The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Beixiang Fang - One of the best experts on this subject based on the ideXlab platform.
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stability of transonic shocks in steady Supersonic Flow past multidimensional wedges
Advances in Mathematics, 2017Co-Authors: Guiqiang Chen, Beixiang FangAbstract:Abstract We are concerned with the stability of multidimensional (M-D) transonic shocks in steady Supersonic Flow past multidimensional wedges. One of our motivations is that the global stability issue for the M-D case is much more sensitive than that for the 2-D case, which requires more careful rigorous mathematical analysis. In this paper, we develop a nonlinear approach and employ it to establish the stability of weak shock solutions containing a transonic shock-front for potential Flow with respect to the M-D perturbation of the wedge boundary in appropriate function spaces. To achieve this, we first formulate the stability problem as a free boundary problem for nonlinear elliptic equations. Then we introduce the partial hodograph transformation to reduce the free boundary problem into a fixed boundary value problem near a background solution with fully nonlinear boundary conditions for second-order nonlinear elliptic equations in an unbounded domain. To solve this reduced problem, we linearize the nonlinear problem on the background shock solution and then, after solving this linearized elliptic problem, develop a nonlinear iteration scheme that is proved to be contractive.
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stability of transonic shocks for the full euler system in Supersonic Flow past a wedge
Mathematical Methods in The Applied Sciences, 2006Co-Authors: Beixiang FangAbstract:We study the stability of transonic shocks in steady Supersonic Flow past a wedge. It is known that in generic case such a problem admits two possible locations of the shock front, connecting the Flow ahead of it and behind it. They can be distinguished as Supersonic–Supersonic shock and Supersonic–subsonic shock (or transonic shock). Both these possible shocks satisfy the Rankine–Hugoniot conditions and the entropy condition. We prove that the transonic shock is conditionally stable under perturbation of the upstream Flow or perturbation of wedge boundary. Copyright © 2005 John Wiley & Sons, Ltd.
Guiqiang Chen - One of the best experts on this subject based on the ideXlab platform.
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stability of transonic shocks in steady Supersonic Flow past multidimensional wedges
Advances in Mathematics, 2017Co-Authors: Guiqiang Chen, Beixiang FangAbstract:Abstract We are concerned with the stability of multidimensional (M-D) transonic shocks in steady Supersonic Flow past multidimensional wedges. One of our motivations is that the global stability issue for the M-D case is much more sensitive than that for the 2-D case, which requires more careful rigorous mathematical analysis. In this paper, we develop a nonlinear approach and employ it to establish the stability of weak shock solutions containing a transonic shock-front for potential Flow with respect to the M-D perturbation of the wedge boundary in appropriate function spaces. To achieve this, we first formulate the stability problem as a free boundary problem for nonlinear elliptic equations. Then we introduce the partial hodograph transformation to reduce the free boundary problem into a fixed boundary value problem near a background solution with fully nonlinear boundary conditions for second-order nonlinear elliptic equations in an unbounded domain. To solve this reduced problem, we linearize the nonlinear problem on the background shock solution and then, after solving this linearized elliptic problem, develop a nonlinear iteration scheme that is proved to be contractive.
Wataru Masuda - One of the best experts on this subject based on the ideXlab platform.
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numerical simulation on Supersonic Flow chemical oxygen iodine laser adopting high mach number ramp nozzle array
Journal of The Japan Society for Aeronautical and Space Sciences, 2007Co-Authors: Wataru Masuda, Masataro Suzuki, Ryo FujitaAbstract:The adoption of three types of nozzle contours, the ramp nozzle, symmetric ramp nozzle, and symmetric swept-ramp nozzle, in chemical oxygen-iodine lasers with Supersonic ejector-nozzle banks is examined by simulating the mixing and reacting Flow fields numerically. The compressible Navier-Stokes equations with a detailed chemical kinetic model are solved using a full-implicit finite volume method. The numerical results show that streamwise vortices induced downstream of the base region of the nozzle array are enhanced with decreasing the length ls of diverging region in I2 nozzle. However, the optimum ls which results in a high small signal gain coefficient exists for each nozzle contour, since the mixing depends also on the size and location of the streamwise vortex. Therefore, the symmetric swept-ramp nozzle which produces strong streamwise vortices even with rather large ls is most preferable among the proposed nozzle contours. The pitot pressure in the mixing region obtained in the present calculation is approximately 10kPa which is ten times higher than that of conventional Supersonic Flow chemical oxygen-iodine lasers.
