1994-03-01

Aeroacoustic Testing Improvements at Pininfarina 940417

Aeroacoustics is playing an increasing role in the development of new passenger cars.
However, most existing wind tunnels, with few recent exceptions, have been designed and built with little or no attention to their aeroacoustic aspects.
Building new wind tunnels with excellent low noise levels is technically feasible today, however it is not often justifiable from an economic standpoint.
In the case of the Pininfarina wind tunnel, built in 1972 without any specific noise target, a decision was taken in 1984 to progressively upgrade the facility and the acoustic measuring techniques. A target of reaching a background noise level low enough to allow satisfactory acoustic development work on new cars, with the contemporary use of more modern measuring techniques, was established.
This decision implicitly assumed that, to do this development work, it is not necessary to reach the very low noise levels of a pure acoustic wind tunnel.
The paper reports a short description of the main modifications made to the facility, in the years 1985-90, and the main results obtained.
Then, it describes some of the new measuring techniques which have been set up in the meantime. They are optimized so as to be as efficient as possible in the presence of the background noise. This noise has a relatively low level and a favorable spectrum when compared with other aerodynamic wind tunnels, but this noise still remains worse than that of the acoustic wind tunnels.
In order to further improve the existing situation, a new three-year research program has been recently started (mid 1992).
Its main aim is to improve the capability of detecting the noise sources on the outer surfaces of cars.
To do that, new measuring techniques are in course of development and testing.
At the same time, further modifications to the facility are going to be carried out, mainly to its fan-drive system, to reduce the background noise level.
An overview of this new research program is reported in the second part of the paper, together with some examples of the latest experimental results.

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