Twenty-Fourth Symposium on Naval Hydrodynamics (2003) / Chapter Skim
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Frontiers in Experimental Techniques
Frontiers in Experimental Techniques
Pages 65-79
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From page 65... ...
Clearly, the simplicity and flexibility of 2-D and stereo PIV are the primary reason that they are overtaking/replacing all other velocity measurement techniques, especially in liquids. As demonstrated in this paper, PIV has already been implemented in our group for measuring the complex flow structure within multistage turbomachines, and for measuring the flow and turbulence structure in the bottom boundary layer of the coastal ocean.
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From page 66... ...
The difficulties occur in part due to the presence of complex, multiple blades and blade rows. In addition, reflection of the laser sheet from boundaries overwhelms the particle traces, which severely reduce the quality of boundary layer data.
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From page 67... ...
Figure 3 shows velocity and turbulent kinetic energy distributions at three phases, positioned to match the relative orientation of the blades. Clearly and not surprisingly, the phase averaged velocity distributions and turbulence are highly non uniform, and the entire domain contains a lattice of interacting wakes.
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From page 68... ...
The flow field is dominated by the interaction with the 1St stage stator and rotor wakes. In the sample shown, a stator wake, characterized by high k and low flow angle, is just starting to impinge on the rotor blade.
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From page 69... ...
Sample phase averaged velocity in the rotor frame of reference; (b) Turbulent kinetic energy (c)
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From page 70... ...
Consequently our goal has been to measure the Reynolds stresses (free of wave contamination) , velocity profile, dissipation rate, production, buoyancy flux and turbulent spectra in the coastal bottom boundary layer, and relate them to oceanographic parameters that represent the local environment (e.g.
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From page 71... ...
the overall average (over all distributions) , whereas URMS is the RMS values, representing mostly the effect of surface waves but also turbulence at scales larger than the instantaneous distributions.
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From page 72... ...
Since Runs C-F represent typical calm weather conditions in coastal water, the results indicate that turbulence in the coastal bottom boundary layer in calm weather has a very low _~0-~ . Reynolds number.
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From page 73... ...
The same technology with appropriate adjustments can be used for studying boundary layers on full-scale models. 3-D VELOCITY MEASUREMENTS USING HPIV Stereo-PIV systems, capable of measuring the all three velocity components in a plane are already available commercially and used extensively.
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From page 74... ...
However, the required window is larger and the sample volume has a triangular shape. Third and most important, the known 3-D coordinates of the particles enable us to quadruple the spatial resolution of the velocity distributions, and significantly increase the accuracy in velocity measurements.
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From page 75... ...
Line fitting through the centroid of particle traces; b. matched perpendicular elongated particle tracers determine the centroid location; c.
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From page 76... ...
The turbomachinery work has been funded by ONR and AFOSR, the oceanic PIV measurements have been funded by ONR and NSF, and development of the HPIV system has been funded by ONR and NSF. REFERENCES Adrian R J., "Particle Imaging Techniques for Experimental Fluid Mechanics", Annual Review of Fluid Mechanics Vol.23 1991 pp.
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From page 77... ...
Nimmo Smith, W.A.M, Katz, J., and Osborn, T.R., "On the Structure of Turbulence and Dynamics of Subgrid-Scale Stresses in the Bottom Boundary Layer of the Coastal Ocean," Submitted to Journal of Physical Oceanography, 2002. Pereira, F., and Gharib, M., "Defocusing Digital Particle Image Velocimetry and The ThreeDimensional Characterization of Two-Phase Flows," Measurement Science and Technology, Vol.
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From page 78... ...
Uzol, O., Chow, Y.C., Katz, J., and Meneveau, C., "Unobstructed PIV Measurements Within An Axial Turbo-Pump Using Liquid and Blades With Matched Refractive Indices," Experiments in Fluids, in press, 2002. Wendt, V., and Furll, M., "Flow Field Measurements Around A Car Using Particle Image Velocimetry," 4th International Symposium on Particle Image Velocimetry, Paper 11 49, Gottingen, Germany, September 17-19, 2001.
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From page 79... ...
, including issues related to spatial resolution, effect of viscosity, etc. Our current effort to develop the new pressure measurement technique includes a detailed uncertainty analysis.
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