船舶螺旋桨低频噪声研究

螺旋桨低频噪声构成了船舶中高速航行时整个辐射噪声中的重要分量。螺旋桨的低频离散谱噪声是由船尾伴流场和叶片的相互作用引起的，而低频宽带噪声是由船尾粘性湍流场和叶片的相互作用产徨的。利用升力面理论和声学方法得到的离散谱噪声的预报公式，对螺旋桨直径、侧斜变化对离散谱噪 声的影响作了数值计算，并得到了工程上有实用意义的结果。在分析螺旋桨低频宽带器材怕成因的基础上得到了理论计算方法，并作为数值计算。整个方法     

Numerical study on the effects of progressive gravity waves on turbulence

The wind-wave-ocean system, which contains complex interactive processes, is of great importance for the momentum, heat and mass transport in the atmosphere and ocean and at their interface. In this work, we perform wave-coupled phase-resolved numerical simulations to investigate the effect of progressive gravity waves on wind and ocean turbulence. Initially homogeneous turbulence under a finite-amplitude monochromatic surface wave is simulated to reveal how the wave influences the subsurface turbulence. For the interaction between wind-driven waves and shear turbulence in the ocean, new wave-phase-resolved simulation approaches are developed to capture Langmuir cells. Lastly, wind turbulence over one and two progressive waves is simulated to elucidate the dynamics of turbulence coherent structures impacted by surface waves for improved understanding of wind-wave growth mechanism.     

Turbulence characteristics in free-surface flow over two-dimensional dunes

The turbulent structure of open-channel flows over two-dimensional dunes is investigated numerically using large-eddy simulation (LES), in order to improve our understanding of the interaction between the dune-generated turbulence and the free surface dynamics. The filtered Navier–Stokes equations in the LES model have been discretised using the finite volume method, with a dynamic sub-grid model being employed for the unresolved scales of turbulence. The partial cell treatment has been implemented in a Cartesian grid form to deal with the dune topography. Both the volume of fluid method and rigid lid approach have been employed in the numerical framework to investigate the effects of the free surface treatment on the flow characteristics. The numerical model predicted mean flow velocities, turbulence intensities and Reynolds stresses have been compared with experimental measurements published in the literature, with a detailed analysis being undertaken to assess the accuracy of the model results and the effects of the free surface treatment on the velocity and turbulence predictions. The instantaneous flow structure has been investigated, with emphasis being focused on the free surface dynamics and coherent structures.     

翼型体广谱声的频域预报方法

本文提出了一种广谱声预报的频域方法，并通过与试验数据的比较证明了方法的有效性，尽管文中以平板翼为例，进行了实例计算，但方法本身适用于任意形体在介质中以亚音速作惯性运动时的广谱声预报。相对于时域方法而言，由于省去了将频域数据转化为时域数据的中间过程，因此该方法较时域方法(Casper and Farassat，2002)更为有效。本文的关键在于具有平均流效果的格林函数的成功应用，由此格林函数所表达的积分算式将在后续文中进一步拓展应用于具有非惯性运动的螺旋桨广谱噪声的预报。     

NUMERICAL SIMULATION OF TURBULENT FREE SURFACE FLOW OVER OBSTRUCTION

A two-dimensional hybrid numerical model, FEM-LES-VOF, for free surface flows is proposed in this study, which is a combination of three-step Taylor-Galerkin finite element method, large eddy simulation with the Smagorinsky sub-grid model and Computational Lagrangian-Eulerian Advection Remap Volume of Fluid （CLEAR-VOF） method. The present FEM-LES-VOF model allows the fluid flows involving violent free surface and turbulence subject to complex boundary configuration to be simulated in a straightforward manner with unstructured grids in the context of finite element method. Numerical simulation of a benchmark problem of dam breaking is conducted to verify the present model. Comparisons with experimental data show that the proposed model works well and is capable of producing reliable predictions for free surface flows. Using the FEM-LES-VOF model, the free surface flow over a semi-circular obstruction is investigated. The simulation results are compared with available experimental and numerical results. Good performance of the FEM-LES-VOF model is demonstrated again. Moreover, the numerical studies show that the turbulence plays an important role in the evolution of free surface when the reflected wave propagates upstream during the fluid flow passing the submerged obstacle.     

THE APPLICATIONS AND STUDY OF NUMERICAL SIMULATION OF TURBULENCE FLOW WITH FREE SURFACE IN HYDRAULIC SPILL WAYS STRUCTURE

The turbulence flow Free Surface has important applications in hydraulic spillways structure,such as the hydraulic jump,energy dissipation flow etc.This is being considered as very complicated flow,and has not yet been solved quite well by numerical method. In this paper,a Large-scale computational software package are developed for numerical laboratory of hydraulic spillway structure.Some methods,such as turbulence model, free surface and irregular boundary treating techniques,scientific computer visualization are put forward and performed.     

