The shape of averaged and smoothed pulsed Doppler spectra from the she
ar layer between jet and recirculation zones, one diameter downstream
of three acrylic stenosis (27, 47 and 65% diameter reduction) in a ste
ady flow dialysis tubing model, were found to be complex. Their shape
contrasted with the shape of spectra from regions of jet breakup. The
latter had a shape suggesting a Gaussian distribution of apparent velo
cities consistent with varying magnitude and direction in turbulent no
w. In contrast, the least complex spectra from the shear layer had a d
ouble-peaked shape suggestive of two distinct major velocity component
s or streamline groups. A subtraction method was used to resolve the l
east complex spectra into two relatively narrow Gaussian components. M
ore complex spectra could be resolved into multiple components by seri
ally subtracting individual Gaussian components. Comparison with the p
attern of particles revealed by flow visualization studies suggests th
at most of the components are due to axially directed streamline group
s of different velocities but that some may be due to radially directe
d streamline groups. Broadened spectral components, which are apparent
at higher flow rates, are consistent with development of vortices in
the shear layer.