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THE DESIGN, BUILD, AND TEST OF AN AIRFOIL: AN EXPERIMENTAL AND NUMERICAL STUDY ON FLOW CHARACTERISTICS
This paper investigates the external flow characteristics over an airfoil. The main goal of this paper is to serve as a nexus between theory and practical applications so that students gain a deeper appreciation for engineering problems. The flow around an airfoil is merely a vehicle to accomplish this. There have been many project based learning (PBL) activities implemented that touch on certain aspects to achieve this. In fact, there are many works that address this particular topic of interest. This paper provides a comprehensive insight into the design, build, testing, and thought process of undergraduate students. The paper is arranged as follows. First, an existing Clark-Y airfoil is utilized so that the students can vary the angle of attack and compute the lift coefficient (CL) using a manometer bank. This introduces students to manometer readings and airfoil theory to compute lift coefficient from the pressure coefficient. The students then model the Clark-Y airfoil (2D) using the commercially available Computational Fluid Dynamics (CFD) software ANSYS FLUENT and compare their experimental and numerical results. Many projects stop here; however, this project provides the students with a more in-depth understanding of external flow and manufacturing processes. Following this step, the students then manufacture their own custom airfoil in-house utilizing 3-D printing methods. There were many challenges involved. For example, the airfoil chord had to be 100 mm in length to keep the blockage ratio low; this was challenging for the students since the tubes connecting the pressure ports to the manometer bank had to fit in a tight space. The initial build cracked due to the tubes impinging on the 3D print material. This exposed the students to the design and build aspects.
Following successful completion of the airfoil, the custom airfoil was then tested in the wind tunnel to obtain CL values at various angles. Next, the CL values were obtained using a 2D and 3D CFD analysis. The numerical and experimental trends matched very well. At the point of stall, flow separation was correctly captured using a very fine mesh at the airfoil surface. The velocity profiles were then compared to what was learned in the theory portion. Utilizing their theoretical knowledge in boundary layer separation and mitigation methods, the students were tasked with modifying the existing airfoil to delay flow separation and improve lift characteristics at stall. This tested the students on their critical thinking and ability to develop and test a practical solution after thorough research. This was done both experimentally and computationally. Finally, visualization techniques were used to observe the improved flow behavior. The first technique used was very simple where disturbance of tufts mounted along the airfoil was observed. The second technique involved using a smoke generator and strobe light to observe the streamlines.