Today I began to look at von
Karman vortex streets. This pattern was developed by Theodore von
Karman. When an obstacle interrupts a constant flow, this street of
organized eddies forms. It is most commonly seen in cloud patterns
around islands. I found many pictures of these clouds, marine
stratocumulus, forming a von Karman vortex street around an
island. In this picture (
von Karman vortices over Broutona ) the wind is blowing from the
upper right of the picture to the lower left. The clouds are moving
along the direction of wind flow. When the flow is interrupted by the
island, the vortex street appears. The rotational velocity of the
vortices decreases as they move downstream. I noticed a similar
vortex stream when I introduced a toothpick into the soap flow. I am
hoping to find a way to relate these cloud patterns and the patterns I
witnessed in the soap film.
Later in the day... I thought of some interesting ways to relate the soap film vortex street to the cloud vortex street on the NASA pages that I was looking at. My idea was that I would poke the soap film with a toothpick and photograph the von Karman vortex street caused by the introduction of the obstacle in the flow. Then, I could change the velocity, temperature, position of the obstacle, etc. and observe how the vortex street changes. There may be a way for me to calculate how much energy the individual eddies are losing as they propagate down the stream with each of the individual conditions. Then, I hope I can relate this to the cloud patterns. If I find out what weather conditions were present at the time of the picture, I may be able to simulate the vortex street from each of the islands that I have found pictures of (Guadalupe Island, Broutona Island, and the Canary Islands). I am going to spend the rest of day researching weather conditions on each of these islands and learning more about Laser Doppler Velocimetry so I will be able to measure the velocity of the soap film.
Figure 1. This is a video of a von Karman vortex street.
I spent the day summarizing
some of the things that I have been researching for the last few days.
I looked over Thin Film Interference, and I understand the way in
which the light is reflected on two surfaces. The first surface, the
air-film interface, and then again at the film-air interface. I wrote
down the formulas for calculating the thickness of the film from the
interference fringes so I will have them when I want to find the
thickness of the soap film. Since I have been thinking about
interference patterns, I need a way to illuminate the film to make it
ideal for photographing it. I found this good site that has a very
detailed picture for diffusing the light and recording the film
Lighting a Soap Film ). I hope I can find a way to relate the von
Karman vortex street that I was looking at yesterday and the thickness
of the film that I can calculate by interference fringes in a way that
shows the practical aspect of analyzing fluid flow. The Simons Brown
Bag lunch speaker was Kim Auletta from the Environmental Health
and Safety Department.
I found this detailed
article that summarizes the soap film device that Maarten Rutgers and
his colleagues use at Ohio State University (
Conducting fluid dynamics experiments with vertically falling soap
films ) This article discusses many different methods of measuring
the velocity and thickness of the soap films. When I begin
experimentation, I think these methods will be important to look at
and consider. It also outlines the exact setup of their soap film
apparatus. The article has caused me to think of some of the ways that
I can fix my soap film device to minimize all variables that may
affect experimentation. Rutgers has built a vacuum around his setup
to eliminate the effects of air currents on the soap flow. He also
regularly replaces his soap solution and uses only stainless steel and
Teflon products to pump the solution for recycling.
Today I finished reading QED:
The Strange Theory of Light and Matter by Feynman. I thought he
approached the topic well by relating many complex ideas to things
that are understandable and are witnessed everyday.
I looked at Feynman's lecture series and read about fluid flows, viscosity, and different vortex patterns. The pattern I want to look at, a von Karman vortex street, exists only at a Reynolds number > 40. I also found some good sites to search for journal articles. (Science Direct and Ingenta)
I organized a list of all my references in the back of my notebook because I know that I soon will be writing a research paper. Dr. Noe also showed me where my soap film device is so when I want to begin work I have a room to work in. I have decided what I am initially going to do for my project. I am going to introduce a fixed rod into the soap flow and look at the vortex street. Then, I am going to vary the flow rate and observe the change in the shedding of the vortices. Another variable that I may use to look at the changes in the vortex street is viscosity. I can do this by adding glycerine to the soap solution or changing the temperature of the solution. I attended the weekly Simons Brown Bag lunch today. Undergraduate researchers from Stony Brook who are part of URECA shared their experiences.
