Aerodynamic response of a hovering rotor to ramp change in pitch input

Karthikeyan Duraisamy, Richard Brown

Research output: Contribution to conferencePaper

4 Citations (Scopus)

Abstract

Under transient conditions, a helicopter rotor generates a complex, time-dependent pattern of shed and trailed vorticity in its wake that has profound effects on its loading. To examine these effects, the response of a two-bladed hovering rotor to a ramp change in collective pitch is investigated using three different computational approaches. Solutions obtained using a Compressible Reynolds Averaged Navier-Stokes approach are compared to results obtained from lifting-line theory coupled to an Eulerian Vorticity Transport Model, and from a simple single-state dynamic inflow model. The different numerical approaches yield very similar predictions of the thrust response of the rotor to ramp changes in collective pitch, as long as the ramp rates are small. This suggests that the basic underlying flow physics is properly represented by all the approaches. For more rapid ramp rates, an additional delay in the aerodynamic response of the rotor, that is related to the finite extent of the wake during its early history, is predicted by the Navier-Stokes and Vorticity Transport approaches. Even though the evolution of the wake of the rotor is strongly three dimensional and highly unsteady, the predictions of the Navier-Stokes and lifting-line models agree very closely as long as the blades of the rotor do not stall. In the pre-stall regime, a quasi two-dimensional representation of the blade aerodynamics thus appears adequate for predicting the performance of such systems even under highly transient conditions. When flow separation occurs, the resulting three dimensionality of the blade aerodynamics forces the predictions of the Navier-Stokes and lifting-line approaches to diverge, however. The characterization of the wake interactions and stall propagation mechanisms that are presented in this study offers some insight into the fundamental fluid dynamic mechanisms that govern the transient aerodynamic response of a rotor to control inputs, and provides some quantication of the limits of applicability of some popular current approaches to rotor aerodynamic analysis.
LanguageEnglish
Number of pages17
Publication statusPublished - 28 May 2008
Event64th American Helicopter Society Annual Forum - Montréal, Canada
Duration: 28 Apr 20081 May 2008

Conference

Conference64th American Helicopter Society Annual Forum
CityMontréal, Canada
Period28/04/081/05/08

Fingerprint

Aerodynamics
Rotor
Rotors
Wake
Navier-Stokes
Vorticity
Blade
Line
Prediction
Helicopter rotors
Flow separation
Flow Separation
Fluid dynamics
Helicopter
Turbomachine blades
Fluid Dynamics
Diverge
Dynamic models
Dimensionality
Physics

Keywords

  • compressible reynolds averaged Navier-Stokes approach
  • lifting-line theory
  • Eulerian vorticity transport model
  • single-state dynamic inflow model
  • fluid dynamics
  • rotor aerodynamic analysis

Cite this

Duraisamy, K., & Brown, R. (2008). Aerodynamic response of a hovering rotor to ramp change in pitch input. Paper presented at 64th American Helicopter Society Annual Forum, Montréal, Canada, .
Duraisamy, Karthikeyan ; Brown, Richard. / Aerodynamic response of a hovering rotor to ramp change in pitch input. Paper presented at 64th American Helicopter Society Annual Forum, Montréal, Canada, .17 p.
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Duraisamy, K & Brown, R 2008, 'Aerodynamic response of a hovering rotor to ramp change in pitch input' Paper presented at 64th American Helicopter Society Annual Forum, Montréal, Canada, 28/04/08 - 1/05/08, .

Aerodynamic response of a hovering rotor to ramp change in pitch input. / Duraisamy, Karthikeyan; Brown, Richard.

