Dynamic Stall Hysteresis in a Pitching Airfoil

ISEF Category: Engineering Technology: Statics and Dynamics

Subcategory: Aerospace and Aeronautical Engineering  ·  Difficulty: Advanced  ·  Setup: University Lab  ·  Time: Full Year

The Hook

A wing can keep lifting, then suddenly lose control, even when the airspeed barely changes. That snap can decide whether a drone stays stable or stalls. Your project asks why the lift curve loops back on itself when an airfoil pitches. You can film that loop and compare it with a CFD model.

What Is It?

Dynamic stall happens when an airfoil changes angle fast enough that the airflow cannot adjust right away. Think of a car turning too fast. The tires do not follow the curve smoothly, so grip changes with delay. An airfoil does something similar, and the lift and drag depend on more than just the angle at that moment.

That delay creates hysteresis, which means the system follows one path on the way up and a different path on the way down. For your project, you would rotate a wing section through a range of angles while air moves past it. Then you would measure how the flow separates, reattaches, and shifts from one state to another. The smoke helps you see the motion, and the video gives you frame-by-frame evidence of when the stall starts and ends.

Why This Is a Good Topic

This topic works well for a science fair because you can test a clear cause and effect. You change pitch rate, angle range, or airspeed, then measure how the lift or flow pattern changes. That gives you real data, not just pictures. It also connects to drones, small aircraft, wind turbines, and any design that faces fast changes in airflow. You can learn fluid mechanics, video analysis, and model validation in one project.

Research Questions

• How does pitching rate change the size of the dynamic-stall hysteresis loop?
• What is the effect of Reynolds number on the angle where stall starts and ends?
• Does airfoil thickness change the timing of flow separation during a pitch cycle?
• To what extent does the phase lag between angle of attack and lift depend on oscillation amplitude?
• Which flow features seen in smoke-wire video appear first before the lift peak collapses?
• What is the effect of surface roughness on the repeatability of the hysteresis loop?

Basic Materials

• Foam wing or airfoil cut from rigid foam board or balsa.
• Stepper motor with controller.
• Microcontroller or motor driver board.
• Open-jet fan or ducted flow source.
• Simple airspeed meter or homemade pitot setup.
• Smartphone or high-speed camera that can record at 240 fps.
• Smoke-wire or another visible tracer setup.
• Tripod or fixed camera mount.
• Angle scale or protractor attachment for the wing mount.
• Basic measuring tools, including ruler, calipers, and digital scale.

Advanced Materials

• Wind tunnel or calibrated open-jet flow rig.
• Airfoil mount with low-friction bearings.
• Stepper motor with encoder feedback.
• Load cell or force balance for lift and drag measurements.
• Smoke-wire power supply and fine wire for flow visualization.
• Hot-wire anemometer or pitot-static measurement system.
• Reference pressure sensor for airspeed calibration.
• Computer with OpenFOAM installed.
• Postprocessing tools for mesh and flow-field inspection.
• Calibration targets for video and geometry alignment.

Software & Tools

• OpenFOAM: Simulates airflow around the airfoil so you can compare measured and predicted stall behavior.
• Python: Processes angle, force, and video data, then plots hysteresis loops.
• ImageJ: Tracks smoke and frame-by-frame flow motion from high-speed video.
• Tracker: Extracts wing angle and motion timing from recorded clips.
• Excel: Organizes trial data and helps you check trends before deeper analysis.

Experiment Steps

1. Define the one motion variable you will change first, such as pitch rate, angle range, or airspeed.
2. Design a mount that keeps the wing aligned and lets you measure angle cleanly during each cycle.
3. Plan how you will record both flow behavior and response data so the timing matches across trials.
4. Build a baseline case that gives you a clean hysteresis loop before you add extra variables.
5. Set up a comparison plan between your measurements and the OpenFOAM output so you can judge agreement.
6. Decide which summary metrics, such as loop area, stall angle, or phase lag, will answer your research question.

Common Pitfalls

• Using a wing mount that flexes, which changes the real angle of attack during the test.
• Changing room lighting between trials, which makes smoke visibility and video tracking inconsistent.
• Skipping calibration of the camera angle, which makes the measured pitch angle differ from the real one.
• Comparing CFD to video without matching Reynolds number and motion timing, which makes the model look wrong for the wrong reason.
• Trying to change several variables at once, which makes it impossible to tell what caused the stall shift.

What Makes This Competitive

A stronger project would pair careful measurements with a comparison model that actually tests your assumptions. You could quantify loop area, stall delay, and phase lag across several motion settings, then compare them against CFD in a way that explains any mismatch. A more competitive version also checks repeatability and uncertainty, not just a single dramatic video. That turns a cool flow demo into a real analysis of unsteady aerodynamics.

Project Variations

• Test how leading-edge roughness changes dynamic-stall timing on the same airfoil.
• Compare two airfoil shapes, such as a symmetric section and a cambered section, under the same pitch motion.
• Use particle tracking or dye visualization instead of smoke-wire and compare how each method reveals separation.

Learn More

• NASA Glenn Research Center: Search for educational pages on airfoils, lift, drag, and stall, which explain the physics behind your project.
• OpenFOAM User Guide: Read the official documentation to learn how pimpleFoam handles transient flow cases.
• MIT OpenCourseWare: Search aerospace or fluid mechanics course notes for unsteady aerodynamics and stall concepts.
• NOAA National Weather Service JetStream: Use the wind and airflow lessons to build intuition about pressure, flow speed, and separation.
• PubMed: Search for review articles on unsteady aerodynamics, flow separation, and dynamic stall in rotating or pitching wings.