Ground Effect Simulation System "G.E.S.S."

A new Ground Effect Simulation System (GESS), called the “T-Belt” and using three belts in combination, has been in operation since September 1st 2006 in the full-scale Automotive Wind Tunnel of the Pininfarina Aerodynamic Center.

It replaces the single-belt system installed in 1995 , which was the first in the world to be able to test full-scale cars by simulating the aerodynamic effects due to wheel rotation and ground relative motion.

he new system substantially improves the simulation of the ground effect and provides a further important technical advantage compared to our competitors.

This system, which is patented to protect the unique geometric layout (three belts in a T-Shape) as well as the driving details of the three belts, is shown in the photographs.

well as the driving details of the three belts, is shown in the photographs.

The main characteristics of the new system are:

• The overall width of the upstream end of the moving ground has been increased from 1.0 m to 2.5 m, for a length of 1.5 m, by the installation of 3 belts side by side. The central belt is 6.7 m long and the two side belts are 1.5 m long, extending from the front of the central belt to the front wheels.
  

  This layout provides an excellent simulation of the ground effect under the car front end, for both passenger and racing cars, and is a major improvement compared to the single narrow belt. The car front-end flow is critical, as the approaching flow is a ‘high energy’ flow, not yet spoiled by the rotating front wheels.

  In particular:

  1. The large width of the moving ground front end is important for front-wing and front-diffuser equipped racing cars, as well as for conventional cars with wheel housings.

  2. The improved simulation of the flow upstream of the front wheels improves the flow around the wheels and within the wheel-housings, and will lead to a better flow under the vehicle. It is known that the front wheels and their wheel housing are the most important source of a car aerodynamic drag and their behaviour will now be better simulated.

  3. Furthermore it improves the simulation for:
  a. Front brake flows
  b. Radiator/cooling-package flows

• The longer, 6.7 m central belt provides a good simulation of road motion even for very long cars, having about 1 m of moving ground ahead of the car and 1 m downstream of the car and its wake. It may also be used to test other long scale models such as trains or trucks, where length is the major dimension. The model scale can be increased, improving model detail, and therefore, measurement accuracy.
• The maximum velocity of the three belts has been increased to 250 km/h (it was 200 in the old system), to reach the same maximum speed as the wind . This increased test speed is necessary to uncover the aero-acoustic sources that appear at high speed only and are caused by the deformation of body parts. It may be also important for the measurement of the deformation of some add-on aerodynamic parts of racing cars.
  
• The four rollers that provide wheel rotation have increased diameter. Now, cars can be tested without removing the suspension springs because the rollers can support the full weight of the car. The supports of the rockers restrain the car from any horizontal motion while the vertical motion is free.
  
• Possibility in the future of measuring Lift and Aerodynamic Torque for each of the four wheels through sensors installed on each wheel drive unit. This information may be of interest mainly in the case of racing cars.
  
• The presence of an upstream car, (racing or passenger), with its down-lifting or up-lifting vortices can be easily simulated with the TGS (Turbulence Generation System) and that further improves the simulation of the road condition.
  

  The car standing heights are remotely controlled by computer through 4 supports acting on the car rockers.
  Any combination of pitch, roll (and yaw, by turning the turn-table) can be achieved in continuous without stopping the wind.This is very important to speed up the tests.

  In order to be able to modify the car underbody, the car can be lifted in less then 30''.
  All these improvements may bring new optimal aerodynamic solutions different from the existing ones and will provide an improved on-track and on-road simulation in the wind tunnel.