Twin Propeller Research Articles

Influence of tunnel cone angle and lip deflection on the performance of coaxial twin propeller

Abstract To investigate the influence of the culvert cone angle and the angle of the mouth on the aerodynamic performance of the culvert coaxial twin rotor and its mechanism, the quasi-steady numerical simulation of the flow field of the culvert coaxial twin rotor under a hovering state was carried out based on the Reynolds mean Navier-Stokes (RANS) equation and the multiple reference coordinate system method (MRF). The influence of cone angle from -6° to 9° and lip deflection angle from -20° to 30° on the aerodynamic performance of coaxial double-rotors with ducted passages is analyzed. The results show that the contractile culvert can generate a large gain lift force, which is conducive to improving the aerodynamic efficiency of the system. The inward deflection of the lip obstructs the flow of air into the culvert, which will worsen the local aerodynamic environment and lead to serious air separation, increasing the power consumption of the system. However, the structure of the outward deflection of the lip (open culvert) better complies with the flow trend of air, helps to reduce aerodynamic interference, and improves the additional lift of the culvert, which is beneficial to improving the aerodynamic performance of the system.

Analysis of the Impact of Structural Parameter Changes on the Overall Aerodynamic Characteristics of Ducted UAVs

Ducted UAVs have attracted much attention because the duct structure can reduce the propeller tip vortices and thus increase the effective lift area of the lower propeller. This paper investigates the effects of parameters on the aerodynamic characteristics of ducted UAVs, such as co-axial twin propeller configuration and duct structure. The aerodynamic characteristics of the UAV were analyzed using CFD methods, while the impact sensitivity analysis of the simulation data was sorted using the orthogonal test method. The results indicate that, while maintaining overall strength, increasing the propeller spacing by about 0.055 times the duct chord length can increase the lift of the upper propeller by approximately 1.3% faster. Reducing the distance between the propeller and the top surface of the duct by about 0.5 times the duct chord length can increase the lift of the lower propeller by approximately 7.7%. Increasing the chord length of the duct cross-section by about 35.3% can simultaneously make the structure of the duct and the total lift of the drone faster by approximately 150.6% and 15.7%, respectively. This research provides valuable guidance and reference for the subsequent overall design of ducted UAVs.

High-Symmetry Co/Ni Triazine Polycarboxylate Diverse Frameworks Constructed by Mx(COO)y Building Blocks: Characterization and Catalytic Performance Evaluation of p-Nitrophenol.

Three new triazine compounds [Co1.5(H3TDPAT)(H2O)3]·6H2O (1), [Co2(TCPT)(μ2-H2O)2]·OH (2), and [Ni3(TCPT)]·3OH (3) were designed and synthesized via the reaction of the symmetrical triazine ligand connected by C-N-C and C-O-C bonds with triazine poly(carboxylic acid)s ligands as the side arms: H6TDPAT (H6TDPAT = 2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine) and H3TCPT (H3TCPT = 2,4,6-tris(4-carboxyphenoxy)-1,3,5-triazine) as well as the corresponding metal salts under the solvothermal condition. Three triazine polycarboxylate frameworks were characterized by elemental analysis, infrared spectroscopy, ultraviolet spectroscopy, thermogravimetric analysis, X-ray powder diffraction, and solid fluorescent spectra in detail. The structural analysis results showed that the three-dimensional porous cage framework of compound 1 was constructed by three different polyhedral cages connected with [Co(COO)4(H2O)2] building blocks. One of the compounds, 2, is formed by twin propeller Co2(μ2-H2O)(COO)3 building blocks connecting two-dimensional layers and the intermolecular π-π interactions involved the triazine rings between the layers. While the structure of compound 3 is similar to that of 2, assembly is by Ni(COO)3 building blocks and adjacent layers of the face-to-face π-π interaction between the triazine rings. In order to explore functional properties, the catalytic reduction of p-nitrophenol (PNP) of compounds 1-3 was investigated. They exhibit excellent catalytic activity of more than 95% for reduction of PNP with a dose of 2.5 mg of the compounds.

