Dynamic Analysis of a Slender Body of Revolution Berthing to a Wall

A slender body of revolution berthing to a wall is studied by extending the classical slender body theory. This topic is of practical importance for a ship berthing to a quay wall. The flow problem is solved analytically using the method of matched asymptotic expansions. The lateral force and yaw moment on the body are obtained in a closed form too. The translation and yawing of the body are modeled using the second Newton law and coupled with the flow induced. Numerical analyses are performed for the dynamic lateral translation and yawing of a slender spheroid, while its horizontal translation parallel to the wall is prescribed at zero speed, constant speed, and time varying speed, respectively. The analysis reveals the interesting dynamic features of the translation and yawing of the body in terms of the forward speed and starting angle of yaw of the body.

Estimates of pressure differences across the head of a swimming clupeid fish

This paper is concerned to estimate, for a regularly swimming clupeid fish, the effective pressure difference that drives those motions in the subcerebral canal which can stim ulate the lateral-line neuromasts (see the preceding paper by D enton & G ray 1993). H ydrodynam ic analysis indicates that pure sideslip of the head (at observed sideslip velocities) would generate a pressure difference so great that the neuromasts would be saturated; however, sim ultaneous yaw ing can enormously reduce the effective pressure difference. For this purpose the angle of yaw would need to be kept in phase with sideslip velocity, with a m agnitude only a little less than the ratio of sideslip velocity to swimming speed, m aking the ‘crossflow’ of w ater across the yawed head small. These moreover are conditions which tend to avoid any serious distortions of the boundary layer on the fish’s surface by ‘crossflow’, such as are known from other evidence to increase significantly the resistance to the fish’s motion. It is noted that the lateral-line sensors would provide an appropriate feedback signal into a possible system for controlling yaw by oscillatory neck deflections so as to minimise the effective pressure difference and any associated crossflow effects. It is suggested that swimming clupeid fishes m ay use such an ‘active’ mechanism for reduction of hydrodynam ic resistance. The same ratio (around 0.87) of yaw angle times swimming speed to sideslip velocity is estimated: (i) to annul the signal sensed by lateral-line neuromasts; and (ii) to remove crossflow in the boundary layer over the head. The succeeding paper (Rowe et al. 1993) gives evidence, both that yaw is kept in phase with sideslip velocity, and that the above ratio (see their figure 4) remains close to 0.87, in a swimming herring.

Heat Transfer From Rectangular Plates Inclined at Different Angles of Attack and Yaw to an Air Stream

Average heat transfer coefficients during forced convection air flow over inclined and yawed rectangular plates have been experimentally determined. Tripping wires at the edges ensured that a turbulent boundary layer prevailed over the plates. The experiments were carried out for a constant surface temperature and covered two plates of different aspect ratios, angles of attack from 0 to 45 deg, angles of yaw from 0 to 30 deg, and Reynolds numbers from 2 times; 104 to 3.5 times; 105. The results show that the average heat transfer coefficient is essentially insensitive to the aspect ratio and angle of yaw. However, it is a function of Reynolds number and the angle of attack. Correlation equations for various angles of attack are suggested.

Experiments on Flow About a Yawed Circular Cylinder

Experiments were performed to evaluate the influence of yaw angle on circular cylinder pressure drag and near wake characteristics in the range of Reynolds numbers 2000 to 10,000. It was found that the transition in the wake from laminar to turbulent motion was significantly promoted as the angle of yaw increased. As a result, wake properties such as base pressure and position of transition to turbulence do not obey the Independence Principle which requires that properties be dependent only on the normal component of the free-stream conditions.

The Profile Drag of Yawed Wings of Infinite Span

SummaryA method is developed for calculating the profile drag of a yawed wing of infinite span, based on the assumption that the form of the spanwise distribution of velocity in the boundary layer, whether laminar or turbulent, is insensitive to the chordwise pressure distribution. The form is assumed to be the same as that accepted for the boundary layer on an unyawed plate with zero external pressure gradient. Experimental evidence indicates that these assumptions are reasonable in this context. The method is applied to a flat plate and the N.A.C.A. 64-012 section at zero incidence for a range of Reynolds numbers between 106 and 108, angles of yaw up to 45°, and a range of transition point positions. It is shown that the drag coefficients of a flat plate varies with yaw as cos½ Λ (where Λ is the angle of yaw) if the boundary layer is completely laminar, and it varies as if the boundary layer is completely turbulent. The drag coefficient of the N.A.C.A. 64-012 section, however, varies closely as cos½ Λ for transition point positions between 0 and 0.5 c. Further calculations on wing sections of other shapes and thicknesses and more detailed experimental checks of the basic assumptions at higher Reynolds numbers are desirable.