1988-02-01

A Two-Component Fiber-Optic LDV System for Automotive Aerodynamics Research 880252

A laser velocimeter of a new type has been recently installed in Che Pininfarina full-scale automotive wind tunnel.
Conventional laser velocimeters have been confined, up to now, to small facilities due to various difficulties which arise when measurements are to be made in large facilities.
A first important feature of the new system is that a fiber-optic link carries the laser beams from the laser generator and the main optical system located outside the test section to a small end-probe. This probe then focuses the laser beams at the measuring point, receives the backscattered light and sends it back through another fiber to a photomultiplier.
As the probe is small and lightweight, it can be easily traversed by the conventional wind tunnel traversing system.
Safety problems are greatly reduced, as beam power is lower and focal distance is short.
The new system has the capability of measuring local velocities (two components) simultaneosly and turbulence at those points of a flow field where conventional mechanical probes cannot provide reliable values.
A second important feature is the new signal processor which greatly improves the capability of the LDV in conditions of very low seeding and low signal-to-noise ratio, which are typical of full-scale wind tunnels.
This paper shows the new LDV system, its main capabilities and its limitations.
Some examples of measurements carried out with this system are also outlined.

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