Proceedings of the Institution of Mechanical
Engineers, Part M: Journal of Engineering for
the Maritime
Environment
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Hydrodynamic analysis of puller and pusher of azimuthing podded drive at various yaw angles
Reza Shamsi and Hassan Ghassemi
Proceedings of the Institution of Mechanical Engineers, Part M: Journal of Engineering for the Maritime Environment
published online 30 April 2013
DOI: 10.1177/1475090213481417
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Original Article
Hydrodynamic analysis of puller and
pusher of azimuthing podded drive at
various yaw angles
Proc IMechE Part M:
J Engineering for the Maritime Environment
0(0) 1–15
Ó IMechE 2013
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DOI: 10.1177/1475090213481417
pim.sagepub.com
Reza Shamsi and Hassan Ghassemi
Abstract
The research explained in this article was carried out to investigate the hydrodynamic characteristics of the puller and
pusher azimuthing podded drive propulsion at various yaw angles and different operating conditions. The method is finite
volume–based Reynolds-averaged Navier–Stokes. The renormalization group k-e model is employed using the differential
viscosity model and swirl-dominated flow to simulate turbulence. For the purposes of this research, two different propellers (B-series and David Taylor Model Basin (DTMB)) are analysed in pusher and puller of azimuthing podded drive
configurations. The performance curves of the propellers obtained by numerical methods are compared and verified by
the experimental results. Characteristic parameters including torque and thrust of propeller and axial force and side
force of the unit are presented as functions of advance coefficients and yaw angles.
Keywords
Propeller, azimuthing podded drive, Reynolds-averaged Navier–Stokes, yaw angles
Date received: 20 May 2012; accepted: 18 January 2013
Introduction
One of the main objectives of this research was to find
the hydrodynamic characteristics and flow field around
the azimuthing podded drive (AZIPOD). For the past
10 years, the AZIPOD systems have been widely used
in the marine industry, not only for passenger ships but
also for offshore drilling units and naval vessels. The
main components of podded propulsor are strut, pod,
and propeller. In this system, an electrical motor is
located inside a steerable pod housing that drives a
fixed pitch propeller. The total unit is hung below the
stern of the ship by strut and can be rotated through
360° around its vertical axis. Therefore, thrust is generated in any direction that gives the better manoeuvrability. This device combines propulsion and
manoeuvring functions mutually.1
Two main configurations of the podded systems are
the puller and pusher types. In the puller type, the propeller is located in the forward face of the pod and on
the upstream of the strut, but in the pusher type, the
propeller is located in the downward face of the pod
and on the downstream of the strut. In general, the efficiency of the podded propulsor is lower than openwater propeller. This is due to the resistance of the pod
and strut. Therefore, the resistance of unit is an
important factor that cannot be ignored. The pushertype propeller has lower efficiency than the puller type.
In the pusher type, the propeller works in the wake of
the strut. Selection of podded propulsor’s type depends
on ship performance, speed, and comfort criteria.2
The AZIPOD systems have many advantages over
conventional propulsion systems such as more uniform
flow, good manoeuvrability, better seakeeping performance characteristics than the conventional vessel, low
noise and vibration, fuel saving, space saving in ship
arrangement, and rudder and shaft elimination.3,4 The
conventional propulsion systems or propeller–rudder
system (PRS) is working behind a ship hull where they
encounter a large wake flow. Due to the presence of
the hull, the flow distribution into the propeller is nonuniform and unsteady. The most significant hydrodynamic advantage of the AZIPOD system is that the
Department of Ocean Engineering, Amirkabir University of Technology,
Tehran, Iran
Corresponding author:
Hassan Ghassemi, Department of Ocean Engineering, Amirkabir
University of Technology, Hafez Ave, No. 424, P.O. Box 15875-4413,
Tehran, Iran.
Email: gasemi@aut.ac.ir
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Proc IMechE Part M: J Engineering for the Maritime Environment 0(0)
propeller is set in a more uniform and axisymmetric
flow. This regular flow reduces unsteady forces and the
propeller radiated hull surface pressures that reduce
cavitation risk on the propeller blades.5
Alternatively, the AZIPOD has a few disadvantages.
These problems may be considered in three sections:
hydrodynamic performance, operational problems, and
environmental aspects.6 The ship’s lateral area is
decreased by using the AZIPOD systems. Therefore,
directional stability of the ship is decreased. Also,
reduced lateral area and increased steering forces generate a large rolling motion for the ship. This may restrict
the ship performance in the turning manoeuvres. The
AZIPOD systems have a few operational problems
such as failure of mechanical and electrical components
of the podded propulsor, electrical power limitation,
accommodating a large motor inside the pod, and high
capital cost relative to conventional propulsion systems. Also, hydrodynamic impacts on the environment
in terms of ship wash effect and wave propagation
should be considered in these systems.7
More recently, due to the market needs and in order
to gain more efficiency by the AZIPOD systems, marine
researchers (such as Ma et al.,8 Islam et al.,9 Bal et al.,10
Lijun and Yanyin,11 and Carlton12,13) have rigorously
pursued this topic, and much effort has been devoted to
explore it numerically and experimentally.14,15
Because of the problems in testing AZIPOD, limited
experimental work has been performed. Experimental
studies of Szantyr16 were one of the early works for
AZIPOD in azimuthing condition. They measured axial
and transverse force and moment for AZIPOD to 615°
yaw angle. Grygorowicz and Szantyr17 measured force
and moments for the puller and pusher podded propulsor models. Woodward et al.18 proposed a practical
method for predicting the global forces and moments
acting on a podded propulsor at any different load condition and yaw angle. This method is validated with
model test. They used these data for the study of the
various modes that may be employed to stop a poddriven ship. Reichel19 also presented results of comprehensive manoeuvring open-water tests of a pusher
AZIPOD. Steering forces were measured in the range
of yaw angles from 245° to +45°.
