scholarly journals Experimental Study on the Relationship Between Cavitation and Lift Fluctuations of S-Shaped Hydrofoil

2021 ◽  
Vol 9 ◽  
Author(s):  
Haiyu Liu ◽  
Pengcheng Lin ◽  
Fangping Tang ◽  
Ye Chen ◽  
Wenpeng Zhang ◽  
...  
Keyword(s):  
High Speed ◽  
Developmental Process ◽  
Angle Of Attack ◽  
Cavitation Number ◽  
High Speed Photography ◽  
Cloud Cavitation ◽  
Cavitation Inception ◽  
Sheet Cavitation ◽  
Hydraulic Machinery ◽  
Stall Angle

In order to study the energy loss of bi-directional hydraulic machinery under cavitation conditions, this paper uses high-speed photography combined with six-axis force and torque sensors to collect cavitating flow images and lift signals of S-shaped hydrofoils simultaneously in a cavitation tunnel. The experimental results show that the stall angle of attack of the S-shaped hydrofoil is at ±12° and that the lift characteristics are almost symmetrical about +1°. Choosing α = +6° and α = −4° with almost equal average lift for comparison, it was found that both cavitation inception and cloud cavitation inception were earlier at α = −4° than at α = +6°, and that the cavitation length at α = −4° grew significantly faster than at α = +6°. When α = +6°, the cavity around the S-shaped hydrofoil undergoes a typical cavitation stage as the cavitation number decreases: from incipient cavitation to sheet cavitation to cloud cavitation. However, when α = −4°, as the cavitation number decreases, the cavitation phase goes through a developmental process from incipient cavitation to sheet cavitation to cloud cavitation to sheet cavitation to cloud cavitation, mainly because the shape of the S-shaped hydrofoil at the negative angle of attack affects the flow of the cavity tails, which is not sufficient to form re-entrant jets that cuts off the sheet cavitation. The formation mechanism of cloud cavitation at the two different angles of attack (α = +6°、−4°) is the same, both being due to the movement of the re-entrant jet leading to the unstable shedding of sheet cavity. The fast Fourier analysis reveals that the fluctuations of the lift signals under cloud cavitation are significantly higher than those under non-cavitation, and the main frequencies of the lift signals under cloud cavitation were all twice the frequency of the cloud cavitation shedding.

Inception and Dynamics of Traveling-Bubble-Type Cavitation in a Venturi

2003 ◽  
Author(s):  
Keiichi Sato ◽  
Kouji Hachino ◽  
Yasuhiro Saito
Keyword(s):  
Tensile Strength ◽  
Count Rate ◽  
High Speed ◽  
Cavitation Number ◽  
Venturi Tube ◽  
Local Pressure ◽  
Cavitation Inception ◽  
Sheet Cavitation ◽  
High Speed Video ◽  
Bubble Cavitation

The inception of cavitation is basically caused by a bubble nucleus which flows into the low pressure region in the liquid flow. Therefore the phenomenon is dependent on the tensile strength or the nuclei concentration of tested water. The cavitation susceptibility of water which controls the cavitation inception point has been made clear though various methods were proposed to measure the nuclei concentration. Cavitation susceptibility meter using a small venturi tube is also one of the methods to measure the nuclei concentration. It is pointed out that this method can be directly related to active nuclei for cavitation inception and gives a useful and simple device to estimate the tensile strength of water. In the present paper, to establish a measurement method of cavitation susceptibility using a venturi tube, the following points are investigated, such as; the relation between the occurrence, count rate of cavitation bubbles and cavitation number, the measurement of positions and local pressure of bubble occurrence and the high-speed video observation of bubble aspects from inception to collapse. As the result, the main points obtained are as follows. A traveling-bubble cavitation appears dominantly in a nozzle-type venturi tube with little possibility of flow separation. Cavitation aspects and the bubble occurrence count rate change with cavitation number and water quality (dissolved gas content). Unstable sheet cavitation can be also observed near the venturi diffuser and at relatively low cavitation number. The various behaviors of traveling bubble cavitation in a venturi are observed from inception to collapse using a high-speed video camera system.

