京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20181号 / 理博第4266号 / 新制||理||1613(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 柴田 一成, 教授 一本 潔, 准教授 浅井 歩 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The MSU Loci/BLAST CFD code was used to study blast wave interactions with structures for different urban environments. A series of analyses which included single building structures inside of ERDC's Blast Load Simulator (BLS) with different obliquity orientations to the flow direction, two building structures inside the BLS with varying gap distances between the structures, and open air blast simulations with four structure scenarios at different building spacings and different blast orientations were performed. Unstructured and overset grid techniques were used during the modeling process and were compared for consistency with shock physics and computational performance. Results show Loci/BLAST's capability to accurately model blast wave interactions in urban environments for both unstructured and overset grids.

No description available.

This thesis by articles addresses the role played by Chapman-Jouguet (CJ) deflagrations in deflagration to detonation transition (DDT) events. By definition, CJ deflagrations are flames propagating with a sonic flow in the burned gases, and are theoretically the fastest subsonic combustion waves able to propagate steadily, predicted using conservation of mass, momentum and energy. DDT is difficult to describe, as many complex phenomena and their interaction take place, including flame instabilities, turbulent combustion, and combustion in compressible medium, among others. Recent experiments and numerical simulations however showed that, prior to transition to detonations, deflagrations plateau at the CJ regime before rapid acceleration. In the present thesis, multiple aspects of the last stages of DDT are studied, and are each presented in published articles or articles in preparation. The two articles presented in Chapter 2 focus on experiments performed on the transition of a shock-flame complex to a detonation downstream of a single obstacle, in a stoichiometric propane-oxygen mixture at low pressure, mimicking the common configuration found at the last stages of DDT in experiments and numerical simulations performed in a channel filled with obstacles. The relative large size of the obstacle and the low gas initial pressure permitted to visualize the details of the initiation of the detonation around the obstacle. Transition to detonation was found to occur in a similar fashion for variously shaped obstacles, after flame acceleration due to the interaction with reflected shocks. This acceleration process was found to occur rapidly in the case where the incident flame propagated with a burning rate close to the Chapman-Jouguet value. The third article presented in Chapter 3 describes a model aimed to predict the properties of shocks followed by a CJ deflagration, in experimental configurations where the burned gases can be vented. The formulation is similar to the double discontinuity problem adapted from the work of Chue (1993), extended to cases where the burned gases are not confined by a rear wall anymore, but can be vented through an opening of known dimensions. The properties of the shock / CJ-deflagration complex could then be predicted and compared to flame measurements done prior the initiation of detonations, obtained on a selection of large scale DDT experiments. The good agreement suggests that DDT occurs when deflagrations reach the CJ regime, corroborating with observations done in shock tubes. The article presented in Chapter 4 is aimed to present a consistent method for calculating the structure of flames propagating at arbitrary burning velocities, from the low-Mach case (isobaric) up to the CJ deflagration regime. The method uses a dynamical system approach to calculate the steady wave structure, described by ordinary differential equations. A stability analysis near the burned and unburned gases permitted to develop a numerical shooting technique, which was used to obtain the flame structure and burning rate eigenvalue. Chapter 5 is a numerical study of the deflagration to detonation transition problem in one-dimension. By linearly increasing the burning rate eigenvalue to increase the flame burning velocity, the flame first reached the CJ condition. Subsequent increase in the burning rate leads to the self-organization of the flame into a CJ deflagration - shock complex. This self-organization triggers a pulsating gasdynamic instability leading to the transition of the flame to detonation.

The advancement of computational fluid dynamics to simulate highly complex fluid flow situations have allowed for simulations that require weeks of computation using expensive high performance clusters. These simulations often generate terabytes of data and hinder the design process by greatly increasing the post-processing time. This research discusses a method to extract shock waves and separation and attachment lines as the simulation is calculating and as a post-processing step. Software agents governed by subjective logic were used to make decisions about extracted features in converging and converged data sets. Two different extraction algorithms were incorporated for shock waves and separation and attachment lines and were tested on four different simulations. A supersonic ramp simulation showed two shock waves at 10% of convergence, but did not reach their final spatial locations until 85% convergence. A similar separation and attachment line analysis was performed on a cylinder in a cross flow simulation. The cylinder separation and attachment lines were within 5% of their final spatial locations at 10% convergence, and at 85% convergence, much of the cylinder and trailing separation and attachment lines showed probability expectation values of approximately 0.90 - 1.00. An Onera M6 wing simulation was used to investigate the belief tuples of the two separate shock waves at full convergence. Probability expectation values of approximately 0.90 - 1.00 were displayed within the two shock waves because they are strong shock waves and because they met the physical requirements of shock waves. A separation and attachment line belief tuple analysis was also performed on a delta wing simulation. The forward portions of these lines showed probability expectation values of approximately 0.90 - 1.00, but dropped to approximately 0.60 - 0.75 as a consequence of their respective vortices breaking down and losing their strength. Similar to shock waves, high probability expectation values meant the separation and attachment lines were strong and physically met separation and attachment line physics. The subjective logic process presented in this research was able to determine which shock waves and separation and attachment lines were most probable, making it easier to view and further investigate these important features.

