GROUND EFFECT OF FLOW AROUND AN ELLIPTIC CYLINDER IN A TURBULENT BOUNDARY LAYER

2000 ◽  
Vol 14 (5) ◽  
pp. 697-709 ◽  
Author(s):  
J.-H. CHOI ◽  
S.-J. LEE
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Elliptic Cylinder ◽  
Ground Effect

scholarly journals Forcing Boundary-Layer Transition on a Single-Element Wing in Ground Effect

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Luke S. Roberts ◽  
Mark V. Finnis ◽  
Kevin Knowles
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Ground Effect ◽  
Boundary Layer Transition ◽  
Single Element ◽  
Trailing Edge ◽  
Layer Transition ◽  
Transition Mechanism ◽  
Edge Separation ◽  
Wing In Ground Effect

The transition from a laminar to turbulent boundary layer on a wing operating at low Reynolds numbers can have a large effect on its aerodynamic performance. For a wing operating in ground effect, where very low pressures and large pressure gradients are common, the effect is even greater. A study was conducted into the effect of forcing boundary-layer transition on the suction surface of an inverted GA(W)-1 section single-element wing in ground effect, which is representative of a racing-car front wing. Transition to a turbulent boundary layer was forced at varying chordwise locations and compared to the free-transition case using experimental and computational methods. Forcing transition caused the laminar-separation bubble, which was the unforced transition mechanism, to be eliminated in all cases and trailing-edge separation to occur instead. The aerodynamic forces produced by the wing with trailing-edge separation were shown to be dependent on trip location. As the trip was moved upstream the separation point also moved upstream, this led to an increase in drag and reduction in downforce. In addition to significant changes to the pressure field around the wing, turbulent energy in the wake was considerably reduced by forcing transition. The differences between free- and forced-transition wings were shown to be significant, highlighting the importance of modeling transition for ground-effect wings. Additionally, it has been shown that while it is possible to reproduce the force coefficient of a higher Reynolds-number case by forcing the boundary layer to a turbulent state, the flow features, both on-surface and off-surface, are not recreated.

The Energetics of Hovering in the Mandarin Fish (Synchropus Picturatus)

1979 ◽  
Vol 82 (1) ◽  
pp. 25-33 ◽  
Author(s):  
R. W. BLAKE
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Ground Effect ◽  
Water Velocity ◽  
Total Power ◽  
Mandarin Fish ◽  
Pectoral Fin ◽  
Frictional Drag ◽  
Hovering Flight ◽  
Negatively Buoyant

The influence of the ground effect on the energetics of hovering in Synchropus picturatus Peters, a negatively buoyant, demersal teleost was studied. Changes in pectoral fin kinematics, the ultimate water velocity in the wake below the fins, the calculated minimum induced thrust and power required to hover are related to the height at which the animal hovers above the substrate. The profile power required to overcome the frictional drag on the fins has been calculated for the case of both a laminar and a turbulent boundary layer over the fins. Reductions in the total power needed to hover (as compared with that required out of ground effect) of 30–60% have been calculated for Synchropus when hovering at commonly observed heights above the bottom. Results are discussed in relation to the hovering flight of birds, insects and helicopters.

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