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Scale Effects on Propeller Cavitating Hydrodynamic and Hydroacoustic Performances with Non-uniform Inflow

Chinese Journal of Mechanical Engineering 2013年第2期26卷 414-426页

作者： YANG Qiongfang WANG Yongsheng ZHANG Zhihong College of Marine Power Engineering Naval University of Engineering College of Science Naval University of Engineering

Considering the lack of theoretical models and ingredients necessary to explain the scaling of the results of propeller cavitation inception and cavitating hydroacoustics from model tests to full scale currently, and the insufficient reflection of the nuclei effects on cavitation in the numerical methods, the cavitating hydrodynamics and cavitation low frequency noise spectrum of three geometrically similar 7-bladed highly skewed propellers with non-uniform inflow are addressed. In this process, a numerical bridge from the multiphase viscous simulation of propeller cavitation hydrodynamics to its hydro-acoustics is built, and the scale effects on performances and the applicability of exist scaling law are analyzed. The effects of non-condensable gas（NCG） on cavitation inception are involved explicitly in the improved Sauer＇s cavitation model, and the cavity volume acceleration related to its characteristic length is used to produce the noise spectrum. Results show that, with the same cavitation number, the cavity extension on propeller blades increases with diameter associated with an earlier shift of the beginning point of thrust decline induced by cavitation, while the three decline slopes of thrust breakdown curves are found to be nearly the same. The power of the scaling law based on local Reynolds number around 0.9R section is determined as 0.11. As for the smallest propeller, the predominant tonal noise is located at blade passing frequency（BPF）, whereas 2BPF for the middle and both 2BPF and 3BPF for the largest, which shows the cavitating line spectrum is fully related to the interaction between non-uniform inflow and fluctuated cavity volume. The predicted spectrum level exceedance from the middle to the large propeller is 6.65 dB at BPF and 5.94 dB at 2BPF. Since it just differs less than 2 dB to the increment obtained by empirical scaling law, it is inferred that the scale effects on them are acceptable with a sufficient model scale, and so do the scaling law. The numerical implementation of cavitating

关键词： propeller cavitation inception cavitation noise scale effect cavitation model turbulence model

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Numerical simulation unsteady cloud cavitating flow with a filter-based density correction model

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Journal of Hydrodynamics 2014年第1期26卷 26-36页

作者：黄彪王国玉赵宇 School of Mechanics and Engineering Beijing Institute of Technology

In this paper, various turbulence closure models for unsteady cavitating flows are investigated. The filter-based model （FBM） and the density correction model （DCM） were proposed to reduce the turbulent eddy viscosities in a turbulent cavitating flow based on the local meshing resolution and the local fluid density, respectively. The effects of the resolution control parameters in the FBM and DCM models are discussed. It is shown that the eddy viscosity near the cavity closure region can significantly influence the cavity shapes and the unsteady shedding pattern of the cavitating flows. To improve the predictions, a Filter-Based Density Cor-rection model （FBDCM） is proposed, which blends the FBM and DCM models according to the local fluid density. The new FBDCM model can effectively represent the eddy viscosity, according to the multi-phase characteristics of the unsteady cavitating flows. The experimental validations regarding the force analysis and the unsteady cavity visualization show that good agreements with experimental visualizations and measurements are obtained by the FBDCM model. For the FBDCM model, the attached cavity length and the resulting hydrodynamic characteristics are subsequently affected by the detail turbulence modeling parameters, and the model is shown to be effective in improving the overall predictive capability.

关键词： CFD cavitating flows resolution control parameter turbulence model

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Description of inverse energy cascade in homogeneous isotropic turbulence using an eigenvalue method

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Applied Mathematics and Mechanics(English Edition) 2021年第9期42卷 1233-1246页

作者： Feng LIU Hantao LIU Hongkai ZHAO Pengfei LYU Research Center of Shanxi Province for Solar Energy Engineering and Technology School of Energy and Power EngineeringNorth University of ChinaTaiyuan 030051China National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics School of Energy and Power EngineeringBeihang UniversityBeijing 100191China

A description of inverse energy cascade(from small scale to large scale)in homogeneous isotropic turbulence is introduced by using an eigenvalue method.We show a special isotropic turbulence,in which the initial condition is constructed by reversing the velocity field in space,i.e.,the time-reversed turbulence.It is shown that the product of eigenvalues of the rate-of-strain tensor can quantitatively describe the backward energy transfer process.This description is consistent to the velocity derivative skewness Sk.However,compared with Sk,it is easier to be obtained,and it is expected to be extended to anisotropic turbulence.Furthermore,this description also works for the resolved velocity field,which means that it can be used in engineering turbulent flows.The description presented here is desired to inspire future investigation for the modeling of the backward energy transfer process and lay the foundation for the accurate prediction of complex flows.