Another important study is the work carried out by
Islam et al.20,21 Particular test equipment was designed,
and several different measurements were considered.
The AZIPOD was tested in the puller and the pusher
conditions in different yaw angles from 230° to +30°.
Their results showed that the unit force and moment
coefficients depend on the propeller advance coefficient, yaw angle, and yaw direction. In the recent work,
Amini and Steen22 reported systematic model test
results of the podded drives in different advance velocities and different yaw angles. The tests were performed
on the pulling and pushing models for both open-water
and in behind conditions.23
It is a common practice to perform a model test to
evaluate the hydrodynamic performance of a marine
propeller or propulsion system. However, the model
test is usually expensive and time-consuming. An alternate approach computational fluid dynamics (CFD) is
a powerful tool for analysing the performance of ship
propulsion system. Numerical analysis of the podded
drive in azimuthing condition has not thus far been
adequately explored. For this reason, a wide numerical
analysis is used in order to understand the flow pattern
around the podded drives in azimuthing condition and
interaction between the propeller, pod, and strut. In
this work, the finite volume–based Reynolds-averaged
Navier–Stokes (RANS) solver is applied to predict the
hydrodynamic performance of propeller alone and a
new design AZIPOD system. By these simulations, the
characteristics of flow around the marine propeller and
AZIPOD are presented including pressure distribution
and open-water performance curves in zero angle and
oblique flow.
Previous work
To date, both inviscid and viscous solvers are used in
hydrodynamic analysis of marine propellers. The viscous method has traditionally been employed for flow
problems, where turbulence, boundary layer, wake, and
viscous resistance are important. The viscous solvers
are based on the solutions of the RANS equations and
are now commonly used in the design of turbomachinery components. In 2002, RANS method was employed
by Funeno24 for analysis of marine propellers. The
most important advantage of RANS method is that the
viscous effects decreasing the propeller efficiency could
be directly captured, and the flow near the hub and tip
of propeller is well investigated. In 2003, Rhee and
Joshi25 used RANS method with unstructured and sliding mesh for analysing a marine propeller in unsteady
conditions.
In order to study the effect of yaw angle on
AZIPOD performance, different numerical methods
have been used from potential method or potential/
viscous method to pure viscous method. Figure 1
shows the numerical methods for the hydrodynamic
analysis of the AZIPOD. In azimuthing condition,
there is interaction between pod, propeller, and strut.
Therefore, the viscous effect is an important phenomenon in hydrodynamic analysis.
The numerical methods based on potential flow theory have been used widely and successfully to predict
the performance of conventional propellers. The modified wake model must be assumed in order to predict
the performance of podded propellers using potential
flow–based numerical method. Ghassemi and
Ghadimi5 predicted AZIPOD performance using
potential flow method. Achkinadze et al.26 presented a
velocity-based panel method improved with semiempirical viscosity corrections for lift and drag of propeller blade and strut sections. Liu et al.27 applied
unsteady panel method code for predicting unsteady
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Shamsi and Ghassemi
3
Figure 1. Numerical methods for hydrodynamic analysis of AZIPOD.
BEM: boundary element method; RANS: Reynolds-averaged Navier–Stokes; VLM: vortex lattice method.
forces, torques, and bending moments for an AZIPOD
unit model at various yaw angles. Their results showed
that at large yaw angles, there is a discrepancy between
numerical results and experimental data. Due to viscous effects at large yaw angles, the interaction between
propeller, pod, and strut increases. Also at these angles,
drag forces of propeller, pod, and strut increase to high
values because of flow separation. For this reason,
potential results should be corrected at large yaw angles
by estimating a proper value for AZIPOD drag.
Different hybrid methods were used to predict flow
characteristics around podded propulsors. In hybrid
potential/viscous approach, the flow around propeller
is simulated by boundary element method (BEM) or
vortex lattice method (VLM) and pod and strut are
modelled by RANS or Euler solvers. Body force
approach is used for coupling these methods. Main
studies in this field have been done by Gupta,2 Mishra,3
and Bal and Guner.28
RANS simulation for AZIPOD has been done by
Sanchez-Caja et al.29,30 They presented a fully viscous
method for analysis of these systems. Koushan and
Krasilnikov31 applied unsteady RANS solver for simulating the flow around pulling and pushing pod propeller in azimuthing condition from 245° and +45° yaw
angles.
