Observations of Oscillating Cavitation of an Inducer

1997 ◽  
Vol 119 (4) ◽  
pp. 775-781 ◽  
Author(s):  
Yoshinobu Tsujimoto ◽  
Yoshiki Yoshida ◽  
Yasukazu Maekawa ◽  
Satoshi Watanabe ◽  
Tomoyuki Hashimoto
Keyword(s):  
High Speed ◽  
Pressure Fluctuations ◽  
Linear Analysis ◽  
Cavitation Number ◽  
Flow Coefficient ◽  
The Other ◽  
General View ◽  
Pressure Measurements ◽  
High Speed Video ◽  
Wide Range

Oscillating cavitation of an inducer was observed through unsteady inlet pressure measurements and by use of high speed video picture, covering a wide range of flow coefficient and cavitation number. One of the purposes of the study is to identify a mode of rotating cavitation predicted by a linear analysis, and the other is to obtain a general view of oscillating cavitation. The number of rotating cavitation cells and their propagation velocity were carefully determined from the phase difference of pressure fluctuations at various circumferential locations. Various kinds of oscillating cavitation were observed: rotating cavitation rotating faster/slower than impeller rotation, cavitation in backflow vortices, and surge mode oscillations. Effects of inlet and outlet (effective) pipelength were also studied.

Effects of Alternate Leading Edge Cutback on Unsteady Cavitation in 4-Bladed Inducers

2001 ◽  
Vol 123 (4) ◽  
pp. 762-770 ◽  
Author(s):  
Yoshiki Yoshida ◽  
Yoshinobu Tsujimoto ◽  
Dai Kataoka ◽  
Hironori Horiguchi ◽  
Fabien Wahl
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Leading Edge ◽  
Cavitation Number ◽  
The Other ◽  
Low Flow ◽  
Pressure Measurements ◽  
High Speed Video ◽  
Cavitation Performance ◽  
Wide Range

A set of 4-bladed inducers with various amounts of cutback was tested with the aim of suppressing the rotating cavitation by applying alternate leading edge cutback. Unsteady cavitation patterns were observed by means of inlet pressure measurements and high-speed video pictures. It was found that the region with the alternate blade cavitation and asymmetric cavitation were enlarged with the increase of the amount of the cutback. As a result, the region with the rotating cavitation was diminished. At low flow rate, two types of alternate blade cavitation were found as predicted theoretically on 4-bladed inducer with smaller uneven blade length. One of them is with longer cavities on longer blades, and the other is with longer cavities on shorter blades. Switch was observed in these alternate blade cavitation patterns depending whether the cavitation number was increased or decreased. For an inducer with larger amount of cutback, the rotating cavitation and cavitation surge were almost suppressed as expected for a wide range of flow rate and cavitation number, although the cavitation performance was deteriorated. However, we should note that an asymmetric cavitation pattern occurs more easily in inducers with alternate leading edge cutback, and that the unevenness due to the cutback causes uneven blade stress.

Numerical and Experimental Analysis of Flow Phenomena in a Centrifugal Pump Operating Under Low Flow Rates

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Yanxia Fu ◽  
Jianping Yuan ◽  
Shouqi Yuan ◽  
Giovanni Pace ◽  
Luca d'Agostino ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
High Speed ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Internal Flow ◽  
Flow Coefficient ◽  
Flow Instabilities ◽  
Low Flow ◽  
Flow Rates ◽  
Wide Range

