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1

Studies on velocity fields around the cavitation vortices generated by the model of a rotating blade

Suchecki W.

Polish Maritime Research

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2018

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nr 2

66--70

EN

The elimination of hazards caused by cavitation phenomena is an important issue to be considered in the design of process equipment including flow machinery. These hazards are: cavitation erosion, efficiency decrease as well as vibration and noise. One of the most intensive and dangerous forms of cavitation is vortex cavitation that accompanies the operation of hydraulic machines in which components comprised of rotating blades are applied. Velocity fields around cavitation vortices generated by the model of a propeller blade were experimentally studied in a cavitation tunnel. Flow images were recorded using a high-speed camera and processed using particle image velocimetry (PIV) complemented with computer-aided techniques that had been developed for the purpose of this research. These techniques included the removal of image distortions on the basis of a calibration mask, determination of instantaneous velocity distributions and removal of air-bubble traces from flow images. Experimental studies result examples were presented in the form of velocity fields determined in the longitudinal plane as well as in three transverse planes remote from the blade. Instabilities of the cavitating vortex stream and of the local liquid-flow velocity in its surrounding were detected. The effect of the angle of attack of propeller blade on the instability of the vortex stream and the effect of the presence of the cavitating vortex kernel on the local velocities of the surrounding liquid, were determined.

2

Numerical prediction of steady and unsteady tip vortex cavitation on hydrofoils

Flaszyński P., Szantyr J. A., Tesch K.

Polish Maritime Research

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2012

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nr 3

3-15

EN

The article presents the numerical method for prediction of tip vortex cavitation generated on hydrofoils. This method has been developed in the course of numerical and experimental research described in earlier publications. The objective of the research was to design the optimum discrete grid structure for this specific computational task and to select the best turbulence model for such an application The article includes a short description of the method and a computational example demonstrating its performance. In this example the results of numerical prediction of the cavitating tip vortex obtained from two commercial CFD codes are compared with experimental photographs taken in the cavitation tunnel in the corresponding flow conditions. Altogether nine different flow conditions are tested and analyzed, but only selected results are included. The accuracy of the numerical predictions is discussed and the reasons for minor existing discrepancies are identified. The unsteady tip vortex calculations are also presented, showing the fluctuations of the transverse velocity components predicted for three cross-sections of the cavitating vortex kernel.

3

An Experimental and Numerical Study of Tip Vortex Cavitation

Szantyr J. A., Flaszyński P., Suchecki W., Alabrudziński S.

Polish Maritime Research

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2011

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nr 4

14-22

EN

The article presents the results of the research project concerning tip vortex cavitation. This form of cavitation is very important in operation of many types of rotary hydraulic machines, including pumps, turbines and marine propellers. Tip vortex cavitation generates noise, vibration and erosion. It should be eliminated or significantly limited during the design of these types of machines. The objective of the project was to develop an accurate and reliable method for numerical prediction of tip vortex cavitation, which could serve this purpose. The project consisted of the laboratory experiments and numerical calculations. Inthe laboratory experiments tip vortex cavitation was generated behind a hydrofoil in the cavitation tunneland the velocity field around the cavitating kernel was measured using the Particle Image Velocimetry method. Measurements were conducted in three cross-sections of the cavitating tip vortex for a number ofangles of attack of the hydrofoil and for several values of the cavitation index. In the course of numerical calculations two commercial CFD codes were used: Fluent and CFX. Several available approaches to numerical modeling of tip vortex cavitation were applied and tested, attempting to reproduce the experimental conditions. The results of calculations were compared with the collected experimental data. The most promising computational approach was identified. Keywords: