The U.S. Army Research Laboratory and the Centre d'Etudes de Gramat, France, executed a cooperative study in which the time dependent flow fields in Le Simulateur de Souffle a Grand Gabarit (SSGG) large blast simulator were examined. The flow characteristics of static and stagnation overpressure were measured at two longitudinal positions in the expansion tunnel of the simulator. Instrumentation rakes were designed and fabricated to support a total of 19 pairs of static and stagnation pressure transducers that were distributed across the expansion tunnel cross section at each of the longitudinal positions. Flow measurements were recorded for eight shots with peak static overpressure levels between 20 kPa and 120 kPa. The measured data were used to assess the flow uniformity and distribution at each of the longitudinal measurement positions in the simulator. A finite difference Euler equation solver and a finite volume Navier Stokes equation solver were employed in a set of detailed, three dimensional (3-D) fluid dynamics calculations that were performed to match the test conditions. The 3-D computational results are compared to the experimental data to further examine the time dependent flow characteristics and to validate the fluid dynamics codes for future blast studies.

An axi-symmetric shock-tube model has been developed to simulate the shock-wave propagation and reflection in both non-reactive and reactive flows. Simulations were performed for the full shock-tube geometry of the high-pressure shock tube facility at Texas A & M University. Computations were carried out in the CFD solver FLUENT based on the finite volume approach and the AUSM+ flux differencing scheme. Adaptive mesh refinement (AMR) algorithm was applied to the time-dependent flow fields to accurately capture and resolve the shock and contact discontinuities as well as the very fine scales associated with the viscous and reactive effects. A conjugate heat transfer model has been incorporated which enhanced the credibility of the simulations. The multi-dimensional, time-dependent numerical simulations resolved all of the relevant scales, ranging from the size of the system to the reaction zone scale. The robustness of the numerical model and the accuracy of the simulations were assessed through validation with the analytical ideal shock-tube theory and experimental data. The numerical method is first applied to the problem of axi-symmetric inviscid flow then viscous effects are incorporated through viscous modeling. The non-idealities in the shock tube have been investigated and quantified, notably the non-ideal transient behavior in the shock tube nozzle section, heat transfer effects from the hot gas to the shock tube side walls, the reflected shock/boundary layer interactions or what is known as bifurcation, and the contact surface/bifurcation interaction resulting into driver gas contamination. The non-reactive model is shown to be capable of accurately simulating the shock and expansion wave propagations and reflections as well as the flow non-uniformities behind the reflected shock wave. Both the inviscid and the viscous non-reactive models provided a baseline for the combustion model iii which involves elementary chemical reactions and requires the coupling of the chemistry with the flow fields adding to the complexity of the problem and thereby requiring tremendous computational resources. Combustion modeling focuses on the ignition process behind the reflected shock wave in undiluted and diluted Hydrogen test gas mixtures. Accurate representation of the Shock-tube reactive flow fields is more likely to be achieved by the means of the LES model in conjunction with the EDC model. The shock-tube CFD model developed herein provides valuable information to the interpretation of the shock-tube experimental data and to the understanding of the impact the facility-dependent non-idealities can have on the ignition delay time measurements.

The nonlinear characteristic differential equations applicable to a quasi-one-dimensional unsteady channel flow with friction and heat transfer are linearized and integrated in functional form for the particular study of small perturbations from ideal shock-tube flows. If the equivalence of unsteady- and steady-flow boundary layers is assumed, the problem of determining the perturbation in the unsteady flow reduces to an evaluation of the drag of a flat plate in the equivalent steady flow.

The main goal of this program was to establish a qualitative and quantitative connection, based on the appropriate dimensionless parameters and scaling laws, between shock-induced distortion of astrophysical plasma density clumps and their earthbound analog in a shock tube. These objectives were pursued by carrying out laboratory experiments and numerical simulations to study the evolution of two gas bubbles accelerated by planar shock waves and compare the results to available astrophysical observations. The experiments were carried out in an vertical, downward-firing shock tube, 9.2 m long, with square internal cross section (25×25 cm2). Specific goals were to quantify the effect of the shock strength (Mach number, M) and the density contrast between the bubble gas and its surroundings (usually quantified by the Atwood number, i.e. the dimensionless density difference between the two gases) upon some of the most important flow features (e.g. macroscopic properties; turbulence and mixing rates). The computational component of the work performed through this program was aimed at (a) studying the physics of multi-phase compressible flows in the context of astrophysics plasmas and (b) providing a computational connection between laboratory experiments and the astrophysical application of shock-bubble interactions. Throughout the study, we used the FLASH4.2 code to run hydrodynamical and magnetohydrodynamical simulations of shock bubble interactions on an adaptive mesh.

The BRL-Q1D code is a computer program that uses quasi-one-dimensional, adiabatic, inviscid, numerical algorithms to solve the Euler equations. The governing equations are derived for arbitrary geometry and transformed into a uniform computational grid. An implicit Beam-Warming solver and an explicit MacCormack solver are employed. The input requirements, the code structure and the output options are discussed. Various flow calculations with the BRL-Q1D code are verified against experiments. Calculations are performed using the experimental geometries and test conditions of a conventional shock tube, a small-scale blast-simulator model and the large blast simulator at the experimental data validates the numerical flow simulation. In addition, two methods are discussed which are helpful for improving the computational prediction.