Investigations on Bluff Bodies as Improved Vortex Shedders Placed Inside a Circular Pipe

In the present study, we visualize the turbulent wake of various bluff bodies placed inside a circular pipe. The objective is to identify shapes which are strong vortex generators and incur minimum irrecoverable pressure loss. The shapes of the bluff bodies are chosen such that they exhibit distinct separation point for strong and stable vortex shedding. The dye used for flow visualization is a shear-thickening and high extension viscosity fluid, which can sustain turbulent separated flows. The planar illumination of the flow field with laser sheet improves the visibility of coherent structures for qualitative and quantitative assessment of the images. The vortex shedding frequency, wake width, and vortex formation length are computed from image analysis. The results highlight that streamlined shapes possess lower wake width and larger vortex formation length, whereas blunt shapes (like triangle and trapezoid) show a larger wake width and a shorter vortex formation length. The vortex shedding frequency is also measured with a piezoelectric sensor to aid flow visualization studies. The optimum location of the piezoelectric sensor is explained based on the vortex formation length to obtain high amplitude signals. Among all the shapes studied, trapezoidal bluff body appears to be the most appropriate shape with strong and stable vortex shedding. This information is useful in the design of vortex flowmeters and other similar applications.