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Hydrodynamic performances and wakes induced by a generic submarine operating near the free surface in continuously stratified fluid

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Journal of Hydrodynamics 2023年第3期35卷 396-406页

作者： Liu-shuai Cao Gang Gao En-kai Guo De-cheng Wan School of Naval Architecture Ocean and Civil EngineeringShanghai Jiao Tong UniversityShanghai 200240China

The wake of a submarine is a crucial element that greatly affects its stealth and hydrodynamic *** investigate the propagation and evolution characteristics of submarine wakes in a stratified fluid,particularly under free surface conditions,a numerical method to simulate the linearly stratified environment was developed.A thermocline model based on Boussinesq assumption was introduced to match the continuously stratified *** volume of fluid(VOF)method was utilized to capture free surface waves,while a fully structured grid and the SST k-ωturbulence model were combined to solve the complex flow of *** independence study in homogenous flow near the free surface was initially ***,the hydrodynamic performance,wake evolution characteristics,free surface signatures as well as decay of velocity under different stratification levels were *** demonstrated that the numerical method employed was efficient in simulating stratified ***,it showed that density stratification had a significant impact on the hydrodynamics and wake characteristics of a submarine,especially under strong density stratification circumstances.

关键词： wakes submarine free surface stratified fluid hydrodynamics

Interaction mechanisms of shock waves with the boundary layer and wakes in a highly-loaded NGV using hybrid RANS/LES

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Chinese Journal of Aeronautics 2020年第1期33卷 149-160页

作者： Xiutao BIAN Qingsong WANG Xinrong SU Xin YUAN Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Tsinghua UniversityBeijing 100084China

Accurate predictions of Shock Waves and Boundary Layer Interaction(SWBLI)and strong Shock Waves and Wake Vortices Interaction(SWWVI)in a highly-loaded turbine propose challenges to the currently widely used Reynolds-Averaged Navier-Stokes(RANS)*** this work,the SWBLI and the SWWVI in a highly-loaded Nozzle Guide Vane(NGV)are studied using a hybrid RANS/LES *** Turbulence Kinetic Energy(TKE)budget and the Proper Orthogonal Decomposition(POD)method are used to analyze flow *** show that this hybrid RANS/LES method can obtain detailed flow structures for flow mechanisms *** shock waves induce boundary layer separation,while the presence of a separation bubble can in turn lead to a Mach reflection *** shock waves cause trailing-edge vortices to break clearly,and the wakes,in turn,can change the shocks intensity and ***,the Entropy Generation Rate(EGR)is used to analyze the irreversible *** turns out that the SWWVI can reduce the flow field *** are several weak shock waves in the NGV flow field,which can increase the irreversible *** work offers flow mechanisms analysis and presents the EGR distribution in SWBLI and SWWVI areas in a transonic turbine blade.

关键词： Boundary layer Hybrid RANS/LES NGV Shock waves wakes

Vortical structures and wakes of a sphere in homogeneous and density stratified fluid

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Journal of Hydrodynamics 2021年第2期33卷 207-215页

作者： Liu-shuai Cao Feng-lai Huang Cheng Liu De-cheng Wan Computational Marine Hydrodynamics Lab(CMHL) School of Naval ArchitectureOcean and Civil Engi-neeringShanghai Jiao Tong UniversityShanghai 200240China Ocean College Zhejiang UniversityZhoushan 316021China

Vortical structures and wakes of bluff bodies in homogenous and stratified environment are common and important in ocean *** on the Boussinesq approximation,a thermocline model is proposed to deal with the variable density stratified fluid,and implemented in the commercial software Simcenter STAR-CCM+*** improved delayed detached eddy simulation(IDDES)modeling method is adopted to resolve the coherent vortical structures and turbulent wakes precisely and *** conditions consisting of one homogenous and three stratified fluid cases with different density gradient past a sphere at Reynolds number 3700 are *** show that density stratification has a great impact on the vortical structures,the vertical motion is suppressed and internal waves will be induced and propagated,which is very different with that of homogenous *** the stratification strength increases,the vortical structures are gradually flattened,the asymmetry and anisotropy between vertical and horizontal motions are enhanced.