关键词： inverse energy cascade homogeneous isotropic turbulence eigenvalue method turbulence model

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An axisymmetric model for draft tube flow at partial load

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Journal of Hydrodynamics 2016年第2期28卷 195-205页

作者： Hosein FOROUTAN Savas YAVUZKURT Department of Mechanical and Nuclear Engineering The Pennsylvania State University

A new Reynolds-averaged Navier-Stokes （RANS） turbulence model is developed in order to correctly predict the mean flow field in a draft tube operating under partial load using 2-D axisymmetric simulations. It is shown that although 2-D axisymmetric simulations cannot model the 3-D unsteady features of the vortex rope, they can give the average location of the vortex rope in the draft tube. Nevertheless, RANS simulations underpredict the turbulent kinetic energy （TKE） production and diffusion near the center of the draft tube where the vortex rope forms, resulting in incorrect calculation of TKE profiles and, hence, poor prediction of the axial velocity. Based on this observation, a new k- c turbulence RANS model taking into account the extra production and diffusion of TKE due to coherent structures associated with the vortex rope formation is developed. The new model can successfully predict the mean flow velocity with significant improvements in comparison with the realizable k - c model. This is attributed to better prediction of TKE production and diffusion by the new model in the draft tube under partial load. Specifically, the new model calculates 31% more production and 46% more diffusion right at the shear layer when compared to the k - ~ model.

关键词： hydropower draft tube turbulence model computational fluid dynamics vortex rope

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A novel Omega-driven dynamic PANS model

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Journal of Hydrodynamics 2020年第4期32卷 710-716页

作者： Chao-yue Wang Fu-jun Wang Ben-hong Wang Yuan Tang Hao-ru Zhao College of Water Resources and Civil Engineering China Agricultural UniversityBeijing 100083China Beijing Engineering Research Center of Safety and Energy Saving Technology for Water Supply Network System Beijing 100083China

A novel Omega(Ω)-driven dynamic partially-averaged Navier-Stokes(PANS)model is proposed in this paper.The ratio of the modeled-to-total turbulent kinetic energies fk is dynamically adjusted by the rigid vorticity ratio(the ratio of the rigid vorticity to the total vorticity),the key parameter of the Ω vortex identification method.Three classical flow cases with rotation and curvature are used to test the model.The results show that the turbulent viscosity is effectively adjusted by the new dynamic fk and the LES-like mode is activated,which can help the revelation of more turbulence information and improve the prediction accuracy.The new PANS model does not contain any explicit dependency on the grid size and enjoys good adaptability to the flow fields,and can be used for efficient engineering computations of the turbulent flows in the hydraulic machinery.

关键词： Dynamic partially-averaged Navier-Stokes(PANS) turbulence model Omega engineering computations

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Improving the hydrodynamic performance of the SUBOFF bare hull model: a CFD approach

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Acta Mechanica Sinica 2020年第1期36卷 44-56页

作者： Kambiz Divsalar Department of Mechanical Engineering Imam Khomeini University of Maritime SciencesNowshahrIran

The main aims of this study are to investigate the hydrodynamic performance of an autonomous underwater vehicle(AUV),calculate its hydrodynamic coefficients,and consider the flow characteristics of underwater bodies.In addition,three important parts of the SUBOFF bare hull,namely the main body,nose,and tail,are modified and redesigned to improve its hydrodynamic performance.A three-dimensional(3D)simulation is carried out using the computational fluid dynamics(CFD)method.To simulate turbulence,the k-ωshear stress transport(SST)model is employed,due to its good prediction capability at reasonable computational cost.Considering the effects of the length-to-diameter ratio(LTDR)and the nose and tail shapes on the hydrodynamic coefficients,it is concluded that a hull shape with bullet nose and sharp tail with LTDR equal to 7.14 performs better than the SUBOFF model.The final proposed model shows lower drag by about 14.9%at u=1.5 m·s^-1.Moreover,it produces 8 times more lift than the SUBOFF model at u=6.1 m·s^-1.These effects are due to the attachment of the fluid flow at the tail area of the hull,which weakens the wake region.

