Coaxial Propellers Research Articles

Design and development of a novel multirotor configuration with counter-rotating coaxial propellers

In this study, a novel multirotor configuration has been developed, which utilizes a coaxial counter-rotating propeller with a large diameter at the center and four propellers with smaller diameters on four arms in an X configuration. The research pursues two main objectives. The first objective is to establish a development method for multirotors based on the well-known V-method approach in system development. The proposed method enables the design team to analyse and evaluate the multirotor at each stage of the design process, from the system to the component level, and improve the design with greater speed and accuracy. Additionally, the proposed approach can be integrated with various optimization methods, if necessary, to achieve an optimal design. The second objective is to provide the proof-of-concept of the novel multirotor configuration. This objective is pursued across different evaluation sections, from evaluating individual components to fully evaluating the multirotor, to assess the performance of this novel configuration and identify its advantages and disadvantages. The results of various evaluations demonstrate the proposed development process's practicality and proves that the novel configuration is operational and competitive with conventional multirotors in various applications.

Aerodynamic Performance Evaluation of a Coaxial Octocopter Based on Taguchi Method

Abstract The design and optimization of propellers for unmanned aerial vehicles (UAVs) are essential for optimal performance and high efficiency. This study presents a numerical investigation of the aerodynamic performance of coaxial octocopters using openfoam as flow solver. While the aerodynamic performance is affected by many parameters, the current study focuses on four main parameters: the propeller type, the horizontal and vertical separation distances between the propellers, and the ratio between the rotational speeds of the upper propeller and the lower one. To find the minimum number of simulations to be performed within defined limits, and reduce the number of computational fluid dynamics (CFD) simulations that cause high computational cost, Taguchi method was employed. In this study, average thrusts were calculated for the preliminary design of the octocopter by examining an isolated single propeller and dual- and quad propellers taking their rotation directions into account. The Taguchi design matrix revealed that for all cases investigated, the propeller type is the most dominant design parameter followed by the velocity ratio of the upper propeller to the lower one (nU/nL) and vertical (z/D) and horizontal (ℓ/D) orientation of coaxial propellers. However, it was shown that ℓ/D and z/D may play a significant role in vortex formation and pressure fluctuations which should be considered as design criteria for coaxial octocopters associated with flow attributes. The results showed that the aerodynamic performance parameters are not dependent on all the selected parameters, and demonstrated that the selected propeller designs improved aerodynamic performance.

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.

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.

Flight simulation from takeoff to yawing of eVTOL airplane with coaxial propellers by fluid-rigid body interaction

In this study, we adopt a coupled fluid-rigid body simulation using the moving computational domain method and multi-axis sliding mesh method for the takeoff, hovering, and yawing flight of an electric vertical takeoff and landing aircraft (eVTOL). The aircraft model has four pairs of coaxial propellers, and the computational domain is divided into three domains to move the aircraft and eight propeller domains to rotate the propellers. As a result, we clarify the behavior and aerodynamic force of the aircraft when the input values are determined by the automatic control. The results in the flow field also show that the downwash spreads in a crisscross pattern on the ground, the wind reaches different ranges on the ground depending on the flight altitude, and that the coaxial propeller causes an asymmetry in the velocity field during yawing. Consequently, we conclude that this method is effective for the flight simulation of an eVTOL.

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.

Numerical Prediction of Unsteady Aerodynamics of a Ducted Fan Unmanned Aerial Vehicle in Hovering

Recently, ducted fan unmanned aerial vehicles (UAVs) have attracted considerable attention due to their potential for application in both civil and military missions. Compared with free propellers, the presence of duct can in principle decrease the flow contraction after propeller, and gives the potential to fly efficiently with high security, compact structure, and low noise. In the present study, a ducted fan UAV is designed using the open source code OpenProp. The computational fluid dynamics (CFD) simulation model using sliding mesh technique is established and validated as a reliable tool for highly vortical flows by propeller thrust experiment. The effect of the duct, revolution speed, and distance between propellers on the aerodynamic characteristics of the ducted fan UAV is evaluated in detail. Results show that the unducted coaxial upper and lower propellers generate 3.8%, 4.3% more thrust than the unducted single propellers, respectively, and the unducted upper and lower propellers generate 55.9%, 34.9% more thrust than ducted propellers, respectively. The ducted fan UAV generates 5.7% more thrust and consumes 39.1% less power than the unducted coaxial propellers. The thrust of the ducted fan UAV increases first and then follows with a decreased tendency as the distance between propellers increases.