The characteristics of flow instabilities as well as the cavitation phenomenon in a centrifugal pump operating at low flow rates were studied by experimental and numerical means, respectively. Specially, a three-dimensional (3D) numerical model of cavitation was applied to simulate the internal flow through the pump and suitably long portions of the inlet and outlet ducts. As expected, cavitation proved to occur over a wide range of low flow rates, producing a characteristic creeping shape of the head-drop curve and developing in the form of nonaxisymmetric cavities. As expected, the occurrence of these cavities, attached to the blade suction sides, was found to depend on the pump's flow coefficient and cavitation number. The experiments focused on the flow visualization of the internal flow patterns by means of high-speed digital movies and in the analysis of the inlet pressure pulsations near the impeller eye by means of fast response pressure transducers. The experimental results showed that the unsteady behavior of the internal flow in the centrifugal pump operating at low flow rates has the characteristics of a peculiar low-frequency oscillation. Meanwhile, under certain conditions, the low-frequency pressure fluctuations were closely correlated to the flow instabilities induced by the occurrence of cavitation phenomena at low flow rates. Finally, the hydraulic performances of the centrifugal pump predicted by numerical simulations were in good agreement with the corresponding experimental data.

scholarly journals Reflected Near-field Blast Pressure Measurements Using High Speed Video

2020 ◽  
Vol 60 (7) ◽  
pp. 875-888 ◽  
Author(s):  
S. E. Rigby ◽  
R. Knighton ◽  
S. D. Clarke ◽  
A. Tyas
Keyword(s):  
High Speed ◽  
Near Field ◽  
Pressure Measurements ◽  
Blast Pressure ◽  
High Speed Video

A Study of Cavitation Flow in a Centrifugal Pump at Part Load Conditions Based on Numerical Analysis

2012 ◽  
Author(s):  
Jianping Yuan ◽  
Yanxia Fu ◽  
Shouqi Yuan
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Suction Side ◽  
Cavitation Number ◽  
Flow Coefficient ◽  
Inlet Pipe ◽  
Part Load ◽  
Cavitation Inception ◽  
Wide Range ◽  
Load Conditions

In order to predict cavitation performance of the centrifugal pump, including cavitating structures and vapour volume at the blade suction side, as well as its relationship with the backflow in the impeller eye, a 3D numerical simulation of detailed steady and unsteady cavitating flow was applied to reproduce its inner flow fields at part load conditions (0.5Qd and 0.4Qd). The comparisons of cavitation characteristics of the current centrifugal pump at an on-design point (1.0Qd) and a high flow rate (1.2Qd) were achieved as well. In addition, Frequency analysis of pressure fluctuations at the blade passages and the inlet pipe were also obtained during cavitation for a flow coefficient of 50%. The results further show that successive blade cavitation patterns and the creeping cavitation number dropping appear for a wide range of flow rates when the inlet total pressure decreases from cavitation inception to the breakdown of the centrifugal pump, as is quite different from that when cavitation occurs at 1.0Qd or 1.2Qd. Unbalanced attached cavities on the blade suction side were also observed at 0.5Qd. Meanwhile, the unsteady behaviour of cavities attached to the blade suction side and cavitation number dropping depend on the flow rate and cavitation number. Another significant characteristic of the phenomenon is that all the domain frequencies in blade passages and inlet pipe at part load conditions are 0.048Hz∼48.285Hz, which is typically lower than the shaft rotational frequency of the model centrifugal pump.

scholarly journals Assessment of the accuracy of different systems for measuring football velocity and spin rate in the field

2019 ◽  
Vol 233 (2) ◽  
pp. 324-330 ◽  
Author(s):  
Katrine Okholm Kryger ◽  
Séan Mitchell ◽  
Steph Forrester
Keyword(s):  
Systematic Error ◽  
Confidence Intervals ◽  
High Speed ◽  
Football Player ◽  
Random Errors ◽  
High Speed Video ◽  
Field Assessment ◽  
Wide Range ◽  
Ball Velocity ◽  
Level Of Agreement

