scholarly journals Spurious PIV Vector Correction Using Linear Stochastic Estimation

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 139 ◽  
Author(s):  
Daniel Butcher ◽  
Adrian Spencer
Keyword(s):  
Particle Image ◽  
Velocity Fields ◽  
Average Error ◽  
Stochastic Estimation ◽  
Linear Stochastic Estimation ◽  
Statistical Measures ◽  
Image Velocimetry ◽  
Significant Difference ◽  
Bicubic Interpolation

Techniques for the experimental determination of velocity fields such as particle image velocimetry (PIV) can often be hampered by spurious vectors or sparse regions of measurement which may occur due to a number of reasons. Commonly used methods for detecting and replacing erroneous values are often based on statistical measures of the surrounding vectors and may be influenced by further poor data quality in the region. A new method is presented in this paper using Linear Stochastic Estimation for vector replacement (LSEVR) which allows for increased flexibility in situations with regions of spurious vectors. LSEVR is applied to PIV dataset to demonstrate and assess its performance relative to commonly used bilinear and bicubic interpolation methods. For replacement of a single vector, all methods performed well, with LSEVR having an average error of 11% in comparison to 14% and 18% for bilinear and bicubic interpolation respectively. A more significant difference was found in replacement of clusters of vectors which showed average vector angle errors of 10°, 9° and 6° for bilinear, bicubic and LSEVR respectively. Error in magnitude was 3% for both interpolation techniques and 1% for LSEVR showing a clear benefit to using LSEVR for conditions that require multiple clustered vectors to be replaced.

scholarly journals Experimental Validation of Falling Liquid Film Models: Velocity Assumption and Velocity Field Comparison

Polymers ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1205
Author(s):  
Ruiqi Wang ◽  
Riqiang Duan ◽  
Haijun Jia
Keyword(s):  
Experimental Data ◽  
Particle Image Velocimetry ◽  
Velocity Field ◽  
Experimental Validation ◽  
Particle Image ◽  
Velocity Fields ◽  
Number Range ◽  
Comparison Results ◽  
Image Velocimetry ◽  
Experimental Particle

This publication focuses on the experimental validation of film models by comparing constructed and experimental velocity fields based on model and elementary experimental data. The film experiment covers Kapitza numbers Ka = 278.8 and Ka = 4538.6, a Reynolds number range of 1.6–52, and disturbance frequencies of 0, 2, 5, and 7 Hz. Compared to previous publications, the applied methodology has boundary identification procedures that are more refined and provide additional adaptive particle image velocimetry (PIV) method access to synthetic particle images. The experimental method was validated with a comparison with experimental particle image velocimetry and planar laser induced fluorescence (PIV/PLIF) results, Nusselt’s theoretical prediction, and experimental particle tracking velocimetry (PTV) results of flat steady cases, and a good continuity equation reproduction of transient cases proves the method’s fidelity. The velocity fields are reconstructed based on different film flow model velocity profile assumptions such as experimental film thickness, flow rates, and their derivatives, providing a validation method of film model by comparison between reconstructed velocity experimental data and experimental velocity data. The comparison results show that the first-order weighted residual model (WRM) and regularized model (RM) are very similar, although they may fail to predict the velocity field in rapidly changing zones such as the front of the main hump and the first capillary wave troughs.

Analysis of local velocity gradients in rapid mixer using particle image velocimetry technique

2002 ◽  
Vol 2 (5-6) ◽  
pp. 47-55
Author(s):  
N.-S. Park ◽  
H. Park
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Velocity Fields ◽  
Local Velocity ◽  
Mixing Condition ◽  
Particle Image Velocimetry Technique ◽  
Velocity Gradients ◽  
Image Velocimetry ◽  
Current Design ◽  
G Value

Recognizing the significance of factual velocity fields in a rapid mixer, this study focuses on analyzing local velocity gradients in various mixer geometries with particle image velocimetry (PIV) and comparing the results of the analysis with the conventional G-value, for reviewing the roles of G-value in the current design and operation practices. The results of this study clearly show that many arguments and doubts are possible about the scientific correctness of G-value, and its current use. This is because the G-value attempts to represent the turbulent and complicated factual velocity field in a jar. Also, the results suggest that it is still a good index for representing some aspects of mixing condition, at least, mixing intensity. However, it cannot represent the distribution of velocity gradients in a jar, which is an important factor for mixing. This study as a result suggests developing another index for representing the distribution to be used with the G-value.

