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Showing papers on "Helicopter rotor published in 2008"


Journal ArticleDOI
TL;DR: In this article, wind tunnel tests were conducted to assess the aerodynamic performance of single-, two-and three-stage Savonius rotor systems with both semicircular and twisted blades.

337 citations


Journal ArticleDOI
TL;DR: In this paper, the concept of sliding meshes is introduced to account for the relative motion between the fuselage and the rotor blades, where a sliding surface forms a boundary between a CFD mesh around a fuselage, and a rotor-fixed CFD meshes which rotates to explain the movement of the rotor.
Abstract: SUMMARY The study of rotor–fuselage interactional aerodynamics is central to the design and performance analysis of helicopters. However, regardless of its significance, rotor–fuselage aerodynamics has so far been addressed by very few authors. This is mainly due to the difficulties associated with both experimental and computational techniques when such complex configurations, rich in flow physics, are considered. In view of the above, the objective of this study is to develop computational tools suitable for rotor–fuselage engineering analysis based on computational fluid dynamics (CFD). To account for the relative motion between the fuselage and the rotor blades, the concept of sliding meshes is introduced. A sliding surface forms a boundary between a CFD mesh around the fuselage and a rotor-fixed CFD mesh which rotates to account for the movement of the rotor. The sliding surface allows communication between meshes. Meshes adjacent to the sliding surface do not necessarily have matching nodes or even the same number of cell faces. This poses a problem of interpolation, which should not introduce numerical artefacts in the solution and should have minimal effects on the overall solution quality. As an additional objective, the employed sliding mesh algorithms should have small CPU overhead. The sliding mesh methods developed for this work are demonstrated for both simple and complex cases with emphasis placed on the presentation of the inner workings of the developed algorithms. Copyright q 2008 John Wiley & Sons, Ltd.

239 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of the crack breathing models on the nonlinear vibration characteristics of the cracked rotors is investigated using two well-known crack models, i.e. switching crack model and response dependent breathing crack model.

114 citations


Journal ArticleDOI
TL;DR: In this article, the authors present an approach for the analysis and design of magnetic suspension systems with large flexible rotordynamics models including dynamics, control, and simulation, and a flywheel system is studied as an example for realizing a physical controller that provides stable rotor suspension and good disturbance rejection in all operating states.

89 citations


Journal ArticleDOI
TL;DR: A harmonic balance technique for the analysis of unsteady flows about helicopter rotors in forward flight and hover is presented and the method is applied to the three-dimensional Euler equations, and the steady and unsteadY aerodynamics about wings and rotors is examined.

83 citations


Proceedings ArticleDOI
10 Sep 2008
TL;DR: A time-spectral and adjoint-based optimization procedure that is particularly efficient for the analysis and shape design of helicopter rotors is developed and shows good performance improvement, amounting to a 2% decrease in torque and 7% increase in thrust compared to the baseline UH-60A.
Abstract: A time-spectral and adjoint-based optimization procedure that is particularly efficient for the analysis and shape design of helicopter rotors is developed. The time-spectral method is a fast and accurate algorithm to simulate periodic, unsteady flows by transforming them to a steady-state analysis using a Fourier spectral derivative temporal operator. An accompanying steady-state adjoint formulation for periodic unsteady problems is then possible and enables an unsteady flow design optimization procedure. The time-spectral CFD analysis is validated against conventional time-accurate CFD and flight test data for a UH-60A Black Hawk helicopter rotor in high speed forward flight. A multidisciplinary structural dynamics and comprehensive analysis coupling is employed for validation study to include blade structural dynamics and to enforce vehicle trim. Application of the adjointbased design method is carried out to optimize blade shape for a UH-60A. An uncoupled aerodynamics only calculation is performed for design application, holding the blade deformations and trim angles fixed to the previously calculated values. Minimization of power is pursued with non-linear constraints on thrust and drag force, resulting in a simplified form of the trim condition. The blade twist distribution, airfoil section shapes, and outboard planform shape comprise over 100 design variables. Starting from the initial configuration, the optimizer found a new design that shows good performance improvement, amounting to a 2% decrease in torque and 7% increase in thrust compared to the baseline UH-60A. The results demonstrate the potential of the time-spectral and adjoint-based design method for helicopter rotors.

