Turbulent Surface Jet Research Articles

Characteristics of instantaneous flow structures of the surface jet over a submerged weir

This paper presents the results of a LES of turbulent surface jets over a submerged weir. The mean flow and turbulent structures are presented for both flat and deformed bed conditions. LES results with the scour hole reveal that the separated shear layer is extended by about three times, locating the reattachment point further downstream. In addition, the presence of the scour hole increases both total and maximum TKE and decreases near-bed TKE. Quantitatively, with the scour hole, the maximum near-bed TKE is decreased by 50%. It turns out that the area of high instantaneous bed shear stress does not match with that of high time-averaged bed shear stress, but does match well with that of the high near-bed TKE. The vortices generated by the weir propagate differently with and without the scour hole and shed light on the generating mechanism of a scour hole.

Turbulent Jet Energy Dissipation at Vertical Drops

The energy loss of the vertical drop with subcritical flow in the upstream channel has been studied experimentally with a physical model of 0.20 m drop height. Experimental data were collected in a range where few data exist. Based on a similarity between a turbulent surface jet and the flow over the drop, a model is developed using the theories of the shear layer and fully developed surface jet to estimate the energy loss. The results were compared with previous and current experimental data and were found to agree well with the proposed model.

Plane Turbulent Surface Jets in Shallow Tailwater

This paper presents a theoretical and laboratory study of plane turbulent surface jets in shallow tailwater. The main objective was to show that when the depth of tailwater is finite, the momentum flux in the forward flow in the surface jet decays appreciably with the distance from the nozzle producing the surface jet. This decay is shown to be due to the entrainment of the return flow which has negative momentum and an increase in the tailwater depth further away from the nozzle produces this return flow. An extensive set of experiments, with different Froude numbers and offset ratios, was conducted to observe and quantify the growth of the surface jet, the decay of the velocity scale, and the momentum flux and the variation of the volume flux. On the whole, the results from this study highlight the effect of the tailwater depth on the behavior of plane turbulent surface jets when the ambient fluid has a limited extent.

Dilution of Circular Turbulent Nonbuoyant Surface Jets in Cross-Flows

This paper presents the results of an experimental study on the dilution of circular nonbuoyant turbulent surface jets of diameter d, discharged perpendicularly into relatively deep cross-flows with depth D in the mixing region. The jet velocity was varied from 2.1 to 12.3 times the velocity of the cross-flow. Concentration measurements were carried out as far as x/d= 630, where x is the distance downstream from the nozzle along the cross-flow. Minimum dilutions of about 100 were attained in this mixing region. A general correlation has been developed to predict the minimum dilution in terms of the transformed distance αx/d, where α is the ratio of the jet to cross-flow velocity. The concentration profiles in the vertical and the transverse directions were found to be similar. Expressions were developed to describe the growth of the width and thickness of the deflected jets. The effect of submergence of the jet nozzle on the minimum dilution was also investigated.

Turbulence Structure of Plane Surface-Jets in a Weak Coflowing Stream for Different Initial Wake Conditions

Plane turbulent surface-jets, in the presence of a weak coflowing ambient current, were experimentally investigated using a single-component Laser Doppler Velocimeter. This study is concerned with the influence on the turbulent mixing characteristics of the relative speed ratio, U′a, and the wake generated behind the plate separating the jet from the ambient stream at the exit. Data were analyzed for similarity characteristics, surface speed decay, jet growth rate, jet momentum flux, jet volume flux, and turbulence decay. An integral analysis of the governing equations was also conducted to examine the turbulent entrainment properties of the surface jets.

