Aerodynamic/Acoustic Analysis for Main Rotor and Tail Rotor of Helicopter (original) (raw)
Related papers
Numerical analysis for main-rotor/tail-rotor interaction of helicopter
2009
A simulation method for full helicopter configuration is constructed by combining an unsteady Euler code and an aeroacoustic code based on the Ffowcs-Williams and Hawkings formulation. The flow field and helicopter noise are calculated using a moving overlapped grid system, and the mutual effect of main rotor and tail rotor are studied for the helicopter in hover or forward flight. In the hovering flight calculation, the tip vortex of the tail rotor is dragged by the induced flow of the main rotor, and the detailed phenomena of the flow pattern are captured well. In a forward-flight calculation, noises from the main rotor and tail rotor are predicted to understand the tail rotor noise for both self noise and the interaction noise with the main-rotor wake. Comparison of noise magnitude shows that the relative importance of tail rotor noise with respect to the main rotor noise according to the flight conditions.
Numerical Analysis of Interaction Noise Between Main Rotor and Tail Rotor of Helicopter
2004
Unsteady calculation of the interaction between tail-rotor and main-rotor wake of helicopter is conducted using an overlapped grid method. A moving overlapped grid system is used with three types of grid including rotor grid, inner background grid and outer background grid for helicopter flight simulation. The rotor grid, consisting of 2 blades for main-rotor and 4 blades for tail-rotor, communicates with inner/outer-background grids during unsteady computations. The Blade-Vortex Interaction (BVI) noise of main-rotor and tail-rotor noise are predicted using a combination method of an unsteady Euler code with an aeroacoustic code based on the Ffowcs-Williams and Hawkings formulation. The effect of tail-rotor onto mainrotor and the tail-rotor noise are studied for the helicopter operating conditions.
Numerical simulations of helicopter aerodynamics and acoustics
Journal of Computational and Applied Mathematics, 1996
This paper demonstrates several new methods for computing acoustic signals from helicopter rotors in hover and forward flight. Aerodynamic and acoustic solutions in the near field are computed with two different finite-volume flow solvers for the Euler equations. A solution-adaptive unstructured-grid Euler solver models a rotor in hover while a more conventional structured-grid solver is used for forward flight calculations. A nonrotating cylindrical surface is then placed around the entire rotor system. This surface moves subsonically with the rotor hub in forward flight. The finite-volume solution is interpolated onto this cylindrical surface at every time step and a Kirchhoff integration propagates the acoustic signal to the far field. Computed values for high-speed impulsive noise in hover and forward flight show excellent agreement with experimental data. Results from the combined finite-volume/Kirchhoff method offer high accuracy with reasonable computer resource requirements.
Helicopter Rotor Noise in the Merged Tip-Vortex and Blade Interaction Condition
International Journal of Aeroacoustics, 2011
BVI (blade vortex interaction) phenomena cause unsteady loading and noise in the helicopter rotor. It is difficult to accurately predict BVI aerodynamics and noise, because rotor wake and tip-vortices are numerically dissipated. In the present study, CFD and a time-marching free-wake coupling analysis were used to describe inflow and outflow without wake dissipation. Rotor noise was also computed using the Farassat formula, derived from the Ffowcs-Williams Hawkings equation. To validate aerodynamics and the noise prediction solver, a two-blade rotor was simulated and the results were compared with experimental data. To investigate the vortex interaction of a multi-blade rotor, a four-blade rotor was also simulated. In a slow descent flight condition, tip vortices are merged at the advancing side. The merged tip-vortex and blade interaction were simulated and are discussed in this paper.
Prediction of helicopter rotor noise in hover
EPJ Web of Conferences, 2015
Two mathematical models are used in this work to estimate the acoustics of a hovering main rotor. The first model is based on the Ffowcs Williams-Howkings equations using the formulation of Farassat. An analytical approach is followed for this model, to determine the thickness and load noise contributions of the rotor blade in hover. The second approach allows using URANS and RANS CFD solutions and based on numerical solution of the Ffowcs Williams-Howkings equations. The employed test cases correspond to a model rotor available at the KNRTU-KAI aerodynamics laboratory. The laboratory is equipped with a system of acoustic measurements, and comparisons between predictions and measurements are to be attempted as part of this work.