77 citations


Journal ArticleDOI
TL;DR: In this paper, the authors examined the vibration response of the cracked rotor in presence of common rotor faults such as unbalance and rotor stator rub, and the full spectrum analysis has been used effectively to extract the distinctive directional features of these rotor faults.

70 citations


Journal ArticleDOI
TL;DR: In this paper, the airwakes of two simplified-frigate shapes were analyzed as part of a study of the complex flow field generated as a helicopter interacts with the airwake of a ship.

70 citations


Journal ArticleDOI
TL;DR: In this paper, the effectiveness of surrogate modeling of helicopter vibrations, and the use of the surrogates for minimization of helicopter rotor vibrations are studied, and accuracies of kriging, radial basis function interpolation, and polynomial regression surrogates are compared.
Abstract: The effectiveness of surrogate modeling of helicopter vibrations, and the use of the surrogates for minimization of helicopter rotor vibrations are studied. The accuracies of kriging, radial basis function interpolation, and polynomial regression surrogates are compared. In addition, the surrogates are used to generate an objective function which is employed in an optimization study. The design variables consist of the cross-sectional dimensions of the structural member of the blade and non-structural masses. The optimized blade is compared with a baseline rotor blade which resembles an MBB BO-105 blade. Results indicate that: (a) kriging surrogates best approximate vibratory hub loads over the entire design space and (b) the surrogates can be used effectively in helicopter rotor vibration reduction studies.

69 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of uncertainty in composite material properties on the cross-sectional stiffness properties, natural frequencies, and aeroelastic responses of a composite helicopter rotor blade is investigated.
Abstract: This study investigates the effect of uncertainty in composite material properties on the cross-sectional stiffness properties, natural frequencies, and aeroelastic responses of a composite helicopter rotor blade. The elastic moduli and Poisson’s ratio of the composite material are considered as random variables with a coefficient of variation of around 4%, which was taken from published experimental work. An analytical box beam model is used for evaluating blade cross-sectional properties. Aeroelastic analysis based on finite elements in space and time is used to evaluate the helicopter rotor blade response in forward flight. The stochastic cross-sectional and aeroelastic analyses are carried out with Monte Carlo simulations. It is found that the blade cross-sectional stiffness matrix elements show a coefficient of variation of about 6%. The nonrotating rotor blade natural frequencies show a coefficient of variation of around 3%. The impact of material uncertainty on rotating natural frequencies varies from that on nonrotating blade frequencies because of centrifugal stiffening. The propagation of material uncertainty into aeroelastic response causes large deviations, particularly in the higher-harmonic components that are critical for the accurate prediction of helicopter blade loads and vibration. The numerical results clearly show the need to consider randomness of composite material properties in the helicopter aeroelastic analysis.

67 citations


Journal ArticleDOI
TL;DR: In this paper, a parametric study on the aeroelastic instability and the nonlinear dynamical behavior of a two-dimensional symmetric rotor blade in the dynamic stall regime is investigated.

Patent
23 Jan 2008
TL;DR: A rotary-wing aircraft with an electric motor mounted along an axis of rotation to drive a rotor system about the axis is a typical example of a single-rotor aircraft.
Abstract: A rotary-wing aircraft with an electric motor mounted along an axis of rotation to drive a rotor system about the axis of rotation.


Journal ArticleDOI
TL;DR: In this article, a generalized version of harmonic balance coupled with arc-length continuation was developed in order to study non-linear responses of a modified Jeffcott rotor system subject to multiple unbalances.

