Study of Half-Ducted Propeller Fan on Aerodynamic Performance and Internal Flow

141 Pages·2014·7.42 MB·English

Study of Half-Ducted Propeller Fan on Aerodynamic
Performance and Internal Flow

September 2014

Department of Science and Advanced Technology
Graduate School of Science and Engineering
Saga University

Pin Liu
CONTENTS

Nomenclature ······································································ I
Abstract ··········································································· IV
Chapter 1 ············································································ 1
Introduction ········································································ 1
1.1 Background and motivation ······················································· 1
1.2 3D flow characteristics of a propeller fan ······································· 2
1.3 Literature review ···································································· 6
1.3.1 Design method ································································· 6
1.3.2 CFD research and internal flow ··········································· 14
1.3.3 Experimental research ······················································ 21
1.4 Objectives and outline of the dissertation····································· 26
Chapter 2 ·········································································· 29
Quasi Three-Dimensional Design Method ································· 29
2.1 Design introduction and parameter selection ································ 29
2.2 Solution of meridional flow ······················································ 30
2.3 Blade selection on the average stream surface ······························· 32
2.3.1 Equivalent velocity triangle method ······································ 34
2.3.2 Imaginary velocity triangle method ······································· 36
2.3.3 Expansion of blade element selection theory ···························· 38
2.4 Correction on blade geometry ·················································· 39
Chapter 3 ·········································································· 43
Numerical Theory and Procedures·········································· 43
3.1 Computational procedures ······················································ 43
3.2 Control volume technique ······················································· 43
3.3 Basic conservation laws ·························································· 45
3.3.1 Multiple rotating frame ····················································· 45
3.3.2 Conservation equations for a rotating reference frame·················· 45
3.4 Turbulence models and acoustics model ······································ 46
3.4.1 RNG k-e model ······························································ 46
3.4.2 LES model ··································································· 48
3.4.3 The Ffowcs Williams and Hawkings model ······························ 51
3.5 Boundary conditions and near wall treatment ······························· 53
3.6 Geometry model and grid generation ········································· 55
3.6.1 Flow field modeling························································· 55
3.6.2 Grid generation ······························································ 57
3.6.3 Convergence and mesh independence ···································· 57
Chapter 4 ·········································································· 59
Experimental Methods ························································· 59
4.1 Experimental apparatus ························································· 59
4.2 Measurement methods ··························································· 60
4.2.1 Working principle of hot wire ·············································· 60
4.2.2 Periodic multi-sampling and ensemble average technique ············· 62
4.3 Uncertainty analysis ······························································ 64
Chapter 5 ·········································································· 68
Experimental Study of Inflow Effect on Performance of Propeller
Fans ················································································ 68
5.1 Introduction on inlet flow of propeller fans ·································· 68
5.2 Study on half-ducted and semi-open inlet structures ······················· 69
5.2.1 Analysis on performance of tested propeller fans ······················· 70
5.2.2 Time-averaged velocity distributions along radius ······················ 72
5.2.3 Phase-lock averaged velocity distributions ······························· 75
5.2.4 Result discussion ···························································· 79
5.3 Performance and flow fields of semi-open propeller fan ··················· 80
5.3.1 Performance curves of tested fans ········································· 82
5.3.2 Circumferentially averaged flow field at fan inlet ······················· 83
5.3.3 Phase locked average velocity field at fan inlet and outlet ············· 86
5.4 Summary on effect of inlet geometry ·········································· 90
Chapter 6 ·········································································· 92
Comparison of Half-Ducted Design with Ducted Design ·············· 92
6.1 Half-ducted design and ducted design ········································· 92
6.1.1 Design parameters and procedures ········································ 92
6.1.2 Blade profiles and streamlines of designed propeller fans ············· 94
6.2 CFD performance of propeller fans ············································ 95
6.3 Internal flow of designed propeller fans ······································ 96
6.3.1 Velocity distributions of designed propeller fans ························ 96
6.3.2 Pressure distributions of designed propeller fans ························ 99
Chapter 7 ········································································· 104
Verification of Designed Propeller Fan···································· 104
7.1 Improvement of half-ducted design ··········································· 104
7.2 Performance curves ······························································ 105
7.3 Internal flow of designed propeller fan······································· 106
7.3.1 Velocity distributions ······················································ 106
7.3.2 Blockage effect of hub stall ··············································· 109
7.3.3 Aerodynamic noise of designed propeller fan ··························· 112
Chapter 8 ········································································· 121
Conclusions ······································································ 121
8.1 Dissertation conclusions ························································· 121
8.2 Research prospects ······························································· 123
Acknowledgment ······························································· 124
References········································································ 125
Nomenclature
A [m2,-] surface area or Glauert series coefficient
a [m/s] so u n d s peed of far field
0
C, C [-] constant, Smagorinsky constant
s
C, W [m/s] absolute velocity and relative velocity
D, D [m] d iameter of the rotor tip and hub
t h
D [-] eq u ivalent diffusion factor
eq
d [m] blade thickness in Y direction or distance
E [m2/s2] re l a ti ve total enthalpy (rothalpy)
re
F, f [m3/s,-] f l u x a n d circulation parameter
G [kg/s] to tal flo w rate
G ,G [-] generation of turbulence kinetic energies
k b
H [m] E ular head
th
DI [m2/s2] th eoretical enthalpy
th
I [N/m2] unit tensor
k [-] bla de blockage coefficient
B
k [-] k i netic energy
L , L [N.m] en ergy and theoretical power
1 2
l, L [m] b la de chord
N [-] specific speed
s
n / u[-/s] ro t ating speed of rotor

