Thesis

Reduction of low speed drag through the use of truncated airfoils

Thesis (M.S., Mechanical Engineering)--California State University, Sacramento, 2016

Reduction of drag has been an important topic recently to improve efficiency. However, most of the research on it has been at high speeds in the aerospace and automotive industries. This study focuses on the reduction of low speed drag with the idea of making bicycles more efficient. This is achieved by focusing on the aerodynamic properties of truncated airfoils as new tube shapes. Two different airfoils, NACA0020 and NACA0030, were studied for the coefficient of drag using Computational Fluid Dynamics. Each airfoil was systematically truncated by removing 10% of the chord length at a time up until the maximum width. Each of these shapes were then simulated at different angles of attack from 0 to 30 degrees in 5 degree increments and the coefficient of drag in the x direction was recorded and compared. The average was taken for each shape from 0 to 30 degrees. The NACA0020 and NACA0030 showed a 16% and a 19% decrease in average drag respectively when comparing the full airfoil to the fully truncated airfoil. Based on these results, two three-dimensional model of the front half of a bike were made, one using standard round tubes and one using the truncated airfoil cross-section. These were then tested at an angle of attack of 0 and 15 degrees. The frame using truncated airfoils had a 48% reduction of drag at both angles of attack.

Reduction of drag has been an important topic recently to improve efficiency. However, most of the research on it has been at high speeds in the aerospace and automotive industries. This study focuses on the reduction of low speed drag with the idea of making bicycles more efficient. This is achieved by focusing on the aerodynamic properties of truncated airfoils as new tube shapes. Two different airfoils, NACA0020 and NACA0030, were studied for the coefficient of drag using Computational Fluid Dynamics. Each airfoil was systematically truncated by removing 10% of the chord length at a time up until the maximum width. Each of these shapes were then simulated at different angles of attack from 0 to 30 degrees in 5 degree increments and the coefficient of drag in the x direction was recorded and compared. The average was taken for each shape from 0 to 30 degrees. The NACA0020 and NACA0030 showed a 16% and a 19% decrease in average drag respectively when comparing the full airfoil to the fully truncated airfoil. Based on these results, two three-dimensional model of the front half of a bike were made, one using standard round tubes and one using the truncated airfoil cross-section. These were then tested at an angle of attack of 0 and 15 degrees. The frame using truncated airfoils had a 48% reduction of drag at both angles of attack.

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