关键词： Vortical structures wakes sphere homogenous stratified fluid

Molecular wakes for ultrashort laser pulses

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Science China(Physics,Mechanics & Astronomy) 2010年第6期53卷 1036-1039页

作者： CAI Hua,WU Jian,LU PeiFen,TONG YuQi,YANG Xuan,BAI XueShi,LI Hao,PAN HaiFeng & ZENG HePing State Key Laboratory of Precision Spectroscopy,East China Normal University,Shanghai 200062,China 1. State Key Laboratory of Precision Spectroscopy East China Normal University Shanghai 200062 China

The molecular wake-assisted interaction between two collinear femotosecond laser pulses is investigated in air,which leads to the generation of a controllable 1.8 mJ super-continuum pulse with an elongated self-guided channel due to the cross-phase modulation of the impulsively aligned diatomic molecules in air. For two parallel launched femtosecond laser pulses with a certain spatial separation,controllable attraction and repulsion of the pulses are observed due to the counter-balance among molecular wakes,Kerr and plasma effects,where the molecular wakes show a longer interaction distance than the others to control the propagation of the intense ultrashort laser pulses.

关键词： molecular wakes ultrashort laser pulse interaction super-continuum generation

Numerical Computations of Wind Turbine wakes Using Full Rotor Modeling

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Numerical Computations of Wind Turbine Wakes Using Full Roto...

GLRT Detectors for Aircraft Wake Vortices in Clear Air

2012 2nd International Conference on Power and Energy Systems(ICPES 2012)

作者： Ali M. Abdelsalam Hari Krishnan Kumar S.S. K. Boopathi Velraj Ramalingam Department of Mechanical Engineering Anna University AU-FRG Institute for CAD/CAM Anna University

In the present work, full rotor modeling was implemented in order to study the wake characteristics of a horizontal axis wind turbine, with an exact representation of the rotor blades. The numerical solution was carried out by solving conservation equations in a rotating reference frame, wherein the blades and grids were fixed in relation to the rotating frame. Results were obtained, using the RANS equations, and turbulence was simulated via the Shear Stress Transport （SST） k-ω turbulence model. The wake behavior was validated and tested at different wind speeds, to find the relation between the wind speed and the wake recovery. Computations were carried out and compared with a 100 kW MOD-0A wind turbine, and they showed good agreement with the available experimental data. Thereafter, a series of full scale analyses was conducted to investigate the wake behavior of a 2 MW wind turbine at different wind speeds. The value of the wind speed was found to have a major influence on the distance required for the wake recovery.

关键词： wakes Full rotor Wind turbines RANS Wind speed

来源： cnki会议评论

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Chinese Journal of Aeronautics 2010年第6期23卷 698-706页

作者： Li Jun Wang Xuesong Wang Tao School of Electronic Science and Engineering National University of Defense TechnologyChangsha 410073China

In this article, radar echoes of aircraft wake vortices are modeled as weighted sums of the frequency components of the echoes with a special covariance matrix for the weighted coefficients. With a proposed detection scheme, two generalized likelihood ratio test (GLRT) detectors are derived respectively for aircraft wake vortices with time-varying and time-invariant Doppler spectra. Then the analytical expressions for detection and false alarm probabilities of the detectors are derived and three factors are investigated which mainly influence the detection performance, i.e., the Doppler extension and uncertainty of the aircraft wake vortex, and the number of the detection cells. The results indicate that, the signal-to-noise ratio (SNR) loss induced by Doppler extension is generally several decibels. The SNR loss due to Doppler uncertainty is approximately proportional to the logarithm of the number of spectrum lines in the uncertain Doppler spectrum intervals. For a large number of detection cells, the SNR gain is approximately proportional to the square root of the number of the detection cells.