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numerical simulation of q switched Supersonic Flow chemical oxygen iodine laser by solving time dependent paraxial wave equation
Jsme International Journal Series B-fluids and Thermal Engineering, 2006Co-Authors: Masataro Suzuki, Hiroshi Matsueda, Wataru MasudaAbstract:The quality and power of an extracted beam from a Q-switched Supersonic Flow chemical oxygen-iodine laser have been investigated by numerical simulation. The Flow system adopted in this study is the throat-mixing system proposed in a previous paper. Three-dimensional calculation for optics is coupled with one-dimensional calculation for gas Flow including chemical reactions. Both geometric and wave optics are calculated and compared to assess the effects of diffraction. Wave optics is calculated with a time-dependent paraxial wave equation. The results indicate that wave and geometric optics are qualitatively similar in the time-dependent behavior of beam power. Quantitatively, it is found that diffraction reduces the extracted power by 9%. It is also found from the spreading half-angle of the beam for wave optics that the beam quality at a maximum power is equivalent to that of a plane wave; however, it is lower than that of continuous extraction.
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numerical simulation of Supersonic Flow chemical oxygen iodine laser with high mach number ramp nozzle array
XV International Symposium on Gas Flow Chemical Lasers and High-Power Lasers, 2005Co-Authors: Masataro Suzuki, Kenichi Ito, Wataru MasudaAbstract:The characteristics of mixing between two Flows of oxygen and iodine, having different Mach numbers, are numerically examined with the intention of improving the pressure recovery of the exhaust gas of Supersonic-Flow COIL. Supersonic, parallel mixing system with ramp nozzle array is adopted. The nozzle array has unevenly-piled shape, which is expected to generate vortices and enhance mixing. Three-dimensional, compressible Navier-Stokes equations are solved by means of full-implicit finite difference method. The Flow fields are calculated for three types of nozzles, namely, ramp nozzle, symmetric ramp nozzle, and symmetric swept-ramp nozzle. The results indicate that the symmetric swept-ramp nozzle has the best performance.
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numerical simulation of a q switched Supersonic Flow chemical oxygen iodine laser solving a time dependent paraxial wave equation
XIV International Symposium on Gas Flow Chemical Lasers and High-Power Lasers, 2003Co-Authors: Masataro Suzuki, Hiroshi Matsueda, Wataru MasudaAbstract:Quality and power of the extracted beam from a Q-switched Supersonic-Flow chemical oxygen-iodine laser has been investigated by numerical simulation. The Flow system adopted in this study is a throat mixing system proposed in the previous paper. The calculation code consists of two parts: one is a code for the gas Flow and chemical reactions, and the other is that for the optics. Because of the difference of characteristic times between the phenomena in these two parts, every 300-time-steps of the latter calculation is coupled with one-time-step of the former. Both geometric and wave optics are calculated in order to assess the effects of diffraction. The wave optics is calculated with a paraxial wave equation derived in this study. The results indicate that the time dependence of the beam power is qualitatively similar between the wave and geometric optics. The peak power reaches to the maximum value at 90 ns after the initiation of oscillation. The peak value for the wave optics is 9% less than that for the geometric optics. The calculated spreading angle of the beam shows that the laser quality at the maximum power is slightly worse compared to that of continuous extraction.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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mixing reacting zone structure and small signal gain coefficient of a Supersonic Flow chemical oxygen iodine laser
XI International Symposium on Gas Flow and Chemical Lasers and High-Power Laser Conference, 1997Co-Authors: Wataru Masuda, Manabu Hishida, Naoki Azami, Hiroo Fujii, Toshio AtsutaAbstract:ABSTRACT The Flow field of a Supersonic Flow chemical oxygen-iodine laser is simulated solving three-dimensionalNavier-Stokes equations, and the dependence of the mixing/reacting zone structure and the resulting gain regionon the effective velocity ratio of '2jet to the primary Flow is studied. It is assumed that the Flow is laminar andthe water vapor condensation due to the Supersonic cooling is ignored. A chemical kinetic model encompassing 21 chemical reactions and 10 chemical species is used to determine the chemical composition of gas mixture. The 12/He ratio and plenum pressure of the secondary Flow are varied in order that the amount of iodine injected intothe primary Flow is kept constant in each effective velocity ratio. The present results demonstrate that a pair ofcontrarotating vortices generated behind the '2jet greatly enhances the mixing and the simultaneous chemicalreaction of '2 and O2('z). It is shown that the optimum condition for the secondary '2
Hamoon Pourmirzaagha - One of the best experts on this subject based on the ideXlab platform.