Although in recent years AZIPOD systems are
installed in many ships, efficient research schemes are
needed to provide more details of the performance at
various operational design conditions. This research
focused on the variation of forces generated by the propeller, pod, and strut at different azimuth conditions
and yaw angles for both pusher and puller types. The
numerical results included are the open-water characteristics of the propeller alone and hydrodynamic performance of the pusher and puller types of the
AZIPOD at various yaw angles. Comparisons of these
two types are also presented and discussed at various
operating conditions.
Governing equations
The governing equations for viscous flow in this study
are the Navier–Stokes (NS) equations for momentum
transport and continuity equation for mass conservation and can be stated as
∂r
+r ðr~
vÞ = 0
∂t
∂
ðr~
vÞ+r ðr~
v~
vÞ = rp+r ðt Þ
∂t
ð1Þ
ð2Þ
where ~
v denotes the velocity vector, p is the static pressure, and t represents the stress tensor given by
2
vI
t = m r~
v+r~
vT r ~
3
ð3Þ
where m is the molecular viscosity and I denotes the unit
tensor. Using the Reynolds averaging approach, the NS
equations can be expressed as
∂r
∂
+
ðrui Þ = 0
∂t ∂xi
∂
∂
∂p
ðrui Þ+
rui uj = ∂t
∂xj
∂xi
∂
∂ui ∂uj 2 ∂uI
∂
+
m
+
dij
ru9i u9j
+
∂xj
∂xj
∂xj ∂xi 3 ∂xI
ð4Þ
ð5Þ
where dij is the Kronecker delta and ru9i u9j shows the
Reynolds stresses.
It is rather difficult to model the components of the
Reynolds stress tensor because it requires detailed and
unavailable data about turbulent structures in the flow.
When a turbulence model is to be chosen, it is worth
considering whether a complicated or a simple model
should be used. The k-e and k-v models are the most
widely used turbulence models for external aerodynamics and hydrodynamics analyses. The continuous
flow problem is to be discretized for the numerical solution of the governing equations in CFD. This can be
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Proc IMechE Part M: J Engineering for the Maritime Environment 0(0)
Figure 2. Model of solution field for propeller alone.
Figure 3. Model of solution field for puller and pusher types of AZIPOD.
done by four different techniques: finite volume, finite
difference, finite element, and finite analytic method.
The most popular technique for discretization of governing equations in marine hydrodynamics is finite volume method, but finite difference and finite analytic
methods are also employed.32
Numerical method
In order to model the propeller in the fluid environment, the solution field is divided into dynamic and static cylindrical frames, as depicted in Figure 2. The
dynamic frame simulates the propeller rotation and
employs the Coriolis acceleration terms in the governing equations for the fluid. The dimensions of this
frame are related to the propeller diameter. The static
frame surrounds the dynamic frame. In this study, the
domain size was chosen based on our previous work33
and some other CFD works on marine propellers.32–34
The proposed dimensions proved to be the proper ones
to achieve this end. The static frame is a cylinder with
3D diameter. The distance between the dynamic frame
and inlet is nearly 2D, while it is nearly 5D for the outlet and dynamic frame. The same method is used for
the AZIPOD, but the dimensions of frames are selected
related to the pod length. Figure 3 shows the sketch of
computational domain for the puller and pusher of the
AZIPOD.
In addition, a mesh convergence study was performed for a single propeller. In this study, different
element sizes are considered. The best compromise
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Shamsi and Ghassemi
5
between element size and accuracy has been obtained
from the results of this work.
For a single propeller and the AZIPOD, the solution
field is divided into six blocks. (Figures 2 and 3).
Unstructured tetrahedral cells are used in rotating
blocks for both the single propeller and the AZIPOD.
Surface of the propeller and hub are meshed with the
size of 0.01D. Four prismatic cells with the size of
0.001D are selected for the boundary layer on the propeller surface. In the single-propeller case, the other
blocks are meshed with structured hexahedral cells,
and in the AZIPOD models, unstructured tetrahedral
cells are used. Number of cells for a single propeller
and an AZIPOD is about 1.5 and 1.8 million, respectively. Value of wall Y-plus parameters for both cases
are in range 30 \ Y+ \ 100.
The advance coefficient is set by altering the inlet
velocity. Here, the propeller rotating speed remains
constant during calculations.32 The inlet boundary condition for the static frame is set as inlet velocity. The
outlet boundary condition can be set as either ‘outflow’
or ‘pressure outlet’ for this frame. The propeller blades,
pod, strut, and the static cylinder are assumed as wall
boundary conditions.
The governing equations of this problem are solved
by the finite volume method based on the RANS equations. The Fluent 6.3 software was used to solve the
RANS equations. On the basis of the literature published in the application of Fluent in the simulation of
the flow around conventional propellers,2,3,14,15,25,32 in
this study, it is used to investigate the open-water
hydrodynamic performance of the podded propeller.
The discretized equations are solved using Green–
Gauss cell-based gradient option. The simple algorithm
is used for solving the pressure–velocity coupling equations. The second-order upwind discretization scheme
is utilized for the momentum, turbulent kinetic energy,
and turbulent dissipation rate in this problem.
