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Turbulence continue to magnetize the investigators as a problem that still requires understanding and the prediction of behavior. Starting from sketches of the turbulent flows of Leonardo Da Vinci, people repeatedly put forth effort to describe the flow properties.

The study of coherent structures embedded in turbulent boundary layer flows is important to understand the dynamics and the transfer processes of momentum, heat and mass in most flows of engineering interest. Also, the automatic and continuous monitoring and identification of the structures present in such flows could be used to control turbulence. For instance, the most meaningful energy saving result could be achieved by the drag forces and pressure gradients reduction, that is feasible only by the control of the turbulence in the flow. Across the years, significant headway has been achieved in the learning and describing the turbulent wall-bounded boundary layer flows. Yet, this prototypic flow (turbulent boundary layer) is far from being adequately understood.

The main goal of this particular research are amplification of the image-processing-based experimental methods and identification post-processing analysis to the level that will give way to the truly quantitative picture of the turbulent structures near the wall. Up to these days, present measurement systems do not allow fully three-dimensional description of the flows, or have not attained the needed temporal resolution for the statistical description of the turbulent flow.

The identification of coherent structures have been done via applying proper orthogonal decomposition on the vorticity field.

The example given above is the reconstruction of the 3D picture of the coherent structure from two-dimensional footprints. The footprints are linear combination of two-dimensional POD modes, achieved experimentally by means of Stereoscopic PIV technique in a boundary layer in a flume.

References:

Liberzon A., Gurka R., Tiselj I. and Hetsroni G. (2005) “Spatial characterization of the numerically simulated vorticity fields of a flow in a flume”, Theoretical and Computation Fluid Dynamics, vol 19, pp. 115-125

Gurka R., Liberzon A. and Hetsroni G. (2005) “Spatial characteristics of the vorticity fields in a flume”, accepted for publication in Int. J. of Heat and Fluid Flow.

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