Patent
18 Jan 2008
TL;DR: A rotary wing vehicle includes a body structure having an elongated tubular backbone or core and a counter-rotating coaxial rotor system having rotors as mentioned in this paper, which is used to move the rotor system in directional flight.
Abstract: A rotary wing vehicle includes a body structure having an elongated tubular backbone or core and a counter-rotating coaxial rotor system having rotors. The rotor system is used to move the rotary wing vehicle in directional flight.

Journal ArticleDOI
TL;DR: In this paper, a conformable airfoil is proposed as an alternative to trailing-edge flaps used for active helicopter vibration reduction through high-frequency changes in camber, which consists of several compliant mechanisms of predetermined topology that are placed serially within the air foil along the chord, aft of the leading-edge spar.
Abstract: A conformable airfoil is proposed as an alternative to trailing-edge flaps used for active helicopter vibration reduction through high-frequency changes in camber. The design consists of several compliant mechanisms of predetermined topology that are placed serially within the airfoil along the chord, aft of the leading-edge spar. A shape optimization approach is used to design the compliant mechanisms, in which the objective is to maximize trailing-edge deflection while minimizing airfoil deflections due to aerodynamic loads. Solutions were obtained using a sequential linear programming method coupled with a finite element analysis. An optimized shape is predicted to achieve a trailing-edge deflection of ±6.0 mm or a ±4.6- deg equivalent flap deflection angle using the tip deflection objective. Results indicate that the deflection is dependent on the amount of passive material allowed and the objective function used. The aerodynamic loads are found to cause only small deformations in comparison with those caused by the actuation. Prototype fabrication and bench-top tests demonstrated that rotor airfoil camber is controllable using the proposed concept.

Journal ArticleDOI
01 Jan 2008
TL;DR: A new balancing method for rotor systems named the holo-balancing method is presented, which successfully applies the holospectral principle in traditional balancing methods of flexible rotor systems and decreases test number, increases precision and efficiency of field balancing.
Abstract: Field balancing of flexible rotor system is a key technique to reduce turbine vibration in power plants. Traditional balancing methods are generally based on the information from a unidirectional sensor. In fact, the motion of a rotor system is a complex spatial motion, which cannot be objectively and reliably described with just a unidirectional sensor in one bearing section. In order to give an accurate description of rotor vibration responses, multi-sensor fusion instead of a single sensor should be used with the purpose of more comprehensive utilization of information. Based on this theory, the paper presents a new balancing method for rotor systems named the holo-balancing method, which successfully applies the holospectral principle in traditional balancing methods of flexible rotor systems. At the same time, genetic algorithm (GA) optimization and computer simulation are used to simplify balancing process. The new method decreases test number, increases precision and efficiency of field balancing. The principle and detailed procedures of the new method are explained in this paper, and the effectiveness of the new method was validated by field balancing of several 300MW turbo-generator units.

01 Jan 2008
TL;DR: In this article, a short review of the rotor-induced vibration problem is given with a link to typical vibration characteristics of Eurocopter helicopters, and the concepts and means to influence and control vibrations are outlined.
Abstract: This paper is about recent advances in Eurocopter’s research activities on passive and active vibration control systems. Emphasis is placed on the reduction of rotor-induced vibrations which is still one of the key challenges in helicopter dynamics. Both passive and active means for the reduction of vibrations are discussed. A short review of the rotor-induced vibration problem is given with a link to typical vibration characteristics of Eurocopter helicopters. The concepts and means to influence and control vibrations are outlined. The main focus of this paper is on recent advances on i) vibration control at the rotor, ii) vibration control at the transmission and iii) vibration control at the fuselage. In the section “vibration control at the rotor”, vibrations are attacked at their source – the rotor itself. Advanced passive and active rotor dynamic layouts are of interest. Here, a 5-bladed bearingless vs. 4bladed main rotor system on EC145 as well as an active flap rotor on the hingeless system of BK117 are discussed. For each system, key parameters of the design, data of the test configuration and test environment and in particular results on vibration reduction are presented. A substantial reduction of the exciting hub loads is achieved thus providing superior airframe vibration levels. In the section “vibration control at the transmission”, a new generation of pylon isolation system is presented. This passive system based on the SARIB principle combines advantages of efficiency, lightness, reliability and low cost design. This technology consists of a compact suspension and a flapping mass integrated in each gear box strut. It provides an important attenuation of the vibrations for all hub loads components and it was successfully tested in-flight. In the section “vibration control at the fuselage”, active anti-vibration control systems (AVCS) installed in the fuselage are presented. The systems rely on single-port active devices which are capable to generate inertia-based control forces which induce a secondary vibration field to compensate the vibration disturbance. Here, systems based on electromagnetic actuation technology for EC225 as well as Piezo-ceramic technology demonstrated on EC135 are presented.


