Vorticity Based (External) Intermittency measurements in a High R$_{\theta}$ Single-Stream Shear Layer

The MSU four-sensor (transverse) vorticity probe has been used to determine the intermittency function (I(t)=0,1) in a single-stream shear layer. The measurements were taken in the self-preserving region (x/$\theta $(0)=484) with R[$\theta $(x)=9$\times $10$^{4}$]. The I(t) signal permits conditionally sampled measures of the intermittent turbulence field. The mean intermittency $<$I$>$ distribution is compared with that previously reported (1) and (2). It is also compared with the $<$I$>$ distribution created from the use of an advanced surrogate method (3). Distinctive conditionally sampled results include: i) a constant [mean(u$'$v$'$)]/[$\sigma $(u)$\sigma $(v)] distribution for the I=1 condition, ii) clear evidence of fluid from both high- and low-speed irrotational streams to the peak $<$I$>$ location ($\bar{\mbox{u}}$/U$_{\circ}$=0.5), and iii) robust dissipation even as $<$I$> \to $ for large values of [(y-y/2)/$\theta $(x)]. 1. Wygnanski, I. and Fiedler, H. E., (1970). ``The two-dimensional mixing region''. \textit{JFM}, Vol. 41, pp. 327-361. 2. R.C. Haw, J.K. Foss and J.F. Foss, ``Vorticity Based Intermittency Measurements in a Single Stream Shear Layer'' \textit{proc. Second European Turb. Conf. Advance in Turbulence 2,} Ed. H.H. Fernholz and H.E. Fiedler Spring Verlag, Berlin (1989). 3. Hedley, T.B., and Keffer, J.F., (1974). ``Turbulent/non-turbulent decisions in an intermittent flow''. \textit{JFM, }Vol. 64, pp. 625-644