observing fluid flows in microgravity using ddpiv

Observing Fluid Flows in Microgravity using DDPIV

The Caltech Student Microgravity Initiative 2010

Caltech1200 E. California Boulevard

Pasadena, CA 91125

Designated Team Contact: Erin Zampaglione, [email protected], 626-395-XXXX

Faculty Supervisor: Dr. Morteza Gharib, [email protected], 626-395-4453Additional Support: Dr. Eugene Trihn, [email protected], 818-354-5359

Team:

Eric Chin Flyer Sr, CNS* [email protected] Forbes Flyer Sr, Physics [email protected]. Max Jones Flyer Sr, Physics [email protected] Kuo Flyer Jr, MechE [email protected] Obenshain Flyer Sr, CS, English [email protected] Zampaglione Flyer Jr, Biology [email protected]

*Computational and Neural Systems

I, Morteza Gharib, approve of this proposal. X___________________

mailto:[email protected]









NASA Microgravity University 2

Table of Contents

Cover Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Flight Week Preference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Test Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Test Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Experiment Safety Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Outreach Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Institutional Letter of Endorsement

From Caltech President Dr. Jean-Lou Chameau . . . . . . . . . . . . . . . . . . . . . . . . . 20

From Caltech Dean of Students Dr. John Hall . . . . . . . . . . . . . . . . . . . . . . . . . . .21

Statement of Supervising Faculty

From Dr. Morteza Gharib, Caltech Professor . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

From Dr. Eugene Trinh, JPL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Funding/Budget Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24


Flight Week Preference

We would prefer to fly in Flight Week 2 (7/08/2010 – 7/17/2010), rather than Flight Week 1 (06/17/2010 to 06/26/2010), but we’re flexible.


Abstract

We will examine the fluid flow caused by the coalescence of a droplet onto the top of a flat surface of a fluid. When the droplet has a large surface tension and minimal velocity as it contacts the surface, corresponding to a low Weber number, a vortex ring is formed upon coalescence. The three dimensional velocity field of the drop and the surface during this process will be quantitatively determined using defocusing digital particle image velocimetry (DDPIV). When this experiment is done under 1 G conditions, it is impossible to separate out the effects of surface tension and gravity. Performing this experiment in microgravity allows us to observe this process in a regime where the influence of surface tension dominates that of gravity.


Test Objectives

We aim to quantitatively describe fluid flows created when a drop of fluid coalesces with a flat surface of the same liquid, particularly in the vortex-forming regime. In doing so, we hope to demonstrate the effectiveness of DDPIV in a microgravity environment.

This experiment is not a follow-up to a previous RGSFOP experiment, although it is closely related to Dooley 1997, in which a drop of water is observed as it coalesces with a surface at zero velocity in 1 G. Dimensional analysis of that situation, with the goal of describing the time scale of vortex ring formation, yields three dimensionless quantities. These quantities respectively correspond to the effects of viscosity, gravity, and surface tension. Assuming that surface tension effects dominate gravity and viscosity, one can conclude that the time scale is related to the surface tension by a simple power law. The results of the 1997 experiment nearly adhere to this, but there is a clear systematic deviation. We hypothesize that in a microgravity environment, the power law would describe this relation much more precisely.


Test Description

We're planning on observing the fluid flow caused by the coalescence of a droplet onto a flat surface of the same fluid. In order to accomplish this in the microgravity environment, the flat surface will be at the interface between two immiscible liquids. The liquids will be contained in one of five relatively small plexiglass containers, filled nearly completely. The composition of these liquids has yet to be decided, but they are likely to be composed of some combination of water, glycerin, corn oil, and isopropyl alcohol. The oil would be immiscible with any mixture of the other liquids. Using the same fluid contained in the lower stratum, drops will be formed from a pipette tip fixed to the top of the container. These will be attached via tubing to a separate box containing plungers, one per plexiglass cell (Figure 1).

The precise method of controlling the plungers has not yet been determined. In all cases, we would have a single button or switch that would trigger the formation of a drop, and the recording of its coalescence with the DDPIV system (see below). Possibilities include experimentally determining a set length of time necessary for each motor to run to produce a drop that will just touch the interface between the two immiscible fluids. This method would require the height of each stratum to be precisely calibrated in all trials, which may prove rather difficult. Another possible method is to complete a circuit by the contact of the drop with the lower stratum.

The velocity field of the fluids will be mapped using a technique called defocusing digital particle image velocimetry (DDPIV) in which small reflective particles are placed in the fluid, illuminated with a laser, and filmed with a high-speed camera. From this we can reconstruct the 3-D velocity field using commercially available software. This method is remarkable in that it is able to view the situation in three dimensions with only one camera. Ideally the camera will be able to interface with a laptop via USB, which will allow in-situ analysis after each trial.