Proceedings ArticleDOI
17 Oct 2008
TL;DR: In this paper, a technique based on time-frequency and tomographic analysis to extract helicopter blade parameters for the purposes of radar non-cooperative target recognition (NCTR) is investigated.
Abstract: A technique based on time-frequency and tomographic analysis to extract helicopter blade parameters for the purposes of radar non-cooperative target recognition (NCTR) is investigated. The proposed algorithm shows that (under certain conditions) it is feasible to extract the number, blade length, blade tip velocity and angular velocity of a helicopterpsilas main rotor. Simulation results from a point scatterer model is validated through results on measured data from several different commercial helicopters. The developed technique is most suited to pulse-Doppler tracking radar and is shown to be feasible at a range of 11 km with a radar not specifically designed for this purpose.

Journal ArticleDOI
01 Oct 2008
TL;DR: In this article, the periodic motions of a rotor system with two discs are investigated where rub-impacts occur at a fixed limiter for a test rig with dual discs and a finite element (FE) model of the rotor system is presented.
Abstract: Periodic motions of a rotor system with two discs are investigated where rub-impacts occur at fixed limiter for a test rig with dual discs. First, a finite element (FE) model of the rotor system is...

Journal ArticleDOI
TL;DR: In this article, the effect of uncertainty in composite material properties on the nonlinear aero-elastic response and vibratory loads of a four-bladed composite helicopter rotor is studied.
Abstract: The effect of uncertainty in composite material properties on the nonlinear aeroelastic response and vibratory loads of a four-bladed composite helicopter rotor is studied. The aeroelastic analysis is done using a finite element method in space and time, and the composite cross section is analyzed using a variational asymptotic approach. The effective material properties of composite laminas are first considered as random variables with a coefficient of variation of 5%. The material uncertainty is propagated to cross-sectional stiffness,rotating natural frequencies, aeroelastic response, and vibratory loadsof the composite helicopter rotor. The stochastic cross-sectional and aeroelastic analyses are carried out with Monte Carlo simulations. The stochastic stiffness values are scattered up to 15% around the baseline stiffness values and show a Gaussian distribution with a coefficient of variation of about 4%. The uncertainty impact on rotating natural frequencies depends on the level of centrifugal stiffening for different modes. The stochastic rotating natural frequencies indicate a possibility of their coincidence with the integer multiples of rotor speed. The propagation of material uncertainty into aeroelastic response causes large deviations from the baseline predictions and affects the crucial higher harmonics content, which is critical for vibration predictions. The magnitudes of 4/rev vibratory loads show a scattering up to 300% from the baseline value,and their probability density functions show non-Gaussian-type distributions. Further, the uncertainty results for a coefficient of variation of 10% in the material properties are obtained. The uncertainty impact on the aeroelastic response is found to be proportional to the coefficient of variation of the composite material properties.

