In this study, the flow characteristics around Two tandem square and equilateral triangle cylinders have been experimentally investigated. Experiments were conducted in an open-circuit subsonic wind tunnel with maximum free-stream turbulence level of 0.3%. Investigations for tandem arrangement were performed by moving the downstream square cylinder along the flow direction at various distances from the upstream triangular cylinder. Measurements were performed using 32-channel pressure transducer, three-component balances and hotwire anemometer. Square cylinder was placed at various distances from the upstream triangular cylinder and the flow Reynolds numbers were chosen to be 26000, 37000, 46000, and 51000. In this study, the mean and fluctuating lift and drag forces were measured for square cylinder at different spacings. Also, the distribution of mean and fluctuating surface pressure on the Two-cylinders were measured. The vortex shedding frequency was measured by using both hotwire and surface pressure fluctuations on both cylinders and the results obtained by these Two different measurement methods were compared. One of the most important outcome of the present study is the observation of Two different flow patterns. It is noticed that the vortex shedding from the upstream cylinder was eliminated for cylinder distances lower than the critical spacing while for distances more than the critical spacing, the vortex shedding occurs from both triangular and square cylinders. The critical distance for this arrangement was obtained to be around three times of the length of the side length of the cylinders.

Flow past Two tandem triangular cylinders forced to oscillate transversely in a uniform flow, is numerically investigated at a Reynolds number Re = 100. The incompressible Navier-Stokes equations in Arbitrary-Lagrangian-Eulerian formulation are solved by four-step fractional finite element method. The Two cylinders are oscillated in phase and their motions are limited to low amplitudes with a wide frequency range. This study focuses on Two typical spacings between the Two cylinders, corresponding to vortex suppression (VS) regime and vortex formation (VF) regime respectively for flow past Two stationary cylinders. Numerical results show that the response characteristics of Two cylinders are significantly affected by the spacing, oscillation amplitude and frequency. For the VS spacing, both cylinders have a wider lock-on region, especially at relatively larger amplitude and higher frequency; the downstream wake patterns are mainly 2S and a combination of 2S* and 2S. However, for the VF spacing, the lock-on frequency range of the cylinders is even slightly narrower than that of a single oscillating cylinder; the wake field is more complex since it may comprises 2S, P+S and 2S* structures at some higher frequencies. Additionally, the hydrodynamic forces are also discussed in terms of mean and root mean square quantities, and reveal large differences between oscillating and stationary cylinders.

The linear stability of Two axially superposed immiscible fluids between Two rotating coaxial cylinders is studied. The fluids are assumed to have equal density but different viscosities. The effect of viscosity ratio of the Two fluids on the condition for onset of instability is studied. The critical Taylor number in the less viscous fluid for onset of instability is obtained as a function of the viscosity ratio. The Two limiting values of this curve correspond to critical Taylor numbers of the one fluid configuration with height of fluid column either equal to that of the less viscous fluid or equal to the sum of those for both liquids. It is found that the variation of the critical Taylor number with viscosity ratio is small when the heights of the fluid columns are large compared to the gap between the cylinders but is significant when the heights are comparable with the gap. The marginal state is found to be stationary.

The dynamics of Two-dimensional vortex shedding from a rotating cluster of three cylinders was investigated using Computational Fluid Dynamics (CFD) and Dynamic Mode Decomposition (DMD). The cluster was formed from three circles with equal diameters in mutual contact and allowed to rotate about an axis passing through the cluster centroid. While immersed in an incompressible fluid with Reynolds number of 100, the cluster was allowed to rotate at non-dimensionalised rotation rates (Ω) between 0 and 1. The rotation rates were non-dimensionalised using the free-stream velocity and the cluster characteristic diameter, the latter being equal to the diameter of the circle circumscribing the cluster. CFD simulations were performed using StarCCM+. Dynamic Mode Decomposition based on the Two-dimensional vorticity field was used to decompose the field into its fundamental mode-shapes. It was then possible to relate the mode-shapes to lift and drag. Transverse and longitudinal mode-shapes corresponded to lift and drag, respectively. Lift–drag polars showed a more complex pattern dependent on Ω in which the flow fields could be classified into three regimes: Ω less than 0. 3, greater than 0. 5, and between 0. 3 and 0. 5. In general, the polars formed open curves in contrast to those of static cylinders, which were closed. However, some cases, such as Ω = 0. 01, 0. 22, and 0. 28, formed closed curves. Whether a lift-drag polar was closed or open was deduced to be determined by the ratio of Strouhal numbers calculated using lift and drag time series, with closed curves forming when the ratio is an integer.

In this paper, the flow around bluff bodies with different cross sections and determination of forces acts on them are investigated. This paper presents the results of a numerical study on the flow characteristics and heat transfer over Two equal square cylinders in a tandem arrangement. Spacing between the cylinders is 5 widths of the cylinder and the Reynolds number ranges from 1 to 200, Pr=0.71. Both steady and unsteady incompressible laminar flow in the Two-dimensional regime is studied. A study of the effects of spatial resolution and blockage on the results is provided. In this paper, the instantaneous and mean streamlines, vorticity and isotherm patterns for different Reynolds numbers are presented and discussed. Also the global quantities such as pressure and viscous drag coefficients, Strouhal number and Nusselt number are determined and discussed for various Reynolds numbers.

The possibility of suppressing laminar vortex shedding after a rectangular cylinder with a pair of rotating controllers has been investigated for Re=150. Drag and lift coefficients of the rectangular cylinder have been measured at different positions of the controller system. Numerical results show that the controller system suppresses the vortex shedding completely when installing at some suitable positions. It was found that the controller system affects the vorticity intensity in the separation bubbles at these suitable positions. The controller system may completely eliminate the separation bubble or may make them remain in attached to the cylinder. Besides, the effectiveness sensitivity of the controller system to its rotation rate and Reynolds number was analyzed when installing at the edge of the cylinder boundary layer where its position is denoted by (r/a=2, q=40o). These analyses show that the controller system can still suppress the laminar vortex shedding completely when the rotation rate of the controller system and Reynolds number of the incoming flow change by less than 50%

A mixed semi-analytical cum numerical approach is presented in this paper which accounts for the coupled mechanical and electrical response of piezoelectric, functionally graded (FG) and layered composite hollow circular cylinders of finite length. Under axisymmetric mechanical and electrical loadings, the three-dimensional problem (3D) gets reduced to a Two-dimensional (2D) plane strain problem of elasticity. The 2D problem is further simplified and reduced to a one-dimensional (1D) by assuming an analytical solution in longitudinal direction (z) in terms of Fourier series expansion which satisfies the simply (diaphragm) supported boundary conditions exactly at the Two ends z=0, l. Fundamental (basic) dependent variables are chosen in the radial direction (thickness coordinate) of the cylinder. The resulting mathematical model is cast in the form of first order simultaneous ordinary differential equations which are integrated through an effective numerical integration technique by first transforming the BVP into a set of initial value problems (IVPs). The cylinder is subjected to internal/external pressurized mechanical and an electrical loading. Finally, numerical results are obtained which govern the active and sensory response of piezoelectric and FG cylinders. Numerical results are compared for their accuracy with available results. New results of finite length cylinders are generated and presented for future reference.