EXPERIMENTAL STUDY ON THE VORTEX FORMATION AND ENTRAINMENT CHARACTERISTICS FOR A ROUND TRANSVERSE JET IN SHALLOW WATER

The vortex formation and entrainment characteristics for a round transverse jet in shallow water were experimentally investigated by means of a combination of LIF flow visualization and PIV measurement. A scarf vortex wrapped around the main body of the jet is formed in the near-wall region due to the interaction between the resulting wall jet and sufficiently shallow crossflow, with some more or less unsteady flow properties and with spreading ranges as functions of both the velocity ratio and the water depth within the near field. The entrainment of the ambient crossflow fluid into the jet main body is closely associated with the time-evolving features of the shear layer between the jet and surrounding fluid as well as the induced vortical structures near the wall. In the case of slight impingement upon the wall, the interaction between the jet shear layer and the weak, unstable scarf vortex gives rise to an appreciable local entrainment enhancement, confined in the near-wall region in the vicinity of the stagnation point. While in the case of intense impingement upon the wall, the well-organized and stable scarf vortex gives rise to a greatly enhanced entrainment and a greatly increased lateral spreading rate nearly throughout the overall near field as compared to the conventional wall jet. In addition, the entrainment of the ambient crossflow fluid by the scarf vortex in this case occurs largely on the surface of the unique spiral roller structure by itself due to the presence of smaller and unorganized eddies, and accordingly the scarf vortex is likely to keep its spiral roller structure steadily to a relatively great downstream distance within the near field.

ON THE FORMATION OF VORTEX RINGS AND PAIRS

The axisymmetric vortex sheet model developed by Nitsche and Krasny had been extended to study the formation of vortex rings (pairs) at the edge of circular (2D) tube and opening. Computations based on this model were in good agreement with the experiments (Didden (1979) for circular tube and Auerbach (1987) for 2D tube and opening). Using this new model, evidences are provided to show that the main failure of the similarity theory (the false prediction of axial trajectory of vortex ring) is due to its ignorance of the self-induced ring velocity (mutual induction for vortex pair). The Glezer (1988)'s summary on the influence of piston speed upon the shedding circulation was also discussed, and finally the variation of core distribution of vortex ring with turning angle and piston speed was given. (Edited author abstract) 22 Refs.

Drag Coefficient of a Non-Convex Polygonal Plate during Free Fall

Waterside creatures or aquatic organisms use a fin or web to generate a thrust force. These fins or webs have a non-convex section, referred to as a non-convex shape. We investigate the drag force acting on a non-convex plate during unsteady motion. We perform the experiment in a water tank during free fall. We fabricate the non-convex plate by cutting isosceles triangles from the side of a convex hexagonal plate. The base angle of the triangle is between 0° to 45°. The base angle is 0 indicates the convex hexagonal thin plate. We estimate the drag coefficient with the force balance acting on the model based on the image analysis technique. The results indicate that increasing the base angle by more than 30° increased the drag coefficient. The drag coefficient during unsteady motion changed with the growth of the vortex behind the model. The vortex has small vortices in the shear layer, which is related to the Kelvin-Helmholtz instabilities.

New Mechanism and Analytical Formula for Understanding the Gravity Constant <i>G</i>

The nature of gravitation and G is not well understood. A new gravitation mechanism is proposed that explains the origin and essence of the gravitational constant, G. Based on general relativity, the vacuum is considered to be a superfluid with measurable density. Rotating bodies drag vacuum and create a vortex with gradient pressure. The drag force of vacuum fluid flow in the arm of the vortex is calculated relative to the static vacuum and a value that is numerically equal to that of G is obtained. Using Archimedes’ principle, it is determined that G is the volume of vacuum displaced by a force equivalent to its weight which is equal to the drag force of the vacuum. It is concluded that the gravitational constant G expresses the force needed to displace a cubic metre of vacuum that weighs one kg in one second. Therefore, G is not a fundamental physical constant but rather is an expression of the resistance encountered by the gravitational force in the vacuum.

New Theory to Understand the Mechanism of Gravitation

Gravitation is still the least understood interaction among the fundamental forces of Nature. A new theory that explains the mechanism of gravitation and the origin Newton’s laws of gravitation and general relativity and distinguishes between two of the Newton’s laws has been proposed. It is shown that the vortex formation created during the Big Bang event is the origin of the gravitational force. The vortex curves the vacuum (space-time) around it, attract and condense energy and dust to its center to form the mass. The gradient pressure in the vortex creates a flow that upon interaction with an object transfers a part of its momentum to the object and pushes it toward the center. The force exercised on the object is equivalent to Newton’s second law. The force of attraction between two vortices is equivalent to Newton’s third law. The drag force between the energy flow of the vortex and the static vacuum diminishes the gravitational force and is equivalent to the G constant. The proposed theory could provide new interesting insights for a comprehensive understanding of gravitation and represents a theoretical starting point for the engineering of anti-gravitation technology.