Open Water Performance Research Articles

Effect of pressure pores size on hydrodynamic and hydroacoustic marine propeller performances under cavitating case

The numerical work presented in the paper investigates the effect of pressure pores on hydrodynamic and hydroacoustic performances. This research aims to reduce cavitation area and underwater noise by mitigating the tip vortex cavitation. Compared to the few studies devoted to the pressure pores technique, several configurations based on the E779A marine propeller have been tested by considering different azimuthal and radial step values, a wider pore region concentrated at the top of the blade, and several pore diameter values. In addition, a numerical simulation was started to verify the effectiveness of the theoretical models in detecting the effect of pressure pores on the acoustic propagation generated by the propellers tested. The numerical approaches combining cavitating flow and noise propagation are performed using a hybrid method, which solves the Ffowcs Williams-Hawkings (FW–H) equation. A validation of the numerical simulation is carried out for cavitating and non-cavitating cases. Open water performances, cavitation area, sound pressure levels, and thrust distributions are analysed for two cavitation numbers. σ= 1,763 and σ= 1,029. The obtained results reveal that the cavitation area decreases as the pressure pore radius increases, but a slight reduction in propulsive efficiency accompanies this. Particularly for the pores radius of 0,00264D, propeller efficiency loss doesn't exceed 2,6 % and 4,05 % for the two cavitation numbers investigated. Nevertheless, this configuration showed better acoustic performances with a diminution of 10 dB in overall sound pressure level compared to the propeller without pressure pores.

Research on the hydrodynamic performance of propellers under oblique flow conditions

The phenomenon of oblique water inflow is widespread in the operation of thrusters, which will cause adverse effects on the hydrodynamic performance of thrusters. In order to investigate the hydrodynamic performance and stress variation of the propeller in oblique flow, based on computational fluid dynamics theory, this paper takes the DTMB4119 propeller as the research object and conducts numerical simulation research on the propeller in oblique flow by solving the RANS equation. By calculating the open water performance curve and surface pressure distribution of the propeller, the rationality of the numerical method and the meshing are verified. Considering the flow field information such as velocity, oblique flow angles, flow line distribution, and pressure distribution, the changes in hydrodynamic characteristics of the propeller are simulated and analyzed. The results show that the uneven distribution of pressure on the propeller blade surface increases with a decrease in the advance coefficient. The force pulsation amplitude of a single blade increases with an increase in oblique flow angles. With the increase in oblique flow angles, the thrust, torque, and efficiency of the propeller show different increasing trends. With the increase in propeller advance coefficient, propeller thrust and torque decrease gradually, and propeller efficiency increases gradually. By using mature propellers, this paper has more reference value for studying the flow field around the ship hull and the hydrodynamic performance of propellers in the process of ship maneuvering.

Comparison Study of the k − kL − ω and γ − Reθ Transition Model in the Open-Water Performance Prediction of a Rim-Driven Thruster

The present work examines the capabilities of two transition models implemented in ANSYS Fluent in the open-water performance prediction of a rim-driven thruster (RDT). The adopted models are the three-equation k−kL−ω and the four-equation γ−Reθ models. Both of them are firstly tested on a ducted propeller. The numerical results are compared with available experimental data, and a good correlation is found for both models. The simulations employing two transition models are then carried out on a four-bladed rim-driven thruster model and the results are compared with the SST k−ω turbulence model. It is observed that the streamline patterns on the blade surface are significantly different between the transition and fully turbulent models. The transition models can reveal the laminar region on the blade while the fully turbulent model assumes the boundary layer is entirely turbulent, resulting in a considerable difference in torque prediction. It is noted that unlike the fully turbulent model, the transition models are quite sensitive to the free-stream turbulence quantities such as turbulent intensity and turbulent viscosity ratio, as these quantities determine the onset of the transition process. The open-water performance of the studied RDT and resolved flow field are also presented and discussed.

