Fluid Flow Around a Sphere

Matt Kuchta and I have been working on several projects involving our sparkly new high speed camera. One thing we are looking at is dropping objects into fluids and looking at the fluid dynamics involved. Here is an interesting video that Matt shot earlier today.

Ball Drop Redux from Matt Kuchta on Vimeo.

The fluid flow up the ball looks to be moving quite quickly so I decided to fire up Tracker to look at the video. Let me tell you something – you have no idea how amazing it is to mix Tracker with a high speed shot.

Tracker Plotted Points for Steel Ball

The best part is the Autotrack feature; you pick an edge or feature on the moving object and Tracker will mark the location in each frame. It works really well. Hat’s off to Doug Brown, creator of Tracker.

Here’s what we see.

Position vs. Time Graph for Steel Ball

The ball itself is falling at about 3.4 m/s, but the water is sliding up at over 5 m/s.  It is interesting the the sphere doesn’t appear to slow appreciably as it enters the water.  Of course it is a little more difficult tracking the motion at that point so I’d like to revisit that point later.

Position vs. Time Graph for Water Front Sliding Up Ball

So the water is in fact moving up faster than the ball is falling!  This really begs the question what is forcing the water up and around the sphere.  Is it a result of surface tension, boundary layer effects, or some other fluid phenomena?  Anybody have suggestions?

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6 Responses to Fluid Flow Around a Sphere

  1. John Burk says:

    What high speed camera did you get? That doesn’t seem like one of the casio jobs….

    • This footage was from our shiny new NAC Memrecam GX-8. We just got it over break and we can’t stop shooting. BTW, we do have a set of 12 Casio EXILIM’s for classroom use, and some of my Schlieren footage is taken using those. They are handy but the GX-8 does put them to shame.

  2. Pingback: Cool Video of the Day | Talking Physics

  3. John Burk says:

    So what does a NAC Memrecam GX-8 run you, just in case I happen to win the high school physics funding lottery?

    • John, I think it only runs about $44,000 with lights and lenses (gulp). We are still in the stage of “oh wow, lets take a video of this, no wait how about this, oh this would be cool…” I think this would be an awesome tool for high school students to get their hands on. Perhaps you can find a neighboring college physics department and put together a grant. One of our goals with the camera is to solicit project proposals from local high school students.

  4. stawastawa says:

    Awesome, the question will linger in my mind to be sure.

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