When water is withdrawn from a STRATIFIED reservoir, the flow at low discharges is confined to a narrow layer adjacent to the level of the sink. This phenomenon, known as selective withdrawal, has widespread applications in lake and reservoir water quality management. It is known that the formation of a selective withdrawal layer is due to the motion of internal waves called "shear waves" from the reservoir outlet to the upstream. The flow becomes steady when the shear waves are either blocked by the inertia of the background flow or damped by viscosity. In this paper, with the assumption of a small reservoir discharge, the weakly nonlinear effects of the reservoir flow on the motion of shear waves are investigated. A multi-scale perturbation technique is used to solve the governing equations. The results indicate that shear wave speeds are reduced by the background flow.

The wake and internal waves of a moving three dimensional (3D) airfoil body in a STRATIFIED FLUID has been investigated in a large STRATIFIED tank with a finite depth using movies of shadowgraphs of the flow fields.Typical Reynolds and Froude numbers of the flow varied between 103 and 104, and 0.3 and 2 respectively.The flows are generated often by towing the body in a uniformly STRATIFIED flow, while limited cases are carried out with body stationary and the channel was in recirculating mode. For some experiments the density profile had a stepped like shape. The wake flow is often consisted of internal waves including random and coherent ones. Distortion of density fields was also observed ahead and above the body in cases where the Froude number was subcritical. Results show that as the Froude number (Fr=U/Nh, where U is the body relative velocity, N is buoyancy frequency and h is the thickness of the body) is increased, the flow undergoes from a subcritical narrow wake (for Fr<1) to an internal waves dominated flow (for Fr~1) and then to a hydraulic jump with a turbulent wake with some mixing (for Fr>1). Typical wavelength of the exited internal waves is increased with Fr, as the theory predicts. The wake of the flow for Fr>1.4 appeared to collapse and some internal waves emission from it could be observed. Usually two types of internal waves, namely random small scale and large scale, more regular waves are observed.

The stability of STRATIFIED Rivlin-Ericksen FLUID in porous medium in the presence of suspended particles and magnetic field has been investigated. Upon application of normal mode technique, the dispersion relation was obtained. The important results obtained in this paper include the instability of non-oscillatory modes and the stability of oscillatory modes. Also, it was found that the system is stable for b<0 and unstable for b>0 under certain conditions.

In this paper, a numerical study was conducted to study the effect of the liquid phase compressibility variability in the two-FLUID single-pressure model. The two-FLUID model is solved by a class of conservative shock-capturing method. The two-FLUID model is solved once with the assumption that the density of the liquid phase and one is assumed, assuming that the liquid phase density is varied. In order to examine the compressibility effect, the liquid phase density of the three sample problems was used with different pressure conditions. The results show that, under atmospheric conditions, variations in the density of the liquid phase can be neglected and have no effect on the accuracy of the results of the two-FLUID single-pressure model. In the case of extreme pressure gradients, the variability of the liquid phase density in a two-FLUID single-pressure model causes deviation of numerical results. Therefore, in the case of extreme pressure gradients, two-FLUID single-pressure model is a more accurate model assuming that the liquid phase density is constant.

Gravity currents, also called density currents or buoyancy currents, are flows driven by the density difference between the flow and its ambient environments. When a gravity current reaches the level of neutral buoyancy in a STRATIFIED water body, it can separate from the bed as an intrusion. Laboratory experiments are performed to investigate dense flow behavior in STRATIFIED ambient in this study. Experiments were carried out on 2.5% bed slope by 4 discharges, 1, 1.5, 2 and 2.5 l/s, and 4 concentrations 5, 10, 15 and 20 mg/l, that created current with a density of 1003.2, 1006.3, 1009.4 and 1012.5 respectively. Stratification was made by mixture of water and salt with vertical gradient. For creating density flow, silica particles with 8 diameters in average and density of 2.673 g/cm3 was used. To investigate the concentration profile, density and concentration were measured in three sections along the flume with three centimeters interval in depth using siphon mechanism. Experimental observations showed that the currents would separate from the bed and then horizontally intrude into the ambience and the density of ambient FLUIDs below the separation point decreases. The measurements in this study indicate that the maximum concentration depth and thickness of body current decreases with increasing concentration in interflow and body current thickness stabilize with increasing discharge.

MHD free convection over an inclined plate in a thermally STRATIFIED high porous medium in the presence of a magnetic field has been studied. The dimensionless momentum and temperature equations have been solved numerically by explicit finite difference technique with the help of a computer programming language Compaq Visual Fortran 6.6a. The obtained results of these studies have been discussed for the different values of well known parameters with different time steps. Also, the stability conditions and convergence criteria of the explicit finite difference scheme has been analyzed for finding the restriction of the values of various parameters to get more accuracy. The effects of various governing parameters on the FLUID velocity, temperature, local and average shear stress and Nusselt number has been investigated and presented graphically.