J. Rickards, R.V. Barrett

The paper describes the use of implanted sub-miniature microphones to detect boundary layer transition, and their use in experimental work on boundary layer control using suction through porous surfaces. Tests in a low turbulence wind tunnel have demonstrated that the microphone signals give a clear distinction in terms of both amplitude and frequency content between the laminar, transitional and turbulent states of the boundary layer, up to background noise levels of around 120dB, obtained at a tunnel speed of 60m/s. Higher noise levels associated with greater tunnel speeds gave a progressive loss of transitional detail in the signal, but even at the maximum background noise level of 132dB (80m/s), the difference between the laminar and turbulent signals was readily distinguished from their RMS levels. Results comparing the microphone signals with hot wire and hot film signals taken concurrently are presented. The surface tapping connecting the microphone to the flow may be as small as 0.2mm. Reducing the diameter further gives a progressive loss in high frequency response, making transitional detail less clear. Signal processing both with and without the use of a laminar reference signal has been used to indicate the degree of turbulent intermittency present in the transitional boundary layer. The microphone transducers have been found to operate equally well on porous surfaces with suction, and are being used to monitor the boundary layer state in work on the effect of discontinuous suction on the boundary layer. Results are presented demonstrating the effect of a spanwise strip of suction on boundary layer development. Comparisons are made with numerical analysis for the same flow conditions.

First European Forum on Laminar Flow Technology, Hamburg, 1992

Conference Paper

englisch

21,0 x 29,7 cm, 9 Seiten

DGLR-Bericht, 1992, 1992-06, First European Forum on Laminar Flow Technology; S.228-236; 1992; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn

NA

aerodynamics, boundary layer transition, laminar flow

Bestellbar

1992