关键词： radar detector generalized likelihood ratio test aircraft wakes vortex flow

Wake flow and vortex structures behind emergent vegetation patches elongated in the longitudinal direction

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Journal of Hydrodynamics 2021年第6期33卷 1148-1161页

作者： Zi-jian Yu Yu-qi Shan Chao Liu Xing-nian Liu State Key Laboratory of Hydraulics and Mountain River Engineering College of Water Resource and HydropowerSichuan UniversityChengdu 610065China Department of Civil and Environmental Engineering University of AlbertaEdmontonCanada Institute for Disaster Management and Reconstruction Sichuan UniversityChengdu 610065China

In natural rivers,patches of vegetation generally expand over their steady wake region in the streamwise direction,forming elongated patches with length(L)greater than their width(b).This paper studies how the wake flows and the vortices develop as the emergent patches expand their length in the streamwise *** patches are modeled with the same width but different lengths in laboratory *** the patches,the steady wake region(L_(w))is not related to the width-related flow blockage(C_(d)ab),where C_(d) is the drag coefficient,a is the vegetation ***,L_(w) is related to the length-related flow blockage(C_(d)aL).On this basis,a model is proposed for predicting L_(w),which is in good agreement with the *** a patch becomes denser and/or longer(as C_(d)aL increases),the steady wake region becomes shorter(L_(w) decreases),and vortices are observed closer to the patch trailing edge,producing a turbulence of a greater magnitude beyond L_(w).When the flow blockage increases to the limit(C_(d)aL>8),the Karman vortices are observed directly behind the porous *** results can be used to explain the longitudinal elongation of the vegetation patches in the field.

关键词： Velocity profiles turbulent kinetic energy wakes vortex streets vegetation patch

Turbulence Modulations in the Boundary Layer of a Horizontal Particle-Laden Channel Flow

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Chinese Physics Letters 2010年第6期27卷 129-132页

作者： LI Jing LIU Zhao-Hui WANG Han-Feng CHEN Sheng LIU Ya-Ming HAN Hai-Feng ZHENG Chu-Guang State Key Laboratory of Coal Combustion Huazhong University of Science and Technology Wuhan 430074

Turbulence modulations are experimentally investigated using particle image velocimetry （PIV） in the lower boundary layer of a fully developed horizontal channel flow. A simultaneous two-phase PIV measurement technique is adopted to acquire the turbulent statistics quantities and to examine the coherent structures in the near-wall region. Polythene beads with diameters of 60 μm are used as dispersed phases, and the PIV measurements have been performed at three mass loadings varying from 2.5 ×10^-4 to 5 × 10^-3. All the experiments are performed at a wall shear Reynolds number of Reτ = 430. The results show that the presence of the particles suppresses the coherent structures, with shorter streamwise extent of the quasistrearnwise structures, and then, the wall-normal velocity fluctuations and shear Reynolds stresses are both decreased in the near-core region. In addition, as a result of the particle wake, the turbulence intensity and shear Reynolds stress both increase in the vicinity of the wall. Due to the drag effects of the particles on the gas, the streamwise velocity gradients decrease in the outer region and increase in the viscous sublayer, meanwhile the thickness of the viscous sublayer also decreases. These results cause the peak values of the streamwise velocity fluctuations adjacent to the wall to increase, and the peak positions shift to the wall. This is the reason for decreasing the near-wall region and increasing the near-core region of the streamwise velocity fluctuations in appearance.

关键词： Reynolds stress wakes Flow in channels Turbulence intensities Statistical analysis Drag

INVESTIGATION OF VISCOUS FLOW FIELD AROUND AN APPENDED REVOLUTION BODY WITH GUIDE VANE PROPELLER

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Journal of Hydrodynamics 2000年第1期12卷 79-86页

作者： Zhou, Liandi Zhao, Feng National Lab of Hydrodynamics Wuxi China

A RANS (Reynolds-averaged Navier-stokes) solver is presented to numerically simulate the viscous wake of an appended revolution body with guide vane propeller at the Reynolds number 107. The k-Ε turbulence model together with wall function is used. The resulting finite difference equations are solved by SIMPLEC and ADI. The technique of rising up the bottom surface is presented to overcome radial contraction problems in the Cartesian coordinate system. The three-dimensional body model is successfully use to represent the guide vane and propeller actions. The detailed flow characteristics, especially the counter-swirl component generated by the guide vane in the propeller inflow, are numerically seized successfully. The qualitative and quantitative consistence between experiment and calculation is shown. The computational axial velocity of the propeller disk plane comes up to engineering requirement.

关键词： Computer simulation Fluid dynamics Propellers Reynolds number wakes