The work of Dooley 1997 examined the coalescence of water drops onto a flat surface formed by a water-air interface. In that situation, the authors assert that the potentially important physical parameters in the problem are surface tension σ, density ρ, time scale of vortex-ring formation τ*, the gravitational acceleration g, the viscosity ν, and a characteristic length scale of the drop L. From these, one can form three dimensionless parameters: (ν τ* / L2), (gτ*

2/L), and (σ τ*2 / ρ L3). For the experiment

described in Dooley 1997, one may well expect that the effects of surface tension dominate both gravity and viscosity. As such, one could theoretically relate surface

Figure 1: This is a wire frame picture of the assembly. The camera and holes for tubing are not included, as we are unsure of their dimensions. The camera will go on the block suspended on the two bars and the tubing will go in holes on the top of the containers. Slots may also be added to the main base for the cargo straps for take off and landing.


tension and time scale by a power law, assuming constant density and drop size. The data (figure 4 of Dooley) fits approximately, but suggests that the other parameters have a non-negligible influence.

In our experiment, we will be able to directly compare results between 1G and microgravity environments, leaving everything else in the experiment unchanged – namely surface tension, densities, drop sizes and viscosities. Not only will we be able to observe the effect of gravity on the relation between surface tension and time scale, but also we will be able to directly observe the difference in velocity fields.


References

Anilkumar, AV, et al. “Surface-Tension-Induced Mixing following Coalescence of Initially Stationary Drops.” Phys. Fluids A 3(11) (1991): 2587-91

Dooley, BS, et al. "Vortex Ring Generation Due to the Coalescence of a Water Drop at a Free Surface." Experiments in Fluids 22.5 (1997): 369-74.

Graff, EC, and M Gharib. "Performance Prediction of Point-Based Three-Dimensional Volumetric Measurement Systems." Measurement Science and Technology 19.7 (2008): 75403-500.

Lu, J, et al. "Three-Dimensional Real-Time Imaging of Cardiac Cell Motions in Living Embryos." Journal of Biomedical Optics 13 (2008): 014006.

Pereira, F, et al. "Microscale 3d Flow Mapping with DDPIV." Experiments in Fluids 42.4 (2007): 589-99.


Experiment Safety Evaluation

Flight Manifest

Primary Fliers: Eric ChinJohn ForbesW. Max JonesCalvin KuoDaniel ObenshainErin Zampaglione

Experiment Description / Background

We will examine the fluid flow caused by the coalescence of a droplet onto the top of a flat surface of a fluid. When the droplet has a large surface tension and minimal velocity as it contacts the surface, corresponding to a low Weber number, a vortex ring is formed upon coalescence. The three dimensional velocity field of the drop and the surface during this process will be quantitatively determined using defocusing digital particle image velocimetry (DDPIV). When this experiment is done under 1 G conditions, it is impossible to separate out the effects of surface tension and gravity. Performing this experiment in microgravity allows us to observe this process in a regime where the influence of surface tension dominates that of gravity.

Equipment Description:

The proposed fluid experiment will require one independent test per microgravity experience during a flight. The equipment was thus designed to contain several independent test chambers that could be switched out instead of having one test chamber that would have to be reset and recalibrated for each test. One benefit of having multiple independent test chambers were that recalibrating a single test chamber for a multitude of different tests would be time consuming, and given the short periods between microgravity experiences during a flight, such long recalibration times would reduce the number of tests that we would be able to complete during one flight. Another benefit for having independent test chambers was that if one test chamber became contaminated or malfunctioned, then it would not comprise me entire experiment (just that one trial), whereas with one test chamber, if there was a mechanical problem or contamination, then it would potentially jeopardize the entire experiment.

Our experiment is also sensitive to vibrations from the aircraft, so the equipment needed to be designed in order to minimize such unwanted flight movements. Thus, the experimental apparatus is designed on top of a platform designed to minimize movements in the plane parallel to the floor of the aircraft. Thus full test apparatus is shown in figure 1. Each component of the proposed apparatus will also be explained in more detail.

