A Experimental Investigation of the Development and Growth of Counter Rotating Vortices in a Curved Rectangular Duct
This thesis presents a detailed investigation of the development and growth of longitudinal counter rotating vortices in laminar flow through a curved rectangular duct. Comprehensive flow visualization experiments were carried out in order to reveal the configuration of the flow both on the wall and away from it. Guided by the visualization results, detailed measurements of the three velocity components, using Laser Doppler Velocimetry, were then conducted in order to provide quantitative data capable of giving a picture of the velocity field within and around the vortices. The various events leading to the evolution and subsequent growth, on the concave wall, of a typical vortex pair are presented. The geometry of the limiting streamlines in the evolution region is revealed, and the associated topological model is presented. In contrast, the flow on the convex side is shown to adhere to the wall and no vortices were detected there. Results within the limited range of flow parameters explored seem to indicate a noticeable effect of Reynolds number and curvature parameter on the spatial growth of a vortex pair. They also show that the spanwise distance between adjacent vortex pairs remains almost constant throughout the curved duct. Constant velocity contour plots show a defect in streamwise momentum within the vortical cores of the vortex pair. They also reveal a marked spanwise variation of the 'boundary layer thickness'. Boundary layer profiles of the streamwise velocity component, taken at spanwise positions corresponding to the middle of the vortex pair and the location of its vortical cores, exhibit single and double reversals respectively. Mean values of the normal and spanwise velocity components reached 32% and 18% of the upstream reference velocity respectively. It is also shown that the streamwise vorticity increases at first but seems to level off later while it continues to spread out.
- Pub Date:
- Physics: Fluid and Plasma