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QUASI-PERIODIC GENERATION OF COHERENT VORTICAL STRUCTURES BEHIND A SURFACE-MOUNTED OBSTACLE

Tillmann Baur
Institute of Hydraulic Engineering and Water Resources Management (IWW), Aachen University of Technology (RWTH Aachen), Kreuzherrenstr., 52056 Aachen, Germany

Joachim von Lukowicz
Institute of Hydraulic Engineering and Water Resources Management (IWW), Aachen University of Technology (RWTH Aachen), Kreuzherrenstr., 52056 Aachen, Germany

Jurgen Kongeter
Institute of Hydraulic Engineering and Water Resources Management (IWW), Aachen University of Technology (RWTH Aachen), Kreuzherrenstr., 52056 Aachen, Germany

Abstract

The paper describes the investigation of the shear layer behind a surface-mounted prismatic obstacle placed in a fully developed water channel flow with rectangular cross-section. In the shear layer the formation of three-dimensional coherent vortical structures is investigated at Reynolds numbers of 24,000 ≤ Re ≤ 72,000 related to the obstacle height. A double structure of turbulence in form of primary and secondary vortices can be observed by flow visualization. With different measurement techniques the characteristics of the vortex shedding is further quantified. For a better insight into the spatial distribution of the vortical flow phenomena, a time-resolved PIV-technique is applied. It can be stated that they are still present and coherent at high Reynolds numbers. Additionally, the auto-correlation of single point velocity data in combination with a conditional sampling technique indicates the quasi-periodic generation of the primary and secondary vortices.