Contra-rotating Propellers Research Articles

Towards a reliable method for extrapolation of propulsion performance for vessels with twin-crp-pod system

The study presents power performance prediction of an Ultra Large Container Ship (ULCS) with hybrid twin-crp-pod propulsion system. Twin crp-pod propulsion system is a combination of three concepts: twin screw, contra-rotating propellers (crp) and conventional shaft propellers with pod propulsors behind. The presented study shows the current extrapolation method for crp propulsion systems and tries to point out its weaknesses. As a case study, a 400 m ULCS has been investigated in full-scale and in model scales of 24 and 37.416. The analyses were carried out for all scales with use of CFD numerical methods and for the scale of 37.416 based on towing tank tests. All the results have been extrapolated with the same method and results have been compared. The investigations clearly show differences in delivered power prediction extrapolated from towing tank results giving the maximum value and from CFD made to scale of 24 the minimum value. Finally, conclusions on possible sources of differences, including the numerical and analytical methods are presented.

Digital Simulation of Coupled Dynamic Characteristics of Open Rotor and Dynamic Balancing Test Research

An aero engine, as the core power equipment of the aircraft, enables safe and stable operation with a very high reliability index, and is an important guarantee in flight. The open rotor turbine engines (contra-rotating propeller) have stood out as a research hotspot for aviation power equipment in recent years due to their outstanding advantages of low fuel consumption, high airspeed, and strong propulsion efficiency. Aiming at the problems of vibration exceeding the standard generated by imbalance during the operation of the dual-rotor system of aircraft development, the difficulty of identifying the coupled vibration under the micro-differential speed condition, and the complexity of the dynamic characteristic law, a kind of numerical simulation of the dynamics based on the finite element technology is proposed, together with an experimental research method for the fast and accurate identification of the coupled vibration of the dual-rotor system. Based on the existing open rotor engine structure design to build a simulation test bed, establish a double rotor finite element simulation digital twin model, and analyze and calculate the typical working conditions of the dynamic characteristics of parameters. The advanced algorithm of double rotor coupling vibration signal identification is utilized to carry out decoupling and dynamic balancing experimental tests, comparing the simulation results with the measured data to verify the accuracy of the technical means. The results of the study show that the vibration suppression rate of the finite element calculation simulation test carried out for the simulated double rotor is 98%, and the average vibration reduction ratio of the actual field test at 850 rpm, 1000 rpm, and 3000 rpm is over 50%, which achieves a good dynamic balancing effect, and has the merit of practical engineering application.

Interaction between the helical vortices shed by contra-rotating propellers

Large eddy simulation is adopted to analyze the interaction between the tip vortices shed by two contra-rotating propellers, by using a computational grid consisting of 4.6 × 109 points. Despite the complexity of the wake topology, the results of the computations show an excellent agreement with the measurements from an earlier experimental study on the same system. The interaction between the tip vortices shed by the two propellers produces vortex rings. Each of them consists of six helical sides, which are connected by U-shaped vortex lobes. The three upstream lobes of each vortex ring move to outer radial coordinates, as a result of their shear with the downstream lobes of the upstream vortex ring. In contrast, the downstream U-shaped lobes move to inner radial coordinates, as a result of their shear with the upstream lobes of the downstream vortex ring. This interaction results in an overall expansion of the wake of the contra-rotating propellers. The regions of shear between the U-shaped lobes of consecutive vortex rings are the areas of the largest turbulent stresses, which achieve higher levels than those produced in the wake of the two front and rear propellers working alone. This complex flow physics also triggers a faster instability of the wake system, breaking its coherence at more upstream coordinates, in comparison with the isolated propellers.

Aerodynamic Performance and Numerical Analysis of the Coaxial Contra-Rotating Propeller Lift System in eVTOL Vehicles

Electric vertical takeoff and landing (eVTOL) vehicles possess high payload transportation capabilities and compact design features. The traditional method of increasing propeller size to cope with high payload is no longer applicable. Therefore, this study proposes the use of coaxial counter-rotating propellers as the lift system for eVTOL vehicles, consisting of two coaxially mounted, counter-rotating bi-blade propellers. However, if the lift of a single rotating propeller is linearly increased without considering the lift loss caused by the downwash airflow generated by the upper propeller and the torque effect of the lift system, it will significantly impact performance optimization and safety in the eVTOL vehicles design process. To address this issue, this study employed the Moving Reference Frame (MRF) method within Computational Fluid Dynamics (CFD) technology to simulate the lift system, conducting a detailed analysis of the impact of the upper propeller’s downwash flow on the aerodynamic performance of the lower propeller. In addition, the aerodynamic performance indicators of coaxial counter-rotating propellers were quantitatively analyzed under different speed conditions. The results indicated significant lift losses within the coaxial contra-rotating propeller system, which were particularly notable in the lift loss of the lower propeller. Moreover, the total torque decreased by more than 93.8%, and the torque was not completely offset; there was still a small torsional effect in the coaxial counter-rotating propellers. The virtual testing method of this study not only saves a significant amount of time and money but also serves as a vital reference in the design process of eVTOL vehicles.

