SMALL SILICON PRESSURE TRANSDUCERS FOR SPACE-TIME CORRELATION-MEASUREMENTS IN A FLAT-PLATE BOUNDARY-LAYER

Silicon based pressure sensors have been used to measure turbulent wal l-pressure fluctuations in a two-dimensional flat plate boundary layer Re-theta = 5072. The side lengths of the diaphragms were 100 pm (d(+) = 7.2) and 300 mu m (d(+) = 21.6), giving a ratio of the boundary lay er thickness to the diaphragm side length of the order of 240 and a re solution of eddies with wave numbers less than ten viscous units. Powe r spectra were measured for the frequency range 13 Hz < f < 13 kHz. Sc aled in outer and inner variables a clear overlap region between the m id and high frequency parts of the spectrum is shown. In this overlap region the slope was found to be omega(-1), while in the high frequenc y part it was omega(-5). Correlation measurements in both the longitud inal and transversal directions were performed and compared to other i nvestigations. Longitudinal space time correlations, including the hig h frequency range, indicated an advection velocity of the order of hal f the freestream velocity. A broad band filtering of the longitudinal correlation showed that the high frequency part of the spectrum is ass ociated with the smaller eddies from the inner part of the boundary la yer resulting in a reduction of the correlation.