The Natural Sciences and Engineering Research Council of Canada (NSERC) and L.B. Foster Rail Technologies, Corp. jointly supported this research through the NSERC Collaborative Research and Development Grant program.

1. Spinning Disk Device
<ol>
	<li>Identify desired test conditions and record test conditions in a table (e.g., ambient temperature, fluid properties, jet and surface speed, etc.).</li>
	<li>Preparation of Materials
	<ol>
		<li>Prepare glycerin-water or PEO-glycerin-water solutions for the impingement tests.
		<ol>
			<li>In the case of PEO-glycerin-water tests, gradually dissolve 4.5 g of PEO powder (viscosity-average molecular weights of one million and four million) into 1495.5 g of distilled water under gentle magnetic stirring over a 24 hr period. Avoid excessively agitating the PEO sample to prevent mechanical degradation.</li>
			<li>Gradually add 1.5 kg of USP-grade glycerin to the aqueous PEO solution over a 24 hr period to reach an aqueous solution of 0.15% PEO concentration and 50% glycerine concentration.</li>
		</ol>
		</li>
		<li>Store the test liquids separately in airtight containers under RT before and after each test to minimize evaporation, water absorption from ambient air and contamination. Characterize and spray liquids within five days of preparation.</li>
	</ol>
	</li>
	<li>Performance of Experiments
	<ol>
		<li>Make sure the spinning disk air bearing&#39;s air supply valve is open and the pressure gauge reading is in the correct working range (60-80 psig). Clear anything that might impede the disk movement and turn the disk by hand in both directions 5 rotations to check for any problems with the disk and bearings.</li>
		<li>Clean and secure the compressed gas closed accumulator for test fluid pressurization. Pour 3 kg of test liquid into the fluid port of the 1-gallon accumulator.</li>
		<li>Connect the gas port of the accumulator to the nitrogen tank via a pressure regulator. Connect the fluid port of the accumulator to the jet spray nozzle.</li>
	</ol>
	</li>
	<li>Set up control system and high-speed imaging system.
	<ol>
		<li>Start the spinning disk control software and VFD control software. Position two high-speed cine cameras 35 cm away from the impingement point and adjust the high magnification lenses to capture the impingement point from two angles.</li>
		<li>Adjust the 150 W&#160;fiber-optic light source to achieve an evenly lit background for best image quality (Figure 1). Power on the control system at this point to facilitate camera adjustment.</li>
		<li>Perform the self-check routine by clicking &#8216;Self-check&#8217; button in the control software to make sure the system is functioning as expected.</li>
	</ol>
	</li>
	<li>Perform a jet impingement test
	<ol>
		<li>Set the disk speed to the desired value with the VFD control software (500-3,000 rpm).</li>
		<li>To perform a test, launch the automated experimental sequence from the control software by clicking the &#8216;Test sequence&#8217; button. The software will determine the optimal parameters automatically and coordinate each component of the system to perform the test accordingly.</li>
		<li>Save the resultant impingement test video (see, for example, the screen shot in Figure 2). Read and record surface speed, nozzle back pressure and temperature from the control software. 
		Note: After each test, a disk cleaning sequence runs automatically to rinse and dry the disk surface. Repeat the cleaning cycle as necessary until all test fluid residue has been removed. 
		CAUTION: While water and glycerin solution test fluids may be cleaned with the cleaning sequence, other LFMs need to be cleaned with organic solvents such as acetone. In such cases, apply the cleaning material to a cloth rather than spraying the disk directly.</li>
	</ol>
	</li>
	<li>Data Analysis
	<ol>
		<li>Prepare a spreadsheet containing information on each test condition (e.g., fluid properties, ambient temperature, surface roughness, etc.).</li>
		<li>Open the recorded jet impingement images with cine viewing software, play full video recordings at normal speed and observe jet impingement behaviors.</li>
		<li>Record impingement behavior characteristics (splash/spattering/deposition; see Figure 3) in the prepared spreadsheet, logging any unusual trends that may indicate complications with the experimental set-up.</li>
		<li>Save test results and conditions in a spreadsheet. Record notable findings and unusual occurrences in test log (e.g., splash/deposition threshold point, splash/deposition transitions, etc.). Save screenshots when necessary.</li>
		<li>Conduct image analysis measurements and record data.
		<ol>
			<li>Launch the on-screen pixel measuring tool. Open impingement images, and calibrate the image scale by measuring a micro-ruler in the images with the on-screen pixel measuring tool (Figure 4).</li>
			<li>Measure dimensions of interest (e.g., lamella spread width, W, and lamella stagnation point radius, R; see Figure 5) with the pixel measuring tool at a point where the jet appears to be most stable in the video and record data in the prepared spreadsheet. Then take another group of measurements 100 frames after the first group of measurements to confirm that both the jet and the lamella are stable. Plot data points on a graph and complete the curve fitting.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
2. Air Cannon Device
<ol>
	<li>Identify desired test conditions and prepare materials as in step 1.1 and step 1.2.</li>
	<li>Performance of Experiments
	<ol>
		<li>Power up the system-control software.</li>
		<li>Insert the projectile into the cannon barrel. Move the stop mechanism close to the barrel exit to properly capture the projectile after a test (Figure 6).</li>
		<li>Open the pressurized building air line leading to the air tank. Pressurize the tank to between 30 psi and 70 psi, depending on the desired projectile velocity. 30 psi tank pressure gives a projectile speed of around 5 m/sec, and 70 psi gives a speed of around 25 m/sec.</li>
		<li>Prepare the compressed gas closed accumulator for test fluid pressurization.
		<ol>
			<li>Pour 3 kg of test liquid into the fluid port of the accumulator. Connect tubing from the accumulator gas valve to the liquid jet spray nozzle, and set the accumulator pressure to up to 300 psig.</li>
		</ol>
		</li>
		<li>Attach the camera to the scissor jack. Secure the scissor jack to the platform positioned next to the jet spray nozzle.</li>
		<li>Secure the high-intensity light source to the platform positioned across from the camera and behind the diffusion sheet. Check lighting and camera positioning using the video camera viewing function of the software control interface, and adjust positioning as necessary (Figure 7).</li>
		<li>Put on earmuffs for protection from the air cannon sound blast.</li>
		<li>Unlock the cannon control panel, and press the warning button on the control panel multiple times to signal the start of an experiment.</li>
		<li>Hit the control panel button that opens the solenoid valve connecting the air tank with the air cannon barrel.</li>
		<li>After the device has been fired and the projectile captured, clean the device by wiping it with cleaning fluid and a sponge to remove residual test fluid. Finally, dry the impingement surface of the projectile.</li>
	</ol>
	</li>
	<li>Measure speed of the projectile in the recorded high-speed video by measuring the amount of time required for the projectile to travel a fixed (10 cm) distance. Analyze data as in step 1.5.</li>
</ol>

