Numerical Simulation of Flow Interference Between Two Circular Cylinders in Tandem and Side-By-Side Arrangements (original) (raw)
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Numerical investigation of the flow around two circular cylinders in tandem
Journal of Fluids and Structures, 2006
The incompressible flow around pairs of circular cylinders in tandem arrangements is investigated in this paper. The spectral element method is employed to carry out two-and three-dimensional simulations of the flow. The centre-tocentre distance (l cc ) of the investigated configurations varies from 1.5 to 8 diameters (D), and results thus obtained are compared to the isolated cylinder case. The simulations are in the Reynolds number (Re) range from 160 to 320, covering the transition in the wake. Our analysis focuses on the small-scale instabilities of vortex shedding, which occurs in the Re range investigated. With the aid of Strouhal data and vorticity contours, we propose mechanisms to explain the interference phenomenon and its interaction with the three-dimensional vortical structures present in the flow field. It is found that, for Re4190, when three-dimensional structures are present in the flow field, two-dimensional simulations are not sufficient to predict the ðRe; l cc Þ pair of drag inversion. r
Numerical Simulation of Flow Around Two Side-by-Side Circular Cylinders at High Reynolds Number
International Journal of Heat and Technology
The fluid flow around a cylinder is one of the classic issues in fluid mechanics because of its various applications. Cylindrical structures, both single and in the group patterns, are present in the design of cooling systems of nuclear power plants, hydro-structures, heat exchangers, chimneys, high buildings, power lines, cables and networks in air and water. In many engineering applications, Karman's vortex shedding produces flow-induced vibrations. To comprehend the fluid structures surrounding the cylinders, it is vital to understand some fundamental issues such as boundary layers, flow separation, free shear layer, sequence and dynamics of vortices. According to the limited studies conducted for the vertical arrangement of two cylinders in a flow with the high Reynolds number, there is no evidence of oblique flow or bi-stable pattern except in the case where cylinders are close to each other. In this paper, the impact of the vertical arrangement of two cylinders on flow with high Reynolds number has been investigated via numerical modelling. The results indicated that the flow pattern is irregular and unstable for denser arrangements while the propagation of vortices does not have any tendency in different spacing.
2021
This research is motivated by understanding the flow characteristics and hydrodynamic forces for cylindrical structures arranged in tandem. Two and threedimensional (2D and 3D) direct numerical simulations (DNS) were conducted to investigate the wake transitions for flow past multiple cylinders. The effect of gap to diameter ratio (/) on flow structures, vortex shedding frequency and hydrodynamic forces on each of the multiple cylinders have been studied. Specifically, the following scenarios have been considered: the far wake features of two circular cylinders at Reynolds number = 150 where the flow is considered laminar (Chapter 2); multiple circular and square cylinders in steady current (Chapters 3 and 4) and two circular cylinders using three-dimensional numerical simulations (Chapter 5). The evolution of the far wake for two circular cylinders at = 150 over a wide range of gap ratios (i.e. / = 0.5~200) where is the surface to surface distance of the cylinders is investigated numerically. The flow structures around the cylinders were categorized into 3 different regimes, namely single bluff body, shear layer re-attachment and co-shedding regimes, based on the influential function of spacing between cylinders. No secondary wake was observed for single bluff body and shear layer reattachment regimes. The co-shedding regime is further classified into three new regions, i.e. synchronized co-shedding, high-order synchronized co-shedding and desynchronized co-shedding regions. For synchronized co-shedding, the secondary wake decayed after primary vortices further downstream while for high-order synchronized co-shedding region, the secondary wake was formed due to merging of primary vortices. For this regime, the relationship 3 = 2 2 − 1 was found valid between 1 , 2 and 3 , corresponding to the primary vortex frequency, secondary vortex frequency and secondary wake undulation frequency. In the Desynchronized coshedding region, the two cylinders have different vortex shedding frequencies and the
Vortex Simulation of Two Cylinders in Tandem Using Overlapping Grid System
2020
To give a considerable time reduction in the calculation of the vortex velocity and in the CPU time, discrete vortex modelling of flows using overlapping grid system for two tandem cylinders is carried out. This simple and time efficient method gives a better scatter of surface vorticity as the vortices around the body are now calculated on grid point. This research is to simulate the loading on structural elements of the structures due to their interaction with anodes or with other members. To show the flow phenomena and interactions involved, the in-line and transverse force coefficients are presented. The comparison of the results with experimental and numerical results and the range for good results is presented.