Visual experiment and numerical simulation of cavitation instability in a high-speed inducer

2019 ◽  
Vol 234 (4) ◽  
pp. 470-480 ◽  
Author(s):  
Baoling Cui ◽  
Jie Chen
Keyword(s):  
Numerical Simulation ◽  
High Speed ◽  
Volume Fraction ◽  
Cavitation Number ◽  
Cavitating Flow ◽  
Design Flow ◽  
Local Pressure ◽  
Cloud Cavitation ◽  
Sheet Cavitation ◽  
Cavitation Instability

Cavitation instabilities in a high-speed inducer at a design flow rate were investigated for different cavitation numbers in numerical simulations and visual experiments. On the basis of a shear stress transport k–ω turbulence model and Zwart–Gerber–Belamri cavitation model, the transient cavitating flow in a high-speed centrifugal pump with an inducer is numerically simulated using ANSYS-CFX 15.0 software. Visual experiments were carried out to capture the evolution of cavitating flow in the inducer by using a high-speed camera. The performance and cavitation characteristic curves from numerical simulation agree with those from experiment. With a decreasing cavitation number, the cavitation development in the high-speed inducer goes through incipient cavitation, developing cavitation, critical cavitation, and deteriorated cavitation and presents vortex cavitation, sheet cavitation, cloud cavitation, backflow cavitation, and a cavitation surge. The region having a high vapor volume fraction basically coincides with the region of low local pressure at the same cavitation number. The position of largish blade loading on the inducer changes with the development of cavitation. A cavitation surge as one type of cavitation instability appears in the inducer at lower cavitation numbers. The drop or rise of the head coefficient is affected by an increasing or decreasing cavitation area in the cycle of a cavitation surge.

Wing Sections for Hydrofoils—Part 3: Experimental Verifications

1985 ◽  
Vol 29 (01) ◽  
pp. 39-50
Author(s):  
Young T. Shen
Keyword(s):  
High Speed ◽  
Design Theory ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Cavitation Inception ◽  
Sheet Cavitation ◽  
Ship Wakes ◽  
Lifting Surfaces ◽  
Propeller Blades ◽  
Force Data

Lifting surfaces such as hydrofoil wings or propeller blades will encounter periodic variations in angle of attack when operated in waves or in nonuniform ship wakes. Undesirable leading-edge sheet cavitation is a common occurrence on hydrofoils and marine propellers. To effectively avoid or delay leading-edge sheet cavitation it is necessary to develop a lifting surface able to tolerate large variations in angle of attack without cavitation. Based on a profile design theory, a series of hydrofoil sections having large cavitation-free bucket widths was developed and presented in previous papers, Part 1 and Part 2. The present paper provides the experimental verification. Profile YS-920 was selected as representative of the series and was tested in a high-speed water tunnel. The measured cavitation inception characteristics and force data of YS-920 were compared with the theoretical predictions. Additionally, they were compared with the measured cavitation and force data of the widely used NACA 66 (MOD) and NACA 16–309 wing sections to show the advantages of using a newly developed hydrofoil section to delay or avoid cavitation.

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.

Investigation of Unsteady Sheet Cavitation and Cloud Cavitation Mechanisms

1999 ◽  
Vol 121 (2) ◽  
pp. 289-296 ◽  
Author(s):  
T. M. Pham ◽  
F. Larrarte ◽  
D. H. Fruman
Keyword(s):  
High Speed ◽  
Leading Edge ◽  
Pressure Measurements ◽  
Foil Surface ◽  
Mean Velocity ◽  
Cloud Cavitation ◽  
Fluctuating Pressure ◽  
Sheet Cavitation ◽  
Cavitation Instability ◽  
Unsteady Characteristics

