E. Timofeev

Development and Application of High-Resolution Adaptive Numerical Techniques in Shock Wave Research Center

A second-order accurate Godunov-0type scheme has been implemented using 2-D and 3-D locally-adaptive unstructured grids. The fundamentals of the method, specifics of vector- and massively parallel processing, and some sample applications are presented in this paper.

The influence of entrance geometry of circular reflectors on shock wave focusing

Abstract The influence of entrance shape bluntness of circular reflectors on the focusing of reflected shock waves was studied numerically and experimentally. The numerical simulation was conducted using a Godunov-type finite-volume scheme on adaptive unstructured grids and the experiment was conducted in a shock tube equipped with a holographic interferometer. The shock wave Mach number was 1.4 in air at atmospheric condition. It is found that, depending on the bluntness of the reflector entrance shape, the peak value of the focusing pressure varies drastically and is strongly influenced by the process of wave interaction during the focusing.

Numerical study of wave processes in a pressure-wave refrigerator

The paper provides some results concerning the numerical study of the strongly transient gasdynamic processes in a pressure-wave refrigerator (PWR). A hierarchical set of numerical models from the simplest one-dimensional to a fully three-dimensional formulation is introduced. The computations show that one-dimensional solutions give a reasonable foundation for the understanding of PWR operational principles but cannot satisfactorily predict the refrigeration efficiency. Good agreement with experiment is achieved by considering two- and three-dimensional effects of gas mixing by overlap of rotating nozzles and expansion tubes.

Artificial Wind — a New Framework to Construct Simple and Efficient Upwind Shock-Capturing Schemes for Complex Hydrodynamic Problems

Using a concept of Artificial Wind based on the Galilean invariance of the hydrodynamic equations, we outline a new framework to design upwind shockcapturing schemes. It allows to get simple, efficient and accurate schemes retaining their simplicity for a broad range of hydrodynamic problems. Test problems demonstrate that the newly derived schemes are quite competitive with traditional ones. For complex hydrodynamics systems (magnetohydrodynamics, relativistic hydrodynamics, complex equations-of-state etc.) they may provide at least one order of magnitude gains in efficiency while maintaining good accuracy.

Holographic interferometric and numerical visualization of three-dimensional unsteady shock wave interactions

Recent results of observation of three-dimensional (3-D) unsteady shockwave reflections are presented. The experiments are carried out using a diaphragmless shock tube in which shock waves are produced by a quickly opening piston valve which separates a high pressure driver gas from a low pressure test gas. This mechanism allows to create shock waves with a higher degree of repeatability than those obtained by conventional shock tubes in which shock waves are generated by rupturing diaphragms. Double exposure diffuse holographic interferometry is used for optical visualization. Instead of using diffusive object beams, collimated object beams are diffused by their reflection from the shock tube wall and the model painted with fluorescent paint. In addition, the time interval between two exposures is set to about 1 microsecond. Hence 3-D shock wave patterns are clearly observable. The experiment is supplemented by numerical visualizations using a 3-D adaptive unstructured Euler code working on the Cray C- 90 supercomputer platform, and then EnSight postprocessor is used to create numerical images. Two cases are examined: shock wave reflection from an inclined cylinder, and shock wave interaction with corner formed by the intersection of to wedges at 90 degree.