Rear wing CFD analysis

By on
Analysis by Russell Harrison

Geometry

This rear wing design was sent to me by a young budding engineer from Spain named Mr Bernat Carreras. The model was cleaned by Keith Young and further cleaned in CFX. This was his first attempt at wing design and he had limited CAD experience. However, it was agreed to run a CFD analysis on the rear wing design. I believe the airfoils are not based on published designs. There were clearly a number of design issues with the rear wings, including the severity of the camber designed in to the airfoils, which was believed to lead to early flow separation.
Image 1 shows the rear wing geometry after geometry cleaning.

Alero Wing Model

Mesh

A mesh picture is currently not available, but will try and post one if anyone wants to see one. The mesh parameters applied to the model included refined inflation layers for more accurate boundary layer analysis. The mesh engine used was the default AFI mesher using triangular surface mesh elements. The mesh data, after volume meshing, is given below:

Mesh Modes: Volume = AFI, Surface = Delaunay
Total Number of Elements:    1,045,075
Total Number of Tetrahedrons:     851,941
Total Number of Prisms:     191,520
Total Number of Pyramids:     1614
Total Number of Faces:     54,828

Flow Conditions

A simple analysis of the rear wing was carried out, ignoring any body interactions with the Formula 1 vehicle. The results from analysis can therefore only be used for initial design of the wing system, and all body interactions must be included and analyzed in further design modifications. The flow velocity at inlet was set at 62.22 m/s (140 mph, 224 KPH) and this was also applied as an global initialisation velocity . All walls of the fluid domain were set to free slip and a no-slip condition applied to the bodies surface.

Fluid Properties:
  • Material: Air Ideal Gas (constant Cp)
  • Molar Mass = 28.96 Kg Kmol -1
  • Dynamic Viscosity = 1.79e-5 Kg m-1 s -1
Simulation Properties:
  • Domain Motion: Stationary
  • Reference Pressure = 1e5 Pa
  • Fluid Temperature = 288 K (this can be changed and re-run to suit a specific circuit the wing will be run on)
  • Turbulence Model = SST
  • Turbulence = Medium Intensity and Eddy Viscosity Ratio

Solution

The residual target for convergence was set to e-4 at an RMS type. This was achieved during solution. Total Run times was 1 hour, 39 Minutes, 18.468 Seconds.

Results

It can be seen from the results (image 2 and 3) that the initial concern of wing stall is clearly apparent. The small flap has completely stalled as has the trailing edge of the main top element. This, obviously greatly reducing the negative lift (downforce) also brings the penalty of increased form drag. It is also clearly visible from images 3, 4 and 5 that with the top front element of the wing system only the upper surface is experience downforce producing effects (positive pressure), however, at the lower surface of the element positive pressure is also present (thus canceling out the positive pressure of the top surface). This lower surface positive pressure is caused by the bi-plane phenomenon, in that the wing elements are vertically to close to each other . There is also noticeably early separation of the thin aerofoil profile of the top front wing element (separation occurs around half the chord)

The poor design of the end plates and positioning of the wing elements has led to large vortex production, the effects of these vortices is to produce a downwash in the area between the them, which results in reduced negative lift (this is high for low aspect ratio wings, since the vortices are closer to the wing) and small for high aspect ratio wings).

Force Data

Downforce = 1285.26 N, Drag = 374.543 N, Pitching moment = 122.388 Nm

Velocity Contour1 Plane 1 Velocity Streamlines4 Plane 1 Pressure Contour 1 Velocity Streamlines3 Plane 1 IsoSurface Pressure Plot for 2000Pa IsoSurface Pressure Plot for -1500Pa IsoSurface Pressure Plot for -5000Pa Surface Pressure Plots Velocity Vector1 Plane 1 Velocity Streamlines1 Plane 1 Velocity Streamlines3 Plane 3 Velocity Streamlines1 Plane 2 Velocity Streamlines1 Plane 3 Velocity Streamlines2 Plane 1 Velocity Streamlines2 Plane 3 Velocity Streamlines2 Plane 2
In