Investigation for bodies in moving frame of reference

• Main Author: Xavier, Briant Benjamin
• Other Authors: Chan Wai Lee
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Aeronautical engineering::Aerodynamics
• Online Access: https://hdl.handle.net/10356/167037
• Institution: Nanyang Technological University

The Galilean invariance assumption is commonly used in Computational Fluid Dynamics (CFD). It states that the forces produced on a stationary body in moving flow is equal to the forces produced on a moving body in stationary flow. This study aims to investigate the accuracy of this assumption for both 2 dimensional (2D) and 3 dimensional cases (3D). CFD was used to compare the stationary body case to the moving body case for 2 different objects, namely a thin airfoil and a thick airfoil. The thin and thick airfoil had a maximum thickness of 12% and 30% of the chord length respectively. Simulations were performed at Reynolds numbers of 40 and 400. Results show that, depending on the thickness of the object and the Reynolds number that the simulations were performed at, the percentage difference in drag coefficient between the stationary body and moving body cases can range from 5% to 10%. Another set of simulations was also performed to compare the difference in drag coefficients for a 3D stationary finite cylinder and moving finite cylinder at Reynolds number of 400. The percentage difference in drag coefficient for the two cases is very large, which suggests that Galilean invariance might not be as applicable for 3D cases. However, there are certain limitations in the results for the 3D case. Lastly, since Galilean invariance is suggested to be invalid for the 3D stationary and moving finite cylinder cases, there is a need to conduct 3D simulations for moving body cases. However, they tend to be more computationally expensive and require larger time periods. Hence, the wrapping boundary technique was tested by splitting the large domain into smaller domains and performing simulations. Based on the results obtained, the continuation from domain to domain works but using velocity magnitude or total pressure as the outlet boundary conditions may not be accurate. Hence, further studies need to be performed to determine suitable boundary conditions.