Evaluation of subgrid scale models in turbulent large eddy simulations of pumpjet propulsor

To assess the effectiveness of subgrid scale (SGS) models on the prediction results of unsteady loads and turbulent fluctuation of pumpjet propulsors equipped with both front and rear stators, a pumpjet propulsor computational model with attached parts at the model scale is developed using a fully structured mesh, and large eddy simulations are conducted. The computational results of the different SGS models are compared based on five aspects: open water characteristics, turbulence parameters, incoming turbulence spectrum, vortex structure, and fluctuating pressure. Their results are also compared with the experimental values, and the correlation between the internal flow characteristics of the pumpjet propulsor and the turbulent fluctuation is analyzed. According to the results, as regards the prediction of the open water performance of the pumpjet propulsor containing both front and rear stators, the overall trend obtained by the three subgrid models is similar, and the error between the values predicted by the SL model and the experimental ones is the smallest. At the same mesh level, the turbulent fluctuating scale obtained by the SL model is larger than that obtained by the WALE and DSL models, and the turbulent time scale obtained by the DSL model has the smallest fluctuation in the circumferential direction. Among the three SGS models, the turbulent fluctuating scale of the SL model is larger than those of the WALE and DSL models. The SL model exhibits the largest energy dissipation among the three SGS models, followed by the DSL model, while that of the WALE model is the smallest. In the WALE model, the leakage vortex at the top of the blade is the longest, followed by the DSL model, while it is the shortest in the SL model. In the WALE and DSL models, the fluctuating load fluctuates more in the transition region from the middle section to the trailing edge of the blade.

Improvement of the efficiency for rim-driven thrusters through acceleration of gap flow

Efficiency optimization of the rim-driven thruster (RDT) has emerged as a prominent research topic in recent years. In this work, the Reynolds-averaged Navier-Stokes (RANS) solver is employed for simulating open water performance of RDTs, aiming at improving the efficiency of RDTs. Specifically, a series of RDTs are obtained by modifying the Ka4-70 propeller with a 19A duct, and their thrust and torque components, as well as efficiency and gap flow, are thoroughly examined. The investigation commences by exploring the impact of different rim sizes on RDT efficiency. A comparison is conducted between the open water performance of RDTs and the ducted propeller. Subsequently, a case with relatively high efficiency is identified, serving as a basis for the development of a series of modified RDTs equipped with acceleration devices. These devices facilitate accelerated axial flow in the gap, thereby enhancing the thrust generated by the duct, while simultaneously reducing the torque exerted on the rim through accelerated circumferential gap flow. Comparative analysis reveals that the improved RDTs can achieve an open water efficiency increase of up to 10.9% when the advance coefficient is set to 0.6, resulting in an efficiency value of 0.519. The findings presented in this paper introduce a novel direction for optimizing the efficiency of RDTs, contributing to the advancement of this field of study.

Does Pool Performance of Elite Triathletes Predict Open-Water Performance?

The capacity of laboratory tests to predict competition performance has been broadly researched across several endurance sports. The aim of the present study was to analyse how pool swimming performance can predict the result of the swimming segment in triathlon competitions and compare predictability differences based on competition level and distance. Eighteen male triathletes participated in the study. Three were ranked world-class, ten elite/international level, and five highly trained/national level. A total of sixty-one graded multi-stage swimming tests were conducted. Blood lactate was measured to calculate the following hypothetical predictor variables: speed at lactate threshold 1 (LT1), speed at lactate threshold 2 (LT2), and speed in the last repetition of the test (SL200). The following data were collected for a total of 75 races: time in the swimming leg (TSL); position after the swimming leg (PSL); time difference with the first triathlete after the swimming leg (DFT); and final race position. The race levels were divided according to participant levels as follows: world series (WS) (n = 22); World Cup (WC) (n = 22); Continental Cup (CC) (n = 19); national championship (N) (n = 5); and local race (L) (n = 5). Based on distance, they were divided into Olympic distance (OD) (n = 37) and sprint distance (SD) (n = 38). A moderate to strong positive association was found between LT1, LT2, SL200 and PSL and TSl at all race levels except for the SD CC, SD WC, and OD CC races, where no or weak-to-moderate correlations were found. The present study demonstrated that performance measured in a graded multi-stage pool lactate test can predict performance in a triathlon swimming segment. This finding is highly useful for coaches as it can help them to obtain a reliable measure of the triathlete's specific capabilities in the swimming leg.

