High speed theory for the planing of a flat plate at high Froude number

2007 ◽  
Vol 34 (11-12) ◽  
pp. 1552-1560 ◽  
Author(s):  
Y.K. Chung ◽  
H.H. Chun
Keyword(s):  
Flat Plate ◽  
Froude Number ◽  
High Speed ◽  
High Froude Number

A Theoretical Approach to Bow Deck Wetness of a High-Speed Ship

1990 ◽  
Vol 34 (03) ◽  
pp. 163-171 ◽  
Author(s):  
Ken Takagi ◽  
Akihiro Niimi
Keyword(s):  
Froude Number ◽  
Theoretical Approach ◽  
Analytical Method ◽  
High Speed ◽  
Theoretical Study ◽  
Two Dimensional ◽  
Long Wavelength ◽  
High Froude Number ◽  
Self Similar ◽  
Deck Wetness

A theoretical study of the phenomenon of deck wetness is presented and effects of the flare shape are discussed. It is shown that two-dimensional (2D) self-similar flow is applicable to the analysis of deck wetness on the assumption of long wavelength and high Froude number. The 2D self-similar flow which includes effects of the deck is calculated by an analytical method. Calculated results are compared with experimental results obtained at the limit of long wavelength, that is, in still water. Calculated results are used to determine the most suitable flare angle, and it is shown that increased flare is more effective than a knuckle to reduce bow deck wetness.

Rupture of Cavity Film Due to Water Entry of Horizontal Superhydrophobic Circular Cylinders

2013 ◽  
Vol 32 (1) ◽  
pp. 59-67 ◽  
Author(s):  
Y. Ueda ◽  
M. Iguchi
Keyword(s):  
Froude Number ◽  
High Speed ◽  
Water Entry ◽  
Circular Cylinders ◽  
Water Model ◽  
Inertia Force ◽  
Fluid Inertia ◽  
Contact Lines ◽  
Low Froude Number ◽  
High Froude Number

AbstractIn materials refining processes such as steelmaking process, bath-entry of agents such as CaCO3 attracts career gas around their entire surface so that the dispersion in the bath can be inhibited. To shed light on the still vague instant phenomenon, this study employs a water model experiment and carries out the visualization. Therefore, this study visually demonstrates the growth and rupture of air cavity due to water entry of horizontal superhydrophobic circular cylinders with the aid of a high-speed camera. Here, we show that the water entry of the horizontal hydrophobic cylinder forms a film of cavity behind the cylinder whereas a hydrophilic cylinder forms a cavity from both ends of the cylinder. In a high Froude number entry, once the cavity film ruptured on both sides of it, the contact lines of the cavity film abruptly move along the surface of the cylinder. In a low Froude number entry, the influence of weak fluid inertia force makes several ruptures on the cavity film which grow individually and split off the cavity. Of a particular interest is the fact that the multi-rupture regime appeals for the spanwise three-dimensionality on the cavity film against the previous studies within two-dimensional treatment. Furthermore, this report finds the trend for some range of Fr that the nondimensionalized closure depth of the cavity film zc with diameter of the cylinder obeys zc/d ∼ Fr1/3 in the range 4.7 ≤ Fr ≤ 40 although it depends on Fr in the water-entry problem of a hydrophobic sphere.

Two-dimensional planing at high Froude number

1958 ◽  
Vol 4 (5) ◽  
pp. 466-478 ◽  
Author(s):  
E. Cumberbatch
Keyword(s):  
Integral Equation ◽  
Pressure Distribution ◽  
Flat Plate ◽  
Froude Number ◽  
Water Surface ◽  
Flow Characteristics ◽  
Iteration Process ◽  
Leading Edge ◽  
Two Dimensional ◽  
High Froude Number

This paper examines the flow characteristics of a body of small slope planing at high Froude number over a water surface. An equation is obtained relating the slope of the planing surface to an integral containing the pressure distribution on the planing surface. The equation is expanded for large Froude number and a solution is obtained by an iteration process. At each stage of the iteration process the integral equation of ordinary thin aerofoil theory is solved. The pressure distribution on the planing surface is derived as a series in inverse powers of the Froude number F, as far as the F−4 term. Computations are performed for the planing of a flat plate, a parabolic surface, and a suitable linear combination of these shapes which results in a flow without a splash at the leading edge.

Optimum air-demand ratio for maximum aeration efficiency in high-head gated circular conduits

2014 ◽  
Vol 70 (5) ◽  
pp. 871-877 ◽  
Author(s):  
Fahri Ozkan ◽  
M. Cihat Tuna ◽  
Ahmet Baylar ◽  
Mualla Ozturk
Keyword(s):  
Froude Number ◽  
High Speed ◽  
Water Mixture ◽  
High Speed Flow ◽  
Mixture Flow ◽  
Speed Flow ◽  
Aeration Efficiency ◽  
High Head ◽  
Closed Conduit ◽  
Air Vent