scholarly journals Comparison of Periodic Flow Fields in a Radial Pump among CFD, PIV, and LDV Results

2009 ◽  
Vol 2009 ◽  
pp. 1-10 ◽  
Author(s):  
Jianjun Feng ◽  
F.-K. Benra ◽  
H. J. Dohmen
Keyword(s):  
Unsteady Flow ◽  
Laser Doppler Velocimetry ◽  
Particle Image ◽  
Velocity Fields ◽  
Image Velocimetry ◽  
Rotating Impeller ◽  
Low Specific Speed ◽  
Radial Pump ◽  
Comparison Of The Results ◽  
Better Than

The interaction between the impeller and the diffuser is considered to have a strong influence on the unsteady flow in radial pumps. In this paper, the unsteady flow in a low specific speed radial diffuser pump has been simulated by the CFD code CFX-10. Both Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) measurements have been conducted to validate the CFD results. Both the phase-averaged velocity fields and the turbulence fields obtained from different methods are presented and compared, in order to enhance the understanding of the unsteady flow caused by the relative motion between the rotating impeller and the stationary diffuser. The comparison of the results shows that PIV and LDV give nearly the same phase-averaged velocity fields, but LDV predicts the turbulence much clearer and better than PIV. CFD underestimates the turbulence level in the whole region compared with PIV and LDV but gives the same trend.

Study on the Characteristics of Turbulent Flow of Viscoelastic Fluid Through a Planar Sudden Expansion by PIV System

2015 ◽  
Author(s):  
Lu Wang ◽  
Jia-Qi Bao ◽  
Tong-Zhou Wei ◽  
Wei-Hua Cai ◽  
Feng-Chen Li
Keyword(s):  
Turbulent Flow ◽  
Particle Image ◽  
Reynolds Shear Stress ◽  
Streamwise Velocity ◽  
Velocity Fields ◽  
Sudden Expansion ◽  
Image Velocimetry ◽  
The Mean ◽  
Cetyltrimethyl Ammonium ◽  
Component Particle

The influences of drag-reducing surfactant additives on the characteristics of a turbulent flow over a planar sudden expansion with expansion ration R = D/d = 3 and aspect ratio A = w/h = 30 were experimentally investigated by a 2D-2C (two dimensional-two component) particle image velocimetry (PIV) system. The 2D-2C velocity fields in the streamwise-wall-normal planes (x-y planes) at three spanwise locations are measured for the flows of water and 50ppm aqueous solution of CTAC/NaSal (CTAC: cetyltrimethyl ammonium chloride; NaSal: sodium salicylate) under the Reynolds number of 1.85 × 104. From the streamline in the x-y plane, it is observed that the reattachment lengths of the vortices in CTAC/NaSal solution are longer. Then the mean streamwise velocity fields and the apparent flow rate at three spanwise locations show that the flow fields in the other two x-y planes are practically symmetrical about the x-y centreplane in CTAC/NaSal solution, as compared with that in water flow. Finally, it is perceived that the Reynolds shear stress for three spanwise locations in CTAC/NaSal solution are obviously decreased.

Flow Pattern Measurements by µ-PIV in the Microchannels of a Heat Exchanger and Solutions to the Particle Fouling Problem

2004 ◽  
Author(s):  
V. Heinzel ◽  
A. Jianu ◽  
H. Sauter
Keyword(s):  
Heat Exchanger ◽  
Particle Image ◽  
Field Measurements ◽  
Velocity Fields ◽  
Particle Image Velocimetry System ◽  
The Past ◽  
Image Velocimetry ◽  
Test Loop ◽  
Transparent Liquid ◽  
Flat Cell

Preliminary experimental results of measuring velocity fields of a transparent liquid flow in a closed circuit, through a 100 μm deep flat cell with heat exchanger microchannel elements are presented. The resolution and possible errors of the microscopic particle image velocimetry system are discussed in relation with the evaluation results. Particle fouling phenomenon, which proved to be the main difficulty in performing velocity field measurements in microchannels in the past, are widely overcome by techniques which avoid or limit it. The test object, which is aimed at being exposed to real technical conditions (pressures up to 0.6 MPa leading to flow velocities up to 15 m/s, as well as temperatures up to 100°C), was up to now operated at a Reynolds number of about 5. The obtained information allows for starting the test loop upgrade.

