Flow Visualization

Hi! My name is Sid! I am a M.S. Mechanical Engineering student here at Duke and my research interest revolve around aerodynamics. I love everything to do with wings. Thus, when I got the opportunity to pick a project on rheoscopic flow visualization, I didn’t think twice. 

A rheoscopic fluid is one that we cans see flow by virtue of small suspended particles that move in the direction of the flow. For years, it has been a powerful tool in 2-D flow visualization.

Through this project, I combine my interest in wings with the ever growing need for more fuel efficient aircraft geometries to build a rheoscopic fluid chamber.  Such a system is essential to visualize a 2-D flow around a wing. This information then allows us to manipulate the geometry of the wing to delay the onset of undesirable and potentially catastrophic phenomena such as wave drag and flutter respectively.

Water Tunnels are very common in the navy and are used to test ships, weapons, etc. However, the standard build of a water tunnel resembles a rectangular skeleton made of tubes with a small see-through enclosure where we place an object. An image is provided below. This particular mini tunnel was build by students at The Citadel, Charleston, SC under the supervision of Dr. Nathan Washuta and Dr. Jason Howison.

One of the primary requirements of the project we  choose to pursue is that our project be portable as well as smaller than the one shown above. Thus, using this setup as a starting point, a needs assessment was carried out. The primary needs of the new experimental setup are:

  1. Transparent outer enclosure help see through the glass and assess the flow.
  2. Rheoscopic particles in the fluid help to observe the effect of the wing geometry on the flow.
  3. As water tight as possible to ensure minimal error in flow rate measurement.
  4. A known volumetric flow rate and inlet area so as to measure velocity.
  5. A platform on which we can place the airfoil at a known angle of attack.

This project aims to break down the basics of aerodynamics. In this field, it is first necessary to understand the basics of fluid statics and dynamics so that we may then use the concepts we learn by adding specifications to account for only a particular fluid of our choice. 

One of the most common testing methods in the field of Flow Vizualization is a water tunnel. These tunnels are helpful because it allows us to spatially scale down a wind tunnel while still testing in a flow regime that is valid. Its applications

Through the means of this project and website, I hope to break down the concepts of Lift, Drag and other aerodynamics concepts. I also hope to set the stage for a future project that increases overall complexity and applicability.

This project and website address the visualization of the following concepts:

  1. Boundary Layer Separation
  2. Lift and Drag

Another important objective is to help set the stage for students to expand their knowledge and skillset

  1.  D’Alembert’s Paradox
  2. Thin Airfoil Theory
  3. The Cambered Airfoil Equation

Explanation of Technical Terms

Skillset Breakup

Listed below are some key skills required to pursue this project. The breakup from beginner to advanced helps the reader get an idea of what skills and concepts they should focus on improving from Freshman to Senior Year.

Project Setup and Layout

For the purpose of this class, the water tunnel in question is one that can be used only for 2-D flow visualization over an airfoil. This is because the rheoscopic fluid method of flow visualization only holds true in 2 dimensions. To clarify, in 3-D, rheoscopic particles would also flow through the plane of the airfoil. This in addition to even the slightest of turbulence would make for chaotic particle movement and hinder the process of flow visualization. A breakdown of each main component has been provided below. 

Testing Procedure

This section includes a comprehensive explanation of the system in action. From the empty tank, to the self circulating for visualization, a step-by-step procedure has been listed below:

  1. First, the pump is used to transfer water from a sink to the smaller reservoir section of the tank until it is filled. Then, the water is allowed to flow over the attaching plane until the other side of the tank has a significant but not excessive amount of water.
  2. The inlet tube of the pump is now submerged in the water present on the larger side of the tank.  This allows for water to be transferred to the reservoir so that it overflows and falls back into the larger section, this allowing for a ‘perpetual’ system.
  3. As the water overflows, it flows over the attaching plane which has a flow straightener at its Leading Edge. The water flows through this structure and its momentum is focused towards the center of the plane.
  4. This water now flows around the airfoil on the plane and allows for the observer to visualize how it changes the direction of the water at different points along the airfoil.

    5.  Once the water flows over the plane, it falls and accumulates at the other end of the tank shown by the scissor lift in the image above. The other end of the pump is attached via a tube to this end and this water is redirected back to the reservoir so that it consistently overflows at the same rate thus allowing for a near constant flow velocity. 

This is how the water keeps recirculating in the tank and we are able to collect data so long as the pump is kept on. A video of the system operating has been attached below. Special focus has been applied throughout the project to ensure that the fluid deflection due to the airfoil and the chosen angle of attack.


About the Author

Hey there! My name is Siddhant (Sid) Bapat and I am a first year M.S. Mechanical Engineering Student at Duke! I love learning about aerodynamics with specific regards to wings and though this project would be a great way to improve my theoretical and hands on knowledge on the subject. Visit my personal page to learn more about me!


[1] Derrick, J., Golub, M., & Shrivastav, V. (n.d.). EEGRC poster: Laboratory Improvements for Mechanical Engineering (phase 2). 2018 ASEE Annual Conference & Exposition Proceedings. https://doi.org/10.18260/1-2–30350 

[2] Matsson, J., Voth, J., McCain, C., & McGraw, C. (n.d.). Aerodynamic performance of the NACA 2412 airfoil at low Reynolds number. 2016 ASEE Annual Conference & Exposition Proceedings. https://doi.org/10.18260/p.26539 

[3] Telenko, C., Jariwala, A., Saldana, C., Sulchek, T., Yee, S., Newstetter, W., & Kurfess, T. (n.d.). Examples of synergies between research and hands-on design-based learning. 2016 ASEE Annual Conference & Exposition Proceedings. https://doi.org/10.18260/p.26798 

[4] Washuta, N., Howison, J., Clark, B., Imhoff, R., & Dos Reis, L. (n.d.). Water tunnel design: A senior capstone project to promote hands-on learning in fluids. 2018 ASEE Annual Conference & Exposition Proceedings. https://doi.org/10.18260/1-2–31230 

[5] Aerodynamic Lift and Drag and the Theory of Flight, https://www.mpoweruk.com/flight_theory.htm.

[6]“Thin Airfoil Theory.” Thin Airfoil Theory – an Overview | ScienceDirect Topics, https://www.sciencedirect.com/topics/engineering/thin-airfoil-theory.