Fast prediction method of propeller hydrodynamic performance based on SPF-LSTM

In order to realize fast and accurate prediction of hydrodynamic performance of UUV propeller, a hydrodynamic performance prediction model based on SPF-LSTM neural network was proposed in this paper, which combined with real propeller flow test and CFD numerical simulation technology. The model comprehensively considered the test data of real paddle and the simulation data based on CFD numerical simulation, and adopted the Sample penalty factor (SPF) to optimize the initial weight of the model, adjust the sensitivity of the model to different samples, and further improve the prediction accuracy. The experimental results show that the prediction results of this model are in good agreement with the test data of real propeller, and the calculation period is very short and the efficiency is high, which meets the requirement of real-time and accurate prediction of the open water performance of propeller.

Best modeling practice for self-propulsion simulation of ship model in calm water

This paper presents the development of best Reynolds-Averaged Navier–Stokes modeling practices for simulations of propeller–hull interaction in calm water using Star-CCM+. Extensive convergence studies were carried out to examine effects of various propeller modeling methods and parameters, such as non-dimensional wall distance, grid resolution/distribution, and turbulence model. Bare-hull resistance and propeller open-water performance were first examined. For propeller–hull interaction, a simplified body-force method and a detailed propeller modeling method were applied to predict the wake fraction and propeller performance behind the hull. The difference in accuracy of the two methods was quantified, and the best modeling practices were recommended based on the convergence studies. Validation studies were carried out for the Korea Research Institute of Ships and Ocean Engineering Container Ship model. The pseudo-effective wake fraction determined from computational fluid dynamics simulations was introduced and compared with the experimental effective wake fraction.

Scale Effect of a Kappel Tip-Rake Propeller

In this paper, the scale effect of Kappel tip-rake propellers with different end plate designs was studied using computational fluid dynamics. Given the base size of the mesh and the appropriate numerical model for the determined simulation, the open-water performance of three Kappel propellers with different bending degrees of the end plate at different scales was calculated. Comparing the scale effect of these propellers, the scale effect of the torque coefficient of a Kappel propeller is more intense than that of the conventional propeller. In addition, the scale effect of the torque coefficient is strong when the bending degree of the end plate increases, dwarfing the scale effect on the thrust coefficient. Following the research on the scale effect of the wake field for the Kappel propeller, the laws that reveal the influence of the scale on the wake field were summarized; that is, the high-speed zone in the wake relatively expands with the increase of the scale in company with a trend of tip cross flow. The research reveals the basic variation trend and rule of the open-water performance and wake distribution for the Kappel propeller under different scales within the Reynolds number range of 4.665×105−8.666×107 considering γ transition, as well as the characteristic differences between the Kappel propellers with different end plate designs, which will be of great significance to its optimization design and application to marine vehicles of different scales.

Analysis on Performances and Flow Fields of a Single Waterjet Propeller Based on SST k −ω Model

As a special method of ship propulsion, waterjet propeller has been widely used in military and civilian fields due to its advantages of simple structures and high propulsion efficiency. Affected by waves of sea and rotation of impeller, the internal flow of waterjet propeller is extremely complex on three dimensions. When waterjet propeller works, its turbulent flow is often accompanied with unstable phenomena like flow separation, secondary flow, and backflow. On the other hand, the impeller of the propeller will be easily cavitated if it runs at high speed. That has a serious impact on performance and structure of the propeller. Therefore, understanding the open water performance and cavitation characteristics is imperative. In this study, we analyze the performance and flow field of a single marine external waterjet propeller based on the SST k−ω model. We focus on examining its performance under various advance coefficients in open water conditions. The experimental results show that the distributions of streamline and inlet velocity are more uniform at the highest efficiency point than other operating conditions. The loss for the generation of entropy is relatively low at the same time. The analysis on cavitation shows that the volume of the cavitation bubble will increase gradually as the cavitation number of the propeller decreases. Meanwhile, the performance of the propeller decreases obviously at the blade tip extending from the rim to the hub.