The rotation of the propeller is modelled using
the moving reference frame (MRF), and the turbulent
fluid is modelled by k-e method. The renormalization
group (RNG) k-e model is employed using the differential viscosity model and swirl-dominated flow. For the
near-wall treatment, the standard wall functions are
applied to wall boundaries. More detailed description
of the numerical method is presented by Kim et al.35
Resulting unit thrust from AZIPOD is the sum of
three components
TUnit = TPro +TPod +TStrut
ð7Þ
where TPro, TPod, and TStrut are the component thrust
from the propeller, pod, and the strut, respectively.
For AZIPODs, coefficients of propeller thrust, unit
thrust, and axial and side forces are defined as
TPro
TUnit
, KTUnit = 2 4
2
4
rn D
rn D
Fx
Fz
KFx = 2 4 , KFz = 2 4
rn D
rn D
KTPro =
ð8Þ
where Fx and Fz are the total forces on the whole unit
in x and z directions, respectively. These coefficients are
important factors in the design of the AZIPODs affecting propulsion and manoeuvring specifications. Also,
the propeller efficiency and the AZIPOD unit efficiency
can be defined as
J KTPro
2p KQ
J KTUnit
hUnit =
2p KQ
hPro =
ð9Þ
Results and discussion
The numerical method mentioned above is employed
for the simulation of viscous flow around conventional
marine propellers and new AZIPOD systems. At first,
we conducted initial studies to investigate the influence
of boundary conditions and computational control
parameters on the results. Therefore, two different propeller models are analysed in open-water condition in
the absence of the pod and strut. Assuming the constant rotational velocity for the propellers, their performance is investigated for different inlet velocities to
obtain the characteristics of the propellers in openwater conditions. Then, the flow around and the total
of units are studied in zero yaw angle and azimuthing
condition. The Cartesian coordinates are used, where
x, y, and z denote the downstream, upward, and starboard directions, respectively. The origin of the coordinates is located at the centre of the propeller hub.
Propeller alone
Hydrodynamic characteristics
The performance characteristics of the propeller can be
defined using the non-dimensional coefficients such as
the advance coefficient, thrust coefficient, and torque
coefficient, which can be computed, respectively, as
follows
KT =
T
,
rn2 D4
KQ =
Q
,
rn2 D5
J=
V
nD
ð6Þ
In this section, two propeller models are selected. The
first propeller test case is designed based on the conventional B-series sections. The characteristic curves and
performance data of the propeller are determined by
the experimental tests in the cavitation tunnel and can
be calculated according to Carlton.1 The second propeller test case is a propeller model that was used by Liu.36
Table 1 gives the main dimensions of two propeller
models A and B. Here, Figures 4–13 are presented and
discussed for the calculations of the propeller alone.
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Proc IMechE Part M: J Engineering for the Maritime Environment 0(0)
Table 1. Main dimension of propeller models.
Propeller models
Model A
Model B
Profile type
B-series
No. of blades
Diameter (mm)
Hub ratio
Pitch–diameter ratio (P/D)
EAR
Skew angle (°)
Rake angle (°)
4
508
0.2
1
0.65
21
10
NACA 66
(DTMB modified)
4
270
0.26
1
0.6
0
0
EAR: expanded area ratio; NACA: National Advisory Committee for
Aeronautics.
Figure 4. Variation of error value for thrust and torque
coefficient at J = 0.6.
The grid dependency study is conducted for propeller model A. Six models for the same domain with different element sizes and cell numbers are generated
(Table 2). These models were simulated at J = 0.6, and
the results were compared to the experimental results.
The variations of error values for the propeller thrust
and torque coefficients are shown in Figure 4. As
shown, the errors were reduced by an increase in the
numbers of element.
The numerical simulations for two propeller models
A and B were carried out in similar working conditions
to experimental conditions. Propeller model A was
simulated at advance velocity coefficients J = 0.2, 0.3,
0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 and model B at J = 0.2,
0.4, 0.6, 0.8, 1.0. Figures 5 and 6 represent the pressure
distribution on back side and face side of the propeller
models A and B, respectively. As observed in the figures, high pressure is at face side and low pressure is at
back side. Also, the pressure and axial velocity distributions for propeller models A and B in transverse and
longitudinal planes are shown in Figures 7 and 8,
respectively. As shown in Figure 8, it is clearly observed
that the velocity at the propeller downstream position
is high, which is shown by red contour line.
Quantitatively, the pressure distribution coefficient
for propeller models A and B at four radii (r/R = 0.3,
0.5, 0.7, and 0.9) is shown in Figure 9. The blade sections of both the propellers are well shaped to generate
the moderate pressure distributions to avoid or mitigate
cavitation.
Figures 10 and 11 show the hydrodynamic characteristic curves obtained by analysis and its comparison
with the experimental data for propeller models A and
B, respectively. The results show that there is a good
agreement between the experimental and CFD results
particularly for advance ratio 0.2–0.8. The results show
that at very high–speed condition (J . 1), there is a
discrepancy between numerical results and experimental data. At light-loaded condition, advance speed
value is close to the value of pitch–diameter ratio, J/(P/
D) ’ 1.0. It means that the propellers work with
Figure 5. Pressure distribution on back (left) and face (right) side of the propeller A at J = 0.5.
