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ISSN Online: 2377-424X

ISBN Print: 1-56032-797-9

International Heat Transfer Conference 11
August, 23-28, 1998, Kyongju, Korea

TRANSITIONAL BOUNDARY LAYERS (INTERMITTENCY MEASUREMENT)

Get access (open in a dialog) DOI: 10.1615/IHTC11.3030
pages 125-130

Resumo

Prediction of the transition zone in both thermal and velocity boundary layers is the key to improving the determination of convection heat transfer. Convection heat transfer and surface friction increase in the transition zone. The work reported here is about an experimental technique developed using a hot wire anemometer and a digital data acquisition system for accurate determination of turbulent intermittency and the positions of the start and end of transition in a boundary layer on a flat plate. The hot wire signal is high pass filtered to remove the low frequency Tollmien-Schlichting waves and a windowing technique is then used to identify the high amplitude turbulent portions of the waveform. Criteria are derived for determining a suitable high pass filter setting, window size (i.e. threshold value) and the minimum permissible time period between turbulent bursts. The measurement system provides a direct and accurate measurement of intermittency over the complete range (i.e. 0 to 100%) and is particularly applicable at determining Stanton number and convection heat transfer coefficient in the transition boundary layers.