Propeller Theory Research Articles

Причины различий между коэффициентами упора винта при работе за корпусом судна и в свободной воде на швартовых

Object and purpose of research. The object of research is the results of self-propelled ship tests in bollard-pull conditions. The purpose is to analyse the hydrodynamic sources giving rise to differences between propeller thrust coefficient in open-water and behind-hull conditions. Materials and methods. Analysis based on the ideal propeller theory shows that the velocity ΔV of inflow on propeller operating behind ship hull in bollard-pull conditions caused by a system of sinks, ensuring flow attachment to hull surface, has a finite value and is actually the effective wake. The wake velocity for an open-water propeller is equal to the behind hull velocity. The open-water propeller thrust coefficient at advance ratio (formula) is due to the opposed jet of its reversal. It is shown that the thrust coefficient deviations at self-propelled tests in open-water has to do with the specifics of propeller thrust variations in the operating area adjacent to bollard-pull conditions. Boundaries of the operating area where the opposed jet affects the propeller curve at self-propelled tests are defined. Practical conclusions and recommendations are given following from the obtained data. Main results. The source of discrepancies between self-propelled test results for open-water propeller in bollard pull conditions and close operating area has been found. Recommendations are given on updating the test procedures for propeller and self-propelled model tests Conclusion. The paper is expected to be useful for understanding the ambiguity of self-propelled test results.

Особливості розрахунку та моделювання обтікання несучих та тягових гвинтів літальних апаратів в умовах сильно розрідженої атмосфери

This article presents the structure of designing and modeling the flow of rotors and pusher propellers in a highly rarefied atmosphere. The aerodynamic characteristics of an airfoil are key factors in determining design accuracy and performance prediction. The blade elements operate at different Reynolds numbers and angles of attack. The blade profile was selected based on an estimate of the lift-to-drag ratio for expected Reynolds numbers under the design conditions. This paper considers the features of the operation of propellers in a highly rarefied atmosphere. When modeling propellers operate in rarefied atmosphere, it is necessary to pay special attention to the choice of a model for the turbulent viscosity of the medium. The greatest difficulties in the design of stratospheric propellers arise when solving the problems of excessive diameter, weight and shape of the blades. To solve this problem, in this paper, it is proposed to use joined double row blades. This approach made it possible to eliminate the aerodynamic shading of the blades and increase their aerodynamic load. The use of double-row blades will provide the necessary rigidity and strength of the blades and will lead to weight reduction. Additionally, due to the double-row design, it becomes possible to reduce the diametrical dimensions of the propeller. An analytical technique for profiling double-row blades has been developed. The proposed approach is based on the joint application of the one-dimensional propeller theory and numerical gas dynamics methods. The one-dimensional theory is used to obtain the original geometric shape of the propeller for given characteristics, and the methods of numerical gas dynamics, which are based on solving the Reynold averages of the Navier-Stokes equations, are used to solve the problems of spatial modeling of the flow and obtain refined propeller characteristics. Considering the design requirements and operational limitations, it is proposed to use propellers with joined double-row blades in conditions of rarefied atmosphere.

George de Bothezat and his contribution into the world aviation and astronautics

The article dedicated the life and scientific way of George de Bothezat, the first Doctor of Sciences in the field of aviation. Together with Nikolay Zhukovsky, Igor Sikorsky, Stephen Timoshenko, Alexander Fan-der-Flit, and Alexey Lebedev, he was one of the organizers of the Air Fleet of the Russian Empire. He is the author of various inventions: gyroscopic sight and other types of aviation equipment. We analyze works by G. Bothezat on the impulse theory of propellers. In particular, the scientist derived formulas for ensuring the flight stability of airplanes and helicopters. He developed training ballistic tables, which allowed making corrections for the speed of the flight and the direction of the wind. We briefly describe a biography of G. Bothezat, focusing on the student period of his life in Kharkiv, Ukraine, and the reasons for G. Bothezat’s departure to the United States in 1918. It is stated that it was there that his talent as a designer and creator of helicopters of the original system was disclosed in the best way. In 1922, George Bothezat obtained the financial support of the American government to build a workable helicopter model without prototypes and experiments, only based on the results of calculations. The reasons why G.Bothezat did not manage to achieve the launch of the serial production of helicopters are analyzed. We also mention the activities of the company founded by G.Bothezat, which was engaged in the production of fans of a new type for the US Navy. The Bothezat system fans were installed at the Rockefeller Center in New York as well as in American tanks. It is emphasized that I. Sikorsky also used the works by G.Bothezat in his research. It is stated that the flight trajectory calculated by G.Bothezat in air and airless space was used in the development of the American program of a manned landing on the Moon using the “Apollo” system.

