Showing papers on "Blade pitch published in 1980"

Flow Curvature Effects on Darrieus Turbine Blade Aerodynamics

Abstract: The effects of curvilinear flow on Darrieus turbine blade aerodynamics are described. Analysis shows that these effects can have a sizeable impact on performance for blades of large chord. Experimental data are presented which verify this forecast. Unusually large boundary-layer radial pressure gradients and virtually altered camber and incidence are identified as causal phenomena. Conformaf mapping techniques are used to transform geometric airfoils in curved flow to their virtual equivalents in rectilinear flow. It is argued that flow curvature is an important determinant of Darrieus turbine blade aerodynamic efficiency and that its proper consideration will yield performance improvements, even for blades of small chord. uncovered blade aerodynamic complexities which were beyond initial expectations. Most noteworthy are the peculiar aerodynamic phenomena associated with the orbital motion of the blades. In essence, these blades are subjected to a curvilinear flow and behave very differently than if they were immersed in a rectilinear flow. Furthermore, centrifugal forces alter the boundary layer of the airfoils rotating in this fashion. This situation presents problems in the design and analysis of all cross-flow wind turbines, because virtually all published airfoil data are derived from tests in rectilinear flow. Recent studiesl show that modest improvements in Cp yield desirable reductions in the cost of energy. Since these Cp improvements can be achieved by increasing blade aerodynamic efficiency, there exists ample incentive for considering the aerodynamic idiosyncrasies of rotating blades. In the material which follows, boundary-layer centrifugal effects will be discussed first. Treatment of this subject is brief; its significance has only recently been appreciated and extensive studies of the phenomenon have not been con- ducted. Flow curvature effects are treated next. A simple kinematic analysis demonstrates that the turbine blade relative inflow velocity and angle of attack are unique everywhere on the chord. It is then shown how conformal mapping techniques, which transform airfoils in the curved flow field to their virtual equivalents in rectilinear flow, may be used in the aerodynamic analysis of the turbine blades. The method indicates that flow curvature effects are strongly dependent upon the blade chord to turbine radius C/R. Experimental data are introduced for two sets of blades, both of NACA 0015 airfoil section. The first set of blades had C/R = 0.114 and the second set had C/R = 0.260.

Blade pitch angle control for a wind turbine generator

Abstract: A blade pitch angle control for a wind turbine-generator establishing an optimum power or torque reference signal which, when operating conditions so warrant, is not limited by the nominal torque or power ratings of various turbine generator components. The reference signal is indicative of a maximum blade angle setting for safe operation of the wind turbine. An integral or lag compensation circuit for enhanced transient and steady-state operation may be employed.

Wind turbine blade pitch control system

Abstract: A pitch control system for a multibladed variable pitch wind turbine. Each of the turbine blades is pivotally driven about the longitudinal axis thereof independently of the other blades by at least a pair of hydraulic actuators. The actuators are supplied with pressurized hydraulic fluid from a first source thereof under conditions of normal pitch change adjustment. Under conditions wherein feathering of the blades is required, the actuators are supplied with hydraulic fluid from second sources thereof such that one of the actuators associated with each of the blades is supplied with fluid from one second source and a second actuator is provided with fluid from a redundant second source whereby blade feathering may be effected despite a malfunction of one of the redundant sources or one of the actuators. In one of the two preferred embodiments disclosed, the first and second fluid sources are maintained in mutual communication whereby fluid from the second sources thereof may supplement fluid from the first source under conditions of normal blade pitch adjustment.

Ram air turbine control system

Abstract: The present invention relates to an improved blade pitch control mechanism for an air driven turbine blade mounted for rotation in a hub assembly. The control mechanism includes a drive member mounted for reciprocation along a central axis of the hub assembly. The drive member has a control member secured to one end and a seat member at the other end. The blade has operatively coupled thereto, a centrifugally responsive means which includes a pin in mating engagement with the control member. A spring is positioned between the hub assembly and the control member to thereby cause the blade to assume a coarse or high pitch position when the blade and hub assembly are in storage. A slide member is mounted on a portion of the hub assembly for reciprocation along the central axis. A spring is positioned between the seat member and the slide member. A flyweight is supported on the hub assembly and engages the slide member. Rotation of the hub assembly causes the flyweight to move the slide member and thereby move the blade pitch from coarse pitch to fine pitch and thereafter, allow the centrifugally responsive means to control the blade pitch.