<ol>
	<li>Cotter, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Top+of+Rail+Friction+Control:+Reductions+in+Fuel+and+Greenhouse+Gas+Emissions.">Top of Rail Friction Control: Reductions in Fuel and Greenhouse Gas Emissions.</a> Proc. Of the 2005 Conference of the International Heavy Haul Association (Rio de Janeiro). , 327-334 (2005).</li><li>Eadie, D. T., Bovey, E., Kalousek, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+friction+control+in+effective+management+of+the+wheel/rail+interface).">The role of friction control in effective management of the wheel/rail interface).</a> Railway Technical Conference. , (2002).</li><li>Stock, R., Eadie, D. T., Elvidge, D., Oldknow, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influencing+rolling+contact+fatigue+through+top+of+rail+friction+modifier+application&#8211;A+full+scale+wheel&#8211;rail+test+rig+study.">Influencing rolling contact fatigue through top of rail friction modifier application&#8211;A full scale wheel&#8211;rail test rig study.</a> Wear. 271 (1), 134-142 (2011).</li><li>Eadie, D. 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A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inclined+to+splash:+triggering+and+inhibiting+a+splash+with+tangential+velocity.">Inclined to splash: triggering and inhibiting a splash with tangential velocity.</a> New Journal of Physics. 11 (6), 063017 (2009).</li><li>Range, K., Feuillebois, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+surface+roughness+on+liquid+drop+impact.">Influence of surface roughness on liquid drop impact.</a> Journal of Colloid and Interface science. 203 (1), 16-30 (1998).</li><li>Crooks, R., Boger, D. 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The authors have nothing to disclose.

The projectile used for the air cannon set-up is composed of a lightweight, wooden base. Though the wooden material chips slightly after numerous tests, it has been found to absorb kinetic energy more effectively than projectiles composed of materials such as plastic or metal, which tend to shatter upon impacting the stop mechanism. The dimensions of the wooden projectile are designed to closely match the steel barrel interior, thus restricting air leakage. A 1/8&#8221; thick rubber sheet secured between two layers of pl...

