Nonparametric estimation of non-stationary velocity fields from 3D particle tracking velocimetry data

2012 ◽  
Vol 56 (6) ◽  
pp. 1566-1580 ◽  
Author(s):  
Michael Kohler ◽  
Adam Krzyżak
Keyword(s):  
Nonparametric Estimation ◽  
Particle Tracking ◽  
Particle Tracking Velocimetry ◽  
Velocity Fields ◽  
Stationary Velocity

Phase-Averaged Particle Tracking Velocimetry Measurements of Propeller Wake

2005 ◽  
Vol 49 (01) ◽  
pp. 43-54
Author(s):  
Sang-Joon Lee ◽  
Bu-Geun Paik ◽  
Choung Mook Lee
Keyword(s):  
Particle Tracking ◽  
Particle Tracking Velocimetry ◽  
Flow Characteristics ◽  
Computation Time ◽  
Velocity Fields ◽  
Tip Vortex ◽  
Wake Flow ◽  
Mean Velocity ◽  
Tip Vortices ◽  
Propeller Wake

The objective of the present paper is to apply an adaptive hybrid two-frame particle tracking velocimetry (PTV) technique for measuring the flow characteristics of turbulent wake behind a marine propeller with five blades. Compared to the conventional particle image velocimetry method, the hybrid PTV technique increases the spatial resolution and measurement accuracy significantly while reducing the computation time. For each of four different blade phases of 0, 18, 36, and 54 deg, 400 instantaneous velocity fields were measured. They were ensemble averaged to investigate the spatial evolution of the propeller wake in the region ranging from the trailing edge to a two propeller diameter (D) downstream location. The phase-averaged mean velocity fields show that the trailing vorticity and the viscous wake are formed by the boundary layers developed on the blade surfaces. The vorticity contours at each phase angle show that the tip vortices are produced periodically. The slipstream contraction occurs in the near-wake region up to about x= 0.5 D downstream. Thereafter the unstable oscillation occurs due to the separation of tip vortex from the wake sheet behind the maximum contraction point. As the tip vortex evolves downstream, its strength is reduced due to turbulent diffusion, viscous dissipation, and active mixing between tip vortices and adjacent wake flow. The technique presented here can be readily extended to investigate the nominal and effective wake distribution as well as the details of the flow field fore and aft of a rotating propeller behind a ship model.

Investigation of Microbubble Boundary Layer Using Particle Tracking Velocimetry

2005 ◽  
Vol 128 (3) ◽  
pp. 507-519 ◽  
Author(s):  
Javier Ortiz-Villafuerte ◽  
Yassin A Hassan
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Particle Tracking ◽  
Particle Tracking Velocimetry ◽  
Buffer Zone ◽  
Continuous Phase ◽  
Velocity Fields ◽  
Turbulence Structure ◽  
Mean Velocity ◽  
Measured Velocity

Particle tracking velocimetry has been used to measure the velocity fields of both continuous phase and dispersed microbubble phase, in a turbulent boundary layer, of a channel flow. Hydrogen and oxygen microbubbles were generated by electrolysis. The average size of the microbubbles was 15μm in radius. Drag reductions up to 40% were obtained, when the accumulation of microbubbles took place in a critical zone within the buffer layer. It is confirmed that a combination of concentration and distribution of microbubbles in the boundary layer can achieve high drag reduction values. Microbubble distribution across the boundary layer and their influence on the profile of the components of the liquid mean velocity vector are presented. The spanwise component of the mean vorticity field was inferred from the measured velocity fields. A decrease in the magnitude of the vorticity is found, leading to an increase of the viscous sublayer thickness. This behavior is similar to the observation of drag reduction by polymer and surfactant injection into liquid flows. The results obtained indicate that drag reduction by microbubble injection is not a simple consequence of density effects, but is an active and dynamic interaction between the turbulence structure in the buffer zone and the distribution of the microbubbles.

Instability waves in a low-Reynolds-number planar jet investigated with hybrid simulation combining particle tracking velocimetry and direct numerical simulation

2010 ◽  
Vol 655 ◽  
pp. 344-379 ◽  
Author(s):  
TAKAO SUZUKI ◽  
HUI JI ◽  
FUJIO YAMAMOTO
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Particle Tracking ◽  
Particle Tracking Velocimetry ◽  
Hybrid Simulation ◽  
Velocity Fields ◽  
Computational Time ◽  
Spatial Problem ◽  
Instability Waves ◽  
Planar Jet

Instability waves in a laminar planar jet are extracted using hybrid unsteady-flow simulation combining particle tracking velocimetry (PTV) and direct numerical simulation (DNS). Unsteady velocity fields on a laser sheet in a water tunnel are measured with time-resolved PTV; subsequently, PTV velocity fields are rectified in a least squares sense so that the equation of continuity is satisfied, and they are transplanted to a two-dimensional incompressible Navier–Stokes solver by setting a multiple of the computational time step equal to the frame rate of the PTV system. As a result, the unsteady hybrid velocity field approaches that of the measured one over time, and we can simultaneously acquire the unsteady pressure field. The resultant set of flow quantities satisfies the governing equations, and their resolution is comparable to that of numerical simulation with the noise level much lower than the original PTV data. From hybrid unsteady velocity fields, we extract eigenfunctions using bi-orthogonal decomposition as a spatial problem for viscous instability. We also investigate stability/convergence characteristics of the hybrid simulation referring to linear stability analysis.

scholarly journals Quantifying the Response of Grass Carp Larvae to Acoustic Stimuli Using Particle-Tracking Velocimetry

Water ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 603
Author(s):  
Hojung You ◽  
Rafael O. Tinoco
Keyword(s):  
Particle Tracking ◽  
Grass Carp ◽  
Particle Tracking Velocimetry ◽  
Quantitative Imaging ◽  
Functional Relation ◽  
Acoustic Signals ◽  
Ecological Impacts ◽  
Ctenopharyngodon Idella ◽  
Response Ratio ◽  
Larval Behavior

Acoustic deterrents are recognized as a promising method to prevent the spread of invasive grass carp, Ctenopharyngodon idella (Valenciennes, 1844) and the negative ecological impacts caused by them. As the efficacy of sound barriers depends on the hearing capabilities of carp, it is important to identify whether carps can recognize acoustic signals and alter their swimming behavior. Our study focuses on quantifying the response of grass carp larvae when exposed to out-of-water acoustic signals within the range of 100–1000 Hz, by capturing their movement using particle-tracking velocimetry (PTV), a quantitative imaging tool often used for hydrodynamic studies. The number of responsive larvae is counted to compute response ratio at each frequency, to quantify the influence of sound on larval behavior. While the highest response occurred at 700 Hz, we did not observe any clear functional relation between frequency of sound and response ratio. Overall, 20–30% of larvae were consistently reacting to sound stimuli regardless of the frequency. In this study, we emphasize that larval behaviors when exposed to acoustic signals vary by individual, and thus a sufficient number of larvae should be surveyed at the same time under identical conditions, to better quantify their sensitivity to sound rather than repeating the experiment with individual specimens. Since bulk quantification, such as mean or quantile velocities of multiple specimens, can misrepresent larval behavior, our study finds that including the response ratio can more effectively reflect the larval response.

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