Measurements and simulations of time-dependent flow fields within an electrokinetic micromixer

We investigate the flow field in an electrokinetic micromixer. The concept of the micromixer is based on the combination of an alternating electrical field applied to a pressure-driven base flow in a meander–channel geometry. The presence of the electrical field leads to an additional electro-osmotic velocity contribution, which results in a complex flow field within the meander bends. The velocity fields within the meander are measured by means of a microparticle-image velocimetry method. Furthermore, we introduce a mathematical model, describing the electrical and fluid-mechanical phenomena present within the device, and perform simulations comparable to the experiments. The comparison of simulations and experiments reveals good agreement, with minor discrepancies in flow topology, obviously caused by small but crucial differences between experimental and numerical geometries. In detail, simulations are performed for sharp corners of the bends, while in the experiments these corners are rounded due to the microfabrication process.

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Experimental Research and Numerical Analysis of Flow Phenomena in Discharge Object with Siphon

Water ◽

10.3390/w12123330 ◽

2020 ◽

Vol 12 (12) ◽

pp. 3330

Author(s):

Milan Sedlář ◽

Pavel Procházka ◽

Martin Komárek ◽

Václav Uruba ◽

Vladislav Skála

Keyword(s):

Experimental Research ◽

Turbulence Models ◽

Free Surface Flow ◽

Stationary Flow ◽

Surface Flow ◽

Flow Structures ◽

Complex Flow ◽

Flow Topology ◽

Image Velocimetry ◽

Flow Phenomena

This article presents results of the experimental research and numerical simulations of the flow in a pumping system’s discharge object with the welded siphon. The laboratory simplified model was used in the study. Two stationary flow regimes characterized by different volume flow rates and water level heights have been chosen. The study concentrates mainly on the regions below and behind the siphon outlet. The mathematical modelling using advanced turbulence models has been performed. The free-surface flow has been carried out by means of the volume-of-fluid method. The experimental results obtained by the particle image velocimetry method have been used for the mathematical model validation. The evolution and interactions of main flow structures are analyzed using visualizations and the spectral analysis. The presented results show a good agreement of the measured and calculated complex flow topology and give a deep insight into the flow structures below and behind the siphon outlet. The presented methodology and results can increase the applicability and reliability of the numerical tools used for the design of the pump and turbine stations and their optimization with respect to the efficiency, lifetime and environmental demands.

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Experimental Analysis of Microchannel Entrance Length Characteristics Using Microparticle Image Velocimetry

Journal of Fluids Engineering ◽

10.1115/1.4001292 ◽

2010 ◽

Vol 132 (4) ◽

Cited By ~ 34

Author(s):

Tariq Ahmad ◽

Ibrahim Hassan

Keyword(s):

Reynolds Number ◽

Flow Field ◽

Entrance Region ◽

Working Fluid ◽

Parallel Plates ◽

Entrance Length ◽

Number Range ◽

Micro Piv ◽

Image Velocimetry ◽

Microparticle Image Velocimetry

The study of the entrance region of microchannels and microdevices is limited, yet important, since the effect on the flow field and heat transfer mechanisms is significant. An experimental study has been carried out to explore the laminar hydrodynamic development length in the entrance region of adiabatic square microchannels. Flow field measurements are acquired through the use of microparticle image velocimetry (micro-PIV), a nonintrusive particle tracking and flow observation technique. With the application of micro-PIV, entrance length flow field data are obtained for three different microchannel hydraulic diameters of 500 μm, 200 μm, and 100 μm, all of which have cross-sectional aspect ratios of 1. The working fluid is distilled water, and velocity profile data are acquired over a laminar Reynolds number range from 0.5 to 200. The test-sections were designed as to provide a sharp-edged microchannel inlet from a very large reservoir at least 100 times wider and higher than the microchannel hydraulic diameter. Also, all microchannels have a length-to-diameter ratio of at least 100 to assure fully developed flow at the channel exit. The micro-PIV procedure is validated in the fully developed region with comparison to Navier–Stokes momentum equations. Good agreement was found with comparison to conventional entrance length correlations for ducts or parallel plates, depending on the Reynolds range, and minimal influence of dimensional scaling between the investigated microchannels was observed. New entrance length correlations are proposed, which account for both creeping and high laminar Reynolds number flows. These correlations are unique in predicting the entrance length in microchannels and will aid in the design of future microfluidic devices.