The aim of this study was to measure the level of agreement of four portable football velocity and spin rate measurement systems (Jugs speed radar gun, 2-D high-speed video, TrackMan and adidas miCoach football) against a Vicon motion analysis system. One skilled male university football player performed 70 shots covering a wide range of ball velocities (12–30 m s−1) and spin rates (94–743 r/min). A Bland–Altman analysis was used to assess the level of agreement. For ball velocity, the 2-D high-speed video had the smallest systematic error, followed by the radar gun, TrackMan and miCoach football at 0.2, 0.4, 0.5 and 4.8 m s−1, respectively. A similar ranking was also observed for the random errors (95% confidence intervals: ±0.4, ±1.5, ±1.9 and ±6.0 m s−1). The first three systems all tracked ball velocity in >90% of shots, while the miCoach football tracked slightly fewer shots (79%). For spin rate, the miCoach football had a much smaller systematic error (4 vs 38 r/min) and random error (95% confidence intervals: ±24 vs ±355 r/min) compared to TrackMan. The miCoach also successfully tracked spin rate in more shots than the TrackMan (79% vs 44%). These results indicate that 2-D high-speed video would be the preferred option for the field assessment of ball velocity; however, radar gun and TrackMan may also be appropriate. A minimum of 10 frames of 2-D high-speed video, captured close to the ball starting position, was demonstrated to be sufficient in providing a reliable measure of ball velocity. The miCoach ball is the preferred option for field assessment of ball spin rate.

The Case of the Singing Vortex

1997 ◽  
Vol 119 (2) ◽  
pp. 271-276 ◽  
Author(s):  
B. Maines ◽  
R. E. A. Arndt
Keyword(s):  
Water Quality ◽  
Cross Section ◽  
High Speed ◽  
Angle Of Attack ◽  
High Amplitude ◽  
Cavitation Number ◽  
Tip Vortex ◽  
Tip Vortex Cavitation ◽  
High Speed Video ◽  
Noise Data

A relatively high amplitude, discrete tone is radiated from fully developed tip vortex cavitation under certain conditions. The phenomenon of the “singing vortex” was first reported by Higuchi et al. (1989). This study more closely examines the singing phenomenon by varying the hydrofoil cross-section, scale, angle of attack, water quality, and cavitation number in two different facilities. Noise data were collected for each condition with visual documentation using both still photography and high speed video in an effort to explain the mechanism of vortex singing. The theory of Kelvin (1880) provides a framework for correlating all the data obtained.

scholarly journals An Instrumented High-Speed Rotor With Embedded Telemetry for the Continuous Spatial Pressure Profile Measurement in Gas Lubricated Bearings: A Proof of Concept

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Karim Shalash ◽  
Jürg Schiffmann
Keyword(s):  
System Identification ◽  
High Speed ◽  
Pressure Field ◽  
Pressure Profile ◽  
Journal Bearings ◽  
Profile Measurement ◽  
Pressure Measurements ◽  
Wide Range ◽  
Static Conditions

Abstract Pressure is the constitutive quantity governing the flow field in gas lubricated bearings. Knowledge of the pressure is of principal importance in the fundamental understanding of such bearings as well as for the validation of their models. Pressure measurements can be done from the bearing side using pressure taps, yet, several details will not be captured. In order to acquire a continuous scan of the pressure field inside the bearing, it is necessary to measure from the rotor side. This paper presents an instrumented measurement high-speed rotor with embedded pressure probes and a wireless telemetry that is capable of the continuous pressure field measurement within the gas film of journal bearings. The rotor was tested on externally pressurized gas journal bearings (EPGJBs) (D = 40 mm and L/D = 1), and pressure profile measurements were acquired up to 37.5 krpm (DN 1.5 M). Measurements at discrete points using pressure taps inside the test bearing were also performed for comparison. The measurements from both sides (bearing and rotor) were in good agreement at quasi-static conditions. At higher operational speeds, it was necessary to perform an in situ system identification and calibration for the embedded pressure probes using the bearing side measurements as a reference. The in situ system identification technique was successful to reconstruct the attenuated pressure signals for a wide range of supply pressures (amplitudes) and rotor speeds (excitation frequencies). The instrumented rotor was proven qualified to perform time-resolved pressure measurements within the gas film of journal bearings up to 37.5 krpm.

scholarly journals Flow instability effects related to purge through a gas turbine chute seal

