Wake Vortices in Jets in Cross-Flow

2011 ◽  
Author(s):  
Ivana Milanovic ◽  
Khairul B. M. Q. Zaman ◽  
Tim Bencic
Keyword(s):  
Boundary Layer ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Boundary Layer Separation ◽  
Tunnel Wall ◽  
Wake Vortices ◽  
Wall Boundary Layer ◽  
The Cross ◽  
Excitation Techniques ◽  
And Behavior

The objective of the current experimental study is to investigate unsteady wake vortices of jets in cross-flow in order to (1) explore the effect of various excitation techniques, their parametric dependence, and impact on the flow field, and (2) provide detailed flow visualizations for a range of velocity ratios. The jet passed through a nozzle and entered the cross-flow with a turbulent boundary layer. While mechanical perturbation did not result in any significant periodic organization of the wake vortices, the database obtained for the unperturbed flow provided an insight into their possible origin and behavior. The key finding was the shedding of wake vortices from the ‘swell’ at the lee side of the jet. The ‘swell’ delineated a region of the flow at the intersection of the jet efflux boundary layer and the cross-flow boundary layer. Separation events released upright vortices and these peeled strands of vorticity convected, twisted and stretched for a few diameters along the wall while still being attached to the bottom of the ‘swell.’ They extended from the tunnel wall and penetrated the jet core where they appeared to burst. In no case were the wake vortices seen to originate either from the wall boundary layer or the jet shear layer at downstream locations. Increasing the jet-to-cross-flow velocity ratio influenced the slope of the wake vortices relative to the jet. The upper part of the vortical strand for VR < 4 was almost perpendicular to the cross-flow. Higher velocity ratios featured a tilt of the vortex structure toward the jet. This angle was particularly pronounced for VR = 8 and 10, and could be observed at all downstream distances. The average convection velocity of the wake vortices for the given cross-flow and all velocity ratios was estimated to be about 0.8 Ucf.

Three-Dimensional Calculation of Wall Boundary Layer Flows in Turbomachines

1987 ◽  
Author(s):  
W. L. Lindsay ◽  
H. B. Carrick ◽  
J. H. Horlock
Keyword(s):  
Boundary Layer ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Cross Flow ◽  
Flow Profile ◽  
Boundary Layer Flows ◽  
Wall Boundary Layer ◽  
Boundary Layer Development ◽  
Flow Through ◽  
The Cross

An integral method of calculating the three-dimensional turbulent boundary layer development through the blade rows of turbomachines is described. It is based on the solution of simultaneous equations for (i) & (ii) the growth of streamwise and cross-flow momentum thicknesses; (iii) entrainment; (iv) the wall shear stress; (v) the position of maximum cross-flow. The velocity profile of the streamwise boundary layer is assumed to be that described by Coles. The cross-flow profile is assumed to be the simple form suggested by Johnston, but modified by the effect of bounding blade surfaces, which restrict the cross-flow. The momentum equations include expressions for “force-defect” terms which are also based on secondary flow analysis. Calculations of the flow through a set of guide vanes of low deflection show good agreement with experimental results; however, attempts to calculate flows of higher deflection are found to be less successful.

scholarly journals Vortical structure in the wake of a transverse jet

1994 ◽  
Vol 279 ◽  
pp. 1-47 ◽  
Author(s):  
T. F. Fric ◽  
A. Roshko
Keyword(s):  
Boundary Layer ◽  
Velocity Ratio ◽  
Adverse Pressure Gradient ◽  
Reynolds Numbers ◽  
Structural Features ◽  
Bluff Bodies ◽  
Wake Vortices ◽  
Transverse Jet ◽  
Wall Boundary Layer ◽  
Crossflow Velocity

Structural features resulting from the interaction of a turbulent jet issuing transversely into a uniform stream are described with the help of flow visualization and hot-wire anemometry. Jet-to-crossflow velocity ratios from 2 to 10 were investigated at crossflow Reynolds numbers from 3800 to 11400. In particular, the origin and formation of the vortices in the wake are described and shown to be fundamentally different from the well-known phenomenon of vortex shedding from solid bluff bodies. The flow around a transverse jet does not separate from the jet and does not shed vorticity into the wake. Instead, the wake vortices have their origins in the laminar boundary layer of the wall from which the jet issues. It is argued that the closed flow around the jet imposes an adverse pressure gradient on the wall, on the downstream lateral sides of the jet, provoking 'separation events’ in the wall boundary layer on each side. These result in eruptions of boundary-layer fluid and formation of wake vortices that are convected downstream. The measured wake Strouhal frequencies, which depend on the jet-crossflow velocity ratio, match the measured frequencies of the separation events. The wake structure is most orderly and the corresponding wake Strouhal number (0.13) is most sharply defined for velocity ratios near the value 4. Measured wake profiles show deficits of both momentum and total pressure.