This research aims to determine strategies for applying LFM (Liquid Friction Modifier) in liquid jet form onto a moving surface while attaining high degrees of transfer efficiency and uniform deposition results. Achieving this objective involves developing a comprehensive understanding of factors that affect liquid jet impingement on moving surfaces.
The project is motivated by a need to improve the efficiency of lubrication application techniques used in the rail sector. As a means of reducing fuel consumption and locomotive maintenance costs, a thin film of friction modifying agent is now being applied to the upper rail surface of conventional railroad tracks. Recent studies have shown that applying one type of water-based LFM for top of rail (TOR) friction control reduced energy consumption levels by 6% and rail and wheel flange wear by in excess of 50%1,2. Other studies have shown that applying LFM to rail tracks reduces lateral force and noise levels as well as, more importantly, track corrugation and damage from rolling contact fatigue, which is a major cause of derailments3,4. These results were further confirmed in field tests on the Tokyo subway system5.
LFMs are currently dispensed from air blast atomizers attached to dozens of locomotives throughout Canada and the United States. In this form of application, LFM is applied to the top of railroad tracks by atomizers mounted beneath moving rail cars. This mode of LFM application is difficult to implement on many railroad locomotives because the required high-volume and high-pressure air supply levels may not be attainable. Air-blast spray nozzles are also believed to produce highly irregular rail coverage when operated in a crosswind, as crosswinds cause fine spray droplets to deviate from their original trajectory. Crosswinds are also known to be implicated in nozzle fouling, likely for the same reason. Due to problems associated with air blast atomizers, the rail sector is currently seeking alternative approaches to LFM application onto rail tracks. One viable solution involves dispensing LFM by means of a continuous (not-atomized) liquid jet, as liquid jets are less susceptible to crosswind effects due to their lower drag-to-inertia ratio. Additionally, because the high air pressure and volume levels needed for atomizing nozzles are not required in liquid jet spray technologies, the latter act as more streamlined and robust spraying mechanisms that maintain effective control over the rate of LFM application.
An area of similar physics, droplet impingement, has been studied intensively. It was found by several researchers that for droplet impingement on a moving dry smooth surface, splashing behavior is dependent on many parameters including viscosity, density, surface tension and the normal component of the impact velocity14,15. Bird et al. demonstrated that both the normal and tangential velocities were of critical importance16. Range et al. and Crooks et al. have shown that for droplet impingement on a stationary dry surface, surface roughness decreases the splash threshold significantly (i.e., it makes the droplet more prone to splash)17,18.
Despite its practical importance, jet impingement on moving surfaces has received little attention in the academic literature. Chiu-Webster and Lister performed an extensive series of experiments that examined steady and unsteady viscous jet impingement on a moving surface, and the authors developed a model for the steady flow case6. Hlod et al. modeled the flow by means of a third-order ODE on a domain of unknown length under an additional integral condition and compared predicted configurations with experimental results7. However, the Reynolds numbers examined in both of these studies are much lower than those associated with typical railroad LFM applications. Gradeck et al. numerically and experimentally investigated the flow field of water jet impingement onto a moving substrate under various jet velocity, surface velocity, and nozzle diameter conditions8. Fujimoto et al. additionally investigated flow characteristics of a circular water jet impinging onto a moving substrate covered by a thin film of water9. However, these two projects used relatively large nozzle diameters and lower surface and jet velocities compared to those employed in the present work. Furthermore, though previous experimental, numerical, and analytical studies provide a large body of data, the majority have focused on heat transfer parameters rather than on liquid flow processes such as jet splashing behavior. The experimental method provided in the present research thus contributes to liquid jet application technologies by refining such techniques under conditions involving smaller jet nozzle diameters and high-speed jet and surface velocities. The present method also refines knowledge on fundamental fluid mechanics problems associated with moving contact lines.
The studies mentioned above have generally involved the interaction of a low speed jet with a low speed moving surface. There have been comparatively few studies of laminar high speed jet impingement onto high-speed moving surfaces. During high speed liquid jet impaction the jet liquid spreads radially in the vicinity of the impingement location, forming a thin lamella. This lamella is then convected downstream by the viscous forcing imposed by the moving surface, producing a characteristic U-shaped lamella. Keshavarz et al. have reported on experiments employing Newtonian and elastic liquid jets impinging onto high-speed surfaces. They classified impingement processes into two distinct types: &#8220;deposition&#8221; and &#8220;splash&#8221;10. For impingement to be classified as deposition, the jet liquid must adhere to the surface, whereas splash is characterized by a liquid lamella that separates from the surface, and subsequently breaks up into droplets. A third impingement regime has also been described &#8212; &#8220;splatter&#8221;. In this, comparatively rare, regime the lamella remains attached to the surface, as for &#8220;deposition&#8221;, but fine droplets are ejected from near the leading edge of the lamella. In a subsequent study of non-Newtonian fluid effects, Keshavarz et al. concluded that the splash/deposition threshold is mainly determined by the Reynolds and Deborah numbers, whereas the jet impingement angle and jet velocity to surface velocity ratios only have a minor effect11. In experiments conducted under variable ambient air pressures, Moulson et al. discovered that the splash/deposition threshold Reynolds number dramatically increases with decreasing ambient air pressure (i.e., higher ambient pressures make jets more prone to splash), while decreasing ambient air pressure below a certain threshold suppresses splash completely12. This finding strongly suggests that aerodynamic forces acting on the lamella play a crucial role in causing lamella lift-off and subsequent splash. In recent work on high-speed impingement on a high-speed substrate, Sterling showed that for substrate speed and jet conditions close to the splash threshold, splash may be triggered by very small localized surface roughness and minor jet unsteadiness. He also showed that under these conditions lamella lift-off and reattachment is a stochastic process13.
The experimental protocol described here may be used to study other physical situations involving the interaction of a fluid with a moving high speed surface. For example, the same approach could be used to study helicopter blade-vortex interaction (provided that the vortex fluid was colored with tracer particles) and robotic spraying of surfaces.

