Propeller Disk Research Articles

Research of scale effect on propeller bearing force of a four-screw ship in oblique flow

To study the scale effect on propeller bearing forces in oblique flow, the propeller bearing forces of a fully appended four-screw ship that refers to a vessel propelled by four propellers are calculated and investigated. The findings reveal that scale effects in wake fields lead to an increase in the axial velocity of the propeller disk in the full-scale ship compared to the model, influenced by boundary layer flow. Moreover, asymmetric differences in the impact of oblique flow on the leeward and windward sides result in varied effects of positive and negative drift angles on the wakefield. The disparity in wake fields between inside and outside disks exacerbates unbalanced load distribution, with time-averaged loads showing an increase with drift angle for both propellers at full scale. Additionally, pronounced scale effects lead to variations in blade loads between model and full scale, with drift angles shifting the locations of single-blade load extremums. Unsteady bearing force components exhibit periodic fluctuations, with larger amplitudes at the blade passage frequency for the model scale propeller compared to the full scale, particularly evident under negative drift angles. The aforementioned findings can provide theoretical guidance for load balancing and vibration reduction of the four-screw ships.

Comparison Of Full-Scale PIV Measurements With CFD Simulations Of A Ship Propeller Inflow

Flow around the ship's hull and specifically the inflow conditions of the propeller(s) critically influence the propeller efficiency and cavitation behaviour. In a typical single-propeller vessel, the hull of the ship creates a velocity deficit in the top part of the propeller disk. This creates suitable conditions for cavitation, which is the main source of noise and vibration both inside the vessel as well as in the marine environment. Recently, two measurement campaigns were performed using a novel full-scale stereo-PIV device built to measure flows around vessels sailing at sea. During the first campaign, performed in one of MARIN's basins, the device was commissioned. The second campaign was performed during a sea trial; it resulted in propeller inflow data that can be used for validating CFD codes. The uncertainty of the PIV measurements was assessed using both campaigns. In the basin, uncertainty bias could be determined by comparing the PIV results with the carriage speed. At sea, the random part of uncertainty was determined by quantifying the standard deviation of the mean velocity for all three velocity components in the wake peak area of the propeller inflow. Overall, the uncertainty was found to be acceptably small, given the scale of the measurement and the necessity to work with naturally occurring seeding particles in the sea. CFD calculations of the same full-scale flow were performed using an in-house flow solver. The CFD results predicted the propeller RPM and the delivered power measured during the full-scale trial well, which gives confidence in the ability of CFD to predict ship trial performance. The comparison of the flow fields was good, with the PIV results demonstrating that full-scale PIV can be done reliably, and that the CFD is able to capture the major features of the flow in the considered area. For a large part of the flow field, the CFD was within the measurement uncertainty band. The wake peak was slightly underpredicted, which may be related to roughness effects on the boundary layer thickness.

Propeller Ceiling Effect in Forward Flight

The study extends the investigation of the fixed-pitch small-scale propeller in the ceiling effect to forward flight conditions at different propeller incidence angles. Force-based experiments, phase-locked particle image velocimetry (PIV), and surface oil flow visualization were conducted on two APC propellers at the University of Dayton Low Speed Wind Tunnel. For propellers in edgewise flight, the power required at constant thrust decreases at small advance ratios for each h/D and then increases with a further increase in the advance ratio. Tilting the propeller forward reduces the ceiling effect benefits in both thrust and power, particularly at higher advance ratios. Performance similarity in the propeller ceiling effect at different h/D is observed, and a performance prediction method is proposed. Phase-locked PIV showed an increase in the propeller inflow angle in the ceiling effect at small advance ratios, resulting in higher thrust generation. This effect reduces with an increase in the advance ratio due to minimized interactions with the ceiling plate. Hence, the measured propeller in-ceiling-effect (ICE) propeller performance cannot represent the propeller ICE performance at a higher forward flight speed. Additionally, PIV and surface flow visualization indicated the presence of a stagnation point on the ceiling plate near the trailing side of the propeller disk at higher advance ratios, leading to a reduction in propeller thrust generation.

