Strategic Control of Transverse Jet Shear Layer Instabilities

AIAA Journal ◽  
2010 ◽  
Vol 48 (9) ◽  
pp. 2145-2156 ◽  
Author(s):  
J. Davitian ◽  
C. Hendrickson ◽  
D. Getsinger ◽  
R. T. M'Closkey ◽  
A. R. Karagozian
Keyword(s):  
Shear Layer ◽  
Strategic Control ◽  
Transverse Jet

Transition to global instability in transverse-jet shear layers

2010 ◽  
Vol 661 ◽  
pp. 294-315 ◽  
Author(s):  
J. DAVITIAN ◽  
D. GETSINGER ◽  
C. HENDRICKSON ◽  
A. R. KARAGOZIAN
Keyword(s):  
Shear Layer ◽  
Near Field ◽  
Single Mode ◽  
Shear Layers ◽  
Global Instability ◽  
Frequency Tracking ◽  
Transverse Jet ◽  
Critical Range ◽  
Crossflow Velocity ◽  
Lock In

In a recent paper (Megerianet al.,J. Fluid Mech., vol. 593, 2007, pp. 93–129), experimental exploration of the behaviour of transverse-jet near-field shear-layer instabilities suggests a significant change in the character of the instability as jet-to-crossflow velocity ratiosRare reduced below a critical range. The present study provides a detailed exploration of and additional insights into this transition, with quantification of the growth of disturbances at various locations along and about the jet shear layer, frequency tracking and response of the transverse jet to very strong single-mode forcing, creating a ‘lock-in’ response in the shear layer. In all instances, there is clear evidence that the flush transverse jet's near-field shear layer becomes globally unstable whenRlies at or below a critical range near 3. These findings have important implications for and provide the underlying strategy by which active control of the transverse jet may be developed.

Transverse-jet shear-layer instabilities. Part 1. Experimental studies

2007 ◽  
Vol 593 ◽  
pp. 93-129 ◽  
Author(s):  
S. MEGERIAN ◽  
J. DAVITIAN ◽  
L. S. DE B. ALVES ◽  
A. R. KARAGOZIAN
Keyword(s):  
Shear Layer ◽  
Near Field ◽  
Experimental Studies ◽  
Single Mode ◽  
Tunnel Wall ◽  
Low Level ◽  
Transverse Jet ◽  
Free Jet ◽  
Instability Modes ◽  
Crossflow Velocity

This study provides a detailed exploration of the near-field shear-layer instabilities associated with a gaseous jet injected normally into crossflow, also known as the transverse jet. Jet injection from nozzles which are flush as well as elevated with respect to the tunnel wall are explored experimentally in this study, for jet-to-crossflow velocity ratiosRin the range 1 ≲R≤ 10 and with jet Reynolds numbers of 2000 and 3000. The results indicate that the nature of the transverse jet instability is significantly different from that of the free jet, and that the instability changes in character as the crossflow velocity is increased. Dominant instability modes are observed to be strengthened, to move closer to the jet orifice, and to increase in frequency as crossflow velocity increases for the regime 3.5 <R≤ 10. The instabilities also exhibit mode shifting downstream along the jet shear layer for either nozzle configuration at these moderately high values ofR. WhenRis reduced below 3.5 in the flush injection experiments, single-mode instabilities are dramatically strengthened, forming almost immediately within the shear layer in addition to harmonic and subharmonic modes, without any evidence of mode shifting. Under these conditions, the dominant and initial mode frequencies tend to decrease with increasing crossflow. In contrast, the instabilities in the elevated jet experiments are weakened as R is reduced below about 4, probably owing to an increase in the vertical coflow magnitude exterior to the elevated nozzle, untilRfalls below 1.25, at which point the elevated jet instabilities become remarkably similar to those for the flush injected jet. Low-level jet forcing has no appreciable influence on the shear-layer response when these strong modes are present, in contrast to the significant influence of low-level forcing otherwise. These studies suggest profound differences in transverse-jet shear-layer instabilities, depending on the flow regime, and help to explain differences previously observed in transverse jets controlled by strong forcing.

Transverse-jet shear-layer instabilities. Part 2. Linear analysis for large jet-to-crossflow velocity ratio

2008 ◽  
Vol 602 ◽  
pp. 383-401 ◽  
Author(s):  
LEONARDO S. DE B. ALVES ◽  
ROBERT E. KELLY ◽  
ANN R. KARAGOZIAN
Keyword(s):  
Shear Layer ◽  
Near Field ◽  
Velocity Ratio ◽  
Base Flow ◽  
Experimental Results ◽  
Dimensional Parameter ◽  
Potential Core ◽  
Transverse Jet ◽  
Spatial Growth ◽  
Crossflow Velocity