System for propulsion of boats by means of winds and streams and for recovery of energy

Abstract: The invention relates to an improved system for propulsion of boats by winds and streams and for recovery of disposable energy from floating stations neither moored nor anchored, the improved system comprising: at least one aerial feathered propeller with its shaft, the propeller being mounted orientable in any azimuth direction contained in a substantially horizontal plane and adapted to function as an aerogenerator as well as a propulsive screw; a superstructure supporting device on the floating unit adapted to permit orientation as desired of the aerial propeller in the direction of the wind; at least one nautic propeller screw with its shaft, mounted under the bottom of the floating unit and adapted to be capable of functioning as energy collecting turbine as well as propeller; a transmission system connecting the aerial propeller shaft to the nautic propeller shaft, the transmission being reversible and capable of including a torque conversion device to select during operations the direction of transmission as well as the transmission ratio; a directional device adapted to ensure the steering of the floating unit; and control devices comprising actuating apparatus adapted to allow the driver to act, in addition upon the directional device and the azimuth orientation of said aerial propeller, upon at least two of three variable parameters of said system, namely the pitch of said aerial propeller, the transmission ratio and the pitch of said nautic propeller, by the actuating apparatus.

Higher harmonic blade pitch control : a system for helicopter vibration reduction

Abstract: Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1980.

Marine vessel with propeller

Abstract: A marine vessel having a propeller tunnel possessing a flow-favorable cross-sectional configuration following the flow lines of the water. Within the propeller tunnel there is mounted a propeller essentially throughout one-half of its circumference. An adjustable control plate can be extended in order to detach the flow of the water from the surface of the tunnel during rapid travel of the marine vessel. In this case, the propeller functions as a partially immersed propeller at a high rotational speed. There can be provided a control device which adjusts the control plate as a function of the rotational speed range within which the propeller operates. The propeller can be an adjustable propeller conjointly adjustable with the control plate.

Wind turbine blade pitch control system

Abstract: Wind turbine blade pitch control system including hydraulic actuators which pivotally drive the blades about the longitudinal axis thereof to adjust the blade pitch. The actuators are supplied with hydraulic fluid from independent sources thereof for normal blade pitch adjustment and feathering. Means are provided which, during feathering, isolate the pressurization and drain of the actuators from certain system components, whereby such pressurization and drain are not hampered by any malfunction of such components.

Summary of advanced methods for predicting high speed propeller performance

Abstract: Three advanced analyses for predicting aircraft propeller performance at high subsonic speeds are described. Two of these analyses use a lifting line representation for the propeller blades and vortex filaments for the blade wakes but differ in the details of the solution. The third analysis is a finite difference solution of the unsteady, three dimensional Euler equations for the flow between adjacent blades. Analysis results are compared to data for a high speed propeller having eight swept blades integrally designed with the spinner and nacelle.

Propeller and vane wheel

Abstract: The vane wheel is a freely rotating device installed on the propeller shaft behind the propeller to provide additional thrust at no increase in power. The wheel, which is larger in diameter than its companion propeller, functions as a turbine by using the otherwise-wasted propeller slipstream to generate the extra thrust. This paper describes a series of tests performed at the Hamburg Ship Model Tank to compare the efficiency of the vane wheel arrangement with other propulsion units, including a conventional propeller, and propeller with fixed guide mechanism. The Appendix provides a mathematical analysis of the performance of the various units investigated.

Method and apparatus for controlling propeller pitch

Abstract: A variable pitch propeller is controlled by a hydraulic mechanism responsive to forces urging an unsymmetrically mounted propeller towards its maximum pitch Spring bias means maintains the propeller at minimum pitch under conditions of rest The propeller is prevented from increasing its pitch by the pressure produced on a closed hydraulic chamber until it reaches a predetermined rpm, when a centrifugal valve opens a first port and relieves the pressure in the cylinder and allows the propeller to increase in pitch The increase in pitch opens a second port communicating with the pressure chamber, but that channel remains closed by a second valve that is normally closed but opens in response to a reduction in the throttle setting The reduction in throttle setting closes the centrifugal valve so that the only channel from the pressure chamber is through the second port When the second port is opened by the action of the reduced throttle, which reduces the forces generated on the control system by the propeller, the pitch immediately increases and in turn closes the second port and locks the propeller in the higher pitch position The propeller is supported for rotation about its radial axis by two pairs of radially-aligned V-blocks and pivot blocks that provides a low-friction, sturdy mount

An active control system for helicopter vibration reduction by higher harmonic pitch

Abstract: An analytical study defining the basic configuration of an active control system to reduce helicopter vibrations is presented. Theoretical results for a nonlinear four-bladed single rotor helicopter simulation are discussed, showing that vibration reductions on the order of 80-90% for airspeeds up to 150 kn can be expected when using a higher harmonic pitch in an active feedback control system. The rotor performance penalty associated with this level of vibration reduction is about 1-3% and the increase in rotor blade stresses is considered to be low. The location of sensor accelerometers proved to be significant for vibration reductions, and it is noted that the RTSA controller is tolerant of sensor signal noise.