<table><tbody><tr><td colspan="4">Equipment for Air Cannon Set-Up</td></tr><tr><td>30-gallon air tank</td><td>Steel Fab</td><td>A10028</td><td></td></tr><tr><td>Solenoid actuated poppet valve</td><td>Parker Hannifin Corp.</td><td>#16F24C2164A3F4C80</td><td></td></tr><tr><td>1.5&quot; NPT rubber hose</td><td></td><td></td><td></td></tr><tr><td>Rectangular steel tubing</td><td></td><td></td><td></td></tr><tr><td>Stop mechanism</td><td>Customized</td><td></td><td></td></tr><tr><td>Stainless steel plates</td><td>Customized</td><td></td><td></td></tr><tr><td>Wooden projectile</td><td>Customized</td><td></td><td></td></tr><tr><td>1 kW high-intensity incandescent light</td><td>Photographic Analysis Ltd.</td><td>T986851</td><td></td></tr><tr><td>Light diffuser sheet</td><td></td><td></td><td></td></tr><tr><td>Optic sensor</td><td>BANNER</td><td>SM312LV</td><td></td></tr><tr><td colspan="4">Equipment for Spinning Disc Set-Up</td></tr><tr><td>Motor</td><td>WEG</td><td>TEFC-W22</td><td></td></tr><tr><td>Bearings</td><td></td><td></td><td></td></tr><tr><td>Disk</td><td>Customized</td><td></td><td></td></tr><tr><td>Fiber optic light source</td><td>Fiberoptics Technology Incorporated</td><td>MO150AC</td><td></td></tr><tr><td>High intensity LED array</td><td>Torshare Ltd.</td><td>TF10CA</td><td></td></tr><tr><td>Vacuum</td><td>Ridge Tool Company</td><td>WD09450</td><td></td></tr><tr><td>Interrupter</td><td>Customized</td><td></td><td></td></tr><tr><td colspan="4">Shared Equipment for Both Devices</td></tr><tr><td>Phantom v611 high-speed cine camera</td><td>Vision Research Inc.</td><td>V611</td><td></td></tr><tr><td>Phantom v12 high-speed cine camera</td><td>Vision Research Inc.</td><td>V12</td><td></td></tr><tr><td>Zoom 7000 lens</td><td>Navitar Inc.</td><td>Zoom 7000</td><td></td></tr><tr><td>Zoom 6000 lens</td><td>Navitar Inc.</td><td>Zoom 6000</td><td></td></tr><tr><td>Compressed nitrogen tank</td><td>Praxair Technology, Inc.</td><td></td><td></td></tr><tr><td>Pressure regulator</td><td>Praxair Technology, Inc.</td><td>PRS20124351CGA</td><td></td></tr><tr><td>Hose for compressed nitrogen</td><td>Swagelok Company</td><td>SS-CT8SL8SL8-12</td><td></td></tr><tr><td>Hose for liquid</td><td>Swagelok Company</td><td>SS-7R8TA8TA8</td><td></td></tr><tr><td>Accumulator</td><td>Accumulators, Inc.</td><td>A131003XS</td><td></td></tr><tr><td>Solenoid Valve</td><td>Solenoid Solutions Inc.</td><td>2223X-A440-00</td><td></td></tr><tr><td>Pressure transducer</td><td>WIKA Instruments Ltd</td><td>#50398083</td><td></td></tr><tr><td>Nozzle assembly</td><td>Customized</td><td></td><td></td></tr><tr><td>Glycerin</td><td></td><td></td><td></td></tr><tr><td>Poly(ethylene oxide)</td><td></td><td></td><td></td></tr></tbody></table>

