Experimental Investigation of a Jet Impinging on a Ground Plane in the Presence of a Cross Flow

Cimbala, John M.; Stinebring, David R.; Treaster, A. L.; Billet, M. L.; Walters, M. M.

doi:10.4271/872326

Cited by 12 publications

(6 citation statements)

References 3 publications

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“…If the jet interacts with the ground plane in the presence of a weak crossflow (VJVj« 1) moving parallel to the ground, then as the radial wall jet slows, the upstream portion of the wall jet separates from the wall and turns back on itself to form an unsteady, recirculating vortex flow termed the ground vortex. This flow is qualitatively similar to the horseshoe or "necklace" vortices Presented as Paper 92-4251 at the AIAA Aircraft Design Systems Meeting, Hilton Head, SC, Aug. [24][25][26]1992; received Sept. 20,1992; revision received April 21, 1993; accepted for publication July 24,1993 formed around bridge piers, etc., but is in fact highly unsteady and much less organized. This ground vortex can have adverse aerodynamic effects on the performance of a V/STOL aircraft in close proximity to the ground.…”

Section: Nomenclaturementioning

confidence: 80%

“…Thus, for example, the present equation for ground vortex shape is (6) The effect of the ground board spacing on the ground vortex size was also examined. Cimbala et al 25 observed a significant difference in ground vortex behavior if the jet board location Z b /D e was equal to the hlD e of the nozzle (no nozzle length). They also observed that a value of Z b ID e equal to two diameters greater than hlD e was the limiting case for the jet board to influence the ground vortex size or shape.…”

Section: Flow Visualization-standard Nozzlesmentioning

confidence: 98%

“…More detailed experimental investigations of ground vortex formation include Cimbala, et al, 25 ' 26 Billet and Cimbala, 27 Paulson and Kemmerly, 28 Kemmerly and Paulson, 29 and Stewart. 30 Cimbala et al studied the effects of crossflow-tojet velocity ratio, approach boundary-layer thickness, and jet exit-to-ground board spacing, on the size of the ground vortex using flow visualization, laser velocimetry, and center line static pressures on the ground board.…”

Section: Nomenclaturementioning

confidence: 98%

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Jet ground vortex formation by annular jets

Kuhlman

Cavage

1994

Journal of Aircraft

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An experimental study has been conducted of the impingement of a single circular jet on a ground plane in a crossflow. This geometry is a simplified model of the interaction of propulsive jet exhaust from a V/STOL aircraft with the ground in forward flight. Jets have been oriented normal to the crossflow and ground plane. Jet size, crossflow-to-jet velocity ratio, ground plane-to-jet board spacing, jet exit turbulence level, and mean velocity profile shape have all been varied to determine their effects on the size of the ground vortex interaction region which forms on the ground plane, using smoke injection into the jet. Variation of observed ground vortex size with crossflow-to-jet velocity ratio was consistent with previous studies. Observed effects of jet size and ground plane-to-jet board spacing were relatively small. Jet exit turbulence level effects were also small. However, an annular jet with a low velocity central core was found to have a significantly smaller ground vortex than an equivalent uniform jet at the same values of crossflow-to-jet velocity ratio and jet exit-to-ground plane spacing. This may suggest a means of altering ground vortex behavior somewhat, and points out the importance of proper simulation of jet exit velocity conditions. Laser velocimeter data indicated unsteady turbulence levels in the ground vortex as high as 80%.

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Section: Nomenclaturementioning

confidence: 80%

Section: Flow Visualization-standard Nozzlesmentioning

confidence: 98%

Section: Nomenclaturementioning

confidence: 98%

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Jet ground vortex formation by annular jets

Kuhlman

Cavage

1994

Journal of Aircraft

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“…This sort of behavior was shown by Schwantes 4 for low pr n jets, and by Stott 9 for a range of pr n up to underexpanded. Cimbala et al 6 show an increase in y p (relative to the impingement point) for height increases from 1 to 4d n at VJw cl = 0.1, but only a decrease in penetration at VJw cl = 0.3 (h < 3d n in this case). For multiple jets, MacLean et al 10 show no height effects at higher velocity ratios (VJw cl > 0.1) with a height dependence at lower velocity ratios (<0.06).…”

