Unsteady Lift Force on a Towed Sphere

Lauchle, Gerald C.; Jones, A. R.

doi:10.1006/jfls.1998.0177

Cited by 6 publications

(4 citation statements)

References 12 publications

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“…Finger et al (1979), and McEachern & Lauchle (1995) have shown that the unsteady forces on such "nite-length cylinders can result in #ow-induced self-noise being the major component of the transducer output signal. Similar results were identi"ed for spherical-shaped hydrophones by Lauchle & Jones (1998).…”

Section: Introductionsupporting

confidence: 84%

Modeling the Unsteady Lift and Drag on a Finite-Length Circular Cylinder in Cross-Flow

Capone

Lauchle

2000

Journal of Fluids and Structures

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Section: Introductionsupporting

confidence: 84%

Modeling the Unsteady Lift and Drag on a Finite-Length Circular Cylinder in Cross-Flow

Capone

Lauchle

2000

Journal of Fluids and Structures

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“…Similar towing tank measurements of the lift have been reported by Lauchle & Jones (1998) for the case in which the sphere mimics a submerged hydrophone, suspended as in practical applications. It was free to move with the unsteadiness created by the flow over its surface, and the force was determined using a geophone of the kind described above.…”

Section: Comparison With Experimentssupporting

confidence: 78%

“…However, the quality of force measurements is crucially dependent on the mode of suspension of the sphere. Lauchle & Jones (1998) used a three-point suspension, but the suspension lines did not lie in the same plane, and oscillations of the sphere were therefore possible in directions other than that of the lift (the z-direction in figure 2). This permitted the geophone to respond to the unsteady drag, to the orthogonal (vertical) component of lift, and to moments created by the flow, causing their measurements to underestimate the unsteady side force.…”

Section: Comparison With Experimentsmentioning

confidence: 99%

Aerodynamic lift and drag fluctuations of a sphere

2001

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An experimental and theoretical investigation is made of the unsteady lift and drag exerted on a sphere in a nominally steady, high Reynolds number, incompressible flow. The net force on the sphere has previously been ascribed to fluctuations in the bound vorticity in the meridian plane normal to the force, produced by large-scale coherent structures shed into the wake. A simplified model of vortex shedding is proposed that involves coherent eddies in the form of a succession of randomly orientated vortex rings, interconnected by pairs of oppositely rotating line vortices, and shed at quasi-regular intervals with a Strouhal number ∼ 0.19. The rings are rapidly dissipated by turbulence diffusion, but it is shown that only the nascent vortex ring makes a significant contribution to the surface force, and that the force spectrum at Strouhal numbers exceeding unity is effectively independent of the shape of the fully formed vortex. Predictions of the lift and drag spectra at these frequencies are found to be in good accord with new towing tank measurements presented in this paper.

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“…These computational studies had very few experimental force measurements to compare with. In the subcritical regime, Lauchle et al 8 indirectly measured the forces using an accelerometer, but only obtained the decay of the frequency spectrum for St > 1.5. For the supercritical regime, Willmarth and Enlow 1 reported the frequency spectrum and the mean squared lift for the case of a rough sphere.…”

Section: Introductionmentioning

confidence: 99%

Forces on a Sphere in the Presence of Static and Dynamic Roughness Elements

Norman

McKeon

2009

39th AIAA Fluid Dynamics Conference

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Though the effect of distributed roughness on flow over a sphere has been examined in detail, there have been few observations as to the effect of an isolated roughness element on the forces induced on a sphere that is in uniform flow. In this experimental study, we examine how the forces are altered due to both a stationary and dynamic three-dimensional roughness element in the Reynolds number range of 5 × 10 4 to 5 × 10 5 . It is found that even a small change to the geometry of the sphere, by adding a cylindrical roughness element with a width and height of 1% the sphere diameter, dramatically alters the drag and lateral forces over a wide range of Reynolds numbers. Of particular interest is that the mean of the lateral force magnitude can be increased by a factor of about seven, compared with a stationary stud, by moving the isolated roughness at a constant angular velocity about the sphere. These results can be applied to tripping a laminar boundary layer, steering a bluff body, and increasing the mixing of two fluids, using a minimal amount of energy input. This research is a first step towards understanding the interaction between time dependent surface motion and the subsequent alteration of the location of the boundary layer separation line and wake development.

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Unsteady Lift Force on a Towed Sphere

Cited by 6 publications

References 12 publications

Modeling the Unsteady Lift and Drag on a Finite-Length Circular Cylinder in Cross-Flow

Modeling the Unsteady Lift and Drag on a Finite-Length Circular Cylinder in Cross-Flow

Aerodynamic lift and drag fluctuations of a sphere

Forces on a Sphere in the Presence of Static and Dynamic Roughness Elements

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