Effect of Artificial Perturbation on Unsteady Wake Vortices in Jets in Cross-Flow

2012 ◽  
Author(s):  
Ivana Milanovic ◽  
Khairul B. M. Q. Zaman ◽  
Timothy J. Bencic
Keyword(s):  
Free Stream ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Wake Vortices ◽  
Smoke Flow ◽  
Unsteady Wake ◽  
Cross Flow Velocity ◽  
Flow Visualizations ◽  
The Cross ◽  
Ratio Range

The current experimental study investigated unsteady wake vortices of jets in cross-flow in order to explore the possibility of periodic perturbation of these vortices with the method of oscillating tabs. Two triangular tabs were placed at the 90° and 270° edges of the jet orifice relative to the direction of the cross-flow. An isolated circular jet passed through a nozzle and entered the cross-flow normal to the wall. Free stream velocities up to 4.1 m/s and jet-to-cross-flow velocity ratio range between 3 and 12 were covered. Strouhal number (fpD/Ucf) for excitation cases was about 0.19. The oscillation frequency was somewhat higher than the ‘preferred’ frequency of the wake vortices. The smoke flow visualizations did not indicate an organization of wake vortices. Artificial excitation simply tilted the jet cross section from side to side in sync with the tab oscillation.

scholarly journals An Experimental Investigation Into the Performance of a Flush Water-Jet Inlet

2007 ◽  
Vol 51 (01) ◽  
pp. 1-21 ◽  
Author(s):  
P. A. Brandner ◽  
G. J. Walker
Keyword(s):  
Boundary Layer ◽  
Experimental Investigation ◽  
High Speed ◽  
Boundary Layer Separation ◽  
Water Jet ◽  
Tunnel Wall ◽  
Cavitation Inception ◽  
Wall Boundary Layer ◽  
Cfd Models ◽  
Flow Features

An experimental investigation of the flow within a generic flush type water-jet inlet has been carried out to identify the principal flow features and provide a basis for development of computational fluid dynamics (CFD) models. Tests were performed in a cavitation tunnel with the model inlet fitted to the test section ceiling, and effects of thickening the ingested tunnel wall boundary layer were investigated. The model was fitted with a range of instrumentation to investigate the ramp pressure distribution and boundary layer development, lip incidence, and pump face flow properties. Observations of lip and duct cavitation inception and behavior were also made. The results showed the inlet performance to be generally improved with the ingestion of a thicker boundary layer. The thickened boundary layer significantly reduced ramp boundary layer separation and distortion of flow at the notional pump face. However, a greater range of lip incidence occurred with the thickened boundary layer with consequent greater likelihood of lip separation and cavitation occurrence. Ideal lip incidence and pump face flow uniformity occurred at flow parameters significantly different from those for ideal pump face pressure recovery. Large developed cavities on the inlet lip were observed for a range of conditions typical of conventional high-speed vessel operation.

Effects of alternating elliptical chamber on jet impingement heat transfer in vane leading edge under different cross-flow conditions

2021 ◽  
pp. 1-17
Author(s):  
K. Xiao ◽  
J. He ◽  
Z. Feng
Keyword(s):  
Heat Transfer ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Leading Edge ◽  
Longitudinal Vortices ◽  
Impingement Jet ◽  
Flow And Heat Transfer ◽  
Impingement Heat Transfer ◽  
Cross Flow Velocity ◽  
The Cross

ABSTRACT This paper proposes an alternating elliptical impingement chamber in the leading edge of a gas turbine to restrain the cross flow and enhance the heat transfer, and investigates the detailed flow and heat transfer characteristics. The chamber consists of straight sections and transition sections. Numerical simulations are performed by solving the three-dimensional (3D) steady Reynolds-Averaged Navier–Stokes (RANS) equations with the Shear Stress Transport (SST) k– $\omega$ turbulence model. The influences of alternating the cross section on the impingement flow and heat transfer of the chamber are studied by comparison with a smooth semi-elliptical impingement chamber at a cross-flow Velocity Ratio (VR) of 0.2 and Temperature Ratio (TR) of 1.00 in the primary study. Then, the effects of the cross-flow VR and TR are further investigated. The results reveal that, in the semi-elliptical impingement chamber, the impingement jet is deflected by the cross flow and the heat transfer performance is degraded. However, in the alternating elliptical chamber, the cross flow is transformed to a pair of longitudinal vortices, and the flow direction at the centre of the cross section is parallel to the impingement jet, thus improving the jet penetration ability and enhancing the impingement heat transfer. In addition, the heat transfer in the semi-elliptical chamber degrades rapidly away from the stagnation region, while the longitudinal vortices enhance the heat transfer further, making the heat transfer coefficient distribution more uniform. The Nusselt number decreases with increase of VR and TR for both the semi-elliptical chamber and the alternating elliptical chamber. The alternating elliptical chamber enhances the heat transfer and moves the stagnation point up for all VR and TR, and the heat transfer enhancement is more obvious at high cross-flow velocity ratio.

