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presence of the winglet can be observed from
the pressure coefficient distribution (Cp). Both
flow calculations were performed at the same
angle of attack. The shock wave causes the
thickening of the boundary layer increasing in
turn the interference drag. In order to avoid
shock waves and their associated drag penalties
in the region close to the basis of the winglet, a
careful design of transition surface must be
performed. The aerodynamicist can change the
airfoil shape of the transition surface as well as
other parameters such as its sweptback and
incidence in order to obtain a good flow
behavior.
Fig. 15 – Winglets accelerate the flow on the
adjacent portion of wing. Cp distributions for a
station located at 94% of the semispan.
In order to illustrate the effect of the
winglet in reducing the wingtip vortex
simulations were performed with FLUENT for
an aircraft configuration with two different
wingtips all other parts remaining the same. The
left wingtip has a winglet and the right one was
truncated (no fairing). Usually, a truncated
wingtip will present a considerably stronger
vortex core even when compared to a faired
one. The FLUENT’s 2nd order explicit algorithm
and the Sparlat-Allmaras turbulence model were
selected for the flow calculation. According to
some specialists, this turbulence model is more
suited to external flow calculations. Fig. 16
shows vorticity magnitude contours in a plane
behind the wing. The vortex magnitude of the
truncated wingtip is considerably stronger
compared to the one generated by the winglet.
The Fig. 16 also shows that the stronger vortex
is located inwards in respect to the wingtip
revealing a considerably lower aerodynamic
aspect ratio with regard to the geometric one.
The calculations for this asymmetrical
configuration at M∞ of 0.76 showed that the
velocity in the vortex core in the vicinities of
the truncated wingtip topped Mach number of
1.70 and in the region around the winglet was
slightly supersonic. The pathlines at the
truncated wingtip can be seen in Fig. 17. The
ribbons clearly reveal the rotational nature of
the flow leaving the wingtip.
Fig. 16 – Vorticity magnitude contours.
After all numerical analysis were
finished, Embraer was able to proceed with the
structural project, manufacture and fit the
winglet on an ERJ 135 prototype within four
months starting just from the aerodynamic
specification. Several important performance
advantages were documented after a flight test
campaign was conducted. One was a
considerable increased weight capacity at
takeoff. The test pilots reported a clearly
noticeable faster climbing. The overall drag at
maximum cruise condition was reduced by 4.5
%.
Fig. 17 – Pathlines at a truncated wingtip of a test
case configuration.
Based on the good results obtained for
the EMB 145 AEW&C and Legacy business jet,
Embraer decided to install winglets to its newest
170/190 family of airliners. The Embraer 170,
which was designed to comfortably transport 70
passengers and should be able to takeoff and
land at London City Airport, is currently under
certification. Three other variants will follow in
this order: the stretched version for 86
passengers, the Embraer 175 aircraft; the
Embraer 195 for 108 passengers, which has a
new larger wing, and its shrink version for 96
passengers, the Embraer 190. Transonic windtunnel
tests for the Embraer 170 in The
Netherlands (DNW) and Russia (TsAGI) (Fig.
18) revealed more–than-expected drag
reductions in the entire flight envelope provided
for some of the tested winglet configurations.
Fig. 18 -Embraer 170 Transonic wind-tunnel
model (Photo Embraer).
Fig. 19 shows a surface triangular
mesh for transonic computational analysis with
the FLUENT code. In Fig. 20 Mach number
contours for a low transonic condition can be
seen.
Fig. 19 - Triangular surface mesh of an Embraer
170 computational model.
Fig. 20 –Mach countours on a computational
model of Embraer 170. M∞ = 0.72, α = 1.5o.
The design of winglets for the Embraer
195 could incorporate improvements and
innovative ideas strongly based on CFD
analysis. Starting from the Embraer 170 final
design a parametric analysis was performed
with VSAERO from AMI Corporation, Seattle
WA, which permitted the estimation of the
reduction in induced drag for several
configurations at subsonic conditions.
Variations in planform, shape, aspect ratio,
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