Cavitation Surge Research Articles

Suppression of Cavitation Instabilities in an Inducer by Circumferential Groove and Explanation of Higher Frequency Components

The purpose of the present research is to suppress cavitation instabilities by using a circumferential groove. The circumferential groove was designed based on CFD so that the tip leakage vortex is trapped by the groove and does not interact with the next blade. Experimental results show that the groove can suppress rotating cavitation, asymmetric cavitation and cavitation surge. However, weak instabilities with higher frequency could not be suppressed by the groove. From the analysis of pressure pattern similar to that for rotor-stator interaction, it was found that the higher frequency components are caused by the interaction of backflow vortices with the inducer blades.

Internal Flow of a Two-Bladed Helical Inducer at an Extremely Low Flow Rate

Abstract The attachment of inducer upstream of main impeller is an effective method to improve the suction performance of turbopump. However, various types of cavitation instabilities are known to occur even at the designed flow rate as well as in the partial flow rate region. The cavitation surge occurring at partial flow rates is known to be strongly associated with the inlet back flow. In the present study, in order to understand the detailed structure of internal flow of inducer, we firstly carried out the experimental and numerical studies of non-cavitating flow, focusing on the flow field near the inlet throat section and inside the blade passage of a two bladed inducer at a partial flow rate. The steady flow simulation with cavitation model was also made to investigate the difference of flow field between in the cavitating and non-cavitating conditions. Keywords : Inducer, Internal flow, Cavitation, Laser Doppler velocimetry measurement, Computational fluid dynamics 1. Introduction

Cavitation in Pump Inducer with Axi-asymmetrical Inlet Plate Observed by Multi-cameras

The attachment of inducer in front of main impeller is a powerful method to improve cavitation performance; however, cavitation surge oscillation with low frequency occurs with blade cavity growing to each throat section of blade passage simultaneously. Then, one conceptual method of installing suction axi-asymmetrical plate has been proposed so as to keep every throat passage away from being unstable at once, and the effect on suppression of the oscillation were investigated. In the present study, cavitation behaviors in the inducer is observed with distributing multi-cameras circumferentially, recording simultaneously and reconstructing multi-photos on one plane field as moving a linear cascade. Observed results are utilized for discussion with other measuring results as casing wall pressure distribution. Then the suppression mechanism of oscillation by installing axi-asymmetrical inlet plate will be clarified in more details.

Experimental Study and Numerical Simulation of Cavity Oscillation in a Diffuser with Swirling Flow

The cavity oscillation with swirling flow in hydraulic power generating systems was studied by a simple experiment and numerical simulation. Several types of fluctuation were observed in the experiment, including the cavitation surge caused by the diffuser effect and the vortex precession by the swirling flow. Both cavitation surge and vortex precession were simulated by CFD. Detailed flow structure was examined through flow visualization and CFD.

Cavitation Surge Suppression of Pump Inducer with Axi-asymmetrical Inlet Plate

The attachment of inducer in front of main impeller is a powerful method to improve cavitation performance. Cavitation surge oscillation, however, often occurs at partial flow rate and extremely low suction pressure. As the cavitation surge oscillation with low frequency of about 10 Hz occurs in a close relation between the inlet backflow cavitation and the growth of blade cavity into the throat section of blade passage, one method of installing an axi-asymmetrical plate upstream of inducer has been proposed to suppress the oscillation. The inlet flow distortion due to the axi-asymmetrical plate makes different elongations of cavities on all blades, which prevent the flow from becoming simultaneously unstable at all throat sections. In the present study, changes of the suppression effects with the axial distance between the inducer inlet and the plate and the changes with the blockage ratios of plate area to the cross-sectional area of inducer inlet are investigated for helical inducers with tip blade angles of and . Then a conceivable application will be proposed to suppress the cavitation surge oscillation by installing axi-asymmetrical inlet plate.

Analysis of Acoustic Cavitation Surge in a Rocket Engine Turbopump

In a liquid rocket engine, cavitation in an inducer of a turbopump sometimes causes instability phenomena when the inducer is operated at low inlet pressure. Cavitation surge (auto-oscillation), one such instability phenomenon, has been discussed mainly based on an inertia model assuming incompressible flow. When this model is used, the frequency of the cavitation surge decreases continuously as the inlet pressure of the turbopump decreases. However, we obtained an interesting experimental result in which the frequency of cavitation surge varied discontinuously. Therefore, we employed one-dimensional analysis based on an acoustic model in which the fluid is assumed to be compressible. The analytical result qualitatively corresponded with the experimental result.