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.

An adaptive composite disturbance rejection for attitude control of the agricultural quadrotor UAV

Aiming at the problem that agricultural quadrotor UAV is easily disturbed in ultra-low altitude phenotype remote sensing and precision hovering of spraying, an adaptive composite anti-disturbance attitude controller is proposed for ground effect and propeller failure disturbances rejection. The adaptive composite disturbance rejection control (ACDRC) is composed of active disturbance rejection control (ADRC) and disturbance observer (DO) based on nominal inverse model, which is used to estimate wind disturbance, payload disturbance and propeller failure disturbance in real time. For the bandwidth tuning of the extended state observer (ESO), an online tuning method based on iterative learning control (ILC) is proposed to realize the adaptive extended state observer (ESO). And the stability of the composite anti-disturbance controller is analyzed. In the experiments, the wind disturbance experiments under the side-down flow and the horizontal flow, the failure experiments under the single propeller failure and twin propeller failure, and the composite disturbances experiments under the simultaneous action of the wind disturbance, propeller failure and payload disturbance are carried out. The experimental results show that under wind disturbance, the anti-disturbance performance of ACDRC is increased by 82.5%; under the disturbance of propeller fault, the anti-disturbance performance of ACDRC is increased by 60%; under the composite disturbance, the anti-disturbance performance of ACDRC is increased by 50%. Finally, the effectiveness of ACDRC is further verified in vegetable and cotton fields.

The effect of appendages on ship resistance

The availability of the robust commercial computational fluid dynamics (CFD) software and the increasing power of high-performance computers (HPC) boosts the use of CFD techniques for numerical investigations of ship hydrodynamimcs performaces. Nowadays, CFD tools provide a rather accurate solution for complex physical phenomena, such as wave braking, turbulence, flow detachment and overturning. Consequently, the ability to capture this fenomena allows a detailed insight into the flow mechanism that trigger and sustain them.The paper focuses on a numerical investigation of flow around hull a fully appended ONR Tumblehome model 5613. Due to special operation conditions, naval ships are equipted with a large number of appendages such as sonar domes, brackets, twin propeller shafts and twin rudders. Position and alignment of these appendages are essential in order to avoid the increased resistance, decreased propulsive efficiency and cavitation. NUMECA/FineMarine commercial code has been used to evaluate the flow field around ONRT (Office of Naval Research Tumblehome) hull and to estimate the effect of the appendages on ship hydrodynamics performances. Comparison with experimental towing tank results showed good agreement with a difference of up to 2%.

Twin propeller time-dependent scouring processes. Physical experiments

We present a new set of experiments in local scour due to confined twin propeller jets aiming to include propeller driving characteristics to the analysis of the scouring action during in-port manoeuvres. The maximum scour depth is studied as a function of the bed clearance, the wall clearance and the efflux velocity of the jet. Aiming to reproduce more realistic manoeuvres, both forward and backward rotation of the propellers are analysed showing a different behaviour. The obtained results are used to propose two different empirical models, one for each regime of rotation. A new non-dimensional parameter obtained from the Buckingham π analysis, proposed as wall Froude number, is used to find a clear threshold triggering the scouring mechanism. The experimental results show that the distance to the vertical wall is the main contributor to the higher scour depths rather than the propeller speed of rotation or the bed clearance.

The effect of uncoupled propulsion and steering on the manoeuvring behaviour in coastal waters

The present paper introduces a mathematical model capable of simulating the behaviour of a twin propeller, twin rudder ship in uncoupled conditions, meaning that the portside and starboard propeller and/or rudder work at different rates, respectively angles. Such conditions are typically applied while manoeuvring in harbour conditions. The mathematical model coefficients are determined based on a captive manoeuvring test program which covers these uncoupled conditions. After implementation in the ship manoeuvring simulator, fast-time simulations have been carried out, which were successfully compared with free running tests in uncoupled conditions as well.

