Twenty-First Symposium on Naval Hydrodynamics (1997) / Chapter Skim
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Macro Wake Measurements for a Range of Ships
Macro Wake Measurements for a Range of Ships
Pages 278-290
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From page 278... ...
No less than 8 ship models were involved in the project, and some of them in more than one operational condition. The measurements comprised: - the three components of the velocity vector - the six components of the Reynolds stress tensor - longitudinal and transverse wave profiles The measurement equipment, a three-component LDV system and two types of wave probes, is described.
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From page 279... ...
The measurements comprised: - the three components of the velocity vector; - the six components of the Reynolds stress tensor; - longitudinal and transverse wave profiles. The velocity and Reynolds stress measurements were made in several transverse planes.
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From page 280... ...
2. Test setup for flow speed measurement 280
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From page 281... ...
3. Test setup for longitudinal wave cuts The wave profile measurement system, using a 1 Watt argon laser, was mounted at a fixed position in the basin and data recording took place while the model passed by.
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From page 282... ...
For the laser type wave cuts the following accuracy limits apply: Wave elevation: Wave slope: When the LDV measurements are non- x-coordinate: dimensionalised with tow speed, the inaccuracy of y-coordinate: the carriage speed is introduced. This applies to tale longitudinal velocity component only.
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From page 283... ...
So each vortex has a nearby imaginary companion and, again by mutual induction, the core position of the side vortices tends to move away from the longitudinal symmetry plane of the ship with increasing distance to the stern. Not all ships produce two clearly identifiable vortex pairs; a dependency on the stern shape is evident.
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From page 284... ...
In the case of a single-screw ship, both the port and the starboard bilge vortex are captured in the screw race and start swirling. Moreover, due to the strong mixing in the propeller jet, the bilge vortices soon loose Weir identity, i.e.
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From page 285... ...
While this flow is clearly outside the propeller jet which is at a much lower position, we suppose that this is accomplished primarily by the bilge vortices which are very effective in transporting momentum from the propeller jet or the outer flow to that location. In ideal-flow propeller models (actuator disk, lifting line or lifting surface models)
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From page 286... ...
The longitudinal wave cuts away from the symmetry plane revealed the change in the direction of propagation of the waves. For the initial part of the wave record consists of contributions of the diverging wave components, the end of the record of transverse waves.
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From page 287... ...
It has been outlined in section 4.1.3 how the combination of bilge vortices, propeller and rudder can produce strong asymmetry. The typical result for ~ righthand single propeller is that the bilge vortex pair migrates to port, causing the apparent symmetry line for the near-free-surface flow to be displaced to starboard.
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From page 288... ...
This scalar quantity typically exhibits peaks in the three lobes of the axial velocity field. A breaking bow wave may cause an additional pair of trails of high turbulence kinetic energy.
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From page 289... ...
Data have been collected for eight hull forms' a supplementing ninth data set being already available. Although macro wake measurements are not new, the scope of the AFDEASR project went beyond that of all previous ones.
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From page 290... ...
nom. = wake of unpropelled hull prop.
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