Influence of bearings on the open water performance of a rim-driven thruster

The rim-driven thruster (RDT) represents an important advance in the marine propulsion system. Its innovative structure introduces several outstanding advantages but also rises some major challenges. This paper aims to investigate the influence of bearings on the rim-driven thruster in terms of hydrodynamic performance with computational fluid dynamics. Bearing parameters including the shape of the contact surface and the number of grooves are considered. The simulation results indicate that the presence of the bearings in the gap has an influence on the overall performance of the thruster by changing the flow regime in the gap and the interactions between different components in the RDT. The shape of the bearings also exhibits significant impacts: the conical bearings, even though with simpler structure, shows the worst performance among all three bearing configurations, while the ordinary bearings always have a higher hydrodynamic efficiency than the other two bearing configurations under all considered advance coefficients. The difference in efficiency at the design point can reach up to 3% between the ordinary and conical bearing configurations.

Numerical study of scale effects on the open water performance of a rim-driven thruster

This paper presents the study of scale effects on the open water performance of a rim-driven thruster (RDT) based on Computational Fluid Dynamics (CFD) simulations. For marine propellers, the effects of viscosity are often significant when there is a dramatic change in Reynolds number, which occurs when the results from model scale tests are extrapolated to propellers at full scale. Reynolds-Averaged Navier–Stokes (RANS) simulations with the Moving Reference Frame (MRF) approach are carried out in ANSYS Fluent for the RDTs under different working conditions. Considering the potential transitional flow on the propeller at model scale, the γ−Reθ transition model is adopted which can better resolve the boundary layer and yield more accurate results for transitional flows. From the simulations, it is observed that the duct and rim are more affected by the scale effects than the propeller. When the Reynolds number increases, there is a small amount of increment in the total thrust coefficient but a significant decrease in the total torque coefficient, resulting in a substantial improvement in hydrodynamic efficiency of the full scale RDT compared to the model scale.

The effect of tip rake distribution on the hydrodynamic performance of shaftless rim-driven contra-rotating thruster

Shaftless rim-driven contra-rotating thruster (RDCRT) has recently become the research focus for marine propulsion, primarily due to low vibration, low overall torque, and energy saving as its advantage. This study applied 4-order B-spline theory to vary the rake distribution of the blade tip for a shaftless rim-driven thruster (RDT) originated from duct propeller Ka4-70+No.19A, and constructed four shaftless RDTs with different blade tip rakes. Through CFD simulation, the impact of blade tip rake on the open water performance, wake distribution, and sheet cavitation performance of the shaftless RDTs with single propeller were evaluated. On the basis of the above, we further compared the effect of tip rake on the open water performance, wake distribution, pressure distribution, and sheet cavitation performance of three shaftless RDCRTs. It was found that the tip rake inclined to the pressure side of shaftless RDCRT is in favor of both propulsion efficiency and anti-cavitation performance, while the tip rake inclined to the suction side adversely exerts opposite effects. With the aid of the tip rake inclined to the pressure side for the front and rear propellers, the maximum propulsion efficiency of shaftless RDCRT tends to rise by 2.6%, together with the wake stretching more uniformly. For shaftless RDCRT, the optimization design from the aspect of tip rake would be capable of validating its performance and advantages.

