Side-Wall Effects on ship Wave Resistance

A new slender-ship theory of wave resistance is presented. Specifically, a sequence of explicit slender-ship wave-resistance approximations is obtained. These approximations are associated with successive approximations in a slender-ship iterative procedure for solving a new (nonlinear integro-differential) equation for the velocity potential of the flow caused by the ship. The zeroth, first, and second-order slender-ship approximations are given explicitly and examined in some detail. The zeroth-order slender-ship wave-resistance approximation, r(0) is obtained by simply taking the (disturbance) potential, ϕ, as the trivial zeroth-order slender-ship approximation ϕ(0) = 0 in the expression for the Kochin free-wave amplitude function; the classical wave-resistance formulas of Michell [1]2 and Hogner [2] correspond to particular cases of this simple approximation. The low-speed wave-resistance formulas proposed by Guevel [3], Baba [4], Maruo [5], and Kayo [6] are essentially equivalent (for most practical purposes) to the first-order slender-ship low-Froude-number approximation, rlF(1), which is a particular case of the first-order slender-ship approximation r(1): specifically, the first-order slender-ship wave-resistance approximation r(1) is obtained by approximating the potential ϕ in the expression for the Kochin function by the first-order slender-ship potential ϕ1 whereas the low-Froude-number approximation rlF(1) is associated with the zero-Froude-number limit ϕ0(1) of the potentialϕ(1). A major difference between the first-order slender-ship potential ϕ(1) and its zero-Froude-number limit ϕ0(1) resides in the waves that are included in the potential ϕ(1) but are ignored in the zero-Froude-number potential ϕ0(1). Results of calculations by C. Y. Chen for the Wigley hull show that the waves in the potential ϕ(1) have a remarkable effect upon the wave resistance, in particular causing a large phase shift of the wave-resistance curve toward higher values of the Froude number. As a result, the first-order slender-ship wave-resistance approximation in significantly better agreement with experimental data than the low-Froude-number approximation rlF(1) and the approximations r(0) and rM.

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Separating and Reattaching Flow Structure in a Suddenly Expanding Rectangular Duct

Journal of Fluids Engineering ◽

10.1115/1.2816809 ◽

1995 ◽

Vol 117 (1) ◽

pp. 17-23 ◽

Cited By ~ 29

Author(s):

G. Papadopoulos ◽

M. V. O¨tu¨gen

Keyword(s):

Aspect Ratio ◽

Flow Structure ◽

Three Dimensional ◽

Side Wall ◽

Stream Velocity ◽

Rectangular Duct ◽

Mean Flow ◽

Wall Effects ◽

Velocity Measurements ◽

Aspect Ratios

The incompressible turbulent flow over a backward-facing step in a rectangular duct was investigated experimentally. The side wall effects on the core flow were determined by varying the aspect ratio (defined as the step span-to-height ratio) from 1 to 28. The Reynolds number, based on the step height and the oncoming free-stream velocity, was 26,500. Detailed velocity measurements were made, including the turbulent stresses, in a region which extended past the flow reattachment zone. Wall static pressure was also measured on both the step and flat walls. In addition, surface visualizations were obtained on all four walls surrounding the separated flow to supplement near-wall velocity measurements. The results show that the aspect ratio has an influence on both the velocity and wall pressure even for relatively large aspect ratios. For example, in the redevelopment region downstream of reattachment, the recovery pressure decreases with smaller aspect ratios. The three-dimensional side wall effects tend to slow down the relaxation downstream of reattachment for smaller aspect ratios as evidenced by the evolution of the velocity field. For the two smallest aspect ratios investigated, higher centerplane streamwise and transverse velocities were obtained which indicate a three-dimensional mean flow structure along the full span of the duct.

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Side wall effects on the instability of thin gravity-driven films—From long-wave to short-wave instability

Physics of Fluids ◽

10.1063/1.3634042 ◽

2011 ◽

Vol 23 (9) ◽

pp. 094110 ◽

Cited By ~ 24

Author(s):

Thilo Pollak ◽

André Haas ◽

Nuri Aksel

Keyword(s):

Side Wall ◽

Short Wave ◽

Wall Effects ◽

Wave Instability ◽

Long Wave ◽

Gravity Driven

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Prediction of tunnel wall upwash for delta wings including vortex breakdown effects

The Aeronautical Journal ◽

10.1017/s0001924000064940 ◽

1999 ◽

Vol 103 (1021) ◽

pp. 139-142 ◽

Cited By ~ 2

Author(s):

L. W. Traub

Keyword(s):

Vortex Breakdown ◽

Side Wall ◽

Vortical Flow ◽

Navier Stokes ◽

Wall Effects ◽

Integral Expression ◽

Image System ◽

Tunnel Wall ◽

Delta Wings ◽

Side Walls

AbstractAn incompressible method is presented to predict the upwash corrections associated with vortical flow as a result of wind-tunnel side wall effects. An image system is used to simulate the tunnel side walls which are assumed to be solid. An integral expression is formulated, representing the average upwash induced over the wing by the image system. Wall effects may be determined for flows with and without vortex breakdown. Comparisons of the results with upwash predictions from a Navier-Stokes study show close accord. The upwash expression also displayed the ability to successfully predict corrections for flows involving vortex breakdown.

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