Blade pitch actuation system

Abstract: Blade pitch actuation system wherein the blades are hydraulically maintained in phase with one another. The system comprises hydraulic actuators each adapted to drive a single blade in a pitch change mode of operation. Fluid flow to the actuators is controlled by a blade actuator control valve in fluid communication with the actuators and an hydraulic fluid source and drain. An input member of the control valve is provided with passages which provide selected communication between the hydraulic fluid source and drain and passages in cooperating control valve feedback members each operated by, and in fluid communication with one of the blade actuators. The input and feedback members are positionable along one another such that selective positioning of the input member causes simultaneous selected pressurization and draining of the blade actuators through the feedback members thereby effecting a desired, phased blade pitch setting. The phased movement of the blades to such setting causes a corresponding movement of the feedback members nulling the actuator control valve and preventing deviation in blade pitch from the desired setting.

Supervisory and monitoring system for helicopter propeller blades

Abstract: The blades of a helicopter propeller are supervised by pressure-sensitive transducers operating a resonance circuit rotating therewith, for determining its frequency. The circuit includes a rotating secondary of a transformer, intermittently coupled to a stationary primary which is energized by a voltage having a frequency equal to the resonance frequency of the resonance circuit when there is no blade defect. An impedance senses the amplitude of these pulses which varies on detuning due to a blade defect. The pulses are processed to yield a warning. Scanning through a range of source frequencies permits identification of the defective blade. The circuit is supplemented for operational testing during flight as well as on the ground.

Propeller brake for a turbo-prop engine

Abstract: A propeller brake for a twin spool turbo-prop engine which permits the propeller to be locked in a stationary position with the engine running is disclosed. The propeller brake has a hydraulically actuated friction brake and hydraulically actuated locking mechanism rotatably connected to the engine spool turning the propeller. The friction brake stops the propeller from rotating in response to an external command. A hydraulic signal indicating the propeller has stopped rotating actuates the mechanical lock holding the propeller in a stationary position. A safety latch prevents the mechanical lock from being actuated in event of a hydraulic pressure or engine failure in flight.

A new approach to active control of rotorcraft vibration

Abstract: A state-variable feedback approach is utilized for active control of rotorcraft vibration. Fuselage accelerations are passed through undamped second-order filters with resonant frequencies at N/rev. The resulting outputs contain predominantly the N/rev vibration components, phase shifted by 180 deg, and are used to drive the blade pitch to cancel this component of fuselage vibration. The linear-quadratic-gaussian (LQG) method is used to design a feedback control system utilizing these filtered accelerations. The design is based on a nine-degree-of-freedom linear model of the Rotor System Research Aircraft (RSRA) in hover and is evaluated on a nonlinear blade-element simulation of the RSRA for this flight condition. The system is shown to essentially eliminate vibrations at N/rev in all axes. The required blade-pitch amplitude is within the capability of conventional actuators at the N/rev frequency.

Propeller blade with small blade

Abstract: PURPOSE: To increase propulsive force of a blade and prevent occurrence of its cavitation, by providing a small blade generating a lift in the point end part of the blade. CONSTITUTION: When a blade 12 of a propeller 11 rotates in a direction C, a lift L is generated to obtain thrust T and rotating torque Q as a component of the life. Then for totary speed N of the blade 12, a flow of speed U is acted upon the point end part of the blade 12, and a flow U 1 having said flow speed U moves around from the front side to the rear side of the blade 12, to act upon a small blade 13 with a certain attack angle. In this way, lift l crossing at a right angle with the flow U 1 is generated in the small blade 13 to obtain its components, thrust (t) and rotating torque (q), reversely operated to the rotating torque Q in the blade 12, in the blade 13. Accordingly, proper thrust T in the blade 12 can be increased by the thrust (t), further the rotating torque Q can be decreased by the rotating torque (q). COPYRIGHT: (C)1982,JPO&Japio

Windmill blade stalling and speed control device

Abstract: The windmill stalling and speed control device is mounted in the blade supporting hub of a windmill and is operative in response to blade rotation induced by a blade pitch control unit. The device includes a biasing assembly mounted to oppose blade rotation in at least one direction and a stage adjustment unit which operates to aid the biasing unit and increase the opposition to blade rotation when the windmill hub and blades reach and remain within predetermined speed ranges.

