Twenty-Fourth Symposium on Naval Hydrodynamics (2003) / Chapter Skim
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PIV Measurements of the Cross-Flow Wake of a Turning Submarine Model (ONR Body 1)
PIV Measurements of the Cross-Flow Wake of a Turning Submarine Model (ONR Body 1)
Pages 655-668
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From page 655... ...
The near wake flow field is observed to be dominated by complex interactions of large-scale vertical structures from the hull separated flow and the tip vortices from the sail and various control surfaces. INTRODUCTION The wake of a maneuvering submarine represents a highly complex three-dimensional flow field, dominated by interactions of large-scale vertical structures from the separated flow around the body and the trailing flow structures from the sail and various control surfaces.
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From page 656... ...
PARTICLE IMAGE VELOCIMETRY Particle image velocimetry (PIV) is a flow-field measurement technique that provides an instantaneous distribution of two velocity components over an entire two-dimensional measurement plane.
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From page 657... ...
The roll angle could be adjusted by rotating the model about the sting axis using roll positioning equipment built into the sting assembly. The roll angle was measured via a
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From page 658... ...
In order to balance the static pitching moment of the sting assembly and model, the sting assembly was mounted to the rotating arm undercarriage in such a way that the model reference point was 2.134 m.
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From page 659... ...
in a plane of measurement. Two sets of laser sheet optics in their housings were installed on a single optical rail to provide two possible measurement planes (although only one is used at a time)
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From page 660... ...
The DaVis software package utilizes advanced algorithms, including local adaptive cell shift and second-order correlation, to enhance accuracy and improve data integrity. A benchmarking test was carried out to measure the stability and accuracy of the software package against a set of"standard" images provided by the PIV-STD project.
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From page 661... ...
FORCE & MOMENT MEASUREMENTS A forward and an aft set of block gages were used to measure the longitudinal, lateral and vertical force components with respect to the body axes, denoted X, Y and Z respectively.
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From page 662... ...
Then, a final mean value and standard deviation was computed for each variable using N= 50. The precision index of the mean was then computed using Equation 12.
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From page 663... ...
An upward force, which acts primarily aft of the CG, will result in a net downward pitching moment, consistent with the measured results. It is important to note that the mechanisms leading to the downward pitching moment discussed above are limited to situations in which cross-flow separation is dominant, i.e., a submarine in a turn with large r'.
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From page 665... ...
1.6 m/s -0.4 14~15 -0.3 -0.1 c) Plane #9 d)
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From page 666... ...
, the interaction of the sail trailing vortex with the hull separated flow results in a net circulation around the body in such a way that the separation zone is rotated toward the deck of the model. Since the separation zone is an area of low pressure and a corresponding area of high pressure exists on the opposite side of the hull, this mechanism contributes to a net upward force on the hull aft of the sail.
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From page 667... ...
E.," PIV Measurements of the Cross-Flow Velocity Field Around a Turning Submarine Model (ONR Body1) ," NSWCCD-50-TR-2001/036 July 2001, Carderock Division, Naval Surface Warfare Center, Hydromechanics Directorate Research & Development Report.
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From page 668... ...
Qualitatively, the variation on the position and strength of the sail tip vortex appears small when compared among the 4 to 5 experimental runs for each PIV configuration. The PIV images were taken with a stationary submersible PIV system as the submarine model passed by.
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