Effect of Baffles on Submerged Flows

This paper introduces the concept of a submerged hydraulic jump being used for energy dissipation. A baffle wall is used to produce a stable deflected surface jet, thereby deflecting the high-velocity supercritical stream away from the bed to the surface. Based on a series of experiments, a diagram was developed that predicts the conditions under which such a surface jet would be produced. A second series of experiments were performed to study the characteristics of the deflected jet, as it travels upward first as a curved turbulent jet to eventually become a turbulent surface jet. The decay of the maximum velocity in the deflected as well as the surface jet was studied and compared with that of a plane turbulent wall jet that is a model for deeply submerged jumps.

Buoyancy effect on three-dimensional turbulent surface jet

A three-dimensional jet of low temperature discharged from a rectangular flume on the horizontal surface of a large water body of higher temperature was investigated experimentally. The longitudinal variations of the location of the jet axis, vertical and lateral widths of the jet and the time-averaged velocity and temperature at the jet axis are well correlated by a scaling law derived from the dimensional analysis of the governing equations and boundary conditions. The vertical and lateral profiles of both the time-averaged velocity and temperature show satisfactory similarity profiles.

Turbulent Surface Jet in Channel of Limited Depth

The synoptic behavior of a two‐dimensional turbulent surface jet is experimentally investigated. Single‐point hot‐film data were obtained for mean and root‐mean‐square velocities in the developing jet to a distance of 240 characteristic lengths downstream of the origin. The growth rates of the length and velocity scales are found to resemble more closely those observed in wall jets than those in free jets. The effects of jet confinement are to retard the ability of the jet to entrain fluid, to decrease the growth rate of the length scale, and to increase the decay rate of the velocity scale. Mean velocity‐profile similarity is still observed when the data is nondimensionalized with the reduced scales. Jet momentum will appear to have been lost due to momentum exchange with the return flow. An approximate analysis provides a means to estimate the momentum loss due to limited‐depth and is shown to correlate well with scale development in several jet configurations for these and prior experiments.

An experimental study of bluff surface discharges with small Richardson number

This paper presents the results ofan experimental study on the near-field diffusion of bluff buoyant turbulent surface jets with small (source) Richardson number in a large body of water without any ambient currents. It has been found that the velocity scale decreases inversely with the axial distance x from the outfall whereas the vertical and surface length scales h and b grow linearly with x. The variation of the coefficients in the relations for these scales, with the source Richardson number has been evaluated using the experimental observations.

TURBULENT NON-BUOYANT SURFACE JETS

This paper presents the results of an experimental study on the diffusion of plane and bluff turbulent surface jets. For plane surface jets, it has been found that its length scale grows at the same rate as a plane wall jet with its velocity scale being about 0.9 times the corresponding value for the plane free jet. For bluff surface jets, the vertical length scale increases at approximately the same rate as bluff wall jet whereas its transverse length scale grows at about half the rate of the corresponding bluff wall jets. The velocity scale decays inversely with the longitudinal distance, but the constant in the velocity scale relation is somewhat higher than that for the corresponding free circular jet.

NON-BUOYANT AND BUOYANT CIRCULAR SURFACE JETS IN COFLOWING STREAMS

The first part of this paper presents the results of an experimental study on the diffusion of circular non-buoyant turbulent surface jets in a coflowing channel. Based on the measurement of the (mean) velocity field and complimented by photographic observations on the width and thickness of the surface jets, it has been found possible to develop useful correlations to predict the behaviour of the velocity scale, the width and thickness of these surface jets by using the concept of the excess momentum thickness. Some observations have also been made on the effect of shallow depths in the channel.

An Experimental Study Of Bluff Buoyant Turbulent Surface Jets

Summary This paper presents an experimental study on the behaviour of bluff turbulent surface jets discharged into a stagnant ambient for moderate and large source Richardson numbers. Based on fairly extensive observations, the velocity and temperature profiles in the Lateral and vertical directions have been found to be similar. Using the results of an earlier theoretical analysis (by the authors) and the present experimental results, the variation of the velocity, temperature excess and length scales have been correlated with the nondimensional longitudinal distance from the outlet (made dimensionless with the square root of the surface jet at source), and the source Richardson number.