P [N/m2] t o t al p ressure
t
p' [N/m2] s o u n d pressure
Dp [N/m2] s tatic pressure rise
s
Q [m3/s] volume flow rate
q [-] q u asi orthogonal direction
q , q [m] r adii of casing and hub in q direction
c h
q [-] intensity of fixed divergence
b
R, r [m] r adius
r* [m,-] r e f e rence radius or non-dimensional radius
S, S , S [-] source terms
k e
S [N] tensor of strain rate
ij
T [N.m] ro tor torque
t [m,s] one pitch length or time
U [m/s] r o tor speed on tip
t
u, v, w [m/s] components of velocity vector
V[m/s,-] velocity or volume

Wb [m/s] d e d uced velocity of fixed vortex and divergence
Y [-] fluctuating dilatation
M
y , y [m] blade camber and thickness
c d
y+ [-] dimensionless wall distance
Z [-] blade number
b
z [-] axial coordinate
I
Greek letters
a [°] attack angle
a,a [-] Prandtl number effecting on k and e
k e
a[-] swirl constant depending on swirl flow density
s
b, Db [°] f l o w angle, turning angle
G, DG [m2/s] c i r c ulation, variation of circulation
g [°] pitch angle or stagger angle
D[-] local grid scale
e [°] angle of q line with normal direction of streamline or dissipation
z[-] total pressure loss coefficient
p
z [1/s] vortex
h [-] efficiency
q, dq [°] camber angle, change of camber angle
c c
k [-] constant of Von Karman
m [kg/m.s] v iscosity
m&[°] divergence
x [-/°] vary ratio of axial velocity or yaw angle
r [kg/m3] a i r d e nsity
s [-] s olidity
s [kg/m.s2] stress tensor due to viscosity
ij
s [-] cascade solidity on XY plane
XY
t [kg/m.s2,-,s] s t re s s or torque coefficient or retarded time
F, f [-] f lo w coefficient or a scalar quantity
j [°] streamline angle with rotating axis
c [-] parameter of stream surface declination
y [-] pressure coefficient
W[-] characteristic swirl number
w [1/s] a ngular velocity or rotating speed of rotor

Superscripts
- average component
' fluctuate quantity
* reference or non-dimensional quantity
. variation
~ defined ratio
^ equivalent quantity
vector
+ relative to y+

II
Subscripts
1, 2 rotor inlet and outlet
a, r, t axial, radial and tangential component
i, j components of tensor
m mean quantity
m, q meridional and circumferential components
re relative quantity
tra translational quantity
t, h blade tip and hub
X, Y components on X, Y axis

Abbreviations
ASD Acoustic Source Data
BPF Blade Passing Frequency
DNS Direct Numerical Simulation
FFT Fast Fourier Transform
FW-H Ffowcs Williams and Hawkings
LE Leading Edge
LES Large Eddy Simulation
MRF Multiple Rotating Frame
PS Pressure Surface
RANS Reynolds Averaged Navier-Stokes
RNG Renormalization Group
rms root-mean-square
SPL Sound Pressure Level
SS Suction Surface
TE Trailing Edge