2021 ◽  
Vol 5 ◽  
pp. 111-125
Author(s):  
Arijit Roy ◽  
Jens Fridh ◽  
James Scobie ◽  
Carl Sangan ◽  
Gary Lock
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Flow Instability ◽  
Flow Coefficient ◽  
Flow Instabilities ◽  
Pressure Measurements ◽  
Flow Conditions ◽  
Seal Design ◽  
Purge Flow ◽  
Unsteady Pressure Measurements

This paper investigates flow instabilities inside the cavity formed between the stator and rotor disks of a high-speed turbine rig. The cavity rim seal is of chute seal design. The influence of flow coefficient on the sealing effectiveness at constant purge flow rate through the wheel-space is determined. The effectiveness at different radial positions over a range of purge flow conditions and flow coefficients is also studied. Unsteady pressure measurements have identified the frequency of instabilities that form within the rim seal, phenomena which have been observed in other studies. Frequencies of these disturbances, and their correlation in the circumferential direction have determined the strength and speed of rotation of the instabilities within the cavity. Large scale unsteady rotational structures have been identified, which show similarity to previous studies. These disturbances have been found to be weakly dependent on the purge flow and flow coefficients, although an increased purge reduced both the intensity and speed of rotation of the instabilities. Additionally, certain uncorrelated disturbances have been found to be inconsistent (discontinuous) with pitchwise variation.

Noise analysis of oil-lubricated journal bearings

2003 ◽  
Vol 217 (3) ◽  
pp. 365-371 ◽  
Author(s):  
B-H Rho ◽  
D-G Kim ◽  
K-W Kim
Keyword(s):  
High Speed ◽  
Sound Pressure ◽  
Noise Analysis ◽  
Pressure Fluctuations ◽  
Plane Waves ◽  
Linear Analysis ◽  
Journal Bearings ◽  
Acoustical Properties ◽  
Rotor Imbalance ◽  
Non Linear

The objective of the paper is to provide a procedure for calculating the noise of oil-lubricated journal bearings. In order to obtain acoustical properties of the bearing, a non-linear analysis including rotor imbalance is performed for a rotor-bearing system. Sound pressure levels of the bearing are obtained through frequency analysis of pressure fluctuations calculated from the non-linear analysis using a transmission theory of plane waves. Results show that the sound pressure level of the bearing increases with the rotational speed of the rotor, although the whirl amplitude of the rotor is decreased at high speed. The noise-estimating procedure presented in the paper could be an aid in the evaluation and understanding of acoustical properties of oil-lubricated journal bearings.

Mechanism and Control of Cloud Cavitation

1997 ◽  
Vol 119 (4) ◽  
pp. 788-794 ◽  
Author(s):  
Y. Kawanami ◽  
H. Kato ◽  
H. Yamaguchi ◽  
M. Tanimura ◽  
Y. Tagaya
Keyword(s):  
High Speed ◽  
Leading Edge ◽  
Generation Mechanism ◽  
Pressure Measurements ◽  
Foil Surface ◽  
Cavitation Noise ◽  
Cloud Cavitation ◽  
High Speed Video ◽  
And Control ◽  
Small Obstacle

Generation mechanism of cloud cavitation on a hydrofoil section was investigated in a sequence of experiments through observation of cloud cavitation by high-speed video and high-speed photo as well as pressure measurements by pressure pick-ups and a hydrophone. The mechanism was also investigated by controlling cloud cavitation with an obstacle fitted on the foil surface. From the results of these experiments, it was found that the collapse of a sheet cavity is triggered by a re-entrant jet rushing from the trailing edge to the leading edge of the sheet cavity, and consequently, the sheet cavity is shed in the vicinity of its leading edge and thrown downstream as a cluster of bubbles called cloud cavity. In other words, the re-entrant jet gives rise to cloud cavitation. Moreover, cloud cavitation could be controlled effectively by a small obstacle placed on the foil. It resulted in reduction of foil drag and cavitation noise.

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