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The influence of surface roughness on cloud cavitation flow around hydrofoils

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Acta Mechanica Sinica 2018年第1期34卷 10-21页

作者： Jiafeng Hao Mindi Zhang Xu Huang School of Mechanical Engineering Beijing Institute of Technology

The aim of this study is to investigate experimentally the effect of surface roughness on cloud cavitation around Clark-Y hydrofoils. High-speed video and particle image velocimetry(PIV) were used to obtain cavitation patterns images(Prog. Aerosp. Sci. 37: 551–581, 2001), as well as velocity and vorticity fields. Results are presented for cloud cavitating conditions around a Clark-Y hydrofoil fixed at angle of attack of α = 8? for moderate Reynolds number of Re = 5.6 × 10~5. The results show that roughness had a great influence on the pattern, velocity and vorticity distribution of cloud cavitation. For cavitating flow around a smooth hydrofoil(A) and a rough hydrofoil(B), cloud cavitation occurred in the form of finger-like cavities and attached subulate cavities, respectively. The period of cloud cavitation around hydrofoil A was shorter than for hydrofoil *** roughness had a great influence on the process of cloud cavitation. The development of cloud cavitation around hydrofoil A consisted of two stages:(1) Attached cavities developed along the surface to the trailing edge;(2) A reentrant jet developed, resulting in shedding and collapse of cluster bubbles or vortex structure. Meanwhile, its development for hydrofoil B included three stages:(1) Attached cavities developed along the surface to the trailing edge, with accumulation and rotation of bubbles at the trailing edge of the hydrofoil affecting the flow field;(2) Development of a reentrant jet resulted in the first shedding of cavities. Interaction and movement of flows from the pressure side and suction side brought liquid water from the pressure side to the suction side of the hydrofoil, finally forming a reentrant jet. The jet kept moving along the surface to the leading edge of the hydrofoil, resulting in large-scale shedding of cloud bubbles. Several vortices appeared and dissipated during the process;(3) Cavities grew and shed again.

关键词： Surface roughness Experiments cloud cavitation Hydrofoils

Investigation on the dynamic behavior of cloud cavitation around a flexible hydrofoil

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Journal of Hydrodynamics 2023年第4期35卷 712-723页

作者： Yun-qing Liu Wei Zhao Zhi Pan Zhi-pu Guo Rui Yuan Qin Wu School of Mechanical Engineering Beijing Institute of TechnologyBeijing100081China Wuhan Second Ship Design and Research Institute Wuhan430205China

The objective of this paper is to investigate the dynamic behavior of cloud cavitating flow around a flexible hydrofoil with experimental and numerical *** tightly coupled fluid-structure interaction(FSI)modeling is applied and validated with the experimental *** Q-criterion andω-criterion are applied to illustrate the interaction between the vortex structures and *** flexibility is seen to result in nose-up twist deformation,causing a reduction of the shedding frequency from an increase in the attached cavity *** to the flexibility,the fluctuation of load coefficients of the flexible hydrofoil is larger than that of the rigid ***,the re-entrant jet propagation speed of the flexible hydrofoil is greater than that of the rigid *** shed cloud cavity is observed to be uniform along the flexible hydrofoil span under the combined influence of the strong vibration and the gap flow.

关键词： cloud cavitation fluid-structure interaction(FSI) vortex structures flexible hydrofoil

Periodical shedding of cloud cavitation from a single hydrofoil in high-speed cryogenic channel flow

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Journal of Thermal Science 2009年第1期18卷 58-64页

