Spatial structure of negative partial derivative(u)over-tilde/partial derivative y in a low R-theta turbulent boundary layer

Multiple line Molecular Tagging Velocimetry (MTV) measurements are used to explore the flow fields associated with wall region negative partial deriva tive (u) over tilde/partial derivative y in a low R-theta turbulent boundar y layer. Velocity and velocity gradient statistical profiles establish the present flow as a canonical flat plate boundary layer. Spatial correlations of partial derivative u/partial derivative y in the (x, y) plane, and the probability of observing negative partial derivative (u) over tilde(+)/part ial derivative y(+) exceeding a negative threshold of -0.25 reveal the high ly significant presence of negative partial derivative (u) over tilde/parti al derivative y in the region 25 less than or equal to y(+) less than or eq ual to 35. Examination of the instantaneous flow fields underlying the cond itional pdf indicates that there are two primary contributing motions: (i) streamwise sheer layers and (ii) compact regions containing +/-partial deri vative (u) over tilde/partial derivative y. The importance of these motions to wall region turbulence production is discussed.