Performance improvements with the free-tip rotor

Abstract: A new rotor configuration called the free-tip rotor was investigated for its potential to improve helicopter forward-flight performance characteristics. This rotor differs from a conventional rotor only in the blade tip region. Free tip is self-adjusting in pitch with respect to the rest of the blade. With this capability, the resulting pitch motion generated a more uniform airload distribution around the azimuth. Computer math models were used to compare performance characteristics of the free-tip rotor with those of a conventional rotor operating at flight speeds from 130 to 160 knots. The free-tip rotor is shown to improve cruise L/DE by at least 22%.

Apparatus for increasing the rearward propulsion of boat motors provided with reverse gears

Abstract: The invention relates to an accessory for outboard motors, Z-drives for boats or the like, the exhaust gas of which is normally conducted through the propeller hub into the water. By means of a valve system, which is suitably automatically changed over by the direction of rotation of the propeller, the exhaust gas, during rearward rotation of the propeller, is conducted to a region which lies outside the propeller suction, while the exhaust gas, during forward rotation of the propeller, flows out in the usual manner through the propeller hub. The success of the invention lies in a significant increase of the propeller propulsion during rearward travel.

MOD-0A 200 kW wind turbine generator design and analysis report

Abstract: The design, analysis, and initial performance of the MOD-OA 200 kW wind turbine generator at Clayton, NM is documented. The MOD-OA was designed and built to obtain operation and performance data and experience in utility environments. The project requirements, approach, system description, design requirements, design, analysis, system tests, installation, safety considerations, failure modes and effects analysis, data acquisition, and initial performance for the wind turbine are discussed. The design and analysis of the rotor, drive train, nacelle equipment, yaw drive mechanism and brake, tower, foundation, electricl system, and control systems are presented. The rotor includes the blades, hub, and pitch change mechanism. The drive train includes the low speed shaft, speed increaser, high speed shaft, and rotor brake. The electrical system includes the generator, switchgear, transformer, and utility connection. The control systems are the blade pitch, yaw, and generator control, and the safety system. Manual, automatic, and remote control are discussed. Systems analyses on dynamic loads and fatigue are presented.

Full-Scale Propeller Disk Wake Survey and Boundary Layer Velocity Profile Measurements on the 154-Foot Ship R/V Athena

Abstract: : Measurements of propeller disk velocity components have been made for the 154-foot ship R/V ATHENA. Longitudinal, tangential, and radial velocity components are presented for three planes perpendicular to the propeller shaft for full-scale speeds of 9 and 15 knots. In addition, several boundary layer velocity profiles were measured on the full-scale hull. Non-dimensional velocity profiles are presented for several speeds. Finally, the results of an attempt at measuring time dependent velocities ahead of an operating propeller are presented.

Vibrations of a Marine Propeller Operating in a Nonuniform Inflow.

Abstract: : The effect of blade vibration on the unsteady forces developed by an elastic marine propeller is investigated for a controlled laboratory situation. The study involves the development of a theory for a flexible propeller operating in a spatially nonuniform inflow velocity field and a series of experimental tests. Measurements of unsteady propeller forces in a 24-inch water tunnel are presented for two model propellers whose fundamental resonance frequencies are excited by a nonuniform inflow field. Measured unsteady thrust and torque, presented as a function of excitation frequency, show distinctly different elastic effects--one propeller demonstrates a large force amplification near its resonance frequency while the other did not. The simple theoretical model explains the difference as being due to the differing amounts of induced hydrodynamic damping; there is a large hydrodynamic damping in one case and a small amount in the other case. Another result of the study is that blade vibration can significantly reduce the unsteady forces transmitted to the propeller shaft over a certain range of excitation frequencies. Calculated forces are in general agreement with the experimental measurements. (Author)

Marine propulsion system with cyclic blade pitch - uses paddle wheel inset in hull and with bevel gear transmission

Abstract: A cyclic pitch control paddle wheel for a ship has the paddles (1) mounted between two rotating flanges (4) rigidly linked by a central axle and driven by bevel gears (14) linked to the engines. The pitch of the paddles varies cyclically for optimum drive. The system gives very good steering and drive control. The blades are mounted in the drive flanges or adjustable pivots to generate the pitch. One or two paddle wheels can be mounted in recessed drive ducts under the hull of the ship.