作者： Yutaka ITO Koichi SETO Takao NAGASAKI Tokyo Institute of Technology

In order to explain criteria for periodical shedding of the cloud cavitation, flow patterns of cavitation around a piano-convex hydrofoil were observed using a cryogenic cavitation tunnel of a blowdown type. Two hydrofoils of similarity of 20 and 60 mm in chord length with two test sections of 20 and 60 mm in width were prepared. Working fluids were water at ambient temperature, hot water and liquid nitrogen. The parameter range was varied between 0.3 and 1.4 for cavitation number, 9 and 17 m/sec for inlet flow velocity, and -8° and 8° for the flow incidence angle, respectively. At incidence angle 8°, that is, the convex surface being suction surface, periodical shedding of the whole cloud cavitation was observed on the convex surface under the specific condition with cavitation number and inlet flow velocity, respectively, 0.5, 9 m/sec for liquid nitrogen at 192℃ and 1.4, 11 m/sec for water at 88℃, whereas under the supercavitation condition, it was not observable. Periodical shedding of cloud cavitation occurs only in the case that there are both the adverse pressure gradient and the slow flow region on the hydrofoil.

关键词： cloud cavitation cryogen visualization hydrofoil

Numerical analysis of the unsteady behavior of cloud cavitation around a hydrofoil based on an improved filter-based model

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Journal of Hydrodynamics 2015年第5期27卷 795-808页

作者：张德胜王海宇施卫东张光建 Van ESCH B.P.M.(Bart) Research Center of Fluid Machinery Engineering and Technology Jiangsu University Department of Mechanical Engineering Eindhoven University of Technology

The unsteady cavitation evolution around the Clark-Y hydrofoil is investigated in this paper, by using an improved filter-base model（FBM） with the density correction method（DCM）. To improve the prediction accuracy, the filter scale is adjusted based on the grid size. The numerical results show that a small filter scale is crucial for the unsteady simulations of the cavity shedding flow. The hybrid method that combines the FBM and the DCM could help to limit the overprediction of the turbulent viscosity in the cavitation region on the wall of the hydrofoil and in the wake. The large value of the maximum density ratio ρ1 /ρv, clip promotes the mass transfer rate between the liquid phase and the vapor phase, which results in a large sheet cavity length and the vapor fraction rise inside the cavity. The cavity patterns predicted by the improved method are verified by the experimental visualizations. The time-average lift, the drag coefficient and the primary oscillating frequency St for the cavitation number σ= 0.8, the angle of attack, α= 8°, at a Reynolds number Re= 7×10^5 are 0.735, 0.115 and 0.183, respectively, and the predicted errors are 3.29%, 3.36% and 8.93%. The typical three stages in one revolution are well-captured, including the initiation of the sheet/attached cavity, the growth toward the trailing edge（TE） with the development of the re-entrant jet flow, and the large scale cloud cavity shedding. It is observed that the cloud cavity shedding flow induces the vortex pairs of the TE vortices in the wake and the shedding vortices. The positive vorticity vortex of the re-entrant jet and the TE vortices interacts and merges with the negative vorticity vortex of the leading edge（LE） cavity to produce the shedding flow.

关键词： filter-based model(FBM) density correction method cloud cavitation hydrofoil unsteady behavior

Large eddy simulation of cloud cavitation and wake vortex cavitation around a trailing-truncated hydrofoil

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Journal of Hydrodynamics 2022年第5期34卷 893-903页

作者： Ting-yun Yin Giorgio Pavesi Ji Pei Shou-qi Yuan Xing-cheng Gan National Research Center of Pumps Jiangsu UniversityZhenjiang212013China Department of Industrial Engineering University of PaduaPaduaItaly Turbomachinery and Energy Systems Group University of PaduaPaduaItaly

