Recording and evaluation methods of PIV investigations on a helicopter rotor model

Three-component particle image velocimetry measurements at moderate speeds and observation distances can now be accomplished on a routine basis. This article discusses the experiment performed on a 4 m-diameter model rotor in the 6-m×8-m open test section of the Large Low Speed Facility of the German–Dutch Wind Tunnels. More than half a terabyte of raw data were recorded at various positions on the advancing and retreating sides of the rotor in order to obtain detailed measurements of the trailing vortex in the frame of an international project. This paper addresses measuring techniques and possible sources of errors and presents a limited number of cases for the purpose of illustrating the solutions to numerous technical challenges relating to the acquisition and analysis of vortical flows.

C _T :

thrust coefficient (T/ρπΩ² R ⁴)

M :

magnification

r _c :

radius of vortex core (mm)

R :

rotor radius (m)

T :

thrust (N)

u,v,w :

velocity components in x, y and z coordinates (m/s)

(u,v,w)_wt :

velocity components in wind tunnel coordinates (m/s)

U _max :

maximum in-plane velocity component (m/s)

W _max :

maximum out-of-plane velocity component (m/s)

x,y,z :

particle image velocimetry (PIV) frame coordinates (m)

(x,y,z)_wt :

wind tunnel coordinates (m)

Δt :

time delay (μs)

ΔZ :

light sheet thickness (mm)

ΔZ :

light sheet thickness (mm)

Ω:

rotor rotation frequency (rad/s)

ψ :

rotor azimuth angle during recording (deg) vortex age

α :

rotor shaft angle (deg)

ε _x :

displacement measurement error

μ :

advance ratio (V/ΩR)

ρ :

air density (kg/m³)

τ :

circulation (m²/s)

ω _z :

vorticity (s⁻¹)

AFDD:

Aeroflightdynamics Directorate

BVI:

blade–vortex interaction

DLR:

Deutches zentrum für Luft- und Raumfahrt

DNW:

German–Dutch Wind tunnel

HART:

HHC aeroacoustic rotor test

LLF:

large low speed facility

NASA:

National Aeronautics and Space Administration

ONERA:

Office National d’Etudes e de Recherches Aerospatiales

RANS:

Reynolds-averaged Navier–Stokes

SPR:

stereo pattern recognition

3C-PIV:

three-component particle image velocimetry

The authors would like to especially thank the engineers and technicians of DLR Braunschweig for their cooperation, as well as many others that took part in the measurements. We would also like to acknowledge C. Schram for his help and support in analyzing the vortex characteristics. We highly appreciate the productive and excellent partnership of the HART II community, who gave us the opportunity to perform these measurements.

Authors and Affiliations

1. Institut für Aerodynamik und Strömungstechnik, DLR, Göttingen, Germany

   M. Raffel, H. Richard & K. Ehrenfried

2. Institut für Flugsystemtechnik, DLR, Braunschweig, Germany

   B. Van der Wall

3. NASA Langley Research Center, Langley, VA, USA

   C. Burley

4. ONERA, Chatillon, France

   P. Beaumier

5. US Army AFDD, NASA Ames Research Center, Moffett Field, CA, USA

   K. McAlister

6. Large Low Speed Facility LLF, DNW, Nordostpolder, The Netherlands

   K. Pengel

Corresponding author

Correspondence to M. Raffel.

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