As part of the Short Haul Civil Tiltrotor (SHCT)
project, an element of the Aviation Systems Capacity
program, a test of an isolated tilt rotor was conducted
in the Duits-Nederlandse Windtunnel (DNW) open-jet
test section in April-May 1998. The model was the
isolated configuration of the Tilt-Rotor Aeroacoustic
Model (TRAM) and consists of a 0.25-scale V-22
right-hand rotor and nacelle. Aeroacoustic data and
rotor wake measurements were acquired for a range
of conditions in which blade-vortex interaction (BVI)
occurs. The test was led by NASA Ames Research
Center in partnership with the U.S. Army, NASA
Langley, and the Boeing Company.
Unlike conventional helicopter rotor blades,
proprotor blades are highly twisted and can generate
negative loading over a large area of the rotor disk.
The negative loading causes multiple vortices (of
opposite sign) to be shed, thereby increasing the
complexity of the wake. Hence, modeling tilt-rotor
wakes and predicting tilt-rotor aeroacoustics are very
challenging tasks.
The positions of wake segments relative to the
rotor blade were acquired for a range of thrust and
shaft angles, and the rotation sense of the wake
video frame depicting a counterrotating vortex pair
upstream of one of the three TRAM blades.
Two-dimensional velocity measurements were also
obtained using the particle image velocimetry (PIV)
technique. Three methods for averaging the PIV
velocity data were investigated with two of the
methods accounting for vortex wander. The core size
and core circulation of the negative vortices were
found to be smaller than the positive circulation
vortices. Figure 2 shows the air-loads distribution for
the same BVI condition as that shown in figure 1.
Note that the blade-tip region is negatively loaded
over a substantial region of the advancing side. This
kind of loading is much different from that on
conventional helicopter blades, where only a small
region may be negatively loaded depending on the
tip twist. Figure 3 shows the resulting BVI directivity
pattern. BVI metric levels were found to increase with
rotor-shaft angle for constant advance ratio and rotor
thrust coefficient. The maximum BVI levels were
found at a much higher shaft angle than would be the
case for a typical helicopter.
Data have also been distributed to NASA's SHCT
industry partners for enabling an improved understanding
and a better prediction of tilt-rotor rotor-noise
mechanisms. The isolated TRAM-DNW data
will complement the full-span (dual rotors with
complete 0.25-scale V-22 airframe representation)
TRAM data that will soon be acquired in the Ames
National Full-scale Aerodynamics Complex 40- by
80-Foot Wind Tunnel in FY00. By comparing the
data from the two tests, an improved understanding
of the interactional aerodynamics and acoustics for
tilt-rotor aircraft will be achieved.
Point of Contact: G. Yamauchi/L. Young/E. Booth
(650) 604-6719/4022/3627
gyamauchi@mail.arc.nasa.gov
layoung@mail.arc.nasa.gov
e.r.booth@larc.nasa.gov
Back To Top
Previous Paper
Return to Global Civil Aviation
Next Paper 