Sam Goldwasser visited the Laser Teaching Center today. He is the author of Sam's Laser FAQ. The lab was very hectic today so I didn't complete that much work. Tomorrow I want to take measurements of my soap film device and make a schematic diagram of the apparatus. Today I also learned some more HTML and played around with changing colors on my web page, etc.
I looked at optical flats this morning and observed the interference fringes with a sodium lamp and a laser. I learned how to calculate the thickness of a piece of hair by using a wedge and counting the interference lines. This is important to know because I can use this method to calculate the change in thickness of my soap film.
The Simons Brown Bag Lunch today was at the Center for Biotechnology . Professor Clint Rubin spoke about his research on Osteoporosis. Today I also read more about thin film interference and made a diagram of interference in soap films. (See: Diagrams) I spent some time learning about the HTML programming language as well.
I think that I have finalized my experimentation plans. The beginning of my project is going to be a continuation of last year's work. I am going to introduce why I built a new soap film device to replace the original one from the Scientific American article (Fun with Flat Fluids). I will explain the problems with the initial device and why I made each specific change to produce the best film to study. Then, I am going to observe the vortex shedding past a stationary cylinder that is introduced normal to the soap flow. After I observe the basic pattern of the vortex street and attempt to count the number of cycles of vortices, I plan to change a specific condition of the soap flow (temperature, velocity, etc.) and observe the change in the vortex street. I like this project because it still has some practical, real-world implications. I can relate the change in velocity and temperature to the change in winds and weather around an island that has been photographed with a cloud vortex street. I am going to try to contact NASA today to see if they know the weather conditions on the days that the pictures of the von Karman cloud vortex streets were taken. I am going to still use some optics in my project when I calculate the change in thickness of the soap film with thin film interference. I enjoyed listening to the talks by the REU students this afternoon, and I look forward to hearing their final presentations tomorrow.
I received a response today from NASA, and they seemed very willing to help me. I just have to forward them the weblinks of the pictures that I found on their websites. Today, I also began to compose a letter to Maarten Rutgers and Ohio State University to ask him some questions on his work. After speaking to Dr. Noe yesterday, I drew an Idea Web summarizing all of the different aspects of soap films that I can look it. (Click Here for Idea Web )
I prepared a short presentation for the Simons Brown Bag Lunch tomorrow. (Presentation Index ) It briefly discusses the structure of a soap film, why they are studied, the device that I built, and my research plans. I also setup my soap film device to make sure that it works for tomorrow. We experimented with different ways of observing the interference patterns. I had a hard time getting the soap film to last for a long time without popping. Also, when observing the interference, I can see that the film is not very uniform. I will have to work on that tomorrow. I heard from NASA today. They provided me with some basic knowledge on why von Karman vortex streets occur in clouds. In basic terms, you need a continuous wind flow, an impediment to the wind flow, and marine stratocumulus clouds to show the shedding from the island.
The Simons program visited our lab for the brown bag lunch today. We presented our projects and did some demonstrations. I showed my soap film apparatus, but it was not working very well. The soap film has not lasted for very long and it often takes multiple tries to create a film that only lasts for a few seconds. I thought of some different ways to fix think problem.
I am also going to waterproof the bottom of my device because it is apparently leaking.
Today the lab took a trip to The Curry Club. Peter helped me waterproof the bottom of my apparatus to fix the leak. The stuff that I originally used was cracked.
I have to wait 24 hours for
the sealant to dry so I cannot use my soap device until at least 4:00.
I spent the day researching because once my device is fixed, I will
not have a lot time to look up background information. I did find an
interesting website that is part of a book entitled, Soap Bubbles
in Art and Education , by Göran Rämme (
Musicolor - Visualizing Music By Means Of A Soap Film). This
project is similar to the work I did with sand vibrations in
Some other links to sites related to this book: Experiments with soap films and soap bubbles, Table of Contents of the Book, Journal of Chemical Education Book Review
I was also taught how to fix a flat tire by myself using Pete's web site (How to Fix a Flat Tire). Later in the day: I poured water in the bottom collection container and tested the seal. It worked, but the water was leaking from the drain pipe as well. So, I have to wait another 24 hours for that seal to dry. I will be able to work tomorrow after the Brookhaven trip.