Nominal wake field of a ship with moonpool

ABSTRACT To investigate the influence of a moonpool on the nominal wake field of a ship during calm water navigation, computational fluid dynamics calculations are performed using the STAR-CCM + software. The analysis found that the influence of boundary layer separation in the moonpool causes the hull boundary layer thicker, which reduces the average axial velocity of the propeller behind the moonpool and enhances the wake. The uniformity of the axial velocity distribution at the propeller disc is also reduced, worsening the uniformity of the wake field. In addition, the wake field characteristics of rear propellers change periodically with the fluctuation of moonpool. As a result the propeller bearing force and vibration characteristics change periodically with not only blade frequency and multiple blade frequency, but also the fluctuation of moonpool. These phenomena make the performance of propellers on ships with moonpool different from that of normal ships.

Influence of scale effect on flow field offset for ships in confined waters

To investigate the flow field characteristics of full-scale ships advancing through confined waters, the international standard container ship (KRISO Container Ship) was considered as a research object in this study. Using the RANS equation, the volume of fluid method and the body force method were selected to investigate the hydrodynamic characteristics of a model-scale ship (the model-scale ratio λ=31.6) and a full-scale ship advancing through confined waters at low speed. A virtual disk was used in the full-scale model to determine the influence of the propeller on the ship’s flow field. First, the feasibility of the numerical calculations was verified. This proves the feasibility of the numerical and grid division methods. The self-propulsion point of the full-scale ship at Fr=0.108 is determined. The calculation cases of model-scale and full-scale ships (with or without virtual disks) at different water depths and distances between the ship and the shore were calculated, and the changes in the hull surface pressure, the flow field around the ship, and the wake fraction near the ship propeller disk in different calculation cases were determined and compared. The variations in the surge force, sway force, and yaw moment between the model- scale and full-scale ships were generally consistent. In very shallow water (H/T=1.3), the non-dimensional force and moment coefficients for model-scale ships increase more rapidly with decreasing distance from shore, suggesting that using model-scale ships to investigate the wall effect in very shallow water will result in predictions that are biased towards safety. By comparing full-scale ships with and without propellers, it was discovered that the surge force, sway force, and yaw moment were marginally greater in the propeller-equipped ship due to the suction effect, and the accompanying flow before and after the propeller was slightly smaller, with less asymmetry.

Design of nonlinear controllers and speed and angular position estimator for an electrically controlled cycloidal propeller

The current research focuses on the design and stability analysis of nonlinear controllers for an electrically driven marine cycloidal propeller, along with estimating propeller disc rotational speed, blade pitch angle, hydrodynamic torque, and thrust using the Extended Kalman Filter. The nonlinear controllers comprise a Lyapunov-based feedback controller for the propeller disc and six Backstepping controllers for the propeller blades. All states and control architecture are defined using an efficient, physics-based, electrically controlled marine cycloidal propeller model. The controller is being investigated to evaluate its ability to accurately receive, process, and respond to multiple control signals. The Monte Carlo simulation technique assesses the robustness of the developed controller and the proposed estimator. A validation investigation is performed to evaluate the performance of the proposed nonlinear controllers. The proposed control system is straightforward to implement for a wide range of applications, including marine cycloidal propellers and cyclorotor-driven unmanned vehicles.

CFD Analysis on the Development of Pre-Duct Shape to Improve Propeller Performance

Energy saving contributions of Energy Saving Device (ESD) Pre-Duct are reducing energy losses and separation at the stern, increasing the ideal propeller efficiency, increasing the capture of viscous wake that passes through the propeller disk, and increasing the interaction of the propeller and ship hull. The effect of ESD Pre-Duct in front of the propeller on saving of energy is influenced by the accuracy and suitability of the geometry, position, and shape of pre-duct. In this study, the shape of the asymmetric un-circular pre-duct was develop and analysis conducted by compared the effect of the shape of pre-duct on the performance of propeller, the shape of pre-duct: circular (conventional), un-circular, and asymmetric un-circular. Computational Fluid Dynamics (CFD) modelling results using the ANSYS CFX software package with Propeller Open Water (POW) test simulations show that the installation of pre-ducts with several shape developments in general has a significant effect on increasing propeller performance at low propeller rotation speeds, whereas on high propeller rotation even though there is an increase in propeller performance but not significant.

