In this paper, a comparison between results of a panel method and a RANS solver is made for a ducted propeller system in open-water. The panel method calculations were made at IST with the panel code PROPAN. Different wake models are used in the inviscid computations: rigid wake model with prescribed wake geometry and a vortex pitch wake alignment model without and with a duct boundary layer correction. For the flow in the gap region a closed gap width and a gap flow model with transpiration velocity are considered. The RANS calculations were carried out at MARIN with the RANS code ReFRESCO. A comparison of the blade and duct pressure distributions, wake geometry and thrust and torque coefficients is presented. In general, good agreement of the pressure distributions, wake geometries and force coefficients between the two codes is achieved. A reasonable agreement between the inviscid blade wake position and the blade wake viscous vorticity field is obtained when using the wake alignment model. It is seen that the correlation improves when introducing the duct boundary layer correction. The force coefficients are also compared with experimental data available from open-water tests. A reasonable to good agreement is seen for the thrust and torque coefficients over the entire openwater range.

1. A Comparison of Panel Method and RANS Calculations
for a Ducted Propeller System in Open-Water
J. Baltazar1, D. Rijpkema2, J.A.C. Falc˜ao de Campos1, J. Bosschers2
1Marine Environment and Technology Center (MARETEC)
Instituto Superior T´ecnico, Technical University of Lisbon, Portugal
2Maritime Research Institute Netherlands (MARIN), the Netherlands
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2. Motivations
The computational time of flow around ducted propellers with RANS
Methods is still reasonably high:
Need of good numerical resolution in small regions dominated by
strong viscous effects such as in the gap between the propeller
blade tip and duct;
Accurate computations are associated with long computational
times, which makes the method less useful for routine design
studies.
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3. Motivations
A number of Panel Methods have been proposed for the analysis of
ducted propellers:
Kerwin et al. (1987), Hughes (1997), Lee and Kinnas (2006);
These methods are nowadays very efficient from the
computational point of view, which makes them suited for
design studies;
However, serious limitations are met due to their inability to
adequately model viscous effects (gap flow, separation
phenomena).
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4. Objectives
Comparison of Panel Code PROPAN (Baltazar et al., 2011)
with RANS Code ReFRESCO (Vaz et al., 2009)
to obtain a better insight:
on the viscous effects of a ducted propeller system;
on the limitations of the inviscid flow model.
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5. Panel Code PROPAN
IST in-house low-order potential-based panel method;
Structured surface grids;
Fredholm integral equation solved by the collocation method;
Constant source and dipole distributions;
Influence coefficients calculated using the formulations of
Morino and Kuo (1974);
Wake models: rigid wake model and wake alignment model
without and with duct boundary layer correction;
Iterative pressure Kutta condition;
Gap flow models: closed gap width and gap model with
transpiration velocity (Hughes, 1997).
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6. RANS Code ReFRESCO
MARIN in-house viscous flow CFD code;
Solves the incompressible RANS equations, complemented with
turbulence models;
The equations are discretised using a finite-volume approach
with cell-centered collocation variables;
Flow is considered turbulent, κ − ω SST 2-equation model by
Menter (1994) is used;
Higher-order convection scheme (QUICK) is used for the
momentum equations;
A fine boundary layer resolution is applied;
No wall functions are used (y+
∼ 1).
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7. Test Case
Ducted propeller in open-water conditions;
five-bladed propeller;
Gap width equal to 0.8% of the propeller radius;
Ducted propeller was tested for J from 0.1 to 1.5;
Re from 8.9×105
to 1.1×106
, with
Re =
c0.7R
√
U2+(nπ0.7D)2
ν
.
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8. Surface grid used for the inviscid calculations
Discretisation: 50×25 blade, 150×200 duct, 67×140 hub
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9. Surface grid used for the RANS calculations
Discretisation: 10 million cells
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10. Gap flow models in panel code PROPAN
Gap Flow Model with Transpiration Velocity:
Non zero-gap width: a partial flow is allowed to pass
in the gap region, Hughes (1997).
Transpiration velocity on the gap strip:
Vn = |U∞|CQ ∆Cpn · nc
Blade
Hub
Duct
Gap
Transpiration
Velocity
Closed Gap with Zero Gap Width:
Blade tip is on the duct surface.
