K. H. M. Ali

Prediction of flow patterns in local scour holes caused by turbulent water jets

The paper describes a testing procedure for investigating the suitability of the FLUENT CFD package in simulating flow patterns, generated by a turbulent water jet impinging on rigid horizontal and scoured beds. The scoured beds were formed at various times of the scouring process. The three turbulence closure models incorporated in FLUENT are:the Standard k-M Model, the Reynolds Stress Model and the ReNormalisation Group Theory-Based Model. Results obtained using these models were examined. In general, flowfields, velocities and shear stresses predicted by FLUENT showed close agreement with relevant experimental results.

Simulation of flow around piers

FLUENT CFD was used to predict the three-dimensional flow field around a circular cylinder. Solutions were obtained for rigid beds and for scour holes of different sizes resulting from different time-durations. The numerical results were used to obtain the variation of bed shear-stress around the cylinder. These results were used in the sediment continuity equation to obtain an expression for the variation of scour depth with time. The asymptotic scour depth was found to depend on three dimensionless numbers: the pile number, the sediment size number and the duration time number. The theoretical relationship was calibrated using various laboratory and field results.

Entrainment studies towards the preservation (containment) of 'freshwaters' in the saline environment

Flexible floating bottomless containment has recently been considered as a potential means of keeping freshwater separated from seawater in an estuary or coastal area. Speculative applications by the authors for marine located waste stabilisation ponds and for water quality management in salt intruded estuarial impoundments are cued herein. Viability assessment for such schemes calls for ihe study of, amongst other environmental disturbance factors, entrainment across the density-stratified interface between (he freshwater and the saltwater flowing underneath. Experiments conducted with a horizontal wall-jet of saltwater discharging beneath a freshwater body retained by a pair of baffles, to create underflow in a two-layered stratified system, are the focus of attention in this paper Results have been appraised against findings from the literature and implications to the proposed practical applications are discussed. In so doing, the form and structure of the interface between two stratified fluids has been investigated together with the rate of entrainment created by shear flow of the heavier saltwater underlayer.

Circulation and mixing in a stratified reservoir

The paper describes an analytical and experimental investigation of the circulation and mixing induced by a buoyant surface jet discharging into an originally stratified reservoir. Several methods were used to study the circulation patterns and the degree of mixing in the model. Systematic experiments were conducted to study the effects of jet-discharge and reservoir-density. Experiments were also conducted to study interfacial shear stresses and the degree of entrainment. Good agreement was obtained between theory and experiment.

Entrainment from a Buoyant Surface Layer Created by an under Baffle Wall-Jet

Pilot study experiments have been conducted with a horizontal wall-jet discharging beneath a baffle to create underflow in a two-layered stratified system. The form and structure of the interface has been investigated together with the rate of entrainment created by the submerged roller (flow gyre) over the incoming jet. Flow fields were monitored by ultrasonic anemometry and mixing determined from a multi-channel conductivity probe system for the fresh/salt water stratification under study. The effect of different blockage factors, created by the baffle and various positions of the interface have been considered. Provisional functional relationships have been established for the rate of salt mass entrainment, Richardson number and jet characteristics being identified as the dominant factors.

Purging studies on a model sea outfall diffuser

This paper describes results of various experiments conducted over the diffuser section of a laboratory representation of a long sea outfall. Detailed measurements of instantaneous riser salinity and velocity for various experimental configurations and under steady and unsteady flow cycles are presented. Findings are discussed with reference to relevant previous investigations. In particular, it is demonstrated that mixing from the intrusive salt wedge stratification front in the main pipe is evident from discharging risers well upstream of the first intrusive riser. This has some implication to application of the well established riser purging criterion at the design stage.

Sedimentation in long sea outfalls

This paper presents results of analytical and experimental investigations of sediment motion and bed morphology in circular outfalls. Behaviour of prototype and model sediments were studied in detail. A two-dimensional finite difference approach has been shown to provide qualitative representation of the experimental observations.

The Improvement of Flow-Distribution to Multiple Sedimentation Tanks

Open channels conveying the inflow to sedimentation tanks at effluent-treatment works are often severely constrained in their horizontal layout. It is usually desired to pass equal flow to each of a number of tanks. Frequently, however, the need for severe directional changes results in flow-patterns so complicated that the subdivision of the flow is difficult to control.

Dispersion of marked fluid in reservoirs

Abstract The paper gives relationships for predicting reservoir circulation generated by radial and tangential jets. These relationships show the importance of the reservoirs aspect-ratio, and the Reynolds number of the jet. Details are also given of concentration-experiments using the conductivity and fluorimetric methods, and incorporating various inlet and outlet arrangements. Peripheral and radial dispersion-coefficients were obtained, and found to be of the same order of magnitude. These coefficients were dependent on the size of the model and on the local Reynolds numbers. The values of dispersion coefficients for reservoirs are similar to those for one-dimensional open channel flow.

Characteristics Of Primary Salt Wedges In Long Sea Outfalls

1. ABSTRACT This paper presents laboratory results and a formulation for predicting the length of arrested salt wedges formed in horizontal circular outfall pipes. The formulation is based on a combination of the energy and the momentum equations. A new expression for the friction factor which takes into account the effect of the two-layer stratification is suggested. Two circular outfall pipes having internal diameters of 5 and 13.75cm were used to conduct the tests and a wide range of various combinations of experimental parameters (saltwater density 1.01 to 1.032g/cnf and densimetnc Froude number 0.42 to 0.92) were used. Measurements of the length of the arrested salt wedge and velocity distributions (for the pipe with diameter = 13.75cm) in the upper moving layer were made. Comparisons between the laboratory results and the suggested theoretical relationships showed reasonable agreement.