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G. Erlebacher M.Y. Hussaini T.L. Jackson 《Theoretical and Computational Fluid Dynamics》1998,11(1):1-29
This paper addresses nonlinear effects which result from the interaction of shock waves with vortices. A series of experiments
are carried out, which involve the interaction of a strong shock wave with a single plane vorticity wave and a randomly distributed
wave system. These experiments are first conducted in the linear regime to obtain a mutual verification of theory and computation.
They are subsequently extended into the nonlinear regime. A systematic study of the interaction of a plane shock wave and
a single vortex is then conducted. Specifically, we investigate the conditions under which nonlinear effects become important,
both as a function of shock Mach number, M
1, and incident vortex strength (characterized by its circulation Γ). The shock Mach number is varied from 2 to 8, while the
circulation of the vortex is varied from infinitesimally small values (linear theory) to unity. Budgets of vorticity, dilatation,
and pressure are obtained. They indicate that nonlinear effects become more significant as both the shock Mach number and
the circulation increase. For Mach numbers equal to 5 and above, the dilatation in the vortex core grows quadratically with
circulation. An acoustic wave propagates radially outward from the vortex center. As circulation increases, its upstream-facing
front steepens at low Mach numbers, and its downstream-facing front steepens at high Mach numbers. A high Mach number asymptotic
expansion of the Rankine--Hugoniot conditions reveals that nonlinear effects dominate both the shock motion and the downstream
flow for ΓM
1 > 1.
Received 28 June 1997 and accepted 25 November 1997 相似文献
3.
S. Sarkar G. Erlebacher M. Y. Hussaini 《Theoretical and Computational Fluid Dynamics》1991,2(5-6):291-305
The purpose of this study is to investigate compressibility effects on the turbulence in homogeneous shear flow. We find that the growth of the turbulent kinetic energy decreases with increasing Mach number—a phenomenon which is similar to the reduction of turbulent velocity intensities observed in experiments on supersonic free shear layers. An examination of the turbulent energy budget shows that both the compressible dissipation and the pressure-dilatation contribute to the decrease in the growth of kinetic energy. The pressure-dilatation is predominantly negative in homogeneous shear flow, in contrast to its predominantly positive behavior in isotropic turbulence. The different signs of the pressure-dilatation are explained by theoretical consideration of the equations for the pressure variance and density variance. We previously obtained the following results for isotropic turbulence: first, the normalized compressible dissipation is of O(M
t
2
), and, second, there is approximate equipartition between the kinetic and potential energies associated with the fluctuating compressible mode. Both these results have now been substantiated in the case of homogeneous shear. The dilatation field is significantly more skewed and intermittent than the vorticity field. Strong compressions seem to be more likely than strong expansions.Dedicated to Professor J.L. Lumley on the occasion of his 60th birthday.This research was supported by the National Aeronautics and Space Administration under NASA Contract No. NAS1-18605 while the authors were in residence at the Institute for Computer Applications in Science and Engineering (ICASE), NASA Langley Research Center, Hampton, VA 23665, U.S.A. 相似文献
4.
Ali Uzun Timothy B. Davis Farrukh S. Alvi M. Yousuff Hussaini 《Theoretical and Computational Fluid Dynamics》2017,31(3):317-348
We report the findings from a theoretical analysis of optimally growing disturbances in an initially turbulent boundary layer. The motivation behind this study originates from the desire to generate organized structures in an initially turbulent boundary layer via excitation by disturbances that are tailored to be preferentially amplified. Such optimally growing disturbances are of interest for implementation in an active flow control strategy that is investigated for effective jet noise control. Details of the optimal perturbation theory implemented in this study are discussed. The relevant stability equations are derived using both the standard decomposition and the triple decomposition. The chosen test case geometry contains a convergent nozzle, which generates a Mach 0.9 round jet, preceded by a circular pipe. Optimally growing disturbances are introduced at various stations within the circular pipe section to facilitate disturbance energy amplification upstream of the favorable pressure gradient zone within the convergent nozzle, which has a stabilizing effect on disturbance growth. Effects of temporal frequency, disturbance input and output plane locations as well as separation distance between output and input planes are investigated. The results indicate that optimally growing disturbances appear in the form of longitudinal counter-rotating vortex pairs, whose size can be on the order of several times the input plane mean boundary layer thickness. The azimuthal wavenumber, which represents the number of counter-rotating vortex pairs, is found to generally decrease with increasing separation distance. Compared to the standard decomposition, the triple decomposition analysis generally predicts relatively lower azimuthal wavenumbers and significantly reduced energy amplification ratios for the optimal disturbances. 相似文献
5.