The dominant non-dimensional parameter for isodensity transverse jet flow is the mean jet-to-crossflow velocity ratio,R. In Part 1 (Megerianet al.,J. Fluid Mech., vol. 593, 2007, p. 93), experimental results are presented for the behaviour of transverse-jet near-field shear-layer instabilities for velocity ratios in the range 1 <R≤ 10. A local linear stability analysis is presented in this paper for the subrangeR>4, using two different base flows for the transverse jet. The first analysis assumes the flow field to be described by a modified version of the potential flow solution of Coelho & Hunt (J. Fluid Mech., vol. 200, 1989, p. 95), in which the jet is enclosed by a vortex sheet. The second analysis assumes a continuous velocity model based on the same inviscid base flow; this analysis is valid for the larger values of Strouhal number expected to be typical of the most unstable disturbances, and allows prediction of a maximum spatial growth rate for the disturbances. In both approaches, results are obtained by expanding in inverse powers ofRso that the free-jet results are obtained asR→∞. The results from both approaches agree in the moderately low-frequency regime. Maximum spatial growth rates and associated Strouhal numbers extracted from the second approach both increase with decreasing velocity ratioR, in agreement with the experimental results from Part 1 in the range 4<R≤10. The nominally axisymmetric mode is found to be the most unstable mode in the transverse-jet shear-layer near-field region, upstream of the end of the potential core. The overall agreement of theoretical and experimental results suggests that convective instability occurs in the transverse-jet shear layer for jet-to-crossflow velocity ratios above 4, and that the instability is strengthened asRis decreased.

On the origins of transverse jet shear layer instability transition

2020 ◽  
Vol 890 ◽  
Author(s):  
Takeshi Shoji ◽  
Elijah W. Harris ◽  
Andrea Besnard ◽  
Stephen G. Schein ◽  
Ann R. Karagozian
Keyword(s):  
Shear Layer ◽  
Shear Layer Instability ◽  
Transverse Jet ◽  
Image Position

Secondary Flow in Variable Stator Vanes With Penny-Cavities

2017 ◽  
Author(s):  
Simon Stummann ◽  
Daniel Pohl ◽  
Peter Jeschke ◽  
Hannes Wolf ◽  
Alexander Halcoussis ◽  
...  
Keyword(s):  
Shear Layer ◽  
Secondary Flow ◽  
Free Stream ◽  
Vortex Pair ◽  
Transverse Jet ◽  
Multi Stage ◽  
Stator Vane ◽  
Flow Phenomena ◽  
Counter Rotating Vortex Pair ◽  
Variable Stator

This paper presents a description of Detached Eddy Simulations being carried out on a variable stator vane with a penny-cavity in order to determine the secondary flow phenomena in the main flowpath. Variable stator vanes are common in multi-stage compressors to prevent flow separations on rotor and stator blades at off-design operation points. The bearing of the stators at hub and tip generate unavoidable circular-shaped ring gaps, which are called penny-cavities. The aim of this paper is to determine secondary flow phenomena in variable stator vanes on an annular cascade testbed resulting from the throughflow of the penny-cavities. Reynolds-Averaged-Navier-Stokes simulations and scale resolving Detached-Eddy-Simulations of a variable stator vane with hub penny-cavity were therefore performed using Ansys CFX. The results of these simulations will be compared to corresponding simulations without penny-cavity. The study shows secondary flow phenomena, which are comparable to the interaction of a transverse jet in a free stream. Due to the low momentum ratio of R = 0.5, the jet immediately veers in the direction of the main flow. The typical vortices which develop from a transverse jet in a free stream are identified. The steady RANS simulation shows an asymmetrical counter-rotating vortex pair. A lack of unsteady secondary flow interaction can be seen in the RANS simulations in contrast to the Detached-Eddy-Simulations, which resolve large turbulent scales. Hence an interaction between the counter-rotating vortex pair and the unsteady shear layer vortices in the stator is visible. In the Detached Eddy Simulations the counter-rotating vortex pair is superimposed by the unsteady shear-layer vortices. The vortices produce significant additional mixing losses, which will be shown in detail. By comparing simulations with and without penny-cavity, the penny-cavity losses are quantified. In conclusion, this paper will help design engineers become more aware of the significance of the penny-cavity with variable stator vanes.

Strategic Control of Transverse Jet Flows

2008 ◽  
Author(s):  
Juliett Davitian ◽  
Cory Hendrickson ◽  
Robert M'Closkey ◽  
Ann Karagozian
Keyword(s):  
Jet Flows ◽  
Strategic Control ◽  
Transverse Jet

Structural and stability characteristics of jets in crossflow

2014 ◽  
Vol 760 ◽  
pp. 342-367 ◽  
Author(s):  
D. R. Getsinger ◽  
L. Gevorkyan ◽  
O. I. Smith ◽  
A. R. Karagozian
Keyword(s):  
Shear Layer ◽  
Structural Characteristics ◽  
Vortex Pair ◽  
Absolute Instability ◽  
Layer Transition ◽  
Cross Sectional ◽  
Transverse Jet ◽  
Planar Laser ◽  
Density Ratios ◽  
Sectional Shape

AbstractThis experimental study examines the relationship between transverse jet structural characteristics and the shear layer instabilities forming on the upstream side of the jet column. Jets composed of mixtures of helium and nitrogen were introduced perpendicularly into a low-speed wind tunnel using several alternative injectors: convergent circular nozzles mounted either flush with or elevated above the tunnel floor, and a flush-mounted circular pipe. Both non-intrusive optical diagnostics (planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV)) and intrusive probe-based (hot-wire anemometry) measurements were used to explore a range of jet-to-crossflow momentum flux ratios and density ratios for which previous studies have identified upstream shear layer transition from convective to absolute instability. Remarkable correspondences were identified between formation of the well-known counter-rotating vortex pair (CVP) associated with the jet cross-section and conditions producing strong upstream shear layer vorticity rollup, arising typically from absolute instability in the shear layer. In contrast, asymmetries in the jet mean cross-sectional shape and/or lack of a clear CVP were observed to correspond to weaker, convectively unstable jet shear layers.

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