Section: Effect Of Nozzle Heightmentioning

confidence: 86%

“…This almost certainly influenced the vortex flowfield (even for y s of the order of 20d n ) and, in this case, may have caused an underpenetration of the vortex at low rig heights. This trend was illustrated by Cimbala et al 6 who introduced a plate in the plane of the nozzle exit, parallel to the ground, and showed a reduction in vortex penetration. It is important from the point of view of wind-tunnel testing to note that the influence of nozzle height on vortex position can be rig-dependent.…”

Section: Effect Of Nozzle Heightmentioning

confidence: 90%

Ground vortex formed by impinging jets in crossflow

Knowles¹,

Bray²

1993

Journal of Aircraft

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The flowfields associated with single and twin jets impinging in crossflows have been studied experimentally using ground plane pressure profiles and flow visualization. The following parameters and their effect on the position of the ground vortex have been investigated: crossflow-to-jet velocity ratio, crossflow boundary-layer thickness, nozzle height, nozzle pressure ratio, vector angle, and nozzle splay with both fixed and moving ground planes. Results show that the ground vortex moves away from the nozzle centerline as crossflow-to-jet velocity ratio is decreased; the rate of change of position, however, depends on other parameters. This article presents an analysis of this experimental data which isolates the effects of these individual parameters. Nozzle pressure ratio is seen to influence ground vortex position independently of velocity ratio, but the definitions of jet equivalent velocity and crossflow velocity ratio are shown to be important. The effect of the moving ground plane is to reduce vortex penetration significantly; this suggests that a moving ground plane simulation (or moving model) is essential when testing design configurations in ground effect in wind tunnels. With twin nozzles there is a distinct effect of nozzle height on the upstream extent of the ground sheet, especially when the nozzles are toedin. It is suggested that the twin nozzle height effect is connected with jet merging. It is also argued that rig design can produce a blockage effect which moves the ground vortex significantly and can change other apparent parametric effects. NomenclatureA n = nozzle exit area C p = pressure coefficient, (pd n = nozzle exit diameter h = height of nozzle above ground, (Fig. 2) p = pressure pr n = nozzle pressure ratio, p$lpT = thrust V = velocity V E = as V e but using thrust-based w cl _____ V e = effective velocity ratio, 'V?p x Vl/( : zpiW*i) v -y direction velocity w = jet velocity x = horizontal distance measured normal to the crossflow from the plane of symmetry y = horizontal distance measured upstream from the nozzle centerline, (Fig. 2) y p = position of peak C p upstream of ground vortex y s = position at which mean C p = 0 y v = position of minimum C p (under vortex core) z = vertical distance above the ground plane 8 = crossflow boundary-layer thickness p = density Subscripts c = I w maximum ground plane impingement wall jet ambient (crossflow) conditions Presented as Paper 91-0768 at

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Impinging jets in cross-flow

Knowles¹,

Bray²,

Bailey³

et al. 1992

Aeronaut. j.

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The flow-fields associated with single and twin jets impinging in cross-flows have been studied. Parameters which affect the position of the ground vortex have been investigated: cross-flow-to-nozzle velocity ratio, cross-flow boundary layer thickness, nozzle height, nozzle pressure ratio, vector angle and nozzle splay with both fixed and moving ground planes. Results show that the ground vortex moves away from the nozzle centre-line as the ratio of cross-flow velocity to nozzle exit velocity is decreased; the rate of change of position, however, depends on other parameters (including the precise definition of nozzle exit velocity). Increasing nozzle height above the ground appears to cause little consistent variation in vortex position for a single jet but a marked forward movement of ground sheet separation point in the case of twin jets. For all cases there is an increase in penetration with increasing nozzle pressure ratio up to choking, with the subsequent behaviour dependent on the definition of nozzle equivalent velocity and cross-flow velocity ratio. The effect of the moving ground plane is to reduce vortex penetration significantly; this suggests that a moving ground plane simulation (or moving model) is essential when testing design configurations in ground effect in wind-tunnels. It is also shown that rig design can produce a blockage effect which moves the ground vortex significantly and can change other apparent parametric effects. Self-similarity laws are proposed for the ground vortex and the wall jet.

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Experimental Investigation of a Jet Impinging on a Ground Plane in the Presence of a Cross Flow

Cited by 12 publications

References 3 publications

Jet ground vortex formation by annular jets

Jet ground vortex formation by annular jets

Ground vortex formed by impinging jets in crossflow

Impinging jets in cross-flow

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