Drag reduction study of imposed axial flow in Taylor Couette flow

Abstract This study investigates effect of externally imposed axial-flow in Taylor-Couette flow (TCF) with smooth rotating inner-cylinder and stationary outer-cylinder for radius ratio = 0.5, and Re = 60 to 650. Previous studies by Razzak et al. M. A. Razzak, B. C. Khoo, and K. B. Lua, “Numerical study on wide gap Taylor Couette flow with flow transition,” Phys. Fluids , vol. 31, no. 11, 2019, M. A. Razzak, B. C. Khoo, and K. B. Lua, “Numerical study of Taylor Couette flow with longitudinal corrugated surface,” Phys. Fluids , vol. 32, no. 5, 2020, Drag reduction study of naturally occurring oscillating axial flow induced by helical corrugated surface in Taylor–Couette flow,” Phys. Fluids , vol. 35, no. 8, p. 083608, 2023 showed that macroscale corrugated surfaces in TCF passively generate axial secondary flows and reduce drag without external power, but their complex design limits practical use in turbomachinery. To overcome this, present study applies external axial-flow without altering cylinder geometry to evaluate its effect on torque and power. Unlike earlier periodic-boundary studies, parabolic inlet velocity and outflow condition are imposed at the cylinder ends. Three axial-flow types are examined steady (non-zero), oscillating with non-zero mean, and oscillating with zero-mean and results are compared with baseline TCF(no axial-flow) from Razzak et al. M. A. Razzak, B. C. Khoo, and K. B. Lua, “Numerical study on wide gap Taylor Couette flow with flow transition,” Phys. Fluids , vol. 31, no. 11, 2019 for same radius and aspect ratios. Based on results, Taylor-vortices are found to be stretched along axial direction under the application of axial-flows. This was found to suppress the strength of jet impingement at the inner wall resulting in torque and power reduction for Re ≤ 450 and Re ≥ 540. In contrast, within range 450 < Re < 540, stronger naturally induced axial-flows in baseline case achieve better suppression, leading to lower torque than the externally applied axial-flow cases. Among the three axial-flow types, steady axial-flow yields the greatest vortex stretching and jet impingement suppression, resulting in the highest torque and power savings. Adding oscillation with non-zero mean slightly weakens these effects, while zero-mean oscillation offers the least suppression and torque reduction. Overall, stronger imposed axial-flow can further enhance drag reduction, offering a geometry-independent control for TCF.