Marine Propulsion Applications Research Articles

Effects of Blade Number on the Propulsion and Vortical Structures of Pre-Swirl Stator Pump-Jet Propulsors

Reducing the noise of the underwater propulsor is gaining more and more attention in the marine industry. The pump-jet propulsor (PJP) is an extraordinary innovation in marine propulsion applications. This paper inspects the effects of blade number on a pre-swirl stator pump-jet propulsor (PJP) quantitatively and qualitatively. The numerical calculations are conducted by IDDES and ELES, where the ELES is only adopted to capture the vortical structures after refining the mesh. The numerical results show good agreement with the experiment. Detailed discussions of the propulsion, the features of thrust fluctuation in time and frequency domains, and the flow field are involved. Based on the ELES results, the vortices in the PJP flow field and the interactions between the vortices of the stator, rotor, and duct are presented. Results suggest that, though changing the blade number under a constant solidity does not affect the propulsion, it has considerable effects on the thrust fluctuation of PJP. The wakes of the stator and rotor are also notably changed. Increasing the stator blade numbers has significantly weakened the high-intensity vortices in the stator wake and, hence, the interaction with the rotor wake vortices. The hub vortices highly depend upon the wake vortices of the rotor. The hub vortices are considerably broken by upstream wake vortices when the load per rotor blade is high. In summary, the blade number is also vital for the further PJP design, particularly when the main concerns are exciting force and noise performance.

Numerical Study of the Hydrodynamic Characteristics Comparison between a Ducted Propeller and a Rim-Driven Thruster

The Rim-Driven Thruster (RDT) is an extraordinary innovation in marine propulsion applications. The structure of an RDT resembles a Ducted Propeller (DP), as both contain several propeller blades and a duct shroud. However, unlike the DP, there is no tip clearance in the RDT as the propeller is directly connected to the rim. Instead, a gap clearance exists in the RDT between the rim and the duct. The distinctive difference in structure between the DP and the RDT causes significant discrepancy in the performance and flow features. The present work compares the hydrodynamic performance of a DP and an RDT by means of Computational Fluid Dynamics (CFD). Reynolds-Averaged Navier–Stokes (RANS) equations are solved in combination with an SST k-ω turbulence model. Validation and verification of the CFD model is conducted to ensure the numerical accuracy. Steady-state simulations are carried out for a wide range of advance coefficients with the Moving Reference Frame (MRF) approach. The results show that the gap flow in the RDT plays an important role in affecting the performance. Compared to the DP, the RDT produces less thrust on the propeller and duct, and, because of the existence of the rim, the overall efficiency of the RDT is significantly lower than the one of the ducted propeller.

Novel Approach for Optical Characterization of Thrust Collar Lubricated Area: Experimental and Numerical Results

Abstract Thrust collars (TCs) are bearing elements used in geared machinery that transmit axial loads from one shaft to another. TCs are primarily used in integrally geared compressors (IGCs) but are also found in gearboxes and marine propulsion applications. TCs are hydrodynamic elements featuring a converging-diverging wedge to generate a pressure field that reacts axial loads. Accurate modeling requires knowledge of the film characteristics such as cavitation, turbulence, and air ingestion, all of which reduce load capacity. Current models in the literature do not include mass-conserving cavitation algorithms or turbulence flow. The following paper introduces a new test rig that optically characterizes the thin film region of a TC. The test rig geometries, speeds, and loads match those typically seen in IGC applications. The test rig utilizes a transparent acrylic window in conjunction with a high-speed camera (HSC) to obtain high-speed images of the oil film. Images are filtered and averaged to obtain areas of interest in the oil film. Cavitation and turbulence areas are measured for pinion speeds of 2.5, 5, and 7.5 krpm and axial loads of 0.5, 1, and 1.5 kN. Cavitation occurs in the diverging (upper) region of the TC and appears at pinion speeds over 5000 rpm but does not change in shape after that speed. The cavitation is independent of applied load. Turbulence at the inlet region (bottom) occurs at all speeds but increases to almost 35% of the total area at the highest speed. This paper also presents a finite element (FE) model that includes predictions for the static characteristics of the TC, specifically the cavitation area. The cavitation modeling uses an iterative Elord's method, which conserves mass. The model predicts a similar cavitation area for all speeds and loads. A computational fluid dynamics (CFD) study predicts a similar cavitation area and pressure field to the FE model. The CFD model predicts turbulence in the lower region that increases for increasing spin speed, which matches the experimental results. The CFD model tends to under-predict the turbulence area compared to the experiments. As IGCs move into new application areas to satisfy new needs, the increase in efficiency and capacity comes at a cost of more load and higher speed requirements on the TCs. This work will help original equipment manufacturers model TCs more accurately to ensure safe and efficient operation.

Optimal design and energy management of hybrid storage systems for marine propulsion applications

This paper discusses the themes of optimal design and management strategies of hybrid energy storage system (HESS) for marine applications. This design and related strategy are aimed to improve battery pack durability, ensuring a smooth profile of the required current, through the complementary action of super-capacitors. A DC/DC bidirectional power converter allows for the integration of these devices and control of on-board power fluxes. The proposed methodology is based upon the solution of a constrained optimization problem. In order to overcome computational issues, proper formulation of the mathematical problem is based upon the Ritz method, which is one of the direct methods for solving problems related to calculus of variations. The solution of the optimization procedure, which is the key finding in this paper, permits to obtain battery voltage and current profile, which enables the designer to determine battery and super-capacitor sizes and also provides battery/super-capacitor reference current profiles to be tracked by the DC/DC bidirectional power converter. The procedure is evaluated with reference to the case study of a water-bus operating in the Venetian lagoon, whose operative cycle has been acquired during proper measurement campaigns. Then, the performance of energy management strategies are verified by means of laboratory experimentations on the hybrid energy storage system, which have been carried out by scaling operative cycles at single storage cell level. The obtained results show the potential advantages of proper design and energy management obtained through this new methodology, in terms of investment and maintenance costs for sustainable maritime transport.