FEM MODEL OF AN UNDERWATER VEHICLE THRUSTER PROPELLER

Propulsion research has been done within the context of the project for the design and optimisation of the Remotely Operated Vehicle (ROV). CFD and FEM simulations that took the undersea vehicle's properties into consideration supported the whole project. Optimising the semi-open duct for horizontal propellers—a quantifiable system that offered controllability and propulsion in a horizontal plane—was one of the goals. It was required to examine the construction of propellers with nozzles and contra-rotating propellers, as well as the numerical approach of propeller design, in order to build a model for this work. Theoretical solutions were presented to it, one of which included operating the examined propeller close to an underwater vehicle. Additionally, first qualitative studies of a streamlined system with a semi-open duct and contra-rotating propellers were performed. Making a choice on the ROVs duct shape was made possible by the findings acquired. An actual propeller model was created using the SLS (Selective Laser Sintering) fast prototyping technique. This meant that the propeller's FEM model, which was based on the load determined by the CFD model, had to be verified. The features of the investigated ROV, the theoretical foundation for propeller design for the situations under analysis, and the outcomes of CFD and FEM simulations are all included in this paper.

Jet engine - construction and modern development examples

The article presents the construction and operating principle of a turbine jet engine. The basic types of engines of this type are presented, such as single-rotor single-flow jet engines, single-flow dual-rotor engines (which are another development version of single-rotor engines, as well as dual-flow engines which are currently most commonly used in passenger aviation, and contra-rotating propeller engines and turbine propeller engines. Also presented their applications, such as propulsion of various types of. In the further part of this paper, the development trends of turbine jet engines are described, based on patents that have been granted in recent years. One of the cited patents is the use of a fuel cell to power an electric motor used to start a turbine jet engine. Also presented the concept of an electric motor providing propulsion of aircraft. An engine of this type is devoid of a turbine and a combustion chamber, and the machine shaft rotates only using electricity.

Aeroacoustic measurements of a contra-rotating UAV vehicle

The aerodynamic sound linked to the increasing presence of Unmanned Aerial Vehicles (UAVs) is becoming a societal concern. Assessing the aeroacoustics of these vehicles is of utmost importance, as it enables the evaluation and mitigation of the associated noise emissions. An experimental wind-tunnel investigation is carried out with an octo-quad multi-rotor model UAV with 4 sets of contra-rotating propellers, representative of a heavy-lifting drone, to assess the acoustic emissions of the vehicle under different flow and thrust conditions. The experiments are performed in the Open Jet Facility of the Delft University of Technology. The acoustic measurements from several microphones are combined to create the noise signature of the UAV, while the data from a balance are processed to compute the thrust. The results of this research demonstrate that it is possible to reduce the noise emissions of the drone by varying the operating input between the fore and aft motors. In particular, an attenuation in the overall sound pressure level of 5 to 8 dBA can be achieved if the RPM of the fore motors is decreased while that of the aft motors is increased.

Comparative Research on Topologies of Contra-Rotating Motors for Underwater Vehicles

Underwater vehicles have been widely used in marine exploration and development. A contra-rotating propeller (CRP) can improve propulsion efficiency, eliminate the roll moment of the propeller acting on underwater vehicles, and significantly improve the dynamic performance of underwater vehicles. Contra-rotating motors (CRMs) are used to drive CRPs. Topologies of CRMs include an armature rotating contra-rotating motor (ARCRM), double contra-rotating motors (DCRMs), and a double rotor contra-rotating motor (DRCRM). In this paper, the design and optimization of these different topological CRMs were realized with analytical calculations of the magnetic field and electromagnetic performance. The efficiency map and losses analysis of CRMs with different topologies are obtained with the finite element method. In order to achieve suitable CRMs to drive the CRPs of underwater vehicles, three topologies for CRMs will be compared comprehensively from the perspective of structure, weight, size, loss, and efficiency. For low-speed, high-torque CRPs, the ARCRM has been proven to improve efficiency and power density. An ARCRM prototype was developed to verify this solution and its reliability.

