Fine Scale Velocity Measurements in a Turbulent Jet in a Confined Crossflow.

Measurements of the fine scale velocity field are made for a turbulent jet in a confined crossflow. With a crossflow velocity of 10.0 m/sec, jet-to-crossflow velocity ratios of 1, 2 and 4 are examined. Velocity measurements are obtained by laser velocimetry. The velocimetry system consists of a 15mW laser with a fringe mode optics setup, operated in the backscatter mode. Signal processing is accomplished with a tracker processer. At each measuring location, 28,400 velocity readings are obtained at a sampling frequency of 38,460 sec$\sp{-1}$. Calculations include construction of autocorrelation functions, Kolmogorov-normalized energy spectra and their moments, skewness and flatness of the velocity derivatives, an estimate of $\mu$ (the constant appearing in Kolmogorov\u27s lognormal hypothesis), and of the fractal dimension of the dissipation structures. Turbulent Reynolds numbers are found to range from 22 to 800. The average value of $\mu$ is found to be 0.31; it is also found to be Reynolds number dependent. The fractal dimension is estimated as 2.45