Experimental investigation of two-dimensional bluff-body wake flows at high Reynolds numbers

This doctoral research provides a systematic investigation of the three-dimensional flow dynamics of the nominally two-dimensional high Reynolds number wake flows behind bluff-bodies. The results reveal important and new information about the three-dimensional wake dynamics that can efficiently be exploited in the context of wake control and three-dimensional vortex models.;The experimental investigation is based on constant temperature hotwire anemometry including complex simultaneous biplane multipoint measurements. Wavelet analysis is the main post-processing tool used being effective in analyzing non-stationary turbulent flow signals. Equilibrium similarity and stability concepts are also applied revealing important information on the wake flow coherent structure evolution which supports the conjectured link between the turbulence "triangle" concepts: coherent structures - equilibrium similarity - stability analysis.;A new finding of this thesis is that at high Reynolds number the wake flow topology in the intermediate region is dominated by the three-dimensional mode A as previously found in laminar wake flows, but with secondary vortical structures alternating in the wake mid plane as in von Karman-Benard street. It is inferred that this mode is mainly responsible for the decaying of the organized von Karman-Benard eddies.;Secondly, based on equilibrium similarity analysis, it is shown that besides the well-accepted far wake self-preservation region, another self-preservation region might exist in the near-wake being characterized by larger normalized wake widths and influenced by viscosity. Moreover, the wake-growth-rate parameters indicate that there are three main regions downstream of the wake generator characterized by different topologies: near, intermediate and far wake.;Finally, various aerodynamic bluff body control techniques are thoroughly reviewed and based on findings regarding the major effect of mode A in the wake flow decay, a surface waviness passive static control technique is analysed and shown to be effective in destroying the von Karman-Benard rolls and reducing both drag and lift variance. Direct applications of the method in Wind Engineering are proposed.