Design and Analysis of Coaxial Ducted Propulsion Systems of Unmanned Aerial Vehicles

Drone Technology is one of the major areas of research in numerous aspects and purposes. Less flight time and more power consumption has become the major problem in flying drones and UAVs. This project aims in analysing the thrust and other parameters of Coaxial propellers by ducting them uniquely and comparing them with conventionally ducted propellers. Ducting increases the thrust and in this, two propellers were individually ducted. Increase in the efficiency will allow the drones to fly effectively with adequate power consumption. The experiment results were tabulated and compared with each different case such as hover and forward flight configurations. In this Coaxial system one propeller rotates in Clockwise whereas the other in Counter-clockwise direction.

ВПЛИВ ЗАЗОРУ МІЖ РЯДАМИ СПІВВІСНОГО ПОВІТРЯНОГО ГВИНТА НА ТЯГУ

The thrust of a turboprop engine depends on many factors, one of which is hydraulic loss when flowing around the propeller blades. When using coaxial propellers, this factor plays an even greater role, since in this case the losses associated with the swirl sheet behind the first propeller were added. The aim of the work is to assess the influence of the axial clearance between the rows of the coaxial propeller on the thrust. The object of the study is a coaxial propeller. The axial clearance between the rows of the propeller ranged from 650 mm to 950 mm. Geometrically, the calculation model was a cylinder with a radius of 75 m and a height of 150 m. A coaxial propeller was located in the center of the cylinder. The investigated computational model is divided into four subregions: the external environment, the input guide vane, the first row of the propeller, the second row of the propeller. Separation of the calculation model into those listed below for the region allows us to evaluate the effect of the engine air intake on the propeller parameters and to ensure the correct modeling of flow around two rows of the propeller. In the first step of the study, a comparison was made of the results of numerical simulation with the results of an approved mathematical model for a version of a propeller with an axial clearance of 650 mm. The calculations were carried out with three models of turbulent viscosity: k-ω, SST, SST Gamma Theta Transitional. Based on the comparison, the SST turbulent viscosity model was selected for further research. The second research step included flow modeling for a modified coaxial propeller with an axial clearance between the propeller rows of 950 mm. According to the results of the study, it was found that the magnitude of the axial clearance between the rows of coaxial propeller affects the thrust. It is shown that when the clearance between the rows of the propeller increases from 650 mm to 950 mm, the thrust of the propeller increases by 17 %. This can be explained by a decrease in the level of unevenness and hydraulic losses behind the second row of the propeller. In the future, the obtained results of a numerical experiment require agreement with a field experiment.

Virtual Modelling and Testing of the Single and Contra-Rotating Co-Axial Propeller

Propellers are a vital component to achieve successful and reliable operation of drones. However, the drone developer faces many challenges while selecting a propeller and a common approach is to perform static thrust measurement. However, the selection of a propeller using a static thrust measurement system is time-consuming. To overcome a need for the static thrust system a virtual model has been developed for measuring both the static and dynamic thrust of a single and coaxial propeller. The virtual model is reliable enough to minimize the need for full-scale tests. The virtual model has been built using two open-source software Qblade and OpenFoam. Qblade is employed to obtain the lift and drag coefficients of the propeller’s airfoil section. OpenFoam is utilized to perform the flow simulations of propellers and for obtaining the thrust and torque data of the propeller. The developed virtual model is validated with experimental data and the experimental data are obtained by developing a multi-force balance system for measuring thrusts and torques of a single and a pair of coaxial contra-rotating propellers. The data obtained from the propeller virtual model are compared with the measurement data. For a single propeller, the virtual model shows that the estimated forces are close to the experiment at lower rotational speeds. For coaxial propellers, there are some deviations at the rear propeller due to the turbulence and flow disturbance caused by the front propeller. However, the computed thrust data are still accurate enough to be used in selecting the propeller. The studies indicate that in the future, these virtual models will minimize a need for experimental testing.

Computerized Fluid Dynamic Study of Parameter Effects on the Performance of Coaxial Propellers

The computerized fluid dynamic (CFD) analysis was performed for 1.8 m diameter coaxial propellers to be applied to the multi-copter type Personal Air Vehicle (PAV) having conceptually 600 kg of Maximum Take-Off Weight (MTOW). Methods/Statistical analysis: Using the commercial CFD program STAR-CCM+ (13.03.11), the coaxial propellers were analyzed at the same RPM under the steady state condition. The three-dimensional Compressible Reynolds Mean Navier-Stokes equation was applied and the Moving Reference Frame (MRF) technique was used. With the optimum single pitch angle of upper propeller, the lower propeller’s pitch was changed for the varying propeller spacing to identify the performance variation and the interference effect. The lower propeller has to be different pitch setting other than the upper propeller’s optimum pitch angle because of the interfered flow effect between propellers. The propeller spacing is not so sensitive to efficiency if the spacing is more than 0.25 of propeller diameter. Study shows that the identified pitches and spacing of coaxial propellers are essential for designing the configuration and control of multi-copter type PAV which uses variable pitch propellers for safety and efficiency.