To study combustion chemistry at low temperatures in a shock tube, it is of great importance to increase experimental test times, and this can be done by tailoring the interface between the driver and driven gases. Using unconventional driver-gas tailoring with the assistance of tailoring curves, shock-tube test times were increased from 1 to 15 ms for reflected-shock temperatures below 1000 K. Provided in this thesis is the introduction of tailoring curves, produced from a 1-D perfect gas model for a wide range of driver gases and the production and demonstration of successful driver mixtures containing helium combined with either propane or carbon dioxide. The He/CO2 and He/C3H8 driver mixtures provide a unique way to produce a tailored interface and, hence, longer test times, when facility modification is not an option. The tailoring curves can be used to guide future applications of this technique to other configurations. Nonreacting validation experiments using driver mixtures identified from the tailoring curves were performed over a range of reflected-shock temperatures from approximately 800 to 1400 K, and some examples of ignition-time experiments that could not have otherwise been performed are presented.

Thesis: Mech. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1979 / Includes bibliographical references. / by Ifiyenia Kececioglu. / Mech. E. / Mech. E. Massachusetts Institute of Technology, Department of Mechanical Engineering

No description available.

Part 1 The coupled shock-tube/mass spectrometer apparatus is characterized in terms of its capabilities for chemical kinetic studies. Criteria for doing kinetic measurements by this experimental technique are discussed. The characterization experiments showed that our apparatus was capable of giving plausible signal shapes for non-reactive dynamic shots at P₁ = 5 torr. Measurements of ion current under static conditions showed that response of the quadrupole mass spectrometer was linear over a range of P₁ = 0-5 torr. Schlieren measurements indicated that the shock wave velocity was erratic and non-reproducible over the last 5 feet of the test section and that the velocity at the endwall could not be predicted from the schlieren data. The electron beam width was found to be ~.1" and the implications of this measurement for further studies on the free jet are outlined. The present beam width is suitable for jet studies in which bulk ionization of gas from a cross-section of the jet is performed. Design improvements needed for future reactive studies on our system are reviewed. In addition, experimental studies of jet risetime with a pulsed molecular beam apparatus showed poor agreement between the experimental and theoretical jet risetimes. The apparent discrepancy is discussed and possible explanations for it are given. Part 2 The rate constant k₁ for the reaction C₅H₁₂ → C₄H₉ + CH₃ was determined from reflected shock experiments (1100-1300°K) in which the progress of reaction was monitored by the appearance of H atoms. Atomic resonance absorption spectrophotometry at the Lyman-α line was performed on three mixtures (20 ppm, 10 ppm, 5 ppm) of neopentane in argon to give k₁ = .17 x 10¹⁸ exp (-84800±6200/RT) sec⁻¹. This result is in very good agreement with earlier single pulse shock tube experiments. In addition, calibration experiments for H atom were performed by shock-heating two mixtures (10 ppm and 5 ppm) of neopentane in argon. The results obtained were in good agreement with previous calibration data. / Doctor of Philosophy

We examine the dense gas behavior of Bethe-Zel'dovich-Thompson (BZT) fluids in two-dimensional, steady, inviscid, supersonic cascade configurations. Bethe-Zel'dovichThompson fluids are single-phase gases having specific heats so large that the fundamental derivative of gas dynamics, Γ, is negative over a finite range of pressures and temperatures. The equation of state is the well-known Martin-Hou equation, and the numerical scheme is the explicit predictor-corrector method of MacCormack. Numerical comparisons between BZT fluids and more classical fluids such as steam are presented in order to illustrate the possible advantages of using BZT fluids in supersonic cascades. It was found that the natural dynamics of BZT fluids can result in significant reductions in the adverse pressure gradients associated with the collision of compression waves with neighboring turbine blades. A numerical example of an entirely isentropic supersonic cascade flow using a BZT fluid is also presented. / Master of Science