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Investigation of a simplified aerodynamic modelling technique for noise predictions using FW–H propagation

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Abstract

This paper addresses the influence of the elastic rotor blade deformation and the aerodynamic interference from the fuselage on the rotor aerodynamics, including rotor noise characteristics. A BO105 main rotor/fuselage configuration is chosen for the numerical simulations. An unsteady aerodynamic code based on free wake three-dimensional panel method (UPM) is used to account for nonlinear effects associated with the mutual interference between main rotor and fuselage. Airbus Helicopters’ (formerly: Eurocopter) rotor code (HOST) is coupled with this aerodynamic code (UPM) to account for the effect of elastic blade deformation. The effect of the fuselage is simulated using two fuselage models in aerodynamic code, (1) potential theory in the form of a panelized fuselage and (2) an analytic fuselage influence formulation derived from isolated fuselage simulation. The advantage of (2) is in its computational efficiency. The aerodynamic modelling is then coupled with an aero-acoustic post-processing tool based on the Ffowcs-Williams–Hawkings (FW–H) approach for evaluating the noise propagation to the far-field. This toolchain is then evaluated in different flight conditions to assess the usability of this approach in the design process. In descending flight, the acoustic prediction is completed at a very mature level, as the blade vortex interaction is well captured. In climb, the major noise peak is underpredicted, while the overall directivity agreement is well matched. In forward flight, due to a phase shift in the airloads prediction, parts of the loading noise directivity are not well captured. The onset of transonic effects further degrades the results obtained at the front of the rotor. For the investigated flight cases, the analytical fuselage formulation brought very similar results to the panelized fuselage model, therefore proving its worthiness for further accelerating the simulation in these flight conditions.

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Abbreviations

ADV:

Advancing side

APSIM:

DLR FW–H code APSIM

BET:

Blade element theory

BPF:

Blade passing frequency

BVI:

Blade vortex interaction

CFD:

Computational fluid dynamics

CSD:

Computational structural dynamics

FUS:

Fuselage

FLOWer:

DLR structured multi-block computational fluid dynamics code

FUS:

Fuselage

FW–H:

Ffowcs-Williams/Hawkings acoustic analogy

HART II:

Higher harmonic control aero-acoustics test campaign

HELINOVI:

HELIcopter NOise and VIbration test campaign

HOST:

Airbus Helicopters’ comprehensive code

HSI:

High-speed impulsive

MR:

Main rotor

OSPL:

Overall sound pressure level

RET:

Retreating side

RPM:

Rotor rotational speed (1/min)

Rev:

Revolution

UPM:

Unsteady panel method with three-dimensional free wake model

\(A_{0}\) :

Peak value of vertically induced velocity by fuselage

\(c_{\infty }\) :

Speed of sound (m/s)

\(C_{\text{T}}\) :

Thrust coefficient

\(c_{n} M^{2}\) :

Normal force coefficient

\(M_{x}\) :

Rotor hub roll moment, positive starboard up (Nm)

\(M_{y}\) :

Rotor hub pitch moment, positive nose up (Nm)

\(M_{\text{h}}\) :

Hover tip Mach number

\(r\) :

Radial coordinate (m)

\(T\) :

Thrust (N)

\(S\) :

Shape function for induced velocity

\(V_{\infty }\) :

Flight speed, m/s

\(v_{izf}\) :

Velocity vertically induced by the fuselage

\(x,y,z\) :

Horizontal, lateral and vertical coordinate

α eff :

Effective rotor shaft angle of attack, wind tunnel corrected (°)

\(\beta\) :

Blade flap angle (°)

\(\psi\) :

Azimuth angle (°)

\(\theta\) :

Blade pitch angle (°)

\(\theta_{\text{FP}}\) :

Flight path angle (negative value: descent) (°)

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Authors and Affiliations

  1. Institute of Aerodynamics and Flow Technology, Helicopter, German Aerospace Center (DLR), Lilienthalplatz 7, 38108, Braunschweig, Germany

    Jianping Yin & Gunther A. Wilke

  2. Institute of Flight Systems, Helicopter, German Aerospace Center (DLR), Lilienthalplatz 7, 38108, Braunschweig, Germany

    Berend G. van der Wall

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  1. Jianping Yin
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  2. Berend G. van der Wall
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Correspondence to Jianping Yin.

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Yin, J., van der Wall, B.G. & Wilke, G.A. Investigation of a simplified aerodynamic modelling technique for noise predictions using FW–H propagation. CEAS Aeronaut J 7, 551–566 (2016). https://doi.org/10.1007/s13272-016-0208-1

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  • DOI: https://doi.org/10.1007/s13272-016-0208-1

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