Fluid Dynamical Drag Coefficient on the Octagonal-Pyramid-Net Relative to Reynolds Number

Abstract

This study deals with the fluid dynamical drag coefficient on the octagonal-pyramid-net with six kinds of Weaver's knot nettings, fixed inside of five types of net-frames hanged at 29.3% of hang-in ratio. Half values of the vertical angle (attack angle) of octagonal-pyramid-frames were 15°, 30°, 45°, 60°and 75°.
The nets were set into a flume tank normal to the flow direction, and the flow was set at seven steped velocities, namely 5, 10, 25, 50, 75, 100 and 125cm/s. The velocities were monitored by a super-sonic digital current-meter which is installed in the flume tank of Kagoshima University. The range of the Reynolds number were from 1.7×10 to 1.8×10³.
The results obtained were as follows:
1) A Reynolds number of 2×10² was determined to be the critical value for transition of drag coefficient.
2) For Reynolds number greater than 2×10², the drag coefficients were determined to be 0.70, 0.80, 0.98, and 1.10 for the octagonal-pyramid-nets with half value of vertical angles of 30°, 45°, 60°and 75° respectively.
3) For Reynolds number less than 2×10² the drag coefficients were proportional to Re^-0.5, except for the net with the half value of vertical angle of 15°.