Zhaolong Han

Partitioned subiterative coupling schemes for aeroelasticity using combined interface boundary condition method

The combined interface boundary condition (CIBC) method has been recently proposed for fluid–structure interaction. The CIBC method employs a Gauss–Seidel-like procedure to transform traditional interface conditions into velocity and traction corrections whose effect is controlled by a dimensional parameter. However, the original CIBC method has to invoke the uncorrected traction when forming the traction correction. This process limits its application to fluid–rigid body interaction. To repair this drawback, a new formulation of the CIBC method has been developed by using a new coupling parameter. The reconstruction is simple and the structural traction is removed completely. Two partitioned subiterative coupling versions of the CIBC method are developed. The first scheme is an implicit strategy while the second one is a semi-implicit strategy. Iterative loops are actualised by the fixed-point algorithm with Aitken accelerator. The obtained results agree with the well-documented data, and some famous flow phenomena have been successfully detected.

Laminar Flow Patterns Around Three Side-By-Side Arranged Circular Cylinders Using Semi-Implicit Three-Step Taylor-Characteristic-Based-Split (3-TCBS) Algorithm

Abstract One limitation of the classical characteristic-based-split (CBS) algorithm is that its computational time step is relatively small because it is an explicit scheme with conditional stability. We present in this paper a semi-implicit form of a three-step Taylor-characteristic-based-split (3-TCBS) Galerkin fmite element (FE) method in the framework of incremental projection method to numerically solve incompressible fluid flow problems. First, the velocities are semi-implicitly estimated by a three-step process. The computational code is then verified by using the benchmark problems of lid-driven cavity and of flow around a fixed circular cylinder at Reynolds numbers in the laminar regime. Comparisons between the current method and the classical CBS algorithm show that the present 3- TCBS scheme can provide a larger time step with more accurate results. Then, this method is employed to investigate the problem of laminar flow over three cylinders which are arranged side-by-side. The Reynolds numbers range from 40 to 160 and the spacing ratios were set as 1.2, 1.4, 1.6, 1.8, 2.2, 2.5, 3.2, and 4.0. Eight different wake patterns were systematically categorized and their relationships with the Reynolds number and spacing ratio are presented.

Modification of turbulent wake characteristics by two small control cylinders at a subcritical Reynolds number

In this paper, the flow around a main circular cylinder with two small control cylinders is numerically investigated at a subcritical Reynolds number of 3900. Two small control cylinders with diameter ratio of d/D = 0.04 (d and D are the diameters of the control cylinders and the main cylinder, respectively) are symmetrically placed inside the separated shear layers emanating from the main cylinder. The computation is performed with highly resolved direct numerical simulations employing a high-order spectral/hp element method. For validation purposes, the results of the flow over a single cylinder are presented at first, and the current simulation is in good agreement with the existing experiments and large eddy simulations. For the main cylinder with the two control cylinders, the dynamics of shear layers is found to be modified strongly owing to the disturbance from the small control cylinders. As a consequence, the recirculation length is decreased by 89% as compared to that of a single cylinder. The presence of the small control cylinders further leads to a significant increase in the fluctuating lift and the mean drag exerting on the main cylinder. Furthermore, the statistical analysis and turbulent wake visualization imply that the turbulent intensity is amplified in the near wake region and becomes weaker further downstream. This study then suggests that the small control cylinders located in the near wake region of the main cylinder may work differently in the turbulent wake against that in the laminar wake.In this paper, the flow around a main circular cylinder with two small control cylinders is numerically investigated at a subcritical Reynolds number of 3900. Two small control cylinders with diameter ratio of d/D = 0.04 (d and D are the diameters of the control cylinders and the main cylinder, respectively) are symmetrically placed inside the separated shear layers emanating from the main cylinder. The computation is performed with highly resolved direct numerical simulations employing a high-order spectral/hp element method. For validation purposes, the results of the flow over a single cylinder are presented at first, and the current simulation is in good agreement with the existing experiments and large eddy simulations. For the main cylinder with the two control cylinders, the dynamics of shear layers is found to be modified strongly owing to the disturbance from the small control cylinders. As a consequence, the recirculation length is decreased by 89% as compared to that of a single cylinder. The p...