Analysis of Flow Instabilities on a Three-Bladed Axial Inducer in Fixed and Rotating Frames

The paper describes the results of recent experiments carried out in the Cavitating Pump Rotordynamic Test Facility for the dynamic characterization of cavitation-induced flow instabilities as simultaneously observed in the stationary and rotating frames of a high-head, three-bladed axial inducer with tapered hub and variable pitch. The flow instabilities occurring in the eye and inside the blading of the inducer have been detected, identified, and monitored by means of the spectral analysis of the pressure measurements simultaneously performed in the stationary and rotating frames by multiple transducers mounted on the casing near the inducer eye and on the inducer hub along the blade channels. An interaction between the unstable flows in the pump inlet and in the blade channels during cavitating regime has been detected. The interaction is between a low frequency axial phenomenon, which cyclically fills and empties each blade channel with cavitation, and a rotating phenomenon detected in the inducer eye.

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Identification of Cavitation Instabilities on a Three-Bladed Inducer by Means of Strain Gages

Journal of Fluids Engineering ◽

10.1115/1.4045186 ◽

2019 ◽

Vol 142 (2) ◽

Author(s):

Ruzbeh Hadavandi ◽

Giovanni Pace ◽

Dario Valentini ◽

Angelo Pasini ◽

Luca d'Agostino

Keyword(s):

High Speed ◽

Strain Gages ◽

Experimental Characterization ◽

Mechanism Of Formation ◽

Pressure Transducers ◽

Cavitation Region ◽

Rotating Frames ◽

Induced Flow ◽

High Head

Abstract This paper reports the experimental characterization of the cavitation-induced flow instabilities of a high head three-bladed inducer at design condition detected simultaneously by means of piezoelectric pressure transducers located at different axial and azimuthal stations on the casing of the pump and strain gages mounted on the pressure side of each blade. The simultaneous analysis performed in the stationary and rotating frames, supported by high-speed movies, suggests that the mechanism of formation of the detected subsynchronous rotating cavitation resembles that of modal stall in compressors, being the cavitation region the source of compliance. In fact, at decreasing cavitation number, a strong attached cavitation, developed preferentially on one blade and capable of completely surrounding and unloading the following blade, starts to be destabilized as consequence of the progressive intensification of a modal oscillation. The developed complex instability, consisting in a strong oscillation of the attached cavitation, is detected in both the frames as the simultaneous presence of a subsynchronous rotating cavitation and a cavitation surge.

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Identification of Cavitation Instabilities on a Three-Bladed Inducer by Means of Strain Gages

Volume 2A: Turbomachinery ◽

10.1115/gt2018-76869 ◽

2018 ◽

Author(s):

Ruzbeh Hadavandi ◽

Giovanni Pace ◽

Dario Valentini ◽

Angelo Pasini ◽

Luca d’Agostino

Keyword(s):

High Speed ◽

Simultaneous Analysis ◽

Tip Vortex ◽

Flow Instabilities ◽

Strain Gages ◽

Pressure Transducers ◽

Rotating Frames ◽

Induced Flow ◽

Mutual Relations

The present paper reports the experimental characterization of the cavitation induced flow instabilities of a high head three-bladed inducer at design condition detected simultaneously by means of piezoelectric pressure transducers located at different axial and azimuthal stations on the casing of the pump and through strain gages mounted on the pressure side of each blade. The purpose of this experimental campaign is a deeper insight of the phenomena associated to the flow instabilities obtained by the simultaneous analysis performed in the stationary and rotating frames. Both the sensors set-ups proved to be able to detect the main flow instabilities such as synchronous and sub-synchronous rotating cavitation, cavitation surge and tip vortex instability. Moreover, the simultaneous analysis of the results supported by high speed movie has allowed for assessing the mutual relations between the instabilities.

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Dynamics of the Blade Channel of an Inducer Under Cavitation-Induced Instabilities

Journal of Fluids Engineering ◽

10.1115/1.4041728 ◽

2018 ◽

Vol 141 (4) ◽

Cited By ~ 1

Author(s):

Angelo Pasini ◽

Ruzbeh Hadavandi ◽

Dario Valentini ◽

Giovanni Pace ◽

Luca d'Agostino

Keyword(s):

Experimental Data ◽

Spectral Analysis ◽

Main Flow ◽

Operating Conditions ◽

Flow Instabilities ◽

Mean Flow ◽

Flow Oscillations ◽

Rotating Frames ◽

The Mean ◽

High Head

A high-head three-bladed inducer has been equipped with pressure taps on the hub along the blade channels with the aim of more closely investigating the dynamics of cavitation-induced instabilities developing in the impeller flow. Spectral analysis of the pressure signals obtained from two sets of transducers mounted both in the stationary and rotating frames has allowed to characterize the nature, intensity, and interactions of the main flow instabilities detected in the experiments: subsynchronous rotating cavitation (RC), cavitation surge (CS), and a high-order axial surge oscillation. A dynamic model of the unsteady flow in the blade channels has been developed based on experimental data and on suitable descriptions of the mean flow and the oscillations of the cavitating volume. The model has been used for estimating at the inducer operating conditions of interest the intensity of the flow oscillations associated with the occurrence of the CS mode generated by RC in the inducer inlet.

