The Experts below are selected from a list of 165 Experts worldwide ranked by ideXlab platform
Thomas F Brooks - One of the best experts on this subject based on the ideXlab platform.
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reduction of Helicopter Blade vortex interaction noise by active rotor control technology
Progress in Aerospace Sciences, 1997Co-Authors: Yung H Yu, Bernd Gmelin, W R Splettstoesser, Jean Jacques Philippe, Jean Prieur, Thomas F BrooksAbstract:Abstract Helicopter Blade-vortex interaction noise is one of the most severe noise sources and is very important both in community annoyance and military detection. Research over the decades has substantially improved basic physical understanding of the mechanisms generating rotor Blade-vortex interaction noise and also of controlling techniques, particularly using active rotor control technology. This paper reviews active rotor control techniques currently available for rotor Blade-vortex interaction noise reduction, including higher harmonic pitch control, individual Blade control, and on-Blade control technologies. Basic physical mechanisms of each active control technique are reviewed in terms of noise reduction mechanism and controlling aerodynamic or structural parameters of a Blade. Active rotor control techniques using smart structures/materials are discussed, including distributed smart actuators to induce local torsional or flapping deformations.
Yung H Yu - One of the best experts on this subject based on the ideXlab platform.
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reduction of Helicopter Blade vortex interaction noise by active rotor control technology
Progress in Aerospace Sciences, 1997Co-Authors: Yung H Yu, Bernd Gmelin, W R Splettstoesser, Jean Jacques Philippe, Jean Prieur, Thomas F BrooksAbstract:Abstract Helicopter Blade-vortex interaction noise is one of the most severe noise sources and is very important both in community annoyance and military detection. Research over the decades has substantially improved basic physical understanding of the mechanisms generating rotor Blade-vortex interaction noise and also of controlling techniques, particularly using active rotor control technology. This paper reviews active rotor control techniques currently available for rotor Blade-vortex interaction noise reduction, including higher harmonic pitch control, individual Blade control, and on-Blade control technologies. Basic physical mechanisms of each active control technique are reviewed in terms of noise reduction mechanism and controlling aerodynamic or structural parameters of a Blade. Active rotor control techniques using smart structures/materials are discussed, including distributed smart actuators to induce local torsional or flapping deformations.
Gordon J Leishman - One of the best experts on this subject based on the ideXlab platform.
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interdependence of diffusion and straining of Helicopter Blade tip vortices
Journal of Aircraft, 2004Co-Authors: Manikandan Ramasamy, Gordon J LeishmanAbstract:An experiment was performed to help quantify the interdependence of viscous/turbulent diffusion and straining effects on the development of Helicopter rotor tip vortices. The properties of the Blade tip vortices were measured in the wake of a small-scale hovering rotor and compared to the results for the case when the wake approached a solid boundary. The presence of the boundary created velocity gradients that forced the tip vortex filaments to strain, allowing the effects of this process on the vortices to be measured relative to the baseline case without the boundary. It is shown that vortex stretching begins to decrease the viscous core size, and when the strain rates become large, this can balance the normal growth in the vortex core resulting from diffusion. The present results were used to help develop a more general tip vortex model suitable for use in a variety of Helicopter rotor aeroacoustic applications. The proposed engineering model combines the effects of turbulent diffusion and strain on the vortex core growth. The empirical coefficients of this model have been derived based on the best available results from rotating-wing tip vortex measurements.
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investigation of Helicopter rotor Blade tip vortex alleviation using a slotted tip
AIAA Journal, 2004Co-Authors: Yong Oun Han, Gordon J LeishmanAbstract:A slotted tip was developed to modify the characteristics of the strong vortex trailed from the tip of a small-scale Helicopter Blade. Forward-facing slots directed a slight amount of the incident flow in the spanwise direction, which was vented at the side edge of the Blade tip. This caused the tip vortex to detach from the Blade tip face, and also introduced turbulent vortlets into the laminar core of the developing vortex. The resulting wake flowfield was investigated using flow visualization and laser Doppler velocimetry. Measurements were conducted to quantify the vortex swirl velocity components, the inner core development, and the overall vortical flow inside the vortex trails. The results were then compared to a baseline Blade with a standard unmodified rectangular tip
Ranjan Ganguli - One of the best experts on this subject based on the ideXlab platform.