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Three-dimensional two-component velocity measurement of the flow field induced by theVorticella pictamicroorganism using a confocal microparticle image velocimetry technique

Biomicrofluidics ◽

10.1063/1.3105106 ◽

2009 ◽

Vol 3 (1) ◽

pp. 014105 ◽

Cited By ~ 17

Author(s):

Moeto Nagai ◽

Masamichi Oishi ◽

Marie Oshima ◽

Hiroshi Asai ◽

Hiroyuki Fujita

Keyword(s):

Flow Field ◽

Velocity Measurement ◽

Three Dimensional ◽

Image Velocimetry ◽

Two Component ◽

Microparticle Image Velocimetry ◽

Component Velocity

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An Analysis of the Secondary Flow Around a Tandem Blade Under the Presence of a Tip Gap in a High-Speed Linear Compressor Cascade

Journal of Turbomachinery ◽

10.1115/1.4051558 ◽

2021 ◽

pp. 1-20

Author(s):

Liesbeth Konrath ◽

Dieter Peitsch ◽

Alexander Heinrich

Keyword(s):

Flow Field ◽

High Speed ◽

Tip Clearance ◽

Compressor Cascade ◽

Complex Flow ◽

Flow Topology ◽

Linear Compressor ◽

Near Surface ◽

Oil Flow ◽

Linear Compressor Cascade

Abstract Tandem blades have often been under investigation, experimentally as well as numerically, but most studies have been about tandem blade stators without tip gap. This work analyzes the influence of a tip gap on the flow field of a tandem blade for engine core compressors. Experiments have been conducted in a high-speed linear compressor cascade on a tandem and a reference geometry. The flow is analyzed using five-hole probe measurements in the wake of the blades and oil flow visualization to show the near surface stream lines. First, the results for design conditions (tandem and conventional blade) are compared to measurements on corresponding blades without tip gap. Similarities and differences in the flow topology due to the tip clearance are analyzed, showing that the introduction of the tip clearance has a similar influence on the loss and turning development for the tandem and the conventional blade. The tandem blade features two tip clearance vortices with a complex flow interaction and the possible formation of a third counter-rotating vortex between them. An incidence variation from 0deg to 5deg for both blades indicates at first a similar behavior. After a separation of the flow field into gap and non-gap half it becomes apparent that the tandem blade shows higher losses on the gap side, while featuring a close-to-constant behavior on the non-gap side. Further investigation of the flow on the gap side shows indicators of the front blade exhibiting tip clearance vortex break down.

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Experimental Study on Flow Structure of Non-Premixed Swirl Burner Flows Using PIV

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.347-353.2587 ◽

2011 ◽

Vol 347-353 ◽

pp. 2587-2592 ◽

Cited By ~ 1

Author(s):

Bing Ge ◽

Shu Sheng Zang ◽

Pei Qing Guo

Keyword(s):

Flow Field ◽

Recirculation Zone ◽

Swirling Flow ◽

Spatial Separation ◽

Complex Flow ◽

Image Velocimetry ◽

Characteristic Modes ◽

Swirling Flame ◽

Development And Validation ◽

Annular Jets

This paper focuses on investigating the characteristic modes and structures in non-premixed swirling methane/air flames. Using the Particle Image Velocimetry (PIV) technique, the experiment measured the velocity distributions of the swirling flame. Cold flow conditions have been included to provide a picture of the flow field and to demonstrate the modifications induced by combustion. The characteristic lengths, velocity vectors, streamlines, and velocity distributions are presented and discussed. The experiment shows that a large spatial separation at the exit between the central and swirling annular jets can expedite the formation of a recirculation zone. Complex flow structures are found in the recirculation zone. Moreover, the differences between cold swirling flow field and combustion swirling flow are analyzed at length. The data from this experiment is helpful for optimization of the non-premixed burner design, and can be established as benchmarks for the development and validation of combustion numerical simulations.

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Time Resolved PIV of the Flow Field Underneath an Accelerating Meniscus

14th International Symposium on Particle Image Velocimetry ◽

10.18409/ispiv.v1i1.129 ◽

2021 ◽

Vol 1 (1) ◽

Author(s):

Manuel Ratz ◽

Domenico Fiorini ◽

Alessia Simonini ◽

Christian Cierpka ◽

Miguel A. Mendez

Keyword(s):

High Resolution ◽

Flow Field ◽

Pressure Head ◽

Contact Lines ◽

Flow Topology ◽

Time Resolved ◽

Image Velocimetry ◽

Measurement Resolution ◽

Temporal Structures ◽

Receding Contact

We present an experimental analysis of the flow field near an accelerating contact line using time-resolved Particle Image Velocimetry (TR-PIV). Both advancing and receding contact lines are investigated. The analyzed configuration consists of a liquid column that moves along a vertical 2D channel, open to the atmosphere and driven by a controlled pressure head. Large counter-rotating vortices were observed and analyzed in terms of the maximum intensity of the Q-field. To compute smooth spatial derivatives and improve the measurement resolution in the post-processing stage, we propose a combination of Proper Orthogonal Decomposition (POD) and Radial Basis Functions (RBF). The RBFs are used to regress the spatial and temporal structures of the leading POD modes, so that “high-resolution” modes are obtained. These can then be combined to reconstruct high-resolution fields that are smooth and robust against measurement noise and amenable to analytic differentiation. The results show significant differences in the flow topology between the advancing and the receding cases despite velocity and acceleration of contact lines are comparable in absolute values. This suggests that the flow dynamics are tightly linked to the shape of the interface, which significantly differs in the two cases.

