Numerical simulation of unsteady flow around a square two-dimensional cylinder

Calculations of two-dimensional unsteady flow around a quadratic two-dimensional cylinder at zero angle of attack are performed. The Reynolds numbers are low (Re = 45 - 250) so that the flow presumably is laminar. At Re > 50 a von Karman vortex street with a well-defined shedding frequency is predicted. An incompressible SIMPLEC finite volume code employing non-staggered grid arrangement is used. A third-order QUICK scheme and a second-order Van Leer scheme are used for the convective terms. The time discretization is implicit and a second-order Crank-Nicolson scheme is employed. At Re = 100, the influence of the location of the inflow, outflow and side walls (blockage), respectively, is investigated. A number of quantities such as lift and drag coefficients and various surface pressure coefficients are presented

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

The effect of corrugation on heat transfer and pressure drop in channel flow with different Prandtl numbers

Large Eddy Simulation and Direct Numerical Simulation are applied to study the turbulent flow field in a wavy channel at two Prandtl numbers, Pr = 0.71 and Pr = 3.5, and Reynolds number Re b = 10,000. The characteristics of the separated shear layer and the near wall recirculating zone are discussed in relation to the turbulent heat transfer. Special attention is paid to the behavior of the flow and thermal boundary layers and various turbulent characteristics and their effects on the distribution of the Nusselt number and friction coefficient in the separation and reattachment regions. The results indicate that the thickness of the thermal boundary layer rather than the turbulent fluctuations has a significant effect on the local variation of the averaged Nusselt number. The results are compared with Direct Numerical Simulation results of a plane channel at the same Reynolds number. \ua9 2013 Elsevier Ltd. All rights reserved

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

CFD applications in offshore engineering

This paper gives a discussion on the Computational Fluid Dynamics (CFD) applications in offshore engineering. Accurate hydrodynamic quantities are essential for engineering design. Offshore structures are generally subject to high Reynolds number flows. These high Reynolds number flow conditions (Re > 106) are difficult and expensive to achieve in an experimental setup. Therefore, it is attractive to use CFD to provide the essential hydrodynamic quantities for practical design. Verification and validation studies are important for determining the validity of the CFD prediction. A procedure of performing CFD simulation is shown. Different types of turbulence modelling are discussed. Three examples of high Reynolds number CFD simulations, covering flow around offshore structural components and waves past partially-submerged horizontal cylinders, are shown and discussed

Numerical Study of Laminar, Transitional and Turbulent Flow Past Rectangular Cylinders

The subject of flow past slender bluff bodies is of relevance to technical problems associated with energy conservation, structural design and acoustic emissions. The present work is restricted to an important sub-class of slender bluff body flow --- the incompressible flow around a stationary cylinder having a rectangular cross section, the cylinder being exposed to a constant free stream velocity. Time-dependent two- and three-dimensional (2D/3D-) numerical simulations are carried out. Some useful quantities such as the dominant wake frequency (the Strouhal number), mean and RMS values of drag and lift, and various surface pressures etc. were calculated for different Reynolds numbers. In 2D-simulations, the effects of cylinder side ratio (B/A, where B is the longest side) and flow incidence (.alpha.) were investigated. In these simulations an incompressible non-staggered arrangement SIMPLEC code was used. The QUICK and Van Leer schemes were used for the convective terms. The time discretization was implicit and a second-order Crank-Nicolson scheme was employed. The influence of Reynolds number (R