1,267 research outputs found
Computational Confirmation of AN Abnormal Mach Reflection Wave Configuration
No full textFor the Mach reflection (MR) of symmetric shock waves of opposite families, only the wave configuration of an overall Mach reflection (oMR) consisting of two direct Mach reflections (DiMR+DiMR) is theoretically admissible. For asymmetric shock waves, an oMR composed of a DiMR and an inverse Mach reflection (InMR) is possible if the two slip layers assemble a converging-diverging stream tube, while an oMR including two inverse Mach reflections (InMR+InMR) is absolutely impossible. In this paper, an overall Mach reflection configuration with double inverse MR patterns is computationally confirmed using the computational fluid dynamics technique. The aerodynamic mechanism behind such an abnormal wave pattern is illustrated. Classical two- and three-shock theories are also applied for the theoretical analysis. (C) 2009 American Institute of Physics. [DOI:10.1063/1.3073006
Peter M. Mach
No full textabstract: Peter was 12 years old when he heard gunshots and bombing at his village.
“Lost Boys Found” is an ongoing, interdisciplinary project that is collecting, recording and archiving the oral histories of the Lost Boys/Girls of Sudan. The collection is a work-in-progress, seeking to record the oral history of as many Lost Boys/Girls as are willing, and will be used in a future book.Age: 28Region: Upper NileThis picture and bio was donated to the Lost Boys Found project from The Arizona Lost Boys Cente
John Mach Nhial
No full textabstract: John witnessed the Arab military shooting people in his villages. When he attended school in Payido he used charcoal from burned trees to write on cardboard.
“Lost Boys Found” is an ongoing, interdisciplinary project that is collecting, recording and archiving the oral histories of the Lost Boys/Girls of Sudan. The collection is a work-in-progress, seeking to record the oral history of as many Lost Boys/Girls as are willing, and will be used in a future book.Age: 27Region: Upper NileThis picture and bio was donated to the Lost Boys Found oral history project from The Arizona Lost Boys Cente
Effects of initial conditions and Mach number in the evolution of Richtmyer-Meshkov instabilities
No full textWe present an experimental study of the effects of shock intensity and initial conditions on the evolution of Richtmyer-Meshkov Instabilities (RMI). This study is carried out in a vertical shock tube with a single interface of sulfur-hexafluoride and air. We use combined particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) to obtain simultaneous measurements of velocity and density. These measurements enable us to determine single- and multi-point statistics of vector, scalar, and combined fields. We use these statistical descriptors to study the evolution of turbulence mixing in RMIs under different Mach numbers and initial conditions
Lattice Boltzmann method for compressible flows with high Mach numbers
No full textIn this paper we present a lattice Boltzmann model to simulate compressible flows by introducing an attractive force. This scheme has two main advantages: one is to soften sound speed effectively, which greatly raises the Mach number (up to 5); another is its relative simple procedure. Simulations of the March cone and the comparison between theoretical expectations and simulations demonstrate that the scheme is effective in the simulation of compressible flows with high Mach numbers, which would create many new applications
The Mach reflection of a detonation based on soot track measurements
No full textThis paper presents a series of soot tracks formed by gaseous detonation waves diffracting around wedges with different wedge angles. These cellular structure patterns describe the Mach-reflection processes of a detonation and reveal some unique characteristics. They can be used to analyze the relationship between the trajectory angle of the triple point, wedge angle, and initial pressure in Mach reflection. Compared to the Mach-reflected one-dimensional shock wave in nonreactive air, all these unique characteristics for a Mach-reflected detonation should be attributed to the transverse-wave structure of the detonation front; meanwhile, the precursor shock wave and transverse wave influence the Mach-reflected detonation, respectively. The experimental results support the recently published numerical simulation of this complex phenomenon
Shock Mach number influence on reaction wave types and mixing in reactive shock–bubble interaction
No full textAbstractWe present numerical simulations for a reactive shock–bubble interaction with detailed chemistry. The convex shape of the bubble leads to shock focusing, which generates spots of high pressure and temperature. Pressure and temperature levels are sufficient to ignite the stoichiometric H2–O2 gas mixture. Shock Mach numbers between Ma=2.13 and Ma=2.90 induce different reaction wave types (deflagration and detonation). Depending on the shock Mach number low-pressure reactions or high-pressure chemistry are prevalent. A deflagration wave is observed for the lowest shock Mach number. Shock Mach numbers of Ma=2.30 or higher ignite the gas mixture after a short induction time, followed by a detonation wave. An intermediate shock strength of Ma=2.19 induces deflagration that transitions into a detonation wave. Richtmyer–Meshkov and Kelvin–Helmholtz instability evolutions exhibit a high sensitivity to the reaction wave type, which in turn has distinct effects on the spatial and temporal evolution of the gas bubble. We observe a significant reduction in mixing for both reaction wave types, wherein detonation shows the strongest effect. Furthermore, we observe a very good agreement with experimental observations
