A Redefined Hydraulic Diameter for Laminar Flow.
Final rept. Jul 85-Dec 86,
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING
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For laminar, steady flow in ducts, the current definition of hydraulic diameter, Dh, does not accurately depict the non-uniform wall shear stress distribution around the perimeter of non-circular duct shapes. In this investigation, a new hydraulic diameter Dh1, was empirically determined. It correlated friction factor data for many non-circular shapes to within approximately 2.4 of the circular duct value. An experiment, using the AFIT oil Flow Rig Set-Up, was run to determine the effect of transition Reynolds number, Retr, and hydrodynamic entrance length, L, of replacing Dh with Dh1. Transition Reynolds number and L were determined, based on Dh and Dh1 for a circular, square, and concentric annular duct. Transition Reynolds numbers, based on Dh, for the square and concentric annular ducts were approximately 12.5 lower than the circular duct Retr. The Retr, based on Dh1, did not correlate well for the concentric annulus, but did correlate for the square duct. Keywords Hydrodynamic length. Theses
- Fluid Mechanics