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A new white-light volumetric flow measurement technique is presented that can be used in large-scale facilities. The technique enables large volumes to be measured with high temporal and spatial resolution and without the need for a class-4 laser. This LED-based Lagrangian particle tracking velocimetry is demonstrated by measuring the tip vortex formation and the near wake of a 1.2 m diameter tidal turbine in a 25 m diameter, 2 m deep tank. Seven streamwise-distributed volumes of interest are combined, each 334 mm long, 244 mm wide and 140 mm deep, reaching up to one diameter downstream of the turbine. The system does not require re-calibration when moved. By assuming a periodic flow field, a phase-averaged flow field was reconstructed with a temporal resolution of 3.9 ms and a spatial resolution of 5.4 mm. The large volume and high time and spatial resolution could enable key research questions to be addressed on high-Reynolds-number flows and could provide valuable benchmark data for numerical model development and code validation. [ABSTRACT FROM AUTHOR]

The inflow ahead of a rotating propeller attached to a container ship model was visualized using a two-frame particle image velocimetry (PIV) technique. For illuminating the inflow region, a transparent window was installed at the stern of the ship model. Ensemble-averaged mean velocity fields were measured at four different blade phases under the design loading condition. The characteristics of the inflow in the upper plane above the propeller axis are quite different from those below the propeller axis. In the far upstream region above the propeller axis, most of the inflow comes from the hull wake and the axial velocity is very small. As the inflow moves toward the propeller plane, its axial velocity component increases rapidly. In addition, the variation of the inflow characteristics with respect to phase angle becomes apparent. The thick hull boundary layer and out-of-plane motion resulting from the propeller rotation produce a large turbulent kinetic energy around the tip of the propeller blade in the upper inflow region. The axial velocity distribution of the propeller inflow is asymmetric with respect to the vertical center axis, exhibiting different axial velocities on the port and starboard sides. [ABSTRACT FROM AUTHOR]

The aerodynamic noise and the wake flow field in a cooling fan under actual operating conditions are studied with and without winglets on the fan blades. In order to understand the influence of the winglet, the aerodynamic noise and the wake velocity distribution are measured. The results indicated that overall noise level decreased and the noise spectrum was changed in a low frequency range when the winglet was installed. It was found from the flow visualization and PIV measurement that the influence of the winglet appeared in the traces of the tip vortices and the magnitude of vorticity was reduced in the near wake region, which suggest the observed reduction in aerodynamic noise. [ABSTRACT FROM AUTHOR]

A stereoscopic PIV (Particle Image Velocimetry) technique has been employed to measure the 3 dimensional flow structure of turbulent wake behind a marine propeller with 5 blades. The out-of-plane velocity component was measured using particle images captured simultaneously by two CCD cameras installed in the angular displacement configuration. 400 instantaneous velocity fields were acquired for each of four different blade phases of 0°, 18°, 36° and 54°. They were ensemble averaged to investigate the spatial evolution of propeller wake in the near wake region up to one propeller diameter (D) downstream. The phase-averaged velocity fields show clearly the viscous wake formed by the boundary layers developed along both surfaces of the blade. Tip vortices were generated periodically and the slipstream contraction occurs in the near-wake region. The out-of-plane velocity component has large values at the locations of tip and trailing vortices. With going downstream, the axial turbulence intensity and the strength of tip vortices. With going downstream, the axial turbulence intensity and the strength of tip vortices were decreased due to the viscous dissipation, turbulence diffusion and blade-to-blade interaction. The difference in the mean velocity fields measured by SPIV and 2-D PIV methods was about 5%–10%. However, the 2-D PIV results also give sufficient information on propeller wake beyond the region of X/D = 0.2. [ABSTRACT FROM AUTHOR]