Malte Kjellander

Experimental determination of self-similarity constant for converging cylindrical shocks

Guderley’s self-similarity solution r = r0(1 – t/t0)α for strong converging cylindrical shocks is investigated experimentally for three different gases with adiabatic exponents γ = 1.13; 1.40; and 1.66 and various values of the initial Mach number. Corresponding values of the similarity exponent α which determines the strength of shock convergence are obtained for each gas thus giving the variation of α with γ. Schlieren imaging with multiple exposure technique is used to track the propagation of a single shock front during convergence. The present experimental results are compared with previous experimental, numerical, and theoretical investigations.

Thermal radiation from a converging shock implosion

High energy concentration in gas is produced experimentally by focusing cylindrical shock waves in a specially constructed shock tube. The energy concentration is manifested by the formation of a hot gas core emitting light at the center of a test chamber at the instant of shock focus. Experimental and numerical investigations show that the shape of the shock wave close to the center of convergence has a large influence on the energy concentration level. Circular shocks are unstable and the resulting light emission varies greatly from run to run. Symmetry and stability of the converging shock are achieved by wing-shaped flow dividers mounted radially in the test chamber, forming the shock into a more stable polygonal shape. Photometric and spectroscopic analysis of the implosion light flash from a polygonal shock wave in argon is performed. A series of 60 ns time-resolved spectra spread over the 8 μs light flash shows the emission variation over the flash duration. Blackbody fits of the spectroscopic data...

Energy concentration by spherical converging shocks generated in a shock tube

Spherical converging shock waves are produced in a conventional shock tube with a circular cross-section. Initially, plane shocks are transformed into the shape of a spherical cap by means of a smoothly convergent cross-section. The wall shape in the transformation section is designed to gradually change the form of the shock wave until it approaches a spherical shape. Thereafter, the shock enters a conical section where it converges towards the apex of the cone. Numerical calculations with the axisymmetric Euler equations show that the spherical form is only slightly dependent on the initial Mach number of the plane shock within the range 1.5 < MS < 5.5, and is preserved to a close vicinity of the focal point. The test gas is heated to very high temperatures as a result of shock convergence and emits a bright light pulse at the tip of the test section. The light radiation is collected by optical fibers mounted at the tip of the convergence chamber and investigated by photometric and spectroscopic measure...

Shock dynamics of strong imploding cylindrical and spherical shock waves with real gas effects

Strong cylindrical and spherical shock implosion in a monatomic gas is considered A simple solution is obtained by Whithams geometrical shock dynamics approach modified to account for the real gas ...

High Energy Concentration by Spherical Converging Shocks in a Shock Tube with Conically Shaped Test Section

Converging shock waves have been extensively investigated during the past several decades. Continuing interest in this research is motivated by the ability to obtain extreme conditions in gas in the focal region. In a pioneering work, Guderley [1], (1942) published a self-similar solution of the amplification of strong converging spherical and cylindrical shock waves close to the center of convergence. Another solution to the problem was presented by Stanyukovich [2], and since then a large number of analytical and numerical studies have been conducted, see e.g. Refs. [3, 4, 5, 6, 7, 8].

Polygonal Shock Waves: Comparison between Experiments and Geometrical Shock Dynamics

The propagation of converging polygonal shocks was studied theoretically and numerically by Schwendeman and Whitham (1987)[1]. Using the approximate theory of geometrical shock dynamics (GSD), they found solutions of the behaviour of cylindrical polygonal shock waves. They showed that an initial polygonal shape repeats at different intervals during the converging process. We have conducted experiments creating similarly shaped shock waves and compared with their work.