"14 hole" probe

The main technique currently used in the Pininfarina Wind Tunnel for mapping the flow fields is the "14-hole" probe. It was designed and developed by Pininfarina in the years 1985-1986.

The local values of total pressure, static pressure and the 3 components of the local velocity, are computed starting from the pressure values measured point by point by each of the 14 holes of the probe.

The probe resolves the local flow angles up to ± 180° with respect to the probe axis.
In that way, time-averaged velocity and pressure maps are computed. They show, with good accuracy and excellent repeatability, the time-averaged flow structure.

Click here to see a gallery of mapping of the car flow field.

See below for a description of some of the quantities mapped with the 14-hole probe

It shows the areas of equal total pressure in plane sections of the flow. Energy losses in the flow perturbed by the car The map allows for the identification of the elements of the vehicle that mostly contribute to the aerodynamic drag. p_tot should be as high as possible.

It shows the areas of equal static pressure in plane sections of the flow. In the wake behind the car , an increase of static pressure is related to an improvement of the shape factor.

It shows the areas of the equal drag in plane sections of the flow. It allows to understand how and where the car aerodynamic drag is generated.

It shows the areas of equal total velocity normalized to V∞ in plane sections of the flow. It allows to identify regions of accelerated or reverse flow.

It shows the Vy and Vz components of the velocity vector normalized to V∞. It allows to identify the vortices and their orientation. Vortices increase the drag coefficient (Vortex Drag).

It clearly shows the vortices magnitude and their orientation. It is computed point by point from the incremental ratios of the Vy and Vz velocities measured by the probe.