Vortex Simulation of Two Cylinders in Tandem Using Overlapping Grid System (original) (raw)
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Numerical Investigation of Vortex Induced Vibration of Two Cylinders in Side by Side Arrangement
In Computational investigation of Vortex Induced Vibrations (VIV) and Vortex Shedding characteristics of an elastically mounted two cylinders system in tandem arrangement has been done. The cylinders withtwo degree of freedomwere allowed to vibrate in both in-line and cross flow directions. The cylinders with a mass ratio (ratio of mass of cylinder and mass of fluid displaced by cylinder), m* = 3 with frequency ratios (ratio of natural frequency in x and y direction), 1 ≤ fr ≤ 2, and different reduced velocity, U* values ranging from 4 to 10 have been studied. The simulation was conducted for incompressible laminar flow at Reynolds Number 160 with longitudinal gap ratio (L/D) 3. The Reynolds number is based on the diameter of cylinder (D) and free stream velocity (U). The numerical simulation was performed using finite volume method (FVM) by solving 2D Navier Strokes Equation with SIMPLE pressure velocity coupling scheme using Block Structured Quadrilateral Grid with pressure based solver in ANSYS Fluent. The interacting vortices producing vibration on the two cylinders were studied by calculating the hydrodynamic force coefficients, oscillating frequency, amplitude of vibration andthe trajectory of both the cylinders.
Discrete Vortex Prediction of Flows around a Cylinder Near a Wall Using Overlapping Grid System
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Modelling of unidirectional and oscillatory flows around a cylinder near a wall using an overlapping grid system is carried out. The circular grid system of the cylinder was overlapped with the rectangular grid system of the wall. The use of such an overlapping grid system is intended to reduce the CPU time compared to the cloud scheme in which vortex-to-vortex interaction is used, i.e., especially in calculating the shedding vortex velocity, since calculating the vortices velocity takes the longest CPU time. This method is not only time efficient, but also gives a better distribution of surface vorticity as the scattered vortices around the body are now concentrated on a grid point. Therefore, grid-to-grid interaction is used instead of vortex-to-vortex interaction. Velocity calculation was also carried out using this overlapping grid in which the new incremental shift position was summed up to obtain the total new vortices position. The engineering applications of this topic are t...
Numerical simulation of flow around three tandem cylinders
The laminar flow model is used to simulate the two-dimensional, constant flow field of three tandem cylinders, focusing on the effect of different cylinder diameters and spacings on the structure and characteristics of the flow field. It is found that under the condition of Re=50, periodic vortices with stable shedding occur in the tail flow field of the cylinder. The increase of the distance between the cylinders will cause the extension of the length of the upstream tail flow field and the growth of the drag coefficient of the cylinders at both ends of the distance, and the increase of the diameter of the cylinders will rise the area of the tail flow field and its drag coefficient while reducing the drag coefficient of the downstream cylinders. The expansion limit value of the reflux zone is positively correlated with the upstream cylinder diameter, and the expansion degree is positively correlated with the spacing and negatively correlated with the downstream cylinder diameter. When the reflux zone is expanded to the limit, complete vortex shedding is formed in the tail flow field.
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.
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.
VIV of two cylinders in tandem arrangement: analytical and numerical modeling
2002
Vortex-induced vibrations of two circular cylinders in tandem arrangement are studied both analytically and numerically. A low-order model for transverse vortex-induced vibrations of one degree-offreedom elastically supported rigid cylinders is analyzed. The model, based on van der Pol oscillators, is first developed addressing the response of a single structure, and then extended to describe vortexinduced oscillations of two interfering circular cylinders in tandem arrangement. Its properties are evaluated analytically and show qualitative and quantitative agreement with both experimental results and flow-field numerical models. In the numerical modeling, the twodimensional turbulent flow around the cylinders is computed using a specifically designed numerical method.
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.
Offshore Technology Conference-Asia, 2014
In this paper, flow past around two cylinders in tandem arrangement at various Reduced velocity (3 < Vr < 10) is numerically investigated with a Fluid Structure Interaction method and the cylinders can oscillate freely in the flow field. To validate the numerical method for incompressible Navier-Stokes equations, experimental data of flow past two tandem cylinders are employed, with the numerical results in a good agreement with the available literatures. Then the study concentrates on the flow characteristics of two groups of cases, respectively, with one degree and two degrees of freedom. By changing the Reduced velocity, Vr from 3.0 to 10.0, the flow characteristics, including the flow patterns, statistical force parameters such as the drag and lift coefficients as well as wake oscillation frequencies (Strouhal numbers) are investigated. Numerical results show that in each case there are differences between the flow pattern and behaviour of single cylinder and double cylinders which are related to the presence of the downstream cylinder in the wake of upstream cylinder.