Acoustic and psychoacoustic characterisation of small-scale contra-rotating propellers

This paper reports an experimental investigation of noise radiation and psychoacoustic evaluation of contra-rotating propellers with different blade counts over multiple emission angles and thrust settings. A series of aeroacoustic and psychoacoustic tests were performed with a contra-rotating propeller rig at the University of Salford, UK, where both propellers’ blade count and their axial separation z were varied at static conditions and constant thrust. The sounds were analysed using conventional acoustic metrics, such as Sound Pressure Level (SPL) and Sound Power Level for tonal, broadband, and overall noise, and using the psychoacoustic Sound Quality Metrics (SQMs) Loudness, Fluctuation Strength, Roughness, Tonality, and Impulsiveness. Configurations with axial separation-to-diameter ratio z/D between 0.2–0.4 exhibited a balance between tonal and broadband noise generation mechanisms, resulting in reduced noise levels and reduced annoyance for on-axis observers. The number of blades played a secondary role on determining noise levels: higher blade counts resulted in lower overall noise levels at larger axial separations, although at shorter distances (z/D<0.2) increasing the blade count led to higher noise levels. The SQMs Loudness, Fluctuation Strength, and Tonality were found to also reach a minimum at z/D=0.3, although increasing the number of propeller blades led to a decrease in Loudness but not in Fluctuation Strength and Tonality. The dominant noise generation mechanisms observed here present a directivity null perpendicular to the propellers’ axis, and no clear trends were observed for acoustic and psychoacoustic metrics at this emission angle. A listening experiment was set up to validate the results of the acoustic and psychoacoustic analysis, and its results suggest that the reported noise annoyance is driven by Loudness, Fluctuation Strength and Tonality metrics (p<0.01) at on-axis radiation, while at 90° emission angle, Loudness (p<0.01) and Tonality (p<0.05) are the main contributors to noise annoyance.

Acoustic imaging of the broadband noise arising in contra-rotating co-axial propellers

The interaction between two contra-rotating co-axial propellers leads to variations in noise strength during the rotation and presents challenges for traditional acoustic measurement methods. In this work, we propose using a wavelet-based beamforming method to study the transient noise generation characteristics of the contra-rotating co-axial propellers. Compared to the conventional beamforming method, the wavelet-based beamforming method can address unsteady and high-speed moving noise sources in the time-frequency domain. A representative set-up is considered herein. The acoustic imaging results show that the transient noise sources increase after the overlap of the propellers and are dominant on the aft propeller, particularly at high frequencies and low rotating speeds. At relatively high rotating speeds, the results show that the contra-rotating propellers noise can be generated at the trailing edge near the hub of the propellers. Overall, the wavelet-based beamforming method deepens the physical understanding of transient aerodynamic and aeroacoustic processes, and could find applications in the design of low-noise contra-rotating propellers.

Effects of Stage Spacing on Contra-Rotating Propeller Aerodynamic Interactions

To identify the law of aerodynamic interactions of contra-rotating propellers (CRPs) and improve their aerodynamics, this study investigates the aerodynamic interactions of 4 CRPs (six blades in front and six in back) with different stage spacings using the Reynolds-averaged Navier-Stokes (RANS) equations-based method. The results showed that the CRP whose stage spacing was 0.25 times the propeller diameter delivered the highest average efficiency and that the aerodynamic interactions between the front and rear propellers decreased as the spacing widened, and compared with the rear propeller, the front one was more sensitive to stage spacing due to the aerodynamic interaction-generated thrust fluctuations. It can be seen that stage spacing exerts a significant effect on CRP aerodynamic interactions. Therefore, choosing an appropriate stage spacing in CRP design is of great significance to enhance its aerodynamics.

Tri-Rotor Propeller Design Concept, Optimization and Analysis of the Lift Efficiency During Hovering

This study introduces the simulation of a tri-rotor contra-rotating propeller for thrust force and hover lift efficiency during vertical take-off. Vertical take-off or landing is a method used by many aircraft and makes the vehicle more convenient and easier to use. The second rotor revolved in the opposite direction of the first and third rotors. The proposed multi-rotor system has NACA 0012 untwisted and symmetric airfoil and includes three rotors with two blades for each. The airflow analysis was optimized with computational fluid dynamics simulation by using different pitch combinations to achieve the highest hover lift efficiency with sufficient overall thrust value. The critical angle of attack for the chosen airfoil gave the boundary conditions for the pitch of rotors. The results showed us that the most efficient combinations for three rotors work better with an increase of pitch angle from top to bottom so that there is a difference of at least two degrees between propellers. Experiments with angles of attack within the boundary conditions showed that the blade combinations starting from three degrees and increasing values gave positive and adequate results in many cases. In addition, the results showed that a regular increase in the angle of attack does not relate to a regular increment in thrust force.