Algorithm of Berthing and Maneuvering for Catamaran Unmanned Surface Vehicle Based on Ship Maneuverability

In the complex port environment, ship berthing manipulation is one of the most difficult operations. In this study, an algorithm of berthing and maneuvering was designed for a catamaran unmanned surface vehicle (USV), which is used for port patrol and protection. Considering the influence of wind, waves, and currents, the mathematical model of the maneuvering movement for the twin-hull and twin-propeller USV was established. Based on the Visual Studio development platform, the USV’s berthing manipulation simulation software was designed. Through the turning simulation experiment of the catamaran USV under different differential rotation speeds of the twin propellers, the relationship between the ship’s turning radius and the propeller speed difference was obtained. A simulation experiment of decelerating and stopping ships at different speeds was carried out, which can provide a reference for speed control when berthing. A berthing maneuvering algorithm based on ship maneuverability was proposed. USV’s berthing algorithm includes three stages: approach process, turning process, and berthing process. In the approach process, the appropriate approach speed was select according to the rotation angle. In the turning process, the right and left propeller speed differences were select. In the berthing process, the berthing speed was controlled according to the berthing distance. In the port environment, a berthing simulation experiment for catamaran USV was carried out. The simulation results show that based on the berthing and maneuvering algorithm, the efficiency and safety of catamaran USV berthing can be improved.

SHIP PROPELLER EFFECTS ON HARBOURS

The increase in marine traffic during the last decades has led to important changes in ship designs. These changes have been directly affecting harbor structures designed to host smaller and less powerful ships. One of the most important consequences is the erosion of the seafloor close to the toes of the docking infrastructures which affects their stability. The World Association for Waterborne Transport Infrastructures published a guideline resuming the most used equations to solve the scouring problem (PIANC 2015). However most of the proposed formulas are empirical based using single propellers. Other common propulsion systems, such as the twin propeller, have been barely studied so far. Moreover, the propeller scouring action by a free developing jet has received much more attention in comparison with confined scour studies, i.e. nearby marine structures. Indeed, only one reference (Mujal-Colilles et al. 2018) with experiments on the effects of twin propeller in a confined scenario is found nowadays, although it is known that most of the ro-ro and ferry ships use this propulsion system when maneuvering near closed quays. This contribution aims to provide new insights about the effects that twin propeller propulsion system has over the seabed through a set of experiments with mobile sand bed. The effects of the propeller pitch ratio are also evaluated in an attempt to better reproduce the behaviour of ferry ships, since most of them use a Controllable Pitch Propeller (CPP) system.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/zx7-kKUZ7HU

Determining the acceptable turning circle manoeuvring modes to avoid loss of efficiency of the twin propeller system

Nowadays, a large number of newly built inland and navy vessels are equipped with a twin propeller-twin rudder configuration (TPTR). Observations of the modes of work of each unit of the TPTR system when performing manoeuvres at curvilinear trajectory show asymmetrical loading. The nature and parameters of the phenomenon are not sufficiently studied, which in specific manoeuvres could create overloading and loss of effectiveness. The purpose of the task is to study the effectiveness of the ship’s TP system in manoeuvring, taking into account the specifics of working in oblique flow of the “internal” and “external” propellers, respectively to the trajectory of motion. Appropriate manoeuvring experiments with self-running ship model have been carried out by which the propeller thrust and torque have been measured. In the present paper, based on obtained investigation results, analysis of interaction effects in the TP system has been performed. Coefficients for estimating the asymmetric efficiency of the twin-screw system have been developed, and related conclusions were summarized.

