Numerical simulation of flow past a cylinder in orbital motion

A finite difference solution is presented for 2D laminar unsteady flow around a circular cylinder in orbital motion placed in a uniform flow for Re = 130, 160, and 180. Four cases displaying full lock-in are presented. The variation of time-mean and root-mean-square (rms) values of lift and drag coeffcients were investigated against the amplitude of vibration in transverse direction. Abrupt jumps were found in the time-mean and rms values of lift and rms values of drag. These jumps seem to be caused by a change in the vortex structure

Computation of unsteady momentum and heat transfer from a fixed circular cylinder in laminar flow

This paper presents a finite difference solution for 2D, low Reynolds number, unsteady flow around and heat transfer from a stationary circular cylinder placed in a uniform flow. The fluid is assumed to be incompressible and of constant property. The governing equations are the Navier-Stokes equations, the continuity equation, a Poisson equation for pressure and the energy equation. The temperature of the cylinder wall is kept constant and the viscous energy dissipation term is neglected in the energy equation. The computed Strouhal numbers, time-mean drag and base pressure coefficients, as well as the average Nusselt numbers compare well with existing experimental results

Lift and drag evaluation in translating and rotating non-inertial systems

In this paper relationships have been derived for lift and drag coefficients for cylindrical bodies for two cases. The relative motion between the body and the fluid is assumed to be two-dimensional and to take place in a plane perpendicular to the axis of the body. Three-dimensional effects are ignored, thus limiting the validity of the formulae to low Reynolds number flows. The fluid is assumed to be an incompressible constant- property Newtonian fluid. In the first case, an inertial system is fixed to a stationary cylindrical body. The motion of the fluid in which the body is placed is an arbitrary function of time not identically zero, e.g. the fluid can have linear and angular acceleration, such as translation, oscillation or rotation. The velocity of the fluid at a single instant is either uniform in space or, in the case of rotation, a linear function of distance from the origin of the system. In the second case, a noninertial system is fixed to an accelerating cylindrical body. The relative flow between fluid and body is kinematically the same as in the first case, but the forces acting upon the bodies differ in the two systems. This is due to the inertial forces that occur in a noninertial system. General formulae are derived for a cylindrical body of arbitrary cross-section and give the relationships between the two systems for each set of coefficients, i.e. the relationship between the lift coefficients for each case, and the same for the drag coefficient. As an example, the relationships are applied to two common cases, a circular and a rectangular cross-section cylinder

Comparison of a grid-based CFD method and vortex dynamics predictions of low Reynolds number cylinder flow

Computational fluid dynamics models range from the finite difference type grid-based method to the Lagrangian style vortex cloud simulation technique for solving the Navier-Stokes equations. This paper undertakes a comparison of these two methods for the classical datum bluff body case of flow past a stationary circular cylinder at low Reynolds numbers in the range 10 to 220. Comparisons include time-history, time-mean and root-mean-square values of oscillating drag and lift coefficients, frequency of vortex shedding and related vortex street wake flow patterns. Particularly close agreement was obtained for Strouhal number versus Reynolds number, and good agreement for time-mean value of drag coefficients; comparison was also made with experimental results. Attempts are also made to calculate the skin friction and surface pressure components of the cylinder drag, revealing the significance of skin friction drag within this range and its relative insignificance above a Reynolds number of 220

Effect of frequency ratio on the force coefficients of a cylinder oscillated in a uniform stream

A finite difference solution is presented for 2D low Reynolds number flow around a circular cylinder placed in a uniform flow. The cylinder is oscillated in-line or transversely or is moved along an elliptical path. Abrupt jumps between two state curves were found in the time-mean (TM) and root-mean-square (rms) values of the force coefficients under lock-in conditions when plotted against frequency ratio. For orbital cylinder motion, jumps were found at certain frequency ratio values in the TM and rms values of all force coefficients and number and location of jumps were identical for all coefficients, similar to previous results plotted against ellipticity. When the cylinder was oscillated in-line, sudden changes were found only for the TM of lift and torque coefficients. However, when the cylinder was oscillated in transverse direction only, none of the TM and rms curves showed any jumps. Pre- and post-jump analysis (flow patterns, limit cycle curves) revealed switches in vortex structure