Oxygen is an important component of water quality and its ability to sustain life. Water aeration is the process of introducing air into a body of water to increase its oxygen saturation. Water aeration can be accomplished in a variety of ways, for instance, closed-conduit aeration. High-speed flow in a closed conduit involves air-water mixture flow. The air flow results from the subatmospheric pressure downstream of the gate. The air entrained by the high-speed flow is supplied by the air vent. The air entrained into the flow in the form of a large number of bubbles accelerates oxygen transfer and hence also increases aeration efficiency. In the present work, the optimum air-demand ratio for maximum aeration efficiency in high-head gated circular conduits was studied experimentally. Results showed that aeration efficiency increased with the air-demand ratio to a certain point and then aeration efficiency did not change with a further increase of the air-demand ratio. Thus, there was an optimum value for the air-demand ratio, depending on the Froude number, which provides maximum aeration efficiency. Furthermore, a design formula for aeration efficiency was presented relating aeration efficiency to the air-demand ratio and Froude number.

High-Speed Boundary Layer Instability on a Flat Plate at Angle of Attack with Porous Walls

2022 ◽  
Author(s):  
Samantha A. Miller ◽  
Derek Mamrol ◽  
Joel J. Redmond ◽  
Karl Jantze ◽  
Carlo Scalo ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
High Speed ◽  
Angle Of Attack ◽  
Boundary Layer Instability ◽  
Porous Walls

Roller Characteristics of Preaerated High-Froude-Number Hydraulic Jumps

2021 ◽  
Vol 147 (4) ◽  
pp. 04021008
Author(s):  
Ruidi Bai ◽  
Hang Wang ◽  
Rongcai Tang ◽  
Shanjun Liu ◽  
Weilin Xu
Keyword(s):  
Froude Number ◽  
Hydraulic Jumps ◽  
High Froude Number

Large-eddy simulation of transition to turbulence in a boundary layer developing spatially over a flat plate

1996 ◽  
Vol 326 ◽  
pp. 1-36 ◽  
Author(s):  
FréDÉRic Ducros, Pierre Comte ◽  
Marcel Lesieur
Keyword(s):  
Boundary Layer ◽  
Structure Function ◽  
Flat Plate ◽  
High Speed ◽  
Large Scale ◽  
Phase Speed ◽  
Transition To Turbulence ◽  
Order Structure ◽  
Spanwise Direction ◽  
Large Eddy

It is well known that subgrid models such as Smagorinsky's cannot be used for the spatially growing simulation of the transition to turbulence of flat-plate boundary layers, unless large-amplitude perturbations are introduced at the upstream boundary: they are over-dissipative, and the flow simulated remains laminar. This is also the case for the structure-function model (SF) of Métais & Lesieur (1992). In the present paper we present a sequel to this model, the filtered-structure-function (FSF) model. It consists of removing the large-scale fluctuations of the field before computing its second-order structure function. Analytical arguments confirm the superiority of the FSF model over the SF model for large-eddy simulations of weakly unstable transitional flows. The FSF model is therefore used for the simulation of a quasi-incompressible (M∞ = 0.5) boundary layer developing spatially over an adiabatic flat plate, with a low level of upstream forcing. With the minimal resolution 650 × 32 × 20 grid points covering a range of streamwise Reynolds numbers Rex1 ε [3.4 × 105, 1.1 × 106], transition is obtained for 80 hours of time-processing on a CRAY 2 (whereas DNS of the whole transition takes about ten times longer). Statistics of the LES are found to be in acceptable agreement with experiments and empirical laws, in the laminar, transitional and turbulent parts of the domain. The dynamics of low-pressure and high-vorticity distributions is examined during transition, with particular emphasis on the neighbourhood of the critical layer (defined here as the height of the fluid travelling at a speed equal to the phase speed of the incoming Tollmien–Schlichting waves). Evidence is given that a subharmonic-type secondary instability grows, followed by a purely spanwise (i.e. time-independent) mode which yields peak-and-valley splitting and transition to turbulence. In the turbulent region, flow visualizations and local instantaneous profiles are provided. They confirm the presence of low- and high-speed streaks at the wall, weak hairpins stretched by the flow and bursting events. It is found that most of the vorticity is produced in the spanwise direction, at the wall, below the high-speed streaks. Isosurfaces of eddy viscosity confirm that the FSF model does not perturb transition much, and acts mostly in the vicinity of the hairpins.

The Wall Effect in Cavity Flow

1966 ◽  
Vol 88 (1) ◽  
pp. 132-136 ◽  
Author(s):  
D. K. Ai
Keyword(s):  
Flow Field ◽  
Flat Plate ◽  
Integral Equations ◽  
Nonlinear Theory ◽  
Digital Computer ◽  
High Speed ◽  
Cavity Flow ◽  
Channel Width ◽  
Wall Effect ◽  
Plate Location

A nonlinear theory for the calculation of the flow field of an oblique flat plate under blockage condition is given using the techniques of integral equations. Numerical results are obtained with the aid of a high-speed digital computer for the plate situated midchannel at values of the angle of attack from 10 to 90 deg and the channel width-chord ratio from 3 to 20. Although the theory is developed for arbitrary plate location, the midchannel case is of great interest due to the fact that most of the tests are performed at this position.

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