Experiments on Gravity Effects in Supercavitating Flow

1966 ◽  
Vol 10 (02) ◽  
pp. 119-121
Author(s):  
T. Kiceniuk ◽  
A. J. Acosta
Keyword(s):  
Gravitational Field ◽  
Froude Number ◽  
Flow Past ◽  
Supercavitating Flow ◽  
Gravity Effects

Experiments on the effect of a transverse gravitational field on the supercavitating flow past a wedge tend to confirm predictions based on linearized free-streamline theory. A small though systematic dependence upon Froude number not accounted for by the existing theory is revealed, however.

scholarly journals The Effect of a Longitudinal Gravitational Field on the Supercavitating Flow Over a Wedge

1961 ◽  
Vol 28 (2) ◽  
pp. 188-192 ◽  
Author(s):  
A. J. Acosta
Keyword(s):  
Gravitational Field ◽  
Drag Coefficient ◽  
Froude Number ◽  
Cavitation Number ◽  
Streamline Flow ◽  
Flow Past ◽  
Supercavitating Flow ◽  
Linearized Theory

The free-streamline flow past a symmetrical wedge in the presence of a longitudinal gravitational field is determined with a linearized theory. The proportions of the cavity depend upon the cavitation number and Froude number. The drag coefficient is likewise affected by gravity, though to a smaller extent.

A Note on Gravity Effects in Supercavitating Flow

1965 ◽  
Vol 9 (01) ◽  
pp. 39-45
Author(s):  
R. L. Street
Keyword(s):  
Gravity Field ◽  
Quantitative Agreement ◽  
Cavitation Number ◽  
Number Range ◽  
First Order ◽  
Average Value ◽  
Flow Past ◽  
Supercavitating Flow ◽  
Gravity Effects ◽  
Linearized Theory

Two approximations to the linearized theory for supercavitating flow about slender bodiesare applied to the case of flow past a slender wedge in a transverse gravity field. The additional lift and moment forces arising as a result of the gravity field are calculated by theories that are expected to hold when the gravity effects are of first-order smallnessconsistent with the linearization appi'oximations. The lift and moment coefficients obtained from the two approximations are in general quantitative agreement over the most important cavitation-number range. The results obtained confirm the validity of the average-value approximation introduced by Parkin.

Regeneration of turbulent fluctuations in low-Froude-number flow over a sphere at a Reynolds number of 3700

2016 ◽  
Vol 804 ◽  
Author(s):  
Anikesh Pal ◽  
Sutanu Sarkar ◽  
Antonio Posa ◽  
Elias Balaras
Keyword(s):  
Reynolds Number ◽  
Froude Number ◽  
Qualitative Change ◽  
Turbulence Energy ◽  
Horizontal Shear ◽  
Near Wake ◽  
Turbulent Fluctuations ◽  
Flow Past ◽  
Low Froude Number ◽  
Flow Past A Sphere

Direct numerical simulations (DNS) are performed to study the behaviour of flow past a sphere in the regime of high stratification (low Froude number $Fr$). In contrast to previous results at lower Reynolds numbers, which suggest monotone suppression of turbulence with increasing stratification in flow past a sphere, it is found that, below a critical $Fr$, increasing the stratification induces unsteady vortical motion and turbulent fluctuations in the near wake. The near wake is quantified by computing the energy spectra, the turbulence energy equation, the partition of energy into horizontal and vertical components, and the buoyancy Reynolds number. These diagnostics show that the stabilizing effect of buoyancy changes flow over the sphere to flow around the sphere. This qualitative change in the flow leads to a new regime of unsteady vortex shedding in the horizontal planes and intensified horizontal shear which result in turbulence regeneration.

A linearized theory for rotational supercavitating flow

1963 ◽  
Vol 17 (4) ◽  
pp. 513-545 ◽  
Author(s):  
Robert L. Street
Keyword(s):  
Shear Flow ◽  
Flow Past ◽  
Supercavitating Flow ◽  
Harmonic Perturbation ◽  
Two Dimensional Flow ◽  
Slender Bodies ◽  
Linearized Theory ◽  
Particular Solution ◽  
Effects Of Rotation ◽  
Rotational Problem

In this paper methods are given for establishing qualitative and quantitative measures of the effects of rotation in supercavitating flows past slender bodies. A linearized theory is developed for steady, two-dimensional flow under the assumption that the flow has a constant rotation throughout. The stream function of the rotational flow satisfies Poisson's equation. By using a particular solution of this equation, the rotational problem is reduced to a problem involving Laplace's equation and harmonic perturbation velocities. The resulting boundary-value problem is solved by use of conformal mapping and singularities from thinairfoil theory. The theory is then applied to asymmetric shear flow past wedges and hydrofoils and to symmetric shear flow past wedges. The presence of rotation is shown to create significant changes in the forces acting on the slender bodies and in the shape and size of the trailing cavities.