The current investigation is concentrated on vortex generated oscillations and vortex shedding owing to elastically fixed pair of cylinders. Several non-dimensional key process parameters such as mass ratio, Reynolds number, transverse gap ratio, frequency ratio and reduced velocity, relating to the present problem are identified and their relative importance are also observed. The investigations are carried out at several frequency ratios and reduced velocities by considering the flow to be laminar and incompressible. The numerical model involves governing transport equations of continuity and momentum in two dimensions. The model uses finite volume method (FVM) with pressure based SIMPLE algorithm to carry out numerical simulation for getting the related flow fields. The oscillations created by the interacting vortices through a pair of cylinders are fully investigated in terms of cylinder trajectory and vibration frequency/amplitude.
Flow past a circular cylinder between parallel walls at low Reynolds numbers
Ocean Engineering, 2010
The flow about a circular cylinder placed centrally inside a channel is studied numerically with an unstructured collocated grid finite volume method based on the primitive variable formulation. The distance between the channel walls is allowed to vary to change the blockage ratio. Simulations are carried out over a range of Reynolds numbers that are consistent with the two-dimensional assumption. The study confirms that transition to vortex shedding regime is delayed when the channel walls are close to the cylinder because of the interaction between the vortices from the channel wall and cylinder wake. In the unsteady vortex shedding regime, the wake pattern is opposite to the classic Karman street in respect of the positions of the shed vortices. The cylinder drag coefficient and Strouhal number are considerably increased at smaller gaps while the root-mean-squared lift coefficient is significantly decreased. Several important flow parameters are correlated with the input parameters, namely Reynolds number and blockage ratio.
Numerical Simulation of Flow Over Two Circular Cylinders in Tandem Arrangement
Journal of Hydrodynamics, 2011
In this article, the 2-D unsteady viscous flow around two circular cylinders in a tandem arrangement is numerically simulated in order to study the characteristics of the flow in both laminar and turbulent regimes. The method applied alternatively is based on the finite volume method on a Cartesian-staggered grid. The great source term technique is employed to identify the cylinders placed in the flow field. To apply the boundary conditions, the ghost-cell technique is used. The implemented computational method is firstly validated through simulation of laminar and turbulent flows around a fixed circular cylinder. Finally, the flow around two circular cylinders in a tandem arrangement is simulated and analyzed. The flow visualization parameters, the Strouhal numbers, and drag and lift coefficients are comprehensively presented and compared for different cases in order to reveal the effect of the Reynolds number and gap spacing on the behavior of the flow. The obtained results have shown two completely distinct flow characteristics in laminar and turbulent regimes.
Numerical predictions of low Reynolds number flows over two tandem circular cylinders
International Journal for Numerical Methods in Fluids, 2005
Flows over two tandem cylinders were analysed using the newly developed collocated unstructured computational uid dynamics (CUCFD) code, which is capable of handling complex geometries. A Reynolds number of 100, based on cylinder diameter, was used to ensure that the ow remained laminar. The validity of the code was tested through comparisons with benchmark solutions for ow in a lid-friven cavity and ow around a single cylinder. For the tandem cylinder ow, also mesh convergence was demonstrated, to within a couple of percent for the RMS lift coe cient. The mean and uctuating lift and drag coe cients were recorded for centre-to-centre cylinder spacings between 2 and 10 diameters. A critical cylinder spacing was found between 3.75 and 4 diameters. The uctuating forces jumped appreciably at the critical spacing. It was found that there exists only one reattachment and one separation point on the downstream cylinder for spacings greater than the critical spacing. The mean and the uctuating surface pressure distributions were compared as a function of the cylinder spacing. The mean and the uctuating pressures were signiÿcantly di erent between the upstream and the downstream cylinders. These pressures also di ered with the cylinder spacing. Copyright ? 2004 John Wiley & Sons, Ltd.