Studies on the Design Models of Horizontal Axis Wind Turbines

Abstract The aim of the paper is to present through a contrastive analysis the main models used in the analysis and design of horizontal axis wind turbines. The basis for designing a rotor for a wind turbine, which is the main element of a turbine that extracts energy from the wind, is the propeller theory. This theory incorporates mathematical models that describe the movement of fluid around the propeller. The paper presents three generically named models, model A, model B and model C respectively, used in the analysis and design of the horizontal axis wind turbine’s rotor.

Application of pressure head theory to determine the aerodynamic characteristics of the helicopter main rotor

A method is proposed for calculating main aerodynamic characteristics of the main rotor of the Mi-26 helicopter: a lift, a reactive moment, a required power of the propulsion system, a speed of the inductive air flow, a throttle response coefficient, a speed of the horizontal flight. This method based on the pressure propeller theory. The parameters of the Mi-26 helicopter and the propeller of the experimental setup calculated according to the pressure theory of the main rotor are experimentally confirmed. The percentage of the discrepancy between the statistical data on the aerodynamic characteristics of the Mi-26 helicopter rotor calculated with the pressure theory does not exceed 1.5%.

Component Velocities and Turbulence Intensities within Ship Twin-Propeller Jet Using CFD and ADV

This study presents the decays of three components of velocity for a ship twin-propeller jet associated with turbulence intensities using the Acoustic Doppler Velocimetry (ADV) measurement and computational fluid dynamics (CFD) methods. Previous research has shown that a single-propeller jet consists of a zone of flow establishment and a zone of established flow. Twin-propeller jets are more complex than single-propeller jets, and can be divided into zones with four peaks, two peaks, and one peak. The axial velocity distribution is the main contributor and can be predicted using the Gaussian normal distribution. The axial velocity decay is described by linear equations using the maximum axial velocity in the efflux plane. The tangential and radial velocity decays show linear and nonlinear distributions in different zones. The turbulence intensity increases locally in the critical position of the noninterference zone and the interference zone. The current research converts the axial momentum theory of a single propeller into twin-propeller jet theory with a series of equations used to predict the overall twin-propeller jet structure.

Improving the propulsion performance of composite propellers under off-design conditions

Pre-deformation design can improve the propulsive efficiency of composite ship propellers under off-design conditions, where propulsive efficiency is related to the geometry of the propeller blade. Material attributes affect the deformation of composite propeller blades, suggesting that these also affect the propulsive efficiency of a pre-deformed composite propeller (PDCP) under off-design conditions. In this study, the hydrodynamic performance and structural response of composite propellers were determined and verified using computational fluid dynamics and the finite element method. The effects of elastic and shear moduli on propulsive efficiency and structural deformation were analyzed, and the influences of changing material attributes and propeller advance ratios were compared. Based on existing propeller theories, an objective function was proposed for selecting the most suitable material attribute scheme for the DTNSRDC 4383 propeller, from 18 different materials. Such a selection allows for an optimization of the comprehensive propulsive efficiency of a composite propeller through pre-deformation design. The results show that when the PDCP has an elastic modulus E = 135 GPa and a shear modulus G = 2.07 GPa, it exhibits optimal comprehensive propulsive efficiency. The findings of this study can be used in the design of composite propellers to maximize performance under a broad range of working conditions.

