The effect of blade aerodynamic modelling on the prediction of high-frequency rotor airloads

Mary E. Kelly, Richard Brown

Research output: Contribution to conferencePaper

2 Citations (Scopus)

Abstract

Interactions between the blades and vortical structures within the wake of a helicopter rotor are a significant source of impulsive loading and noise, particularly in descending flight. Brown's Vorticity Transport Model has been used to investigate the influence of the fidelity of the local blade aerodynamic model on the accuracy with which the high-frequency airloads associated with blade-vortex interactions can be predicted. The Vorticity Transport Model yields a very accurate representation of the structure of the wake, and allows significant flexibility in the way that the blade loading, and hence the source of vorticity into the wake, can be represented. Two models for the local blade aerodynamics are compared. The first is a simple lifting-line model and the second is a somewhat more sophisticated lifting-chord model based on unsteady thin aerofoil theory. A marked improvement in accuracy of the predicted high-frequency airloads of the HART II rotor is obtained when the lifting-chord model for the blade aerodynamics is used instead of the lifting-line type approach. Errors in the amplitude and phase of the loading peaks are reduced and the quality of the prediction is affected to a lesser extent by the computational resolution of the wake. Indeed, the lifting-line model increasingly overpredicts the amplitude of the lift response to blade-vortex interactions as the computational grid is refined, exposing clearly the fundamental deficiencies in this commonly-used approach particularly when modelling the aerodynamic response of the blade to interactions with vortices that are much smaller than its chord. In comparison, the airloads that are predicted using the lifting-chord model are relatively insensitive to the resolution of the computation, and there are fundamental reasons to believe that properly converged numerical solutions may be attainable using this approach.

Conference

Conference65th American Helicopter Society Annual Forum
CityTexas, USA
Period27/05/0929/05/09

Fingerprint

Blade
Aerodynamics
Rotor
Rotors
Prediction
Wake
Chord or secant line
Modeling
Vorticity
Vortex
Vortex flow
Interaction
Model
Line
Helicopter rotors
Helicopter
Fidelity
Airfoils
Turbomachine blades
Flexibility

Keywords

  • blade aerodynamic modelling
  • high-frequency rotor airload prediction
  • vorticity transport model
  • blade-vortex interaction
  • unsteady thin aerofoil theory
  • HART II rotor

Cite this

Kelly, M. E., & Brown, R. (2009). The effect of blade aerodynamic modelling on the prediction of high-frequency rotor airloads. Paper presented at 65th American Helicopter Society Annual Forum, Texas, USA, .
Kelly, Mary E. ; Brown, Richard. / The effect of blade aerodynamic modelling on the prediction of high-frequency rotor airloads. Paper presented at 65th American Helicopter Society Annual Forum, Texas, USA, .
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title = "The effect of blade aerodynamic modelling on the prediction of high-frequency rotor airloads",
abstract = "Interactions between the blades and vortical structures within the wake of a helicopter rotor are a significant source of impulsive loading and noise, particularly in descending flight. Brown's Vorticity Transport Model has been used to investigate the influence of the fidelity of the local blade aerodynamic model on the accuracy with which the high-frequency airloads associated with blade-vortex interactions can be predicted. The Vorticity Transport Model yields a very accurate representation of the structure of the wake, and allows significant flexibility in the way that the blade loading, and hence the source of vorticity into the wake, can be represented. Two models for the local blade aerodynamics are compared. The first is a simple lifting-line model and the second is a somewhat more sophisticated lifting-chord model based on unsteady thin aerofoil theory. A marked improvement in accuracy of the predicted high-frequency airloads of the HART II rotor is obtained when the lifting-chord model for the blade aerodynamics is used instead of the lifting-line type approach. Errors in the amplitude and phase of the loading peaks are reduced and the quality of the prediction is affected to a lesser extent by the computational resolution of the wake. Indeed, the lifting-line model increasingly overpredicts the amplitude of the lift response to blade-vortex interactions as the computational grid is refined, exposing clearly the fundamental deficiencies in this commonly-used approach particularly when modelling the aerodynamic response of the blade to interactions with vortices that are much smaller than its chord. In comparison, the airloads that are predicted using the lifting-chord model are relatively insensitive to the resolution of the computation, and there are fundamental reasons to believe that properly converged numerical solutions may be attainable using this approach.",
keywords = "blade aerodynamic modelling, high-frequency rotor airload prediction, vorticity transport model, blade-vortex interaction, unsteady thin aerofoil theory, HART II rotor",
author = "Kelly, {Mary E.} and Richard Brown",
year = "2009",
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language = "English",
note = "65th American Helicopter Society Annual Forum ; Conference date: 27-05-2009 Through 29-05-2009",

}

Kelly, ME & Brown, R 2009, 'The effect of blade aerodynamic modelling on the prediction of high-frequency rotor airloads' Paper presented at 65th American Helicopter Society Annual Forum, Texas, USA, 27/05/09 - 29/05/09, .

