共查询到20条相似文献，搜索用时 15 毫秒
1.
Experimental Investigation of the Decay from A Ship’s Propeller 总被引：1，自引：0，他引：1
In the present study,an experimental investigation of the decay of the maximum velocity and its turbulent characteristics behind a ship propeller,in "bollard pull" condition(zero speed of advance),is reported.Velocity measurements were performed in laboratory by use of a Laser Doppler Anemometry(LDA) measurement system.Earlier researchers described that the maximum axial velocity is constant at the initial stage of a ship’s propeller jet(Fuehrer and Rmisch,1977;Blaauw and van de Kaa,1978;Berger et al.,1981;Verhey,1983) as reported in a pure water jet(Albertson et al.,1950;Lee et al.,2002;Dai,2005),but a number of researchers disagreed with the constant velocity assumption.The present study found that the maximum axial velocity decays in the zone of flow establishment and the zone of established flow with different rates.The investigation provides an insight into the decays of both the maximum velocity and the maximum turbulent fluctuation in axial,tangential and radial components and the decay of the maximum turbulent kinetic energy.Empirical equations are proposed to allow coastal engineers to estimate the jet characteristics from a ship’s propeller. 相似文献
2.
Predicting the velocity within the ship’s propeller jet is the initial step to investigate the scouring made by the propeller jet. Albertson et al. (1950) suggested the investigation of a submerged jet can be undertaken through observation of the plain water jet from an orifice. The plain water jet investigation of Albertson et al. (1950) was based on the axial momentum theory. This has been the basis of all subsequent work with propeller jets. In reality, the velocity characteristic of a ship’s propeller jet is more complicated than a plain water jet. Fuehrer and Römisch (1977), Blaauw and van de Kaa (1978), Berger et al. (1981), Verhey (1983) and Hamill (1987) have carried out investigations using physical model. Current paper reviews the state-of-art of the equations used to predict the time-averaged axial, tangential and radial components of velocity within the zone of flow establishment and the zone of established flow of a ship’s propeller jet. 相似文献
3.
4.
The purpose of the present study is to investigate the performance and three-dimensional flow fields in a water-jet pump. TASCflow is employed to simulate the rotator-stator coupling flow field. A standard k-ε turbulence model combined with standard wall functions is used. In order to investigate the effect of a rear stator on flow fields, the flows in two water-jet pumps with and without a rear stator are studied. Computational fluid dynamics (CFD)-predicted overall performances are in good agreement with the experimental results. Then the flow fields, such as the pressure distribution on the blade surfaces, and the axial and tangential velocity distribution, especially the radial loading distribution, are investigated at different flow rates. In addition, the effects of a rear stator and different spacings between the rotor and the stator on the overall performance and the flow fields of the water-jet pump are also investigated. 相似文献
5.
The paper analyses the flow around a marine propeller ducted with a so-called decelerating nozzle both through the axial momentum theory and the nonlinear semi-analytical actuator disk model. While the well-known and widely diffused axial momentum theory can be successfully employed only to qualitatively investigate the characteristics of the flow around a ducted propeller, the nonlinear and semi-analytical method can instead evaluate the thrust exerted by the duct for different values of the overall thrust and advance coefficients. There are several advantages characterising the more advanced actuator disk method. Specifically, the wake convergence and rotation may be fully taken into account, the shape of the duct and of the radial distribution of the load can be of general type, and, finally, the mutual interaction between the duct and the propeller may be readily dealt with. The methods are employed to investigate the effects of the decelerating nozzle on the efficiency and on the cavitation condition of the propeller. In particular, the influence of some duct geometrical parameters on the device performance is thoroughly analysed providing useful insights on the operating principles of this kind of propulsive systems. 相似文献
6.