I just got back from Brookhaven National Laboratory. I set up my soap device, and it seems to be working well now. The film has a relatively long life and there is no leakage. On Monday, I have to replace the fishing wires because they have some kinks in them. Then, I will start photographing and testing. Besides from inserting a cylinder into the flow, I am thinking about using a wing-shaped object and observing the flow past an airfoil.
I replaced the wires on my soap film device and had it running today for a long time. I wanted to try this Lighting Setup, so I used some old poster boards for the white and black backgrounds. I did not take any pictures, but the interference patterns were extremely visible.
The last Simons brown bag lunch was hosted by the Honors College. They spoke about college admissions, scholarships, stress, and Stony Brook. I spoke to Dr. Rutgers today. He recommended changing all of the plastic and vinyl that I have in my setup to glass and silicone tubing for extended film life. He also gave me some other ideas for projects that I am going to read about.
Today, when Pete was poking his
finger into the soap film, he noticed that the temperature felt as if
it was changing drastically from the top of the film to the bottom.
It felt very cold near the bottom, where the film is drastically
thicker. I tried to do some experimentation on this, but the
thermometers that we had did not seem to be working correctly. Later
in the day, Alex and Waldo helped me take some photographs with the CCD camera of the soap
flow and then with an object introduced. Some of the vortex pictures
came out very clear. Tomorrow, I am going to play around with the
Scion Imaging Program to try and analyze the light intensity changes
of the vortices, which will show how the thickness is changing.
Here are some pictures that I took today:
I analyzed the CCD pictures in two ways. The first plot, on the left, is a light intensity surface plot. The green areas that are raised show a concentration of pixels, and therefore light intensity. This is where constructive interference occurs. The red and orange areas show a decrease in intensity where destructive interference occurs. In the next analysis, I used the Scion Imaging Software to plot intensity across a line (graph on the right). I used a line that cut the soap film horizontally and showed the changes in light intensity across the film. In this graph, the low points show the minimum light intensity at destructive interference patterns, and the peaks show the high intensity at constructive interference patterns. If I look at the pixel numbers, I may be able to analyze what percentage of light is reflected at the dark and bright fringes.
Today is the start of my last week of the Simons
Fellowship. For some reason my soap device was extremely stable
today. The films could easily last for tens of minutes without
breakage. I used the Scion Imaging Software again today to look at
light intensity changes across an individual vortex in the vortex
street. The surface plot shows that the swirl is rotating inward in a
clockwise direction. Tomorrow I want to take some more pictures and
see if vortices in opposite rows are swirling in opposite directions.
Wednesday, August 14, 2002
Today, the high school students in the Laser Teaching Center and the other Physics and Astronomy Labs gave talks on their project. To see mine, Click Here. Then, I spent the rest of the day on lab tours with other Simons Students. I went to Rachel's Hematology Lab in the Health Science Center, Katherine's cell biology lab in Life Sciences, Kevin's lab in Biotechnology, Unaza and PuiSee's lab in Material Science, and Karen's lab in Psychology. It was a long day, but they all had really great projects to share. I didn't have time to set up my device today because of all of these activities.
Thursday, August 15, 2002
We presented our talks again today to Professor Metcalf. Afterwards, I was talking to Dr. Noé about different ways to measure the velocity and the thickness of the film. We thought of different methods of measuring the velocity. The first way is measure the flow rate in cubic centimeters/second by timing how fast the reservoir empties. Then I can solve the formula: Volume=velocity * time * width of the soap channel * thickness of the film. Another way is to put some speckles, glitter or some comparable material, into the soap solution and manually clock how long it takes to travel a specific distance. The final way is to move a needle in and out of the flow and time how long it takes a wave to move a specific distance. I think that the proposal that Dr. Rutgers emailed to me explained a similar method. I will think about this tomorrow. I just found out that it takes 23 minutes for the height of the soap in the reservoir to decrease by 1 cm. Tomorrow, I will do some more measurements and hopefully have an initial result to compare to the speckles method.