Investigations of turbulent jets interacting with standing water waves
by Chen Xingwei
Ph.D. Mechanical Engineering
xx, 169 leaves : ill. (some col.) ; 30 cm
The flow fields and the tracer concentrations of turbulent jets discharged vertically into standing water wave environments are studied theoretically and experimentally....[ Read more ]
The flow fields and the tracer concentrations of turbulent jets discharged vertically into standing water wave environments are studied theoretically and experimentally.
The governing equations of the jet-wave interacting flow have been derived based on the Navies-Stokes equations and the technique of dimensional and scale analysis. An integral momentum equation along the jet axis is obtained. An expression for the variation of the axial velocity along the jet axis is developed in the jet dominated flow field.
Experiments are performed in a water tank equipped with a jet generation mechanism and a surface standing wave generator. The wave displacements are measured by a capacitance wave height gage. The technique of laser-induced fluorescence is used to visualize the flow patterns. A laser Doppler velocimetry system is used to measure the flow field. The velocity signal is synchronized with the signal from the wave height gage. The signals are processed by time and phase averaging techniques for the investigations of the mean flow field and turbulence structures.
Verification of experimental results for standing waves and for pure jets, respectively, shows that the generated waves are nearly perfect standing waves and the behaviors of the pure jets are consistent with previous researches.
Visualization of the flow pattern and measurement of longitudinal velocity along the jet axis at the node of waves indicates that there are three flow regions, namely, the Jet Dominated Near Field (JDNF), Jet Dominated Far Field (JDFF) and Wave Dominated Far Field (WDFF). The distinction among these fields depends strongly to the relative importance of the wave motion and the jet initial velocity.
The mean flow characteristics of JDFF are studied to determine its range and the variation of its longitudinal velocity along jet axis. The coefficient of velocity decay shows a nearly constant trend when the ratio between the jet initial velocity and wave-induced velocity at the exit of the jet nozzle, w0/û0, is sufficiently large.
The behaviors of the interacting flow in JDFF for large w0/û0 are studied in detail. The results of the flow characteristics and tracer concentration under node and antinode of wave reveal that imposition of the surface water waves is to deform the axial symmetric circular cross-section for pure jet into an elliptical cross-section for a jet with wave. The results also show that the effect of wave oscillations can enhance greatly the spreading of jet mixing, turbulent intensity and Reynolds stresses. The enhancement caused by horizontal oscillations at node is larger than that caused by vertical oscillations at antinode.
Modifications of wave-induced velocity, turbulent intensity and Reynolds stresses by the discharging of jet flow are also investigated and reported.
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