A Data Acquisition System for the Investigation of Dynamic Stall

Summary

This paper describes a test facility for the investigation of dynamic stall as may be experienced on the retreating blade of a helicopter rotor (1). The facility has recently been commissioned after two and a half years of development by a small team of researchers.

The dynamic stall phenomenon was investigated by vertically mounting, in a low-speed wind tunnel, a typical two-dimensional aerofoil and oscillating it in pitch about the quarter chord position. Just below the surface of the aerofoil 30 minature pressure transducers were mounted around the chord at the mid-span and these were logged at a maximum rate of 625 Hz per channel. The logged data were stored on floppy discs and processed using a micro computer. It is the logging, storing and presentation of these data that forms the core of the present paper.

The test sequence is discussed and typical results presented. The major conclusion of the report is simply, that, care must be taken, when using the developed systems, to only record the data of interest and avoid the logging of superfluous data.