Podded Propulsor Research Articles

A surface panel method for the analysis of hybrid contra-rotating shaft pod propulsor

The present work is devoted to the hydrodynamic performance prediction of the hybrid contra-rotating shaft pod (HCRSP) propulsors. The HCRSP propulsor is divided into two parts, a single forward propeller and a podded propulsor. For the podded propulsor, an unsteady surface panel method is developed to analyze the open water performance; also the wake model is modified according to wake flow analysis. Then a podded propulsor in uniform flow is simulated by the unsteady surface panel method and the numerical results show a good agreement with experimental data. To improve the computational efficiency and simplify the analysis of HCRSP propulsor, we present a steady surface panel method that treats the propeller and pod unit as a single unit. Numerical results of the steady surface panel method also show good agreement with experimental data. Based on this study, an iterative steady surface panel method program for the HCRSP propulsor is presented and a model test is carried out in a cavitation tunnel to verify the numerical results.

Hydrodynamic Performance Analysis of Electric POD Propulsor Based on CFD Method

This paper analyzed the hydrodynamic performance of POD electric propulsor under the circumstance of different advance ratios. ANSYS-CFX solver was adopted to solve Narvier-Stokes equations with the standard SST turbulence model. The gridded 3-D model of Wageningen B4-70 propeller was implemented in this study as a thrust unit on the based both of push-POD and pull-POD propulsor. The accuracy of the numerical results of B4-70 hydrodynamic performance, including propeller thrust coefficient, torque coefficient and propeller efficiency, were verified by comparing with experimental results of open water test. Numerical analyses of hydrodynamic performance of pull-push POD propulsor were implemented respectively in one propeller revolution. The simulation results were rewarding references for designing electric propulsion system.

Prediction of manoeuvring abilities of 10000 DWT pod-driven coastal tanker

This paper aims to present a new approach in the prediction of manoeuvring abilities of pod-driven ships. A new mathematical model of motions based on MMG methodology was developed and a new type of description of forces acting on azimuth drives is presented. Captive model tests of medium-size coastal tanker and pod open water tests were carried out in CTO S.A. (Ship Design and Research Centre S.A.) to obtain hull hydrodynamic derivatives and pod propulsor hydrodynamic coefficients. Fast-time simulations were carried out and results were compared with free running model tests. Validation shows acceptable agreement between numerical and experimental results, i.e. confirms the usability of developed mathematical model to identify the trends in performance also for course unstable ship.

Experimental study on hydrodynamics of L-type podded propulsor in straight-ahead motion and off-design conditions

Experimental tests were conducted to evaluate the hydrodynamic performance of an L-type podded propulsor in straight-ahead motion and off-design conditions using an open-water measuring instrument developed by the authors for podded propulsors, a ship model towing tank, and under water particle image velocimetry (PIV) measurement systems. Under the three types of conditions, the main parameters of an L-type podded propulsor were measured, including the propeller thrust and torque, as well as the thrust, side force, and moment of the whole pod unit. In addition, the flow field on the section between the propeller and the strut was analyzed. Experimental results demonstrate that the dynamic azimuthing rate and direction and the turning direction affect the forces on the propeller and the whole pod unit. Forces are asymmetrically distributed between the left and right azimuthing directions because of the effect of propeller rotation. The findings of this study provide a foundation for further research on L-type podded propulsors.

A general equation for performance analysis of multi-component propulsor with propeller

An integral panel method (IPM) that treats the different components of multi-component propulsors as a whole is presented for efficient propulsor performance analysis. The IPM requires consider only one blade of the propeller in the performance analysis, which significantly reduces the number of computation grid. The control equations of the IPM are derived in detail for podded propulsors, contra-rotating propellers and hybrid contra-rotating shaft pod propulsors, and based on these derivations, a general control equation for multi-component propulsors with propeller is derived. Comparison between numerical results and experimental data show that the IPM provides good accuracy for the performance analysis of multi-component propulsors with propeller. In addition, the error sources of IPM are discussed, and the reasonableness of these errors is evaluated.