A validation study of the model test method for propeller cavitation noise prediction

Propeller cavitation noise, one of the main sources of ship noise, has recently gained much attention owing to its possible adverse effects on marine life. In order to predict full-scale propeller cavitation noise, a model test method using the large cavitation tunnel at the Korea Research Institute of Ships & Ocean engineering (KRISO) was developed. The standard procedure consists of reproduction of the noise source, noise measurement, postprocessing, and noise scaling. The propeller cavitation is reproduced in the same manner as in the cavitation observation test, and the noise is measured. After correcting the multipath effect and the background noise, the model-scale source level (SL) is estimated. The transfer function (TF), which represents the multipath effect, can be measured using a virtual source (or two sources for the twin propeller). Finally, the full-scale SL is predicted by a scaling method. This paper focused on validation of the TF correction and the scaling methods that most affect noise prediction. Validation tests were performed on two ships: a 14,000 TEU container carrier with a single propeller and a 176 K LNG carrier with twin propellers. The validation study confirmed the effectiveness of the model test method in predicting full-scale propeller cavitation noise.

Performance estimation of Twin Propeller in Unmanned Aerial Vehicle

The article deals with the experimental investigation of the thrust performance of a twin propeller used in a typical Unmanned Aerial Vehicle. The propeller is fabricated and tested using low speed subsonic wind tunnel to study the performance characteristics. The results obtained show better performance compared to conventional propellers. The presence of twin propeller has increased the stall characteristics at low Reynolds number. The results indicate a substantial increase in thrust generation of up to 25 percent. The payload carrying capacity and handling quality will improve using this technique during pandemic to spray disinfectants. The results obtained provide an alternate design for future propellers applications. Further it is observed that the endurance of the Unmanned Aerial Vehicle can be reduced considerably, by few alternate solution.

An UAV with Twin Propellers Driven by Single Motor

As the technology is looping and far applications of UAV is improving so there is need to develop an UAV with optimum propulsive efficiency and also producing high thrust. So our mission is to build an UAV with twin propellers propelled by single motor. A fixed wing UAV which has a unique type of propulsion system. In this fixed wing UAV, two propellers are driven by single motor to enhance the propulsive efficiency. The bevel gear mechanism is the most important. This is the propulsion system for the aircraft model which runs the two propellers with a single motor. Bevel gears are used to transfer the power from the motor to the propeller. The bevel gear train is 80cm long through which a long shaft is passed that holds the bevel gears. Totally six bevel gears are housed inside the box which connects the motor shaft to the propeller shaft. The bevel gears are arranged in such a way that the when motor shaft rotates the propeller connected rotates both in opposite direction.

The Influence and Anslysis of Gas Content on the Pressure Fluctuation induced by Cavitating Propeller

A ship hull model with all accessories is used to simulate the wake field of the propeller of a twin propeller ship in a large circulating water channel.The similarity of propeller wake field is guaranteed.The influence of air content in water on pressure fluctuation by cavitating propeller is studies.The cavity form of propeller was observed under the condition of different air content in water.The pressure fluctuations induced by cavitating propeller behind ship hull is also measured.The results showed that the air content has a significant influence on the pressure fluctuations. Each measuring points and each order frequency of pressure fluctuations amplitudes increase with the decrease of air content.The main reasons of influence of air content on pressure fluctuations are analyzed.It is proposed that how to set the air content in the model tests.

Scour Induced by Single and Twin Propeller Jets

Single and twin ship propeller jets produce scour holes with deposition dune. The scour hole has a maximum depth at a particular length downstream within the propeller jet. Existing equations are available to predict maximum scour depth and the corresponding scour length downstream. Experiments conducted with various physical propeller models, rotational speeds, propeller-to-propeller distances and bed clearances are presented. The measurements allowed a better understanding of the mechanism of temporal scour and deposition formation for scour caused by single-propeller and twin-propeller. Results show that the propeller jet scour profiles can be divided into three zones, which are the small scour hole, primary scour hole and deposition dune. An empirical 2D scour model is proposed to predict the scour profile for both a single-propeller and twin-propeller using a Gaussian normal distribution.