Experimental investigation of shock–shock interactions with variable inflow Mach number
No full textExperiments on shock–shock interactions were conducted in a transonic–supersonic wind tunnel with variable free-stream Mach number functionality. Transition between the regular interaction (RI) and the Mach interaction (MI) was induced by variation of the free-steam Mach number for a fixed interaction geometry, as opposed to most previous studies where the shock generator angles are varied at constant Mach number. In this paper, we present a systematic flow-based post-processing methodology of schlieren data that enables an accurate tracking of the evolving shock system including the precise and reproducible detection of RI⇄ MI transition. In line with previous experimental studies dealing with noisy free-stream environments, transition hysteresis was not observed. However, we show that establishing accurate values of the flow deflections besides the Mach number is crucial to achieve experimental agreement with the von Neumann criterion, since measured flow deflections deviated significantly, up to 1. 2 ∘, from nominal wedge angles. We also report a study conducted with a focusing schlieren system with variable focal plane that supported the image processing by providing insights into the three-dimensional side-wall effects integrated in the schlieren images.Aerodynamic
The roles of transverse waves in Mach reflection of detonation wave
No full textExperiments were conducted with smoke foil techniques in a detonation tube to study the roles of transvers waves in Mach reflection of H-2/O-2/Ar detonation waves. We had observed changes of transverse tracks through Mach reflection and we had also observed that triple trajectory showing different shapes with the increase of wedge angle. The analyses showed the interaction between reflection wave and transverse wave deciding Mach reflection configurations and effecting the properties of transverse tracks after Mach reflection at different wedge angle
Mach Number Estimation and Pressure Profile Measurements of Expanding Dense Organic Vapors
No full textThis paper describes an experiment conducted within the nozzle test section of the Organic Rankine Cycle Hybrid Integrated Device (ORCHID) aimed at providing accurate data for the validation of NICFD flow solvers [5]. A supersonic flow of the dense vapor siloxane MM established in the nozzle of the setup was characterized by means of the schlieren technique and by pressure taps along the nozzle profile. The nozzle inlet conditions corresponded to a stagnation temperature and pressure of T0=253∘C and P0=18.36bara. At these inlet conditions, the compressibility factor of the fluid is Z0= 0.58. The nozzle backpressure was equal to Pb=2.2bara. The experimental data-set includes: 1) the average mid-plane local Mach number, which was derived from the schlieren images by estimating the angle of the Mach waves originating from the roughness of the upper and lower nozzle surfaces, 2) the angle of a shock wave generated by a 5∘ wedge placed at the nozzle exit, also detectable in the schlieren images, and 3) the static pressure distribution along the flow expansion acquired with a Scanivalve DSA3218 pressure scanner device. The Mach number at the nozzle exit estimated based on the schlieren images is M= 1.95 ± 0.05, very close to the expected value of M= 2 according to the design conditions of the experiment. The static pressure measurements have a maximum absolute uncertainty amounting to ± 1.80 kPa in the initial stages of the expansion. This information was used to assess the capability of the open-source SU2 flow solver in evaluating the NICFD effects in a supersonic flow of MM when the fluid thermodynamic properties are modeled with a cubic equation of state. For this purpose, two-dimensional Euler simulations were carried out with SU2 for the operating conditions achieved in the experiment. The numerical results are in good agreement with the experimental data. The largest deviation between the simulation and experiment is observed in the nozzle uniform region, where two dips in the Mach number occur due to a slight local decrease in flow velocity owing to two weak shock waves. The shock wave generated by the wedge located at the nozzle outlet propagates with two different angles, namely, βabove= 37. 6∘± 0.86, and βbelow= 31. 6∘± 0.64, due to the axial misalignment of the wedge with respect to the flow.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Facility Aerodynamics LaboratoryAerodynamicsFlight Performance and Propulsio
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