Simplified hydrodynamic models for the analysis of marine propellers in a wake-field

This paper presents a comparison among different hydrodynamic models for the analysis of the unsteady loads delivered by a marine propeller working in an axial, non-uniform inflow. Specifically, for a propeller subjected to a wake-field dominated by local high-frequency changes in space, the unsteady hydroloads predicted by the Nakatake formulation are compared with those given by the Theodorsen and Sears theories, respectively. Drawbacks and potentialities of these approaches are highlighted to assess a computationally efficient hydrodynamic solver for the analysis of operating conditions where propeller blades are significantly perturbed by a multi-harmonic onset-flow. Guidelines coming from this investigation may drive the choice of a fast and reliable unsteady propeller modeling that represents a good trade-off between accuracy of simulation and cost of computation within implementation in Computational Fluid Dynamics （CFD） solvers. The hydrodynamic formulations herein proposed are validated through numerical comparisons with the （accurate but computationally expensive） propeller loads predicted by a fully 3-D panel-method Boundary Element Method （BEM） solver, suited for the analysis of propellers operating in a complex hydrodynamic environment.     

An integral calculation approach for numerical simulation of cavitating flow around a marine propeller behind the ship hull

In this paper, the unsteady cavitating turbulent flow around a marine propeller is simulated based on the unsteady Reynolds averaged Navier-Stokes(URANS) with emphasis on the hull-propeller interaction by an integral calculation approach, which means the propeller and hull are treated as a whole when the cavitating flow is calculated. The whole calculational domain is split to an inner rotating domain containing a propeller and an outer domain containing a hull. And the two split sections are connected together in ANSYS CFX by using the GGI interfaces and the transient rotor stator frame change/mixing model. The alternate rotation model is employed for the advection term in the momentum equations in order to reduce the numerical error. Comparison of predictions with measurements shows that the propeller thrust coefficient can be predicted satisfactorily. The unsteady cavitating flow around the propeller behind the ship hull wake shows quasi-periodic features including cavity inception, growth and shrinking. These features are effectively reproduced in the simulations which compare well to available experimental data. In addition, significant pressure fluctuations on the ship hull surface induced by the unsteady propeller cavitation are compared with experimental data at monitoring points on the hull surface. The predicted amplitudes of the first components corresponding to the first blade passing frequencies match well with the experimental data. The maximum error between the predictions and the experimental data for the pressure pulsations is around 8%, which is acceptable in most engineering applications.     

NUMERICAL PREDICTION OF PROPELLER EXCITED ACOUSTIC RESPONSE OF SUBMARINE STRUCTURE BASED ON CFD,FEM AND BEM

A mesh-less Refined Integral Algorithm (RIA) of Boundary Element Method (BEM) is proposed to accurately solve the Helmholtz Integral Equation (HIE).The convergence behavior and the practicability of the method are validated.Computational Fluid Dynamics (CFD),Finite Element Method (FEM) and RIA are used to predict the propeller excited underwater noise of the submarine hull structure.Firstly the propeller and submarine’s flows are independently validated,then the self propulsion of the "submarine+propeller" system is simulated via CFD and the balanced point of the system is determined as well as the self propulsion factors.Secondly,the transient response of the "submarine+ propeller" system is analyzed at the balanced point,and the propeller thrust and torque excitations are calculated.Thirdly the thrust and the torque excitations of the propeller are loaded on the submarine,respectively,to calculate the acoustic response,and the sound power and the main peak frequencies are obtained.Results show that:(1) the thrust mainly excites the submarine axial mode and the high frequency area appears at the two conical-type ends,while the torque mainly excites the circumferential mode and the high frequency area appears at the broadside of the cylindrical section,but with rather smaller sound power and radiation efficiency than the former,(2) the main sound source appears at BPF and 2BPF and comes from the harmonic propeller excitations.So,the main attention should be paid on the thrust excitation control for the sound reduction of the propeller excited submarine structure.     

高负荷螺旋桨水动力性能试验研究

以某大型集装箱船高负荷螺旋桨为研究对象,分别采用大侧斜、反弯扭叶片和毂帽鳍等技术进行螺旋桨优化设计,以改善螺旋桨的空泡和水动力性能.设计了5型螺旋桨,分别在空泡水筒进行了模拟伴流场中的空泡和激振力试验,并在拖曳水池进行了敞水试验.试验结果表明,采用大侧斜可有效减小螺旋桨诱导船艉激振力;反弯扭叶片螺旋桨空泡性能较好,有较低的螺旋桨诱导船艉激振力水平;桨毂帽鳍可改善毂涡空泡,模型试验状态下可提高推进效率2%左右.     

