Chapt06

0 516 529 533 529 520 511 495 483 480 a in principle

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Dh for the particular geometry of the duct. For laminar flow in rectangles and triangles, the wall friction varies greatly, being largest near the midpoints of the sides and zero in the corners. In turbulent flow through the same sections, the shear is nearly constant along the sides, dropping off sharply to zero in the corners. This is because of the phenomenon of turbulent secondary flow, in which there are nonzero mean velocities v and w in the plane of the cross section. Some measurements of axial velocity and secondary-flow patterns are shown in Fig. 6.16, as sketched by Nikuradse in his 1926 dissertation. The secondaryflow “cells” drive the mean flow toward the corners, so that the axial-velocity contours are similar to the cross section and the wall shear is nearly constant. This is why the hydraulic-diameter concept is so successful for turbulent flow. Laminar flow in a straight noncircular duct has no secondary flow. An accurate theoretical prediction of turbulent secondary flow has...
View Full Document

This note was uploaded on 10/27/2009 for the course MAE 101a taught by Professor Sakar during the Spring '08 term at UCSD.

Ask a homework question - tutors are online