TEORIA DA TRÍPLICE HÉLICE: UMA PROPOSTA DE MODELO DE GESTÃO ESTRATÉGICA APLICADO À AGÊNCIA DE INOVAÇÃO DO CAFÉ (INOVACAFÉ)

O objetivo neste estudo foi criar, por meio de uma pesquisa-ação, um modelo de gestão estratégica para a Agência de Inovação do Café (InovaCafé), integrando o Balanced Scorecard (BSC) à teoria da Tríplice Hélice. O alinhamento da pesquisa-ação às teorias da Tríplice Hélice, do Planejamento Estratégico e à abordagem do BSC forneceu os subsídios necessários à formulação de um modelo de gestão estratégica capaz de contemplar a complexidade da InovaCafé enquanto organização articuladora da Tríplice Hélice. Com o desenvolvimento de um mapa estratégico adaptado à InovaCafé, os objetivos indicadores, metas e iniciativas constituem inovações que podem ser exploradas em outras pesquisas.

Acoustic theory of the many-bladed contra-rotating propeller: the effects of sweep on noise enhancement and reduction

In the asymptotic theory of propeller noise the far-field noise is dominated by small regions of the propeller representing interior stationary points or boundary critical points. For contra-rotating propellers, the wake-interaction solutions can thereby be written in closed form as simple algebraic expressions which still retain the effects of swept blade-gust interaction. In this paper, these asymptotic solutions are used to investigate how blade sweep can lead to enhanced or reduced noise radiation. In particular, it is shown how the locations of the interior stationary points vary with sweep and, consequently, how sweep can be used to control noise. Results are shown for a family of critical designs that have enhanced noise radiation arising from a continuum of interior stationary points. The dominant interior stationary points can be completely removed for particular tones and directions (sub-critical designs), even in cases for which the wake-rear propeller aerodynamic interaction remains super-critical. Furthermore, the interior stationary points can be completely removed for all tones and directions (universally sub-critical designs); in these cases the wake interactions are sub-critical across the entire span of the blade, the resultant tones have low radiation efficiency and further increases in sweep lead to significant reductions in noise levels. Designs are presented, with corresponding noise calculations, that demonstrate these substantial noise benefits.

Numerical Study on Flow Around Modern Ship Hulls with Rudder-Propeller Interactions

Reducing the fuel consumption of ships presents both economic and environmental gains. Although in the past decades, extensive studies were carried out on the flow around ship hull, it is still difficult to calculate the flow around the hull while considering propeller interaction. In this paper, the viscous flow around modern ship hulls is computed considering propeller action. In this analysis, the numerical investigation of flow around the ship is combined with propeller theory to simulate the hull-propeller interaction. Various longitudinal positions of the rudder are also analyzed to determine the effect of rudder position on propeller efficiency. First, a numerical study was performed around a bare hull using Shipflow computational fluid dynamics (CFD) code to determine free-surface wave elevation and resistance components. A zonal approach was applied to successively incorporate “potential flow solver” in the region outside the boundary layer and wake, “boundary layer solver” in the thin boundary layer region near the ship hull, and “Navier-Stokes solver” in the wake region. Propeller open water characteristics were determined using an open-source MATLAB code OpenProp, which is based on the lifting line theory, for the moderately loaded propeller. The obtained open water test results were specified in the flow module of Shipflow for self-propulsion tests. The velocity field behind the ship was recalculated into an effective wake and given to the propeller code that calculates the propeller load. Once the load was known, it was transferred to the Reynolds-averaged Navier-Stokes (RANS) solver to simulate the propeller action. The interaction between the hull and propeller with different rudder positions was then predicted to improve the propulsive efficiency.

Maximal Speed of Underwater Locomotion

Background. An increasing interest in unmanned underwater vehicles continues to draw attention to swimming in aquatic animals. Their high speed continues to surprise researchers. In particular, the high dolphin speed caused a series of attempts to explain its paradox, which continues to this day. Some researchers believe that even rigid bodies, shaped like water animals, provide an attached flow pattern, as opposed to the widespread view of the inevitable separation. The possible explanation may be in the perfect body form, which provides an attached flow pattern (without boundary layer separation). Elongated unseparated shapes can not only reduce the pressure drag but also delay the laminar-to-turbulent transition in the boundary layer, significantly reducing the friction drag. Thus, the highest possible swimming speeds are expected in aquatic animals. Objective. We will try to prove that the low drag and the high speed of aquatic animals can only be ensured by their unseparated shape (as a rigid body), neglecting flexibility and compliance. Methods. We will use: a) shape calculations of special bodies of revolution with negative pressure gradients near the tail similar to fish trunks with the use of the developed before approach; b) the known drag estimations of such shapes for laminar and turbulent cases; c) the swimming power balance and the theory of ideal propeller; d) statistical analysis of available data about the length, the speed and the aspect ratio of aquatic animals. Results. The swimming speed of most aquatic animals is proportional to the length of the body in power 7/9. The exception is whale locomotion that occurs in turbulent mode at supercritical Reynolds numbers. Conclusions. The perfect body shapes of most aquatic animals provide an attached laminar flow pattern. Estimated maximum speeds for laminar and turbulent cases show that the special shaped unseparated hulls can greatly increase the speed of underwater vehicles and SWATH ships. Further increase in speed can be achieved by using supercavitation and greater than animal capacity-efficiency.