Comprehensive computational analysis of the impact of regular head waves on ship bare hull performance

This paper focuses on investigating the impact of waves on ship hydrodynamic performance, enhancing our understanding of seakeeping characteristics and contributing to advanced ship and propeller design. It examines the resistance, motions, and nominal wake of the KVLCC2 bare hull, which is free to surge, heave, and pitch, in both calm water and regular head waves using a RANS approach. The research reveals a substantial dependency of the wake on grid resolution, particularly in calm water and shorter waves, while motions and resistance display a weaker dependency. The computed nominal wake is compared against towing tank SPIV measurements. Utilizing Fourier analyses and reconstructed time series, the study examines correlations among various factors influencing the bare hull’s performance in waves. The axial velocity component of the wake in waves demonstrates significant time variations, mainly driven by higher harmonic amplitudes. This dynamic wake is influenced by instantaneous propeller disk velocities due to hull motions, orbital wave velocities, boundary layer contraction/expansion, bilge vortex and shaft vortex dynamics. The wake distribution at the propeller plane not only differs significantly from the calm water wake in longer waves but also exhibits notably larger time-averaged values (up to 21%).

A Numerical Study of the Hydrodynamic Noise of Podded Propulsors Based on Proper Orthogonal Decomposition

Podded propulsors have become a focal point of research in the field of marine propulsion in recent years due to their high efficiency, low noise, and excellent maneuverability. To investigate the acoustic characteristics induced by the flow field of podded propulsors, a high-precision unsteady numerical simulation was conducted using the Delayed Detached Eddy Simulation (DDES) coupled with Ffowcs Williams–Hawkings (FW-H) equations. Multiple spatial acoustic receiving arrays were employed, and analysis methods including Proper Orthogonal Decomposition (POD) and Fast Fourier Transform (FFT) were utilized to determine the spatial distribution of the acoustic field of the podded propulsor. The results show that the blade passing frequency and the shaft frequency consistently dominate as the primary characteristic frequencies. On the plane of the propeller disk, the distribution of sound pressure levels is uniform without distinct directivity. Across the space curved surface, approximately the first ten POD modes encompass 99.8% of the total energy, and their spatial distribution characteristics of sound pressure are closely related to the pod structure. Additionally, these modes exhibit characteristic frequencies such as the blade passing frequency and shaft frequency. The spatial distribution of sound pressure at a single frequency on the spatial surface corresponds well with the results obtained from the POD analysis.

Study on the influence of shaft brackets on the scale effect of the four-screw ship wake field

In the four-screw ship navigation, the load difference between the inner and outer propeller is found to be more than twice of that in the model test, indicating a serious scale effect. The stern attachment of the four-screw ship has a significant impact on the inner and outer propeller wake which directly affecting the load distribution. Thus, to investigate the impact of the brackets on the scale effect of the four-screw ship flow field, this paper conducted multi-scale simulations of a four-screw ship with and without bracket using the Reynolds-averaged Navier-Stokes (RANS) method. The feasibility and accuracy of the numerical method was verified by comparing with PIV test results. The result shows that the scale effect is more pronounced in the outer propeller compared to the inner propeller. The presence of bracket reduces the wake fraction difference between the inner and outer propellers, but significantly affects the inner radius region of the outer propeller disk, more than doubling the wake fraction in this region at full-scale. When the bracket Reynolds number falls below its critical Reynolds number, the inner radius region of the outer propeller flow field deviates notably from the full-scale results and loses its practical significance.

