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Flow field characteristics in the neighbourhood of a finite height circular cylinder mounted on a horizontal plate have been investigated numerically. Three-dimensional simulations are carried out for low Reynolds number (Re) incompressible flow using commercial software ANSYS Fluent 14.0. Topological characteristics of the flow have been investigated near the cylinder of aspect ratio (AR) ranging from 0.5 to 3.0 with Re varied in the range from 40 to 300. Time-averaged streamline plots are presented in various planes for different values of AR and Re to understand the flow field characteristics. For a developing flow impinging on the cylinder, flow separation in upstream of cylinder close to the cylinder-bottom wall junction leads to horseshoe vortex formation. Various topological characteristics like saddle, node have been identified in upstream and downstream of the cylinder. Positions of saddles are shown to depend on the values of AR and Re. Development of recirculation region and formations of vortex bubble have been studied in form of their projections on different planes. The variation of mean drag coefficient on the cylinder with Re for different values of AR has also been presented. [ABSTRACT FROM AUTHOR]

A density-based solver for turbomachinery application is developed based on the central-upwind scheme of Kurganov using the open source CFD-library OpenFOAM. Preconditioning of Weiss and Smith is utilised to extend the applicability down to the incompressibility limit. Implicit residual averaging, bulk viscosity damping and local time stepping are employed to speed up the simulations. A low-storage four-stage Runge-Kutta scheme and dual time-stepping are used for time integration. The presented solver is validated using measurement data from three well-known reference cases. The inviscid performance is investigated using the circular bump test cases at incompressible, subsonic, transonic and supersonic conditions. The laminar flow around a circular cylinder is analysed and compared to analytical and experimental data. Finally, a low speed centrifugal compressor is simulated. All three cases show a very good agreement with the reference data. [ABSTRACT FROM AUTHOR]

The present numerical study aims at the control of vortex shedding and drag reduction by shaping the rear geometry of a circular cylinder. The ratio of the semi-major/minor axis dimension (A) of the rear half to the radius of the circular part (R) is varied over a range of values between 0.0 and 4.0. A two-dimensional flow solver has been developed using body-fitting coordinate transformation with Cartesian velocity components as dependent variables and solved using a modified MAC algorithm. The flow solver offers a fast and accurate procedure for modelling viscous incompressible flows in complex geometries. The effect of elongation on the wake characteristics and hydrodynamic coefficients has been investigated for different values of Reynolds number (Re) ranging from 40 to 200. The predicted results indicate that vortex suppression occurs primarily due to reduction in the amplitude of fluctuation than by reduction in the vortex shedding frequency. The critical value of Re for the onset of vortex shedding has been correlated with elongation ratio ER, based on the numerical predictions. [ABSTRACT FROM AUTHOR]

This study proposed a transient 2-D hydrodynamic model adopting streamline upwind/Petrov-Galerkin (SU/PG) scheme for the analysis of discontinuous wave propagations by the sudden collapse of circular cylinder as well as by the dam break. The computation of sudden collapse in the circular cylinder problem identified both the outward-propagating circular shock waves and inward-propagating circular rarefaction waves. It was also confirmed that the advancing front and the depressive wave preserve the cylindrical symmetry, and the bore wave without oscillations was computed. The simulation results of the dam break shows that the bore and depressive waves which are propagating downstream and upstream, respectively are effectively developed and the shock front is sharply captured. The SU/PG scheme needs no tuning of adjustable parameters such as the artificial viscosity coefficient to be a viable option for accurate prediction of the flow characteristics in a discontinuous free surface case. [ABSTRACT FROM AUTHOR]

We develop a low-dimensional tool to predict the effects of unsteadiness in the inflow on force coefficients acting on a circular cylinder using proper orthogonal decomposition (POD) modes from steady flow simulations. The approach is based on combining POD and linear stochastic estimator (LSE) techniques. We use POD to derive a reduced-order model (ROM) to reconstruct the velocity field. To overcome the difficulty of developing a ROM using Poisson's equation, we relate the pressure field to the velocity field through a mapping function based on LSE. The use of this approach to derive force decomposition coefficients (FDCs) under unsteady mean flow from basis functions of the steady flow is illustrated. For both steady and unsteady cases, the final outcome is a representation of the lift and drag coefficients in terms of velocity and pressure temporal coefficients. Such a representation could serve as the basis for implementing control strategies or conducting uncertainty quantification. [ABSTRACT FROM AUTHOR]

In this paper, flow over a circular cylinder with detached short splitter-plates is numerically simulated so as to assess the flow behaviour and its characteristics. A finite-volume solver based on the Cartesian-staggered grid is implemented. Furthermore, the ghost-cell method in conjunction with Great-Source-Term technique is employed 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 completely compatible with the experimental data. Eventually, the flow over a circular cylinder with splitter-plate in its downstream in Re = 40, 100 and 150, 0 ≤ G/D ≤ 10, and 0 ≤ Z/D ≤ 1.25 (where D is the cylinder diameter, G and Z are the horizontal and vertical distances between leading edge of the splitter-plate and the cylinder base, respectively) are simulated and analysed. For these configurations that are being studied, the drag and lift coefficients, the Strouhal number and the flow visualising parameters are obtained. The same simulations are also performed for the cases where dual splitter-plates are in a parallel arrangement embedded in the downstream of the cylinder. These compounds can be applied in many mechanical types of equipment to minimise flow-induced forces and suppress periodic vortex shedding. [ABSTRACT FROM AUTHOR]

This study determines the intrusiveness of endoscopic tools within multiphase flows. A liquid-air blast atomiser continuously discharges within a test section of air at atmospheric pressure, with and without a circular cylinder placed 25 diameters (D = 10 mm) downstream of the nozzle. Data was collected using Particle Image Velocimetry (PIV), drop sizing and Computational Fluid Dynamics (CFD). Numerical predictions are compared against the PIV results for wake flow characterisation. Using a non-intrusive droplet sizing technique it has been observed that the average droplet diameter increases when the circular cylinder is introduced and so does the frequency of occurrence of these large particles. Smaller particles are re-circulated, whereas the larger drops continued in the general direction of the spray cone. [ABSTRACT FROM AUTHOR]

The dynamics of flow past a circular cylinder is investigated at Reynolds number (Re) between 20 and 3900 using the rectangular mesh. The Re is defined based on the cylinder diameter D and the free-stream velocity U∞. This is achieved by using the Immersed Boundary (IB) method that helps to impose boundary conditions on a given surface not coinciding with the computational grid. Two interpolation techniques, namely bi-linear proposed by the authors and unidirectional quadratic by Muldoon and Acharya (2005), are compared for both the laminar and the turbulent flow regime. The unsteady Navier-Stokes (N-S) equations are solved using a symmetry-preserving finite-difference scheme of second-order spatial and temporal accuracy. Large-Eddy Simulations (LES) with the dynamic subgrid model are used to resolve the turbulent flow at Re = 1000 and 3900. When compared with experiments, it reveals that the IB method is worth pursuing and both the interpolations generate almost identical results for a wide range of Reynolds numbers. The bi-linear interpolation is easy to implement and take less computational time because of its simplicity. [ABSTRACT FROM AUTHOR]