Hydrodynamic Shape Design and Self-Propulsion Analysis of a Hybrid-Driven AUG

Due to the lack of a powerful propulsion device in conventional autonomous underwater gliders (AUGs), their mobility and flexibility are insufficient, thus not being capable of also ensuring the stability of the motion route. Thus, it is necessary to further develop hybrid-driven AUGs. This paper applied CFD simulation and experimental analysis methods to study and design a hybrid-driven AUG with a propeller optimized from a type of AUG with swept-forward and swept-back wings. Through parameter adjustment, the hydrodynamic configuration was optimized, and the optimal hull design and hydrofoil type selection were proposed. The lift–drag ratio could be improved by up to 22.5% at an angle of attack of 8 degrees. The optimized AUG was combined with a single propeller for self-propulsion simulation. Aiming at the problem caused by the propeller torque on the AUG, the strategy of a contra-rotating propeller (CRP) was conducted to self-eliminate the propeller torque. The simulation results show that in the self-propulsion state, the torque of the contra-rotating propeller could be reduced by more than 92% compared with that of a single propeller, greatly reducing the impact on the hybrid-driven AUG and raising the navigation stability.

First thrust measurements in ionic multi-propeller rotational engines

Rotary ionic engines (RIEs) with multi-coaxial contra-rotating propellers (12.6 cm diameter) and their axial thrust are investigated in laboratory conditions, in air at atmospheric pressure, for the first time. The goal is to evaluate more advantageous configurations that may be scaled up and further help with development of rotary ionic drones. The propellers are designed with regular pin-emitter electrodes placed coaxially inside a cylindrical collector electrode. When high voltage is applied, propellers spin generating conventional axial thrust which is measured with an electronic scale in a “see-saw” setup. Up to 40 mN thrust was obtained in single propeller RIE at 2600 rpm, 0.34 mA, 37.5 kV, and an optimal collector electrode diameter of 17 cm. More thrust can be obtained with two and three propellers at constant current per propeller but at a decreased efficiency. Varying the axial propeller-separation showed that propeller-interaction is minimal above 5 cm. Thrust-to-power and thrust-to-current ratios were calculated and compared. We experimentally confirm here for the first time that within certain limits, the thrust-to-power variation can be assessed by the propeller kinetic energy-to-power ratio and also by the impedance of the gap (voltage-to-current ratio). A comparison of RIE arrays performance with one, two, and three coaxial propellers and the same total number of propellers per array (six) is also performed. RIE arrays with multi-coaxial propellers can provide larger thrust densities than single-propeller arrays. Also, arrays employing two coaxial propeller unit may be more weight effective.

Optimization of a contra-rotating propeller rig for reduced psychoacoustic impact

With unmanned aerial vehicles emerging as potential alternatives for people and cargo transport, their noise impact will be a determining factor in their acceptance by the general public. Contra-rotating propeller configurations are often explored due to their improved aerodynamic performance and redundancy in case of failure compared to conventional single-propeller aircraft, but can be much noisier than their single-propeller equivalent. This work describes the optimization of a custom-made contra-rotating propeller rig for reduced psychoacoustic impact. The rig consists of two electric motors mounted on a rotating stand, positioned 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. The axial distance between the propellers is varied between 0.1 and 1 rotor diameters, and the number of blades is varied between 2 and 6 on both propellers. Meanwhile, the rpm is adjusted to maintain constant thrust across the different configurations. Acoustic pressure signals are investigated in terms of their physical acoustic characteristics and psychoacoustic features (such as Loudness, Sharpness, Tonality, Fluctuation Strength, Roughness and Impulsiveness) in order to determine the trade-offs and optimal choices in reducing the psychoacoustic impact of the rig.

Rapid Blade Shape Optimization for Contra-Rotating Propellers for eVTOL Aircraft Considering the Aerodynamic Interference

The rising interest in the evolvability of electric vertical takeoff and landing (eVTOL) promises substantial potential in the field of urban air mobility (UAM). Challenges in energy storage density and geometry restriction both emphasize the propeller efficiency for endurance and takeoff weight, whereas the contra-rotating propellers (CRP) advantage is balancing high thrust and efficiency over a single propeller. The aim of this paper is twofold: (i) to present a novel rapid CRP blade shape optimization framework and (ii) to study the impact of the dual propellers revolution speed allocations on the overall CRP power efficiency. The core of the framework is the blade element momentum theory (BEMT)-based blade shape optimization considering the wake effect of the upper propeller by the rotational CFD (computational fluid dynamics) actuator-disc simulation method. The results show that for the same thrust, the optimized CRP at the equal revolution speed is superior to the original (upper-lower-identical) one by 5.9% in thrust-to-power ratio. The overall efficiency can be additionally lifted by 5.3% when the dual propellers share similar torques. By excluding the integral propeller CFD simulation and empirical parameters estimation, the framework enables the swift obtaining of an optimized CRP scheme while maintaining robustness as well.

