CFD of turbulent flow around a 90deg bend

Topics: Fluid dynamics, Turbulence, Fluid mechanics Pages: 33 (5404 words) Published: February 20, 2014
Proceedings of the Institution of Mechanical
Engineers, Part C: Journal of Mechanical
Engineering Science
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A Study of Turbulent Flows in Pipe Bends
W N Al-Rafai, Y D Tridimas and N H Woolley
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 1990 204: 399
DOI: 10.1243/PIME_PROC_1990_204_120_02
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399

A study of turbulent flows in pipe bends
W N Al-Rafai, BEng, AMIMechE, Y D Tridimas, BSc, MA, PhD and N H Woolley, BSc, MSc, PhD School of Engineering and Technology Management, Liverpool Polytechnic An experimental and numerical study oj turbulent air flow in circular section pipe bends was carried out in order to determine the f

influence o bend curvature on theflow.
Two bends were used, with inside diameters o 43 mm and curvature ratios o 1 :13.95 and I :6.98. The corresponding Dean numbers f
f
were 9138 and 12 919. The Reynolds number for both cases was 34 132. Measurements o mean streamwise and r.m.s. velocities were made using laser Doppler anemmetry. Numerical modelling was based on f

the commercial computer package 'PHOENICS', employing a k-& turbulence model, standard wall functions and a three-dimensional elliptic solution procedure.
The results showed that the secondary p o w as more prevalent in the smaller bend. In view o certain simplifyins assumptions in the f
theoretical model, encouraging agreement between experimental results and numerical predictions was obtained.

NOTATION
cd, '
p

De
fD

k
p.d.f.
r
I1

r*
rc

ri

Re

Ub
U
J
Y
"
i

WI

w:

Z
Z*

a
6
&

e
1
Vlf

Vtf

P
Pi
0 .f
1
01, f

4i

turbulence model constants
Dean number
Doppler frequency
turbulent kinetic energy
probability density function
radial coordinate
pipe radius, channel half-width
normalized radial coordinate
pipe or channel bend radius of curvature
phase volume fraction
flow Reynolds number
fluid bulk velocity
scatterer velocity normal to fringes
velocity vector of phase i
mean streamwise velocity
normalized mean stream velocity
cross-stream coordinate
normalized cross-stream coordinate
bend angle
curvature ratio = rl/rc
dissipation rate of turbulent kinetic energy
angle between beams
laser wavelength
fluid laminar kinematic viscosity
fluid turbulent kinematic viscosity
fluid density
phase density
laminar Prandtl number = 1
turbulent Prandtl number = 1
any conserved property of phase i
1 INTRODUCTION

Investigation of flows in pipe bends can play a major
role in improving the design of commercial equipment
and the understanding of the heat-transfer rate
occurring in different pipe bends. Enayet et al. (1)
carried out a study in laminar and turbulent flow round
a 90" pipe bend with a curvature ratio of 1 :5.6. The
results for laminar flow revealed stronger secondary
maxima in the axial velocity profiles than those
The M S was received on I March 1990 and was accepted for publication on 27 July 1990.
C01290@ IMechE 1990

0954-4062/90

observed by Agrawal et al. (2). Taylor et al. (3)reported
measurements in a 90" square-section bend with a curvature ratio of 1:4.6 and two Reynolds...

Citations: http://pic.sagepub.com/content/204/6/399.refs.html
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