Performance aspects of podded propulsor in dynamic operating conditions

This paper presents various aspects of propulsive performance of a dynamic azimuthing puller podded propulsor in open water condition derived from an experimental research. A model podded propulsor was instrumented to measure thrust, torque and rotational speed of the propeller, three orthogonal fo rces and moments, azimuthing angle and azimuthing rate of the unit. Experiments were carried out in which the azimuthing angle was varied dynamically at multiple azimuthing rates and propeller rotational speeds for different advance speeds. The model podded propulsor was capable of azimuthing or yawing continuously in the range of −180° to +180°, 0° (straight-ahead) being the design operating condition and positive azimuthing means a counter-clockwise rotation. The performance coefficients of the propeller and the pod unit showed a strong dependence on the propeller loading and azimuthing angle. The open water characteristics were mostly irregular for the astern thrust conditions in the azimuthing angle beyond the normal inflow condition and the fluctuation of the magnitude of the performance coefficients showed a considerable range. The azimuthing rate showed little or no effect on the performance coefficients in the range of azimuthing angles examined. Both at high and moderate propeller loading conditions, an increase in the shaft speed resulted in slight change in the performance coefficients and the change was more obvious as the azimuthing angle was increased. The increase in the performance coefficients due to the increase of propeller shaft speed was not noticeably affected by the change of azimuthing rate.

Uncertainty of measurements of podded propulsor performance characteristics

One of the fundamental aspects of any physical experiment is the uncertainty or error limits of the measurement. Unfortunately, majority of published model experimental results do not come with the much needed error analysis. It is imperative that a fundamental and rigorous uncertainty assessment is carried out for all measurements, especially for measurements using a newly designed apparatus. This paper presents the uncertainty analysis methodology and results for a newly designed fully functional podded propulsor performance measurement apparatus. The measurements include propeller thrust, torque, rotation rate and advance speed as well as global forces and moments of a pod unit. The facility and measurement systems are briefly described, and detailed uncertainty assessment methodologies with examples for each measurement are provided with descriptions of bias and precision limits and total uncertainties. The generalized methodology can also be used for other relevant measurements.

Experimental Analysis of Podded Propulsor on Naval Vessel

This paper describes the effect of pod propulsor attachment to the existing Naval Vessel hull form which was designed for conventional propulsor in aspects of resistance and motion characteristics. These investigations were carried out on a 3.0 m model by experimental works in the towing tank 120m x 4m x 2.5m at the Marine Technology Centre (MTC), Universiti Teknologi Malaysia (UTM). The basis ship chosen for this study is Sealift class type MPCSS (Multi Purpose Command Support Ship). In this study, the design for the new pod propulsor is based on a proven design and scaled down to suit this type of hullform accordingly. This paper describes the resistance comparison between bare and podded hulls in calm water as well in waves. The seakeeping test for hull with and without pod in regular waves at service speed of 16.8 knots were carried out at wavelength to model length ratio, Lw/Lm between 0.2 and 1.2. The outcomes from this experimental works on hull with and without pod were compared.

Study on Propulsive Performance of Two Geometrically Similar Podded Propulsors

This paper presents the outcome of a research to evaluate the effect of size on the propulsive performance of podded propulsors in cavitating and non-cavitating open water conditions. Two cases are examined, namely: propeller-only case and pod-unit case. In the propeller-only case, a commercial propeller dynamometer is used to measure the thrust and torque of two propellers of different size at the four quadrants of propellers with varied shaft and flow speeds. Also, both propellers are tested at different tunnel pressure to study and compare the behaviour under similar cavitation conditions. In the pod-unit case, two geometrically similar but different sized pod-units are tested using two separate custom-made pod dynamometer systems in two towing tank facilities in straight-ahead and static azimuthing conditions. The study showed that the performance characteristics stabilize at lower Reynolds Number for the smaller propeller than the larger propeller. The propulsive performance of the two propellers was comparable in the four-quadrant experiments. Also, the experiments at the cavitating conditions showed that the cavitation characteristics of the two propellers were consistent at corresponding operating conditions. The experiment results of the two pod-units were also comparable for forces and moments in the three coordinate directions in the straight-ahead and static azimuthing conditions. A brief discussion on the uncertainty assessments for each of the measurements is also presented.