The cavitation has received considerable attention for decades because of its negative influence on the performance and the safety of the hydraulic *** this study,a large eddy simulation is carried out to numerically investigate the unsteady cavitating flow around a trailing-truncated NACA 0009 hydrofoil for determining the underlying physical *** types of cavitation morphologies are identified:The large-scale bubble cluster and the von Kármán vortex cavity,named as the cloud cavitation and the wake vortex cavitation,*** is shown that the velocity profiles obtained over the hydrofoil suction surface are in good agreement with the experimental data,indicating the accuracy of the current *** dynamic evolution of the sheet/cloud cavity is also well reproduced,covering the sheet cavity breakup,the sheet/cloud transformation,and the collapse of the cloudy bubble *** wake-vortex cavitation is caused by the blunt geometry at the hydrofoil trailing edge,where pairs of vortex cavities are *** the cloud and vortex cavities significantly affect the lift oscillation,which makes it difficult to decompose the *** fundamental shedding mechanisms of the wake vortex cavitation are discussed based on the finite-time Lyapunov exponent ***,the suction-side bubble grows and squeezes the giant pressure bubble away from the trailing *** the pressure bubble detaches,a new counterclockwise vortex or a new bubble appears at the pressure side,thus lifting the ridge towards the suction trailing edge and generating a strong vortex eye that pinches off the trailing portion of the suction-side bubble.

关键词： cloud cavitation wake vortex cavitation trailing-truncated hydrofoil large eddy simulation

On the numerical simulations of vortical cavitating flows around various hydrofoils

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Journal of Hydrodynamics 2017年第6期29卷 926-938页

作者：王本龙刘志辉李颢钰王雅赟刘登成张凌新彭晓星 Department of Engineering Mechanics Shanghai Jiao Tong UniversityShanghai 200240China MOE Key Laboratory-of Hydrodynamics Shanghai Jiao Tong UniversityShanghai 200240China Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration Shanghai 200240China National Key Laboratory on Ship Vibration and Noise China Ship Scientific Research CenterWuxi 214082China Department of Mechanics Zhejiang UniversityHangzhou 310027China

This paper reviews the numerical models of various cavitating flows around hydrofoils. Numerical models relating to cavitation flows, including mass transfer models and turbulence models, are summarized at first. Then numerical results and analysis of flow characteristics for the cavitating flows around twisted hydrofoils, truncated hydrofoil and tip leakage are discussed respectively. For mean flow fields, Reynolds averaged Navier-Stokes（RANS） simulation associated with a kind of nonlinear turbulence model is found to be an economic and robust numerical approach for different kinds of cavitating flows including cloud cavitation, tip cavitation and tip leakage cavitation. To predict the fluctuations of pressure and velocity, large eddy simulation（LES） and detached eddy simulation（DES） are two effective approaches. Finally, a few open questions are proposed for future research.

关键词： Mass transfer model turbulence model sheet cavitation cloud cavitation tip cavitation

Numerical investigations of the transient cavitating vortical flow structures over a flexible NACA66 hydrofoil

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Journal of Hydrodynamics 2020年第5期32卷 865-878页

作者： Ren-fang Huang Te-zhuan Du Yi-wei Wang Cheng-guang Huang Key Laboratory for Mechanics in Fluid Solid Coupling Systems Institute of MechanicsChinese Academy of SciencesBeijing 100190China

In this paper,the cavitating flow over a flexible NACA66 hydrofoil is studied numerically by a modified fluid-structure interaction strategy with particular emphasis on understanding the flow-induced vibration and the cavitating vortical flow *** modified coupling approaches include(1)the hydrodynamic solution obtained by the large eddy simulation(LES)together with a homogenous cavitation model,(2)the structural deformation solved with a cantilever beam equation,(3)fluid-structural interpolation and volume mesh motion based on the radial basis functions and greedy *** the flexible hydrofoil,the dominant flow-induced vibration frequency is twice of the cavity shedding *** cavity shedding frequency is same for the rigid and flexible hydrofoils,demonstrating that the structure vibration is not large enough to affect the cavitation *** predicted cavitating behaviors are strongly three-dimensional,that is,the cavity is(a)of a triangular shape near the hydrofoil tip,(b)of a rectangular shape near the hydrofoil root,and(c)with a strong unsteadiness in the middle of the span,including the attached cavity growth,oscillation and shrinkage,break-off and collapse *** unsteady hydroelastic response would strongly affect the cavitation shedding process with small-scale fragments at the cavity rear ***,three vortex identification methods(i.e.,the vorticity,the Q-criteria and the Ω method)are adopted to investigate the cavitating vortex structures around the flexible *** is indicated that the cavity variation trend is consistent with the vortex *** vortex structures are distributed near the foil trailing edge and in the cavitation region,especially at the cavity-liquid *** the transporting downstream the shedding cavities,the vortices gradually increase in the wake flows.

