Front Propeller Research Articles

Aerodynamic and aeroacoustics investigation of tandem propellers in hover for eVTOL configurations

The present study investigates the aerodynamic interactions and the aeroacoustic footprint of a tandem propellers configuration typical of a multi-rotor eVTOL aircraft in hover conditions. In particular, an experimental campaign was conducted to collect a comprehensive aerodynamic and aeroacoustic database over two scaled propellers models in tandem. Aerodynamic loads and acoustic measurements were performed in an anechoic test chamber. Measurements also included flow field surveys using stereoscopic PIV technique. The configurations tested included twin propellers in side-by-side and staggered configurations with partial overlap between rotor disks. The activity was completed by numerical simulations performed with the mid-fidelity aerodynamic solver DUST. The analysis of experimental and numerical results enabled to provide a robust comprehension of the different flow mechanisms that characterise aerodynamic interaction between propellers wakes by changing longitudinal and lateral distances as well as blades sense of rotation. In particular, the effects of these interactions on both the aerodynamic performance and aeroacoustic footprint was investigated. Specifically, the partial overlap between propellers disks leads to a conspicuous reduction of aerodynamic performance of the propeller invested by front propeller slipstream as well as an increase of the acoustic emission of the dual propeller system.

Research on layout optimization for propellers of a submarine operation vehicle

The submarine operation vehicle was an important equipment for exploring the marine environment and performing underwater tasks. In this paper, the calculation and analysis of hydrodynamic performance and the layout optimization of the propellers under different layouts were completed. Based on the left-right symmetrical layout of the four ducted propellers, the two ducted propellers were taken as the research object to optimize its vector layout, and an approximate model was constructed according to the numerical calculation results under different combinations of propeller spacing and deflection angle. The simulation calculation and verification are carried out, and the optimal layout of the four ducted propeller were determined considering the interference between the ducted propellers on both sides. Finally, an experimental platform for the thrust test of the two ducted propellers were built. It was found that the axial thrust ratio of the rear propeller and the front propeller in experimental results were in good agreement with the simulation results, which verified the feasibility of using the numerical simulation method to study the mutual interference between the ducted propellers.

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.

Numerical investigation of ventilated cavity dynamics over a submerged body in the wake of a propeller

The front propeller designed on the cavity ship will promote the development of ventilated cavity downstream. The characteristic of interference from the submerged body on the propeller wake flow is a challenging hydrodynamic problem. In this paper, the detached eddy simulation (DES) method and the Schnerr-Sauer cavitation model are used to simulate a propeller-ventilated submerged body. The numerical method is verified by comparing simulations of a single propeller to available experimental data. This work shows that the submerged body interferes with the characteristics of the propeller blade tip vortex downstream and affects the hydrodynamic performance of the structure, including thrust and drag. Ventilation over the surface of the submerged body results in lower propeller efficiency and less drag. Meanwhile, ventilated cavity presents an obvious effect on the velocity field and vorticity field around the submerged body. Moreover, analyses of the vortex structure, indicate that the addition of the submerged body suppresses the attenuation of the vortex downstream, which makes it easier for the propeller blade tip vortex to develop downstream.

Aerodynamic interaction between tandem overlapping propellers in eVTOL airplane mode flight condition

The architecture of new electric aircraft concepts (eVTOLs) for urban air mobility is typically characterised by multi-propellers in tandem configurations with different degrees of rotor disks overlapping. Consequently, the aerodynamic interaction between front propellers slipstream and rear propellers represents one of the key-phenomena which influenced the performance and design of these novel aircraft configurations. A wind tunnel campaign was performed to investigate the aerodynamic interaction between two propellers in tandem with particular focus to airplane mode flight condition of eVTOLs. A systematic series of tests, including thrust and torque measurements and stereoscopic Particle Image Velocimetry (PIV) surveys, were performed on two co-rotating propellers models. The axial distance was fixed during tests while the lateral separation distance was changed to evaluate the effects of aerodynamic interaction on propellers performance and flow field due to different propeller disks overlapping. Load measurements pointed out a remarkable loss of rear propeller thrust occurring when the degree of overlapping between rotors disks is increased. On the other hand, spectral analysis of measured loads signals showed a higher amount of thrust fluctuations amplitude occurring when the degree of overlapping between propeller disks is partial. Stereo PIV results provided insights on the effects of aerodynamic interaction on rear propeller inflow and wake flow physics. Moreover, numerical simulations performed using a mid-fidelity aerodynamic solver based on vortex particle method (VPM) provided enhanced insights to comprehend the interacting flow mechanisms between front propeller slipstream and rear propeller blades responsible for the detrimental effects observed on rear propeller performance.

