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Effect of the vortical structures on the hydrodynamic performance of a pitching hydrofoil

Journal of Hydrodynamics 2024年第2期36卷 406-420页

作者： Rui Yuan Hui-yun Hao Qin Wu Yun-qing Liu Biao Huang School of Mechanical Engineering Beijing Institute of TechnologyBeijing100081China

The objective is to study the vortical structural behaviors of a transient pitching hydrofoil and their effects on the hydrodynamic performance. The pitching motion of the hydrofoil is set to pitch up with an almost constant rate from 5° to 15° and then back to 5°, with the Reynolds number 4.4×10^(5) and the frequency 2 Hz. The results show that the main coherent structures around the pitching hydrofoil include small-scale laminar separation bubble (LSB), large-scale second vortex (SV) and trailing edge vortex (TEV) which are all vortical. The relationship between the vortical structure and the lift is investigated with the finite-domain impulse theory. It indicates that the major part of the lift is contributed by the LSB, whereas the shedding and the formation of the SV and TEV cause the fluctuation of the lift. The proper orthogonal decomposition (POD) method is applied to capture the most energetic modes, revealing that the LSB mode occupies a large amount of energy in the flow field. The dynamic mode decomposition (DMD) method accurately extracts the dominant frequency and modal characteristics, with the first mode corresponding to the mean flow, the second mode corresponding to the LSB structure and the third and fourth modes corresponding to the vortex shedding.

关键词： Hydrodynamics vortical structures finite-domain impulse theory proper orthogonal decomposition(POD) dynamic mode decomposition(DMD) pitching hydrofoil

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Numerical simulation of unsteady cavitating flows around a transient pitching hydrofoil

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Science China(Technological Sciences) 2014年第1期57卷 101-116页

作者： HUANG Biao WU Qin WANG GuoYu School of Mechanical and Vehicular Engineering Beijing Institute of Technology

The objective of this paper is to improve the understanding of the influence of multiphase flow on the turbulent closure model, the interplay between vorticity fields and cavity dynamics around a pitching hydrofoil. The effects of pitching rate on the sub- cavitating and cavitating response of the pitching hydrofoil are also investigated. In particular, we focus on the interactions between cavity inception, growth, and shedding and the vortex flow structures, and their impacts on the hydrofoil performance. The calculations are 2-D and performed by solving the incompressible, multiphase Unsteady Reynolds Averaged Navier Stokes （URANS） equations via the commercial CFD code CFX. The k-co SST （Shear Stress Transport） turbulence model is used along with the transport equation-based cavitation models. The density correction function is considered to reduce the eddy viscosity according to the computed local fluid mixture density. The calculation results are validated with experiments conducted by Ducoin et al. （see Computational and experimental investigation of flow over a transient pitching hydrofoil, Eur J Mech/B Fluids, 2009, 28：728-743 and An experimental analysis of fluid structure interaction of a flexible hydrofoil in vari- ous flow regimes including cavitating flow, Eur J Mech B/fluids, 2012, 36： 63-74）. Results are shown for a NACA66 hydro- foil subject to slow （quasi static, t2=6~/s, ＆＊ =0.18） and fast （dynamic, ＆=63~/s, dr＂ =1.89） pitching motions from a =0~ to a =15~. Both subcavitaing （or =8.0） and cavitating （cr=3.0） flows are considered. For subcavitating flow （or=8.0）, low frequency fluctuations have been observed when the leading edge vortex shedding occurs during stall, and delay of stall is ob- served with increasing pitching velocity. For cavitating flow （tr=3.0）, small leading edge cavities are observed with the slow pitching case, which significantly modified the vortex dynamics at high angles of attack, leading to high frequency fluctuations of the

关键词： unsteady cavitating flow pitching hydrofoil turbulence model

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Investigation of Transient Cavitating Flows around a Fast pitching hydrofoil

Investigation of Transient Cavitating Flows around a Fast Pi...

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第二十五届全国水动力学研讨会暨第十二届全国水动力学学术会议

作者： HUANG Biao WU Qin WANG Guo-yu School of Mechanical and Vehicular Engineering Beijing Institute of Technology

The objective of this paper is to improve the understanding the influence of multiphase flow on the turbulent closure model,the interplay between vorticity fields and cavity dynamics around a pitching *** particular,we focus on the interactions between cavity inception, growth,and shedding and the vortex flow structures,and their impacts on the hydrofoil performance. The calculations are 2-D and performed by solving the incompressible,multiphase Unsteady Reynolds Averaged Navier Stokes(URANS) Equations via the commercial CFD code *** k-ωSST turbulence model is used along with the transport equation-based cavitation *** density correction function is considered to reduce the eddy viscosity according to the computed local fluid mixture *** calculation results are validated with experiments conducted by Ducoin et *** are shown for a NACA66 hydrofoil subject to fast pitching motions fromα=0°toα= 15°.Both subcavitaing(σ=8.0) and cavitating(σ=3.0) flows are *** subcavitating flow,low frequency fluctuations have been observed when the leading edge vortex shedding occurs during stall,and delay of stall is observed with increasing pitching *** cavitating flow,large-scale sheet/cloud cavitation is observed,the cavity behavior is unsteady and has a strong impact on the hydrodynamic response,which leads to high amplitude fluctuations of the hydrodynamic coefficients,as well as significantly changes in the stall and post-stall *** numerical results also show that the local density modification helps to reduce turbulent eddy viscosity in the cavitating region,which significantly modifies the cavity lengths and shedding frequencies, particularly for the fast pitching *** general,compared with the experimental visualizations, the numerical results with local density correction have been found to agree well with experimental measurements and observations for transient pitching cases.

关键词： pitching hydrofoil Vortex flow structures Cavitation

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Investigation of hysteresis effect of cavitating flow over a pitching Clark-Y hydrofoil

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Acta Mechanica Sinica 2022年第6期38卷 95-105,I0002页

作者： Mengjie Zhang Fuyong Feng Meijing Wang Zhipu Guo Zhong Kang Biao Huang China North Vehicle Research Institute Beijing100072China School of Mechanical Engineering Beijing Institute of TechnologyBeijing100081China

The objective of this paper is to investigate the hysteresis effect of cavitating flow over a Clark-Y hydrofoil undergoing a transient pitching motion at Reynolds number Re=4.55×105,cavitation numberσ=1.33,pitching frequency f*=2 Hz via combined experimental and numerical studies.A hysteresis phenomenon is observed in the hydrodynamic curve and cavity area in increasing and decreasing of the angle of attackα.The hydrodynamic curves are divided into three regions:Regions A,B and *** Region A,the lift coefficient of downstroke is lower than that of the upstroke,and the lift coefficient curve of the downstroke is more *** formation and development of counterclockwise trailing edge vortex(TEV)are responsible for the decline and fluctuation of lift during the downstroke,thus leading to the increase of the hysteresis *** with the upstroke,the hydrodynamic curve in downstroke is shifted laterally to some extent in Region *** delay effect is the main factor leading to the shift of the hydrodynamic curve,which corresponds to the minimum hysteresis *** Region C,the hysteresis loop is maximum and the evolution trend of the hydrodynamic curve is peak-valley *** the direction of oscillation changes,the detachment and dwell time of the cavity are advanced,thus leading to the difference of hydrodynamic curve and the increase of hysteresis loop.

关键词： Hysteresis effect Cavitating flow pitching hydrofoil

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