Journal ArticleDOI
TL;DR: In this paper, the contribution of the torsional deflection of the rotor blades to the phase difference between the minimum lift coefficient and the minimum of the blade pitch on the advancing side of a helicopter rotor during high-speed forward flight is quantified.
Abstract: The prediction of airloads and the corresponding structural response in high-speed forward flight of rotors poses a significant challenge to predictive rotorcraft aeromechanics methods. One of the issues identified in the flight test data of the Puma and Black Hawk aircraft is the phase difference between the minimum lift coefficient and the minimum of the blade pitch on the advancing side of the rotor during high-speed forward flight. This is commonly referred to as the advancing-side lift-phase delay. In the present work, the unsteady three-dimensional flowfield on the advancing side of a helicopter rotor is analyzed using computational fluid dynamics in an attempt to quantify contributions to the preceding effect. Time-dependent two-dimensional computational fluid dynamics simulations of blade sections with combined pitch/freestream Mach number oscillation were carried out to isolate the contribution to the phase difference of pitch angle and Mach number variations in the absence of the complex rotor-induced flowfield, sideslip, and rotor blade dynamics. The results for the freestream Mach number oscillations show that the lift coefficient lags the Mach changes at outboard stations, but this effect is reduced for combined pitch/Mach number oscillations. Finite span and sideslip contributions to the phasing were quantified by investigating the chordwise extent of supersonic flow on the advancing side for two nonlifting rotors in high-speed flight. Finally, the UH-60A rotor in high-speed forward flight was considered. By comparing results for rigid blades with results for a prescribed blade torsional deflection, the contribution of the blade torsion to the advancing-blade lift phasing was also quantified. Furthermore, rigid-blade simulations with different flapping schedules demonstrated the sensitivity of the lift phasing to trim-state variations. It was found that Mach number effects are dominant and the lift phasing depends primarily on the encountered Mach number and pitch schedule. Further, the elastic torsional deflection of the blades effectively changes the pitch schedule of the blade sections and also plays a role in the phasing of the lift and pitching moment coefficients.

Journal ArticleDOI
TL;DR: In this article, the effects of geometric scaling on the static and dynamic behavior of a multi-rim hybrid press-fitted composite flywheel rotor are investigated and applied to its design procedure.
Abstract: The effects of geometric scaling on the static and dynamic behavior of a multi-rim hybrid press-fitted composite flywheel rotor are investigated and applied to its design procedure. It is verified that the stresses among the scaled multi-rim hybrid rotors remain the same as long as press-fit interferences are linearly scaled, curing temperature remains unchanged, and the rotational speed is inversely proportional. With the linearly scaled supporting stiffness of the scaled rotor and shaft, a relationship between inversely scaled critical speeds and rotational speeds remains unchanged. Double rim rotors of 5 kWh and 100 kWh energy storage are designed by scaling an optimized 0.5 kWh multi-rim rotor. Then, the rotors of 5 kWh were manufactured by wet-winding E-glass and T-700 fibers with a low-temperature cured epoxy system.


01 Oct 2008
TL;DR: In this paper, five analytical tools have been used to study rotor performance at high advance ratio and the major finding is that the decades spent by many rotorcraft theoreticians to improve prediction of basic rotor aerodynamic performance has paid off.
Abstract: Five analytical tools have been used to study rotor performance at high advance ratio. One is representative of autogyro rotor theory in 1934 and four are representative of helicopter rotor theory in 2008. The five theories are measured against three sets of well documented, full-scale, isolated rotor performance experiments. The major finding of this study is that the decades spent by many rotorcraft theoreticians to improve prediction of basic rotor aerodynamic performance has paid off. This payoff, illustrated by comparing the CAMRAD II comprehensive code and Wheatley & Bailey theory to H-34 test data, shows that rational rotor lift to drag ratios are now predictable. The 1934 theory predicted L/D ratios as high as 15. CAMRAD II predictions compared well with H-34 test data having L/D ratios more on the order of 7 to 9. However, the detailed examination of the selected codes compared to H-34 test data indicates that not one of the codes can predict to engineering accuracy above an advance ratio of 0.62 the control positions and shaft angle of attack required for a given lift. There is no full-scale rotor performance data available for advance ratios above 1.0 and extrapolation of currently available data to advance ratios on the order of 2.0 is unreasonable despite the needs of future rotorcraft. Therefore, it is recommended that an overly strong full-scale rotor blade set be obtained and tested in a suitable wind tunnel to at least an advance ratio of 2.5. A tail rotor from a Sikorsky CH-53 or other large single rotor helicopter should be adequate for this exploratory experiment.