Streamwise evolution of longitudinal vortices in a turbulent boundary layer

2009 ◽  
Vol 623 ◽  
pp. 27-58 ◽  
Author(s):  
OLA LÖGDBERG ◽  
JENS H. M. FRANSSON ◽  
P. HENRIK ALFREDSSON
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Vortex Core ◽  
Cross Flow ◽  
General Point ◽  
Natural Setting ◽  
Viscous Effects ◽  
Array Configuration ◽  
The Cross ◽  
Flow Plane

In this experimental study both smoke visualization and three-component hot-wire measurements have been performed in order to characterize the streamwise evolution of longitudinal counter-rotating vortices in a turbulent boundary layer. The vortices were generated by means of vortex generators (VGs) in different configurations. Both single pairs and arrays in a natural setting as well as in yaw have been considered. Moreover three different vortex blade heights h, with the spacing d and the distance to the neighbouring vortex pair D for the array configuration, were studied keeping the same d/h and D/h ratios. It is shown that the vortex core paths scale with h in the streamwise direction and with D and h in the spanwise and wall-normal directions, respectively. A new peculiar ‘hooklike’ vortex core motion, seen in the cross-flow plane, has been identified in the far region, starting around 200h and 50h for the pair and the array configuration, respectively. This behaviour is explained in the paper. Furthermore the experimental data indicate that the vortex paths asymptote to a prescribed location in the cross-flow plane, which first was stated as a hypothesis and later verified. This observation goes against previously reported numerical results based on inviscid theory. An account for the important viscous effects is taken in a pseudo-viscous vortex model which is able to capture the streamwise core evolution throughout the measurement region down to 450h. Finally, the effect of yawing is reported, and it is shown that spanwise-averaged quantities such as the shape factor and the circulation are hardly perceptible. However, the evolution of the vortex cores are different both between the pair and the array configuration and in the natural setting versus the case with yaw. From a general point of view the present paper reports on fundamental results concerning the vortex evolution in a fully developed turbulent boundary layer.

Wall Boundary Layers in Turbomachines

1972 ◽  
Vol 14 (6) ◽  
pp. 411-423 ◽  
Author(s):  
H. Marsh ◽  
J. H. Horlock
Keyword(s):  
Boundary Layer ◽  
Integral Equations ◽  
Cross Flow ◽  
Inlet Guide Vanes ◽  
Wall Boundary Layer ◽  
Wall Boundary ◽  
Alternative Approach ◽  
Flow Through ◽  
The Many ◽  
Momentum Integral

Equations for the passage-averaged flow in a cascade are used to derive the momentum integral equations governing the development of the wall boundary layer in turbomachines. Several existing methods of analysis are discussed and an alternative approach is given which is based on the passage-averaged momentum integral equations. The analysis leads to an anomaly in the prediction of the cross flow and to avoid this it is suggested that for the many-bladed cascade there should be a variation of the blade force through the boundary layer. This variation of the blade force can be included in the analysis as a force deficit integral. The growth of the wall boundary layer has been calculated by four methods and the predictions are compared with two sets of published experimental results for flow through inlet guide vanes.

The Effect of a Wall Boundary Layer on Local Mass Transfer From a Cylinder in Crossflow

1984 ◽  
Vol 106 (2) ◽  
pp. 260-267 ◽  
Author(s):  
R. J. Goldstein ◽  
J. Karni
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Two Dimensional ◽  
Tunnel Wall ◽  
Wall Boundary Layer ◽  
Naphthalene Sublimation Technique ◽  
Displacement Thickness ◽  
Two Dimensional Flow

A naphthalene sublimation technique is used to determine the circumferential and longitudinal variations of mass transfer from a smooth circular cylinder in a crossflow of air. The effect of the three-dimensional secondary flows near the wall-attached ends of a cylinder is discussed. For a cylinder Reynolds number of 19000, local enhancement of the mass transfer over values in the center of the tunnel are observed up to a distance of 3.5 cylinder diameters from the tunnel wall. In a narrow span extending from the tunnel wall to about 0.066 cylinder diameters above it (about 0.75 of the mainstream boundary layer displacement thickness), increases of 90 to 700 percent over the two-dimensional flow mass transfer are measured on the front portion of the cylinder. Farther from the wall, local increases of up to 38 percent over the two-dimensional values are measured. In this region, increases of mass transfer in the rear portion of the cylinder, downstream of separation, are, in general, larger and cover a greater span than the increases in the front portion of the cylinder.

An Approach to Three-Dimensional Turbulent Boundary Layers

1966 ◽  
Author(s):  
A. D. Carmichael
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Shape Factor ◽  
Basic Assumption ◽  
Three Dimensional ◽  
Cross Flow ◽  
Turbulent Boundary Layers ◽  
Factor H ◽  
Simple Method ◽  
The Cross

A relatively simple method for predicting some of the characteristics of three-dimensional turbulent boundary layers is presented. The basic assumption of the method is that the cross-flow is small. An empirical correlation of a basic shape factor of the cross-flow boundary layer against the streamwise shape factor H is provided. This correlation, together with data for the streamwise boundary layer, is used to predict the cross flow. The solution is very sensitive to the accuracy of the streamwise boundary-layer data which is predicted by conventional two-dimensional methods.

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