Numerical investigation of yaw angle effects on propulsive characteristics of podded propulsors

The present paper deals with the problems of yaw angle effects on podded propulsor performance. The study aims at providing insights on characteristics of podded propulsors in azimuthing condition. In this regard, a wide numerical simulation that concerned yaw angle effect measurement on podded propeller performance was performed. The Reynolds-Averaged Navier Stokes (RANS) based solver is used in order to study the variations of hydrodynamic characteristics of podded propulsor at various angles. At first, the propeller is analyzed in open water condition in absence of pod and strut. Next flow around pod and strut are simulated without effect of propellers. Finally, the whole unit is studied in zero yaw angle and azimuthing condition. Structured and unstructured mesh techniques are used for single propeller and podded propulsor. The performance curves of the propeller obtained by numerical method are compared and verified by the experimental results. The characteristic parameters including the torque and thrust of the propeller, the axial force and side force of unit are presented as function of velocity advance ratio and yaw angle. The results shows that the propeller thrust, torque and podded unit forces in azimuthing condition depend on velocity advance ratio and yaw angle.

Numerical investigation of yaw angle effects on propulsive characteristics of podded propulsors

The present paper deals with the problems of yaw angle effects on podded propulsor performance. The study aims at providing insights on characteristics of podded propulsors in azimuthing condition. In this regard, a wide numerical simulation that concerned yaw angle effect measurement on podded propeller performance was performed. The Reynolds-Averaged Navier Stokes (RANS) based solver is used in order to study the variations of hydrodynamic characteristics of podded propulsor at various angles. At first, the propeller is analyzed in open water condition in absence of pod and strut. Next flow around pod and strut are simulated without effect of propellers. Finally, the whole unit is studied in zero yaw angle and azimuthing condition. Structured and unstructured mesh techniques are used for single propeller and podded propulsor. The performance curves of the propeller obtained by numerical method are compared and verified by the experimental results. The characteristic parameters including the torque and thrust of the propeller, the axial force and side force of unit are presented as function of velocity advance ratio and yaw angle. The results shows that the propeller thrust, torque and podded unit forces in azimuthing condition depend on velocity advance ratio and yaw angle.

Design Method for Contra-Rotating Propellers for High-Speed Crafts: Revising the Original Lerbs Theory in a Modern Perspective

The main theoretical and numerical aspects of a design method for optimum contrar-rotating (CR) propellers for fast marine crafts are presented. We propose a reformulated version of a well-known design theory for contra-rotating propellers, by taking advantage of a new fully numerical algorithm for the calculation of the mutually induced velocities and introducing new features such as numerical lifting surface corrections, use of an integrated modern cavitation/strength criteria, a modified method to consider different numbers of blades among the two propellers, and to allow for an unloading function in the search for the optimal circulation distribution. The paper first introduces the main theoretical principles of the new methods and then discusses the influence of the main design parameters on an emblematic example of application in the case of counter rotating propellers for a pod propulsor designed for fast planing crafts (35 knots and above).

Manoeuvring performance of podded propulsors behind a ship

This study investigates the performance of podded propulsors in various operating conditions: open water and different ice conditions. The model used in this study is an icebreaker driven by twin-podded propulsors. Preliminary results from ice tank tests are presented. These include steering moment generated by the propulsors, thrust and torque of the propellers and the forces exerted on the hull at the location of the connection of the propulsors for different levels of ice and pack ice conditions, as well as in open water.

Recent Research on Podded Propulsor and Analysis of Key Technologies for Naval Vessels

Podded propulsor has been adapted for both commercial and naval vessels because of its unique features and excellent performance.Researches of pod propulsion system have been made by many naval sectors worldwide.This paper starts with an elaboration of the podded propulsor in terms of principle,structure,flaws and merits,and summarizes a range of typical products and the characteristics of the podded propulsor,with particular atte ntion to the analysis of recent researches and developments both domestic and abroad.Key technologies for naval application are then discussed,an overview of technical developments trends and future challenges is prese nted.

