The Turbulence Generation System "T.G.S."

The 5 Turbulence Generators (TGS) are designed to produce a flow of controlled turbulence to simulate a light ambient wind (3-5 m/s) that is common on the road.

The TGs are installed on lifters under the nozzle. When needed, they can be raised into the nozzle or removed in a short time (set up time < 2‘).
The aim is to use the TGS in addition to the standard tests to check the aerodynamics and the aeroacoustics of new cars in a turbulent flow, during the usual development process.
The Pininfarina TGS is an active system: this is the key feature in order to generate large scale turbulence. Another important consequence is that it can reproduce the correct ratio between transversal and longitudinal turbulence intensity, i.e. Iv > Iu, as it can be found on-road with natural wind and roadside obstacles.
Each of the 5 TGs can be operated independently from each other, in a variety of modes. Currently the possible modes of operation include:

• Fixed wings at a given opening angle
• Flapping at a given constant frequency, ranging from < 0.1 up to 1.0 Hz
• Flapping at a frequency varying continoulsy from a minimum to a maximum value in a given period T, following different possible laws

Furthermore, the five TGs can be operated in-phase or out-of-phase.
This multeplicity of operating modes, allows for the generation of different kind of turbulent flows. We can produces a (pseudo) random turbulent flow, with a broad frequency spectrum. Alternatively we can produce a turbulent flow with a given frequency characteristics to study the response of the tested vehicle (or structure) to that frequency. We can also generate couples of vortices which simulate the presence of either a passenger car or a racing car, ahead of the vehicle in test section. The Main Characteristics of the flow generated by the TGs are:

• Log law of the wall velocity profile, α ~ 0.16 - 0.24
• Turbulence intensity up to I = 7- 8 % [ 0.3 ~ 0.7 % ]
• Iv / Iu ~ 1.3 – 1.4
• TLS (Length Scale) up to 1.0 – 2.0 m [ < 0.1 m ]

values [ ] = base wind tunnel without TGS.

In the following pictures some examples of results we were able to obtain with the aid of the Turbulence Generation System are shown: the drag, front and rear lift of a station wagon car are measured in the base wind tunnel and in the wind tunnel plus the TGS (in a pseudo-random configuration).