Experimental investigation of turbulent flow in a two-pass channel with different U-shaped bends
Authors: Liu, Runzhou; Li, Haiwang; You, Ruquan; Tao, Zhi
Time-resolved particle image velocimetry is used to study internal flow field characteristics in U-shaped channels of square cross section and different structures of the bend section. The Reynolds number based on the hydraulic diameter of the channel is 8888, 13 333, or 17 777. The mean flow and Reynolds stress are considered, and proper orthogonal decomposition (POD) is used to investigate the flow characteristics. A series of important conclusions are drawn from the results. For the main flow, the structure of the bend section has an obvious influence on the flow field characteristics. The size and number of vortices in the corner area are significantly reduced because the increase in the Reynolds number makes the impact of the influx stronger. It can be seen from the clear differences in the Reynolds stress for different bend sections that the fluctuations caused by the mixing of the main flow and the vortices are significantly stronger than those at the boundary. The flow in the bend section is complex, there is a relatively high proportion of turbulent kinetic energy in the low-order modes, and there is an obvious stripe-like structure in the bend section of the channel in which the bend has both inner and outer circular walls, which matches the velocity field from the POD.
Using baseball seams to alter a pitch direction: The seam shifted wake
PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART P-JOURNAL OF SPORTS ENGINEERING AND TECHNOLOGY
Authors: Smith, Andrew W.; Smith, Barton L.
An experimental investigation of how seams and their orientation relative to the spin axis and flight direction can alter the formation of a wake around a baseball was conducted. Particle Image Velocimetry (PIV) was used to examine the velocity field around a baseball in specific orientations and to find the boundary layer separation location, which is the location on the baseball where the wake begins to form. Certain orientations can advance the separation point on one side of the baseball, generating a pressure force on the baseball and modifying its flight path. Using this information as a guide, baseballs were launched 55 feet (a realistic pitching distance) in orientations designed to have an asymmetric separation point. These pitches were 90 mph at spin rates near 1200RPM with a vertical spin axis perpendicular to the initial flight direction. A Rapsodo 1.0 system was used to compare the pitch locations for different seam orientations. The results of this study showed a significant and repeatable difference in the path of the baseball depending on the orientation of the seams relative to the spin axis. This effect was more significant for baseballs with larger seams.