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Shamsi and Ghassemi
7
Figure 6. Pressure distribution on (a) back and (b) face side of the propeller B at J = 0.6.
Figure 7. Pressure distribution in transverse plane at J = 0.5 for (a) propeller A and (b) at J = 0.6 for propeller B.
Figure 8. Axial velocity distribution in longitudinal plane (a) at J = 0.5 for propeller A and (b) at J = 0.6 for propeller B.
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Proc IMechE Part M: J Engineering for the Maritime Environment 0(0)
Figure 9. Pressure coefficient distribution for propeller A (a) at J = 0.5 and (b) for propeller B at J = 0.6.
Figure 10. Experimental and computational characteristic
curves of the propeller model A.
positive rotational speed and produce a positive (forward) thrust in the first quadrant.27
In this range of advance ratio (J = 0.2–0.8), the
error percentage for thrust coefficient, torque coefficient, and efficiency for propeller models A and B at
different advance ratios (J) are shown in Figures 12
and 13, respectively. According to these figures, the
error is slight in design condition.
In lifting bodies like propellers, the effect of viscosity
is much smaller on the thrust but significant on the torque. The maximum force is due to pressure that may be
determined by potential methods based on lifting surfaces and panel methods. Tables 3 and 4 present the viscous force/pressure force and viscous moment/pressure
moment for propeller models A and B, respectively. It
can be seen that the viscous force contributes a greater
part in the torque than in the thrust of the blades.
Figure 11. Experimental and computational characteristic
curves of the propeller model B.
Performance of AZIPOD system
In this section, a model of propeller including pod and
strut has been established and the whole of the unit has
been analysed in RANS solver. Flow characteristics
around the propeller, pod, and strut were evaluated.
The AZIPOD is studied in zero yaw angle and azimuthing condition. These investigations are performed for
two AZIPOD configurations: puller and pusher.
The propeller model A was selected and set with a
pod and strut. The non-dimensional data of the pod
and the strut are presented in Table 5. Profiles of the
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Shamsi and Ghassemi
9
Figure 12. Error percentage for propeller model A at different J.
Figure 13. Error percentage for propeller model B at different J.
Table 2. Element number of grid dependency cases.
Cases
Element no.
1
2
3
4
5
6
128,856
296,469
654,901
1,028,906
1,567,804
2,492,314
pod and the strut are similar to the one used by
Szantyr,16 but its dimensions are adjusted to propeller
size. More details about the profiles of the pod and the
strut can be found in the study by Gupta.2
Table 3. Comparison between viscous and pressure force and
moment for propeller model A.
Advance
velocity (J)
Viscous force/
pressure force (%)
Viscous moment/
pressure moment (%)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.35
0.40
0.47
0.56
0.70
0.94
1.45
3.10
7.54
1.55
1.77
2.01
2.31
2.71
3.34
4.50
7.30
12.71
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Proc IMechE Part M: J Engineering for the Maritime Environment 0(0)
Figure 14. Pressure distribution on pod, strut, and (a) face and (b) back sides of the propeller at zero yaw angle for puller
propeller (J = 0.6).
Table 4. Comparison between viscous and pressure force and
moment for propeller model B.
Advance
velocity (J)
Viscous force/
pressure force (%)
Viscous moment/
pressure moment (%)
0.2
0.4
0.6
0.8
1.0
0.62
0.83
1.24
2.62
6.71
2.72
3.50
4.67
7.43
11.45
Table 5. Non-dimensional main particulars of pod and strut.
Parameters
Value
Maximum pod diameter ratio, Dpod/Dprop A
Pod length ratio, Lpod/Dprop A
Strut height ratio, Sheight/Dprop A
Strut chord ratio, Schord/Dprop A
Strut width ratio, Swidth/Dprop A
0.295
1.624
0.551
0.433
0.187
The model was first studied in puller configuration.
The total forces on unit in each direction and propeller
thrust and torque are computed for a range of advance
coefficients from 0.2 to 1. Yaw angles of the pod are
changed from +15° to 215° with 5° increments. Then,
the podded model was tested in pusher condition.
These tests include studies on pusher podded propeller
at yaw angles from +15° to 215° with varying advance
coefficients from 0.2 to 1.
Figures 14 and 15 show pressure distribution on
pod, strut, and propeller at zero yaw angle at an
advance coefficient of J = 0.6 for puller and pusher
types, respectively. High pressure is on the face side
and low pressure is on the back side. Also, the velocity
pathlines at downstream of the puller and pusher
AZIPOD for zero yaw angle at an advance coefficient
of J = 0.6 are shown in Figure 16. In puller type, since
the strut and the pod are located in the downstream of
the propeller, the induced velocities from the propeller
change the inflow to the strut and pod. In pusher type,
those elements are located in the upstream of the propeller and the propeller works in the wake of the strut
and pod.