Influence of Aerodynamic Interaction on Performance of Contrarotating Propeller/Wing System

This paper gives a quantitative account of the influence of slipstream on the aerodynamic performance of a contrarotating propeller (CRP)/wing system, and compares it with the CRP and clean wing. To accurately evaluate the complex aerodynamic interaction, the unsteady Reynolds-averaged Navier–Stokes approach using the sliding mesh method is performed at a typical freestream velocity of 30 m/s. Four different critical parameters, including the freestream angle of attack (AoA), axial spacing between the front propeller (FP) and rear propeller (RP), number of blades, and rotational speed, are considered in the present work. The results show that the thrust coefficient, power coefficient, and propulsion efficiency of the CRP/wing system change sharply and the difference in amplitude between adjacent waves is large. In particular, the propeller slipstream has a significant impact on the lift–drag performance of the wing in the case of a nonzero AoA. The presence of a wing also increases the efficiency of propulsion due to the recovery of vortices. In the case of a small axial spacing, the thrust coefficient value of the FP is significantly smaller than that of the RP. However, when the axial spacing exceeds a certain value, the opposite relationship is obtained. When the rotational speed increases from 3695 RPM to 8867 RPM, the lift coefficient and drag coefficient of the wing gradually increase.

Historical development of the coaxial contra-rotating propeller

AbstractWe review the development of the contra-rotating propellers from the origins to the present. Initially, these systems were proposed to increase speed, then to increase propulsive efficiency, and thus reduce fuel burn. Ultimately, they hit another environmental limit: too much noise. Acoustics has been in fact the main focus of the development in the past 30 years. Pioneering work done across countries demonstrated several unique features of this propulsor. Various embodiments are available, namely contra-rotating, counter-rotating, co-axial, tandem, open rotor and prop-fans, collectively named contra-rotating propellers. This review only considers concepts that have been applied to real aircraft, prototypes that are known to have been flight tested (about 70 vehicles), or representative laboratory models. Five classifications are proposed: pioneers (before 1940), golden years (1940–1950), Western airplanes (1950s onwards), Soviet-Russian airplanes (1950s onwards) and modern developments (1980s onwards). Selected experimental aircraft and laboratory concepts are mentioned, where these appear to advance the state-of-the-art. Power plants evolved from internal combustion engines to the modern gas turbine engines requiring new solutions. Engine layouts and propulsion configurations are analysed where appropriate. It is concluded that propulsive efficiency can only be achieved at a cost of multiple engineering problems, some of which remain unsolved.

Numerical simulation of unsteady hydrodynamic performance of CRP

Strong hydrodynamic interference between forward and aft contra-rotating propellers (CRP) can result in load fluctuations, local blade vibrations, and noise. This study adopts a Reynolds-averaged Navier–Stokes solver (RANS) and a shear stress transport (SST) k−ω turbulence model to investigate the unsteady hydrodynamic performance of CRPs during uniform flow. The influences of time step and grid scale on the numerical simulation are discussed first. The numerical results of the open-water hydrodynamic performances of the CRPs agree well with experimental data. The fluctuation patterns of the hydrodynamic loads (i.e., force and torque) and propulsion efficiency of CRPs having different advance coefficients induced by the mutual hydrodynamic interference between the forward and aft propeller are investigated. A series of probes that rotate with the propellers are set upon the surface of the blades to analyze the unsteady local pressures under the hydrodynamic interference between the forward and aft propellers.

Towards Fuel Consumption Reduction Based on the Optimum Contra-Rotating Propeller

This paper presents the effect of selecting a contra-rotating propeller (CRP) for a bulk carrier at the engine operating point with minimum fuel consumption, as well as ensuring the safety of the propeller in terms of cavitation and noise. Using a developed optimization model, the geometry of a CRP was selected for different propeller diameters, the same propeller diameter as that of a fixed pitch propeller (FPP) installed on the bulk carrier, and at 90% of the FPP diameter. Additionally, each case was optimized with both no-cup and heavy-cup configurations. In general, the CRP showed better performance than the FPP in terms of efficiency, cavitation, and fuel economy. At the same time, the level of performance was increased when considering the CRP cupping percentage. It was concluded that the CRP can achieve a gain in fuel economy of up to 6.2% in a no-cup configuration when compared to an FPP, and up to 11.7% with a cupped configuration.