Effect of Tip-Mounted Propeller and Trailing-Edge Flap on Wing's Lift and Drag Coefficients and Vortical Wake

Abstract The lift and drag forces and vortical wake of a rectangular semiwing equipped with a tip-mounted propeller and a plain trailing-edge flap both outside and in ground effect were investigated experimentally at Re = 2.49 × 105. Outside the ground effect, the slipstream of the inboard-up propeller rotation attenuated the wingtip vortex, significantly decreasing the lift-induced drag. The propeller rotation also led to an increased maximum lift and stall angle. At a fixed lift condition, the propeller rotation led to a reduced drag. The deployment of the flap further increased the lift curve slope and maximum lift but at the expense of an increased drag and earlier stall as compared to the unflapped wing. In ground effect, the lift augmentation of the unflapped wing increased pronouncedly with propeller rotation as the ground was approached. For the flapped wing, the propeller rotation, however, produced a smaller lift increment than the unflapped wing due to the recirculation of the deflected slipstream into the propeller disk. The extent of this recirculation increased with flap deflection and propeller rotation, contributing to the inferior lift production of the flapped wing with a tip-mounted propeller in ground effect.

Experiments and Modeling of the Ceiling Effect with Drone-Scale Propellers

Aircraft designs involving aerodynamic interactions between rotors and other aerodynamic surfaces are becoming increasingly popular. Studying these interactions is key to developing good models for design and aspects of the system such as control. This paper seeks to understand the effect of obstructing the upstream of a propeller at varying distances, also called the ceiling effect, by examining in depth the canonical case of a theoretically infinite obstruction and its interaction with a propeller or actuator disk. Experimental studies of force and pressure are compared to results from computational fluid dynamics (CFD), and good agreement is shown. The CFD results are then compared against the Morillo flowfield model, and a correction is found to match the results. The data indicate that some propellers experienced a nearly twofold increase in thrust. However, a matching force on the surface develops, and the net force drops to nearly zero. The force interaction between the two nearly disappears once the separation exceeds half a propeller diameter. These results are independent of propeller size and pitch. The implemented theoretical model also has low computational cost, and it could be used to improve low-order models such as panel methods or provide a foundation for future rotor–body interaction modeling.

The Effect of the Fillets on Submarine Wake Field and Propeller Unsteady Bearing Force

The uniformity of the wake on the submarine propeller disk is the key factor affecting the vibration and noise performance of the propeller. To study the influence of the fillets on the uniformity of submarine wake field and propeller unsteady bearing force, the submarine resistance calculation and self-propulsion calculation were carried out using the Detached-Eddy Simulation (DES) method. The characteristics of the wake field and hydrodynamic performance of the original and improved plan were compared and analyzed in detail. The fillets improve the wake distribution at the propeller disk by reducing the horseshoe vortex, and the fillets mainly affect the flow field characteristics of the inner radius area. The fillets can effectively reduce the axial velocity pulsation and improve the quality of the wake field. The frequency–domain curve shows that the bearing force and torque pulsation value of the improved plan are smaller than that in the original one, indicating that the fillets are conducive to controlling the vibration and noise performance of the submarine propeller. The results show that the fillets can effectively improve the flow field quality in the wake fields and reduce the propeller unsteady bearing force.

A self-rotating, single-actuated UAV with extended sensor field of view for autonomous navigation.

Uncrewed aerial vehicles (UAVs) rely heavily on visual sensors to perceive obstacles and explore environments. Current UAVs are limited in both perception capability and task efficiency because of a small sensor field of view (FoV). One solution could be to leverage self-rotation in UAVs to extend the sensor FoV without consuming extra power. This natural mechanism, induced by the counter-torque of the UAV motor, has rarely been exploited by existing autonomous UAVs because of the difficulties in design and control due to highly coupled and nonlinear dynamics and the challenges in navigation brought by the high-rate self-rotation. Here, we present powered-flying ultra-underactuated LiDAR (light detection and ranging) sensing aerial robot (PULSAR), an agile and self-rotating UAV whose three-dimensional position is fully controlled by actuating only one motor to obtain the required thrust and moment. The use of a single actuator effectively reduces the energy loss in powered flights. Consequently, PULSAR consumes 26.7% less power than the benchmarked quadrotor with the same total propeller disk area and avionic payloads while retaining a good level of agility. Augmented by an onboard LiDAR sensor, PULSAR can perform autonomous navigation in unknown environments and detect both static and dynamic obstacles in panoramic views without any external instruments. We report the experiments of PULSAR in environment exploration and multidirectional dynamic obstacle avoidance with the extended FoV via self-rotation, which could lead to increased perception capability, task efficiency, and flight safety.