NEAR WAKE OF A MODEL HORIZONTAL-AXIS WIND TURBINE

An experimental investigation on the properties of the near wake behind the rotor of a Horizontal-Axis Wind Turbine (HAWT) was carried out at model scale. Measurements were made with a stationary slanted hot-wire anemometer using the technique of phase-locked averaging. The primary aim is to study the formation and development of the three-dimensional wake. Five axial locations were chosen within four chord lengths of the blades over a range of tip speed ratios. The results show that during the downstream development of the wake, the wake centre traces a helical curve with its rotation direction opposite to that of the rotor. The distribution of mean velocity behind the HAWT rotor reveals an expansion and a decay of the three-dimensional wake. The shapes of the mean velocity distribution are similar along the blades span at the same downstream axial location. It is shown that the turbulence levels in the wake are higher than those in the non-wake region. The circumferential component and the radial component of the turbulence intensity are higher than the axial component. Our study offers some food of thought for better understanding of the physical features of the flow field as well as the performance of HAWT.     

NUMERICAL SIMULATION OF 3-D TURBULENT FLOWS OF PLUNGE POOL AND ENERGY DISSIPATION ANALYSIS

A 3-D numerical model for simulating the complicated turbulent flows was developed and the code was made. A numerical calculation of the plunge pool of Laxiwa project in China was carried on. Those 3-D distributions of velocity,pressure on bottom wall,turbulence kinetic energy and turbulence energy dissipation rate are revealed in detail and the detailed flow patterns of plunge pool were shown. By studying on the characteristics of turbulent diffusion and energy dissipation,the calculated results show that the major turbulence and energy dissipation are taken place near the axis of water jet. The calculated results also indicated that the calculated maximum impact pressures on the bottom wall of the plunge pool have a good agreement with those obtained by physical hydraulic model test.     

EXPERIMENTAL MEASUREMENT AND NUMERICAL SIMULATION FOR FLOW FIELD AND FILM COOLING EFFECTIVENESS IN FILM-COOLED TURBINE

Numerical simulation of three-dimensional flow field and film cooling effectiveness in film-cooled turbine rotor and stationary turbine cascade were carried out by using the k - ε turbulence model, and the predictions of the three-dimensional velocities were compared with the measured results by Laser-Doppler Velocimetry (LDV). Results reveal the secondary flow near the blade surface in the wake region behind the jet hole. Compared with the stationary cascade, there are the centrifugal force and Coriolis force existing in the flow field of the turbine rotor, and these forces make the three-dimensional flow field change in the turbine rotor, especially for the radial velocity. The effect of rotation on the flow field and the film cooling effectiveness on the pressure side is more apparent than that on the suction side as is shown in the computational and measured results, and the low film cooling effectiveness appears on the pressure surface of the turbine rotor blade compared with that of the stationary cascade.     

NUMERICAL STUDY OF TURBULENT JETS CONFINED BETWEEN TWO CONCENTRIC SPHERES

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宽顶堰水流数值模拟分析

本文利用紊流模型模拟了带有曲线自由表面的宽顶堰流的紊流流场,采用VOF法来确定自由表面,采用气液两相流计算模型对宽顶堰流场进行了数值模拟,计算结果与试验数据较为吻合.模拟结果表明,数值模拟是作为研究水利工程中带有自由表面的水流结构的一个强有力的工具,其结果对物理试验也是一个很好的补充.     

RE-AERATION LAW OF WATER FLOW OVER SPILLWAYS

1. INTUODUCTION Due to the strong turbulence of the flow over the spillway, air is entrained into water body making the oxygen content increased. It is important for river, especially for city-river to maintain favorable water quality and ecological envir…     

海气界面动量、热量及水汽交换系数的数值模拟

本文采用了有效波加表面粗糙度的风浪模型R 糊涂980）的浮力修正k-ε模式数值模拟了不同风速=大气稳定度及风浪发展状态下的海面大气湍流边界层，计算了不同海气状况下的速度、温度、湿度湍流流场，得出阻力系数CD、Stanton数CH、Dalton数CE随风速U10和大气稳定度的变化规律，也讨论了它们与波龄的依赖关系，与理论及实测数据进行比较，证明计算结果与实际情况符合良好。     

