Research Summary
As I began graduate school I started to work in an unsteady flow and vortex dynamics lab within my department. The labs focus is to observe, characterize, and model these unsteady flows and their interactions with bodies. The models developed by this research are intended to be used by advanced controllers for drones which operate in unsteady conditions.
So far, my participation has been on the observation and characterization side of things.
The observation technique I use is known as Particle Image Velocimetry (PIV). With this technique, a flow is seeded with tracer microparticles, which can then be tracked to reconstruct the velocity field. To illuminate the particles, a high-power laser is fired in sequence with the imaging cameras.
Equipment
My 2D imaging set up in the lab uses the following equipment.
- 2x Nd Yag Pulse Lasers
- 2x PIV Cameras
- 40 Gallon Water Tank
- Belt Driven Wing Carraige
- Limit Switch
- Triggering Unit
- Hardware Computer
- Software & Timing Computer
- Enclosure
System Diagram
On the right is a diagram I threw together for an outreach event of how all the equipment interacts.
Taking Data
Firing the lasers is always the fun part. This video is actually from some routine maintenance but it's a good representation of what's going on during data acquisition.
The laser fires in a sheet which illuminates only a specific layer of the flow, and you can see this sheet where the particles appear to be concentrated. It almost looks like the surface of the water but it's not.
Raw Velocity Data
After I run the setup, the software outputs raw velocity fields. This velocity data needs to go through a significant amount of post processing for us to make meaningful insights about the flow.
Post Processing
After I have my velocity fields I can perform any appropriate masking and outlier removal before converting the fields into vorticity. From the vorticity field, I can identify and track individual vortices as they travel and evolve through the flow.
In the image on the right I show the boundaries of each identified positive and negative vortex, their assigned identities, and the trajectory of the leading-edge vortex (LEV).
Outreach
Since the lab is sometimes funded through NSF grants, we have to host outreach events from time to time.
This is a short video of a demo set up that I built as a station for one of these events. The students perform dye visualization of flows off rotating wings of various planforms.
Discrete Vortex Model
This is a modeling technique I tried to develop for a course project. I invested a fair bit of time into this because it has a lot of potential uses in my own research.
The idea is that as a wing moves through a flow (or if flow moves over a wing) at high angles of attack, the vortex growth and shedding can be adequately approximated by finite vortex elements whose kinematics are governed by the Lamb-Oseen vortex.
While I got a great grade on this project, I was never able really finish it. The physics model breaks down after a few dozen timesteps or so. If I ever get enough free time to work on this again I have a good idea of how to go about fixing this, but unfortunately that won't be for a while.
