An experimental study of the large scale coherent structures in a forced free shear layer

1990 ◽  
Vol 6 (1) ◽  
pp. 9-14
Author(s):  
Zhang Hongquan ◽  
Shu Wei
Keyword(s):  
Experimental Study ◽  
Shear Layer ◽  
Coherent Structures ◽  
Large Scale ◽  
Free Shear Layer

An Experimental Study of the Effect of Grid Turbulence on Shear Layer Evolution

2004 ◽  
Vol 126 (2) ◽  
pp. 286-290 ◽  
Author(s):  
Amy Warncke Lang ◽  
Begon˜a Gomez
Keyword(s):  
Experimental Study ◽  
Shear Layer ◽  
Reynolds Stress ◽  
Coherent Structures ◽  
Growth Rates ◽  
Free Stream ◽  
Water Tunnel ◽  
Grid Turbulence ◽  
Free Shear Layer ◽  
Entrainment Process

An experiment was performed in a shear layer water tunnel to determine the effect that grid turbulence, introduced within the meeting of the two streams, had on the evolution of a free shear layer. DPIV results show that the presence of grid turbulence inhibited the growth of the large coherent structures formed in the undisturbed shear layer, and thus led to an alteration of the entrainment process of free stream fluid into the shear layer. This caused more symmetry and various growth rates in the shear layer evolution. Also, the peak Reynolds stress magnitudes increased with the presence of grid turbulence.

Phase decorrelation of coherent structures in a free shear layer

1991 ◽  
Vol 230 ◽  
pp. 319-337 ◽  
Author(s):  
Chih-Ming Ho ◽  
Yitshak Zohar ◽  
Judith K. Foss ◽  
Jeffrey C. Buell
Keyword(s):  
Shear Layer ◽  
Coherent Structures ◽  
Physical Mechanism ◽  
Mixing Layer ◽  
Single Frequency ◽  
Free Shear Layer ◽  
Phase Jitter ◽  
Laminar Mixing

The vortices near the origin of an initially laminar mixing layer have a single frequency with a well-defined phase; i.e. there is little phase jitter. Further downstream, however, the phase jitter increases suddenly. Even when the flow is forced, this same transition is observed. The forcing partially loses its influence because of the decorrelation of the phase between the forcing signal and the passing coherent structures. In the present investigation, this phenomenon is documented and the physical mechanism responsible for the phase decorrelation is identified.

Self-Sustained Oscillations of High Speed Impinging Planar Jets

2010 ◽  
Author(s):  
David Arthurs ◽  
Samir Ziada
Keyword(s):  
Shear Layer ◽  
High Speed ◽  
Large Scale ◽  
Impinging Jets ◽  
Free Shear Layer ◽  
Planar Case ◽  
Axisymmetric Case ◽  
Choked Flow ◽  
Tone Generation ◽  
Flow Velocities

High speed impinging jets are frequently used in a variety of industrial applications including thermal and coating control processes. These flows are liable to the production of very intense narrow band acoustic tones, which are produced by a feedback mechanism between instabilities in the jet free shear layer which roll up to form large scale coherent structures, and pressure fluctuations produced by the impingement of these structures at the impingement surface. This paper examines tone generation of a high speed planar gas jet impinging normally on a flat, rigid surface. Experiments are performed over the complete range of subsonic and transonic jet flow velocities for which tones are generated, from U0 = 150m/s (M≈0.4) to choked flow (U0 = 343m/s, M = 1), and over the complete range of impingement distance for which tones occur. The effect of varying the jet thickness is also examined. The behavior of the planar impinging jet case is compared to that of the axisymmetric case, and found to be significantly different, with tones being excited at larger impingement distances, and at lower flow velocities. The Strouhal numbers associated with tone generation in the planar case are on average an order of magnitude lower than that of the axisymmetric case when using similar velocity and length scales. The frequency behavior of the resulting tones is predicted using a simple feedback model, which allows the identification of the various shear layer modes of the instabilities driving tone generation. Finally, a thorough dimensionless analysis is performed in order to quantify the system behavior in terms of the appropriate scales.

Experiments on nonlinear interactions in the transition of a free shear layer

1973 ◽  
Vol 59 (1) ◽  
pp. 1-21 ◽  
Author(s):  
Richard W. Miksad
Keyword(s):  
Experimental Study ◽  
Shear Layer ◽  
Upper Bound ◽  
Finite Amplitude ◽  
Mode Competition ◽  
Nonlinear Interactions ◽  
Free Shear Layer ◽  
Number Of Components ◽  
Frequency Components ◽  
Fluctuation Energy

An experimental study is made of nonlinear interactions in a laminar free shear layer. Two disturbances (f1 and f2), excited by sound, amplify and grow independently for small amplitudes. At larger amplitudes the disturbances interact to generate fluctuations of sum and difference frequencies (f2 ± f1). Harmonics and subharmonics of f1 and f2 are also generated and all fluctuations interact to generate additional fluctuations of the form (nf2/m) ± (pf1/q); n, p = 1,2,3,…, m, q = 1,2. Nonlinear mode competition suppresses the growth of f1 or f2, depending on their relative amplitudes, and contributes to finite amplitude equilibration. An upper bound on the modal integral of total u′r.m.s.2 fluctuation energy is found. Fluctuation energy tends to be distributed among all possible frequency components, and its upper bound does not increase as the number of components increases.

On the interactions between large-scale structure and finegrained turbulence in a free shear flow II. The development of spatial interactions in the mean

1978 ◽  
Vol 359 (1699) ◽  
pp. 497-523 ◽  
Keyword(s):  
Shear Flow ◽  
Shear Layer ◽  
Large Scale ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Turbulent Shear ◽  
Turbulent Shear Flow ◽  
Free Shear Layer ◽  
Mean Flow ◽  
The Mean

Organized structures in turbulent shear flow have been observed both in the laboratory and in the atmosphere and ocean. Recent work on modelling such structures in a temporally developing, horizontally homogeneous turbulent free shear layer (Liu & Merkine 19766) has been extended to the spatially developing mixing layer, there being no available rational transformation between the two nonlinear problems. We consider the kinetic energy development of the mean flow, large-scale structure and finegrained turbulence with a conditional average, supplementing the usual time average, to separate the non-random from the random part of the fluctuations. The integrated form of the energy equations and the accompanying shape assumptions are used to derive ‘ amplitude ’ equations for the mean flow, characterized by the shear layer thickness, the non-random and the random components of flow (which are characterized by their respective energy densities). The closure problem was overcome by the shape assumptions which entered into the interaction integrals: the instability-wavelike large-scale structure was taken to be two-dimensional and the local vertical distribution function was obtained by solving the Rayleigh equation for various local frequencies; the vertical shape of the mean stresses of the fine-grained turbulence was estimated by making use of experimental results; the vertical shapes of the wave-induced stresses were calculated locally from their corresponding equations.

Experimental study of free-shear layer transition above a cavity at Mach 3.5

1989 ◽  
Author(s):  
RUDOLPH KING ◽  
THEODORE CREEL, JR. ◽  
DENNIS BUSHNELL
Keyword(s):  
Experimental Study ◽  
Shear Layer ◽  
Free Shear Layer ◽  
Layer Transition
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