An improved body force method for simulation of self-propulsion AUV with ducted propeller

The body force method (BFM) is an efficient computational method used for maneuvering simulations of marine vehicles with ordinary propellers. In this paper, an improved BFM is proposed to perform maneuvering simulations of a self-propelled AUV with a ducted propeller. Initially, the conventional BFM is applied to numerically investigate the open water performance of a ducted propeller(No. 19A+Ka4-70). However, significant prediction errors have been observed, which were mainly caused due to ignorance of the interaction between the duct and the propeller. To increase the prediction accuracy, an improved BFM is proposed to perform maneuvering simulations of the ducted propeller AUV by considering the mass flow correction. In addition, the external diameter of the actuator is proposed to be a function of real-time advance velocity. To investigate the efficacy of the proposed method, the simulated results have been compared with the model testing carried out in a towing tank and with the discretized propeller method. The proposed improved BFM is used to simulate the 20°/20° zigzag tests of AUV in both vertical and horizontal planes with different advance speeds. Simulated results, particularly propeller thrust, advance speed, pitch (or yaw), resistance, and especially duct thrust of AUV have significantly improved as compared to the conventional BFM. The improved BFM results were found in close agreement with discretized propeller method and thus, the proposed method is considered a highly efficient and computationally cost-effective method to perform maneuvering simulations of ducted-propeller marine vehicles. The present work can contribute to the fast optimization of the manoeuvrability of marine vehicles with ducted propeller.

Construction and application of numerical diagram for high-skew propeller based on machine learning

The field of machine learning has experienced rapid growth, and it has introduced a new methodology for constructing propeller diagrams. To meet the high demand for designing high-skew propellers, a series of high-skew propeller schemes are generated, utilizing the INSEAN E1619 as the parent propeller. The Computational Fluid Dynamics (CFD) method was validated using the E1619 test results and was subsequently employed to perform virtual open water tests for all the series schemes. This effort produced 819 open water performance data of 42 propellers. The study trained and validated the traditional multivariate polynomial regression model and five conventional machine learning regression models based on the CFD calculation data. The analysis of the model prediction accuracy indicated that the Support Vector Machine (SVM) model had the least error among them for the digital expression of diagram hydrodynamic data. The prediction error of KT, KQ, and η decreased by over 20% compared to the LM model. The study subsequently developed a high-skew propeller diagram design program using the SVM regression model and applied it to a specific underwater vehicle's propeller design. The design results demonstrated that, compared to the B-series propeller, the design scheme provided by this numerical diagram had a comparable efficiency and a 6% smaller optimum diameter under unlimited diameter and a 7% higher efficiency under limited diameter for this case. Consequently, the developed numerical diagram in this paper provides a new tool for the propulsion performance evaluation and parameter selection of the propulsion system in the preliminary design stage for the high-skew propeller.

Effect of Tip Rake Distribution on the Hydrodynamic Performance of Non-Planar Kappel Propeller

Taking advantage of end-plate effects to enhance propeller efficiency is engaging. This paper applied a 4-order B-spline curve to design the rake distribution of Kappel propellers using five types of Kappel propellers that each possesses different tip rakes, and one type has no constructed end-plate. The RANS method coupled with the γ transition model was utilized to analyze the open-water performance of the six propellers, considering cavitating flow. It was found that the tip rake is conducive to the thrust capacity of the Kappel propellers, mostly improving the propulsion efficiency by 2.5% at a designed advance speed with the appropriate tip rake. The increase in the tip rake will magnify the low-pressure value and area on the suction side blade surface, together with the phenomenon of the stretching tip vortex and the inhibition of wake vortex contraction, which are both beneficial to the elevation of propulsion efficiency. However, the sheet cavitation behavior of the six propellers aggravates as the tip rake rises. Accordingly, the reasonable range of a tip rake for the design of a Kappel propeller in favor of the propulsion performance is suggested in this paper, exhibiting the promising potential of energy savings for the application to marine vehicles.

