Twenty-Fourth Symposium on Naval Hydrodynamics (2003) / Chapter Skim
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A New Propeller Design Method for the POD Propulsion System
A New Propeller Design Method for the POD Propulsion System
Pages 839-851
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From page 839... ...
Two major features of this method are first the propeller geometry is designed on a conical coordinate system instead of the traditionally used cylindrical coordinate system. Secondly, the inflow of the propeller is simulated by a coupled viscous/potential flow calculation including both the POD body and the propeller for the purpose of designing a propeller in a more realistic condition.
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From page 840... ...
Figure 2 shows that the calculated circulation distributions are different when the blade sections defined on a cylindrical coordinate system and on a conical coordinate system with the same blade outline, and the difference is not negligible. Notice that when the blade geometry defined on the conical coordinate system, the centerline is vertical to the conical surface; therefore, there is a negative rake distribution for the above case (Figure 3~.
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From page 841... ...
has suggested that the coupling of viscous and potential flow calculations can be carried out consistently only under the assumption that both the ship flow and the propeller flow at the propeller plane are axis-symmetric. This assumption is reasonable since that the induced velocity upstream of a propeller is usually dominated by the circumferential mean value.
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From page 842... ...
The procedure to solve the propeller-hull interaction is described as follows: (1) The viscous flow around a ship hull without the propeller in operation is first solved by the RANS code UVW; The circumferential mean value of the flow velocity at the propeller plane is then extracted from the solution of UVW, and then used as the inflow of propeller flow calculations; For solving the analysis problem, MIT-PSF-2 is used to calculate the circumferential mean induced velocities and propeller forces.
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From page 843... ...
Table 1: The measured and the calculated forces on the ship hull and on the propeller of a self-propulsion test J Measured 0.852 Calculated 0.863 Error 1.20% I KT 0.175 0.183 4.39% KQ 0.0261 0.0281 7.66% Figure 7: The computer depiction of a POD propulsor and its calculated pressure distribution. NUMERICAL COMPUTATIONS In this section, we will first demonstrate the flow around a POD propulsor calculated by a potential flow boundary element method, and then the same flow calculated by a coupled viscous/potential flow code.
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From page 844... ...
From Figure 18, we can see that the forces on the POD propulsor calculated by the viscous flow code are indeed asymmetrical with respect to the yaw angles. After studying the computational results, it is found that the over-prediction of frictional forces (negative axial force)
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From page 845... ...
. ~.00 -10.00 0.00 10.00 20.00 yaw Figure 9: The calculated and measured axial force on the POD propulsor at different yaw angles (J=0.8~.
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From page 846... ...
CONCLUSIONS In this paper, the blade geometry definition and the propeller inflow are studied for a new, integrated propeller design method applied to a POD propulsor. The presented design method can also be used for propellers installed on any axis-symmetrical bodies, or for the design of propellers on a traditional propulsion system.
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From page 847... ...
Therefore, when designing a propeller on a POD propulsor, the inflow calculation should include the viscous computation. For the further research, the boundary element method used in the POD propulsor calculation should include the unsteady effect, not just the circumferential mean values.
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From page 848... ...
dS (13) where ~ is the strength of perturbation potentials, or equivalent to the dipole strength, an is the source an strength, ha ~ is the potential induced by a unit strength dipole, and ~ is the potential induced by a unit strength source.
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From page 849... ...
For a multi-component propulsor with both rotating and static components, such as a POD propulsor (the propeller is rotating, and the nacelle is not) , a circumferential mean of the component-to-component induced potential is taken to simplify the solution procedure.
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From page 850... ...
In the computations of pod propulsors in yaw angles, we take the mean velocities as the inflow of the propeller; therefore, the wake alignment is not critical. For propellers in a yaw angle, if we take the inclined flow as the propeller inflow, then it is an unsteady flow problem, and the wake geometry has to be changed at each time step.
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From page 851... ...
· _ cylindrical ,~ Figure R1. The mean sections of two propellers computed.
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