Onset of Vortex Shedding and Hysteresis in Flow over Tandem Sharp-Edged Cylinders of Diverse Cross Sections

Numerical simulations are conducted to analyze flow characteristics around two tandem sharp-edged cylinders with cross sections of square (b*1 = 1) for the upstream cylinder and rectangle (b*2) for the downstream cylinder (b* = b/a, where a and b are the sides of cylinders). The study investigates the effects of Reynolds numbers (Re = 30 - 150), cross-sectional aspect ratios of the downstream cylinder (b*2 = 1 - 4), and scaled gap-spacing between cylinders (S* = 1 - 6) on the flow structure, onset of vortex shedding, hysteresis and aerodynamic parameters. The results reveal that increasing b2* suppresses the vortex shedding of the upstream cylinder, depending on S*. The suppression is attributed to the interference effect and the adhesion of the shear layers on the downstream cylinder. Three distinct time-mean flow patterns are identified based on the separation and reattachment of shear layers. The first flow pattern (I) exhibits parallel flow along the side faces of the upstream cylinder, while the separation bubbles associated with reattachment points are formed in flow pattern II on these faces. For pattern III, no reattachment point is observed and the separation bubbles cover the upstream cylinder' side faces. Additionally, two instantaneous flow patterns of extended-body and co-shedding are apperceived within the ranges of examined Re and S*. The behaviors of time-mean and varying forces as well as the vortex shedding frequency are correlated with the flow structures. The onset of vortex shedding and hysteresis dependence are discussed comprehensively. The results show that the critical Reynolds numbers for the onset of vortex shedding decrease from 128 to 50 with S* increasing from 1 to 6 (b*1 = 1 and b*2 = 4). The hysteresis limit is found within the range of 3.5 < S* < 4.5 for flow over two tandem cylinders (b*1 = 1 and b*2 = 4) at Re = 150

Dynamic Analysis of Small Pig through Two and Three- Dimensional Liquid Pipeline

The derivation and solution of the two and three dimensional dynamic equations for a small pipeline inspection gauge (Pig) through a liquid pipeline is the main aim of this work. These equations can be used for synthesis of speed controller of a pig by using a bypass port in Pig. Momentum and energy equations are employed to study the influence of flow field on the Pig’s trajectory. The pig is assumed to be a small rigid body with a bypass hole in its body. The variation of the diameter of the bypass port, which is controlled by a valve, is considered in this formulation. The path of the pig or geometry of the pipeline is assumed to be 2D and 3D curve. 2D and 3D simulations of the pig motion are performed individually and a case has been solved and discussed for each of them. The simulation results show that the derived equations are valid and effective for online estimating of the position, velocity and forces acting on the pig at any time of its motion

Numerical Simulation of Turbulent Half-corrugated Channel Flow by Hydrophilic and Hydrophobic Surfaces

In the first part of the present study, a two dimensional half-corrugated channel flow is simulated at Reynolds number of 104, in no-slip condition (hydrophilic surfaces( using various low Reynolds turbulence models as well as standard k-&epsilon;&nbsp;model; and an appropriate turbulence model (k-&omega;&nbsp;1998 model( is proposed. Then, in order to evaluate the&nbsp;proposed solution method in simulation of flow adjacent to hydrophobic surfaces, turbulent flow is simulated in simple channel and the results are compared with the literature. Finally, two dimensional half-corrugated channel flow at Reynolds number of 104&nbsp;is simulated again in vicinity of hydrophobic surfaces for varoius slip lengths. The results show that this method is capable of drag reduction in such a way that an increase of 200 &mu;m in slip length leads to a massive drag reduction up to 38%. In addition, to access a significant drag reduction in turbulent flows, the non-dimensionalized slip length should be larger than the minimum