关键词： Autonomous underwater vehicle Computational fluid dynamics Hydrodynamic performance Drag turbulence model Hull shape

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Non-equilibrium turbulent phenomena in transitional flat plate boundary-layer flows

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Applied Mathematics and Mechanics(English Edition) 2021年第4期42卷 567-582页

作者： Feng LIU Le FANG Jian FANG School of Energy and Power Engineering North University of ChinaTaiyuan 030051China Laboratory of Mathematics and Physics Ecole Centrale de P′ekinBeihang UniversityBeijing 100191China Scientific Computing Department STFC Daresbury LaboratoryWarrington WA44ADU.K.

Many recent laboratory experiments and numerical simulations support a non-equilibrium dissipation scaling in decaying turbulence before it reaches an equilibrium state.By analyzing a direct numerical simulation(DNS)database of a transitional boundary-layer flow,we show that the transition region and the non-equilibrium turbulence region,which are located in different streamwise zones,present different non-equilibrium scalings.Moreover,in the wall-normal direction,the viscous sublayer,log layer,and outer layer show different non-equilibrium phenomena which differ from those in grid-generated turbulence and transitional channel flows.These findings are expected to shed light on the modelling of various types of non-equilibrium turbulent flows.

关键词： non-equilibrium turbulence flat plate boundary layer turbulence model

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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

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A HYBRID model FOR SIMULATING VELOCITY FIELD OF A RIVER WITH COMPLEX GEOMETRY PLUNGED BY MULTIPLE JETS

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Journal of Hydrodynamics 2006年第6期18卷 752-759页

作者： LI Lian-xia LIAO Hua-sheng LI Tian-xiang State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University Chengdu 610065China

A hybrid model that combines both physical and numerical models was employed to simulate the velocity field in a river area in complex geometry with multiple plunging jets. The simulation was based on experiments concerning energy dissipation and scour prevention at the Xiluodu Hydropower Station on the Yangtze River. The calculated results indicate that the complex geometry of the river area has a significant influence on the velocity field, especially on the circulation flow pattern at upstream and downstream of the plunging area and on the asymmetric characteristics of the spiral flow near both banks. The scour characteristics of the downstream river bed caused by the multiple jets were also predicted and analyzed according to the characteristics of the calculated velocity field. The good agreement between the simulated and experimental results indicates that the hybrid model can be used to effectively solve complicated 3-D problems with complex geometric and inlet conditions. Such problems may not easily be solved by using either a physical or a numerical model alone, and therefore the method presented in this article is considered to be a practical and effective way of dealing with this kind of problems.

关键词： hybrid models turbulence model scour multiple jets

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New constitutive relation for eddy viscosity models

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航空动力学报 2016年第10期31卷 2485-2492页

作者： JIANG Li-jun GAO Ge Hunan Aviation Powerplant Research Institute Aero Engine Corporation of China School of Energy and Power Engineering Beijing University of Aeronautics and Astronautics

A new turbulent constitutive relation was directly derived from Boussinesqs hypothesis and mixing length theory,and then implemented in the standard k-ε model.The performance of this constitutive relation was validated in zero pressure gradient flat-plate boundary layer flow,fully-developed turbulent channel flow and separated flow in a plane asymmetric diffuser.The investigation demonstrated that,this new constitutive relation gave very accurate results in the former two basic cases and provided significant improvement in prediction of separated and reattachment points in the plane asymmetric diffuser.Separation and reattachment points at x/H =7.5and 29 were calculated accurately in comparison to experimental results,and the static pressure coefficient of 0.82 was very close to large eddy simulation calculation.These results are very encouraging but further verification and extensive application of the new constitutive relation to other two-equation eddy viscosity model are needed.

关键词： constitutive relation turbulence model flat-plate flow channel flow separated flow

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