Flow Visualization and analysis by PIV Measurement System using Micro-bubbles as Tracer in Ship Model Basin-Measurement in Still Water and Regular Waves -
To measure and analyze the flow around ship model, use of micro-babbles as tracer is proposed here. The system has two high speed cameras for stereo photography with continuous laser light sheet. Using continuous laser light sheet flow around ship can be observed directly. To make validation of the present system flow analysis of uniform flow and regular waves in ship model basins is carried out. From the comparison between flow velocity analyzed by the present system and that measured by current meter in different three ship model basins, it is found that the correlation factors of the basins are over 0.99 for flow velocity of ship advance direction. In regular waves the trajectory of the wave motion is compared to small amplitude wave theory and analyzed value. From the comparison it is found that the agreement is well for different wave frequencies. Continuously, flow measurement using a ship model of large tanker has performed in still water and in regular head waves. From the analysis it is found that the difference of the flow vector between still water and regular head waves can be evaluated qualitatively. Thereafter to understand the flow around propeller the tank tests in self propelling condition of the ship model are performed. From the comparison between the tests with propeller and without propeller, the effect of propeller suction is revealed. From the various comparisons the effectiveness of the PIV system using micro-bubbles to obtain flow information around ship is confirmed.
Phase-Averaged SPIV Flow Field Measurement for Ballast Condition of KVLCC2 in Waves
When the propulsion performance in waves were considered, the averaged value and fluctuation of effective inflow velocity to the propeller is very important. But even for the nominal velocity distribution, very few results are presented. The Stereo PIV measurements near the propeller plane were shown by the authors’ group and phase-averaged velocity fields are discussed. The freesurface effect including the incident wave effect seems to be larger for ballast condition due to the shallower draft. So, in this paper, force and motion measurements for various wave and ship length ratio(λ/L) and nominal velocity field measurements using stereo Particle Image Velocimetry(PIV) system for three λ/L (0.6, 0.9, 1.5) for ballast condition are presented. λ/L=0.6 shows the condition in which the motion is small and added resistance is medium. The peak value is observed for added resistance at λ/L=0.9. The motion is large and relatively small added resistance is observed at λ/L=1.5. Phase averaged nominal velocity fields are discussed through measurement results with respect to the wave orbital velocity effect and the effect of motion. The low velocity region is affected by pressure gradient and ship motion and the shape of wake distribution is changed by phase to phase.
Simulations of the viscous flow normal to an impulsively started and uniformly accelerated flat plate
The development of a two-dimensional viscous incompressible flow generated from an infinitesimally thin flat plate, impulsively started or uniformly accelerated normal to the free stream is studied computationally. An adaptive numerical scheme, based on vortex methods, is used to integrate the vorticity–velocity formulation of the Navier–Stokes equations. The results of the computations complement relevant experimental works while providing us with quantities such as the vorticity field and the unsteady forces experienced by the body. For the uniformly accelerated plate the present simulations capture the development of a number of centers of vorticity along the primary separating shear layer. This phenomenon has been observed in experimental works but has not been predicted by inviscid models. The present simulations suggest that this Kelvin–Helmholtz-type instability is driven by the interaction of primary and secondary vorticity near the tips of the plate and depends on the acceleration of the plate.