visualization of high speed liquid jet impaction on a moving surface

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds between 0 and 25 m/sec) and a spinning disk device (for examining surface speeds between 15 and 100 m/sec). The air cannon linear traverse is a pneumatic energy-powered system that is designed to accelerate a metal rail surface mounted on top of a wooden projectile. A pressurized cylinder fitted with a solenoid valve rapidly releases pressurized air into the barrel, forcing the projectile down the cannon barrel. The projectile travels beneath a spray nozzle, which impinges a liquid jet onto its metal upper surface, and the projectile then hits a stopping mechanism. A camera records the jet impingement, and a pressure transducer records the spray nozzle backpressure. The spinning disk set-up consists of a steel disk that reaches speeds of 500 to 3,000 rpm via a variable frequency drive (VFD) motor. A spray system similar to that of the air cannon generates a liquid jet that impinges onto the spinning disc, and cameras placed at several optical access points record the jet impingement. Video recordings of jet impingement processes are recorded and examined to determine whether the outcome of impingement is splash, splatter, or deposition. The apparatuses are the first that involve the high speed impingement of low-Reynolds-number liquid jets on high speed moving surfaces. In addition to its rail industry applications, the described technique may be used for technical and industrial purposes such as steelmaking and may be relevant to high-speed 3D printing.

As discussed in the introductory section, the three main behaviors associated with liquid jet impingement are deposition, splatter and splash. These jet impingement behaviors are observed using video data recorded by high-speed cine cameras positioned at various optical points. Examples of still images, obtained from the video recordings, which depict the three liquid jet outcomes are shown in Figure 3. Figure 3A depicts liquid jet deposition, in which the jet flows in a completely strai...

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Visualization of High Speed Liquid Jet Impaction on a Moving Surface

Two experimental devices for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device and a spinning disk device. The apparatuses are used to determine optimal approaches to the application of liquid friction modifier (LFM) onto rail tracks for top-of-rail friction control.

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds ...

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11.4K Views.  University of British Columbia. Two experimental devices for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device and a spinning disk device. The apparatuses are used to determine optimal approaches to the application of liquid friction modifier (LFM) onto rail tracks for top-of-rail friction control.

Video: Visualization of High Speed Liquid Jet Impaction on a Moving Surface

High-speed Particle Image Velocimetry Near Surfaces

Multi-dimensional and transient flows play a key role in many areas of science, engineering, and health sciences but are often not well understood. The complex nature of these flows may be studied using particle image velocimetry (PIV), a laser-based imaging technique for optically accessible flows. Though many forms of PIV exist that extend the technique beyond the original planar two-component velocity measurement capabilities, the basic PIV system consists of a light source (laser), a camera, tracer particles, and analysis algorithms. The imaging and recording parameters, the light source, and the algorithms are adjusted to optimize the recording for the flow of interest and obtain valid velocity data. 
Common PIV investigations measure two-component velocities in a plane at a few frames per second. However, recent developments in instrumentation have facilitated high-frame rate (&gt; 1 kHz) measurements capable of resolving transient flows with high temporal resolution. Therefore, high-frame rate measurements have enabled investigations on the evolution of the structure and dynamics of highly transient flows. These investigations play a critical role in understanding the fundamental physics of complex flows.
A detailed description for performing high-resolution, high-speed planar PIV to study a transient flow near the surface of a flat plate is presented here. Details for adjusting the parameter constraints such as image and recording properties, the laser sheet properties, and processing algorithms to adapt PIV for any flow of interest are included.

