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Aerodynamic Analysis of High-Speed Compound Unmanned Rotorcraft Using an Unstructured Flow Solver

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Abstract

In the present study, numerical simulations of a high-speed compound unmanned rotorcraft were carried out by employing an unstructured Reynolds-Averaged Navier–Stokes solver. For the simulations, a conceptually designed rotorcraft was used which includes two propellers, a fuselage with main and tail wings and a co-axial rotor. Aerodynamic characteristics of the propulsion components were studied by comparing aerodynamic coefficients with the following modes: hovering, transitional low-speed, high-speed, and maximum flight speed conditions. Furthermore, the effects of the fluid dynamic interactions between the co-axial rotor, propellers, and wings were investigated. Lastly, the impact of ground on the aerodynamic performance on the rotorcraft was studied.

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Abbreviations

\(HCUR\) :

High-speed compound unmanned rotorcraft

\(\mathrm{V}\) :

Arbitrary control volume

\(\mathrm{\delta V}\) :

Arbitrary control surface

\(\overrightarrow{Q}\) :

Conservative variable

\(\overrightarrow{n}\) :

Normal vector

\(\overrightarrow{F}(\overrightarrow{Q})\) :

Inviscid flux

\(\overrightarrow{G}(\overrightarrow{Q})\) :

Viscous flux

\(FDS\) :

Flux difference splitting

\(\mathrm{SA}\) :

Spalart–Allmaras

\(H\) :

Height from the ground

\(\mathrm{D}\) :

Diameter of rotor

\(MPI\) :

Message passing interface

\({C}_{T}\) :

Thrust coefficient

\({C}_{Q}\) :

Torque coefficient

\({C}_{F}\) :

Normalized force coefficient

\({C}_{p}\) :

Pressure coefficient

\(\widehat{{e}_{x}}\) :

Unit vector in x-direction

\(\widehat{{e}_{y}}\) :

Unit vector in y-direction

\(\widehat{{e}_{z}}\) :

Unit vector in z-direction

\(u\) :

Velocity in x-direction

\(\mathrm{v}\) :

Velocity in y-direction

\(w\) :

Velocity in z-direction

\(F\) :

Force

\({S}_{ref}\) :

Fuselage wing surface area

\(\uprho \) :

Air density

\(\mathrm{T}\) :

Thrust

\(Q\) :

Torque

\(\mathrm{A}\) :

Area of rotor disk

\(\mathrm{R}\) :

Radius of rotor blade

\({v}_{tip}\) :

Blade tip speed

\({v}_{free}\) :

Freestream velocity

\(H\) :

Distance from the ground to the lower rotor of rotorcraft

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Acknowledgements

This research was funded by the Korea Agency for Infrastructure Technology Advancement (Grant Number N04220134), the Korea Institute of Science and Technology Information (Grant Number C22002), and the Korea Institute of Energy Technology Evaluation and Planning (Grant Number 20213030020200), and the BK21 FOUR Program of the National Research Foundation Korea (NRF) grant funded by the Ministry of Education (MOE) (Grant Number N20220006), and the Agency For Defense Development Grant funded by the Korean Government.

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Authors and Affiliations

  1. Agency for Defense Development, Daejeon, 34186, Republic of Korea

    Sang Hyun Park

  2. Department of Aerospace Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 34141, Republic of Korea

    Oh Joon Kwon & Sang Lee

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  1. Sang Hyun Park
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  2. Oh Joon Kwon
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  3. Sang Lee
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Correspondence to Sang Lee.

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Appendix A: Definition of Terms

Appendix A: Definition of Terms

1.1 Vortex Intensity / Eddy Current Strength

$$\overrightarrow{\omega }=\overrightarrow{\nabla }\times \overrightarrow{u}=\mathrm{det}\left|\begin{array}{ccc}\widehat{{e}_{x}}& \widehat{{e}_{y}}& \widehat{{e}_{z}}\\ \frac{\partial }{\partial x}& \frac{\partial }{\partial y}& \frac{\partial }{\partial z}\\ u& v& w\end{array}\right|.$$

\(\widehat{{e}_{x}}\), \(\widehat{{e}_{y}}\) and \(\widehat{{e}_{z}}\) refer to unit vectors in x-, y- and z-direction respectively, whereas each of \(u\), \(\mathrm{v}\) and \(\mathrm{w}\) represents flow velocity in each x-, y- and z-direction.

1.2 Dimensionless Force

$${C}_{F}=\frac{F}{\rho {{v}_{free}}^{2}{S}_{ref}/2}.$$

\(\mathrm{F}\) refers to vertical/horizontal force, whereas each of \({v}_{free}\) and \({S}_{ref}\) represents the freestream velocity and the main wing planform area of the fuselage.

1.3 Thrust and Torque Coefficients

$${C}_{T}=\frac{T}{\rho A{{v}_{tip}}^{2}}, {C}_{Q}=\frac{Q}{\rho A{{v}_{tip}}^{2}R}.$$

\(\rho \) stands for air density, and each of \(\mathrm{T}\) and \(\mathrm{Q}\) refers to thrust and torque of rotor/propeller. \(\mathrm{A}\) represents the area of the rotor/propeller disk and \(\mathrm{R}\) means the radius of a rotor/propeller blade. \({v}_{tip}\) refers to the speed of the rotor/propeller blade tip.

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Park, S.H., Kwon, O.J. & Lee, S. Aerodynamic Analysis of High-Speed Compound Unmanned Rotorcraft Using an Unstructured Flow Solver. Int. J. Aeronaut. Space Sci. 24, 1077–1085 (2023). https://doi.org/10.1007/s42405-023-00595-3

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