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.

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.

A numerical investigation into the effects of compressibility and total enthalpy difference on the development of a laminar free shear layer

1971 ◽  
Vol 50 (4) ◽  
pp. 785-799 ◽  
Author(s):  
Peter W. Carpenter
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Free Stream ◽  
Equations Of Motion ◽  
Initial Boundary ◽  
Free Shear Layer ◽  
Total Enthalpy ◽  
Enthalpy Difference ◽  
Coefficient Of Viscosity ◽  
Boundary Layer Profile

A method is presented for integrating numerically the equations of motion for a compressible free shear layer developing from a boundary-layer profile of arbitrary shape. Sutherland's law is used to determine the coefficient of viscosity and the Prandtl number is taken as 0·72. Calculated results are reported for free-stream Mach numbers ranging from 0 to 10 and for stagnation-enthalpy ratios ranging from 0 to 5·0. The effects of varying the initial boundary-layer profile and of a discontinuity in temperature at the origin are also studied. The results include graphs showing the development of dividing-streamline velocity, of local Nusselt number, and of dividing-streamline location.

The Effect of Inlet Turbulence Intensity on the Reattachment Process Over a Backward-Facing Step

1989 ◽  
Vol 111 (1) ◽  
pp. 87-92 ◽  
Author(s):  
K. Isomoto ◽  
S. Honami
Keyword(s):  
Shear Layer ◽  
Turbulence Intensity ◽  
Negative Correlation ◽  
Free Stream ◽  
Grid Turbulence ◽  
Two Dimensional ◽  
Reattachment Length ◽  
Backward Facing Step ◽  
Strong Negative Correlation ◽  
Separated Shear Layer

Behavior of a separated shear layer over a backward-facing step and its reattachment is presented when a two-dimensional cavity or rod is installed upstream of the step in order to change local turbulence intensity in addition to grid turbulence in the free-stream. The reattachment length has a strong negative correlation with maximum turbulence intensity near the wall at the separation point. Turbulence in the entrainment region immediately downstream of the step plays an important role in determining the reattachment length.

Initial Development of Turbulent, Compressible Free Shear Layers

1969 ◽  
Vol 91 (1) ◽  
pp. 67-73 ◽  
Author(s):  
W. G. Hill ◽  
R. H. Page
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Free Stream ◽  
Turbulent Shear ◽  
Mixing Zone ◽  
Free Shear Layer ◽  
Tunnel Wall ◽  
Approximate Methods ◽  
Initial Development ◽  
Number Range

The mixing zone between a two dimensional free stream and a fluid essentially at rest is studied experimentally and analytically. Turbulent shear layer velocity profiles were measured behind rearward facing steps and over cavities for equivalent free stream Mach numbers from 2.1 to 3.7, utilizing a wind tunnel wall boundary layer. Approximate methods are derived for calculating the shear layer change from an attached turbulent boundary layer to a fully developed free shear layer. A linearized equation of motion is used for the early stages of development, whereas the downstream stages are calculated by using a similarity profile. Both methods permit rapid calculations of the shear layer profile at any location along the mixing zone, without the necessity of determining the intermediate profiles. Comparison of the approximate methods with these experiments, and with experiments of other investigators, shows good agreement over the subsonic to supersonic Mach number range examined.

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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