Some streamwise vorticity characteristics of coherent structures

A new probe, which measures the streamwise vorticity component and all three velocity components, was used to recognize and analyze coherent structures quantitatively in a fully-developed, turbulent, channel flow. A quadrant analysis was applied to classify events related to the four possible combinations of signs of the velocity components u and v. To isolate the most energetic events, a threshold was introduced in the instantaneous value of the Reynolds shear stress. It was found that the ejections provided the major contribution to streamwise vorticity, regardless of the threshold and distance from the wall. Information on the scales of detected events is also given.