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11. Influence of the gap model in the inviscid
calculations, J = 1.0
r/R
∆φ/(ΩR
2
)
0.2 0.4 0.6 0.8 1.0
-0.05
0.00
0.05
0.10
Closed Gap Model
Transpiration Velocity Gap Model
Position between blades [º]
∆φ/(ΩR
2
)
0.0 25.0 50.0 75.0
0.00
0.03
0.06
0.09
Closed Gap Model
Transpiration Velocity Gap Model
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12. Wake models in panel code PROPAN
Rigid Wake Model:
Propeller Blade Wake
Constant pitch of vortex lines
Geometrical blade pitch is used in the present study
Duct Wake
Constant radius vortex sheet
Shedding line at the duct trailing edge
Wake Alignment Model for Blade Wake:
Euler scheme in (x,r,θ) coordinate system
To control wake alignment stability,
the radial coordinates are kept constant
Inside duct boundary layer (δ/R = 4%):
power lay function for the axial velocity
(Baltazar et al., 2011)
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13. Influence of the wake model in the inviscid
calculations, J = 0.3 (left) and J = 1.0 (right)
s/c
-Cp
0.0 0.2 0.4 0.6 0.8 1.0
-0.5
0.0
0.5
Rigid Wake Model
Wake Alignment Model (WAM)
WAM with Duct Boundary Layer Correction
r/R=0.90
s/c
-Cp
0.0 0.2 0.4 0.6 0.8 1.0
-0.5
0.0
0.5
1.0
Rigid Wake Model
Wake Alignment Model (WAM)
WAM with Duct Boundary Layer Correction
r/R=0.90
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14. Comparison Between PROPAN and ReFRESCO
J = 0.3, x/R = 0.3 (left) and x/R = 0.5 (right)
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15. Comparison between PROPAN and ReFRESCO
J = 1.0, x/R = 0.3 (left) and x/R = 0.5 (right)
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16. Comparison between PROPAN and ReFRESCO
Blade pressure for J = 0.3
s/c
-Cp
0.0 0.2 0.4 0.6 0.8 1.0
-0.5
0.0
0.5
1.0
PROPAN
ReFRESCO
r/R=0.70
s/c
-Cp
0.0 0.2 0.4 0.6 0.8 1.0
-0.5
0.0
0.5
PROPAN
ReFRESCO
r/R=0.90
s/c
-Cp
0.0 0.2 0.4 0.6 0.8 1.0
-0.5
0.0
0.5
PROPAN
ReFRESCO
r/R=0.99
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17. Comparison between PROPAN and ReFRESCO
Duct pressure for J = 0.3
s/c
-Cp
0.0 0.2 0.4 0.6 0.8 1.0
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
PROPAN
ReFRESCO
θ=0º
s/c
-Cp
0.0 0.2 0.4 0.6 0.8 1.0
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
PROPAN
ReFRESCO
θ=30º
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18. Comparison between PROPAN and ReFRESCO
Blade pressure for J = 1.0
s/c
-Cp
0.0 0.2 0.4 0.6 0.8 1.0
-1.0
-0.5
0.0
0.5
1.0
PROPAN
ReFRESCO
r/R=0.70
s/c
-Cp
0.0 0.2 0.4 0.6 0.8 1.0
-1.0
-0.5
0.0
0.5
1.0
PROPAN
ReFRESCO
r/R=0.90
s/c
-Cp
0.0 0.2 0.4 0.6 0.8 1.0
-0.4
0.0
0.4
0.8
PROPAN
ReFRESCO
r/R=0.99
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19. Comparison between PROPAN and ReFRESCO
Duct pressure for J = 1.0
s/c
-Cp
0.0 0.2 0.4 0.6 0.8 1.0
-0.1
0.0
0.1
0.2
PROPAN
ReFRESCO
θ=0º
s/c
-Cp
0.0 0.2 0.4 0.6 0.8 1.0
-0.1
0.0
0.1
0.2
PROPAN
ReFRESCO
θ=30º
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20. Comparison between PROPAN and ReFRESCO
Wake geometry at z = 0 for J = 0.3
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21. Comparison between numerical
and experimental results
J
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
Experiments
PROPAN
ReFRESCO
KTP
10KQ
η
KTD
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22. Conclusions
Similar potential flow results were obtained between the two gap
models;
Good agreement of the pressure distributions and loadings
between the panel code and the RANS calculations;
The comparison of the wake location predictions suggested that
the proposed mechanism of interaction of the tip vorticity with
the duct boundary layer flow may be important in the inviscid
modelling of the interaction between propeller and duct;
A reasonable to good agreement of the force coefficients
between the numerical and experimental results is obtained.
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