On Focusing of Shock Waves

Veronica Eliasson Postdoctoral ScholarGALCIT California Institute of TechnologyPasadena, CA In this project we study converging shocks in gas, both experimentally and numerically. The interest in converging shocks stems from their ability to concentrate energy in a small volume. However, it has proven difficult to experimentally obtain a stable cylindrical converging shock wave because initial shape perturbations are amplified during the nonlinear focusing event. In this talk, we address the issue of generating and studying stable converging shocks with various geometrical shapes.
A shock tube is used to transform an initially planar shock into a cylindrical ring-shaped shock. These cylindrical shock waves are then further transformed into different geometrical shapes during the focusing phase by two methods. One method consists of changing the shape of the outer boundary of the test section of the shock tube, while the other introduces cylindrical obstacles in specific patterns inside the test section. As a result, a polygonal shape is most often obtained and depending on the number of sides of the shock, either a Mach or regular reflection occurs at the corners during the focusing event.
The shock wave focusing is also studied numerically using Euler equations of gas dynamics for a gas obeying the ideal gas law with constant specific heats with a high-order accurate Godunov method. The governing equations are discretized on body-fitted overlapping structured grids, and adaptive mesh refinement is used to dynamically track the shocks and contact surfaces. Two problems are analyzed; an axisymmetric model of the shock tube used in the experiments and a cylindrical shock wave diffracted by cylinders in a two-dimensional test section.

Location: Seaver Science Library (SSL) - Rm 150

Audiences: Everyone Is Invited

Contact: April Mundy