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Investigation of the Noise Induced by Unstable Flow in a Centrifugal Pump

Energies ◽

10.3390/en13030589 ◽

2020 ◽

Vol 13 (3) ◽

pp. 589

Author(s):

Jiaxing Lu ◽

Xiaobing Liu ◽

Yongzhong Zeng ◽

Baoshan Zhu ◽

Bo Hu ◽

...

Keyword(s):

Centrifugal Pump ◽

Frequency Band ◽

Acoustic Pressure ◽

Low Frequency ◽

Internal Flow ◽

Rotating Stall ◽

Operating Conditions ◽

Flow Instabilities ◽

Unstable Flow ◽

Pump Inlet

In order to investigate the mechanism and the characteristics of the noise induced by unstable flow in a centrifugal pump, the internal flow characteristics in the pump were numerically researched, and the acoustic pressure fluctuations at the pump inlet and outlet were experimentally investigated. Obvious corresponding relationships between the flow instabilities, the cavitation and the noise were established. It was found that the rotating stall, the backflow, the hump, the occurrence of unstable flow and the cavitation in such a centrifugal pump were effectively detected through the noise, which could help to provide fundamental information on flow instabilities and guarantee safe and steady operating conditions for the system. The recirculation and prewhirl regions in the pump upstream pipe, which were caused by the backflow and the rotation of the impeller, presented the circumferential movement with a spiral shape, causing apparent broadband fluctuations at low frequency band of the acoustic pressure. The backflow and rotating stall could also result in broadband fluctuations of the pump outlet noise, which was distributed from 100 Hz to 150 Hz. Meanwhile, the broadband fluctuations of the pump outlet acoustic pressure distributed in the low frequency range, which was produced by the occurrence of cavitation, moved to the lower frequency band as the flow rate increased. The enhanced broadband fluctuations of the pump inlet and outlet noise distributed from 1 kHz to 6 kHz were caused by the coupling between the cavitation-induced noise and the system-produced noise. The broadband fluctuations of the pump inlet noise distributed between 6 kHz and 9 kHz were regarded as the typical frequency band of cavitation in the centrifugal pump.

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Thermal Cavitation Instability Analysis in Axial Inducers by Means of Casing and Hub-Mounted Pressure Sensors

Volume 3B: Fluid Applications and Systems ◽

10.1115/ajkfluids2019-5620 ◽

2019 ◽

Author(s):

Ruzbeh Hadavandi ◽

Angelo Pasini ◽

Dario Valentini ◽

Giovanni Pace ◽

Luca d’Agostino

Keyword(s):

Fluid Dynamic ◽

Pressure Sensors ◽

Operating Conditions ◽

Design Flow ◽

Flow Instabilities ◽

Test Facility ◽

Pressure Measurements ◽

Rotating Fluid ◽

Wide Range ◽

Cavitation Instability

Abstract The effects of thermal cavitation on the flow instabilities developing in a three-bladed, tapered-hub, variable-pitch space turbopump inducer are described by illustrating the results of similarity experiments in water carried out at Sitael in the Cavitating Pump Rotordynamic Test Facility (CPRTF). The operating conditions have been varied as required for investigating the onset and response of the fluid dynamic instabilities occurring in the test inducer over a wide range of cavitation numbers from noncavitating to heavy cavitation conditions, both at design and off-design flow. The CPRTF water temperature has been varied from room conditions to 80 °C ca. in order to induce thermal cavitation effects of increasing intensity capable of reproducing in the experiments the occurrence of typical cavitation phenomena in cryogenic space propellants. A wide variety and number of axial and rotating fluid dynamic instabilities have been detected, identified and characterized by spectral analysis of the pressure measurements obtained from statoric and rotoric transducers flush-mounted on the casing and the hub of the test inducer. The results indicate that thermal cavitation significantly affects the types of flow instabilities developing in cavitating inducers and the range of flow and suction conditions for their occurrence.

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