A procedure for studying transient flows near boundaries using high-resolution, high-speed particle image velocimetry (PIV) is described here. PIV is a non-intrusive measurement technique applicable to any optically accessible flow by optimizing several parameter constraints such as the image and recording properties, the laser sheet properties, and analysis algorithms.

Multi-dimensional and transient flows play a key role in many areas of science, engineering, and health sciences but are often not well understood. The ...

Fast Imaging Technique to Study Drop Impact Dynamics of Non-Newtonian Fluids

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for detailed observation, scenarios that make it challenging to observe with conventional imaging systems. One of these is the drop impact of liquids, which usually happens within one tenth of millisecond. To tackle this challenge, a fast imaging technique is introduced that combines a high-speed camera (capable of up to one million frames per second) with a macro lens with long working distance to bring the spatial resolution of the image down to 10 &#181;m/pixel. The imaging technique enables precise measurement of relevant fluid dynamic quantities, such as the flow field, the spreading distance and the splashing speed, from analysis of the recorded video. To demonstrate the capabilities of this visualization system, the impact dynamics when droplets of non-Newtonian fluids impinge on a flat hard surface are characterized. Two situations are considered: for oxidized liquid metal droplets we focus on the spreading behavior, and for densely packed suspensions we determine the onset of splashing. More generally, the combination of high temporal and spatial imaging resolution introduced here offers advantages for studying fast dynamics across a wide range of microscale phenomena.

Drop impact of non-Newtonian fluids is a complex process since different physical parameters influence the dynamics over a very short time (less than one tenth of a millisecond). A fast imaging technique is introduced in order to characterize the impact behaviors of different non-Newtonian fluids.

In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for ...

Three-dimensional Particle Tracking Velocimetry for Turbulence Applications: Case of a Jet Flow

3D-PTV is a quantitative flow measurement technique that aims to track the Lagrangian paths of a set of particles in three dimensions using stereoscopic recording of image sequences. The basic components, features, constraints and optimization tips of a 3D-PTV topology consisting of a high-speed camera with a four-view splitter are described and discussed in this article. The technique is applied to the intermediate flow field (5 &#60;x/d &#60;25) of a circular jet at Re &#8776; 7,000. Lagrangian flow features and turbulence quantities in an Eulerian frame are estimated around ten diameters downstream of the jet origin and at various radial distances from the jet core. Lagrangian properties include trajectory, velocity and acceleration of selected particles as well as curvature of the flow path, which are obtained from the Frenet-Serret equation. Estimation of the 3D velocity and turbulence fields around the jet core axis at a cross-plane located at ten diameters downstream of the jet is compared with literature, and the power spectrum of the large-scale streamwise velocity motions is obtained at various radial distances from the jet core.

A three-dimensional particle tracking velocimetry (3D-PTV) system based on a high-speed camera with a four-view splitter is described here. The technique is applied to a jet flow from a circular pipe in the vicinity of ten diameters downstream at Reynolds number Re &#8776; 7,000.

3D-PTV is a quantitative flow measurement technique that aims to track the Lagrangian paths of a set of particles in three dimensions using stereoscopic ...

Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions

Two different experimental methods for determining the threshold of particle motion as a function of geometrical properties of the bed from laminar to turbulent flow conditions are presented. For that purpose, the incipient motion of a single bead is studied on regular substrates that consist of a monolayer of fixed spheres of uniform size that are regularly arranged in triangular and quadratic symmetries. The threshold is characterized by the critical Shields number. The criterion for the onset of motion is defined as the displacement from the original equilibrium position to the neighboring one. The displacement and the mode of motion are identified with an imaging system. The laminar flow is induced using a rotational rheometer with a parallel disk configuration. The shear Reynolds number remains below 1. The turbulent flow is induced in a low-speed wind tunnel with open jet test section. The air velocity is regulated with a frequency converter on the blower fan. The velocity profile is measured with a hot wire probe connected to a hot film anemometer. The shear Reynolds number ranges between 40 and 150. The logarithmic velocity law and the modified wall law presented by Rotta are used to infer the shear velocity from the experimental data. The latter is of special interest when the mobile bead is partially exposed to the turbulent flow in the so-called hydraulically transitional flow regime. The shear stress is estimated at onset of motion. Some illustrative results showing the strong impact of the angle of repose, and the exposure of the bead to shear flow are represented in both regimes.

Two different methods for characterizing the incipient particle motion of a single bead as a function of the sediment bed geometry from laminar to turbulent flow are presented.