液力变矩器三元流场计算的一种近似方法

本文提出了一种在两类相对流面基础上的液力变矩器三元流场计算的近似方法，建立了求解的数学模型并给出了计算方法和步骤。用这一方法计算了YB355-2型液力变矩器三元流场分布，并将计算结果与试验数据进行了比较和分析。计算结果与实际相吻合，能满足一定的精度，该方法在透平机械流场计算中也有较高的应用价值。     

A PRACTICAL METHOD TO PREDICT FLUCTUATING PRESURE INDUCED BY A PROPELLER OPERATING IN WAKE FIELD AND ITS VALIDATION

1.INTRODUCTIONThepredictionoffluctuatingpressurecausedbyapropellerisanimportantsubjectforevaluatingvibrationperformanceduringshipdesignstage.Inthispaper,apracticalmethodandaprogramareintroducedanddescribedinthreeparts.Inthefirstpart,aquasi--steadypropellerliftinglinetechniqueplusliftingsurfaceandviscouscorrectionsisusedtodeterminekinematicsparameters.Thecurvedflowofthewakeisconsideredasanequivalentaddedcambertobladesection.Inthesecondpart,cavityextentonbladeatdifferentangularpositionshasb…     

PREDICTION OF LOADING DISTRIBUTION AND HYDRODYNAMIC MEASUREMENTS FOR PROPELLER BLADES IN A RIM DRIVEN THRU-STER

This article presents an approach which employs a commercial Reynolds-Averaged Navier-Stokes(RANS)solver to predict the steady wake field and loading distributions for a rim driven thruster.Four different cases of propeller blades are chosen to be calculated with the presented method.The propeller blade radial circulation and chordwise circulation density distributions are analyzed.The maximum radial circulation is found at the blade tip,which is different from conventional shaft driven propeller.The numerical results indicate that there is no tip leakage vortex in rim driven propulors.But there exist the tip joint vortex and the root region vortex.Bollard characteristics are calculated by taking rim surface effect into account.From the predicted results the second case in this paper is selected as the final one to perform hydrodynamic experiment.The calculation results with empirical rim surface corrections are compared with the measurement.It shows that the developed numerical method can well predict hydrodynamic performances of the rim driven thruster.     

UNSTEADY PROPELLER SURFACE PRESSURE PREDICTION WITH A POTENTIAL BASED PANEL METHOD

ＵＮＳＴＥＡＤＹＰＲＯＰＥＬＬＥＲＳＵＲＦＡＣＥＰＲＥＤＩＣＴＩＯＮＷＩＴＨＡＰＯＴＥＮＴＩＡＬＢＡＳＥＤＰＡＮＥＬＭＥＴＨＯＤ￥ＣｈｅｎＪｉａ－ｄｏｎｇ（ＣｈｉｎａＳｈｉｐＳｃｉｅｎｔｉｆｉｃＲｅｓｅａｒｃｈＣｅｎｔｅｒ，Ｂｏｘ１１６，Ｗｕｘｉ２１...     

船舶螺旋桨周围粘流场数值预报与流场分析

本文叙述了通过直接求解雷诺平均应力方程（ＲＡＮＳ）来获得船舶螺旋桨粘流场数值解的方法与数值求解步骤，该方法采用非交错网格系统，利用幂函数格式离散动量方程，预报－校正方法求解速度－压力耦合问题，应用Ｂａｌｄｗｉｎ－Ｌｏｍａｘ代数湍流模式求解雷诺应力项使方程组封闭，以此来获得螺旋桨粘流场，为了验证数值方法的稳定性和可靠性，文中以ＤＴＲＣ４１１９桨为算例，对螺旋桨粘流场进行了数值求解，通过对计算结果的分     

Numerical prediction of effective wake field for a submarine based on a hybrid approach and an RBF interpolation

A hybrid approach coupled with a surface panel method for the propeller and a Reynolds averaged Navier-Stokes(RANS) model for the hull with the propeller body forces are presented for predicting the self-propulsion performance and the effective wake field of underwater vehicles. To achieve a high accuracy and simplicity, a radial basis function(RBF) based approach is proposed for mapping the force field from the blade surface panels to the RANS model. The effective wake field is evaluated in two ways, i.e., by extrapolation from the flat planes upstream of the propeller disk, and by direct computation in a curved surface upstream of and parallel to the blade leading edges. The hull-propeller system of a real propeller geometry is further simulated with the sliding mesh model to numerically verify the hybrid approach. Numerical simulations are conducted for the fully appended SUBOFF submarine model. The high accuracy of the RBF-based interpolation scheme is confirmed, and the effective wake fraction predicted by the hybrid approach is found consistent with that obtained by the sliding mesh model. The effective wake fractions predicted by the two methods are, respectively, 4.6% and 3% larger than the nominal one.     