A thermodynamic optimization of a gas turbine cycle with a supplementary regenerator

International concern regarding pollution related to maritime transport sector and energy efficiency desiderate have determined specialists to search for more suitable alternatives to internal combustion engines. Due to their advantages, gas turbine systems are met in different marine propulsion applications, such as passenger ships or military vessels. Gas turbines will be even more intensively used in the future, an outcome of this reality being the need of their performance increment. A direction to be followed, considered in this study, is the combination between the improvement of the gas turbine efficiency by including a regenerator in the layout of the plant and, also, the rise of the temperature at the inlet of the turbine (TIT). Will be considered an open cycle gas turbine. The thermodynamic analysis is about the assessment of different influences such as: regenerative effectiveness versus the heat added in the combustor, regenerative effectiveness versus the work consumed by the compressor, regenerative effectiveness versus the thermal efficiency, regenerative effectiveness versus the specific fuel consumption, temperature at inlet of the turbine (TIT) versus the thermal efficiency. The results obtained will indicate the fact that both actions will lead to a gain in the performance of this technology.

Multi-objective Design Optimization of High-Power Circular Winding Brushless DC Motor

This paper proposes a novel circular winding brushless dc (CWBLDC) motor, which offers high torque density as BLDC motors and low-torque ripple as permanent-magnet synchronous machines (PMSMs). The novelty of the proposed machine is the circularly connected windings and its way of commutation, which make it suitable for high-power high-performance marine propulsion applications. First, the structure and the operation principle of CWBLDC are described. The method for calculating phase current of CWBLDC is subsequently introduced and validated by prototype experiment. Then, the multiobjective optimization problem for designing a high-power low-speed CWBLDC is formulated. Through large-scale design parameter sweeping, the best type of slot–pole combination and the best design scheme is selected and validated by finite element method (FEM) simulation. Finally, a multifactor regression analysis is performed to establish the relationship between performance objectives and design variables.

Design of Synchronous Motor with High-temperature Superconductive Field Windings for Marine Propulsion Applications

High-temperature superconductive technology is currently under development and is attracting the attention of researchers. As a result, high temperature superconductive tapes have found their way to the electrical machines industry all around the world. First-generation high-temperature superconductive motors were introduced in the past decade. In high-temperature superconductive motors, conventional copper windings are mainly replaced by superconductive tapes, and a cryogenic system is added to decrease the temperature until the superconducting state can be achieved. Their significant capabilities, such as their high efficiency, persuade engineers to replace conventional motors with the new high-temperature superconductive ones. Their expense is the main barrier to their commercial penetrations; therefore their usage is limited to exclusive applications, such as marine applications. In this article, a marine propulsion synchronous motor with high-temperature superconductive field windings was designed initially; an appropriate high-temperature superconductive power supply and cooling structure were then also designed. A marine propulsion motor should be assimilated with real marine conditions, so size and AC supply limitation are the given examples, with the above-mentioned points also considered for the designed model motor.

Experiments on radiated noise and vibration from a lifting surface at high Reynolds numbers

One of the main hydroacoustic noise sources from fully submerged lifting surfaces is the unsteady separated turbulent flow near the surface’s trailing edge that produces pressure fluctuations on the surface and induces vibratory motions of the lifting surface itself. However, the hydrodynamic forcing and subsequent structural response of lifting surfaces are largely undocumented at the high Reynolds numbers typical of many marine propulsion applications. This talk describes a new experimental effort to identify and experimentally document the turbulent flow, induced surface pressures, structural response, and radiated noise of a hydrofoil at chord-based Reynolds numbers up to 60 million. The experiments are conducted at the US Navy’s Large Cavitation Channel with a two-dimensional test-section-spanning hydrofoil (2.1-m chord, 3.0-m span) at flow speeds from 0.5 to 18 m/s. The foil section is a modified NACA 16 with a flat pressure side. At a zero angle of attack, the lift load on the foil approaches 700 kn. The results presented here cover the first phase of the experiments and illustrate flow-structure coupling phenomena that will be investigated in greater detail in the second phase of experiments planned for later this year. [Work sponsored by ONR, Code 333.]

Development of the General Electric LM 1500 Gas Turbine as a Marine Power Plant

Many unique advantages have stemmed from the use of aircraft-type gas turbine power plants in selected marine propulsion applications; and, as expected, special problems have arisen because of the marine environment, primarily in the areas of parts integrity resulting from cold and hot corrosion and performance deterioration due to compressor fouling. Sulfur in the fuel, together with sea salt in the fuel and combustion air, creates major problems. Programs directed to reduce the detrimental effects, and the results attained are described.

Marinization of the General Electric LM1500 Gas Turbine

After presenting some of the attractive features and characteristics of the aircraft gas turbine for selected marine-propulsion applications, this paper looks at those features of such engines that need improvement in order that they may become true marine power plants. Both cold and hot-corrosion problems are created by the marine atmosphere and the change from aircraft-type fuels to higher-sulfur-content marine fuels. Phases of a development program to produce the required features in the General Electric LM-1500 gas-turbine power plant are discussed.