Contra-rotating Propellers Research Articles

Effect of contra-rotating propeller boss cap fins (CRPBCF) on the performance of marine propellers

Based on the enlightenment of contra-rotating propellers (CRP) and propeller boss cap fins (PBCF), a numerical study of the contra-rotating propeller boss cap fins (CRPBCF) is carried out by using the STAR-CCM + software and the large eddy simulation (LES) model. The geometric model of the auxiliary propeller is obtained by transforming the blades of the propeller VP1304. To simulate the phenomenon of vortex cavitation as accurately as possible, local mesh refinement is performed in the region, where cavitation may occur. The effects of the CRPBCF on the open water characteristics and cavitation behaviors of marine propellers are analyzed. The numerical results show that the propulsive efficiency of the propeller can be significantly improved by setting an appropriate rotation rate of the auxiliary propeller. Another advantage of the CRPBCF is that it can suppress the generation of hub vortex cavitation (HVC). In addition, the reasons for the advantages of the CRPBCF are analyzed from the pressure distribution and velocity distribution in the wake of the hub.

Многорежимный винт изменяемого шага и эффективность его работы в составе соосных гребных винтов противоположного вращения

Object and purpose of research. This paper discusses possible applications of multi-mode adaptive-pitch propeller in coaxial contra-rotating propeller systems. The study compares efficiency calculation results for these propellers and their conventional FPP counterparts. The authors also give a design calculation layout for coaxial propellers as per hydrodynamic test diagrams for solitary FPPs, as well as demonstrate their hydrodynamic calculation. Calculation results confirm that multimode adaptive-pitch propellers may considerably increase the efficiency of a coaxial propeller system in high-load conditions. The study also demonstrates that coaxial propeller systems have greater efficiency also when they are made up by solitary FPPs. These results might be useful in practical design of various ships. Subject matter and methods. The study relies on hydrodynamic test data for solitary FPPs and gives layouts for design and verification calculations of coaxial propeller systems. Main results. These data could be used to estimate the efficiency of coaxial propulsion for given ship design. Conclusion. The study shows that multi-mode adaptive pitch propeller tend to increase overall efficiency of coaxial propeller systems in high-load conditions as compared to FPPs.

Numerical prediction of underwater noise on a flat hull induced by twin or podded propeller systems

In this article, the numerical prediction of underwater noise induced by multi-propulsor systems is investigated on a flat hull by solving the Ffowcs Williams–Hawkings (FW–H) equation in the form proposed by Farassat. To get the noise source, the hydrodynamic analysis is first performed using twin propellers and contra-rotating propellers via a boundary element method (BEM) in non-cavitating flow. In order to fully consider viscous interactions between neighboring propellers, incoming flow, and non-axisymmetric pod, a BEM/Reynolds-averaged Navier–Stokes (RANS) interactive method is utilized, in which two coaxial propellers are handled by a separate BEM model, and their mutual interactions are considered via a RANS solver. The predicted hydroacoustic and hydrodynamic performance from various configurations is validated with experimental data and results from viscous RANS simulations. Along with the noise spectrum in the flow field, the time history of acoustic pressures on the top wall is investigated to see how the mutual interactions among neighboring propellers and the pod affect the acoustic characteristics. A proper way of considering scattered/reflected noise from underwater geometry in a half-space domain is discussed, and importantly, the limited influence of the linear noise terms of the FW–H equation is pointed out, especially when the flow non-linearities, such as wake turbulence and structure-induced vortices, start to dominate the downstream flow.