III
Abstract
Propeller fan, which is an axial flow fan with no casing and guide vane, not only
has large flow rate but also satisfies the requirement of the spatial restriction. In some
applications, the propeller with simple structure is installed with a bell-mouth at the
fan inlet to make the flow enter into the rotor smoothly. As for the half-ducted
propeller fan, the inlet bell-mouth and the short casing are formed by a whole one.
Due to its commonly applications for heat-exchange and ventilation in the vicinity of
people, the desires to own high performance and low noise level of propeller fans
have been strongly demanded from the viewpoint of energy saving and quiet living
conditions. In order to understand the internal flow and aerodynamic performance of
the half-ducted propeller fan, the following studies have been conducted.
Firstly, the inflow performance of the propeller fan has been investigated by
experimental method, and a single I type and a single slant type of hotwire probes
have been used to measure the flow field of a propeller fan which is designed by
traditional axial design method. Periodic multi-sampling and ensemble average
technique have been applied in the data process. As a result, the radial inflow interfere
with the flow in axial direction makes the inlet flow field of the propeller fan very
complex and three-dimensional. In comparison with semi-open type, the half-ducted
propeller fan has relatively good performance and smooth inlet flow with a
bell-mouth.
Secondly, according to the particular flow characteristics, a half-ducted propeller
fan has been designed by flexible use of the design method of diagonal flow fans. And
non-free vortex design method of diagonal flow fans is applied to design a half-ducted
propeller fan by taking the radial velocity component into account. In comparison
with the ducted design method, the half ducted design can avoid highly twisted blade,
obtain better performance characteristics, and improve velocity flow field and blade
loading distributions.
Then, a half-ducted propeller fan designed by the second time was made by three
dimensional printer and tested in the wind tunnel in order to validate the half-ducted
IV
design method. The pressure performance of the half-ducted propeller fan was
improved comparing to the first time. And both of the simulation method and
experiment measurement got the same results. In the performance curves, the
designed propeller fan is near stall condition at the design flow rate. However, the
half-ducted design is still feasible and practicable comparing to the traditional ducted
design for a propeller fan.
Finally, the internal flow and aerodynamic performance were analysed by
numerical method. Large Eddy Simulation (LES) and the Ffowcs Williams and
Hawkings (FW-H) equation are used to compute the unsteady flow field and obtain
the acoustic signal, respectively. And the Fast Fourier Transform (FFT) has been
applied to process the acoustic signal. As a result, the low energy flow fluid
concentrated near hub region blocks flow in the flow passage and makes energy loss.
And the high energy fluid with very low axial velocity focused near casing and
suction surface are considered to be vortex. The total sound pressure level is 93 dB
and 47.7dB at outlet of fan rotor and 1 m away from rotor center. The discrete
frequency might be caused by large fluctuation flow especially the hub stall.

V
Chapter 1
Introduction
1.1 Background and motivation
Propeller fan is an axial flow fan with no casing and guide vane [1]. It sucks the fluid from
infinite space upstream, and makes them get out of it in axial direction downstream. It not only
produces large flow rate but also satisfies the requirement of the spatial restriction in setup
processing. The simple structure and high performance make it used in many applications. Such as,
heat-exchange system for engines, cooling system for outdoor unit of air-conditioner and ventilation
system for relatively sealed rooms or tunnels. In many of the applications, the propeller is installed
with a bell-mouth at the fan inlet to make the flow enter into the rotor smoothly. As for the
half-ducted propeller fan, the inlet bell-mouth and the short casing are formed by a whole one.
Since the design of axial flow fan is believable by using two dimensional cascade data, Inoue et
al. (1980) [2] have extended this method to design the diagonal flow fan. Some other researchers
[3][4] have also investigated in the design method of diagonal flow fan and obtained satisfying
results. However, the more effective design of the propeller fan, especially non-ducted, could not
follow the design methods of axial fans. The blade shape of propeller fans has long chord length at
blade tip and short one at blade hub. The blade tip as the main work part make the opened inlet suck
in air at radial direction. The radial inflow interfere with the flow in axial direction make the inlet
flow field of the propeller fan very complex and three-dimensional. There are not so many
researches involved in this field. The special inlet flow field and the short casing of half-ducted
propeller fan make the design different with the traditional design method of axial and centrifugal
fans. According to the particular flow characteristics, the design method of diagonal flow fans can
be used to design this kind of propeller fans. As so far almost nobody uses diagonal flow fan design
method to design axial fan conversely.
Due to its special use in the vicinity of people, the desires to own high performance and low
noise level of propeller fan have been strongly demanded from the viewpoint of energy saving and

1