Experimental and Numerical Investigation of Turbulent Vortex Shedding

Wake structures as well as flow properties formed behind bluff bodies have received great interest among researchers for years. As a result of various application of bluff bodies in different engineering topics and industry, there has been a growing interest on this phenomenon. As a significant feature of these geometries has been the formation of various vortices in the wake, possible suppression of such phenomenon is the desired outcome in order to reduce the fluctuation forces act on the structures in civil engineering application. The Reynolds de-composition is a very common technique to approach these problems. However, some researchers tackle such problems with an alternative technique known as the triple decomposition. Since the flow structure of a bluff body comprises large-scale organized motion, the timevarying component in the wake region of a bluff -body flow consists of a periodic component (coherent structure) that can be distinguished from a random (incoherent) component. In the present study, incoherent turbulent flow structures in the near-wake region downstream of a square cylinder have been studied by employing triple decomposition. It was observed that the main incoherent turbulent kinetic energy production occurs in the region with the same width of square cylinder. Moreover, it was demonstrated that while a vortex is developing from one edge with maximum incoherent streamwise stress, the initiated shear layers from the other edge exhibit a maximum in incoherent transverse stress production. In addition, wake region behind three modified geometries namely Circular Cylinder (CC), Semi Circular Cylinder (SC) and C shape (CS) are investigated experimentally and numerically for Re of 20000 to identify the effects of shape modification on the wake region. These effects have been discussed in regards to flow structure, Turbulent Kinetic Energy (TKE), pressure and vorticity. It was observed that while CC and SC demonstrated almost similar level of TKE peak value with just 6% rising on SC, CS wake region exhibit a significant increase of 40% in the peak value with respect to CC. It was also illustrated that the vorticity in the wake region of SC is mostly concentrated along the edges of separated shear layers.