First Rotary Ionic Engine with Contra-Rotating Propellers

Ionic propeller systems have recently demonstrated potential for the development of an ionic rotorcraft/drone to fly in planetary atmosphere. Such rotorcraft would use the ionic wind to spin the propellers that will further generate conventional thrust. The propeller, the associated electrodes, and electrical power source are the only source of propulsion. We demonstrate and study coaxial ionic contra-rotating propeller (CRP) systems for the first time. Experiments indicate that ionic-activated axial propellers can spin in opposite directions (no axial/shaft adaptors) creating zero-angular-momentum systems. If further developed, such systems can be useful to the design of zero-angular momentum ionic drones with no shaft adaptors. Emitter electrodes on a 25-cm-diam (propeller 1) and 12.6-cm-diam (propeller 2) propellers were optimized for speed in grounded cylinder electrodes. For propeller 1 systems, up to 936 rpm was recorded for single-propeller systems, whereas for CRPs 710 rpm was the maximum obtained. For propeller 2 single-propeller systems a maximum of 2812 rot/min was recorded versus 1720 rot/min previously reported. CRPs spinning up to 2035 rpm, , and (source limit) were also designed. The power-to-speed ratio was proportional to the current for all the systems. The propeller kinetic energy-to-power ratio presents a maximum with respect to voltage, current, speed, and power, and it can be used to differentiate between systems.

Design of Magnetic Levitation Shaftless Contra-Rotating Propeller and Feasibility Analysis of Drive System

In order to solve the problems of vibration, noise, shaft seal and complex structure of the marine propeller, the author proposes a new type of magnetic levitation(Maglev) shaftless contra-rotating propeller(CRP), analyzes the mechanical structure design and component layout of the propeller, and uses 3D modeling software to model and assemble components. The propeller is mainly composed of rotors, shroud, stator winding, sensors, control circuit and other components, and its control system is further divided into a levitation system and drive system. Then the drive system of the propeller is studied, its mathematical model is analyzed, and the drive system model is built in MATLAB/Simulink to analyse the feasibility of the propeller drive system, and a PID controller is added to make the system have good dynamic response performance.

Acoustic optimization of a contra-rotating propeller rig

With the advance of unmanned aerial vehicles as a viable alternative for urban transportation, it is imperative that these vehicles have a low impact on community noise. Contra-rotating propeller technologies offer interesting advantages over traditional single-propeller equivalents, such as improved aerodynamic performance and redundancy in case of failure, but can be exceedingly noisy when not carefully designed. This work presents a parametric study for the acoustic optimization of a custom-made contra-rotating propeller rig. The rig consists of two commercially available motors mounted on a rotating stand built in-house and mounted inside an anechoic chamber. A far-field microphone arc is used to collect acoustic pressure data, and a load cell is used to measure total thrust. We investigate the effect of variations in the number of blades (between 2 and 6 on both rotors) and axial spacing (between 0.1 and 1 rotor diameter) on the radiated noise, while adjusting the rpm to maintain constant thrust. Overall sound pressure levels, far-field spectra, and directivities (overall SPL, tones, and broadband) are assessed to determine trade-offs and optimal choices in designing a contra-rotating propeller rig.

Effect of Reynolds Number on Performance of Contra-Rotating Propeller Wind Turbines

In recent years, growing concern over global warming caused by the use of fossil fuels has led to a demand for clean power generation that can be used semi-permanently and is environmentally friendly. Wind power generation is expected as the development of new energy sources accelerates. Propeller wind turbines are widespread for large wind turbines. On the other hand, a wide variety exists for small wind turbines. Among them, the authors consider that 1kW wind power generation is important for the spread of small wind turbines, and are focusing on contra-rotating propeller wind turbines, which are expected to achieve high power. In this research, we aim to increase the power of a small wind turbine by installing a wind collecting device suitable for a contra-rotating propeller. However, the aerodynamic characteristics of a contra-rotating propeller inside a hollow structure have not been clarified. In addition, small wind turbines are operated under low Reynolds number conditions, and change in Reynolds number due to fluctuation in wind speed are expected to have a significant effect on performance. In this paper, the effect of Reynolds number on the performance of a contra-rotating propeller wind turbine is investigated by numerical flow analysis using a model with a contra-rotating propeller installed in the pipe.

