A coupled free-wake/panel method for rotor/fuselage/empennage aerodynamic interaction and helicopter trims

Abstract

A coupled free-wake/panel method to predict the rotor downwash aerodynamic interaction and helicopter trims is presented. Free-wake method was developed to analyze aerodynamics interference of rotor wake, based on lifting-surface theory and vortex method, which relates the core radius, span station, and circulation of initial tip vortex with the blade-bound circulation distribution, and eliminates the empirical parameters during rotor free wake analysis. Helicopter fuselage with empennage was discretized into source panels. The vortex line mirror method was adopted to account for wake acceleration phenomenon that resulted from the close interaction between rotor wake and fuselage surface. The rotor wake geometry and downwash simulations were investigated including comparisons with the available measured data. Combined with the helicopter flight dynamics model and embedded in the trim procedure, the free-wake/panel coupled method was applied to calculate the rotor wake and its interference on other components of a full-scale UH-60A rotorcraft in level flight. Comparisons among predictions, referenced results, and experimental results are made for rotor wake geometries, blade-bound vortex, blade tip vortex, rotor downwash velocity, and control stick positions, and encouraging results were obtained. To validate the present method, this paper discusses the fundamental formulation, the numerical algorithms, and the simulation results.

Keywords

Aerodynamics interference rotorcraft aerodynamics helicopter trim vortex wake free-wake/panel method

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References

Johnson W. Wake model for helicopters in high speed flight. Report no. NACA 1177507, 1988.

Narayanan

Marilyn

Chee

. A review of rotor wake physics and modeling. J Am Helicopter Soc 2010; 56: 1–19.

Bhagwat

Leishman

. Stability consistency and convergence of time-marching free-vortex rotor wake algorithms. J Am Helicopter Soc 2001; 46: 59–71.

Strawn

Caradonnna

Duque

EPN

. 30 years rotorcraft computational fluid dynamics research and development. J Am Helicopter Soc 2006; 51: 5–21.

Zhao

. Modeling rotor wake dynamic with viscous vortex particle method. AIAA J 2009; 47: 902–915.

Cheng

Greengard

Rokhlin

. A fast adaptive multipole algorithm in three dimensions. J Computat Phys 1999; 155: 468–498.

Bagai

Leishman

. Rotor free-wake modeling using a pseudo implicit relaxation algorithm. J Aircraft 1995; 32: 1276–1285.

Tan

Wang

. Panel/full-span free-wake coupled method for unsteady aerodynamics of helicopter rotor blade. Chinese J Aeronaut 2013; 26: 535–543.

Richason

Katz

. Unsteady panel method for flows with multiple bodies moving along various paths. AIAA J 1994; 32: 62–68.

10.

Zhu

. Subsonic, supersonic unsteady potential flow panel method, Beijing: National Defense Industry Press, 1981, pp. 20–180. (in Chinese).

11.

Bettschart N. Rotor Fuselage Interaction: Euler and Navier–Stokes Computations with an Actuator Disc. In: 55th annual forum of the American Helicopter Society [CD-ROM], Montreal Canada, 25–27 May 1999.

12.

Cao

Zhao

. Numerical simulation of rotor-fuselage-cylinder interaction in forward flight. J Aircraft 2010; 47: 1426–1430.

13.

Leishman JG. Rotor blade system with reduced blade-vortex interaction noise. Patent US 6948906B2, USA, 2005.

14.

Leishman

. Principles of helicopter aerodynamics, 2nd ed. Cambridge: Cambridge University Press, 2006.

15.

Betz A. Behavior of vortex systems. Report no. NACA TM-713, 1932.

16.

Bhagwat MJ. Mathematical modeling of the transient dynamics of helicopter rotor wakes using a time accurate free vortex methods. PhD Thesis, University of Maryland, USA, 2001.

17.

Bhagwat MJ and Leishman JG. Trailing vortex measurements in the wake of a hovering rotor blade with various tip shapes. In: 58th annual forum of the American Helicopter Society [CD-ROM], Montreal Canada, 11–13 June 2002.

18.

Crouse

Leishman

Naipei

. Theoretical and experimental study of unsteady rotor/body aerodynamic interactions. J Am Helicopter Soc 1992; 37: 55–65.

19.

Hilbert KB. A mathematical model of UH-60 helicopter. Report no. NASA TM-85890, 1984.

20.

Cao

Hess

. Helicopter flight characteristics in icing conditions. Aeronaut J 2012; 116: 963–979.

21.

Zhao

. A viscous vortex particle model for rotor wake and interference analysis. J Am Helicopter Soc 2010; 55: 1–14.