Flow Visualization and LDV of Flow around a Circular Cylinder – Arnab Ganguly & Jérémy Nabeth 1 ALBUM Circular Cylinder at Re = 900, at this Reynolds number, transition waves referred to as Gerard-Bloor waves develop along the shear surface. The transition waves are seen as undulations on the shear surface, which then curl up to form eddies. The eddy formation lengthfor this flow configuration was found to be at ~2.8D-2.9D from the cylinder. The development of the turbulence can be noticed far downstream (the flow is from right to left) Circular Cylinder at Re= 3600. For the same dye pressure, there was a noticeable increase in the angle at which the free shear layer departs the cylinder surface with reference to the flow direction. It was also noticed that the eddy formation length reduced to ~2 times the diameter into the wake. The formation of the turbulent wake can be seen on the left side of the image along with the alternating vortices. However, it was noticed that for the same dye station opening, the water carried a smaller quantity of dye from the dye ports.
Flow Visualization and LDV of Flow around a Circular Cylinder – Arnab Ganguly & Jérémy Nabeth 2 Circular Cylinder at Re= 8100. At higher Reynolds numbers, the eddy formation length reduces to merely ~1.3 times the diameter, bringing the eddies closer to the cylinder surface. As the Reynolds number is increased, the eddies develop in almost fixed locations which then diffuse and decay along their movement downstream. This is accompanied with the shift in the transition region towards the separation point. The formation of the turbulent eddies in the wake can be seen and the lower dye trace in the near wake region develops vortices which are shed with a frequency of ~0.8 Hz (detected through a video capture of the dye trace) This image illustrates the importance of carefully controlling the dye injection flow rate to match the flow velocity. Having a large velocity component of the dye flow perpendicular to the cylinder reduces the accuracy of representation of the flow. In the image above, it is seen that even though the flow is at a Re ~2000, the near wake suggests the formation of turbulent eddies which is not true for this flow configuration.
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