REDUCTION OF TOTAL DRAG FOR FINITE CYLINDERS IN TURBULENT FLOW WITH A HALF-C SHAPE UPSTREAM BODY

Abstract

The effect of an upstream half-C shape body on the reduction of the total drag of a finite circular cylinder is investigated experimentally. Five main cylinders, each with an upstream half-C shape body placed at five upstream positions, a total of 25 different configurations, are considered during the experimentation at a Reynolds number in the range of 1.2 × 10⁴ to 1.6 × 10⁵. The aspect ratios of the main cylinders are 1.25, 2.09, 3.03, 3.78, and 4.90 and the upstream bodies are taken as 90° peripheral cut-outs of the respective main cylinder. The total configuration drag coefficient is calculated from the time-averaged drag force on the configuration and compared with the drag coefficient of the respective main cylinder. Results suggest that at least 20% of the total drag of the configuration might be reduced with the upstream half-C shape body, and the reduction varies with the main cylinders' aspect ratio and the upstream body placement distance. The maximum drag reduction is about 55% if the half-C shape body is placed at an upstream distance of 66% of the main cylinder diameter with an aspect ratio of 3.03 and at a Reynolds number of 1.8 × 10⁴. A critical distance ratio is found beyond which drag cannot be reduced by the upstream half-C shape body, and the attribution might be given to a formation of intermittent swirling flow in the cavity mode.