Sheet cavitation on a foil section and, in particular, its unsteady characteristics leading to cloud cavitation, were experimentally investigated using high-speed visualizations and fluctuating pressure measurements. Two sources of sheet cavitation instability were evidenced, the re-entrant jet and small interfacial waves. The dynamics of the re-entrant jet was studied using surface electrical probes. Its mean velocity at different distances from the leading edge was determined and its role in promoting the unsteadiness of the sheet cavitation and generating large cloud shedding was demonstrated. The effect of gravity on the dynamics of the re-entrant jet and the development of interfacial perturbations were examined and interpreted. Finally, control of cloud cavitation using various means, such as positioning a tiny obstacle (barrier) on the foil surface or performing air injection through a slit situated in the vicinity of the leading edge, was investigated. It was shown that these were very effective methods for decreasing the amplitude of the instabilities and even eliminating them.

Numerical Prediction of Cavitating Flow on a Two-Dimensional Symmetrical Hydrofoil and Comparison to Experiments

2006 ◽  
Vol 129 (3) ◽  
pp. 279-292 ◽  
Author(s):  
Olivier Coutier-Delgosha ◽  
François Deniset ◽  
Jacques André Astolfi ◽  
Jean-Baptiste Leroux
Keyword(s):  
Cavitating Flow ◽  
Physical Models ◽  
Experimental Investigations ◽  
Condensation Process ◽  
Two Dimensional ◽  
Homogeneous Fluid ◽  
Two Phase ◽  
Cloud Cavitation ◽  
Cavitation Inception ◽  
Sheet Cavitation

This paper presents comparisons between two-dimensional (2D) CFD simulations and experimental investigations of the cavitating flow around a symmetrical 2D hydrofoil. This configuration was proposed as a test case in the “Workshop on physical models and CFD tools for computation of cavitating flows” at the 5th International Symposium on cavitation, which was held in Osaka in November 2003. The calculations were carried out in the ENSTA laboratory (Palaiseau, France), and the experimental visualizations and measurements were performed in the IRENav cavitation tunnel (Brest, France). The calculations are based on a single-fluid approach of the cavitating flow: the liquid/vapor mixture is treated as a homogeneous fluid whose density is controlled by a barotropic state law. Results presented in the paper focus on cavitation inception, the shape and the general behavior of the sheet cavity, lift and drag forces without and with cavitation, wall pressure signals around the foil, and the frequency of the oscillations in the case of unsteady sheet cavitation. The ability of the numerical model to predict successively the noncavitating flow field, nearly steady sheet cavitation, unsteady cloud cavitation, and finally nearly supercavitating flow is discussed. It is shown that the unsteady features of the flow are correctly predicted by the model, while some subtle arrangements of the two-phase flow during the condensation process are not reproduced. A comparison between the peer numerical results obtained by several authors in the same flow configuration is also performed. Not only the cavitation model and the turbulence model, but also the numerical treatment of the equations, are found to have a strong influence on the results.

scholarly journals Investigation of Cavitation Noise in Cavitating Flows around an NACA0015 Hydrofoil

2019 ◽  
Vol 9 (18) ◽  
pp. 3736
Author(s):  
An Yu ◽  
Xincheng Wang ◽  
Zhipeng Zou ◽  
Qinghong Tang ◽  
Huixiang Chen ◽  
...  
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
Leading Edge ◽  
Acoustic Power ◽  
Cavitation Number ◽  
Acoustic Analogy ◽  
Cavitation Noise ◽  
Cloud Cavitation ◽  
Sheet Cavitation ◽  
Power Spectral

To provide theoretical basis for cavitation noise control, the cavitation evolution around a hydrofoil and its induced noise were numerically investigated. A modified turbulence model and Zwart cavitation model were employed to calculate the flow field and predict the cavitation phenomenon accurately. Then, the acoustic analogy method based on the Ffowcs Williams-Hawking (FW-H) equation was applied to analyze the cavitation-induced noise. Seven cavitation numbers were selected for analysis. Acoustic power spectral density (PSD) and acoustic pressure were investigated to establish the relationship between cavitation number and their acoustic characteristics. It was indicated that as cavitation number decreases, cavitation cycle length gets shorter and the magnitude of acoustic power spectral density increases dramatically. One peak value of acoustic power spectral density induced by the extending and retracting of leading-edge cavitation can be obtained under sheet cavitation conditions, while under cloud cavitation, two peak values of acoustic power spectral density can be obtained and are induced by superposition from leading-edge cavitation and trailing vortex.