2000
This paper presents a combined methodology consisting of rotor aerodynamic and aeroacoustic computation modules. Aerodynamic calculations utilise the Vortex Element Method for the description of free vortex wake, which determines the rotor flowfield. The mathematical model discretizes the wake into vortex elements. The induced velocity is calculated for the distorted wake geometry, by means of the Biot-Savart law, integrated in closed form over each of these elements. Bound circulation variations and unsteady blade airloading are computed as a result of the nonuniform induced downwash. Wake roll up process, vortex core modelling, vorticity dissipation, blade section boundary layer growth are incorporated in numerical modelling of aerodynamic computations. Computed blade loading variations are used as the basis of loading noise predictions. Aeroacoustic analysis concentrates on helicopter rotor noise prediction in time domain. The formulation is based on the Ffowcs-Williams and Hawki...
Comparative helicopter noise analysis in static and in-flight conditions
The Journal of the Acoustical Society of America, 2008
Rotary wing aircraft, i.e. helicopter, is a source of intense noise, external and internal alike, in conclusion becoming serious environmental and health issue. The generated noise is in some aspects similar to propeller noise in fixed wing aircraft (airplane), while differing in main noise source alignment in respect to the relative airflow: in helicopters, both rotors, i.e. main and tail, that produce forces necessary for flight, are inline with the direction of flight, while in airplanes rotor(s) are perpendicular to it. Another distinctive noise in helicopters, well known as "slapping", comes from the rotor cutting its own wake/vortex air inflow, especially while descending. In this article main helicopter noise sources will be discussed and most significant results of various static and in-flight noise measurements on two different types of helicopters will be presented and analyzed.
Simultaneous Vibration and Noise Reduction in Rotorcraft Using Aeroelastic Simulation
Journal of the American Helicopter Society, 2006
A study of helicopter vibration and blade-vortex interaction (BVI) noise reduction is conducted using the actively-controlled trailing edge flap (ACF) approach implemented in single and dual flap configurations. The effectiveness of a passive approach based on varying the sweep on the tip of the rotor to modify noise and vibration characteristics of the rotor is also considered. The study is based on a comprehensive rotorcraft aeroelastic/aeroacoustic simulation code that was validated against the experimental data obtained in the Higherharmonic-control Aeroacoustic Rotor Test (HART) program. The effectiveness of the ACF system for vibration and noise reduction is explored on two different helicopter configurations, one resembling a four-bladed MBB BO-105 hingeless rotor and the other similar to a five-bladed MD-900 bearingless rotor. Issues associated with the practical implementation of the ACF approach are emphasized and examined such as: the effects of practical flap saturation limits, constant and 1/rev control inputs and flap overhang. The simulation results demonstrate the capability of the ACF system for effective vibration and BVI noise reduction. * Ph.D. Candidate, Student Member aiaa. † François-Xavier Bagnoud Professor, Fellow aiaa, ahs ‡ Postdoctoral Researcher, Member aiaa.
Computation of Helicopter Rotor Acoustics in Forward Flight
Journal of the American Helicopter Society, 1995
This paper presents a new method for computing acoustic signals from helicopter rotors in forward flight. The aerodynamic and acoustic solutions in the near field are comouted with a finite-difference solver for the Euler eauations. A uonrotating cylindrical Kirchhoff surface is then placed around the entire rotor system. This Kirchhoff surface moves suhsonically with the rotor in forward flight. The finite-difference solution is interpolated onto this cylindrical surface at each time step and a Kirchhoff integration is used to carry the acoustic signal to the far field. Computed values for highsaeed imuulsive noise show excellent aereement with model-rotor and flieht-testexnerimental data. Results from theuew-method offer high accuracy with reasonable computer resource requirements.
AIAA Journal, 2005
Helicopter noise is an increasingly important issue, and at large forward flight speeds transonic rotor noise is a major contributor. In this paper, a method for predicting transonic rotor noise is developed which is more computationally efficient than previous methods, and which furthermore offers physical insight into the noise generation. These benefits combine to make it of potential use to helicopter rotor designers. The permeable surface form of the Ffowcs Williams -Hawkings (FW-H) equation is used to express the sound field in terms of a distribution of monopole and dipole sources over a permeable control surface, and a distribution of quadrupole sources over the volume outside of this surface. By choosing the control surface to enclose the transonic flow regions, the noise from the quadrupole distribution becomes negligible. Only the more straightforward surface sources then need be considered, making the acoustic approach computationally efficient. By locating the control surface close to the blade subject to enclosing the transonic flow regions, efficiency in the CFD approach is also attained. To perform noise predictions, an Euler CFD method to calculate the flow-field was combined with an acoustic method incorporating the retarded time formulation of the FW-H equation. Several rotor blades in hover and steady forward ¡ PhD Student, Student Member AIAA † Post-Doctoral Research Associate, Member AIAA ‡ Professor of Mechanical Engineering and Head of the Division of Energy, Fluid Mechanics and Turbomachinery, Senior Member AIAA § Lecturer, Member AIAA 1