Formation Of Vortex Street Research Articles

Experimental Investigation of the Vortex Street Generated by a Plane Jet in a Counter Flow

Exploratory studies have indicated the existence of periodic oscillations associated with vortex street formation for a two-dimensional plane jet in a counter flowing stream. Potentially this appears to be a promising way of insuring dilution of industrial effluents in a stream. The present paper deals with experiments related to the near wake characteristics of a counter jet and specifically explores the geometric and fluid dynamic parameters that are associated with the jet oscillation. Both visual observations and hot film surveys have been made in the region of vortex street formation. The results indicate that the jet Strouhal number Sj attains a value of 0.18 when blockage and body (injection device) effects become negligible. Both these effects were greatly reduced in the test program by adopting a multiple port injection device. The circular jets issuing from the orifices developed into a two-dimensional plane jet.

The interaction between a pair of circular cylinders normal to a stream

This paper describes how the flows around two circular cylinders, displaced in a plane normal to the free stream, interact as the two bodies are brought close together. Surface pressure measurements at a Reynolds number of 2·5 × 104, based on the diameter of a single cylinder, show the presence of a mean repulsive force between the cylinders. An instability of the flow was found when the gap between the cylinders was in the range between one diameter and about 0·1 of a diameter. Correlation measurements of hot-wire outputs indicate how mutual interference influences the formation of vortex streets from the two cylinders. Spanwise correlation measurements show that the correlation length doubles as the cylinders are brought into contact.

Mechanism of bond zone wave formation in explosion-clad metals

Results of experiments in which the collision variables were carefully controlled showed that bond zone wave formation during explosion cladding is analogous to the formation of vortex streets in fluid flow around an obstacle or in the collision of liquid streams. The fluid flow analogy explains the observed transition from a smooth metal-to-metal bond zone to a wavy bond zone above a critical collision velocity. This model is capable of predicting the minimum collision velocity necessary for bond zone wave formation in different metal systems and it also predicts correctly the strong dependence of wave size on collision angle. The magnitude of the wave size agrees with that predicted from fluid flow past a flat plate. Two other mechanisms of bond zone wave formation were explored experimentally and found to be invalid.

The formation of vortex streets

The formation of vortex streets in the wake of two-dimensional bluff bodies can be explained by considering the non-linear interaction of two infinite vortex sheets, initially a fixed distance, h, apart, in an inviscid incompressible fluid. The interaction of such sheets (represented in the calculation by rows of point-vortices) is examined in detail for various ratios of h to the wavelength, a, of the initial disturbance. The number and strength of the concentrated regions of vorticity formed in the interaction depend very strongly on h/a. The non-linear interaction of the two vortex sheets explains both the cancellation of vorticity and vortex-street broadening observed in the wakes of bluff bodies.

Formation of Vortex Streets

It is shown that, for vortex trails in a nonviscous fluid, the mean longitudinal spacing a and mean transverse spacing h are invariant. It follows from this and other known facts, that the periodicity of a vortex trail is unstable, not the ratio h/a. In a viscous fluid, a is invariant but h increases. This fact explains various known experimental observations. A rough explanation is given for the order of magnitude of the Strouhal number S, based on the inertia opposed by the wake to transverse oscillations. Finally, using the theory of logarithmic potential, it is shown that, even in a nonviscous fluid, the concentration of vorticity is limited to circles whose diameter is about a/4.