(129d) Vortex Characteristics In a Turbulent Incompressible Wake Flow

Authors: 
Nilsen, K. M., Iowa State University
Kong, B., Iowa State University
Hill, J. C., Iowa State University
Fox, R. O., Iowa State University


Vortex characteristics and behavior in a confined rectangular wake were examined using vortex swirling strength as a defining characteristic. 10,000 PIV velocity realizations at six downstream locations were collected and used in this analysis.  The experiments were carried out at a Reynolds number of 37,500, based on channel hydraulic diameter and bulk average velocity. Swirling strength fields were calculated from velocity fields and then filtered. Clusters of filtered swirling strength were identified as vortex structures.

The characteristics of vortices, such as population density, average size, strength and deviation velocity, were calculated and analyzed, in both the cross-stream direction and the stream wise direction. In the region close to the channel inlet, the population density, average size and strength all show high values in the wake regions.  The average size and strength of the vortices decrease with downstream distance.

As the vortices convect downstream, the vortices spread throughout the channel. The signs of vortex deviation velocity indicate the vortices move from the high vortex population regions to the low vortex population regions.

Finally, two point spatial cross-correlations of swirling strength with velocity fluctuation and concentration fluctuation were calculated using simultaneous PIV/PLIF experiment data. The correlations were performed about the locations of peak of turbulent kinetic energy. The correlations show one positively correlated region and one negatively correlated region, and the orientations and strength of the correlation fields varied with increasing downstream distance.