Protuberances in velocity-gradient flow



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An experimental investigation of circular-cylindrical protuberances of finite length extending into fully-developed turbulent channel flow (9.3x10^3 ≤ NRh ≤ 8.9x10^4) is presented. Three protuberance specimens were tested with length-to-diameter ratios of 5/3, 5/4, and 5/6. The investigation established the secondary flow characteristics in the region near the protuberance and the pressure distribution on the protuberance surface. Results indicate that secondary flow developed about the protuberance with components of flow both up and down the forward radial surface of the protuberance and with an upward component on the rear radial surface. The magnitude of the velocities of these secondary flows is established. Generally, the secondary flow characteristics are similar for all three protuberances and the Reynolds number dependency for the flow rates investigated was not substantial. A reverse (upstream) secondary flow occurred immediately forward of the protuberance near the floor of the channel; the size of this region is dependent on Reynolds numbers.