Figure 1 depicts the entire apparatus for our experiment

The experimental apparatus is split into three distinct sections. The first section is the suspension system described earlier (figure 2). The suspension system will support the base plate and all the experimental components and damp the vibrations of the aircraft. The suspension is comprised of two sets of parallel bars set perpendicular to each other. Each set is designed to provide suspension in one axis (the x or the y axis parallel to the floor of the aircraft) in order to minimize vibrations from the aircraft. The sets of bars are connected by sliders that will slide along the x-directional suspension bars

while supporting the y-directional bars as shown. The suspension system has four feet that are designed to be bolted to the aircraft floor using the 3/8 inch diameter bolts provided. Each foot has two legs where a bolt will be secured to the aircraft floor, and each foot will be bolted 40 inches away from its closest neighbors as shown in figure 2. The springs used to provide the damping for the vibrations of the aircraft as of now are 12 inches in length. The springs will be further constrained in order to ensure that the edges of the base plate will not go beyond the perimeter defined by the feet of the apparatus (for safety reasons, the entire apparatus will be confined to the area defined by the feet of the apparatus). The final pieces in the suspension system are the base plate holders, which will support the base plate. The base plate holders will also be able to slide along the y-directional suspension bars, thus allowing the entire system to provide a 2-dimensional suspension solution for the base plate and the experimental apparatus.

Figure 2: 2-dimensional suspension system

The second part of the experimental setup is the base plate that sits on top of the suspension system (figure 3). The base plate will have #8-32 tapped holes spaced 6 inches apart in a 36 inch square grid. We decided upon such a configuration so that the apparatus could be as versatile as possible. The base plate will be able to support a wide variety of experimental components that we can switch out in order to perform different experiments, instead of switching out the entire apparatus. This allows us to perform experiments that might require different hardware components while in midflight, so long as the components are compatible with the base plate. The entire base plate will be 42 inches square and will be constrained by the suspension system to remain within the 54 inch square perimeter set by the suspension feet. During take-off and landing procedures, the base plate will be strapped down further in order to keep it stable. The straps will also provide extra support during the periods of increased accelerations that are expected

during the take-off and landing procedures. Handles for the straps will be placed at the midpoint along the sides of the base plate.

Figure 3: Base plate

The final piece of the system comprises all of the experimental components that will be used for the flight. Specifically modeled here are the fluid containers and the camera support. We expect to also add components to control the droplets in each container and an interface for user input. The container component (figure 4) is actually series of 5 fluid containers at 7 inches cubed each. Each container will also have an input on the top where the syringe mechanisms that will create the droplets can be applied. The camera apparatus (figure 5) will allow the camera to traverse from container to container in order to provide data for each experiment as they are done. Notice that each of these components are designed to fit onto the base plate with screw holes placed in line with those on the base plate. Other components will be designed similarly.

Figure 4: Fluid Container

Figure 5: Camera Apparatus

As a final note, all the components for our experimental setup were designed in Solidworks 2005 under a California Institute of Technology license.

Structural Design:

We will be constructing the experimental setup out of cast alloy steel, 1060 alloy aluminum, and medium-high impact acrylic. These materials were defined in Solidworks 2005 and the properties that the program lists are in table 1:

Material: Cast Alloy Steel1060 alloy Aluminum

Medium-High impact Acrylic

Elastic Modulus (lb/in^2) 2.76E+07 1.00E+07 348091Poissons Ratio

0.26 0.33 0.35Shear Modulus (lb/in^2) 1.13E+07 3.92E+06 129084Thermal Expansion Coefficient 1.50E-05 2.40E-05 5.20E-05Density (lb/in^3)

0.263729 0.0975439 0.0433527Thermal Conductivity (W/mK) 38 200 0.21Specific Heat (J/kgK)

440 900 1500Table 1: Properties of proposed materials

The cast alloy steel will mostly be used in the suspension system, which takes the highest loads because it has to support the entire experimental apparatus. The acrylic is used for the base plate as well as in experimental components that require a transparent material (fluid containers). The aluminum is also mostly used in experimental components as well. The setup will also require a variety of steel screws. The design thus far only implements #8-36 and #10-32 screws. The properties for these screws are provided in table 2 from McMaster Carr assuming a 1 inch length screw.

Screw Type:Rockwell Hardness

Minimum Tensile Strength (psi) Thread Fit ASTM Specification

#8-36 Minimum C39 180,000 Class 3A ASTM A574#10-32 Minimum C39 180,000 Class 3A ASTM A574

Table 2: Properties of screws used

The entire apparatus will be bolted to the aircraft floor using the 3/8 inch bolts that are specified by NASA. We will also use 4 cargo straps to further secure the base

plate and keep it stable during take-off and landing because of the higher expected accelerations.