199 ロケットエンジン用ターボポンプ試験設備における音響効果を考慮したキャビテーションサージの一次元解析 : 第2報 : アキュムレータの影響(流体工学I,一般講演)

199 ロケットエンジン用ターボポンプ試験設備における音響効果を考慮したキャビテーションサージの一次元解析 : 第2報 : アキュムレータの影響(流体工学I,一般講演)

ロケットエンジン用ターボポンプの入口配管の音響効果を考慮したキャビテーションサージの一次元解析 : 第1報,変動周波数の不連続性(流体工学,流体機械)

In a liquid rocket engine, cavitation in the inducer of a turbopump sometimes cause instability phenomena when the inlet pressure of the inducer is decreased. Cavitation surge, one such instability phenomenon, has been discussed mainly in connection with an inertia model. When such a model is used, the frequency of oscillation changes continuously as the inlet pressure decreases. However, we obtained interesting data on an experimental turbopump that showed that the surge frequency changed disconnectedly. With the aim of explaining this phenomenon, we conducted a one-dimensional analysis applying an acoustic model, combining the inlet pipeline with the sonic velocity of liquid oxygen. It was found that this phenomenon is a kind of self-excited vibration coupling the cavitation characteristics with the acoustic resonance of the inlet pipeline. Furthermore, as the inlet pressure decreases, the characteristic of the turbopump changes from a closed boundary condition to an open boundary condition, the frequency of the cavitation surge slightly decreasing.

ロケットエンジン用ターボポンプの入口配管の音響効果を考慮したキャビテーションサージの一次元解析 : 第2報,キャビテーション非定常特性の位相遅れ/進み及びPSDの影響(流体工学,流体機械)

ロケットエンジン用ターボポンプの入口配管の音響効果を考慮したキャビテーションサージの一次元解析 : 第2報,キャビテーション非定常特性の位相遅れ/進み及びPSDの影響(流体工学,流体機械)

J0501-4-1 ロケットエンジン用ターボポンプ試験設備における音響効果を考慮したキャビテーションサージの一次元解析 : 第3報 : キャビテーション非定常特性の周波数応答性の影響([J0501-4]流体機械の研究開発におけるEFD/CFD(4))

J0501-4-1 ロケットエンジン用ターボポンプ試験設備における音響効果を考慮したキャビテーションサージの一次元解析 : 第3報 : キャビテーション非定常特性の周波数応答性の影響([J0501-4]流体機械の研究開発におけるEFD/CFD(4))

Experiments on cavitation instability of a two-bladed turbopump inducer

The turbopump is a pressurizing system that supplies liquid propellants to the combustion chamber of a rocket engine at high pressure. As an integral component of a high-speed pumping system, the inducer used in a turbopump is forward-attached to an impeller to improve suction performance. This paper describes an experimental investigation on the flow instabilities of a two-bladed axial inducer due to cavitation. Cavitation development and its instabilities were analyzed. Asymmetric cavitation and cavitation surge were observed, and characterized by measuring the inlet pressure fluctuation for various cavitation numbers and flow coefficients. As flow coefficient decreases, the increased intensity of asymmetric cavitation was observed with an increased inception number of asymmetric cavitation. The frequency of the detected cavitation surge in the 4–10Hz range varied depending on the cavitation number. The instantaneous transition to cavitation surge appeared at the end of asymmetric cavitation as the cavitation number decreased. However, a further decrease in cavitation number resulted in the stable operation of the inducer with low values of pressure fluctuation. Finally, an intensive cavitation surge appeared after a significant amount of head loss.

Rotating Choke and Choked Surge in an Axial Pump Impeller

Unlike usual turbopump inducers, the axial flow pump tested operates very stably at design flow rate without rotating cavitation nor cavitation surge. Flow visualization suggests that this is because the tip cavity smoothly extends into the flow passage without the interaction with the leading edge of the next blade. However, at low flow rate and low cavitation number, choked surge and rotating choke were observed. Their correlation with the performance curve under cavitation is discussed and their instantaneous flow fields are shown.

Cause of Cavitation Instabilities in Three Dimensional Inducer

Alternate blade cavitation, rotating cavitation and cavitation surge in rocket turbopump inducers were simulated by a three dimensional commercial CFD code. In order to clarify the cause of cavitation instabilities, the velocity disturbance caused by cavitation was obtained by subtracting the velocity vector under non-cavitating condition from that under cavitating condition. It was found that there exists a disturbance flow towards the trailing edge of the tip cavity. This flow has an axial flow component towards downstream which reduces the incidence angle to the next blade. It was found that all of the cavitation instabilities start to occur when this flow starts to interact with the leading edge of the next blade. The existence of the disturbance flow was validated by experiments.

Numerical and experimental approach to cavitation surge obstruction in water pump

PurposeThis study aims to present the analysis of methods for cavitaion surge obstruction in water pump systems with particular focus on the two different inlet geometry configurations.Design/methodology/approachA cavitating flow field was simulated by RANS based computational fluid dynamics (CFD) program for different pump configurations operating in the unstable cavitation regime, inducing surging process. Numerical simulation results were compared to visualization and measurements results.FindingsPresented results show that a hydro dynamically induced surging regime could be limited and further advantages regarding operating characteristics of radial pumps could be achieved with presented geometry modifications.Originality/valueThis study provides insight into complicated transient cavitation flow patterns in conventional centrifugal pumps and introduces effective geometry optimization ideas useful to researchers and engineers in the area of fluid dynamics and hydromachinery.