scholarly journals Cavitation onset caused by acceleration

2017 ◽  
Vol 114 (32) ◽  
pp. 8470-8474 ◽  
Author(s):  
Zhao Pan ◽  
Akihito Kiyama ◽  
Yoshiyuki Tagawa ◽  
David J. Daily ◽  
Scott L. Thomson ◽  
...  
Keyword(s):  
High Speed ◽  
Equation Of Motion ◽  
Cavitation Number ◽  
High Speed Photography ◽  
Impulsive Force ◽  
Research Groups ◽  
Independent Research ◽  
Series Of Experiments ◽  
Intuitive Interpretation ◽  
Dimensionless Term

Striking the top of a liquid-filled bottle can shatter the bottom. An intuitive interpretation of this event might label an impulsive force as the culprit in this fracturing phenomenon. However, high-speed photography reveals the formation and collapse of tiny bubbles near the bottom before fracture. This observation indicates that the damaging phenomenon of cavitation is at fault. Cavitation is well known for causing damage in various applications including pipes and ship propellers, making accurate prediction of cavitation onset vital in several industries. However, the conventional cavitation number as a function of velocity incorrectly predicts the cavitation onset caused by acceleration. This unexplained discrepancy leads to the derivation of an alternative dimensionless term from the equation of motion, predicting cavitation as a function of acceleration and fluid depth rather than velocity. Two independent research groups in different countries have tested this theory; separate series of experiments confirm that an alternative cavitation number, presented in this paper, defines the universal criteria for the onset of acceleration-induced cavitation.

High‐speed photography and acoustic emission synchronized observation of ultrasound induced acoustic cloud cavitation

2004 ◽  
Vol 116 (4) ◽  
pp. 2508-2508 ◽  
Author(s):  
Teiichiro Ikeda ◽  
Masataka Tosaki ◽  
Shin Yoshizawa ◽  
Yoichiro Matsumoto
Keyword(s):  
Acoustic Emission ◽  
High Speed ◽  
High Speed Photography ◽  
Cloud Cavitation

Scale Effects on the Cavitation Development in Fluid Machinery

2011 ◽  
Author(s):  
Weiping Yu ◽  
Xianwu Luo ◽  
Yao Zhang ◽  
Bin Ji ◽  
Hongyuan Xu
Keyword(s):  
Turbulence Model ◽  
High Speed ◽  
Scale Effects ◽  
Design Procedure ◽  
Leading Edge ◽  
Characteristic Size ◽  
Cavitation Model ◽  
Fluid Machinery ◽  
Cloud Cavitation ◽  
Sheet Cavitation

The prediction of cavitation in a design procedure is very important for fluid machinery. However, the behaviors of cavitation development in the flow passage are believed to be much different due to scale effects, when the characteristic size varies greatly for fluid machines such as pumps, turbines and propellers. In order to understand the differences in cavitation development, the evolution of cavity pattern in two hydro foils were recorded by high-speed video apparatus. Both foils have the same section profile, and their chord lengths are 70mm and 14mm respectively. For comparison, the cavitating flows around two foils were numerically simulated using a cavitation model based on Rayleigh-Plesset equation and SST k-ω turbulence model. The experiments depicted that for both hydro foils, there was attached sheet cavitation near the leading edge, which separated from the rear part of the cavity and collapsed near the foil trailing edge. There was clear cloud cavitation in the case of the mini foil. The results also indicated that the numerical simulation captured the cavitation evolution for the ordinary foil quite well compared with the experiments, but could hardly predict the cloud cavitation for the mini foil. Thus, it is believed that both the cavitation model and the turbulence model should be carefully treated for the scale effect on cavitation development in fluid machinery.

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