Analysis and Optimization of Unsteady Flow Past a Circular Cylinder Using a Harmonic Balance Method PDF Download
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Author: Emily Buckman Clark Publisher: ISBN: Category : Languages : en Pages : 122
Book Description
Two-dimensional laminar flow over a circular cylinder was investigated in this work. Three cases were considered in which the cylinder was either stationary, in constant rotation, or in periodic rotation. The purpose of this work was to investigate the effects of a rotating cylinder for lift enhancement, drag reduction, and the suppression of vortex shedding. The governing coupled nonlinear Navier-Stokes equations were solved using a finite difference discretization and Newton's method. In this way, three flow solvers were developed for this research: a steady solver, an unsteady time-accurate solver, and an unsteady harmonic balance solver. The force coefficients were of prime interest in this study. Favorable results were obtained using rotation as an active control for the flow over the cylinder. The cylinder in constant rotation resulted in lift enhancement, drag reduction and vortex suppression for increasing rotational speeds. Lift enhancement and drag reduction were also noted for a rotationally oscillating cylinder. The trade-offs for these goals were discussed. Lastly, a finite difference sensitivity analysis was performed for a rotationally oscillating cylinder with the harmonic balance solver. The mean drag coefficient was taken as the objective function, and the Strouhal number was the investigated design variable. The goal was to use the sensitivity analysis to determine a forcing frequency, which minimized the mean drag coefficient. Two iterative techniques were investigated, but neither converged to a minimum drag coefficient with the harmonic balance solver. It was determined that a minimum drag coefficient occurs near the boundary between the lock-on and non lock-on regions or in the non lock-on region, where the harmonic balance solver does not converge.
Author: Emily Buckman Clark Publisher: ISBN: Category : Languages : en Pages : 122
Book Description
Two-dimensional laminar flow over a circular cylinder was investigated in this work. Three cases were considered in which the cylinder was either stationary, in constant rotation, or in periodic rotation. The purpose of this work was to investigate the effects of a rotating cylinder for lift enhancement, drag reduction, and the suppression of vortex shedding. The governing coupled nonlinear Navier-Stokes equations were solved using a finite difference discretization and Newton's method. In this way, three flow solvers were developed for this research: a steady solver, an unsteady time-accurate solver, and an unsteady harmonic balance solver. The force coefficients were of prime interest in this study. Favorable results were obtained using rotation as an active control for the flow over the cylinder. The cylinder in constant rotation resulted in lift enhancement, drag reduction and vortex suppression for increasing rotational speeds. Lift enhancement and drag reduction were also noted for a rotationally oscillating cylinder. The trade-offs for these goals were discussed. Lastly, a finite difference sensitivity analysis was performed for a rotationally oscillating cylinder with the harmonic balance solver. The mean drag coefficient was taken as the objective function, and the Strouhal number was the investigated design variable. The goal was to use the sensitivity analysis to determine a forcing frequency, which minimized the mean drag coefficient. Two iterative techniques were investigated, but neither converged to a minimum drag coefficient with the harmonic balance solver. It was determined that a minimum drag coefficient occurs near the boundary between the lock-on and non lock-on regions or in the non lock-on region, where the harmonic balance solver does not converge.
Author: Huang Huang (Aerospace engineer) Publisher: ISBN: Category : Computational fluid dynamics Languages : en Pages : 202
Book Description
The high-dimensional harmonic balance (HDHB) method has recently become popular in the field of periodic unsteady flow prediction due to its accuracy and high efficiency. In the present dissertation research, two and three-dimensional parallelized computational fluid dynamic (CFD) codes based on the HDHB method are developed and validated for unsteady turbulent flows. It is found that the stability condition for an explicit solver is highly dependent on the reduced grid frequency, a non-dimensional parameter that depends on the grid size, characteristic wave speed, and the highest frequency retained in the harmonic balance solver. Furthermore, for certain moderately and highly nonlinear problems, the pseudo-spectral operator used in the HDHB method is found to introduce aliasing errors, which may lead to nonlinear instabilites or non-physical solutions. As a remedy, a temporal spectral viscosity operator is proposed for de-aliasing purpose so as to stabilize HDHB solver. The proposed method is validated for a simple nonlinear Duffing oscillator case and laminar vortex shedding over an oscillating circular cylinder at Re=500. Another focus of this research is the design optimization of the turbomachinery blades for unsteady flows. The "steady state" nature of the HDHB technique makes it very-well suited for an adjoint sensitivity analysis mainly due to the fact that the storage requirements are greatly reduced. To date, the investigators have used the adjoint technique mainly for steady shape optimization. To the author's best knowledge, the technique has not been applied for unsteady design optimization of turbomachinery blades. In this dissertation, a discrete adjoint HDHB method is employed for unsteady turbomachinery shape optimization. With the help of the automatic differentiation (AD) tool, TAPENADE, the development time for an optimization solver can be reduced substantially. Both inverse design and optimization problems are considered to validate the optimization solver.
Author: Emily Buckman Clark
Author: Emily Buckman Clark
Author: Huang Huang (Aerospace engineer)
Author: Chiipei A. Liu
Author: 
Author: Xuegeng Wang
Author: Jiunn Fang
Author: Jianfeng Zhang
Author: Anders Nordlander
Author: Ming Cheng
Author: Srinivasan Gopalkrishnan