Backflow Vortex Cavitation and Its Effects on Cavitation Instabilities

Cavitation instabilities in turbo-machinery such as cavitation surge and rotating cavitation are usually explained by the quasi-steady characteristics of cavitation, mass flow gain factor and cavitation compliance. However, there are certain cases when it is required to take account of unsteady characteristics. As an example of such cases, cavitation surge in industrial centrifugal pump caused by backflow vortex cavitation is presented and the importance of the phase delay of backflow vortex cavitation is clarified. First, fundamental characteristics of backflow vortex structure is shown followed by detailed discussions on the energy transfer under cavitation surge in the centrifugal pump. Then, the dynamics of backflow is discussed to explain a large phase lag observed in the experiments with the centrifugal pump.

Occurrence Mechanism and Oscillation Characteristics of Pulsation Phenomenon Arising in Cavitation Surge in Cascade

In this study, numerical analysis of cavitating three-blade cyclic flat-plate cascade is performed with paying attention to cavitation surge which is a type of cavitation instabilities. A numerical method employing “locally homogeneous model for compressible gas-liquid two-phase medium” is applied to solve the unsteady cavitating flowfield. From results of numerical analysis, few typical tendency of cavitation surge which is well known in experiments was reproduced numericaly, that frequency of cavitation surge decreases with lowering σ, and that cavitation surge is easy to occur at low flow rate condition. Additionaly, mechanism of pulsation phenomenon of cavitation surge in flat-plate cascade was clarified, that collapse pressure of cloud cavity in downstream of cascade propagates upstream on contact with re-entrant jet which is flowing backward inside a sheet cavity and causes oscillation in upstream pressure, also that negative angle of attack and choking of cascade throat are considered to cause of oscillation in flow rate. About dynamic transfer function of cavitation, certain degree of possibility is confirmed in quasi-steady mass flow gain factor Mquasi and cavitation compliance Kquasi for prediction of occurrence limit of cavitation instabilities. Additionally, for prediction of frequency of cavitation surge, it was confirmed that local cavitation compliance Klocal is more available than quasi-steady one.

1116 ロケットエンジン用ターボポンプ試験設備における音響効果を考慮したキャビテーションサージの1次元解析(OS11-3 流体機械の諸問題,オーガナイズドセッション)

In a liquid rocket engine, cavitations around the inducer of the turbopump sometimes cause the instability phenomena when the inlet pressure decreases. The cavitation surge, one of the instability phenomena, has been discussed mainly "the inertia model". A data of the surge mode oscillation on a experimental turbopump in JAXA showed that its frequency was not changed continuously related to the decrease of inlet pressure, but changed disconnectedly. In this article, aiming at explaining this phenomena, an one-dimensional analysis is examined applying "an acoustic model" combined the inlet line with the sonic velocity of liquid oxygen.

J0501-3-6 低流量における平板ヘリカルインデューサの内部流れに関する研究(流体機械の研究開発におけるEFD/CFD(3))

The attachment of inducer upstream of main impeller is an effective method to improve the suction performance of turbopump. However, various types of cavitation instabilities are known to occur even at the designed flow rate as well as in the partial flow rate region. The cavitation surge occurring at partial flow rates is known to be strongly associated with the inlet back flow. In the present study, in order to understand the detailed structure of internal flow of inducer, we firstly carried out the experimental and numerical studies of non-cavitating flow, focusing on the flow field near the inlet throat section and inside the blade passage of a two bladed inducer at a partial flow rate. The steady flow simulation with cavitation model was also made to investigate the difference of the flow field between in the cavitating and non-cavitating conditions.

Cavitation Surge Suppression of Pump Inducer with Axi-asymmetrical Inlet Plate

Cavitation Surge Suppression of Pump Inducer with Axi-asymmetrical Inlet Plate

Thermodynamic Effect on Cavitation Performances and Cavitation Instabilities in an Inducer

Based on the length of the tip cavitation as an indication of cavitation, we focused on the effect of thermodynamics on cavitation performances and cavitation instabilities in an inducer. Comparison of the tip cavity length in liquid nitrogen (76K and 80K) as working fluid with that in cold water (296K) allowed us to estimate the strength of the thermodynamic effect on the cavitations. The degree of thermodynamic effect was found to increase with an increase of the cavity length, particularly when the cavity length extended over the throat of the blade passage. In addition, cavitation instabilities occurred both in liquid nitrogen and in cold water when the cavity length increased. Subsynchronous rotating cavitation appeared both in liquid nitrogen and in cold water. In the experiment using liquid nitrogen, the temperature difference between 76K and 80K affected the range in which the subsynchronous rotating cavitation occurred. In contrast, deep cavitation surge appeared only in cold water at lower cavitation numbers. From these experimental results, it was concluded that when the cavity length extends over the throat, the thermodynamic effect also affects the cavitation instabilities as a “thermal damping” through the unsteady cavitation characteristics.