Influences of thermal effects on cavitation dynamics in liquid nitrogen through venturi tube

Abstract

Investigation on cavitation features in cryogenic liquids is of great importance to rocket engine design due to their complicated physics. This paper experimentally investigates the characteristics of unsteady liquid nitrogen (LN2) cavitating flow through a transparent venturi tube with image processing techniques. The numerical simulations based on the computational fluid dynamic approach are also performed to help explain the mechanisms. A pressure ratio (Pr) associated with the inlet and the outlet subcooling is found to have a linear relationship with the cavitation number. The nondimensional thermal effect parameter derived from the single bubble dynamics is used to quantify thermal effect intensity. The cavity length derived from standard derivation results has an inversely linear relation with Pr, and there exists an inflection point of the pressure ratio (Prc) below which the cavity length growth rate is relatively larger. The effects of the bulk temperature on the magnitude of Prc are numerically investigated, which reveals that Prc increases as the liquid temperature increases. The oscillating frequencies of the sheet and cloud cavitating flow are also analyzed according to two Strouhal numbers based on cavity length (Stc) and venturi throat diameter (Std), respectively. For cloud cavitation, Stc lies in between 0.30 and 0.40 for all Pr values, while for sheet cavitation, it decreases to 0.04-0.08. Besides, in the cloud cavitation region, Std increases linearly with Pr but has a weak relation with ς·√ C/uth3. It is also found that with increased values of ς·√C/uth3, the transition point of Pr from sheet cavitation to cloud cavitation is delayed.