Electrical System

We will use a motorized injection system to produce drops. Appropriate signals (either preprogrammed or according to a feedback system) will be generated using a PIC microcontroller signaling a PWM motor driver. Feedback system (if used) may rely on changes in resistance across a drop-surface liquid bridge as in Dooley 1997. Both initiation of drop formation and image acquisition may be triggered either manually or via accelerometer.

Microcontrollers will run on 5VDC; motor drivers will run off of the supplied 28VDC. Computers and cameras will either run on 120VAC provided or internal batteries.

Pressure / Vacuum System

No Pressure/Vacuum Systems included in this experiment.

Laser System

We plan to use one laser, class 3a or lower rating, for the purpose of illuminating the particles used for DDPIV.

Crew Assistance Requirements

The experiment is fairly self-contained and we expect the operation to be mostly digital. Thus, we will probably not need any help from the in flight crew. The flight crew might be required to help us switch out some of the experimental components on the base plate. We will need the ground crew to help us install the apparatus in the aircraft.

Institutional Review Board (IRB)

No human test subjects, animal test subjects, and/or biological substances will be used in this experiment.

Hazard Analysis:

We will design the experimental apparatus to the best of our ability such that it will not fail. However, we have conceived two failure scenarios that would compromise experimental integrity and safety of the cabin crew. The first scenario involves a fluid leak in one of the compartments. If such a leak does occur, then we will lose the data for that particular test; however the remainder of the test can still be performed. The free

liquid could; however, compromise on board systems unless it is contained properly and prove to be a mild safety hazard for the cabin crew. We do not plan to use toxic fluids in any of our experiments, however, the fluids might make conditions in the cabin more slippery.

The second scenario we have envisioned involves the failure of a part in the suspension system. Such a scenario would result in the entire experimental apparatus becoming unstable and potentially separating from the base parts that hold the suspension to the aircraft floor. Such loose equipment would prove to be a hazard to both the aircraft and the cabin crew, as the base plate and the experimental apparatus are expected to be over 100lbs and could either damage the aircraft or injure the in-flight crew.

Again, we will be designing the experimental apparatus with as much structural integrity as possible to ensure that neither scenario will occur and to ensure the general safety of the in flight crew and the aircraft.

Tool Requirements

We expect to be using many off the shelf tools in order to secure mechanical devices. We will require hex screwdrivers to secure the screws in the device and wrenches to secure components in the device. We will also require a drill to make adjustments to the apparatus if necessary and a soldering iron to make electrical adjustments.

Ground Support Requirements

We would ask Ground Support for storage space for the liquids that we will be loading onto our experiment, which will possibly include water, glycerin, and corn oil.

Hazardous Materials

It is possible that we could use standard fluorescing dye, such as fluorescein, in order to perform the DDPIV. Fluroescein is hazardous if it comes in contact with skin, or is ingested. However, there are alternative (and highly preferred) possibilities for DDPIV tracking, such as Molecular Probes ® FluoSpheres.

Procedures:

Ground Operations: While on the ground, we propose to construct the designed apparatus and then perform the tests that we will be performing in flight to ensure that the mechanisms work in the allotted 20 seconds of microgravity. The apparatus as it is designed will lower a pipette to the fluid interface and then release a small droplet onto the interface. This process is completely automated and should not take longer than 10 seconds. The remaining 10 seconds will be used to observe the interactions between the droplet and the fluid layer using a high speed camera that will record data from the DDPIV particles suspended in the fluids. The droplet coalescence should take no more

than 5 seconds and thus, one droplet test can be conducted within the time frame of the microgravity experience in flight.

Once we have repeatedly tested the system to ensure that it will consistently operate in the time frame given, we will perform the several test regimens with different fluids in order to obtain 1g data that we can use to compare to the microgravity data and to determine which fluid combinations will be best to test in a microgravity environment. With 30 parabolic arcs in a single flight, we will plan on having at least 25 fluid combination tests to perform in microgravity.

Pre-Flight: During the pre-flight stage, we will first fill all of the fluid containers with the fluid combinations that we have determined during ground testing. These fluid containers will be stored in the larger container (46.5 x 22.5 x 17.5 as specified in the Interface Control Document AOD 33912) in preparation for take-off so that the base plate will not have as great a load during the high acceleration period. We will then secure the apparatus to the base of the aircraft and also attach the straps that will be used during take-off. Other experimental components will also be attached to the base plate once the suspension system is secured and ready for take-off.

In-Flight: There are 4 phases that were specified during the parabolic flight. For the purposes of this proposal, the first part of the parabolic flight will be the apex of the curve, where the aircraft will begin its freefall back to earth. During this period, the in flight crew will prepare to initiate the experiment while the ground crew ensures that all the systems are operational. Experimental data cannot be obtained during this section of the flight curve because the gravity will vary between 0 and 1.8g's ("dirty air") and will not provide any useful data.

