Abstract
The present study refers to a cavitating Venturi type section geometry characterized by a convergent angle of 18° and a divergent angle of about 8° where the sheet cavity presents typical self-oscillation behavior with quasi-periodic vapor clouds shedding. This work is an extension of previous works concerning void ratio measurements and velocity fields using double optical probe and constitutes a complete analysis of the two-phase structure of unsteady cavitating flow. This paper provides a new method based on conditional and phase averaging technique with wall pressure signal to treat experimental data in order to evaluate more precisely time-averaged and rms values of the void ratio and instantaneous velocity fields. Conditional analysis shows a different behavior of the two-phase flow dynamics leading to highlight high void ratio events linked to the break-off cycle. Unsteady phase averaging of the optical probe signal gives the evolution of the void ratio at each studied location in the venturi and shows that the fluctuations close to the wall (where the re-entrant jet is predominant) are in phase with the upper part of the cavity instead of the thickness of the cavity which is unchanged.
Highlights
In cryogenic rocket engines, an inducer stage is used to protect the main turbopump from cavitation
This paper provides a new method based on conditional and phase averaging technique with wall pressure signal to treat experimental data in order to evaluate more precisely time-averaged and rms values of the void ratio and instantaneous velocity fields
Velocity Fields we firstly present the probability density function (PDF) of the velocity for each station at different vertical position in the sheet cavity
Summary
An inducer stage is used to protect the main turbopump from cavitation. To get the unsteady behavior of quasi-peridodic cavitating structures, Large Eddy Simulations may be used to simulate the sheet/cloud cavitation phenomena In this way, Dittakavi et al [16] performed a LES of cavitation in a venturi nozzle in order to capture at the venture throat the specific irregular shedding of small scale vapor structures near the turbulent cavity closure region. Dittakavi et al [16] performed a LES of cavitation in a venturi nozzle in order to capture at the venture throat the specific irregular shedding of small scale vapor structures near the turbulent cavity closure region They showed that these structures were responsible of vorticty production resulting in the formation of hair-pin vortices. An overview of experimental results concerning void ratio and vapor phase velocity is given in Sections 3 and 4
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