NUMERICAL INVESTIGATIONS ON THE FREE SURFACE FLOW AROUND WING-BODY JUNCTIONS

Starting with January 2013, all ships greater than 400 tons engaged in international voyages must comply with the Energy Efficiency Design Index (EEDI), and starting with January 2023 also with the Efficiency Existing Ship Index (EEXI), issued by the International Maritime Organization, (IMO). Knowing that, in general, a ship hull is the result of a compromise between the main dimensions imposed by the size of the locks, navigation route depth, port depth, taxes, transport capacity (deadweight, volume), ship equipment (machinery, deck installations, piping systems), hydrostatic performances and last but not least the hydrodynamic performances, from ship hydrodynamics point of view the available approaches are the optimization of the ship size and hull forms or the design of propellers adapted to the ship's wake. The main purpose is to reduce the ship resistance and increase the efficiency of the propulsion system which ultimately leads to a reduction in the power placed on board the ship. For this, there can be used the so-called flow control devices or Energy Saving Devices (ESD hereafter), as hydrofoils or nozzles, to improve the flow parameters entering the propeller disc in order to increase the efficiency of the propulsion system and decreasing the fuel consumption leading to reducing of the carbon and greenhouse gasses emissions. For ballast loading condition the ESD may intersect the free surface, the flow becoming complicated and combining nonlinear, three-dimensional and turbulent phenomena such as the boundary layer on solid surfaces, the horseshoe vortex system developed around junctions and their effects turbulence, and also wave breaking. Therefore, this paper presents the results of the numerical study on the viscous free surface flow around junctions between a hydrofoil mounted on a plate, more precisely the study of the influence of the angle between hydrofoil and plate. It was observed that from a hydrodynamic point of view the angle between hydrofoil and base plate to be less than 15 degrees in respect to the vertical direction on the hydrofoil so that horseshoe vortex to be reduced in intensity and the value of the hydrofoil drag to be minimal.

Multi-fidelity model and reduced-order method for comprehensive hydrodynamic performance optimization and prediction of JBC ship

The multi-fidelity Co-Kriging surrogate model can be applied to combine the accuracy advantage of high-fidelity sample evaluation with the efficiency advantage of low-fidelity sample evaluation. In this paper, the hull form optimization process for resistance and wake performance of a Japan bulk carrier (JBC) hull at design speed is given in detail, where the evaluation results from medium and coarse grids are regarded as the high- and low-fidelity data, respectively. 60 high-fidelity hydrodynamic evaluations have been done to construct the Kriging model, while the Co-Kriging model uses 30 high-fidelity and 60 low-fidelity evaluations with a 25% reduction of the total computation time. The optimization results show that, for the total drag, the Kriging-based optimal hull has a 4.57% reduction, while the Co-Kriging-based optimal hull has 5.67%; for the axial wake fraction reduction at the propeller disk, the Kriging-based optimal hull has a 7.20% reduction, while the Co-Kriging-based optimal hull has 10.37%. Furthermore, in the latter stage of hull form optimization, dimensionality reduction field learning can be performed to fully use the viscous-flow-based calculation results. An accurate and efficient viscous-flow-based wake field learning method is proposed based on the Kriging model and the Proper Orthogonal Decomposition (POD) method with qualitative and quantitative error analysis, which can guide the sensitivity analysis of the design variables, the selection of the design variables and spaces, and new flow field prediction for comprehensive hull form performance optimization.

Numerical research on the effect of brackets installation angle on the propeller wake field and propulsion performance in a four-screw ship

A series of full-scale self-propulsion simulations of a four-screw ship with different bracket installation angles using the Reynolds-averaged Navier–Stokes (RANS) method were conducted. The effects of the bracket installation angle on the propeller wake field and propulsion performance were investigated and studied. The result shows that the nominal wake low-speed region generated by the shedding vortex moved inward with the bracket angle increased. When the bracket angle turns inward 3°, the effect of shedding vortex almost disappeared in the outer propeller disc. The outer propeller shows a significant increase in thrust and torque, and the time-average load difference between inner and outer propeller drops to below 5%. The research conducted in this paper fills a gap in the study of full-scale four-screw ship appendages. The design method for determining the bracket installation angle by inflow direction is of practical significance to the design of four-screw ships.

