Flow over a circular cylinder with detached short splitter-plates is numerically simulated in order to assess the suppression of periodic vortex shedding. A finite-volume solver based on the Cartesian-staggered grid is implemented, and the ghost-cell method in conjunction with Great-Source-Term technique is employed in order to enforce directly the no-slip condition on the cylinder boundary. The accuracy of the solver is validated by simulation of the flow around a single circular cylinder. The results are in good agreement with the experimental data reported in the literature. Finally, the flows over a circular cylinder with splitter-plate in its downstream (off and on the centerline) are computed in Re=40 as a nonvortex shedding case and in Re=100 and 150 as cases with vortex shedding effects. The same simulations are also performed for the case where dual splitter-plates are in a parallel arrangement embedded in the downstream of the cylinder. The optimum location of the splitter-plate to achieve maximum reduction in the lift and drag forces is determined.
Prediction of fluid-elastic instability onset is a great matter of importance in designing cross-flow heat exchangers from the perspective of vibration. In the present paper, the threshold of fluid-elastic instability has been numerically predicted by the simulation of incompressible, unsteady, and turbulent cross flow through a tube bundle in a normal triangular arrangement. In the tube bundle under study, there were single or multiple flexible cylinders surrounded by rigid tubes. A finite volume solver based on a Cartesian-staggered grid was implemented. In addition, the ghost-cell method in conjunction with the great-source-term technique was employed in order to directly enforce the no-slip condition on the cylinders' boundaries. Interactions between the fluid and the structures were considered in a fully coupled manner by means of intermittence solution of the flow field and structural equations of motion in each time step of the numerical modeling algorithm. The accuracy of the solver was validated by simulation of the flow over both a rigid and a flexible circular cylinder. The results were in good agreement with the experiments reported in the literatures. Eventually, the flow through seven different flexible tube bundles was simulated. The fluid-elastic instability was predicted and analyzed by presenting the structural responses, trajectory of flexible cylinders, and critical reduced velocities.
The viscous, incompressible and laminar flow around rectangular cross sections is simulated via a Cartesian-Staggered grid finite volume method for various of aspect ratios. Simulations were carried out for a range of 10–150 Reynolds number and aspect ratios of 0.5–4. In the present work, The Great-Source Technique is used to satisfy directly the no slip condition. The grid is refined in the same size in the back and front regions of the body, but for increasing computation accuracy, the region of rectangular section has been refined more. Because of widespread application of rectangular cross sections and less attendance on it than circular sections, especially in laminar flow and low Reynolds, the aim of this study is to investigate the range of harmonic instability and estimation of its critical Reynolds number. For this purpose, The shedding frequency and The variation of lift and drag coefficients with time and Reynolds numbers have been analyzed for various of aspect ratios. The results show that increase in aspect ratios leads the rise in critical Reynolds number.
A new algorithm is proposed for solving the time-dependent Navier-Stokes equations in a sequential uncoupled manner. The algorithm, known as PISO (Pressure Implicit with Splitting of Operators) is extended to the Smoothed Particle Hydrodynamics (SPH) context (PISO-SPH). The algorithm consists of one prediction and two correction steps, based on a full Navier-Stokes equation, therefore, a modified Poisson equation is derived which makes the algorithm more stable with less pressure fluctuations. The proposed PISO-SPH method is applied to solve a number of benchmark problems including both unsteady and steady state test cases. Comparing the results with analytical solutions and other numerical methods, it is shown that the proposed method is accurate and straightforward for the simulation of incompressible fluid flows.
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