Investigation of Field Amplified Sample Stacking With Particle Image Velocimetry

2002 ◽  
Author(s):  
Shankar Devasenathipathy ◽  
Rajiv Bharadwaj ◽  
Juan G. Santiago
Keyword(s):  
Particle Image Velocimetry ◽  
Electroosmotic Flow ◽  
Particle Image ◽  
Velocity Fields ◽  
Concentration Profiles ◽  
Conductivity Ratio ◽  
Number Density ◽  
Electrokinetic Flow ◽  
Sample Stacking ◽  
Image Velocimetry

This paper presents an experimental investigation of field amplified sample stacking (FASS) with micron resolution particle image velocimetry (μPIV). The preliminary experiments reported in this work show particle velocity fields in electrokinetic flow in a glass microchannel with a single buffer-buffer interface. The buffer-to-buffer conductivity ratio is 10. Stacking of latex microspheres (i.e., increases in their number density) in the presence of a background electroosmotic flow is demonstrated. The generation of an internal pressure gradient is quantified using μPIV. This work is part of an ongoing study of the spatial and temporal development of the velocity and concentration profiles of FASS systems.

Flow Field Analysis of Dielectrophoretically-Suspended Particles

2007 ◽  
Author(s):  
Stuart J. Williams ◽  
Steven T. Wereley
Keyword(s):  
Electric Fields ◽  
Particle Image ◽  
Fluid Velocity ◽  
Microfluidic Channel ◽  
Velocity Fields ◽  
Field Analysis ◽  
Tracer Particles ◽  
Image Velocimetry ◽  
Flow Field Analysis ◽  
Complete Investigation

Understanding the fluid dynamics around a particle in suspension is important for a complete investigation of many hydrodynamic phenomena, including microfluidic models. A novel tool that has been used to analyze fluid velocity fields in microfluidics is micro-resolution particle image velocimetry (μPIV) [1]. Dielectrophoresis (DEP) is a technique that can translate and trap particles by induced polarization in the presence of nonuniform electric fields. In this paper, DEP has been used to capture and suspend a single 10.1μm diameter spherical particle in a microfluidic channel. μPIV is then used with smaller tracer particles (0.5μm) to investigate the hydrodynamics of fluid flow past the trapped particle.

Experimental Investigations inside the Wind Tunnel at the University of Stralsund

2016 ◽  
Vol 831 ◽  
pp. 117-125
Author(s):  
Thomas Panten ◽  
Heiko Meironke
Keyword(s):  
Applied Sciences ◽  
Wind Tunnel ◽  
Particle Image ◽  
Velocity Fields ◽  
Experimental Investigations ◽  
Wake Structure ◽  
Image Velocimetry ◽  
University Of Applied Sciences ◽  
Simple Body ◽  
The University

In this paper the wind tunnel at the University of Applied Sciences Stralsund and few construction details as well as the calibration of the nozzle are presented. Furthermore some approaches to visualization and measurement of velocity fields of a simple body of vehicle are shown. The wake structure behind of simple car models was investigated experimentally using Particle Image Velocimetry (PIV). Furthermore the visualization of flow field by the fog probe systems supports the evaluation of the flow and drag behavior.

scholarly journals Spatial signatures of retrograde spanwise vortices in wall turbulence

2007 ◽  
Vol 574 ◽  
pp. 155-167 ◽  
Author(s):  
V. K. NATRAJAN ◽  
Y. WU ◽  
K. T. CHRISTENSEN
Keyword(s):  
Particle Image ◽  
Spatial Relationship ◽  
Alternative Interpretation ◽  
Velocity Fields ◽  
Wall Turbulence ◽  
Image Velocimetry ◽  
Measurement Plane ◽  
Shoulder Region ◽  
Cross Correlations ◽  
Spanwise Vortex

The spatial signatures of retrograde spanwise vortices in wall turbulence are assessed from particle-image velocimetry measurements in the streamwise–wall-normal plane of a zero-pressure-gradient turbulent boundary layer at Reτ≡u*δ/ν=2350. The present results suggest that a proportion of retrograde spanwise vortices have a well-defined spatial relationship with neighbouring prograde vortices. Two-point cross-correlations and conditionally averaged velocity fields given a retrograde vortex reveal that such structures are typically oriented either upstream of and below or downstream of and above a prograde core. While these pairings are consistent with the typical-eddy patterns reported by Falco and co-workers, we offer an alternative interpretation for a proportion of these retrograde/prograde pairs. In particular, the arrangement of a retrograde spanwise vortex upstream of and below a prograde core is also consistent with the spatial signature revealed if an omega-shaped hairpin structure were sliced through its shoulder region by a fixed streamwise–wall-normal measurement plane.

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