Numerical Analysis of the Effect of Ducted Propeller Configuration Parameters on Aerodynamic Performance

In this paper, a numerical calculation method is applied to investigate the influences of ducted propeller aerodynamic configuration parameters. The thrust, torque and power of the propeller in the duct and the decoupled propeller are compared under identical conditions. The performance with equal input power is analysed considering the additional thrust of the duct. The relationships of system thrust, power and efficiency with the axial position of the propeller disk in the duct, the propeller disk diameter and the propeller-duct clearance are investigated.

CFD Analysis on Propeller at Varying Propeller Disc Angle and Advance Ratio

The purpose of this study is to see the feasibility of using Computational Fluid Dynamic (CFD) analysis over wind tunnel testing for propeller performance measurement. Computational Fluid Dynamic (CFD) analysis is conducted on APC 6X4E propeller and 9X6E propeller at propeller disc angle, α of 0°, 30°, 60°, and 90° using commercially available software ANSYS FLUENT at advance ratio ranging from 0 to 0.88 and angular velocity ranging from 1000rpm to 8000rpm. CFD analysis was also performed for different advance ratio at different rotational speed of 4000rpm and 8000rpm. Multiple Reference Frame model is used to simulate the rotating propeller in a flowing airstream by constructing a rotating and static domain around the propeller. The non-zero propeller disc angle is achieved by changing the inlet direction of the static domain. The SST k-ω turbulence model is used, and tetrahedral mesh is constructed. The propeller thrust and torque obtained from the CFD simulation is used to calculate the aerodynamic characteristics of the propellers. The thrust coefficient, torque coefficient and propeller efficiency obtained for both propellers follow the trend of the wind tunnel testing. The results obtained from the CFD simulation matches with the results trend obtained by another researcher performing wind tunnel analysis, where the thrust coefficient decreases with increasing advance ratio at propeller disc angle less than 60° and increases with increasing advance ratio at propeller disc angle more than 70°. The error produce for thrust estimation is lower than 12% for both 6x4E and 9x6E propellers. The error for torque and efficiency estimation is between 15-30% and 12% respectively. In conclusion, CFD simulation can predict the aerodynamic characteristics of Low Reynolds Number propeller at different propeller disc angle.

Enhanced body-force propeller model for non-uniform inflow flow and application to turning circle test of KCS in calm water

An enhanced body-force propeller model is developed to consider propulsion effects without solving the actual propeller geometry in ship maneuvering problems. Application to the KCS turning circle test in calm water (starting at the self-propulsion point) is conducted using the computational fluid dynamics solver, snuMHLFoam, which was developed on OpenFOAM-plus. Based on the original Hough and Ordway model, the non-uniform advance velocity of the propeller is considered using the local velocity on the inflow plane, to compute the local advance coefficient for different parts of the propeller disk when the propeller works behind a hull. The original overset algorithm is revised by introducing more flexible hole-patch definitions for the hole-cutting procedure and an iterative procedure for the donor-searching procedure to remove invalid donors. The motion decomposition of ship and rudder motions with the revised overset is implemented in order to handle body motions effectively. Self-propulsion and turning circle tests for KCS ships are successfully conducted in calm water. The predicted results, including the PI control results, turning trajectory and parameters, ship motions and velocities, forces and moments, and flow and vortical structures are illustrated and compared with the benchmark experimental data, as well as the numerical results obtained using the Maneuvering Modeling Group (MMG) model. The results indicate that the developed body-force propeller model can provide more reasonable predictions of the propulsive performance when the propeller works behind a hull. The snuMHLFoam solver, which is coupled with motion decomposition using the revised overset grid methodology, is validated to be effective and reliable.