Two different experimental methods for determining the threshold of particle motion as a function of geometrical properties of the bed from laminar to ...

Film Control to Study Contributions of Waves to Droplet Impact Dynamics on Thin Flowing Liquid Films

Droplet impact is a very common phenomenon in nature and attracts attention due to its aesthetic fascination and wide-ranging applications. Previous studies on flowing liquid films have neglected the contributions of spatial structures of waves to the impact outcome, while this has recently been shown to have a significant influence on the drop impact dynamics. In this report, we outline a step-by-step procedure to investigate the effect of periodic inlet forcing of a flowing liquid film leading to the production of spatiotemporally regular wave structures on drop impact dynamics. A function generator in connection with a solenoid valve is used to excite these spatiotemporally regular wave structures on the film surface while the impact dynamics of uniform-sized droplets are captured using a high-speed camera. Three distinct regions are then studied; viz. the capillary wave region preceding the large wave peak, the flat film region, and the wave hump region. The effects of important dimensionless quantities such as film Reynolds, drop Weber and Ohnesorge numbers parameterized by the film flow rate, drop speed, and drop size are also examined. Our results show interesting, hitherto undiscovered dynamics brought about by this application of film inlet forcing of the flowing film for both low and high inertia drops.

A protocol to study the contributions of waves to droplet impact dynamics on flowing liquid films is presented.

Droplet impact is a very common phenomenon in nature and attracts attention due to its aesthetic fascination and wide-ranging applications. Previous ...

Impacts of Free-falling Spheres on a Deep Liquid Pool with Altered Fluid and Impactor Surface Conditions

Vertical impacts of spheres on clean water have been the subject of numerous water entry investigations characterizing cavity formation, splash crown ascension and Worthington jet stability. Here, we establish experimental protocols for examining splash dynamics when smooth free-falling spheres of varying wettability, mass, and diameter impact the free surface of a deep liquid pool modified by thin penetrable fabrics and liquid surfactants. Water entry investigations provide accessible, easily assembled and executed experiments for studying complex fluid mechanics. We present herein a tunable protocol for characterizing splash height, flow separation metrics, and impactor kinematics, and representative results which might be acquired if reproducing our approach. The methods are applicable when characteristic splash dimensions remain below approximately 0.5 m. However, this protocol may be adapted for greater impactor release heights and impact velocities, which augurs well for translating results to naval and industry applications.

This protocol demonstrates the basic experimental configuration for water entry experiments with free-falling spheres. Methods for the alteration of liquid surface with penetrable fabrics, the preparation of chemically non-wetting spheres, and steps for splash visualization and data extraction are discussed.

Vertical impacts of spheres on clean water have been the subject of numerous water entry investigations characterizing cavity formation, splash crown ...

High Throughput Analysis of Liquid Droplet Impacts

Experimental studies of liquid drop impacts on surfaces are often restricted in their scope due to the large range of possible experimental parameters such as material properties, impact conditions, and experimental configurations. Compounding this, drop impacts are often studied using data-rich high-speed photography, so that it is difficult to analyze many experiments in a detailed and timely manner. The purpose of this method is to enable efficient study of droplet impacts with high-speed photography by using a systematic approach. Equipment is aligned and calibrated to produce videos that can be accurately processed by a custom image processing code. Moreover, the file structure setup and workflow described here ensure efficiency and clear organization of data processing, which is carried out while the researcher is still in the lab. The image processing method extracts the digitized outline of the impacting droplet in each frame of the video, and processed data are stored for further analysis as required. The protocol assumes that a droplet is released vertically under gravity, and impact is recorded by a camera viewing from side-on with the drop illuminated using shadowgraphy. Many similar experiments involving image analysis of high-speed events could be addressed with minor adjustment to the protocol and equipment used.

This protocol enables efficient collection of experimental high-speed images of liquid drop impacts, and speedy analysis of those data in batches. To streamline these processes, the method describes how to calibrate and set up apparatus, generate an appropriate data structure, and deploy an image analysis script.

Experimental studies of liquid drop impacts on surfaces are often restricted in their scope due to the large range of possible experimental parameters ...

