The Effectiveness of Dimples on a NACA Airfoil: A Numerical Investigation Conducted via an Independent Study

Abstract

This paper integrates research and education in an effort to enhance the critical thinking skills of an undergraduate Mechanical Engineering student while also promoting graduate engineering education. To achieve this, a three-credit undergraduate independent study was conducted where the research topic of interest was mitigating boundary layer separation, a topic covered in the undergraduate Fluid Mechanics course. Delaying boundary layer separation to improve airfoil aerodynamic performance can be achieved by passive techniques which include the use of vortex generators, rough patches, uniform suction/blowing, and dimpled surfaces. Dimpled surfaces have been known to generate swirl by the creation of vortices thereby energizing the flow. It is believed that the generation of vortices and swirl can be used to mitigate boundary layer separation thus improving lift, reducing drag, and delaying stall for an airfoil. Dimples were chosen since conflicting observations exist in the literature, and this would be a good challenge for the student. This paper numerically investigates the effectiveness of dimples on a NACA 4414 airfoil while also addressing the conflicting observations available in literature and the thought process of the student. First, an extensive literature review was conducted by the student to observe the use of dimpled surfaces with respect to airfoils. The various configurations pertaining to a single dimple shape, size, and axial location and their efficacy were considered. Following this, the NACA 4414 airfoil was numerically analyzed using the Computational Fluid Dynamics software, ANSYS FLUENT. Parametric studies were then conducted to determine the optimal configuration of a single dimple and multiple dimples. At this stage, the student conducted the investigation independently without any guidance from the instructor. Different geometrical shapes, sizes, placement along the airfoil, and multiple arrangements were all considered. The designs were driven by fundamental fluid mechanics principles that were applied by the student. This forced the student to think outside of the box and develop critical thinking ability. The project was a challenge for the student as the findings were in direct contrast with many other researchers. While reporting the results is important, of equal importance is the understanding and articulating the physics behind the flow behavior. Through this independent study, the student contributed to the gaps in knowledge, enhanced the critical thinking ability, learned how to conduct thorough literature review and improve technical writing skills. The student's academic growth via this study was remarkable, and the student was highly appreciative of the various lessons learned while also deciding to take on more research by pursuing graduate education.