Florimond Guéniat Lionel Mathelin M. Yousuff Hussaini 《Theoretical and Computational Fluid Dynamics》2016,30(6):497-510
This work discusses a closed-loop control strategy for complex systems utilizing scarce and streaming data. A discrete embedding space is first built using hash functions applied to the sensor measurements from which a Markov process model is derived, approximating the complex system’s dynamics. A control strategy is then learned using reinforcement learning once rewards relevant with respect to the control objective are identified. This method is designed for experimental configurations, requiring no computations nor prior knowledge of the system, and enjoys intrinsic robustness. It is illustrated on two systems: the control of the transitions of a Lorenz’63 dynamical system, and the control of the drag of a cylinder flow. The method is shown to perform well. 相似文献
6.
A general framework is developed to treat inverse problems with parameters that are random fields. It involves a sampling
method that exploits the sensitivity derivatives of the control variable with respect to the random parameters. As the sensitivity
derivatives are computed only at the mean values of the relevant parameters, the related extra cost of the present method
is a fraction of the total cost of the Monte Carlo method. The effectiveness of the method is demonstrated on an example problem
governed by the Burgers equation with random viscosity. It is specifically shown that this method is two orders of magnitude
more efficient compared to the conventional Monte Carlo method. In other words, for a given number of samples, the present
method yields two orders of magnitude higher accuracy than its conventional counterpart. 相似文献
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Koduri ND Scott H Hileman B Cox JD Coffin M Glicksberg L Hussaini SR 《Organic letters》2012,14(2):440-443
The Grubbs first-generation catalyst has been found to be an effective catalyst for the synthesis of enaminones by coupling thioamides with α-diazodicarbonyl compounds. The reaction is successful in converting primary, secondary, and tertiary thioamides into their corresponding enaminones. The reaction is also suitable for the synthesis of chiral enaminones. 相似文献
9.
This paper reports on the simulation of the near-nozzle region of an isothermal Mach 0.6 jet at a Reynolds number of 100,000
exhausting from a round nozzle geometry. The flow inside the nozzle and the free jet outside the nozzle are computed simultaneously
by a high-order accurate, multi-block, large eddy simulation (LES) code with overset grid capability. The total number of
grid points at which the governing equations are solved is about 50 million. The main emphasis of the simulation is to capture
the high frequency noise generation that takes place in the shear layers of the jet within the first few diameters downstream
of the nozzle exit. Although we have attempted to generate fully turbulent boundary layers inside the nozzle by means of a
special turbulent inflow generation procedure, an analysis of the simulation results supports the fact that the state of the
nozzle exit boundary layer should be characterized as transitional rather than fully turbulent. This is believed to be most
likely due to imperfections in the inflow generation method. Details of the computational methodology are presented together
with an analysis of the simulation results. A comparison of the far field noise spectrum in the sideline direction with experimental
data at similar flow conditions is also carried out. Additional noise generation due to vortex pairing in the region immediately
downstream of the nozzle exit is also observed. In a second simulation, the effect of the nozzle exit boundary layer thickness
on the vortex pairing Strouhal frequency (based on nozzle diameter) and its harmonics is demonstrated. The limitations and
deficiencies of the present study are identified and discussed. We hope that the lessons learned in this study will help guide
future research activities towards resolving the pending issues identified in this work.
Presented as AIAA Paper 2006-2499 at 12th AIAA/CEAS Aeroacoustics Conference, 8–10 May 2006, Cambridge, MA, USA. 相似文献
Presented as AIAA Paper 2006-2499 at 12th AIAA/CEAS Aeroacoustics Conference, 8–10 May 2006, Cambridge, MA, USA. 相似文献
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We go back and forth between, on the one hand, presentations of arithmetic and Kac-Moody groups and, on the other hand, presentations of profinite groups, deducing along the way new results on both. 相似文献