Twenty-Third Symposium on Naval Hydrodynamics (2001) / Chapter Skim
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Experimental and Numerical Investigation of the Unsteady Flow Around a Propeller
Experimental and Numerical Investigation of the Unsteady Flow Around a Propeller
Pages 511-526
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From page 511... ...
The typical configuration is a twin screw controllable pitch propeller with quite a long shaft, due to the gradual rise of the keel in the aftbody, and a set of shaft brackets with a L arrangement so that the vertical bracket is in the shaft wake. The request of large thrust and the constraint on the maximum diameter posed by tip clearance naturally lead to high expanded area ratios; rather extreme skew distributions are adopted to decrease induced pressure pulses, while large pitch variations allow to avoid excessive loading at the propeller tip.
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From page 512... ...
Next, the computed wake surface is used as input of a prescribed wake unsteady flow computation in which the actual non uniform inflow is used. EXPERIMENTAL ANALYSIS Experimental setup Measurements have been carried out at the INSEAN free surface Circulating Water Channel, having a test section of 10 m x 3.6 m x 2.25 m; the maximum flow speed is 5 m/s, and pressure may be reduced to 4 KPa.
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From page 513... ...
Signals from the encoder are processed by a synchronizer which provides the propeller angular position to a two-bytes digital port available on the LDV master processor. In order to improve the processor data rate and to reduce the time acquisition length per point, the channel water is seeded upstream the ship model with titanium dioxide (TiO2)
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From page 514... ...
where (p denotes the unbounded fluid region surrounding the propeller and its trailing wake. As usual in potential flow analyses of lifting bodies, the wake is included by assuming that the vorticity generated on each blade is shed into a zero thickness layer which is replaced by a discontinuity surface for the velocity potential.
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From page 515... ...
°w are determined by applying mass and momentum conservation laws across the surface. One obtains ~ ta¢> = 0 yang Ap = 0 on Low, (6)
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From page 516... ...
Discretization A numerical solution of the boundary integral formulation for the velocity potential outlined above is obtained here by using a boundary element method. The propeller surface and the wake are divided into hyperboloidal quadrilateral elements.
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From page 517... ...
FLOW FIELD INVESTIGATIONS Tests have been carried out with propeller angular velocity of 7.7 rps and channel upstream velocity of 2.4 m/s, corresponding to an advance ratio J = 1.133 and a blade Reynolds number at r = 0.7R, Reo.7 = 3.7.
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From page 518... ...
Downstream plane First flow measurements and theoretical predictions downstream the propeller are considered. Here, the flow field is characterized by the propeller trailing vorticity path.
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From page 519... ...
.~0 0.18 :a.1:~6 0.14 0.1~2 .~0 O.~$ 0.06 0.04 ~0.0~2 Figure 7: Experimental turbulence levels of the axial velocity component and location of the trailing wake by numerical simulations on the downstream measurement plane.
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From page 520... ...
~ = 0° (experiments) ~ = 30° (experiments)
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From page 521... ...
= 0° (experiments) ~ = 0° (numerical)
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From page 522... ...
In fact, both experimental and numerical results show that the perturbation induced by the propeller tends to smooth any difference between the velocity fields incoming to the propeller. Upstream plane Figures 10 and 11 show the axial velocity component in the upstream plane at the representative angular position of ~ = 0° for the two bracket arrangements.
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From page 523... ...
Phase sampling is performed by means of a Tracking Trigger Technique, by which velocity samples are arranged into angular slots according to the propeller position at measurement time. The procedure provides a satisfactory compromise between statistical requirements and angular resolution.
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From page 524... ...
81-92. Stella, A., Guj, G., Di Felice, F., Elefante, M., and Matera, F., 1998, "Propeller flow field analysis by means of LDV phase sampling techniques," in Proc.
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From page 525... ...
= 0° (suction side) = 30° (suction side)
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From page 526... ...
Japan The authors should be congratulated for their efforts to measure the complicated flow fields around a propeller operating in non-uniform flow by LDV and develop a panel method with a flow-aligned wake. I have the following questions.
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