Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session LM: Supersonic and Hypersonic Flows |
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Chair: Gary Settles, Pennsylvania State University Room: Hilton Chicago PDR 1 |
Tuesday, November 22, 2005 8:00AM - 8:13AM |
LM.00001: Determining the TNT equivalence of gram-sized explosive charges using shock-wave shadowgraphy and high-speed video recording Michael Hargather, Gary Settles Explosive materials are routinely characterized by their TNT equivalence. This can be determined by chemical composition calculations, measurements of shock wave overpressure, or measurements of the shock wave position vs. time. However, TNT equivalence is an imperfect criterion because it is only valid at a given radius from the explosion center (H. Kleine et al., \textit{Shock Waves} 13(2):123-138, 2003). Here we use a large retroreflective shadowgraph system and a high-speed digital video camera to image the shock wave and record its location vs. time. Optical data obtained from different explosions can be combined to determine a characteristic shock wave x-t diagram, from which the overpressure and the TNT equivalent are determined at any radius. This method is applied to gram-sized triacetone triperoxide (TATP) charges. Such small charges can be used inexpensively and safely for explosives research. [Preview Abstract] |
Tuesday, November 22, 2005 8:13AM - 8:26AM |
LM.00002: Shock Structure and Ultrasound Emission in a Supersonic Jet Catalina Stern, Cesar Aguilar, Jose Manuel Alvarado, Carlos Azpeitia We study the shock structure and the ultrasound emission in a supersonic jet using Rayleigh Scattering in two different ways. On one side we visualize the shock waves and on the other we obtain the frecuency spectrum of density fluctuations for a wave-vector determined by the optics. In an axisymmetric jet we have found that besides the ultrasound fluctuations that travel at the speed of sound there are others that travel at slow velocity and are apparent very close to the shocks. We are trying to understand the origin of these slow fluctuations and determine their relationship with shocks and if they appear in other geometries. We also present the ultrasound emission pattern inside and outside the jet. [Preview Abstract] |
Tuesday, November 22, 2005 8:26AM - 8:39AM |
LM.00003: Hypersonic Boundary Layer/Oblique Shockwave Interaction Haile Lindsay, Frederick Ferguson The hypersonic boundary layer/oblique shockwave interaction problem was defined with the use of the full Navier-Stokes (NS) equations and a FORTRAN code was developed to provide numerical solutions to this problem. Further, this problem was studied under two specified sets of boundary conditions: adiabatic wall and constant wall conditions. The MacCormack Technique was used in developing this NS code. To validate the numerical code, the flat plate problem was solved, and the results compared to that published in established journals. In solving these problems, engineering tools such as, FORTRAN, TECPLOT, and EXCEL, were used to generate plots of the primitive variables, such as, the velocity components, u and v, density, and the temperature T. Selected plots were reproduced from various references in validating the work done for the flat plate and hypersonic boundary layer/oblique shockwave interaction problems. All preliminary results indicated that the code was validated and the results obtained agreed with the physical behavior of the flow fields. Now that an aerospace engineering tool was developed, it is recommended that future designers seek to further its development by making the code user-friendly and that they further test accuracy of the code by solving other 2D fluid dynamic problems. [Preview Abstract] |
Tuesday, November 22, 2005 8:39AM - 8:52AM |
LM.00004: Three Dimensional Attached and Separated Hypersonic, Turbulent Shock/Boundary Layer Interactions Neil Murray, Richard Hillier Current understanding of three-dimensional shock/boundary layer interactions in hypersonic flows is limited. Existing two-dimensional experimental results can only be perceived as nominally two-dimensional as end wall effects and other secondary effects introduce parasitic three-dimensionality into an otherwise planar flow. Since any three-dimensional study requires an excellent bench mark two-dimensional flow, we believe that the use of bodies of revolution (2D axisymmetric) is paramount. Here we introduce results from a study into shock boundary layer interactions in a Mach 8.9, turbulent flow. During the study, attached and separated interactions produced by an axisymmetric cowl surrounding an axisymmetric centrebody are investigated using schlieren photography and pressure and heat transfer sampling along the centrebody surface at points 1mm apart. A highly accurate dataset of two-dimensional axisymmetric results, produced when the cowl and centre-body are aligned has been recorded. This is then compared with a three-dimensional dataset produced when the cowl is offset relative to the centrebody giving a controlled insight into the nature of the three-dimensional interaction. [Preview Abstract] |
Tuesday, November 22, 2005 8:52AM - 9:05AM |
LM.00005: Visualization and quantitative measurements of mixing in a supersonic injector flow. Carrie Noren, C. Randall Truman, Peter Vorobieff, Timothy Madden, Gordon Hager We present an experimental study of a supersonic nozzle with supersonic injection simulating chemical oxygen-iodine (COIL) flow, with the injected flow seeded with iodine. Presence of iodine in the flow is convenient for the use of planar laser-induced fluorescence (PLIF) diagnostics for flow visualization. To facilitate the latter, we use a pulsed 565 nm tunable dye laser producing a laser sheet to illuminate a streamwise or a spanwise cross-section of the flow. We acquire flow images revealing the flow structure, including the counter-rotating vortex pair that forms as the result of the interaction of the injected material with the mean flow, with sufficient quality for quantitative analysis. Quantitative characteristics of the flow, such as penetration depth and mixing quality at various downstream distances, are extracted. The results will be compared to and enable validation of computational fluid dynamics (CFD) predictions of supersonic mixing flows in regimes relevant for chemical laser design. [Preview Abstract] |
Tuesday, November 22, 2005 9:05AM - 9:18AM |
LM.00006: Kinetic Monte Carlo Simulation for Atomic Oxygen Recombination on Silica Surface Seiji Shiozaki, Yukinori Sakiyama, Shu Takagi, Yoichiro Matsumoto Many studies have been reported about the catalytic recombination of N and O atoms on SiO$_{2}$ surface, which is quite important for the reentry of a space vehicle. But, the reaction mechanism is not fully understood. Hence, in this study, we construct a catalytic reaction model using the \textit{ab initio} calculations and the Monte Carlo calculations in order to reveal the reaction mechanism. As the first step of this study, the Kinetic Monte Carlo (KMC) calculation was performed, in which the adsorption of incident atoms, the surface diffusion, and the thermal desorption events can be considered. Here, the two different reaction processes were taken into account. One was the Langmuir-Hinshelwood (L-H) mechanisms, which corresponds to the reaction between two adsorbed species, and the other was the Eley-Rideal (E-R) mechanisms, which corresponds to the reaction between gaseous atoms and the adsorbed atom. The recombination efficiency of O atoms on a SiO$_{2}$ surface was calculated and compared with the results in literatures. Agreement between the KMC result and experimental data was good and the contributions of E-R and L-H mechanism were discussed. [Preview Abstract] |
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