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Helicopter Blade flapping with and without small angle assumption in the presence of dynamic stall
Applied Mathematical Modelling, 2010Co-Authors: Jyoti Ranjan Majhi, Ranjan GanguliAbstract:The flapping equation for a rotating rigid Helicopter Blade is typically derived by considering (1) small flap angle, (2) small induced angle of attack and (3) linear aerodynamics. However, the use of nonlinear aerodynamics such as dynamic stall can make the assumptions of small angles suspect as shown in this paper. A general equation describing Helicopter Blade flap dynamics for large flap angle and large induced inflow angle of attack is derived. A semi-empirical dynamic stall aerodynamics model (ONERA model) is used. Numerical simulations are performed by solving the nonlinear flapping ordinary differential equation for steady state conditions and the validity of the small angle approximations are examined. It is shown that the small flapping assumption, and to a lesser extent, the small induced angle of attack assumption, can lead to inaccurate predictions of the Blade flap response in certain flight conditions for some rotors when nonlinear aerodynamics is considered.
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modeling Helicopter rotor Blade flapping motion considering nonlinear aerodynamics
Cmes-computer Modeling in Engineering & Sciences, 2008Co-Authors: Jyoti Ranjan Majhi, Ranjan GanguliAbstract:The flapping equation for a rotating rigid Helicopter Blade is typically derived by considering 1) small flap angle, 2) small induced angle of attack and 3) linear aerodynamics. However, the use of nonlinear aerodynamics can make the assumptions of small angles suspect. A general equation describing Helicopter Blade flap dynamics for large flap angle and large induced inflow angle of attack is derived in this paper with nonlinear aerodynamics . Numerical simulations are performed by solving the nonlinear flapping ordinary differential equation for steady state conditions and the validity of the small angle approximations are examined. It is shown that the small flapping assumption, and to a lesser extent, the small induced angle of attack assumption can lead to inaccurate predictions of the Blade flap response in certain flight conditions for some rotors when nonlinear aerodynamics is considered.
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structural damage detection in a Helicopter rotor Blade using radial basis function neural networks
Smart Materials and Structures, 2003Co-Authors: Roopesh Kumar R Reddy, Ranjan GanguliAbstract:A neural network approach is used for detection of structural damage in a Helicopter rotor Blade using rotating frequencies of the flap (transverse bending), lag (in-plane bending), elastic torsion and axial modes. A finite element method is used for modeling the Helicopter Blade. Radial basis function (RBF) neural networks are used and several combinations of modes are investigated for training and testing the neural network. Using the first 10 modes of the rotor Blade for damage detection yields accurate results for the soft in-plane hingeless rotor considered in this study. Using a parametric study of the Blade rotating frequency in conjunction with the neural network, it is found that a reduced measurement set consisting of five modes (the first two torsion modes, the second lag mode and the third and fourth flap modes) also gives good results for damage detection. Furthermore, taking only the first four flap modes also results in good damage detection accuracy. Three rotating frequency sets are therefore identified in this paper for structural damage detection in a Helicopter rotor using RBF neural networks.
Marcel Ilie - One of the best experts on this subject based on the ideXlab platform.
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numerical study of Helicopter Blade vortex mechanism of interaction using the potential flow theory
Applied Mathematical Modelling, 2012Co-Authors: Patricia X. Coronado Domenge, Marcel IlieAbstract:Abstract The Blade–vortex interaction (BVI) phenomenon plays a key role in the rotorcraft aerodynamics. Numerical investigations of BVI using classical CFD approaches are computationally expensive. In the present research we propose a numerical approach, based on the potential flow theory, for the numerical investigation of Helicopter Blade–vortex mechanism of interaction. This approach overcomes the computational expenses posed by the CFD techniques. The influence of vertical miss distance, angle of attack, airfoil camber, and vortex strength on the Helicopter Blade–vortex mechanism of interaction is subject of investigation. The study reveals that the magnitude of the aerodynamic coefficients decreases with the increase of vertical miss distance and angle of attack, and the decrease of vortex strength and core size.