ACOUSTIC EMISSION DIRECTIVITY PATTERN OF THE COAXIAL PROPELLER FAN

The problem of further aircraft noise abatement is one of the priority issues in civil aviation. In order to improve engine efficiency, the coaxial propellers (propeller fans) may be used. The review of literature sources shows that parameters of the propeller fan have an effect on directivity of acoustic emission of the propeller fan. The objective of this work is the assessment of increased clearance effect between rows of propellers of the coaxial propeller fans on intensity and directivity of acoustic emission of the propeller fan. The engine with two row coaxial propeller fan has been selected as the object. Diameter of the propeller fan is 4.5 m. There is base and modified propeller fan addressed in the work. The work includes acoustic emission patterns for base and modified propeller fan made by research results. The acoustic emission pattern illustrates change of acoustic power when increasing a distance between rows of propeller fan. The peaks of directivity characteristic of total emission exist in backward semi-sphere in the direction of 110º-150º. Based on the results of numerical simulation of the air flow in base propeller fan it is demonstrated that in the inlet of second row of propeller fan there is high level of air distortion. The research results of intensity and directivity of acoustic emission of the coaxial propeller fan shows that the air distortion in the inlet of second row of propeller fan is an additional source of acoustic emission into the backward semi-sphere. When increasing axial clearance between rows of propeller fan by 300 mm, the total acoustic power is reduced by 2.5 — 4.6 dB in the backward semi-sphere. In future it is planned to assess acoustic characteristics of the propeller fan when changing geometry of the second row of the propeller.

A compactly integrated cooling system of a combination dual 1.5-MW HTS motors for electric propulsion

The high temperature superconducting (HTS) contra-rotating propulsion (CRP) systems comprise two coaxial propellers sited on behind the other and rotate in opposite directions. They have the hydrodynamic advantage of recovering the slipstream rotational energy which would otherwise be lost to a conventional single-screw system. However, the cooling systems used for HTS CRP system need a high cooling power enough to maintain a low temperature of 2G HTS material operating at liquid neon (LNe) temperature (24.5 - 27 K). In this paper, a single thermo-syphon cooling approach using a Gifford-McMahon (G-M) cryo-cooler is presented. First, an optimal thermal design of a 1.5 MW HTS motor was conducted varying to different types of commercial 2G HTS tapes. Then, a mono-cryogenic cooling system for an integration of two 1.5 MW HTS motors will be designed and analyzed. Finally, the 3D finite element analysis (FEA) simulation of thermal characteristics was also performed.

Experimental Investigation on Aerodynamic Characteristics of Propeller in a Ducted-Fan Type VTOL UAV

An experimental investigation was completed with the objective of determining the performance characteristics of propeller in a Ducted-Fan Type VTOL UAV. The model consisted of three groups of two-bladed propellers with or withou an annular duct. The propellers share the same diameter but differernt blade pitchs.Model variations included the changes of the propeller and the duct shrouded combination. Static propulsion test data showed figure of lift increases with increasing blade pitch. The coaxial propellers lift did not perform as 2 times of the single propeller lift.The duct increase the duct fan system lift effectively.

Mathematical model of acceleration of three-shaft turbofan engines with coaxial propellers

Наведена математична модель турбогвинтовентиляторних двигунів, яка враховує вплив газодинамічної неусталеності і призначена для діагностування авіаційних двигунів на перехідних режимах

Aero Engines and Their Laboratory Testing Under Flight Conditions

T author begins by discussing recent drag and cooling improvements of both air-cooled and liquid-cooled aircraft engines and mentions the latest cooling versions as being the baffled air-cooled engine enclosed in an N.A.C.A. cowl and the high-coolanttemperature liquid-cooled engine with encased or buried radiators. The latest Hispano engine, which is an H type, liquid-cooled model is described. I t drives two oppositely-rotating coaxial propellers, each of which is geared to half of the total number of cylinders as a complete operating unit which may be stopped at any time without impairing the operation of the other half of the unit.