Occurrence characteristics of gaseous cavitation in oil shear flow

Yuka Iga,Shunpei Takahashi,Yousuke Ibata,Junnosuke Okajima

doi:10.1063/5.0075659

Abstract

In the present study, a decompression experiment involving two rotating concentric cylinders with hydraulic oil between the clearances was performed. The dependency of the occurrence condition of gaseous cavitation in the oil was investigated not only based on rotation speed, which corresponds to the shear strength of a flow, but also on decompression speed, which corresponds to the pressure history in a flow. As a result, the characteristics of occurrence of gaseous cavitation were found to be divided into two regions of separation: equilibrium separation in which the occurrence pressure is constant with respect to the decompression speed, which occurs under lower decompression conditions, and non-equilibrium separation in which the occurrence pressure decreases according to the increase in the decompression speed, which occurs under higher decompression conditions. In addition, the boundary decompression speed between the equilibrium and non-equilibrium separations and the non-equilibrium separation pressure were formulated.

Highlights

Phase equilibrium at the saturated vapor pressure is assumed in cavitation models in computational fluid dynamics (CFD) in which evaporation occurs when and where the local pressure becomes below the saturated vapor pressure, and condensation occurs when and where the local pressure exceeds the saturated vapor pressure
The characteristics of occurrence of gaseous cavitation were found to be divided into two regions of separation: equilibrium separation in which the occurrence pressure is constant with respect to the decompression speed, which occurs under lower decompression conditions, and non-equilibrium separation in which the occurrence pressure decreases according to the increase in the decompression speed, which occurs under higher decompression conditions
The separation pressure increases with increasing rotation speed and with decreasing decompression speed because a higher separation pressure indicates that separation occurs more

Summary

INTRODUCTION

Phase equilibrium at the saturated vapor pressure is assumed in cavitation models in computational fluid dynamics (CFD) in which evaporation occurs when and where the local pressure becomes below the saturated vapor pressure, and condensation occurs when and where the local pressure exceeds the saturated vapor pressure. Yamaguchi reported that the condition of the shear flow affects the occurrence of cavitation in oil because the incipient and developed pressures of cavitation vary when the rotation speed of concentric rotating cylinders varies.[21]. Yamaguchi et al.[28] derived an equation for the threshold viscosity for the existence of nuclei from the probability equation for nuclei using Brownian motion and statistical mechanics and showed that nuclei are formed in a liquid having lower viscosity They performed experiments with 11 kinds of oil and showed that cavitation is easy to occur in low viscosity oil such as petroleum oil or spindle oil. In the present study, in order to clarify the occurrence conditions for gaseous cavitation, an experiment of separation of dissolved gas in a simple flow field is performed. In the present study, the influence of the rotation speed, which corresponds to the shear strength, and the decompression speed, which corresponds to the pressure history, is investigated regarding the occurrence of gaseous cavitation

EXPERIMENTAL APPARATUS AND METHODS

RESULTS AND DISCUSSION

Influence of decompression speed on separation pressure

Influence of rotation speed on separation pressure in equilibrium separation

Characteristic map of occurrence of gaseous cavitation

CONCLUSIONS