| wo plane turbulent wakes, one generated by a solid flat plate, and the other by a porous mesh strip (with 30% porosity and a mesh Reynolds number of 55) were subjected to a uniform irrotational distortion. Both wakes had Reynolds numbers of 3000, based on the width of the wake-generator. In the wake of the solid flat plate, it was observed that nearly two-dimensional, quasi-periodic coherent structures dominated the distorted flow. Rapid distortion theory applied to a kinematic ;In the wake of the porous mesh strip, it was observed that the distorted coherent structures in this flow were similar to the undistorted coherent structures in the solid-body wake. This was because there was a lack of fluctuating spanwise vorticity in the porous-body wake, yielding structures that were similar to double rollers. These differences in the coherent structures yielded distinctly different behaviour in the mixing and entrainment of the distorted wakes. From pattern-recognition analysis of the near region of a similar porous-body wake, it was apparent that, because of the initial conditions, extremely weak ribs were formed. This allowed the rolls to decay into the background, rather than deform into... |