Research and Development for High Performance Contra-Rotating Propeller Wind Turbine

Research and Development for High Performance Contra-Rotating Propeller Wind Turbine

Development of a new hull adsorptive underwater climbing robot using the Bernoulli negative pressure effect

Climbing on a vertical ship hull underwater while using surface cleaning tools remains a great challenge for climbing robots. In this study, we design a negative-pressure adsorptive underwater climbing robot using the Bernoulli negative-pressure generation mechanism. Computational fluid dynamics modelling is performed with a sliding mesh to explore the optimal adhesion performance. The factors that influence the adsorptive force are investigated, such as the contra-rotating propellers (CRPs) speed and gap distance between the bottom plate of the robot and the adsorbate, and their cause and effect are established by taking into consideration the fluid pressures and velocities for the Bernoulli negative-pressure effect on the bottom plate of the robot. Based on the optimal parameters determined from the numerical simulations, a prototype adsorptive climbing robot is fabricated and tested in a water pool. Comparisons with the experimental results show that the numerical model predicts the adsorptive force with an accuracy of 94.1%. The proposed method and the findings reported in this paper are valuable in guiding the design of negative-pressure adsorptive parameters for climbing robots, and will significantly improve the robot's capability to precisely adjust the adsorptive force by driving the CRP motor accordingly.

Numerical simulation of the cavitating noise of contra-rotating propellers based on detached eddy simulation and the Ffowcs Williams–Hawkings acoustics equation

Contra-rotating propellers (CRPs) are widely used in different kinds of underwater vessels, owing to their excellent stability, propulsive efficiency, and balanced torque distribution characteristics. However, the cavitation that occurs due to their high rotational speeds also generates high levels of cavitation noise. In this study, CRP noise radiations were predicted via detached-eddy simulations with the shear stress transfer k-ω turbulence model, the Ffowcs Williams–Hawkings (FW–H) acoustics model, and the Schnerr–Sauer cavitation model. The cavitation noise of the CRP was predicted using sound radiation theory for spherical bubbles and compared to non-cavitation noise levels from the FW–H equation. It was found that the non-cavitation noise of the CRP is significantly louder in the axial direction than in the radial direction. Furthermore, the noise sound-pressure levels (SPLs) of the flow field generally decrease with increasing frequency. When the effects of cavitation on the flow are taken into account, the SPLs of the CRP noise become significantly higher at all equidistant positions from the center of the propeller. The anisotropy in sound pressure also becomes insignificant when cavitation is present.

Enhancing the dynamics of an oceanic AUV by a Coupled-Fins-Propulsors roll control system

Autonomous Underwater Vehicles (AUVs) are exposed to several internal or external forces or moments causing roll instabilities. The coupled nonlinear dynamics of an AUV requires designing and utilizing an appropriate roll control system to operate well in various missions. In this paper, the roll dynamics and control enhancement of a REMUS AUV is studied using a Coupled-Fins-Propulsors (CFP) system by developing a six-degrees-of-freedom (6DOF) simulator. The results show that: 1) The roll angle deflections usually have adverse effects on coupled dynamics of the AUV in both open-loop and closed-loop systems; 2) In large roll angle deflections, the CFP system show a proper selection of 30% CRP (contra-rotating-propellers) and 70% FDF (Four-Decoupled-Fins) (49% SF (Stern Fins) and 31% RF (Rudder Fins)) can better control the roll dynamics by reducing the oscillations. 3) For φd < 18°, the FDF, CRP, and CFP, for 18°<φd < 60°, the FDF and CFP, and for 60°<φd < 70°, the CFP system could produce the adequate roll control forces and moments. 4) A limited desired roll angle can be achieved at a given forward speed; the maximum value is φd = 70 for ud > 4 m/s.

Comparison of self-propulsion performance between vessels with single-screw propulsion and hybrid contra-rotating podded propulsion

The present work compares the self-propulsion performance between vessels with single-screw propulsion and hybrid contra-rotating podded propulsion. The viscous flow fields of 4000 TEU container vessels with single-screw, single-rudder propulsion and hybrid contra-rotating propeller (CRP) podded propulsion systems were solved numerically by the Reynolds-averaged Navier–Stokes equations (RANS), the shear stress transport (SST) k−ω turbulence model, and the sliding mesh method. Numerical uncertainty analysis of the resistance and self-propulsion factor were employed according to ITTC Quality Manual 7.5-03-01-01. Self-propulsion factor, viscous flow field, and pressure distribution at the stern of the vessels were analyzed in detail. Numerical results suggested that the vessel with the hybrid CRP podded propulsion showed a 17.59% larger effective wake fraction, a 40.2% smaller thrust deduction fraction, a 15.1% higher hull efficiency, and a 4.12% higher overall propulsive efficiency compared with the single-screw vessel. In addition, the vessel with the hybrid CRP podded propulsion showed a basically symmetric, smaller velocity gradient and more uniform flow field at the stern, resulting in a much smaller propeller-induced fluctuating pressure on the hull, compared with the single-screw vessel. In conclusion, the hybrid CRP podded propulsion system exhibited high efficiency and low vibration levels.