The effect of blade aerodynamic modelling on the prediction of high-frequency rotor airloads. / Kelly, Mary E.; Brown, Richard.

2009. Paper presented at 65th American Helicopter Society Annual Forum, Texas, USA, .

Research output: Contribution to conferencePaper

TY - CONF

T1 - The effect of blade aerodynamic modelling on the prediction of high-frequency rotor airloads

AU - Kelly, Mary E.

AU - Brown, Richard

PY - 2009/5/27

Y1 - 2009/5/27

N2 - Interactions between the blades and vortical structures within the wake of a helicopter rotor are a significant source of impulsive loading and noise, particularly in descending flight. Brown's Vorticity Transport Model has been used to investigate the influence of the fidelity of the local blade aerodynamic model on the accuracy with which the high-frequency airloads associated with blade-vortex interactions can be predicted. The Vorticity Transport Model yields a very accurate representation of the structure of the wake, and allows significant flexibility in the way that the blade loading, and hence the source of vorticity into the wake, can be represented. Two models for the local blade aerodynamics are compared. The first is a simple lifting-line model and the second is a somewhat more sophisticated lifting-chord model based on unsteady thin aerofoil theory. A marked improvement in accuracy of the predicted high-frequency airloads of the HART II rotor is obtained when the lifting-chord model for the blade aerodynamics is used instead of the lifting-line type approach. Errors in the amplitude and phase of the loading peaks are reduced and the quality of the prediction is affected to a lesser extent by the computational resolution of the wake. Indeed, the lifting-line model increasingly overpredicts the amplitude of the lift response to blade-vortex interactions as the computational grid is refined, exposing clearly the fundamental deficiencies in this commonly-used approach particularly when modelling the aerodynamic response of the blade to interactions with vortices that are much smaller than its chord. In comparison, the airloads that are predicted using the lifting-chord model are relatively insensitive to the resolution of the computation, and there are fundamental reasons to believe that properly converged numerical solutions may be attainable using this approach.

AB - Interactions between the blades and vortical structures within the wake of a helicopter rotor are a significant source of impulsive loading and noise, particularly in descending flight. Brown's Vorticity Transport Model has been used to investigate the influence of the fidelity of the local blade aerodynamic model on the accuracy with which the high-frequency airloads associated with blade-vortex interactions can be predicted. The Vorticity Transport Model yields a very accurate representation of the structure of the wake, and allows significant flexibility in the way that the blade loading, and hence the source of vorticity into the wake, can be represented. Two models for the local blade aerodynamics are compared. The first is a simple lifting-line model and the second is a somewhat more sophisticated lifting-chord model based on unsteady thin aerofoil theory. A marked improvement in accuracy of the predicted high-frequency airloads of the HART II rotor is obtained when the lifting-chord model for the blade aerodynamics is used instead of the lifting-line type approach. Errors in the amplitude and phase of the loading peaks are reduced and the quality of the prediction is affected to a lesser extent by the computational resolution of the wake. Indeed, the lifting-line model increasingly overpredicts the amplitude of the lift response to blade-vortex interactions as the computational grid is refined, exposing clearly the fundamental deficiencies in this commonly-used approach particularly when modelling the aerodynamic response of the blade to interactions with vortices that are much smaller than its chord. In comparison, the airloads that are predicted using the lifting-chord model are relatively insensitive to the resolution of the computation, and there are fundamental reasons to believe that properly converged numerical solutions may be attainable using this approach.

KW - blade aerodynamic modelling

KW - high-frequency rotor airload prediction

KW - vorticity transport model

KW - blade-vortex interaction

KW - unsteady thin aerofoil theory

KW - HART II rotor

UR - http://www.vtol.org/forum65/f65_programOverview.pdf

M3 - Paper

ER -

Kelly ME, Brown R. The effect of blade aerodynamic modelling on the prediction of high-frequency rotor airloads. 2009. Paper presented at 65th American Helicopter Society Annual Forum, Texas, USA, .