The effects of heave motion on the performance of a floating counter-rotating type tidal turbine under wave-current interaction

Wave induced motions due to actual sea state conditions will impact the performance of floating counter-rotating type tidal turbines. The wave-current interaction is a significant factor in determining the heave motion of turbines. The present study aims at investigating the effects of heave motion on the performance of a floating counter-rotating turbine under wave-current interaction. In this study, the numerical method is used to study how the heave amplitude and frequency affect the main hydrodynamic coefficients of the turbine, including the power coefficient and thrust coefficient. The form of sliding mesh combined with overset mesh is adopted, and the heave motion of the turbine is realized by the movement of the overset mesh. The simulation results show that the heave motion has an adverse effect on the hydrodynamic performance of the counter-rotating tidal turbine. The heave motion will reduce the mean power coefficient and the mean thrust coefficient by about 9% and 5% respectively. The reduction in mean thrust and power is mainly due to less optimal rotor operation caused by the hydrodynamic effects associated with oscillating inflow. The front propeller is more susceptible to heave motion than the rear propeller. Furthermore, the effects of wave on the hydrodynamic performance of turbine are studied by changing the immersion depth of the turbine. The wave will increase the power coefficient slightly, but at the same time, also increase the probability of heave motion. The results can provide data to study motion response of floating tidal turbines under wave-current interaction and control design of the output electricity.

Aerodynamic performance of mutual interaction tandem propellers with ducted UAV

This paper describes progress made on the new design and analysis of a twin-propeller (front and rear) with duct. Major advantage of this design is that the Unmanned Aerial Vehicle (UAV) could complete the mission with only one engine, in the case of failure in one of the engines. Such a design also makes a fair weight distribution within the UAV, which makes it more stable. Furthermore, this design makes it possible to arm the UAV with missiles and other military equipment easily. Ducts traditionally increase the propulsive force produced by propeller at high speeds. Improper design of the duct can result in performance loss of the UAV. Therefore, the UAV model with Six different duct configurations is analyzed to find the most appropriate duct design. The Moving Reference Frame (MRF) method is implemented and examined in CFD simulations for flows around a moving rigid body. Variations included rotational speed of the propeller, incident angle allowing a comprehensive understanding of the overall aerodynamic characteristics of this design. The results of this study show good conformity with the experimental outcomes. Lift force and drag force are studied with different angles of attack. This work shows that rear and front propeller design with duct improves the efficiency by 6%, which offers better performance than two-propeller (without duct) designs.

Numerical investigation on hydrodynamic performance of new canard-configuration tandem propellers

The complex flow field interference between the front and rear propellers will affect the efficiency of the tandem propeller. To reduce or utilize this kind of interference and improve efficiency, inspired by the excellent aerodynamic performance (lift-drag ratio) of the plane with canard-configuration wings, an exploratory numerical study has been carried out to investigate the hydrodynamic performance of new canard-configuration tandem propellers based on RANS method with SST k-ω turbulence model and moving reference frame using the STAR-CCM+ solver. The effect of diameter ratio, axial distance and angular displacement on the hydrodynamic performance of the tandem propeller has been widely investigated. In order to get a general conclusion, the new tandem propellers were designed based on two traditional tandem propellers, CLAU3-30-1-10-20-0 and CLB4-55-1-10-21-23.7. The numerical approach was applied to simulate the open water performance of the two traditional propellers first and the comparison of numerical results with the experimental data was in a good agreement. The study reveals that the efficiency of the tandem propeller can be improved by decreasing the diameter of the front propeller to a certain extent. Generally, the efficiency is also increasing with the increase of axial distance, but an extreme small axial distance with a specified angular displacement can improve the efficiency significantly, and the flow field interaction between the front and rear propeller blades was investigated to explain the efficiency improvement. The optimum angular displacement, which is important for a tandem propeller design, is related to the axial distance and the working condition (advance coefficient) of the propeller. Furthermore, the redistribution of the negative pressure on the front and rear propeller blades using the canard-configuration may lead to a better cavitation performance than that of the traditional tandem propeller. Generally, this study presents a comprehensive study on the effect of three important geometrical parameters on the performance of the tandem propellers and demonstrates some advantages of the new canard-configuration tandem propellers over the tradition tandem propellers. The results have certain significance for the design and development of new tandem propellers.

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.

