EFFECT OF WALL CONFINEMENT ON THE AERODYNAMICS OF BLUFF BODIES by SAAD EL

202 Pages·2010·7.57 MB·English

EFFECT OF WALL CONFINEMENT ON THE
AERODYNAMICS OF BLUFF BODIES
by
SAAD EL-SAYED EL-SHERBINY
B.Sc, Ain Shams University, Egypt, 1964
A THESIS SUBMITTED IN PARTIAL FULFILMENT OF
THE REQUIREMENT FOR THE DEGREE OF
' DOCTOR OF PHILOSOPHY
in the Department
of
Mechanical Engineering
We accept this thesis as conforming to the
required standard
THE UNIVERSITY OF BRITISH COLUMBIA
September, 1972
In presenting this thesis in partial fulfillment of the
requirements for an advanced degree at the University
of British Columbia, I agree that the Library shall make
it freely available for reference and study. I further
agree that permission for extensive copying of this
thesis for scholarly purposes may be granted by the Head
of my Department or by his representatives. It is under
stood that publication, in part or in whole, or the
copying of this thesis for financial gain shall not be
allowed without my written permission.
SAAD EL-SHERBINY
Department of Mechanical Engineering
The University of British Columbia,
Vancouver 8, Canada
flnl 27 . / ? 7Z
Date
ABSTRACT
The effect of wall confinement on the aerodynamics
of a set of stationary circular cylinders and flat plates,
representing the blockage ratio range of 3 - 35.5%, is
investigated experimentally to obtain data on mean and un
steady pressure distributions, Strouhal number, and wake
geometry. In general, the influence of the Reynolds number
4 4
in the range of 10 - 1 2 x 10 was found to be confined to
the mean pressure distribution at the higher blockage
(circular cylinder only) and the unsteady surface loading.
The results showed the base pressure to decrease
and consequently the drag coefficient to increase with bluff-
ness; however, the pressure distribution in the potential
flow region remained relatively unaffected by the confinement.
The wake geometry does not change appreciably under constraint
and thus leads to a similarity of the several flow parameters.
Variation in the vortex shedding frequency was found to be
essentially proportional to the increase of separation
velocity in accordance with Roshko's universal Strouhal
number. The shape of the fluctuating surface pressure
distribution curves also remains unaffected by the constraint.
However, the pressure intensity increases with an increase
in bluffness and shows considerable dependence on the
Reynolds number and the three-dimensionality of the flow.
i ii
Validity of the correction methods due to Glauert
and Maskell for the mean drag coefficient is checked in the
light of the experimental results. They were found to be
inadequate particularly at higher blockage ratios. However,
modification of these methods through inclusion of the
higher order terms improved their applicability. Least
square f it of the results showed linear variation [e.g.,
C = C + Const (C S/C)] of the parameters.
D Dc D
A potential flow model is developed for two-dimensional
symmetrical bluff bodies under wall confinement. It provides
a procedure for predicting the mean surface loading on a bluff
body over a range of blockage ratios. Experimental results
with normal flat plates and circular cylinders for blockage
ratios up to 35.5% substantiate the validity of the approach.