Journal ArticleDOI
TL;DR: In this article, the authors explored the feasibility of using vibratory hub loads and support vector machine (SVM) to predict damage and hence the life consumption of the composite helicopter rotor blade.
Abstract: This work explores a feasibility of using vibratory hub loads and support vector machine (SVM) to predict damage and hence the life consumption of the composite helicopter rotor blade. Generally, the initial part of the composite's life is dominated by matrix cracking; the intermediate part by debonding/delamination and the final failure due to fiber breakage. The simulated hub loads under various damage levels are obtained using a comprehensive aeroelastic analysis of the composite rotor blade with physics based damage modes and are then linked with the life consumption of the blade using a phenomenological model. The SVM is used for classification of the useful life of the blade into three classes which are useful to decide the prognostic action. The performance of the blade damage detection system is demonstrated using simulated hub loads obtained using a two-cell airfoil section representing the stiff-inplane blade. The model based hub load variations are contaminated with noise to simulate the real data. It is observed that the SVM based damage detection system is more robust, reliable and easy to implement than the rotating frame measurement based methods.

Journal ArticleDOI
TL;DR: In this article, an advanced active twist rotor (AATR) blade incorporating single crystal macro fiber composite (single crystal MFC) actuators is designed and the aeroelastic analysis is performed.
Abstract: The advanced active twist rotor (AATR) blade incorporating single crystal macro fiber composite (single crystal MFC) actuators is designed and the aeroelastic analysis is performed. The AATR blade is designed based on an existing passive blade and the NASA/ARMY/MIT active twist rotor (ATR) prototype blade. The AATR blade is designed to satisfy all the requirements and the properties of the AATR blade are compared with those of the ATR prototype blade. The aeroelastic analysis of the designed AATR blade for the hover condition is conducted. In order to predict the vibration reduction capability, the twist actuation frequency response of the AATR blade is investigated by the numerical simulation. As a result, although lower input voltage is used, the AATR blade can achieve higher twist actuation that is sufficient to alleviate the helicopter vibration as compared with the ATR blades using the AFC and the standard MFC.

Journal ArticleDOI
TL;DR: In this paper, the orthogonal blade-vortex interaction (BVI) has been simulated using unsteady Reynolds-averaged Navier-Stokes equations, and the cases investigated are relative to an interaction between a lifting blade at high angle of attack and an orthogon vortex that travels either head-on or at 45 degrees to the leading edge.
Abstract: The orthogonal blade-vortex interaction (BVI) has been simulated using unsteady Reynolds-averaged Navier-Stokes equations. The cases investigated are relative to an interaction between a lifting blade at high angle of attack and an orthogonal vortex that travels either head-on or at 45 degrees to the leading edge...

Proceedings ArticleDOI
01 Jan 2008
TL;DR: In this article, it has been demonstrated that the crack-induced changes in the rotor dynamic behavior produce unique vibration signatures, which are the result of the coexistence of a parametric excitation term and different frequencies present in the system.
Abstract: It has been widely recognized that the changes in the dynamic response of a rotor could be utilized for general fault detection and monitoring. Current methods rely on the monitoring of synchronous response of the machine during its transient or normal operation. Very little progress has been made in developing robust techniques to detect subtle changes in machine condition caused by rotor cracks. It has been demonstrated that the crack-induced changes in the rotor dynamic behavior produce unique vibration signatures. When the harmonic excitation force is applied to the cracked rotor system, nonlinear resonances occur due to the nonlinear parametric excitation characteristics of the crack. These resonances are the result of the coexistence of a parametric excitation term and different frequencies present in the system, namely critical speed, the synchronous frequency, and excitation frequency from the externally applied perturbation signals. This paper presents the application of this approach on an experimental test rig. The simulation and experimental study for the given rig configuration, along with the application of active magnetic bearings as a force actuator, are presented.