Waves and wave resistance of thin bodies moving at low speed: the free-surface nonlinear effect

1975 ◽  
Vol 69 (2) ◽  
pp. 405-416 ◽  
Author(s):  
G. Dagan
Keyword(s):  
Free Surface ◽  
Froude Number ◽  
Surface Condition ◽  
Perturbation Expansion ◽  
Wave Resistance ◽  
The Body ◽  
Thin Body ◽  
Two Dimensional ◽  
First Order ◽  
Flow Past

The linearized theory of free-surface gravity flow past submerged or floating bodies is based on a perturbation expansion of the velocity potential in the slenderness parameter e with the Froude number F kept fixed. It is shown that, although the free-wave amplitude and the associated wave resistance tend to zero as F → 0, the linearized solution is not uniform in this limit: the ratio between the second- and first-order terms becomes unbounded as F → 0 with ε fixed. This non-uniformity (called ‘the second Froude number paradox’ in previous work) is related to the nonlinearity of the free-surface condition. Criteria for uniformity of the thin-body expansion, combining ε and F, are derived for two-dimensional flows. These criteria depend on the shape of the leading (and trailing) edge: as the shape becomes finer the linearized solution becomes valid for smaller F.Uniform first-order approximations for two-dimensional flow past submerged bodies are derived with the aid of the method of co-ordinate straining. The straining leads to an apparent displacement of the most singular points of the body contour (the leading and trailing edges for a smooth shape) and, therefore, to an apparent change in the effective Froude number.

Nonlinearity of the three-dimensional flow past a flat blunt ship

1981 ◽  
Vol 108 ◽  
pp. 345-361 ◽  
Author(s):  
Gilles Fernandez
Keyword(s):  
Froude Number ◽  
Asymptotic Expansions ◽  
Three Dimensional ◽  
Matched Asymptotic Expansions ◽  
Three Dimensional Flow ◽  
Order Unity ◽  
Dimensional Flow ◽  
Flow Past

The nonlinearity of the gravity sea flow past a three-dimensional flat blunt ship with a length-based Froude number of order unity is studied using the method of matched asymptotic expansions. It is shown that the nonlinearity is important in an inner domain near the ship, whereas the flow in the rest of the fluid domain is the solution of a Neumann-Kelvin problem. Two possible inner solutions – a jet and a wave – are obtained and discussed.

scholarly journals Free surface flow past topography: A beyond-all-orders approach

2012 ◽  
Vol 23 (4) ◽  
pp. 441-467 ◽  
Author(s):  
CHRISTOPHER J. LUSTRI ◽  
SCOTT W. MCCUE ◽  
BENJAMIN J. BINDER
Keyword(s):  
Free Surface ◽  
Froude Number ◽  
Numerical Solutions ◽  
Power Series Expansion ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Asymptotic Results ◽  
Stagnation Points ◽  
Flow Past ◽  
Stokes Lines

The problem of steady subcritical free surface flow past a submerged inclined step is considered. The asymptotic limit of small Froude number is treated, with particular emphasis on the effect that changing the angle of the step face has on the surface waves. As demonstrated by Chapman & Vanden-Broeck, (2006) Exponential asymptotics and gravity waves. J. Fluid Mech.567, 299–326, the divergence of a power series expansion in powers of the square of the Froude number is caused by singularities in the analytic continuation of the free surface; for an inclined step, these singularities may correspond to either the corners or stagnation points of the step, or both, depending on the angle of inclination. Stokes lines emanate from these singularities, and exponentially small waves are switched on at the point the Stokes lines intersect with the free surface. Our results suggest that for a certain range of step angles, two wavetrains are switched on, but the exponentially subdominant one is switched on first, leading to an intermediate wavetrain not previously noted. We extend these ideas to the problem of flow over a submerged bump or trench, again with inclined sides. This time there may be two, three or four active Stokes lines, depending on the inclination angles. We demonstrate how to construct a base topography such that wave contributions from separate Stokes lines are of equal magnitude but opposite phase, thus cancelling out. Our asymptotic results are complemented by numerical solutions to the fully nonlinear equations.

scholarly journals Reynolds and froude number effect on the flow past an interface-piercing circular cylinder

2014 ◽  
Vol 6 (3) ◽  
pp. 529-561 ◽  
Author(s):  
Bonguk Koo ◽  
Jianming Yang ◽  
Seong Mo Yeon ◽  
Frederick Stern
Keyword(s):  
Circular Cylinder ◽  
Froude Number ◽  
Flow Past
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