The paper presents the results of the application of a new hybrid URANS-LES method for the investigations of the ship wake behind the tanker KVLCC2. The switching between URANS and LES models is based on the ratio between the turbulence scale and the cell size of the mesh. Ship resistance, fields of the axial velocity and turbulent kinetic energy in the propeller plane are calculated and compared with measurements. Much attention is paid to the analysis of the unsteady velocities, their PDF distributions and spectra. Numerical analysis shows that the instantaneous velocities deviate substantially from their mean values which are usually used as the estimated velocities in modern engineering methodologies. The thrust variation in the unsteady wake is more than twice as large as that in the time averaged (frozen) wake. The results of the present study point out that the unsteadiness in the wake behind full ships can be very large and should be taken into account when propulsion and unsteady loadings are determined. 相似文献
7.
Accurate propeller shaft speed controllers can be designed by using nonlinear control theory and feedback from the axial water velocity in the propeller disc. In this paper, an output feedback controller is derived, reconstructing the axial flow velocity from vehicle speed measurements, using a three-state model of propeller shaft speed, forward (surge) speed of the vehicle, and the axial flow velocity. Lyapunov stability theory is used to prove that a nonlinear observer combined with an output feedback integral controller provide exponential stability. The output feedback controller compensates for variations in thrust due to time variations in advance speed. This is a major problem when applying conventional vehicle-propeller control systems. The proposed controller is simulated for an underwater vehicle equipped with a single propeller. The simulations demonstrate that the axial water velocity can be estimated with good accuracy. In addition, the output feedback integral controller shows superior performance and robustness compared to a conventional shaft speed controller 相似文献
8.
A two-frame particle image velocimetry (PIV) technique is used to investigate the wake characteristics behind a marine propeller with 4 blades at high Reynolds number. For each of 9 different blade phases from 0° to 80°, 150 instantaneous velocity fields are measured. They are ensemble averaged to study the spatial evolution of the propeller wake in the region ranging from the trailing edge to one propeller diameter (D) downstream location. The phase-averaged mean velocity shows that the trailing vorticity is related to radial velocity jump, and the viscous wake is affected by boundary layers developed on the blade surfaces and centrifugal force. Both Galilean decomposition method and vortex identification method using swirling strength calculation are very useful for the study of vortex behaviors in the propeller wake region. The slipstream contraction occurs in the near-wake region up to about X/D=0.53 downstream. Thereafter, unstable oscillation occurs because of the reduction of interaction between the tip vortex and the wake sheet behind the maximum contraction point. 相似文献
9.
The instantaneous turbulent velocity field created by the breaking of spilling regular waves on a plane slope was measured in a plane running parallel to the slope using particle image velocimetry. The measurement plane was located at a height of about 1 mm above the bed. The measurement area encompassed the region where the large eddies generated at incipient wave breaking impinged on the bottom inside the surf zone. A total of 30 trials were conducted under identical experimental conditions. In each trial, six consecutive wave cycles were recorded. The measured velocity fields were separated into a mean flow and a turbulence component by ensemble averaging. The instantaneous turbulent velocity fields were analyzed to determine the occurrence frequency, location, geometry and evolution of the large eddies, and their contributions to instantaneous shear stresses, turbulent kinetic energy and turbulence energy fluxes. The motion of single glass spheres along the bed was also investigated. The two-phase flow measurements showed that the velocity and displacement of large solid particles on a smooth bed were significantly affected by the magnitude and direction of turbulence velocities. Overall, this study has examined the kinematic and dynamic properties of large eddies impinging on the bed and the interaction of these large-scale turbulent flow structures with the mean flow. The study has also highlighted the important role of large eddies in sediment transport. 相似文献
10.