Analysis of propeller bearing loads by CFD. Part I: Straight ahead and steady turning maneuvers

Marine propellers in behind-hull conditions develop, in addition to thrust and torque, in-plane loads that are strictly related to fatigue stress of the propulsive shaft bearings, hull-induced vibrations and the dynamic response of the ship while maneuvering or experiencing wave induced motions. An in-depth understanding of their nature as well as their quantification in typical design and off-design operative scenario is fundamental for improving ship design criteria. This issue is tackled in the present work by means of URANS simulations and simplified propeller theories to assess the correlation between inflow conditions and propeller loads. In particular, the analysis is carried out for the same twin screw model recently considered in free running maneuvering model tests (Ortolani et al., 2015a, 2015b) and further aims to provide a complementary and deeper insight to the outcome of these experiments. The first part of the study is focused on the straight ahead motion and the steady turning maneuvers with rudder deflections of 15°, 25° and 35° and Froude number equal to 0.26.

Design of a quadrotor flight test stand for system identification

AbstractThis paper presents the design, development and construction of a flight test stand for a quadrotor UAV. As opposed to alternate forms of UAV, the power plant in the case of the quadrotor serves a dual purpose of control and propulsion. Since control and propulsion are coupled, the power plant (BLDC motor coupled with propeller) was studied in detail using a black box structure. Extractions of motor parameters in previous studies used traditional BLDC motor equations and propeller theory however the accuracy achievable and confidence in the extracted parameters remained questionable. The developed data acquisition process served to satisfy this need by the construction of a test bench that allows for the extraction of the unknown parameters instilling confidence in the modelling process. The established relationships are then used as inputs into a developed six degree of freedom Euler based mathematical model. A mission profile was constructed with distinct phases of which the mathematical model was used to simulate. Each phase in the mission profile excited different modes of the quadrotor dynamics creating an ideal simulation environment in which changes can be implemented and studied.

Optimum Loading and Induced Swirl Effects in Hover

Optimum hover performance is the quintessential goal of rotor design. Yet it is not entirely clear what exactly is the optimum loading for a hovering rotor. Propeller theory gives the Betz loading as the optimum for an actuator disk in axial flight, which is commonly believed to be the optimum in hover as well. Helicopter textbooks often give uniform loading (and the corresponding uniform inflow) as the optimum in hover based on simple momentum theory, which ignores induced swirl. Glauert derived optimum loading solution in hover, including swirl and showed that it differs from the Betz loading. The present work uses combined blade element momentum theory to examine these loadings and to better understand optimum hover performance. The analysis is applicable to both ideal (actuator disks) and realistic rotors. The analysis is further augmented with a profile drag model to calculate rotor performance and is successfully applied to several rotor configurations.

Single theory of movers on the continuous flows. Short theory of concurrent-rotating propellers

Concurrent-rotating propellers have second rotor wheel with higher productiveness compared to the first one, so the water-gas stream is injected (absorbed) through the channels between the blades of the first rotor wheel, which in this mode does not compress the water-gas flow, and functions as rotating guiding device only, which helps to obtain the sinusoidal characteristics of the axial velocity changes with providing zero acceleration of the water-gas flow at the input edges of the second rotor wheel blades which compresses the flow and produces thrust. Injection (absorption) of the water-gas flow through the channels between the blades of the first rotor wheel also promotes the swirling of the water-gas flow in the area B1-H and emergence of additional static pressures gradient, grad Pd, that pulls the flow into the bundle before and after the section B 1 -B 1 , while before the section B 1 -B 1 this additional gradient of static pressure facilitates further acceleration, and in a B 1 -B 2 section slows down the water-gas flow, providing its sinusoidal characteristics in the H-B 2 section. Thus, the sinusoidal characteristics of the change of the axial velocity of the water-gas flow in the H-B 2 section helps to eliminate the kinematic zone of rigid (elastic) impact in the section B 2 -B 2 , which enables to increase the turnover, and therefore the thrust of the second rotor wheel of the concurrent-rotating propellers at 200-300% compared to the turnover and thrust of the one-row propellers.