Numerical study on the hull–propeller interaction of autonomous underwater vehicle

The hull–propeller interaction of autonomous underwater vehicle (AUV) in straight and oblique flow is numerically studied. The study is performed based on computational fluid dynamics (CFD) and the general commercial software ANSYS Workbench. The multiple reference frames (MRF) method and the shear stress transport (SST) k−ω turbulence model are adopted. Firstly, the drag of Suboff AUV and the open water performance of the Wageningen B-3-50 propeller are simulated numerically. The errors are all within 5%, validating the reliability of the method in this paper. Then, the Sailfish AUV and B-3-35 propeller developed by the Underwater Vehicle Laboratory (UVL) of Ocean University of China are simulated. The maximum incremental drag produced by the appendages reaches even more than 1.5 times the hull drag. Propeller rotation causes an additional hull drag increment of over 25%. With an inlet velocity of 1.5 m/s, the thrust and torque behind the bare hull increase by 16.7% and 6.4%, respectively. The effect of angle of attack on drag is more significant at high velocity. Finally, the numerical simulation result 1.825 m/s and experimental result 1.75 m/s are compared. This study has implications for guidance on AUV integration analysis.

Experimental study on the propulsion performance of a partially submerged propeller

The present study concerns an open water performance of a partially submerged propeller. To investigate the free surface effects on the propulsion performance, the force and moment were measured, and the ventilation phenomena were visualized with respect to submergence ratios and advance coefficients. The thrust loss in heavy load conditions due to ventilation at the suction side of the propeller blade was observed. The extent of the ring-shaped ventilation phenomena increased as the advance coefficients decreased, resulting in thrust loss. Using the underwater camera and the fast Fourier transform results of the thrust, the ventilation phenomena were classified into five types. Also, the shaft excitation force of the propeller was analyzed. The shaft-bearing load was approximately 100% greater than the propeller weight in the ballast draft condition. A larger load was applied to the shaft due to the movement of the thrust eccentricity near the free surface.

Research on self-propulsion simulation of a polar ship in a brash ice channel based on body force model

Main engine power prediction is important for polar ships operating in brash ice channels, which is one of the most important concerns of shipowners. Self-propulsion simulation is an efficient method to predict the developed power. At present, such models as the discretized propeller model (DPM) and the body force model (BFM) are used for self-propulsion simulation. However, these models are often limited to open water. There is little research on self-propulsion calculations in ice-infested water. This paper presents the BFM to carry out self-propulsion simulations in a brash ice channel. Research on simulation strategy for open water performance based on the BFM is carried out. Ship–ice–water interactions are simulated using computational fluid dynamics-discrete element method (CFD-DEM) coupling method. Both loaded and ballast conditions are considered in the model-scale self-propulsion simulations. Numerical results based on the BFM are compared with the simulation results based on the DPM, as well as model test results. Ship–propeller–ice interactions and propeller suction effects are also compared with photographs taken at an ice tank test. The results show that the differences of the developed power based on the BFM for both loaded and ballast conditions are 8.94% and 15.25%, respectively. The prediction accuracies of the developed power based on the BFM for both loaded and ballast conditions are 1.56% and 7.01%, respectively; lower than those based on the DPM. However, the computation efficiency based on the BFM is 12 times higher than that based on the DPM. To conclude, the proposed BFM could be used as an effective means to calculate the developed power and to evaluate the trend of hull-line optimization at the development stage.

CFD predictions of unsteady cavitation for a marine propeller in oblique inflow

In this paper the Potsdam Propeller Test Case is numerically investigated in oblique inflow conditions. We consider three different topics: open water performance curves, cavitation observations, and pressure pulses induced by the propeller to the ceiling of the cavitation tunnel. In the oblique flow case, the inflow is not uniform from the perspective of the propeller, which results in the dependency of the propeller blade loading and cavitation on the blade rate frequency. The numerical simulations were compared to experimental results for each investigated case. Additionally, we analyzed the unsteady features of the cavitation on the blades as well as the pressure peaks in the propeller wake due to collapsing cavities. We found that the global performance and cavitation patterns close to the blades agree well with the tests in the numerical simulations. The agreement with the tests for the pressure pulses on the tunnel ceiling was better in the non-cavitating case. The unsteady cavitation shed behind the propeller and the subsequent collapse events induced a vast increase in recorded maximum pressure values. Root cavitation collapse produced pressure pulses an order of magnitude greater than the collapse of tip vortex cavitation. Also the collapse of cavities on the blades contributed to a significant increase in the pressure fluctuations on the blades.