The Design of Multi-Element Wings in Ground Effect
The racecar aerodynamicist is only too aware of the difficulties of
optimising the performance of multiple element wings in ground
effect. Experimental testing of a series of configurations usually
answers the question "which of these is best?", but to determine why
requires detailed and time consuming instrumentation to provide
pressure distributions, wake surveys and surface flow visualisation
studies. CFD techniques can be of some help at this stage by providing
more detailed information on the flowfield than is usually available
through wind tunnel tests alone.
Even with this level of capability, however, it is still difficult for
the aerodynamicist to know how to change the geometry to eliminate
diagnosed problems, and to make further improvements to the
design. Usually a whole series of "cut and try" models need to be
manufactured and tested in the hope of arriving at one demonstrating
an improvement. Resorting to this approach for the design of
multi-element wings is particularly hit and miss, since small changes
to the profiles can have substantial effects on the characteristics of
the wing, and such changes are usually non-intuitive.
Most CFD methods do not get around this problem. They simply mimic a
wind tunnel in providing an analysis of the existing geometry, but do
not provide any assistance as a design tool. The loadings on the wing
assembly, and any areas of separation, are determined by the shape of
the pressure distribution generated by the profiles. To achieve
optimum performance from a wing assembly it is essential to be able to
specify the pressure distribution and to compute the shape of the
aerofoil sections required to achieve it. Careful control of the
pressure distribution allows design for maximum downforce, for
instance, with no flow separation over a given speed range.
Flow Solutions is now able to offer such a procedure for 3D wing
design in ground effect. The design procedure is coupled to the NEWPAN
panel method. Mainplane and flap elements can then be redesigned
individually or simultaneously, at each section across the span,
including the effects of interaction with other components.
Results for a typical front wing design procedure are shown in the
following figure. At an inboard section the original design showed
significant flow separation on the mainplane at low speed; after
redesigning the pressure distribution an aerofoil is obtained
generating more downforce and with no flow separation at low
speed. Note that it would have been almost impossible to achieve this
result by a trial and error process in the wind tunnel, not least
because of scaling problems between the model and the full scale car.
(click for larger image)
There follows an example of the way in which we perform this process
using NEWPAN2D in conjunction with NEWPAN and the post-processor
VIEWPAN.
An Example of NEWPAN F1 Racecar Front Wing Design
|