Noise from unmanned aerial vehicle contra-rotating propellers

This paper presents an analysis of the noise produced by contra-rotating propeller systems used on small unmanned aerial vehicles. Selected results from an extensive experimental campaign are presented. In these experiments a commercially available contra-rotating propeller with 2- and 3-blade propellers was statically tested in a large anechoic chamber. It was observed that the noise spectrum contained a large number of tones which occurred at the sum of integer multiples of the blade passing frequency of each propeller. These tones exhibit some interesting features including: the amplitude of the interaction tones decays rapidly with increasing propeller spacing; tones for which the azimuthal mode number is equal to zero generally have a dipole like radiation pattern radiating strongly along the propeller axis. This is in contrast to the tones at the blade-passing frequency which radiate strongly in the plane of the propeller. A simple theoretical model for predicting the tones produced by the contra-rotating propeller is presented and is used to explain some of the observed phenomena.

Optimal matching investigation of marine contra-rotating propellers for energy consumption minimization

To minimize the energy consumption of contra-rotating propellers (CRPs), the optimal matched rotational speeds of the forward propeller (FP) and rear propeller (RP) of CRP are investigated based on the potential-based panel method. The optimal matching problem of a set of CRP405 is investigated. The open-water hydrodynamic performances of CRP405 with the FP and RP having the same rotational speed are calculated and the method is validated. The hydrodynamic characteristics of CRP405 with changing FP and RP rotational speeds are investigated. The cubic spline interpolation method is used to determine the equal thrust line at which CRP405 generates the target thrust while keeping the inflow velocity constant. A series of equal thrust points on the equal thrust line is selected for the analysis of the delivered power. The rotational speeds of the FP and RP corresponding to the minimal delivered power are the optimal matched rotational speeds of CRP405. The optimal matching calculations are carried out at different inflow velocities. The results show that, under the condition of a low inflow velocity, properly increasing the rotational speed of the FP and decreasing the rotational speed of the RP are the most direct and efficient ways to reduce the energy consumption and avoid the negative effect of the net torque of the CRP on the transverse stability.

Preliminary Design Framework for the Power Gearbox in a Contra-Rotating Open Rotor

Abstract Geared contra-rotating open rotors have the potential to further reduce fuel consumption relative to geared turbofans, but require a more-complex speed-reducing transmission system to drive the propellers. Hitherto, the preliminary design for such transmission systems has been reported independently of the overall engine modeling or has been limited by many predetermined engine constraints. This has restricted the feasible design space of the transmission systems. A simple transmissions preliminary design approach is needed that does not involve complicated mechanical assessments and can be integrated with engine preliminary design studies. This paper presents a novel design framework for sizing a double-helical differential planetary gearbox for a contra-rotating open rotor. An up-to-date methodology is proposed for the design of maximum load capacity gears for this application based on the power-transmitted, durability, and space envelope requirements. The methodology was validated with published data, demonstrating only very minor differences in geometry dimensions. Parametric analyses have been made to assess the impact of the design assumptions on gearbox dimensions. The framework also enables the identification of feasible torque ratios between the output shafts of the speed-reducer and the contra-rotating propellers driven by them. The impact of the torque ratio on the size of the gearbox has been analyzed for equal propeller rotational speeds and different speed ratios between the output shafts. This study shows that potential torque ratios lie between 1.1 and 1.33, with the higher ratios enabling more compact gearboxes having four or five planet gears.

Psychoacoustic analysis of contra-rotating propeller noise for unmanned aerial vehicles.