Uniform theory of movers on continuous flows. Brief theory of counter-rotating propellers

The developed brief theory of the counter-rotating propellers is a logical chain of a series of articles relating to the development of the theory of one-row propellers, brief theory of counter-rotating propellers, brief theory of concurrent-rotating propellers, a comparative analysis of one-row, counter-rotating and concurrentrotating propellers in order to select the most effective variant. It is shown that counter-rotating propellers have high energy consumption and very low flight (traction) EF (efficiency factor), 35% and 7.5% respectively on the first and second rotor wheels. Therefore, the ultimate goal of a series of articles will be: to show and prove that among the one-row, counter-rotating and concurrent-rotating propellers the latter are the most efficient, as they allow to completely eliminate the main drawback of one-row and counter-rotating propellers associated with the kinematic zone of rigid (elastic) impact, Figure 1, section B 1 -B 1 , generating powerful impact waves in an oscillatory mode into environment. Another drawback of the counter-rotating propellers is the flow swirling after the first rotor wheel, regulating the counter flow swirling at the entry of the second counter-rotating rotor wheel, which in turn regulates the higher hydrodynamic load of the blades edges of the second counter-rotating rotor wheel and low speed compared to the first. Hence, the next article will cover the creation of the brief theory of concurrent-rotating propellers, which contains their full analysis

ブレストストロークのプロペラのようなキック推力の解析方法

Kicking like a propeller in breaststroke is nowadays widely used by breaststrokers. Maglischo5) explains that a breaststroker kicks until legs are stretched straightly to generate thrust, drawing a semicircle with both legs like a propeller. It is said that the breaststroke kick like the propeller is supposed to generate big thrust. But in the process of this study, the calculation result of propeller-like kick thrust revealed that enough thrust does not occur in the usual propeller theory. It seems that the application of Dynamic Stall is to be supposed to generate enough thrust to apply the second law of Newton. The purpose of this study is to obtain the method for the analysis of this big thrust using Dynamic Stall.

Chapter 6. Foundations for unified theory of propeller a continuous stream. Derivation of formula rod

Рассматриваются недостатки современной теории воздушно -реактивных двигателей, связанные с ошибочной теоремой о подъемной силе продуваемого профиля, выведенной профессором Н.Е.Жуковским в 1912г.

Advanced brake state model and aerodynamic post-stall model for horizontal axis wind turbines

Abstract In scientific literature, when the aerodynamic design of a horizontal axis wind turbine is discussed, different brake state models are presented. The brake state models are implemented within a BEM code which is a 1-D numerical code, based on Glauert propeller theory, and able to predict HAWT performance. This code provides reliable results only if a proper brake state model and aerodynamic post-stall model are implemented. In this research, the authors have produced a numerical code based on BEM theory in conjunction with an aerodynamic post-stall model, indispensable for taking into account radial flow along the wind turbine blades (Himmelskamp Effect), and the brake state models by Buhl, combined with the calculation of Jonkman's tangential induction factor. In scientific literature, Shen's brake state model is commonly implemented within 1-D numerical codes, based on BEM theory. Subsequently, a comparison with Shen's brake state models was carried out. With the numerical code presented in this work, the power for an NREL wind rotor was predicted. With the numerical simulation, it was possible to notice when these different brake state model furnish results close to experimental data.

Charlie Ellington FRS retires

In 1973, a young student from Duke University arrived at the Department of Zoology in the University of Cambridge to begin his PhD with Torkel Weis-Fogh. The young student was Charlie Ellington, and he was destined to ‘rewrite the book’ on insect flight aerodynamics. Charlie recalls his arrival