Surface manifestations of internal waves investigated by a subsurface buoyant Jet: 1. The mechanism of internal-wave generation |
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Authors: | V G Bondur Yu V Grebenyuk E V Ezhova V I Kazakov D A Sergeev I A Soustova Yu I Troitskaya |
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Institution: | (1) Department of Mechanical Engineering, National Taiwan University of Science and Technology, 43 Sec. 4 Keelung Rd., Taipei, 106, Taiwan |
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Abstract: | In a large test reservoir with artificial temperature stratification at the Institute of Applied Physics, Russian Academy
of Sciences, we have performed a major laboratory simulation of the nonstationary dynamics of buoyant turbulent jets generated
by wastewater flows from underwater collector diffusers. The interaction of buoyant jets with the pycnocline leads to an active
generation of internal waves. An analysis of the dependence of wave amplitude on the control parameter proportional to the
rate of liquid flow from the collector diffuser has indicated that this dependence is adequately described by a function that
is characteristic for the presence in the Hopf bifurcation system, which occurs for a soft actuation mode of self-oscillations
of the globally instable mode. To check the conditions for the actuation of the globally instable mode, we have performed
an auxiliary experiment in a small reservoir with a salt stratification formulated similar to the experiment in the big reservoir.
Using the particle image velocimetry (PIV) method, we have measured the velocity field in the buoyant jet and constructed
the profiles of transverse velocity in several sections. When the jet approaches the pycnocline, a counterflow is generated
at the edges. A stability analysis for the resulting profiles of flow velocities performed by the method of normal modes has
revealed that, for the jet portions with counterflow, the condition of absolute instability by the Briggs criterion for axisymmetric
jet oscillations is satisfied, which testifies to the fact that the globally instable mode is actuated. The estimates for
oscillation frequencies of the globally instable mode are well consistent quantitatively with the measured spectrum of jet
oscillations. |
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