POD of vorticity
Proper Orthogonal Decomposition (POD) of Vorticity = Identification of Coherent Structures in a Turbulent Boundary Layer Flow
Turbulence and turbulent flows 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. Additional comprehension should be achieved by means of innovative experiments, extensive direct numerical simulations (DNS) and theory developments.
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.
Hence, one of the objectives of this study have been chosen to improve the abilities of the Particle Image Velocimetry (PIV) measurement technique by itself and by combination with Hot-Foil Infrared Imaging technique, in order to achieve the experimental characterization of the three-dimensional features in the turbulent boundary layer flow. The obtained measurements designated to the extensive post-processing procedure, including the statistical analysis and coherent structures identification processes. These two main parts of the research would provide the essential understanding of the turbulent boundary layer flow.
Heat transfer, combustion, chemical reaction, drag, and aerodynamic noise generation are fields in which better understanding of coherent structures should produce substantial technological benefits.
RESULTS
The example given below 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.
3D image, reconstructructed from POD mods
References
(see also Publications page):
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, DOI. 10.1007/s00162-004-0156-y
Liberzon A., Gurka R., Lampert S. and G. Hetsroni, (2005) "Multi-dimensional characterization of coherent structures using three-plane stereoscopic PIV", accepted for oral presentation, 6th Int. Symposium on PIV, Pasadena, CA, September 2005.
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.[link]
