Improved measurement of turbulent intensities by use of photon correlation

An experimental approach to the improvement of the accuracies of turbulence intensity determinations obtained by photon correlation processing schemes associated with laser velocimeters and frequency shifting devices is presented. The procedure is used in the calculation of turbulent intensities in the near field region of a two-dimensional wake from the autocorrelation functions of the turbulent velocity field as determined from the laser scattering signal. It involves the fitting of second-order polynomials to the first several maxima and minima of the autocorrelation function, followed by the averaging of the polynomials, to correct for any distortion in the autocorrelation function. Experimental results have confirmed the effectiveness of the scheme in cases when the autocorrelation function is skewed due to few fringes in the control volume or significant background light.