In this study, the flow around the pod unit is analysed and the performance characteristics of the propeller on the pod are investigated. The main objective of the present work is to further improve the original numerical method developed before for the prediction of performance of podded propellers and to further validate the earlier developed numerical model with a specific emphasis on the hydrodynamic interaction amongst the propulsor components. While in the earlier numerical method, the axial induced velocities by pod and strut parts were included into the calculations on the propeller disc plane, in the present method the tangential induced velocities on the propeller disc plane are included in the calculations as well. The flow domain around the podded propeller is mainly divided into three parts; the axisymmetric pod part, the strut part and the propeller part. While the pod and strut parts are modelled by a low-order boundary element method (BEM), the propeller is represented by a vortex lattice method (VLM). Coupling of the BEM and the VLM is carried out in an iterative manner to incorporate the effect of the pod on the propeller, and vice versa. The present numerical method is applied to two different podded propellers with zero yaw angles in order to compare the results with those of experimental measurements. The present numerical method is also validated in the case of 15° of yaw angle for a podded propulsor. The effect of pod and strut on the propeller and vice versa are discussed. 相似文献
11.
对挡潮闸枢纽中矩形中孔、底孔鱼道中紊流结构进行了较为系统的试验研究,并做了放鱼试验。选择了一种鱼类偏爱流速所对应的流量作为典型流量,考虑了不同的孔口位置(中孔和底孔),用声学多普勒测速仪(ADV)量测了测点的三维瞬时流速及流向,分析了矩形孔口鱼道的三维时均流速分布特征、断面最大流速沿程变化规律、流速矢量场、紊动强度分布及雷诺应力分布。此外,还通过放鱼试验,利用在鱼体植入T形标签和高速摄影机观察了过鱼对象对中孔、底孔的反应情况,分析了过鱼对象与矩形孔口鱼道紊流结构的关系。试验结果表明:水流经中孔形成三维紊动自由射流,经底孔形成三维壁面射流,中孔纵向流速呈高斯分布,而底孔纵向流速则近似为高斯分布,流速由孔口向两侧逐渐减小;中孔和底孔横向流速在位于孔口范围内的纵剖面上沿程减小,孔口之外则变化较小;中孔和底孔垂向流速分布特征表现为在铅垂方向上均存在旋涡;在中孔水平面和纵剖面上,纵向最大流速均沿程衰减;中孔和底孔情形孔口处紊动强度和雷诺应力比非孔口处大得多,而非孔口处不同水深平面上紊动强度和雷诺应力变化趋于平缓;过鱼对象喜爱在紊动强度分布的峰值区和雷诺应力较大变幅区溯游。 相似文献
12.
The hydrodynamic performance of a hybrid CRP pod propulsion system was studied by RANS method with SST turbulence model and sliding mesh. The effect of axial spacing on the hydrodynamic performance of the hybrid CRP pod propulsion system was investigated numerically and experimentally. It shows that RANS with the sliding mesh method and SST turbulence model predicts accurately the hydrodynamic performance of the hybrid CRP pod propulsion system. The axial spacing has little influence on the hydrodynamic performance of the forward propeller, but great influence on that of the pod unit. Thrust coefficient of the pod unit declines with the increase of the axial spacing, but the trend becomes weaker, and the decreasing amplitude at the lower advance coefficient is larger than that at the higher advance coefficient. The thrust coefficient and open water efficiency of the hybrid CRP pod propulsion system decrease with the increase of the axial spacing, while the torque coefficient keeps almost constant. On this basis, the design principle of axial spacing of the hybrid CRP pod propulsion system was proposed. 相似文献
13.
The horizontal movement of inertial particles in the intensive vortices, where the centrifugal force can be substantially higher than the gravity, is studied analytically. A similar problem was studied earlier for small (Stokes) particles at low Reynolds number, which allow one to be limited to the linear resistance law. It is shown that the previous results to a great extent can be extrapolated to the case of considerably heavier particles (e.g., water droplets with a diameter up to 1 mm at Reynolds numbers up to 103). The nonlinear nature of the resistance, i.e., its dependence on the particle velocity relative to the medium, should be taken into account for such particles. Some general laws are established for particle dynamics. In particular, their tangential velocity is close to the velocity of the medium, while the radial velocity is substantially lower (it is close on the order of magnitude to the geometric mean of the particle tangential velocity and the difference between the latter and the tangential velocity of the medium). The limits of applicability of the results are found, i.e., the restrictions to the size and mass/density of particles. 相似文献
14.
