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Computational Investigation on Unsteady Loads of High-Speed Rigid Coaxial Rotor with High-Efficient Trim Model

  • Haotian Qi
  • Guohua XuEmail author
  • Congling Lu
  • Yongjie Shi
Original Paper

Abstract

A computational fluid dynamics method is built to study the unsteady aerodynamic loads of a high-speed rigid coaxial rotor model, taking account of lift offset (LOS). The flowfield is simulated by solving Reynolds Averaged Navier–Stokes equations, and moving overset mesh is adopted to include blade motions. A high-efficient trim model for coaxial rotor is developed, where the “delta method” is implemented. Performance of Harrington rotor-1 is calculated for validation. Forward flight cases in three advance ratios are conducted. Results indicate that the temporal thrusts of coaxial rotor at low advance ratio share some fluctuations similar to hover state. In forward flight, the impulsive thrust fluctuations caused by blade-meeting are obviously exhibited around 270° for upper blades, and the strengths increase with the increase of LOS and advance ratio. At higher advance ratios, the blade thrusts of the upper and lower rotors tend to be the same. At the advance ratio of 0.6, two new kinds of Blade–vortex interaction (BVI) are captured. One is the parallel BVI caused by the root vortex and the other is the complex interaction among the tip vortex, root vortex and the rear blade.

Keywords

Rigid coaxial rotor Aerodynamic loads High speed Rotor trim CFD Lift offset 

List of Symbols

A

\( \pi R^{2} \), rotor disk area (m2)

c

Chord (m)

CT

\( {T \mathord{\left/ {\vphantom {T {(\rho A\varOmega^{2} R^{2} )}}} \right. \kern-0pt} {(\rho A\varOmega^{2} R^{2} )}} \), rotor thrust coefficient

CQ

\( {Q \mathord{\left/ {\vphantom {Q {(\rho A}}} \right. \kern-0pt} {(\rho A}}\varOmega^{2} R^{3} ) \), rotor torque coefficient

CL

\( {L \mathord{\left/ {\vphantom {L {(\rho A}}} \right. \kern-0pt} {(\rho A}}\varOmega^{2} R^{3} ) \), rotor rolling moment coefficient

CM

\( {M \mathord{\left/ {\vphantom {M {(\rho A}}} \right. \kern-0pt} {(\rho A}}\varOmega^{2} R^{3} ) \), rotor pitching moment coefficient

cl

\( {{\text{lift}} \mathord{\left/ {\vphantom {{\text{lift}} {\left( {\frac{1}{2}\rho V^{2} c} \right)}}} \right. \kern-0pt} {\left( {\frac{1}{2}\rho V^{2} c} \right)}} \), blade sectional lift coefficient

Cn

\( {{F_{n} } \mathord{\left/ {\vphantom {{F_{n} } {\left( {\frac{1}{2}\rho V^{2} c} \right)}}} \right. \kern-0pt} {\left( {\frac{1}{2}\rho V^{2} c} \right)}} \), blade sectional normal force coefficient

Cp

\( {{(p - p_{\infty } )} \mathord{\left/ {\vphantom {{(p - p_{\infty } )} {\left( {{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-0pt} 2}\rho V_{\text{tip}}^{2} } \right)}}} \right. \kern-0pt} {\left( {{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-0pt} 2}\rho V_{\text{tip}}^{2} } \right)}} \), pressure coefficient

L1

Blade 1 of the lower rotor

L2

Blade 2 of the lower rotor

\( \mu \)

\( {{V_{\infty } } \mathord{\left/ {\vphantom {{V_{\infty } } {\varOmega R}}} \right. \kern-0pt} {\varOmega R}} \), lift offset of coaxial system

Ma

Mach number

R

Rotor radius (m)

S1

Blade 1 of the single rotor

S2

Blade 2 of the single rotor

U1

Blade 1 of the upper rotor

U2

Blade 2 of the upper rotor

Vy

Velocity in y direction (m/s)

Vtip

Rotor tip speed (m/s)

\( V_{\infty } \)

Forward flight speed (m/s)

\( \psi \)

Azimuth angle (°)

\( \theta_{0} \)

Collective pitch angle (°)

\( \theta_{1s} \)

Longitudinal cyclic pitch angle (°)

\( \theta_{1c} \)

Lateral cyclic pitch angle (°)

\( \varOmega \)

Rotor angular velocity (rad/s)

Subscripts

L

Lower rotor in coaxial system

U

Upper rotor in coaxial system

Notes

Acknowledgements

This work was supported by the National Natural Science Foundation of China (no. 11302103).

Compliance with ethical standards

Conflicts of interest

All authors declare that they have no conflict of interest.

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Copyright information

© The Korean Society for Aeronautical & Space Sciences 2019

Authors and Affiliations

  • Haotian Qi
    • 1
  • Guohua Xu
    • 1
    Email author
  • Congling Lu
    • 1
  • Yongjie Shi
    • 1
  1. 1.National Key Laboratory of Science and Technology on Rotorcraft AerodynamicsNanjing University of Aeronautics and AstronauticsNanjingChina

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