Unmanned aerial vehicle (UAV) technologies are rapidly advancing due to the unlimited number of applications from parcel delivery to people transportation. As the UAV market expands, community noise impact will become a significant problem for public acceptance. Compact drone architectures based on contra-rotating propellers bring significant benefits in terms of aerodynamic performance and redundancy to ensure vehicle control in case of component failure. However, contra-rotating propellers are severely noisy if not designed appropriately. In the framework of a perception-influenced design approach, this paper investigates the optimal rotor spacing distance configuration to minimise noise annoyance. On the basis of a series of psychoacoustic metrics (i.e., loudness, fluctuation strength, roughness, sharpness, and tonality) and psychoacoustic annoyance (PA) models, the optimal rotor axial separation distance (expressed as a function of propeller blade diameter) is at a range from 0.2 to 0.4. This paper also discusses the performance of currently available psychoacoustic models to predict propeller noise annoyance and defines further work to develop a PA model optimised for rotating systems.

Experimental and analytical investigation of contra-rotating multi-rotor UAV propeller noise

Contra-rotating propellers could increase the efficiency and lifting capacity of multi-rotor unmanned aerial vehicles (UAVs); however, contra-rotating propellers can produce significant noise levels. This work experimentally investigated the noise from static contra-rotating UAV propellers in an anechoic chamber. The effects of propeller diameter were studied by testing different configurations of 12″ and 15″ propellers. The effects of propeller spacing, rotational speed and blade number were also investigated; around 1400 propeller configurations were tested in total. It was observed that interaction tones were a dominant contributor to the overall noise level, which also contained rotor-alone tones and broadband noise. A theoretical model for the far-field interaction tone noise produced by a contra-rotating propeller is presented and used to explain the tonal noise levels observed in the experimental results. It was found that the tones with a zero azimuthal mode order dominate the noise spectrum close to the propeller axis. It was shown that the amplitude and number of these tones with zero azimuthal mode order could be reduced by using contra-rotating propellers with mismatched blade numbers. It was also experimentally shown that increased spacing between the propellers generally reduced the amplitude of the interaction tones. The rate of this reduction in amplitude with spacing between the propellers was dependent on frequency and spacing. High rates of decay were generally observed at small spacings and lower rates at larger spacings. However, the decay was neither monotonic nor at a uniform rate for all frequencies, which suggests that there could be a change in the noise generation mechanism as the spacing increases. Finally, the validity of the indoor static results was demonstrated by comparing the results to an in-flight test of a quadcopter with contra-rotating propellers.

On the flow field induced by two counter-rotating propellers at varying load conditions

The hydrodynamics of the flow between and in the wake of contra-rotating propellers is investigated experimentally via Particle Image Velocimetry (PIV) at different advanced coefficients. Results show that the flow dynamics is deeply influenced by the interplay between the two systems of helical vorticity that develop in the wake. The forward and aft propellers’ slipstream structure is analyzed in terms of blade loading and relative phase angle. The onset of tip vortex break-up, reconnection and pairing processes occurring within the wake is discussed with a focus on instability mechanisms. Flow field measurements between propellers highlight that the distribution of the tangential component is balanced more effectively by the aft propeller at specific loading conditions.

Effect of geometrical features on the contra-rotating propeller hydrodynamic performances

New contra-rotating four-bladed DTMB propeller configurations operating in open water are numerically studied to determine their hydrodynamic performances. The unsteady turbulent flow around propellers is modelled by RANS equations with Kω SST model then solved by a CFD code. The computational domain is divided in two blocks linked with a rotating interface. The obtained results show that thrust and efficiency of the contra-rotating (CRP) increase compared to the single propeller, leading to a significant reduction of the propeller diameter. The variation in axial spacing and angular displacement seems to have little effect on the CRP efficiency. The results also show that the thrust can be further improved by adopting a moderate negative twist angle of the rear propeller.&#x0D; Keywords: CRP contra-rotating propeller, axial spacing, angular spacing, twist angle, CFD.

Acoustic theory of the many-bladed contra-rotating propeller: the event line and the precession of the interaction source

Abstract