The propeller thrust and torque coefficients for a
range of advance coefficients and yaw angles are shown
in Figures 17 and 18. In puller type, for all advance
coefficients, the propeller thrust coefficient increases
with increasing yaw angle. This behaviour is similar for
negative angles and positive angles, and the propeller
thrust coefficients are symmetrical at positive and negative yaw angles. The same behaviour is found in the
propeller torque coefficient. In this simulation, the
advance velocity coefficient is defined in the x direction
of the coordinate system. Therefore, the effective
advance velocity in the direction of the propeller axis is
J cos c, where c is the yaw angle. This means that when
yaw angle is changed from straight condition to positive or negative angle, the effective advance coefficient
in the direction of the propeller axis is reduced. This
results in higher thrust in the corresponding operating
conditions.
But in pusher type, for all advance coefficients, the
propeller thrust coefficient decreases when yaw angle is
increased from negative angles to positive yaw angles
and the propeller thrust coefficients are not symmetrical at positive and negative yaw angles. Alternatively,
in pusher type, propeller works in the wake of strut,
and the inflow on the propeller is strongly non-uniform.37 Due to differences in the inflow condition for
positive and negative yaw angles, asymmetry is seen in
the propeller thrust curves. Also, the effect of the propeller direction of rotation should be considered in this
asymmetry. The same trend can be seen for the torque
coefficient, as shown in Figure 18. At any yaw angle,
for all advance coefficients, the propeller thrust
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Shamsi and Ghassemi
11
Figure 15. Pressure distribution on pod, strut, and (a) face and (b) back sides of the propeller at zero yaw angle for pusher
propeller (J = 0.6).
Figure 16. Velocity pathlines on pod, strut, and propeller at zero yaw angle for (a) puller propeller and (b) pusher propeller at
J = 0.6.
Figure 17. Variation of propeller thrust coefficient with yaw
angle for puller and pusher AZIPOD.
Figure 18. Variation of propeller torque coefficient with yaw
angle for puller and pusher AZIPOD.
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12
Proc IMechE Part M: J Engineering for the Maritime Environment 0(0)
Figure 19. Variation of total unit axial force coefficient with
yaw angle for puller and pusher AZIPOD.
Figure 20. Variation of pod and strut axial force coefficient
with yaw angle for puller AZIPOD.
coefficient of the pulling AZIPOD is greater than the
pushing one.
Figure 19 shows the total unit axial force coefficient
for the puller and pusher AZIPOD. The maximum
value is obtained at yaw angle 25° for all advance velocities. Also, variation of the pod and strut axial force
coefficient with yaw angle for the puller and pusher
AZIPOD are shown in Figures 20 and 21, respectively.
In puller type (Figure 20), the inflow on the pod and
the strut is influenced by propeller-induced wake flow
and the interaction between the propeller wake and the
strut is dominated. This results in asymmetry in total
unit axial force curve. In pusher type (Figure 21), the
inflow on the pod and the strut is uniform. For this reason, the axial force of the pod and the strut is almost
symmetric.
Figure 21. Variation of pod and strut axial force coefficient
with yaw angle for pusher AZIPOD.
Figure 22. Total unit efficiency for puller AZIPOD at different
yaw angles.
The total unit efficiency for the puller and pusher
AZIPOD at different yaw angles is presented in Figures
22 and 23. As shown, for all advance coefficients, total
unit efficiency is not equal at opposite yaw angles.
Total unit efficiency for the puller and pusher AZIPOD
increases with yaw angle variation in the following
manner: +15, +10, +5, 215, 210, 0, and 25.
Figure 24 shows the side force coefficient for the
puller and pusher AZIPOD. In puller and pusher types,
for all advance coefficients, the side force coefficient
increases when yaw angle is increased to the left (negative yaw angle) or right (positive yaw angle). Also, side
force coefficients for puller and pusher pod increase
with increasing advance coefficient. The side force components are propeller transverse force and pod and
strut side forces. These components are presented in
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Shamsi and Ghassemi
13
Figure 26. Variation of propeller side force coefficient with
yaw angle for puller and pusher AZIPOD.
Figure 23. Total unit efficiency for pusher AZIPOD at different
yaw angles.
Figure 27. Variation of strut side force coefficient with yaw
angle for puller and pusher AZIPOD.
Figure 24. Variation of total unit side force coefficient with
yaw angle for puller and pusher AZIPOD.
Figures 25–27. In puller and pusher AZIPOD, zero side
force is found at the small yaw angle about 1°. Due to
the propeller wake rotation and strut interactions, there
is a small side force in straight condition (zero yaw
angle) for both puller and pusher types.
Conclusion
In this article, the hydrodynamic analysis of a propeller
alone and pusher/puller of the AZIPOD at various yaw
angles and operating conditions was investigated. A
finite volume–based RANS solver has been used to
evaluate the performance of these systems. Based on
the numerical findings, the following conclusions can
be drawn:
1.
Figure 25. Variation of pod side force coefficient with yaw
angle for puller and pusher AZIPOD.
Open-water characteristics of the propeller show
that the numerical results are in good agreement
with the experimental data.
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14
2.
