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Executive summaries of Action Groups of Group of Responsables in Aerodynamics
AD(AG28) was established in 1997
with the participation of DLR (Chair), NLR, Airbus France, ONERA, Airbus
Germany, QinetiQ, and Airbus UK. Later, ETW and FOI joined the team, whereas
QinetiQ could not continue due to funding problems. The
objective of AD(AG28) was to make available experimental results suitable for
the validation of advanced numerical methods. At that time, improvements in
numerical algorithms, grid generation, physical modelling and the development
of powerful computers had made the prediction of the flow development about
complex aircraft configurations possible. But there was a lack of
corresponding experimental results necessary to validate these codes
especially at transonic speeds. Therefore,
AD(AG28) carried out high quality, high accuracy experiments on a transonic
transport-type wing-body configuration to establish a data set for the
validation of three-dimensional Navier-Stokes and coupled Viscous-Inviscid
Interaction (VII) codes. The experiments, which met the requirements needed
for the validation of industrial codes, included precise balance and pressure
distribution measurements, detailed boundary layer and wake surveys and flow
visualisations. The
configuration investigated had a wing with moderate rear loading and featured
a planform, aspect ratio, sweep and twist typical for a modern subsonic
transport aircraft. For the determination of the overall forces and moments a
full-model was investigated while
for the detailed boundary layer and wake measurements a larger half-model was
utilised. The
free-stream conditions for the experiments included transonic cruise conditions
with attached flow as well as off-design conditions up to and beyond the drag
rise and buffet boundaries where flow separation is present. At least the full-model
tests have been carried out in more than one wind tunnel in order to increase
the reliability of the data. In all tests, special attention has been paid to
wind tunnel wall interference, sting and support interference and model
deformation due to wing loading. After
exploring various options, the existing Aerospatiale AS 28 half-model (scale
1/7.5) has been chosen for the half-model tests and a corresponding complete
model (scale 1/38) was designed and manufactured from cryogenic steel by DLR
(design and wing section), NLR (aft body) and FOI (nose section). The
AS28 was designed in the early 1980s for research and development purposes on
the basis of Airbus family standards. The half-model has a semi-span of 3.7 m
and was refurbished by Airbus France for the tests in the S1MA wind tunnel.
The model provides 11 pressure sections (eight were actually used) and was
additionally equipped with six boundary layer probes on the upper wing
surface by ONERA. Three of these probes were located in the supersonic flow
regime and the other three were positioned at a short distance downstream of
the shock.
Figure 1 AS 28
half-model in the ONERA S1MA wind tunnel The
full-model with a span of 1.46 m was designed for testing in the HST and ETW.
It was equipped with four pressure sections. To minimize the cut-outs for the
tubing and thus maintain maximum structural strength of the wing, on the
right wing each section at a given spanwise position was provided with about
half the total number of pressure tabs and with the other half on the left
wing at the same spanwise location. A fin sting support was chosen to reduce
sting interference. The stings were not identical for ETW and HST, since due
to the higher loads in the ETW the sting had to be stronger and therefore
dimensioned somewhat thicker in
this tunnel. The
half-model S1MA tests were performed in February 2001. In addition to the
pressure and boundary layer measurements, six-components force and wake
measurements as well as transition checks by acenaphtene visualization and
wing deformation measurements by means of a photogrammetry method have been
performed. The test programme was centered around the design point at M=0.8 and
Figure 2 AS 28
full-model in the DNW-HST wind tunnel After
the manufacturing of the full-model had been completed in early 2002, wind
tunnel tests were carried out in the slotted wall test-section of the HST in
July/August 2002. Mach numbers between 0.6 and 0.85 and lift coefficients
between about zero and buffet onset at Reynolds numbers of 3.3 Mio. have been
investigated. The results for the force and pressure measurements have been
corrected for wall and sting interference.
Figure 3
Comparison of lift polars measured in the HST and ETW The
ETW campaign followed in 2003 with ambient temperature runs (Re=3.3 and
Re=4.5 Mio.) in February and cold runs (Re=10.4 and Re=18.8 Mio.) in March.
Again, wall and sting interference corrections have been applied. The
exploitation of the wind tunnel tests showed that a comprehensive, high
quality data set could be established. Comparison of HST and ETW data shows
very good correspondence and the significant influence of dynamic pressure on
the results at a given Reynolds number was demonstrated. A further analysis
concentrating on results of the force measurements in HST and ETW suggests
that the small differences between the data from the two facilities might
even be reduced by an improved sting interference correction.
Figure 4
Comparison of drag polars measured in the HST and ETW
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