Gap Effect on Performance of Podded Propulsors in Straight-Ahead and Azimuthing Conditions

This paper presents results of an experimental study on the effect of gap distance on propulsive characteristics of puller and pusher podded propulsors in straight-ahead and static azimuthing open-water conditions. The gap distance is the axial distance between the rotating (propeller) and stationary (pod) parts of a podded propulsor. The propeller thrust and torque, unit forces, and moments in the three-coordinate directions of a model podded unit were measured using a custom-designed pod dynamometer in various operating conditions. The model propulsor was tested at the gap distances of 0.3%, 1%, and 2% of propeller diameter for a range of advance coefficients combined with the range of static azimuthing angles from +20_ to 20_ with a 10_ increment. The tests were conducted both in puller and pusher configurations in the same loading and azimuthing conditions. In the puller configuration, the gap distance did not have any noticeable effect on propeller torque in straight course condition, but had an effect in azimuthing conditions. The propeller thrust and efficiency were also influenced by the change of gap distance, and the effects were more pronounced at high azimuthing angles and high advance coefficients. For pusher configuration, however, the gap distance did not affect the propeller performance characteristics in straight-ahead and azimuthing conditions. Both in straight course and azimuthing conditions, the unit thrust and efficiency were not influenced by the gap distance in either puller or pusher configurations. The gap distance had a noticeable effect on unit transverse force and steering moment both in puller and pusher configurations, and both in straight course

Analysis of electric power demands of podded propulsors

The authors investigate and analyse the electric power operating conditions of podded electric motor drives, mainly in an attempt to explain the high failure rates of the electric components in pod propulsion installations.The analysis is based on simulations, where the pod torque demands are obtained from experimental results recently published in the literature. Thus, the same series of loading scenarios for an entire range of turning azimuth angles of a twin pod configuration are considered. The approach is rather generic as only nameplate data of the motor drives are required while, as the simulations focus on the electric motors, the rest of the ship electric system considered, including generator sets, is represented by a simplified network.Two different sets of simulations are considered, one comprising a synchronous ac motor drive and one with an asynchronous motor of similar rating. In all cases, it is shown that during manoeuvring in a certain range of azimuth angles significant overloading occurs exceeding the apparent power capacity of the motors.

Influence of fins on tractor-type podded propulsor performance

A mathematical model of podded propulsors was established in order to investigate the influence of fins. The hydrodynamic performance of podded propulsors with and without fins was calculated, with interactions between propellers and pods and fins derived by iterative calculation. The differential equation based on velocity potential was adopted and hyperboloidal panels were used to avoid gaps between surface panels. The Newton-Raphson iterative procedure was used on the trailing edge to meet the pressure Kutta condition. The velocity distribution was calculated with the Yanagizawa method to eliminate the singularity caused by use of the numerical differential. Comparisons of the performance of podded propulsors with different fins showed that the thrust of propeller in a podded propulsor with fins is greater. The resistance of the pod is also reduced because of the thrust of the fin. The hydrodynamic performance of a podded propulsor with two fins is found to be best, the performance of a podded propulsor with one fin is not as good as two fins, and the performance of the common type is the worst.

Unsteady hydromechanics of a steering podded propeller unit

Unsteady forces, torques and bending moments were predicted for a model podded propulsor unit at various azimuth angles. Predictions in time history include propeller shaft thrust, propulsor unit thrust, normal forces to the propeller shaft bearing, total forces acting on the propulsor unit, propeller shaft torque, blade spindle torque, in-plane and out-of-plane bending moments, and propulsor unit stock shaft torque and bending moments. Analysis was performed for averaged forces and their fluctuations as well. A time-domain unsteady multi-body panel method code, PROPELLA, was further developed for this prediction work. Predictions were compared with a set of time averaged in-house experimental data for a puller-type podded propulsor configuration in the first quadrant operation. Unsteady fluctuations of forces were predicted numerically. Analysis was made for the bending moment on propeller blades, shaft and the propulsor unit stock shaft for azimuth angles from 0° to 45°. It indicates that the magnitude and fluctuation of the forces are significant and they are essential for structural strength and design optimization. The predicted bending moment and global forces on the propulsor unit provide some useful data for ship maneuvering motion and simulation in off-design conditions.

Performance analysis of podded propulsors

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.

Numerical Simulation of a Podded Propulsor in Viscous Flow

A podded propulsor in viscous flow is numerically simulated in this article. The region of fluid is divided into efficient calculation grids. The pressure and viscous force of blades, pod and strut are obtained as functions of an advance coefficient. The steady result is used as a base in the unsteady simulation to obtain a solution more quickly. The distributions of the thrust and torque fluctuations of the key blade in one revolution are obtained. The calculation results from the mixing plane on steady conditions are compared with those obtained from the sliding mesh model on unsteady conditions. The User-Defined Function (UDF) method is used to simulate the influence of ship hull on the non-uniform wake of the propeller.