The hydrodynamic characteristics of a marine propeller operating in oblique inflow are investigated by using CFD method. Two propellers with different geometries are selected as the study subjects. RANS simulation is carried out for the propellers working at a wide range of advance coefficients and incidence angles. The effects of axial inflow and lateral inflow are demonstrated with the hydrodynamic force on the propeller under different working conditions. Based on the obtained flow field details, the hydrodynamic mechanism of propeller operating in oblique inflow is analyzed further. The trailing vortex wake of propeller is highly affected by the lateral inflow, resulting in the deflected development path and the circumferentially non-uniform structure, as well as the enhanced axial velocity in slipstream. Different flow patterns are observed on the propeller blade with the variation of circumferential position. Combined with the computed hydrodynamic forces and pressure distribution on propeller, the mechanism resulting in the increase of propulsive loads and the generation of propeller side force is explored. Finally, a systematic analysis is carried out for the propulsive loads and propeller side force as a function of axial and lateral advance coefficients. The major terms that play a dominant role in the modeling of propulsive loads and propeller side force are determined through the sensitivity analysis. This study provides a deeper insight into the hydrodynamic characteristics of propeller operating in oblique inflow, which is useful to the investigation of propeller performance during ship maneuvers. 相似文献
15.
在Fudide-Krylov假设条件下,依据船舶分离建模理论在固定和运动坐标系中计算海面船只六自由度运动数学模型。主要包括:对风、浪、流的单独建模并进行矢量叠加,并在风浪流联合作用下对船舶六自由度运动构建简化的数学建模,完成实时仿真。基于Simulink和V-Realm Builder虚拟现实技术创建船舶运动模型、海洋表面环境及船只的几何模型,对船舶六自由度运动进行视景仿真,给出了有风无浪、有浪无风和风浪兼有三种情况下船只旋回路径和船舶运动轨迹。在VR视景浏览器中创建动态海面上船舶六自由度运动模型,不仅易于实现且结果逼真。得到的结果为进一步研究动态船只目标声散射特性的精确预报提供基础。 相似文献
16.
Marine cycloidal propulsion system is efficient in maneuvering ships like tugs, ferries, etc. It is capable of vectoring thrust in all direction in a horizontal plane. When used in pair, the system enables a vessel to perform maneuvers like moving sideways, perform rotation about a point, i.e. turning diameter of its own length, etc. In this system, the propeller blades have to change their angle of attack at different angular position of the disc. Due to this reason, the inflow velocity vector to propeller blades changes continuously. The propeller blade oscillates about a vertical axis passing through its body and at the same time rotates about a point. Superposed on these motions is the dynamics of the ship on which the propulsion system is installed. This results in a formidable and challenging hydrodynamics problem. Each of the propeller blade sections could be considered as an aerofoil operating in combined heave and pitch oscillation mode. Due to the constantly varying inflow velocity, the hydrodynamic flow is unsteady. The unsteady hydrodynamic flow is simulated by incorporating the effect of shed vortices at different time instant behind the trailing edge. Due to the kinematics of the problem, the blade is subjected to higher structural deformation and vibration load. The structural deformation and vibration when coupled with the hydrodynamic loading add another level of complexity to the problem. In this paper, the variation of hydrodynamic load on the propeller blade due to steady and unsteady flow is compared. We also model the structural dynamics of the blade and study its effect on the hydrodynamic loading. Finally, we couple the structural dynamics with hydrodynamics loading and study its influence on the propeller blade for different operating regimes. 相似文献
17.