A flight investigation of performance and loads for a helicopter with 10-64C main rotor blade sections

Abstract: A flight investigation produced data on performance and rotor loads for a teetering rotor, AH-1G helicopter flown with a main rotor that had the NLR-1T airfoil as the blade section contour. The test envelope included hover, forward flight speeds from 34 to 83 m/sec (65 to 162 knots), and collective fixed maneuvers at about 0.25 tip speed ratio. The data set for each test point describes vehicle flight state, control positions, rotor loads, power requirements, and blade motions. Rotor loads are reviewed primarily in terms of peak to peak and harmonic content. Lower frequency components predominated for most loads and generally increased with increased airspeed, but not necessarily with increased maneuver load factor. Detailed data for an advanced airfoil on an AH-1G are presented.

A note on the design of wake-adapted propellers

Abstract: Problems associated with the design of wake-adapted propellers are illustrated by results obtained from a simple propeller and wake model. It is shown that the widely used approach of the vortex theory gives much-too-low induced axial velocities at the inner radii of the propeller, which results in too-low blade pitch ratios. The reason for this is that no regard is paid to the fact that the vorticity of the approaching flow is changed by the propeller. If this changing vorticity is introduced in the vortex theory, its shortcomings are eliminated. An effect of the improvement is that the effective wake at the propeller plane differs from the nominal wake. The difference depends upon the propeller load. The propeller is shown to have a leveling effect on a nonuniform axisymmetric nominal wake.

Effects of rotor parameter variations on handling qualities of unaugmented helicopters in simulated terrain flight

Abstract: A coordinated analysis and ground simulator experiment was performed to investigate the effects on single rotor helicopter handling qualities of systematic variations in the main rotor hinge restraint, hub hinge offset, pitch-flap coupling, and blade lock number. Teetering rotor, articulated rotor, and hingeless rotor helicopters were evaluated by research pilots in special low level flying tasks involving obstacle avoidance at 60 to 100 knots airspeed. The results of the experiment are in the form of pilot ratings, pilot commentary, and some objective performance measures. Criteria for damping and sensitivity are reexamined when combined with the additional factors of cross coupling due to pitch and roll rates, pitch coupling with collective pitch, and longitudinal static stability. Ratings obtained with and without motion are compared. Acceptable flying qualities were obtained within each rotor type by suitable adjustment of the hub parameters, however, pure teetering rotors were found to lack control power for the tasks. A limit for the coupling parameter L sub q/L sub p of 0.35 is suggested.

Feasibility study of the effectiveness of tip sails on propeller performance

Abstract: Tip sails are appendages placed at the tips of airplane wings for the purpose of reducing drag. The authors set out to test the hypothesis that similar appendages placed at the tips of marine propeller blades are also likely to improve the performance characteristics of marine propellers. A propeller was tested in various configurations with the tip sails in place. Results were compared with those obtained from tests of the bare propeller. Maximum efficiency did not rise above that for the bare propeller in any of the tests.

Controlling system for variable pitch type circulation pump

Abstract: PURPOSE:To maximize the efficiency of operation of a plant having a variable pitch type circulation pump by providing a controlling system in which the rate of supply of cooling water is determined so as to provide a vacuum level which maximizes the efficiency with minimum pump driving power at each load level and sea water temperature. CONSTITUTION:A controlling system for variable pitch type circulation pump having blades the pitch of which being variable includes a pump optimum controller 19 for operating a blade driving device 13, a blade angle detector 16 adapted for delivering an input signal to the controller 19, a generator load detector 17, a sea water temperature detector 18 and a condenser vacuum detector 20. The pump optimum controller determines, upon receipt of detection signals from the detectors 16, 17, 18 and 20 a blade pitch which maximizes the efficiency of the plant, and delivers a signal representing such a blade pitch to the blade driving device 13. Thus, the pitch of the blades is controlled in accordance with a cooling water flow rate which maximizes the plant efficiency with minimum pump driving power at each load level and sea water temperature to maximize the efficiency of the plant.