2008. Paper presented at 64th American Helicopter Society Annual Forum, Montréal, Canada, .

Research output: Contribution to conferencePaper

TY - CONF

T1 - Aerodynamic response of a hovering rotor to ramp change in pitch input

AU - Duraisamy, Karthikeyan

AU - Brown, Richard

PY - 2008/5/28

Y1 - 2008/5/28

N2 - Under transient conditions, a helicopter rotor generates a complex, time-dependent pattern of shed and trailed vorticity in its wake that has profound effects on its loading. To examine these effects, the response of a two-bladed hovering rotor to a ramp change in collective pitch is investigated using three different computational approaches. Solutions obtained using a Compressible Reynolds Averaged Navier-Stokes approach are compared to results obtained from lifting-line theory coupled to an Eulerian Vorticity Transport Model, and from a simple single-state dynamic inflow model. The different numerical approaches yield very similar predictions of the thrust response of the rotor to ramp changes in collective pitch, as long as the ramp rates are small. This suggests that the basic underlying flow physics is properly represented by all the approaches. For more rapid ramp rates, an additional delay in the aerodynamic response of the rotor, that is related to the finite extent of the wake during its early history, is predicted by the Navier-Stokes and Vorticity Transport approaches. Even though the evolution of the wake of the rotor is strongly three dimensional and highly unsteady, the predictions of the Navier-Stokes and lifting-line models agree very closely as long as the blades of the rotor do not stall. In the pre-stall regime, a quasi two-dimensional representation of the blade aerodynamics thus appears adequate for predicting the performance of such systems even under highly transient conditions. When flow separation occurs, the resulting three dimensionality of the blade aerodynamics forces the predictions of the Navier-Stokes and lifting-line approaches to diverge, however. The characterization of the wake interactions and stall propagation mechanisms that are presented in this study offers some insight into the fundamental fluid dynamic mechanisms that govern the transient aerodynamic response of a rotor to control inputs, and provides some quantication of the limits of applicability of some popular current approaches to rotor aerodynamic analysis.

AB - Under transient conditions, a helicopter rotor generates a complex, time-dependent pattern of shed and trailed vorticity in its wake that has profound effects on its loading. To examine these effects, the response of a two-bladed hovering rotor to a ramp change in collective pitch is investigated using three different computational approaches. Solutions obtained using a Compressible Reynolds Averaged Navier-Stokes approach are compared to results obtained from lifting-line theory coupled to an Eulerian Vorticity Transport Model, and from a simple single-state dynamic inflow model. The different numerical approaches yield very similar predictions of the thrust response of the rotor to ramp changes in collective pitch, as long as the ramp rates are small. This suggests that the basic underlying flow physics is properly represented by all the approaches. For more rapid ramp rates, an additional delay in the aerodynamic response of the rotor, that is related to the finite extent of the wake during its early history, is predicted by the Navier-Stokes and Vorticity Transport approaches. Even though the evolution of the wake of the rotor is strongly three dimensional and highly unsteady, the predictions of the Navier-Stokes and lifting-line models agree very closely as long as the blades of the rotor do not stall. In the pre-stall regime, a quasi two-dimensional representation of the blade aerodynamics thus appears adequate for predicting the performance of such systems even under highly transient conditions. When flow separation occurs, the resulting three dimensionality of the blade aerodynamics forces the predictions of the Navier-Stokes and lifting-line approaches to diverge, however. The characterization of the wake interactions and stall propagation mechanisms that are presented in this study offers some insight into the fundamental fluid dynamic mechanisms that govern the transient aerodynamic response of a rotor to control inputs, and provides some quantication of the limits of applicability of some popular current approaches to rotor aerodynamic analysis.

KW - compressible reynolds averaged Navier-Stokes approach

KW - lifting-line theory

KW - Eulerian vorticity transport model

KW - single-state dynamic inflow model

KW - fluid dynamics

KW - rotor aerodynamic analysis

UR - http://www.vtol.org/64exhinfo.html

M3 - Paper

ER -

Duraisamy K, Brown R. Aerodynamic response of a hovering rotor to ramp change in pitch input. 2008. Paper presented at 64th American Helicopter Society Annual Forum, Montréal, Canada, .