基于重叠网格模型,通过非定常RANS数值模拟与结果分析,研究了块状冰的尺寸、轴向运动和冰桨位置对螺旋桨水动力性能的影响。选用切割体网格绘制整体静止计算域的背景网格,之后结合棱柱层网格绘制螺旋桨子计算域和冰块子计算域的重叠网格,不同的计算域之间通过两者的重叠区域进行数据传递和插值。计算结果显示,当冰块固定在桨前时,螺旋桨产生的非定常推力和扭矩均以叶频为基频进行周期性变化,而且两者的时间平均值和振幅主要受冰块在螺旋桨盘面内的轴向投影面积、冰桨轴向位置和冰桨水平位置的影响;当冰块在桨前沿轴向匀速靠近螺旋桨时,冰桨轴向距离逐渐变小,冰桨周向相对位置发生周期性的变化,使得推力和扭矩两者均以叶频振荡,而且两者的时间平均值和振幅均随着冰桨轴向距离减小而增加。 相似文献
18.
Flow characteristics of the hull wake behind a container ship model were investigated under different loading conditions (design and ballast loadings) by employing the particle image velocimetry (PIV) technique. Measurements were made at four transverse locations and two longitudinal planes for three Reynolds numbers (Re) (=U0Lpp/ν, where U0 is the freestream velocity, Lpp is the length between two perpendiculars of the ship model and ν is the kinematic viscosity) of 5.08×105, 7.60×105, and 1.01×106. It was observed that symmetric, large-scale, longitudinal counter-rotating vortices (with respect to centerline) of nearly the same strength were formed in the near wake. For the ballast-loading condition, the vortices appear at propeller plane below the propeller-boss. The vortex center exhibits a significant upward shift near the propeller-boss as the Reynolds number increase, and as the flow moves downstream. Under the design-loading condition, the vortices first appear at a further downstream location than that for the ballast-loading condition above the propeller-boss. This difference in the flow structure can significantly change the inflow conditions to the propeller blades, such as the streamwise mean velocity profiles and turbulence intensity distributions at the propeller plane. In particular, under the ballast-loading condition, asymmetric inflow may weaken the propulsion and cavitation performance of the marine propeller. 相似文献
19.
V. I. Bukreev 《Oceanology》2013,53(1):110-118
A technique and some results of laboratory experiments, in which the densification during mixing of the salt water masses with the same initial densities occurs, are presented. A graphical interpretation of the densification during mixing and an empirical formula describing the dependence of the water density on temperature and concentration of the dissolved salt NaCl at atmospheric pressure are given. Examples of spreading of the initially horizontal, inclined and vertical round jets as well as a vertical plane jet are considered. In all examples, the jet submerged up to the bottom of the experimental setup. It was found that the submergence velocity was on the order of 0.5 ± 0.1 cm/s. The influence of the double diffusion on the jet submergence velocity in the salt water is discussed. 相似文献
20.
O. A. Druzhinin 《Izvestiya Atmospheric and Oceanic Physics》2008,44(6):768-780
The onset of a three-dimensional jet flow in a stratified fluid is studied with the aid of a direct numerical simulation. An initially cylindrical jet with a Gaussian velocity profile is considered in a fluid with stable linear density stratification. The results indicate that, if an initial small perturbation of the velocity field has a wide spectrum, an exponential growth of the isolated quasi-two-dimensional mode occurs and its spectral maximum is shifted toward smaller wave numbers in comparison with the maximum of the helical mode of the instability of a nonstratified jet. The growth rate is proportional to Ri0.5, where Ri is the global Richardson number. The onset of the instability leads to the formation of the flow’s vortex structure, which consists of a collection of different-polarity quasi-two-dimensional vortices located in a horizontal plane near the longitudinal axis of the jet. At sufficiently long times (Nt > 100, where N is the buoyancy frequency and t is time), the growth of instability reaches the saturation stage and further fluctuations in velocity and density decay under the effect of viscous diffusion. At this stage, the flow becomes self-similar and the time dependences of the transverse and vertical widths of the jet are consistent with the asymptotic behaviors of integral parameters of the flow that are observed experimentally in the far stratified wake. The results suggest that the onset of the instability of a quasitwo-dimensional mode can play the determining role in the dynamics of flow in the far stratified wake. 相似文献