Numerical investigation on the flow characteristics and hydrodynamic performance of tandem propeller

The hydrodynamic performance of tandem propeller (two co-rotating KP458 propellers) is investigated by an FVM (Finite Volume Method) based approach in this study. The effects of advance ratio J (0 ≤ J ≤ 0.7), spacing ratio (0.26 ≤ L/Df ≤ 0.34) and diameter ratio (0.92 ≤ Da/Df ≤ 0.97) are comprehensively studied and analyzed. A three-dimensional cubic computational domain is considered in this study, and the MRF (Moving Reference Frame) approach is adopted to handle the rotation of the tandem propeller mathematically. Turbulence is accounted for with the RNG k-ε model. It is demonstrated that the hydrodynamic forces maximize at a spacing ratio of 0.29 if the diameter ratio equals 1.0. It is also found that the efficiency is improved by approximately 45% for the tandem propeller with the diameter ratio being 0.95 at L/Df = 0.29, compared to the single propeller, at J = 0.7. In addition, by appropriately specifying the spacing ratio or the diameter ratio, the rotation of rear propeller could well absorb the energy of the trailing vortices shed from the front propeller. Consequently, the trailing vortices are rapidly dissipated and disappear in the wake field after merging, and a better hydrodynamic performance can be obtained.

Acoustic noise measurement in counter-rotating propellers

The acoustic noise and flow condition of tandem propellers in a horizontal axis-type tidal stream power unit, which is composed of counter-rotating propellers and double-rotational armature-type generator without traditional stators, were experimentally investigated. The front and rear propellers rotate in opposite directions and drive the inner and outer armatures, respectively; the rotational torque of the front propeller coincides with the torque of the rear propeller. The front blade profile exerts a great effect on noise generation from the tandem propellers, but the effect of the rear blade profile is comparatively small. The sound pressure level is largely concentrated at low frequencies, and most predominant frequencies can be predicted by Hanson’s method. These predominant frequencies are mainly caused by the tip vortex shedding from the front and rear blades in the counter-rotating propellers. The vortex shedding from the front blade does not affect the rear blade. As a result, the acoustic noise is weakened as long as the diameter of the rear propeller is smaller than the diameter of the front propeller.

A numerical study on performance improvement of counter-rotating type tidal stream power unit

One of the forms of ocean energy, tidal stream energy is attracting attention as a sustainable, predictable and eco-friendly ocean energy source. Unique tandem propellers that can counter-rotate have been designed to generate electric power effectively from a tidal stream. This type of power unit has several advantages compared to the conventional unit with a single propeller and the increase in efficiency of counter-rotating type tidal stream power unit has already been proven. The counter-rotating type tidal stream power unit has a complex interrelationship between the front and rear propeller contrary to the conventional single propeller type tidal turbine. Such as, the no-load area on the front propeller, the diameter ratio of front and rear propeller and the rotational speed of each propeller, etc.. And the inlet condition of the rear propeller is very important to improve the efficiency. Thus, we have to consider these parameters to optimize tidal stream power unit. In this research, the numerical optimization algorithm with response surface method and adaptive single-objective optimization method are applied to obtain desirable propeller performance.

Counter-rotating type tidal stream power unit: Excellent performance verified at offshore test

A counter-rotating type tidal stream power unit, composed of tandem propellers and a peculiar generator with double rotatable armatures, was provided for verification tests at offshore. The front propeller with diameter of 1 m has three blades, and the rear propeller with diameter of 0.95 m has five blades. The blade profiles were optimized with the blade element-momentum theory and CFD, and then covered with CFRP. The front and the rear propellers connect to inner and outer armatures in a synchronous type generator with net output 1.5 kW, whose efficiency was improved by heat pipes and the modification of the armature profiles. The shafts are equipped with mechanical seals to protect electric circuits from seawater. A rotational speed control system was also prepared not only to adjust the output but also to overcome the static friction torque due to bearings, slip rings and mechanical seals while starting-up. The power unit takes the maximum output with excellent efficiency at the relative tip speed ratio specified in the unit design. The unit can start-up after maintenance works and the output can be adjusted smoothly in the stream.

Modeling and Analysis of Chaos and Bifurcations for the Attitude System of a Quadrotor Unmanned Aerial Vehicle

A model of the attitude system for a quadrotor unmanned aerial vehicle (QUAV), assumed to be a rigid body, is developed. For specific parameter configurations, a chaotic region with a saddle and two stable node‐focus equilibrium points is identified. The chaotic model provides an important reference for dynamic analysis and a challengeable task of controller design once the flight enters the chaotic region of parameters. The pitchfork bifurcation of the equilibrium points is provided. Rich dynamics of the system are revealed by two bifurcation regions, which demonstrates the diversity of the flight behaviors as the parameters vary. One bifurcation analysis is with respect to the speed of the front propeller and the speed difference of the front and left propellers, and another one is with respect to the speed of the front propeller and moment of inertia. The dynamic characteristics of the QUAV are further verified by the Casimir power bifurcations. The trajectories of three settings with different structural parameters are analyzed in detail. The stability of the QUAV is found to be enhanced for certain optimized values of the structural parameters. Finally, using the Casimir power and Lagrange multiplier method, a supremum bound of the chaotic attractor is presented.

