Drag Coefficient Testing of Various Geometries

This team project was the final project for a course in Experimental Engineering. Experimental Engineering at the University of Iowa College of Engineering is often regarded as the most difficult class for ME students as it involves extensive uncertainty analysis for every project, but I actually had a lot of fun with it! It was very satisfying to see how accurate results could be achieved even when using a 3D printed apparatus.

For the project, our team of 4 was tasked with designing an experiment to measure something, and carrying out an advanced uncertainty analysis to determine the uncertainty in the final measured result. My primary focus through this project was in designing and 3D printing an apparatus to calculate the drag coefficient of 3 different shapes in a wind tunnel. Our team chose to measure the drag force, to then calculated the drag coefficient, using two different methods. The first method was by calculating the drag force by measuring the change in pressure profile at the back of the shape using an already existing pressure rake with 7 pitot tubes. The second method was by measuring the drag force directly using a load cell.

To design the apparatus that would hold the load cell and different shapes, I first took several measurements of the existing mounting holes on the wind tunnel from previous experiments. I then modeled the main part that bolted to the wind tunnel in Creo Parametric. The reason I used Creo was because of its ability to create parametric models that simplify the prototyping process. After the main bracket that bolted underneath the wind tunnel was modeled, I simply modeled all of the other parts off of that while in an assembly file, being sure that parameters were set to make the parts dependent on each other for simple adjustments if things weren’t fitting. After all the parts were modeled I 3d printed them in a performance PLA and tested the fitment in the wind tunnel. I did have to redesign the main bracket once after that to make it more rigid and reduce vibrations on the load cell when taking measurements.