Computation of Steady and Unsteady Shock-Induced Combustion Over Hypervelocity Blunt Bodies.

Details Computation of Steady and Unsteady Shock-Induced Combustion Over Hypervelocity Blunt Bodies. Computation of Steady and Unsteady Shock-Induced Combustion Over Hypervelocity Blunt Bodies.

Jan 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt........64w&link_type=abstract

Thesis (PH.D.)--STANFORD UNIVERSITY, 1992.Source: Dissertation Abstracts International, Volume: 53-01, Section: B, page: 0410.

Statistics

Computation

Scientific paper

Ballistic-range experiments performed in the 1960s and early 1970s provide excellent data for studying the coupling between supersonic fluid dynamics and nonequilibrium chemical kinetics and for evaluating combustion flow codes. In these experiments, small projectiles were fired at supersonic speeds into a variety of premixed combustible mixtures. Depending on the conditions of the experiment, one will observe either steady or unsteady phenomenon in these complex flows. The unsteady flows are notable for remarkable periodic, high -frequency oscillations (often over 1 MHz) which are still not fully understood. In this dissertation, previous difficulties in numerically simulating ballistic-range exothermic flows are investigated and solutions to both the steady and unsteady cases are presented. A detailed hydrogen-air chemical reaction mechanism with thirteen species and thirty-three reactions is coupled to the Navier-Stokes equations for this purpose. The resulting differential equations are solved using a finite-volume formulation with flux-vector splitting for the spatial differencing and a two-step predictor -corrector scheme to advance the solution in time. A fully -implicit scheme is utilized for the steady cases and a time-accurate point-implicit scheme is used for the unsteady cases. Solutions for the steady ballistic-range flows are used to establish the physical and numerical modeling requirements for accurate computations. The computations of the unsteady ballistic-range cases, believed to be the first such calculations to include a detailed chemical reaction mechanism, help explain the physical mechanism responsible for the observed periodic oscillations. Shadowgraphs made from the numerical solutions are able to reproduce intricate features observed in the experimental shadowgraphs. Further validation is obtained by comparing calculated oscillation frequencies to measured values. In the present work, grid requirements are significantly reduced by the application of a recently proposed logarithmic transformation of the species conservation equations for chemically reacting flow. The choice of the transformation is motivated by the exponential growth of species concentrations seen in combustion flows and the assumption that a more accurate numerical discretization can be made in a logarithmic space.

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