Energy transfer between an orbiting cylinder and moving fluid

This paper deals with the numerical simulation of low Reynolds number flow past a circular cylinder in orbital motion. Energy transfer between the incompressible fluid and a circular cylinder forced to follow an orbital path is investigated as a function of ellipticity. Limit cycles were investigated and show that ellipticity can have a large effect on the energy transfer. Sudden changes in state (jumps) were found when energy transfer is plotted against ellipticity. Phase angle was altered by about 180º at the jumps. The effect of direction of orbit and initial conditions was also investigated

Ellipszis pályán mozgó henger körüli kis Reynolds számú áramlás numerikus vizsgálata

Ez a dolgozat a párhuzamos áramlásba helyezett, ellipszis pályán mozgó körhenger körül kialakuló kis Reynolds számú összenyomhatalan folyadékáramlás kétdimenziós numerikus szimulációjával foglalkozik. A felhajtóerő-tényező, az ellenállás-tényező és a hátsó nyomástényező (base pressure coefficient) időátlagát és rms értékét, valamint a henger és a folyadék közötti energiacserére jellemző energiaátadási tényezőt a pálya ellipticitása függvényében ábrázolva, azok értékeiben ugrásszerű változások tapasztalhatók. Egy “ugrás” előtt és után határciklus analízist végeztünk, időbeli, fázisszög és áramkép változásokat vizsgáltunk. A vizsgálatok azt mutatják, hogy az ellipticitás nagy hatással lehet a mechanikusan mozgatott henger és folyadék közötti energiaátadásra, és hogy a transzverzális mozgás amplitúdójának kis mértékű megváltoztatása erősen befolyásolhatja az erőtényezőket. A felhajtóerő-tényező és a henger transzverzális elmozdulása közötti fázisszög az ugráson áthaladva 180º-ot változik. Ezeket a változásokat az okozhatja, hogy ennek a nemlineáris rendszernek valószínűleg két attraktora van, és hogy megoldás ezek melyikéhez vonzódik, az a probléma paramétereinek értékeitől függ

Effect on wake flow of abrupt alterations in ellipticity of an orbiting cylinder

A finite difference solution is presented for 2D laminar unsteady flow around a circular cylinder in orbital motion placed in a uniform flow in the Reynolds number domain of Re=120-180. Abrupt jumps between two state curves were found in the time-mean and root-mean-square values of the force coefficients under lock-in conditions. This study focuses upon the effect of abrupt alteration of transverse amplitude during computation. It was found that the solution tended to remain in the same state curve after amplitude alteration, inhibiting jumps between states

Effect of oscillation amplitude on force coefficients of a cylinder oscillated in transverse or in-line directions

A finite difference solution is presented for 2D low Reynolds number flow (Re=140 and 160) past a circular cylinder placed in a uniform flow. The cylinder is oscillated mechanically either in-line or transversely under lock-in conditions. Abrupt jumps between two state curves were found for a cylinder oscillated in in-line direction in the time-mean (TM) values of lift and torque coefficients when plotted against amplitude of oscillation. Pre- and post-jump analysis carried out included the investigation of phase angle differences, limit cycles and flow patterns confirming the existence of switches in the vortex structure at certain oscillation amplitude values. The TM of drag and base pressure coefficient and the rms values of all force coefficients were continuous functions of oscillation amplitude. When the cylinder was oscillated transversely to the main stream, however, no jumps were found in the corresponding curves. Here the TM of lift and torque were found to be zero (true also for a stationary cylinder) at all amplitude values. Even though the transverse oscillation breaks the symmetry of the flow, there appears to be symmetry over a period

Sudden and gradual alteration of amplitude during the computation for flow around a cylinder oscillating in transverse or in-line direction

This study investigates the effect of altering oscillation amplitude on time-mean and root-mean-square values of force coefficients when plotted against amplitude of oscillation. The cylinder is placed in a uniform flow and is oscillated mechanically in transverse or in-line direction. The two dimensional numerical computations are carried out at Re=140 and 160, at 90% of the natural vortex shedding frequency. For in-line oscillation, jumps were found in the time-mean values of lift and torque. Both abrupt and gradual alteration of amplitude in the course of a computation had the effect of keeping the solution in one state curve, i.e., of conserving state, or inhibiting changes in vortex structure. Transverse oscillation displayed no jumps, and alteration of amplitude had no effect on the solution. Keywords: circular cylinder, in-line oscillation, lift, low Reynolds number flow, transverse oscillation