关键词： cloud cavitation flexible hydrofoil Ωmethod flow-induced vibration

Numerical simulation of multi-scale cavitating flow with special emphasis on the influence of vortex on micro-bubbles

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Journal of Hydrodynamics 2022年第6期34卷 1032-1043页

作者： Ming-zhe Zhou Zi-yang Wang Xiao-rui Bai Huai-yu Cheng Bin Ji State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan UniversityWuhan430072China

A multi-scale Euler-Lagrange method is applied in the current paper to investigate the characteristics of turbulent cloud cavitating flow around a Clark-Y hydrofoil,in which macroscopic cavitating structures are simulated by volume of fluid(VOF)approach,while micro-scale bubbles are modelled based on Rayleigh-Plesset equation and bubble motion *** numerical results are in reasonable agreement with the available experiments,and the transition between multi-scale structures is captured *** evolution of microscopic bubble behaviors is statistically *** one typical cycle,numbers and Sauter mean radius of the bubbles show a similar variation tendency which both sharply spike to their maxima after the breakup of the sheet cavity,and then decrease continuously to their minima before the next *** bubbles are mainly concentrated at the tail of the attached cavity,in front of the cloud cavity and in the region quite close to the hydrofoil suction ***,vortices are extracted to account for the micro-scale *** is found that intense vortices aggravate turbulence fluctuation,thus spalling cavity to generate massive micro ***,the vortices provide microscopic bubbles low pressure and detain them so that numerous bubbles are able to *** effects are remarkable after the breakup of attached sheet cavity,owing to the violent vortices *** the contrary,when sheet cavity develops,the flow field becomes comparatively stable since the strong vortices travel *** micro-scale bubbles are produced,and their volume is generally small.

关键词： cloud cavitation Euler-Lagrange method bubble-vortex interaction bubble dynamics

Numerical analysis of cavitation shedding flow around a three-dimensional hydrofoil using an improved filter-based model

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Journal of Hydrodynamics 2017年第2期29卷 361-375页

作者：张德胜施卫东张光建陈健 B.P.M.(Bart)van Esch Research Center of Fluid Machinery Engineering and Technology Jiangsu UniversityZhenjiang 212013China Department of Mechanical Engineering Eindhoven University of TechnologyEindhoven 5600MBTheNetherlands

The cavitation shedding flow around a 3-D Clark-Y hydrofoil is simulated by using an improved filter-based model （FBM） and a mass transfer cavitation model with the consideration of the maximum density ratio effect between the liquid and the vapor. The unsteady cloud cavity shedding features around the Clark-Y hydrofoil are accurately captured based on an improved FBM model and a suitable maximum density ratio. Numerical results show that the predicted cavitation patterns and evolutions compare well with the experimental visualizations, and the prediction errors of the time-averaged lift coefficient, drag coefficient and Strouhal number St for the cavitation number o- = 0.8, the angle of attack a= 8°at a Reynolds number Re = 7 x 10^5 are only 3.29%, 2.36% and 9.58%, respectively. It is observed that the cavitation shedding flow patterns are closely associated with the vortex structures identified by the Q- criterion method. The predicted cloud cavitation shedding flow shows clearly three typical stages：（1） Initiation of the attached sheet cavity, the growth toward the trailing edge. （2） The formation and development of the re-entrant jet flow. （3） Large scale cloud cavity sheds downstream. Numerical results also indicate that the non-uniform adverse pressure gradient is the main driving force of the re-entrant jet, which results in the U-shaped cavity and the 3-D bubbly structure during the cloud cavity shedding.

关键词： cloud cavitation shedding flow filter-based model turbulent viscosity Clark-Y hydrofoil