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An Analysis of the Secondary Flow Around a Tandem Blade Under the Presence of a Tip Gap in a High-Speed Linear Compressor Cascade

Volume 2A: Turbomachinery ◽

10.1115/gt2020-14175 ◽

2020 ◽

Author(s):

Liesbeth Konrath ◽

Dieter Peitsch ◽

Alexander Heinrich

Keyword(s):

Flow Field ◽

High Speed ◽

Tip Clearance ◽

Compressor Cascade ◽

Complex Flow ◽

Flow Topology ◽

Linear Compressor ◽

Near Surface ◽

Oil Flow ◽

Linear Compressor Cascade

Abstract Tandem blades have often been under investigation, experimentally as well as numerically, but most studies have been about tandem blade stators without tip gap. This work analyzes the influence of a tip gap on the flow field of a tandem blade for engine core compressors. Experiments have been conducted in a high-speed linear compressor cascade on a tandem and a reference geometry. The flow is analyzed using five-hole probe measurements in the wake of the blades and oil flow visualization to show the near surface stream lines. First, the results for design conditions (tandem and conventional blade) are compared to measurements on corresponding blades without tip gap. Similarities and differences in the flow topology due to the tip clearance are analyzed, showing that the introduction of the tip clearance has a similar influence on the loss and turning development for the tandem and the conventional blade. The tandem blade features two tip clearance vortices with a complex flow interaction and the possible formation of a third counter-rotating vortex between them. An incidence variation from 0° to 5° for both blades indicate at first a similar behavior. After a separation of the flow field into gap and non-gap half it becomes apparent that the tandem blade shows higher losses on the gap side, while featuring a close-to-constant behavior on the non-gap side. Further investigation of the flow on the gap side shows indicators of the front blade exhibiting tip clearance vortex break down, while the rear blade seems unaffected.

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Simulation of Water Wave Interaction with Large Submerged Square Obstacles

Journal of Advanced Research in Fluid Mechanics and Thermal Sciences ◽

10.37934/arfmts.86.1.1426 ◽

2021 ◽

Vol 86 (1) ◽

pp. 14-26

Author(s):

Mona Gomaa ◽

Tamer Kasem

Keyword(s):

Flow Field ◽

Water Waves ◽

Wave Interaction ◽

Wave Forces ◽

Complex Flow ◽

Piv Measurements ◽

Image Velocimetry ◽

Flow Phenomena ◽

Induced Flow ◽

Resultant Wave

Water waves propagation over submerged obstacles is considered. The problem serves as an efficient model for modeling breakwaters. A numerical wave tank is developed to simulate the induced flow field. The model is based on multiphase viscous flow assumptions. Computations are performed adopting clustered grids and suitable initial and boundary conditions. The results are verified using the flow field particle image velocimetry (PIV) measurements. Spatial and temporal resolutions are validated. Complex flow phenomena occurring due to the presence of the relatively large sized obstacle are visualized. The effect of wave parameters on the flow structure is investigated. A brief parametric study is presented and the resultant wave forces and turning moments are provided.

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Quantification of added-mass effects using particle image velocimetry data for a translating and rotating flat plate

Journal of Fluid Mechanics ◽

10.1017/jfm.2019.231 ◽

2019 ◽

Vol 870 ◽

pp. 492-518 ◽

Cited By ~ 16

Author(s):

S. J. Corkery ◽

H. Babinsky ◽

W. R. Graham

Keyword(s):

Boundary Layer ◽

Particle Image Velocimetry ◽

Flow Field ◽

Flat Plate ◽

Potential Flow ◽

Particle Image ◽

Flow Theory ◽

Added Mass ◽

Flow Topology ◽

Image Velocimetry

Added mass characterises the additional force required to accelerate a body when immersed in an ideal fluid. It originates from an asymmetric change to the surrounding pressure field so the fluid velocity satisfies the no-through-flow condition. This is intrinsically linked with the production of boundary vorticity. A body in potential flow may be represented by an inviscid vortex sheet and added-mass forces determined using impulse methods. However, most fluids are not inviscid. It has been theorised that viscosity causes the ‘added-mass vorticity’ to form in an intensely concentrated boundary layer region, equivalent to the inviscid distribution. Experimentally this is difficult to confirm due to limited measurement resolution and the presence of additional boundary layer vorticity, some the result of induced velocities from free vorticity in the flow field. The aim of this paper is to propose a methodology to isolate the added-mass vorticity experimentally with particle image velocimetry, and confirm that it agrees with potential flow theory even in separated flows. Experiments on a flat-plate wing undergoing linear and angular acceleration show close agreement between the theoretical and measured added-mass vorticity distributions. This is demonstrated to be independent of changes to flow topology due to flow separation. Flow field impulse and net force are also consistent with theory. This paper provides missing experimental evidence coupling added mass and the production of boundary layer vorticity, as well as confirmation that inviscid unsteady flow theory describes the added-mass effect correctly even in well-developed viscous flows.

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