TABLE OF CONTENTS
Chapter Page
1. INTRODUCTION 1
1.1 Preliminary Remarks 1
1.2 Brief Review of the Literature 3
1.3 Purpose and Scope of the
Investigation 9
2. EXPERIMENTAL PROCEDURE . 11
2.1 Models and Supporting System . H
2.1.1 Circular Cylinder Models 12
2.1.2 Flat Plate Models 15
2.2 Wind Tunnel 20
2.3 Instrumentation and Calibration 22
2.4 Test Procedure 28
2.4.1 Mean Static Pressure on the
Model Surface 28
2.4.2 Vortex Shedding Frequency . . .. 30
2.4.3 Fluctuating Static Pressure on
the Model Surface 30
2.4.4 Wake Survey 30
3. EXPERIMENTAL RESULTS AND DISCUSSION 34
3.1 Mean Pressure Distribution and
Forces . . . .. 34
3.1.1 Circular Cylinder 34
3.1.2 Flat Plate 44
3.1.3 A Comparative Study 58
V
Chapter Page
3.2 Strouhal Number 62
3.2.1 Circular Cylinder 63
3.2.2 Flat Plate 63
3.2.3 Universal Strouhal Number . . .. 66
3.3 Unsteady Surface Loading 71
3.3.1 Circular Cylinder 72
3.3.2 Flat Plate 80
3.3.3 Observations on the Influence
of Three-Dimensionality of the
Flow and Vortex Formation on
the Unsteady Surface Loading . .. 9 2
3.4 Wake Geometry 95
3.4.1 Circular Cylinder 97
3.4.2 Flat Plate 108
4. ANALYTICAL PROCEDURE FOR WALL CONFINEMENT
CORRECTION 121
4.1 Evaluation of the Reported
Theories . . . . . . . . .. 121
4.1.1 Glauert's Correction Method . . . 122
4.1.2 Application of Maskell's
Theory 125
4.2 Empirical Correction Formulae 130
4.3 Free-Streamline Model 137
4.3.1 Analytical Development 138
4.3.2 Application of the Theory . . .. 146
4.3.2.1 Normal Flat Plate . . .. 146
4.3.2.2 Circular Cylinder . . .. 149
vi
Chapter Page
4.3.3 Discussion of Results 154
4.3.3.1 Normal Flat Plate . . .. 154
4.3.3.2 Circular Cylinder . . .. 159
4.3.4 Concluding Comments 162
5. CLOSING COMMENTS I 66
5.1 Concluding Remarks 166
5.2 Recommendation for Future Work 170
BIBLIOGRAPHY 175
LIST OF TABLES
Table Page
2-1 Physical Properties of Circular Cylinder
Models and Regions of Wake Survey 13
2- 2 Physical Properties of Flat Plate Models
and Regions of Wake Survey 20
*
3- 1 S for Circular Cylinders under Constraint . . 70
3-2 S for Inclined Flat Plates 70
3-3 Maximum Fluctuating Pressure in the Wake
of Circular Cylinders 100
LIST OF FIGURES
Figure Page
2-1 A typical circular cylinder model with
notation for the model and wake
geometries . . . . .. 14
2-2 Details of the microphone model 16
2-3 Sectional geometry of the flat plate
models showing distribution of the
pressure taps 18
2-4 Constructional details of a typical flat
plate model . . . . . . . . .. 19
2-5 Schematic diagram of the low speed wind
tunnel used in the test program 21
2-6 Calibration plots for Barocel pressure
transducer with damping bottle 24
2-7 A schematic diagram of the fluctuating
pressure measuring set-up using Barocel
pressure transducer . . . .. 25
2-8 The arrangement for measuring fluctuating
pressure using condenser microphone 27
2-9 Disc probe dimensions with the mean pres
sure calibration plots showing its relative
insensitivity to pitch and yaw . 29
2-10 Instrumentation lay-out for wake survey . . .. 32
3-1 Effect of the Reynolds number on the
mean static pressure distribution around
circular cylinders of different blockage:
(a) S/C = 4.5%;. 36
(b) S/C = 20.5%; 36
(c) S/C = 35.5%. 37
3-2 Mean static pressure distribution on cir
cular cylinders showing the effect of wall
confinement:
(a) R = 1.5 x 104; 39
(b) R = 5 x 104; 40
(c) R = 10 x 104 41
ix
Figure Page
3-3 Effect of the Reynolds number on C at
180° for circular cylinders of ^
different blockage ratios:
(a) present results; . 42
(b) comparison with the available data 43
3-4 Effect of wall confinement and the Reynolds
number on:
(a) the average base pressure; 45
(b) the drag coefficient 45
3-5 Independence of the pressure distribution
on a flat plate from the Reynolds number:
(a) S/C = 9%, a = 30°; 47
(b) S/C = 35.5%, a = 90° 47
3-6 Variation of the mean pressure distribu
tion with plate orientation for the
blockage ratios of J
(a) S/C = 9%; 48
(b) S/C = 20.5%; . .. 48
(c) S/C = 35.5%. . .. 49
3-7 Surface loading over a flat plate as
affected by wall constraint:
(a) a = 30°; 51
(b) a = 60°; 51
(c) 0t = 90^e e> © © © a © • • © © © • © • • • • • 52
3-8 Base pressure coefficient for flat plates
as a function of:
(a) plate orientation; 53
(b) blockage ratio . 53
3-9 Plots showing independence of the flat plate
force coefficients from the Reynolds number:
(a) S/C = 9%; 55
(b) S/C = 35.5%. . .. 56