3.
4.
5.
6.
Proc IMechE Part M: J Engineering for the Maritime Environment 0(0)
In puller type of AZIPOD, propeller thrust and
torque coefficient curves are symmetrical to yaw
angles. But, in pusher type, propeller thrust and
torque coefficients decrease when yaw angle is
increased from negative angles to positive angles.
Comparison of the pusher/puller types show that
the puller types make more thrust, torque, and
axial force coefficients than pusher type at yaw
angles investigated.
The thrust, torque, and unit force coefficients
showed a strong dependence on the propeller
advance coefficient and azimuth angle. These coefficients were decreasing with the increasing
advance coefficients for both azimuth directions
(615°).
The variation of the pod and strut axial force coefficient against yaw angle is asymmetric for the
puller and symmetric for the pusher type of the
AZIPOD.
In puller and pusher types, for all advance coefficients, the side force coefficient increases when yaw
angle is increased to the left (negative yaw angle) or
right (positive yaw angle). Zero side force is found
at the small yaw angle of about 1°.
8.
9.
10.
11.
12.
13.
14.
Funding
This research was supported by High Performance
Computing Research Center (HPCRC) at Amirkabir
University of Technology.
15.
Acknowledgements
The authors wish to thank the reviewers for their valuable comments and suggestion.
16.
17.
References
1. Carlton JS. Marine propeller and propulsion. 2nd ed.
Oxford: Butterworth-Heinemann, 2007.
2. Gupta A. Numerical prediction of flows around podded
propulsors. MSc Thesis, University of Texas at Austin,
Austin, TX, 2004.
3. Mishra B. Prediction of performance of podded propulsors
via coupling of a vortex-lattice method with an Euler or a
RANS solver. MSc Thesis, University of Texas at Austin,
Austin, TX, 2005.
4. Sarioz K, Atlar M, Sarioz E, et al. Operability of fast
podded RoPax vessels in rough seas. Proc IMechE, Part
M: J Engineering for the Maritime Environment 2005;
219(1): 37–46.
5. Ghassemi H and Ghadimi P. Computational hydrodynamic analysis of the propeller rudder and the AZIPOD
systems. Ocean Eng 2008; 35(1): 117–130.
6. Atlar M, Woodward MD, Besnier F, et al. FASTPOD
project an overall summary and conclusions. In: Proceedings of 2nd T-POD conference, Brest, France, 3–5 October 2006. Brest: University of Brest.
7. Atlar M, Wang D and Glover EJ. Experimental investigation into the impact of slipstream wash of a podded
propulsor on the marine environment. Proc IMechE,
18.
19.
20.
21.
22.
Part M: J Engineering for the Maritime Environment
2007; 221(2): 67–79.
Ma C, Qian Z, Yang C, et al. Research on wake model
of pod propulsion. In: Proceedings of 1st T-Pod conference, Newcastle upon Tyne, UK, 14–16 April 2004.
Newcastle upon Tyne: Newcastle University.
Islam M, Taylor S, Quinton J, et al. Numerical investigation of propulsive characteristics of podded propellers of
pusher configuration. In: Proceedings of 1st T-Pod conference, Newcastle upon Tyne, UK, 14–16 April 2004,
pp.513–526. Newcastle upon Tyne: Newcastle University.
Bal S, Akyildiz H and Guner M. Preliminary results of a
numerical method for podded propulsors. In: Proceedings
of 2nd T-POD conference, Brest, France, 3–5 October
2006. Brest: University of Brest.
Lijun Z and Yanyin W. Discussion on the hydrodynamic
performance for podded propeller in steady flow by using
surface panel method. In: Proceedings of 2nd T-POD conference, Brest, France, 3–5 October 2006. Brest: University of Brest.
Carlton JS. Podded propulsors: some design and service
experience. In: Proceedings of the Motor ship marine propulsion conference, Copenhagen, Denmark, 9–10 April
2002, p.7. London: Motor Ship.
Carlton JS. Podded propulsors: some results of recent
research and full scale experience. J Mar Eng Technol
2008; 11: 1–14.
ITTC. The specialist committee on azimuthing podded
propulsion. Final report and recommendations to the
24th ITTC. In: Proceedings of the 24th ITTC, Edinburgh,
UK, 5–10 September 2005, vol. 2, pp.543–600. Newcastle
upon Tyne: Newcastle University.
ITTC. The specialist committee on azimuthing podded
propulsion. Final report and recommendations to the
25th ITTC. In: Proceedings of the 25th ITTC, Fukuoka,
Japan, 14–20 September 2008, vol. 2, pp.563–603.
Fukuoka: JASNAOE.
Szantyr JA. Hydrodynamic model experiments with pod
propulsor. Ocean Eng Int 2001; 5(2): 95–103.
Grygorowicz M and Szantyr JA. Open water experiments
with two pods propulsor models. In: Proceedings of the
1st international conference on technological advances in
podded propulsion, Newcastle upon Tyne, UK, 14–16
April 2004, pp.357–370. Newcastle upon Tyne: Newcastle
University.