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The influence of micro air jets on mixing augmentation of transverse hydrogen jet in Supersonic Flow
International Journal of Hydrogen Energy, 2016Co-Authors: M. Barzegar Gerdroodbary, Mojtaba Mokhtari, Keivan Fallah, Hamoon PourmirzaaghaAbstract:Abstract In this paper, numerical simulation is performed to investigate the effects of micro air jets on mixing of the micro hydrogen jet in a transverse Supersonic Flow. The fundamental Flow feature of the interaction between an array of fuel and air jets is investigated in a Mach 4.0 crossFlow with a fuel global equivalence ratio of 0.5. Parametric studies were conducted on the various air jet conditions by using the Reynolds-averaged Navier–Stokes equations with Menter's Shear Stress Transport (SST) turbulence model. Numerical study of eight streamwise transverse sonic fuel and air jets in a fully turbulent Supersonic Flow revealed an extremely complex feature of fuel and air jet interaction. The results present various Flow features depending upon the number and mass Flow rate of micro air jets. These Flow features were found to have significant effects on the mixing of hydrogen jets. Results also show a different Flow structure as air jet is presented in the downstream of each fuel jet. According to the obtained results, mixing rate is low in micro fuel jets without air jets. When the air jets are injected in the downstream of each fuel jet, the mixing of the hydrogen jet significantly increases (more than 60%) in the downstream. As the number of air jets is increased, the mixing performance of the fuel jet is increased more than 150%. Therefore, an enhanced mixing zone is obtained in downstream of the injection slots which leads to flame-holding.
J S B Gajjar - One of the best experts on this subject based on the ideXlab platform.
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on unsteady boundary layer separation in Supersonic Flow part 1 upstream moving separation point
Journal of Fluid Mechanics, 2011Co-Authors: A I Ruban, D Araki, R Yapalparvi, J S B GajjarAbstract:This study is concerned with the boundary-layer separation from a rigid body surface in unsteady two-dimensional laminar Supersonic Flow. The separation is assumed to be provoked by a shock wave impinging upon the boundary layer at a point that moves with speed V sh along the body surface. The strength of the shock and its speed V sh are allowed to vary with time t, but not too fast, namely, we assume that the characteristic time scale t « Re -1/2 / V 2 w . Here Re denotes the Reynolds number, and V w =-V sh is wall velocity referred to the gas velocity V ∞ in the free stream. We show that under this assumption the Flow in the region of interaction between the shock and boundary layer may be treated as quasi-steady if it is considered in the coordinate frame moving with the shock. We start with the Flow regime when V w = O(Re -1/8 ). In this case, the interaction between the shock and boundary layer is described by classical triple-deck theory. The main modification to the usual triple-deck formulation is that in the moving frame the body surface is no longer stationary; it moves with the speed V w =-V sh . The corresponding solutions of the triple-deck equations have been constructed numerically. For this purpose, we use a numerical technique based on finite differencing along the streamwise direction and Chebyshev collocation in the direction normal to the body surface. In the second part of the paper, we assume that 1 » V w » O(Re -1/8 ), and concentrate our attention on the self-induced separation of the boundary layer. Assuming, as before, that the Reynolds number, Re, is large, the method of matched asymptotic expansions is used to construct the corresponding solutions of the Navier-Stokes equations in a vicinity of the separation point.