泄水建筑物体型优选的数值模拟研究

本文针对泄洪洞水流的特点，建立了适体坐标系下带自由表现、强紊动水流的数学模型。利用该模型编制程序对泄洪洞中复杂水流进行了数值模拟，通过分析输出的数据和图形，可以灵活地修改模型和体型的形状和参数，方便地进行系列数值实验或不同体型方案的比较，从而为泄水建筑物体型方案的选择和设计提供了足够精细和准确的数据，有助于数学模型逐步地取代费时耗财的物理模型实验。     

猴子岩水电站深孔泄洪洞水力学试验及数值模拟

深孔泄洪洞是猴子岩水电站4套泄洪设施之一,其落差超过100m,洞内泄流流速最大可达22.5m/s,有高水头大流速这一特点。本文采用双方程紊流模型及基于水气两相流的VOF方法,对猴子岩深孔泄洪洞有压洞弯段及无压洞段的多种水力学要素进行三维数值模拟。数值模拟结果与1:25单体模型试验数据对比表明,采用该紊流模型与数值计算方法,能够很好地模拟这种高水头、大流量且带有自由表面的掺气水流的水力特性。计算模拟出的多种水力特性,从变化趋势到数值精度可满足水工设计的要求。     

Experimental and Numerical Investigation of Flow Over Ogee Spillway

Ogee type spillway is one of the most preferred sluice types due to its functional suitability and high safety factor. It is used for controlling the flow rates and water levels in reservoirs, such as lowering the water level in emergency situations, maintaining normal river functions and discharging excess water. The main aim of this study is to investigate the flow over ogee type spillway by performing experiments in an open channel flume in the laboratory and simulating with numerical model. The numerical model having the same dimensions with the physical model is modeled with two different programs of ANSYS-Fluent and OpenFOAM. The flow depths of the models were measured at four points, H₁, H₂, H₃, H₄. In the numerical analysis, two different turbulence models, K-ε and K-ω SST turbulence model were used in order to investigate the accuracy of the turbulence models in the open channel. According to the results, R² values, obtained from ANSYS- Fluent for the each measurement points where H₁, H₂, H₃, H₄, are 0.9776, 0.9859, 0.9701, 0.9916 and obtained from OpenFOAM for the each measurement points 0.9920, 0.9687, 0.9855, 0.9926 respectively. The findings show that the numerical tools have been sufficiently developed to simulate flow depths and water surface profiles.

     

NUMERICAL SIMULATION OF TWO-DIMENSIONAL OVERTOPPING AGAINST SEAWALLS ARMORED WITH ARTIFICIAL UNITS IN REGULAR WAVES

A new mathematical model for the overtopping against seawalls armored with artificial units in regular waves was established. The 2-D numerical wave flume, based on the Reynolds Averaged Navier-Stokes (RANS) equations and the standard k-ε turbulence model, was developed to simulate the turbulent flows with the free surface, in which the Volume Of Fluid (VOF) method was used to handle the large deformation of the free surface and the relaxation approach of combined wave generation and absorbing was implemented. In order to consider the effects of energy dissipation due to the armors on a slope seawall, a porous media model was proposed and implemented in the numerical wave flume. A series of physical model experiments were carried out in the same condition of the numerical simulation to determine the drag coefficient in the porous media model in terms of the overtopping discharge. Compared the computational value of overtopping over the seawall with the experimental data, the values of the effective drag coefficient was calibrated for the layers of blocks at different locations along the seawalls.     

水垫塘三维紊流数值模拟及消能分析

开发了能模拟复杂紊流的三维数学模型，编制了大型计算程序，针对拉西瓦水垫塘进行了数值模拟，揭示了水垫塘内速度，压力，紊动能及其耗散率的三维分布规律，获得了详细的水垫塘流态特性。研究了水流紊动扩主消能特性，反映出紊动和消能大量地发生在射流轴线附近，计算所得的底板最大冲击动压与实验值进行了比较，二者符合良好。     

受控振动柱体对波浪影响的数值模拟研究

以不可压缩黏性流体的Navier-Stokes方程为控制方程,采用RNG k-ε湍流模型,利用VOF方法追踪运动的自由表面的方法,建立了三维数值波浪与振动柱体相互作用的模型.基于经典绕射理论验证了波浪绕固定柱体传播的数值模型的可靠性,再采用动边界技术赋予柱体振动规律,研究受控振动柱体对波浪传播的影响,并通过控制柱体初始振动相位变化,系统地给出了在柱体振动的不同初始相位下柱体前后波浪变化的规律.     

三维宽顶堰紊流场数值模拟及分析

本文利用三雏标准k-ε紊流数学模型,选择VOF方法追踪自由表面,采用气液两相流计算模型对宽顶堰流场进行了数值模拟,计算结果与试验数据较为吻合.模拟结果表明,数值模拟能够广泛应用于数值模拟带有复杂自由表面的泄水建筑物紊流场.