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Experimental evidence for non-linear growth in compressible mixing layer

Science China(Physics,Mechanics & Astronomy) 2014年第5期57卷 963-970页

作者： WANG TieJin CHEN Jun SHI XiaoTian HU Ning SHE ZhenSu State Key Laboratory for Turbulence and Complex Systems College of EngineeringPeking University China Academy of Aerospace Aerodynamics

An experimental study of compressible mixing layers(CMLs)was conducted using planar laser Mie scattering(PLMS)visualizations from condensed ethanol droplets in the *** ensembles of digital images were collected for two flow conditions at convective Mach numbers Mc=0.11 and *** coherent vortices,braids and eruptions in the mixing zone were observed,interpreted as evidence of multi-scale,three-dimensional structures at a high Reynolds *** mixing layers with a large visualized range present two stages along the streamwise direction,corresponding to the initial mixing and the well-developed stage.A new method,the gray level ensemble average method(GLEAM),by virtue of the similarity of the mixing layer,was applied to measure the growth rate of the CML *** evidence for a nonlinear growth of CML is reported,providing an interpretation of previous observations of the scattering of the growth rate.

关键词： compressible mixing layer growth rate coherent structures flow visualization

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Optimization Study of a Coanda Ejector

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Journal of Thermal Science 2006年第4期15卷 331-336页

作者： H.D.Kim G.Rajesh T.Setoguchi S.Matsuo School of Mechanical Engineering Andong National University388Songcheon-dongAndongGyeongbuk 760-749Korea Department of Mechanical Engineering Saga University1HonjoSaga 840-8502Japan

The Coanda effect has long been employed in the aerospace applications to improve the performances of various devices. This effect is the ability of a flow to follow a curved contour without separation and has well been utilized in ejectors where a high speed jet of fluid emerges from a nozzle in the ejector body, follows a curved surface and drags the secondary flow into the ejector. In Coanda ejectors, the secondary flow is dragged in the ejector due to the primary flow momentum. The transfer of momentum from the primary flow to the secondary flow takes place through turbulent mixing and viscous effects. The secondary flow is then dragged by turbulent shear force of the ejector while being mixed with the primary flow by the persistence of a large turbulent intensity throughout the ejector. The performance of a Coanda ejector is studied mainly based on how well it drags the secondary flow and the amount of mixing between the two flows at the ejector exit. The aim of the present study is to investigate the influence of various geometric parameters and pressure ratios on the Coanda ejector performance. The effect of various factors, such as, the pressure ratio, primary nozzle and ejector configurations on the system performance has been evaluated based on a performance parameter defined elsewhere. The performance of the Coanda ejector strongly depends on the primary nozzle configuration and the pressure ratio. The mixing layer growth plays a major role in optimizing the performance of the Coanda ejector as it decides the ratio of secondary mass flow rate to primary mass flow rate and the mixing length.

关键词： Coanda ejector compressible mixing layer flow dragging mixing length induced flow

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Vortex structure simulation for supersonic mixing layers using nonlinear PSE method

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Theoretical & Applied Mechanics Letters 2012年第3期2卷 53-56页

作者： Xin Guo Qiang Wang China Academy of Aerospace Aerodynamics Beijing 100074China

The method of nonlinear parabolized stability equations（PSE） is applied in the simulation of vortex structures in compressible mixing *** spatially-evolving unstable waves,which dominate the vortex structure,are investigated through spatial marching *** instantaneous flow field is obtained by adding the harmonic waves to basic *** results show that T-S waves do not keep growing exponentially as the linear evolution,the energy transfer to high order harmonic modes,and that finally all harmonic modes get saturated due to nonlinear *** mean flow distortion induced by the nonlinear interaction between the harmonic modes and their conjugate harmonic ones,makes great change of the average flow and increases the thickness of mixing layer. PSE methods can well capture the two- and three-dimensional large scale nonlinear vortex structures in mixing layers such as vortex roll-up,vortex pairing,and A vortex.

关键词： compressible mixing layer parabolized stability equations nonlinear stability vortex rollup vortex pairing A vortex

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