NUMERICAL ANALYSIS FOR CIRCULATION DISTRIBUTION OF PROPELLER BLADE

A process for numerical analysis of radial circulation distribution of propeller blade is proposed and presented. It is based on the results of numerical simulation of the velocity field around propeller blades and in the wake. The well-known traditional method using tangential velocity data in the wake and applying Stockes's theorem was also examined in the investigation. The results from two approaches are compared with each other. It is found that if the traditional way is utilized, in many cases an unexpected “hump” appears in the circulation distribution at certain outer radius. The authors calculated the circulations directly around blade sections, and it is referred as direct method. The unexpected hump of the circulation distribution disappears in the results of direct method. This article also discusses the reasons of the appearance of the unexpected hump in traditional approach. The direct method is proposed to have a potential in analyzing or verifying the radial road distribution for designed propeller and the numerical analysis instead of experimental validation for circulation distribution can be as a tool in the propeller design process.     

The method to control the submarine horseshoe vortex by breaking the vortex core

The quality of the inflow across the propeller is closely related with the hydrodynamic performance and the noise characteristics of the propeller. For a submarine, with a horseshoe vortex generated at the junction of the main body and the appendages, the submarine wake is dominated by a kind of highly non-uniform flow field, which has an adverse effect on the performance of the submarine propeller. In order to control the horseshoe vortex and improve the quality of the submarine wake, the flow field around a submarine model is simulated by the detached eddies simulation （DES） method, and the vortex configuration is displayed using the second invariant of the velocity derivative tensor. The state and the transition process of the horseshoe vortex are analyzed, then a modified method to break the vortex core by a vortex baffle is proposed. The flow numerical simulation is carried out to study the effect of this method. Numerical simulations show that, with the breakdown of the vortex core, many unstable vortices are shed and the energy of the horseshoe vortex is dissipated quickly, and the uniformity of the submarine wake is improved. The submarine wake test in a wind tunnel has verified the effect of the method to control the horseshoe vortex. The vortex baffle can improve the wake uniformity in cases of high Reynolds numbers as well, and it does not have adverse effects on the maneuverability and the speed ability of the submarine.     

An iterative Rankine boundary element method for wave diffraction of a ship with forward speed

A 3-D time-domain seakeeping analysis tool has been newly developed by using a higher-order boundary element method with the Rankine source as the kernel function. An iterative time-marching scheme for updating both kinematic and dynamic free-surface boundary conditions is adopted for achieving numerical accuracy and stability. A rectangular computational domain moving with the mean speed of ship is introduced. A damping beach at the outer portion of the truncated free surface is installed for satisfying the radiation condition. After numerical convergence checked, the diffraction unsteady problem of a Wigley hull traveling with a constant forward speed in waves is studied. Extensive results including wave exciting forces, wave patterns and pressure distributions on the hull are presented to validate the efficiency and accuracy of the proposed 3-D time-domain iterative Rankine BEM approach. Computed results are compared to be in good agreement with the corresponding experimental data and other published numerical solutions.     

EXPERIMENTAL STUDY OF EFFECTS OF AIR CONTENT ON CAVITATION AND PRESSURE FLUCTUATIONS

This article studies the effects of air content on propeller cavitation and pressure fluctuations. The cavitation is observed while the pressure fluctuations on the hull are measured. When adjusting the air content, the sheet cavitation range does not change distinctly, but the pressure fluctuations see obvious differences. The amplitudes of the pressure fluctuations increase with the decrease of the air content. The results indicate that the air content has little effect on the sheet cavitation range but has an important effect on the bubble cavitation and the tip vortex cavitation. When the air content decreases, the water tensile force increases, which results in the instability of the bubble cavitation and the tip vortex cavitation and the increase of the pressure fluctuations. To minimize the scale effects, the experiments should be run at a high Reynolds number with a high nuclei content. The high Reynolds number is often realized by increasing the flow velocity and the propeller rotation speed, and the high nuclei content is often made by increasing the dissolved air content.     