Woodward MD, Atlar M and Clarke D. Comparison of
stopping modes for pod-driven ships by simulation based
on model testing. Proc IMechE, Part M: J Engineering
for the Maritime Environment 2005; 219(2): 47–64.
Reichel M. Manoeuvring forces on azimuthing podded
propulsor mode. Polish Marit Res 2007; 14: 3–8.
Islam MF, Veitch B and Liu P. Experimental research on
marine podded propulsors. Journal of Naval Architecture
and Marine Engineering 2007; 4(2): 57–71
Islam MF, Veitch B, Akinturk A, et al. Experiments with
podded propulsors in static azimuthing conditions. In:
Proceedings of the 8th CMHSC, St John’s, NL, Canada,
16–17 October 2007. St. John’s, NRC.
Amini H and Steen S. Shaft side force and bending
moment on steerable thrusters in off-design conditions.
In: Proceedings of the 11th international symposium on
practical design of ships and other floating structures, Rio
de Janeiro, Brazil, 19–24 September 2010. Rio de Janeiro:
PRADS.
Downloaded from pim.sagepub.com at University of Sydney on April 30, 2013
Shamsi and Ghassemi
15
23. Amini H and Steen S. Shaft loads on azimuth propulsors
in oblique flow and waves. Int J Marit Eng 2011;
153(Part A1): 9–22.
24. Funeno I. On viscous flow around marine propellers-hub
vortex and scale effect. J Kansai Soc Nav Archit Jpn 2002;
238: 17–27.
25. Rhee SH and Joshi S. CFD validation for a marine propeller using an unstructured mesh based RANS method.
In: Proceedings of FEDSM’03, Honolulu, HI, 6–11 July
2003. Honolulu: ASME
26. Achkinadze AS, Berg A, Krasilnikov VI, et al. Numerical
analysis of podded and steering systems using a velocity
based source boundary element method with modified
trailing edge. In: Proceeding of the propellers/shafting
2003 symposium, Virginia Beach, VA, 17–18 September
2003. Virginia Beach: SNAME.
27. Liu P, Islam M and Veitch B. Unsteady hydromechanics
of a steering podded propeller unit. Ocean Eng 2009;
36(12–13): 1003–1014.
28. Bal S and Guner M. Performance analysis of podded propulsors. Ocean Eng 2009; 36: 556–563.
29. Sanchez-Caja A, Rautaheimo P and Siikonen T. Computation of the incompressible viscous flow around a tractor
thruster using a sliding-mesh technique. In: Proceedings
of 7th international conference on numerical ship hydrodynamics, Nantes, France, 1999. Nantes: Ecole Centrale de
Nantes.
30. Sanchez-Caja A, Ory E, Salminen E, et al. Simulation of
incompressible viscous flow around a tractor thruster in
model and full scale. In: Proceedings of the 8th Conference on numerical ship hydrodynamics, Busan, Korea, 22–
25 September 2003. Busan: ONR.
31. Koushan K and Krasilnikov VI. Experimental and
numerical investigation of an open thruster in oblique
flow conditions. In: Proceedings of the 27th symposium on
naval hydrodynamics, Seoul, Korea, 5–10 October 2008.
NY: Curran Associates, Inc.
32. Kulczyk J, Skraburski L and Zawislak M. Analysis of
screw propeller 4119 using fluent system. Arch Civ Mech
Eng 2007; 7(4): 129–137.
33. Shamsi R, Soheili S and Hamooni A. Hydrodynamic
analysis of marine propellers using computational fluid
dynamics. In: Proceedings of the 17th international conference on mechanical engineering, Tehran, Iran, 12–14 May
2009. Tehran: ISME.
34. Guo C, Ma N and Yang C. Numerical simulation of a
podded propulsor in viscous flow. J Hydrodyn 2009;
21(1): 71–76.
35. Kim SE, Mathur SR, Murthy JY, et al. A Reynolds-averaged Navier-Stokes solver using unstructured mesh-based
finite-volume scheme. In AIAA 98–0231, 36th AIAA
Aerospace Sciences Meeting and Exhibit, Reno, NV, January 12–15, 1998. Reston: AIAA.
36. Liu P. The design of a podded propeller base model geometry and prediction of its hydrodynamics. Report, Report
no. TR-2006-16, June 2006. St. John’s: Institute for
Ocean Technology, National Research Council Canada
(IOT-NRC).
37. Molland AF and Turnock SR. Marine rudders and control
surfaces. 1st ed. Oxford: Butterworth-Heinemann, 2007.
Appendix 1
Notation
D
Fx
Fz
J
KFx
KFz
KQ
KT
n
p
Q
TPod
TPro
TStrut
TUnit
V
~
v
propeller diameter
axial force
side force
propeller advance ratio
axial force coefficient
side force coefficient
propeller torque coefficient
propeller thrust coefficient
propeller angular velocity (r/s)
static pressure
propeller torque
pod thrust
propeller thrust
strut thrust
unit thrust
axial velocity
velocity vector
dij
hPro
hUnit
m
r
c
t
Kronecker delta
propeller efficiency
total unit efficiency
molecular viscosity
fluid density
yaw angle
stress tensor
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