In this paper the results of an experimental study concerning the separated flow region which develops upstream from a cylindrical obstacle vertically placed on a rough surface and subjected to a fully developed turbulent boundary layer, will be analyzed. This region is characterized by a strongly time-variant vortex system, whose main features were described by a great number of authors through velocity and pressure measurements and flow visualizations, for a wide range of Reynolds number. The experimental results were interpreted using the topological approach by Hunt et al. (1978), Baker (1980), Dargahai (1989). However for a turbulent inlet boundary layer the number of vortices observed is still a controversial issue. This type of flow occurs in several technical applications, e.g. local scouring at bridge piers. To this avail bed roughness could play an important role in defining the vortex system structure and stability. In this paper, the instantaneous characteristics of the vortical structure were highlighted by the flow visualizations. LDV measurements of the longitudinal and vertical velocity components were carried out for three different Reynolds numbers. In one of these conditions, the crosswise mean velocity component was computed and a statistical analysis of the instantaneous velocity signals was performed. Furthermore by applying the topological concepts of critical point and sectional streamline the main features of the separated flow were identified.
Experimental investigation of 3D separation in a cylinder rough flat plate junction
ESPA, PAOLO;
1995-01-01
Abstract
In this paper the results of an experimental study concerning the separated flow region which develops upstream from a cylindrical obstacle vertically placed on a rough surface and subjected to a fully developed turbulent boundary layer, will be analyzed. This region is characterized by a strongly time-variant vortex system, whose main features were described by a great number of authors through velocity and pressure measurements and flow visualizations, for a wide range of Reynolds number. The experimental results were interpreted using the topological approach by Hunt et al. (1978), Baker (1980), Dargahai (1989). However for a turbulent inlet boundary layer the number of vortices observed is still a controversial issue. This type of flow occurs in several technical applications, e.g. local scouring at bridge piers. To this avail bed roughness could play an important role in defining the vortex system structure and stability. In this paper, the instantaneous characteristics of the vortical structure were highlighted by the flow visualizations. LDV measurements of the longitudinal and vertical velocity components were carried out for three different Reynolds numbers. In one of these conditions, the crosswise mean velocity component was computed and a statistical analysis of the instantaneous velocity signals was performed. Furthermore by applying the topological concepts of critical point and sectional streamline the main features of the separated flow were identified.
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