Enhanced mixing through perforated discs on round buoyant jet.

摘要

Jets have been widely used in submarine outfall diffuser systems for discharging the sewage effluents into large bodies of sea water. The primary goal of an outfall diffuser system is to accomplish rapid mixing of the effluent with the ambient water. In an effort to enhance the near field mixing, various obstruction devices may be placed exterior to the diffuser nozzle. This experimental study focuses on the enhanced mixing mechanisms of the jets obstructed with perforated discs.;Experiments are conducted in a deep water tank with glass walls on four sides of the tank. The tank has the dimension of 3.35 m in depth with a square cross-section of 1.15 m. The water particle velocities of the resulting flow field are measured by using a portable four-beam, two-component, fiber-optic Laser-Doppler Velocimeter system (LDV). The fiber-optic probe is mounted on an instrument carriage which can be moved vertically and horizontally to measure the fluid velocity at desired locations. The concentration of the entrained fluid is measured by using a Laser-Induced Fluorescence system (LIF). The data acquisition system used for obtaining data on the concentration profiles is processed by Labview's programmable virtual instruments software.;The experimental data consist of the axial (vertical) and radial (horizontal) velocities, turbulent intensities, Reynolds stresses and concentrations. From the results of the velocity measurements, it is found that fluctuations in both the axial and radial velocities help to generate vorticity and to induce mixings over a larger area in the neighboring flow region. Moreover, the velocity gradient is significantly increased over the region based on the experimental data involving the perforated discs. The results also show that a large reduction in the concentration of the entrained fluid can be achieved due to the obstructing disc. The results demonstrate quite convincingly the ability of the perforated disc to enhance the mixing and entrainment of the discharging fluid with the ambient fluid.