21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-3.10.3

SKIN FRICTION MEASUREMENTS DOWNSTREAM OF A BACK-FACING STEP

Spazzini P. G., luso G., Onorato M., De Ponte S.*
Turin Polytechnical University, Italy; *Milano Polytechnical Univ., Italy

Keywords: skin friction, back-facing step

The flow behind a back-facing step in a channel with fully developed turbulent flow has been analysed, with reference to the unsteady behaviour of the separated region. Time resolved skin friction measurements have been made using a double hot wire wall probe, ad hoc designed, for three Reynolds numbers, Re =3200,6500, 13000. Details of the primary and secondary recirculation regions have been shown in terms of probability distribution of having forward flow and in terms of skin friction coefficients. Large negative values of the wall shear stress, depending on the Reynolds number, have been measured in the reverse recirculation region; the larger negative value, Gf= -0.0042, has been found for the lowest Reynolds number. A spectral analysis of the Tw fluctuations has revealed that the most energetic frequencies are around 10 Hz in the secondary bubble and in the range from 30 to 80 Hz in the main bubble.

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