. These features potentially make them well suited to operation in extreme environments produced in short-duration high-enthalpy wind tunnel facilities where spatial and temporal resolution are essential, but attrition rates for sensors are typically very high. The sensors we consider utilize a zirconia ferrule substrate and a thin copper foil which are bonded together using an adhesive. The sensors show a fast response and can measure fluctuations with a frequency up to 250 kHz. The sensors also have a high spatial resolution on the order of 0.1 mm. However, with the interrogation and calibration processes adopted in this work, apparent errors of up to 30% of the maximum pressure have been observed. Such errors are primarily caused by mechanical hysteresis and adhesive viscoelasticity. If a dynamic calibration is adopted, the maximum measurement error can be limited to about 10% of the maximum pressure. However, a better approach is to eliminate the adhesive from the construction process or design the diaphragm and substrate in a way that does not require the adhesive to carry a significant fraction of the mechanical loading.      

An alternative procedure for approximating hyperbolic systems of conservation laws

This work presents an alternative numerical procedure for simulating a class of nonlinear hyperbolic systems, using Glimm's method for advancing in time. The standard procedure to implement this methodology suffers from the disadvantage of requiring a complete solution of the associated Riemann problem—a task, in general, not easily reached. The alternative procedure introduced in this article consists in approximating the solution of the associated Riemann problem by piecewise constant functions always satisfying the jump condition—thus circumventing the difficulty of solving the Riemann problem and giving rise to an approximation easier to implement with lower computational cost. In order to illustrate the good performance of the alternative methodology proposed, two problems are considered—namely the transport of a pollutant in the atmosphere and the dynamics of the filling up of a rigid porous medium, modeled under a mixture theory viewpoint. Comparison with the standard procedure, employing the complete solution of the associated Riemann problem for implementing Glimm's scheme, has shown good agreement.