鱼尾舵水动力性能研究

本文提出了一种计算带制流板的鱼尾舵在螺旋桨流中水动力性能的方法。舵的水动力及其对周围流场的影响面元法计算，螺旋桨性能及尾流场通过无了叶数的简易螺旋桨理论来预估，而舵上下制流板的影响则应用升力面理论涡格法来计算。     

PRESSURE TRANSIENT ANALYSIS OF HETEROGENOUS RESERVOIRS WITH IMPERMEABILITY BARRIER USING PERTURBATION BOUNDARY ELEMENT METHOD

The transient flow mathematical model of arbitrary shaped heterogeneous reservoirs with impermeability barrier is proposed in this paper. In order to establish this model, the perturbation method is employed and the solution of model is expanded into a series in powers of perturbation parameter. By using the Boundary Element Method (BEM) and Duhamel principle, wellbore pressure with effects of skins and wellbore storage is obtained. The type curves are plotted and analyzed considering effects of heterogeneity, arbitrary shape and impermeable barriers. Finally, the results obtained by perturbation boundary element method is compared with the analytical solution and is available for the transient pressure analysis of arbitrary shaped reservoirs.     

BLADE SECTION DESIGN OF MARINE PROPELLERS WITH MAXIMUM CAVITATION INCEPTION SPEED

Kuiper and Jessup(1993)developed a design method for propellers in a wake based on the Eppler foil design method.The optimized section is transformed into the three-dimensional propeller flow using the approach of the effective blade sections.Effective blade sections are two-dimensional sections in two-dimensional flow which have the same chordwise loading distribution as the three-dimensional blade sections of a propeller.However,the design procedure is laborious in two aspects:finding an optimum blade section using the Eppler program requires much skill of the designer,and transforming the two-dimensional blade section into a propeller blade section in three-dimensional flow is complex.In this work,these two problems were coped with.A blade section design procedure was presented using an optimization technique and an alternative procedure for the effective blade section is developed using a lifting surface design method.To validate the method a benchmark model of a naval ship was used.This benchmark model was extended by new appendices and a reference propeller,and designed using conventional design methods.This reference propeller was optimized using the new design procedure and model tests were carried out.Special attention was given to the data of the model and the reference propeller,to make the configuration suitable for the Reynolds-Averaged Navier-Stokes(RANS)calculations.     

NUMERICAL PREDICTION OF BLADE FREQUENCY NOISE OF CAVITA- TING PROPELLER

The blade frequency noise of a cavitating propeller in a uniform flow is analyzed in the time domain. The unsteady loading (of a dipole source) and the sheet cavity volume (of a monopole source) on the propeller surface are calculated by a potential-based surface panel method. Then the time-dependent pressure and the cavity volume data are used as the input for the Fowcs Williams-Hawkings formulation to predict the acoustics pressure. The integration of the noise source is performed over the true blade surface rather than the ideal blade surface without thickness. The noise characteristics of the cavitating propeller are discussed. With the sheet cavitation, the thickness (cavitation) noise is larger than the loading noise and is the dominant noise source.The noise directivity is not as clear as that of the noise under a non-cavitation condition. The cavitation noise is attenuated mores lowly than the non-cavitation noise.     

A NEW NUMERICAL WAVE FLUME COMBINING THE 0-1 TYPE BEM AND THE VOF METHOD

A new coupling numerical wave model, based on both the Boundary Element Method (BEM) and the Volume Of Fluid (VOF) method, is established by taking advantages of the both methods to solve the wave-structure interaction problems. In this model, the wave transformation in front of structures is calculated by the 0-1 type BEM, and the intense wave motions near the structures are calculated by the VOF method. In this paper, the characteristics of the BEM and the VOF method are discussed first, and then the coupling treatments are described in detail. In the end, the accuracy and the validity of the coupling model are examined by comparing the numerical results with experiment results and other numerical results available for the interactions between regular waves with a monolayer horizontal plate.     

PREDICTION OF HYDRODYNAMIC PERFORMANCE OF THE FLAP RUDDER

1.　INTRODUCTIONAs an unconventional type of rudder,the flap rudder can enhance the lift force,improve the hydrodynamic performance and delay the occurrence of separation comparedwith normal rudders.Therefore flap rudders have been used on ships in many cases.In1 968,Kato etal.did the experimental researches on flap rudder in open water[1 ] .In 1 992 ,Kose et al.carried out tests to study the hydrodynamic performance of flap rudder in openwater and behind a propeller[2 ] .The researches …