The second phase of the parabolic flight path will be defined as the free fall back to earth, where microgravity is experienced. During this time, the experiment will be initiated. The syringe within thee fluid container will be lowered to the fluid interface and a droplet will be released. The coalescence will then be recorded by the camera and the data will be transmitted to storage by either an onboard computer or a ground based linked computer. One test should take no longer than 20 seconds, which is the amount of time that microgravity is expected to last.

The third phase of the parabolic flight will be defined as the bottom of the arc, where the aircraft will begin its climb back to the top of the parabola. During this time, the ground crew of the flight crew will confirm the success or failure of that particular test and ensure that the data collected is properly stored.

The final stage of the parabolic arc is the climb back to the top. During this time, a period of approximately 1.8g's is experienced, and thus experimental data will not be collected. This time will be used to set up the next test for the next period of microgravity. To do this, the commands for the next fluid test container will be initiated and readied while the camera will move to the appropriate container in order to collect data. This time will also be used by the flight crew to switch out test container apparatus if necessary in order to perform the next set of tests. The ground crew meanwhile will briefly analyze the data in order to advise the flight crew as to which tests should be

performed and what adjustments, if any, to either the hardware or the software needs to be made. Once the aircraft has completed its climb, the next test should be set up and ready to go.

The aircraft will undergo 30 parabolic flights, so the above-mentioned procedure will be repeated 25-30 times depending on how many tests we are able to setup (we presume that a majority of the flight crew will be trying to cope with the changes in acceleration during the first few parabolic arcs).

Outreach Plan

We have a blog, currently hosted at http://csmi2010.wordpress.com/. This will provide a means for students who are interested in following our progress to do so.

Our main target audience for outreach will be local high school students. We have contacted Arcadia High School, Maranatha High School, Polytechnic School, and Pasadena High School. We have also contacted the California Science Center Museum. We will be working with the Caltech Educational Outreach office to find even more opportunities for outreach.

Our objective is to provide the students with a more concrete understanding of basic scientific principles, such as free fall, intermolecular forces in polar and nonpolar liquids, and the importance of observation and the scientific method.

We plan to accomplish this by small-scale presentations at multiple schools and other venues. We would have three potential presentations, which we would give at times that would be convenient for the teachers involved.

From January to February, we would provide the students with a discussion of gravity and free fall. This is a very common area for misconceptions, and is the focus of a number of the California State science content standards in physics. The discussion in this case could follow a pattern wherein a team member poses a question which may be the source of some confusion (e.g. “Why do objects on Earth fall with the same acceleration?”, “How does that acceleration compare to objects near the moon?”, and “Why do objects in free fall feel weightless, despite still feeling a gravitational force?”).

From February to March, we would present the students with a demonstration of fluid dynamics. The general setup would include a container of some sort – likely the size of a small fishtank, and a high-speed camera. The phenomenon of vortex-ring generation, which is the object of our scientific study, can be qualitatively demonstrated with a drop of milk and a container of water. The vortex ring could be viewed in slow motion, thereby showing an analog of the experiment we would actually be carrying out. If the fluid is sufficiently viscous (e.g. corn oil or a water-glycerin mixture), the phenomenon of terminal velocity could be easily demonstrated. This is a prime application of Newton's Second Law – namely that an object experiencing no net force will experience no acceleration, yet may have a nonzero velocity. With the addition of a small amount of dye or a small number of tracer particles, it may be possible to view turbulent flows, the effect of various-size objects traveling through the fluid, or convective flows.

From March to May, we would bring our finished experimental apparatus to the schools in order to demonstrate collection of the 1 G control data. We would discuss the importance of the scientific method, in particular the ideas of control, repeatability, and designing an experiment to test a hypothesis.

http://csmi2010.wordpress.com/

Institution’s Letter of Endorsement

From the President

Institution’s Letter of Endorsement

From the Dean


From Dr. Morteza Gharib


From Dr. Eugene Trinh

Funding/Budget Statement

Mechanical PartsPlexiglass - $200Aluminum - $100Machine Shop - $1000Misc. parts and labor - $700

Electrical PartsLaser - $200Computer - $1000Optics - $1000Camera - $5000Misc. parts - $500

Travel and ExpensesPlane tickets? - $3000Alternatively: Car and gas - $1000Shipping - $500Lodging - $1500

TOTAL - approx. $13000

Potential Funding SourcesCaltech EAS DivisionSpace Grant

observing fluid flows in microgravity using ddpiv

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