A Numerical Investigation of Rectangular Cylinders with Interest in Maximizing Drag

Abstract

In this dissertation, rectangular cylinder flow is explored through a series of numerical simulations. First, rectangular cylinders at a Reynolds number of 20,000 are simulated using Reynolds-Averaged Navier-Stokes (RANS) simulations and detached eddy simulations (DES). 2-D and 3-D simulations are performed using a variety of turbulence models. It is found that unlike 2-D simulations, the 3-D simulations are found to be in agreement with the experimental data over the entire range of aspect ratios simulated. The results of the 2-D and 3-D simulations was found to be consistent with existing literature. Unfortunately, RANS simulations are not ideal for learning about the physics of the flow due to a different set of governing equations than nature. A switch to direct numerical simulations (DNS) is made and 3-D simulations of rectangular cylinders at Re = 500 are performed. For the aspect ratios considered at Re = 500, it is uncharted territory due to the lack of experimental data and simulation results. A significant change in drag coefficient vs. aspect ratio is found when compared to the higher Reynolds number case. This change is thought to be due to the lack of vortex roll-up in the free shear layer that only appears in the high Reynolds number case. In addition, there is a local increase in the drag coefficient that corresponds to the mean spanwise flow and free shear layer impingement. Last, we perform a series simulations where suction and blowing are applied to an aspect ratio 0.62 rectangular cylinder. Through this method, we attempt to increase its drag coefficient from its value at Re = 500 (2.24) to its value at Re = 20,000 (2.94). It is found that the drag coefficient does indeed increase, but not for the reasons originally expected.