A Microfluidic System with Surface Patterning for Investigating Cavitation Bubble(s)&#8211;Cell Interaction and the Resultant Bioeffects at the Single-cell Level

In this manuscript, we first describe the fabrication protocol of a microfluidic chip, with gold dots and fibronectin-coated regions on the same glass substrate, that precisely controls the generation of tandem bubbles and individual cells patterned nearby with well-defined locations and shapes. We then demonstrate the generation of tandem bubbles by using two pulsed lasers illuminating a pair of gold dots with a few-microsecond time delay. We visualize the bubble-bubble interaction and jet formation by high-speed imaging and characterize the resultant flow field using particle image velocimetry (PIV). Finally, we present some applications of this technique for single cell analysis, including cell membrane poration with macromolecule uptake, localized membrane deformation determined by the displacements of attached integrin-binding beads, and intracellular calcium response from ratiometric imaging. Our results show that a fast and directional jetting flow is produced by the tandem bubble interaction, which can impose a highly localized shear stress on the surface of a cell grown in close proximity. Furthermore, different bioeffects can be induced by altering the strength of the jetting flow by adjusting the standoff distance from the cell to the tandem bubbles.

A microfluidic chip was fabricated to produce pairs of gold dots for tandem bubble generation and fibronectin-coated islands for single-cell patterning nearby. The resultant flow field was characterized by particle image velocimetry and was employed to study various bioeffects, including cell membrane poration, membrane deformation, and intracellular calcium response.

In this manuscript, we first describe the fabrication protocol of a microfluidic chip, with gold dots and fibronectin-coated regions on the same glass ...

Bioengineering

Visualization of Flow Past a Bluff Body

Source: Ricardo Mejia-Alvarez, Hussam Hikmat Jabbar and Mahmoud N. Abdullatif, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
Owing to the non-linear nature of its governing laws, fluid motion induces complicated flow patterns. Understanding the nature of these patterns has been the subject of intense scrutiny for centuries. Although personal computers and supercomputers are extensively used to deduce fluid flow patterns, their capabilities are still insufficient to determine the exact flow behavior for complex geometries or highly inertial flows (e.g. when momentum dominates over viscous resistance). With this in mind, a multitude of experimental techniques to make flow patterns evident have been developed that can reach flow regimes and geometries inaccessible to theoretical and computational tools.
This demonstration will investigate fluid flow around a bluff body. A bluff body is an object that, due to its shape, causes separated flow over most of its surface. This is in contrast to a streamlined body, like an airfoil, which is aligned in the stream and causes less flow separation. The purpose of this study is to use hydrogen bubbles as a method of visualizing flow patterns. The hydrogen bubbles are produced via electrolysis using a DC power source by submerging its electrodes in the water. Hydrogen bubbles are formed in the negative electrode, which needs to be a very fine wire to ensure that the bubbles remain small and track fluid motion more effectively. This method is suitable for steady and unsteady laminar flows, and is based on the basic flow lines that describe the nature of the flow around objects. [1-3]
This paper focuses on describing the implementation of the technique, including details about the equipment and its installation. Then, the technique is used to demonstrate the use of two of the basics flow lines to characterize the flow around a circular cylinder. These flow lines are used to estimate some important flow parameters like flow velocity and the Reynolds number, and to determine flow patterns.

Flow Around a Bluff Body, Bubbles and Von Karman Vortex Street

Source: Ricardo Mejia-Alvarez, Hussam Hikmat Jabbar and Mahmoud N. Abdullatif, Department of Mechanical Engineering, Michigan State University, East ...

JoVE Science Education

Jet Impinging on an Inclined Plate

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
The goal of this experiment is to demonstrate how a fluid flow exerts forces on structures by conversion of dynamic pressure into static pressure. To this end, we will make a plane jet impinge on a flat plate and will measure the resulting pressure distribution along the plate. The resultant force will be estimated by integrating the product between the pressure distribution and appropriately defined area differentials along the surface of the plate. This experiment will be repeated for two angles of inclination of the plate with respect to the direction of the jet and two flow rates. Each configuration produces a different pressure distribution along the plate, which is the result of different levels of conversion of dynamic pressure into static pressure at the plate's surface.
For this experiment, pressure will be measured with a diaphragm pressure transducer connected to a scanning valve. The plate itself has small perforations called pressure taps that connect to the scanning valve through hoses. The scanning valve sends the pressure from these taps to the pressure transducer one at a time. The pressure induces mechanical deflection on the diaphragm that the pressure transducer converts into voltage. This voltage is proportional to the pressure difference between the two sides of the diaphragm.

Jet Impinging and Conversion of Dynamic Pressure into Static Pressure

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
The goal of this ...