CFD Analysis of Contrarotating Open Rotor Aerodynamic Interactions

High efficiency and low fuel consumption make the contrarotating open rotor (CROR) system a viable economic and environmentally friendly powerplant for future aircraft. While the potential benefits are well accepted, concerns still exist with respect to the vibrations and noise caused by the aerodynamic interactions of CROR systems. In this paper, emphasis is placed on the detailed analysis of the aerodynamic interactions between the front and aft propellers of a puller CROR configuration. For the first step, unsteady Reynolds-averaged Navier-Stokes (URANS) simulations coupled with dynamic patched grid technology are implemented on the isolated single-rotating propeller (SRP) configuration in various operating conditions in order to test the accuracy and feasibility of the numerical approach. The numerical results are verified by a wind tunnel test, showing good agreements with the experimental data. Subsequently, the URANS approach is applied to the CROR configuration. The numerical results obtained through the URANS approach help to improve the understanding of the complex flow field generated by the CROR configuration, and the comparison of SRP flow field and CROR flow field allows for a detailed analysis of the aerodynamic interactions of the front propeller blade wakes and tip vortices with the aft propeller. The main reason of the aerodynamic interactions is the mutual effects of the blade tip vortices, and the aft propeller reduces the strength of the blade tip vortices of the front propeller. Aerodynamic interactions will lead to the periodic oscillations of the aerodynamic forces, and the frequency of the oscillations is linked to the blade numbers. In addition, a CROR has a larger thrust and power coefficient than that of the SRP configuration in the same operating conditions. The URANS approach coupled with a dynamic patched grid method is tested to be an efficient and accurate tool in the analysis of propeller aerodynamic interactions.

Numerical investigation of the performance of Contra-Rotating Propellers for a Remotely Piloted Aerial Vehicle

The present work aims at the numerical prediction of the performance of a Contra-Rotating Propellers (CRP) system for a Remotely Piloted Aerial Vehicles (RPAV). The CRP system was compared with an equivalent counter-rotating propellers configuration which was set by considering two eccentric propellers which were rotating at the same speed. Each contra-rotating test case was built by varying the pitch angle of blades of the rear propeller, while the front propeller preserved the original reconstructed geometry. Several pitch configurations and angular velocities of the rear propeller was simulated. Comparisons showed an improvement of the propulsive efficiency of the contra-rotating configuration in case of larger pitch angles combined with slower angular velocities of the rear propeller.

Month in the Patent Office

Screw propellers arranged in tandem and oppositely rotated are adapted to be varied in pitch by a double sun and planet control of one propeller by an operating gear passing through the hollow propeller shaft whilst the first propeller through a second set of double sun and planet gears adjusts the second propeller. An electric motor 29, or a hydraulic motor, is employed to actuate the shaft 25 carrying at its lower end a bevel wheel 24 which meshes with a bevel wheel 23 on a tubular shaft 20 which passes through the hollow hub and at its forward end carries a spur‐wheel 30. Within this shaft 20 is a second shaft 19 which is fixed at its inner end to the engine casing 21, and at its other end carries a gear wheel 22. These wheels 22 and 30 constitute twin sun wheels and between them is a spider 31 carrying planet wheels 32, 33 of which the wheels 32 which mesh with the fixed sun wheel 22 also coact with an internally toothed ring 34 mounted to rotate as one with the front propeller 11, while the planet wheels 33 which mesh with the adjustable sun wheel 30 also coact with an internally toothed ring 35 which is freely mounted on the propeller and which by reason of the outer ring of teeth 36 and the pinions 37 provide for the actuation of the shaft 38 whereby the pitch of the blades is adjusted. The shaft 38 is continued to carry a pinion 41 which meshes with the second pinion 42 freely mounted on the hub and continued to drive a similar double sun and planet wheel layout which in turn actuates the adjusting shaft 52 of the second propeller 12. The arrangement for actuating the pitch adjusting gear is also utilized to actuate a pitch indicator and for this purpose the spindle 25 carries an extension which through suitable gearing is conveyed to the indicator. Specification 398,993 is referred to.