Stern Twin-Propeller Effects on Harbor Infrastructures. Experimental Analysis

The growth of marine traffic in harbors, and the subsequent increase in vessel and propulsion system sizes, produces three linked problems at the harbor basin area: (i) higher erosion rates damaging docking structures; (ii) sedimentation areas reducing the total depth; (iii) resuspension of contaminated materials deposited at the seabed. The published literature demonstrates that there are no formulations for twin stern propellers to compute the maximum scouring depth. Another important limitation is the fact that the formulations proposed only use one type of maneuvering during the experimental campaign, assuming that vessels are constantly being undocked. Trying to reproduce the real arrival and departure maneuvers, 24 different tests were conducted at an experimental laboratory in a medium-scale water tank using a twin propeller model to estimate the consequences and the maximum scouring depth produced by stern propellers during the backward/docking and forward/undocking scenarios. Results confirm that the combination of backward and forward scenario differs substantially from the experiments performed so far in the literature using only an accumulative forward scenario, yielding deeper scouring holes at the harbor basin area. The results presented in this paper can be used as guidelines to estimate the effects of regular vessels at their particular docking location.

MANEUVERING PERFORMANCE OF A 30 GT FISHING VESSEL WITH ASYMMERICAL PROPELLER CONFIGURATION

Fishing vessels are designed with a specific mission. That mission is to locate, catch, and preserve fish while out at sea, meanwhile the vessel needed to have good maneuverability. This research describes a study on asymmetrical propeller configuration of a fishing vessel to improve its maneuvering quality. MATLAB-simulink program was used to simulate, the turning circle and the zigzag maneuvers. The simulation program was developed based on the mathematical model for a fishing vessel maneuvering. The mathematical model involved the setting-up a 3 DOF (Degres of Freedom) mathematical model in a modular of MMG (Mathematical Modeling Group) of the hull, propeller and rudder component. The result indicated that twin propeller with asymmetrical had an advantages of turning circle ability of 8% to 14 %, meanwhile the zigzag maneuver 20°/20° had 9 to 20 % 1st overshoot different between left and right heading. Keywords: Configuration, propeller, assymetrical, fisheries, simulation

Research on Ducted Propeller and Rudder Interactions in Extreme Conditions

This paper presents the results and analyses of a combined numerical-experimental study into the performance of three types of rudders to quantify the interactions between propeller, nozzle, and rudder at extreme rudder angles. Conventional, flapped and triple rudders are studied numerically as well as experimentally to evaluate the drag, lift, and moment generated by the rudders at moderate-to-extreme rudder angles and at forward propeller shaft speeds and inflow speeds. The experiments were carried out to evaluate the suitability of the three rudder types for a proposed cargo carrier in terms of controllability. The experiments were carried out at the selfpropulsion condition of the model equipped with twin stock ducted propellers along with each of the rudder systems. An extensive numerical study was carried out to evaluate the performance of the three rudders in terms of flow velocity, pressure, and wake fields. Drag and lift for different angles of attack are obtained for complicated propeller-nozzle-rudder arrangements. Investigations are carried out to study the effects of the interaction of the rudder with the propeller-nozzle assembly at extreme rudder angles as high as ±40°. For simplicity, the geometry of the vessel was not modeled in these simulations. The experimental results are presented along with the computational results for all three rudder cases. The lift and drag measurements are in good agreement with the corresponding predictions for each of the rudder arrangements. The mutual interactions between the rudder and the propulsion system were captured in the simulations and were comparable with the corresponding measurements. The research reveals the nature of the velocity and pressure fields due to the complex interactions between the propeller, nozzle, and rudders at extreme rudder angles. It is expected that the current investigation will assist naval architects, at the early design stage, to select the rudder type for their ships such that suitable maneuvering characteristics are obtained and stringent International Maritime Organization maneuvering criteria are met.

Study of the Bed Velocity Induced by Twin Propellers

Twin propellers without a rudder were studied using a physical model with a fixed clearance distance and three different rotating velocities. Experimental results were compared with results from theoretical expressions developed over the past 50 years for the efflux velocity, axial velocity, and maximum bed velocity. It was found that the efflux velocity equations overestimated the experimental results, whereas the computed axial velocities matched the experimental data reasonably well. However, when maximum bed velocity expressions were compared with experimental results, only one method was found to behave better; overestimation resulted if a quadratic superposition of single jets was used.