Numerical Analysis of the Influence of Acceleration on Cavitation Instabilities that arise in Cascade

Abstract

In the turbopump inducer of a liquid propellant rocket engine, cavitation is affected by acceleration that occurs during an actual launch sequence. Since cavitation instabilities such as rotating cavitations and cavitation surges are suppressed during launch, it is difficult to obtain data on the influence of acceleration on cavitation instabilities. Therefore, as a fundamental investigation, in the present study, a three-blade cyclic cascade is simulated numerically in order to investigate the influence of acceleration on time-averaged and unsteady characteristics of cavitation that arise in cascade. Several cases of acceleration in the axial direction of the cascade, including accelerations in the upstream and downstream directions, are considered. The numerical results reveal that cavity volume is suppressed in low cavitation number condition and cavitation performance increases as a result of high acceleration in the axial-downstream direction, also, the inverse tendency is observed in the axial-upstream acceleration. Then, the regions in which the individual cavitation instabilities occur shift slightly to a low-cavitation-number region as the acceleration increases downstream. In addition, in a downstream acceleration field, neither sub-synchronous rotating cavitation nor rotating-stall cavitation are observed. On the other hand, rotating-stall cavitation occurs in a relatively higher-cavitationnumber region in an upstream acceleration field. Then, acceleration downstream is robust against cavitation instabilities, whereas cavitation instabilities easily occur in the case of acceleration upstream. Additionally, comparison with the Froude number under the actual launch conditions of a Japanese liquid propellant rocket reveals that the cavitation performance will not be affected by the acceleration under the current launch conditions.

Numerical Analysis of Damping Effect of Liquid Film on Material in High Speed Liquid Droplet Impingement

“…This locally homogeneous medium model is also used for the gas-liquid two-phase flow like cavitation flow [9]. The equation of state for a locally homogeneous gas-liquid two-phase medium is written as follows:…”

Numerical Simulation of Unsteady Cavitation in a Submerged Water Jet by Compressible Bubbly Mixture Flow Method

“…, which denotes the mean radius of bubbles in a local area x at an arbitrary instant t. Then, the bubble radius may be estimated according the liquid pressure and the compressibility of bubbly mixture may be evaluated by equation (4). The variation of gas volume fraction is then determined by mass conversation of the gas phase under the effect of bubble radius oscillation.…”

“…However, the flow structure of cavitating jet and the behavior of unsteady cavitation clouds are still unclear for the difficulty to observe the interior of cavitating flow [1] [2]. For the purpose of performance prediction and optimum design of water jet devices numerical simulation of high-speed water jets with intensive cavitation becomes a task full of challenges [3] [4]. In the present work, unsteady turbulent cavitating flows caused by high-speed submerged water jet are calculated numerically by applying a simplified compressible mixture-flow bubble-cavitation model.…”

Numerical Simulation of Unsteady Cavitation in a High-speed Water Jet

“…For the difficulty to consider all these different characteristics numerical simulations of cavitating flow have been conventionally performed by introducing certain simplifications on a special flow field concerned [5]. Although many simulation works on cavitation phenomena in various hydraulic machineries, especially hydrofoil have been reported [6][7][8][9], only a few ones have been done on high-speed water jets accompanying by intensive cavitation [10]. Most of numerical simulations of turbulent cavitating flow are based on Unsteady Reynolds Averaged Navier-Stokes (URANS) equations and cavitation models applied may be mainly classified into two-fluid and two-phase mixture flow method.…”