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.

An analytical solution is presented for the steady state and purely tangential flow of a nonlinear viscoelastic fluid obeying the constitutive FENE-P model in a concentric annulus with inner cylinder rotation. The effect of fluid elasticity (Weissenberg number), the extensibility parameter of the model (L2 ) and aspect ratio on the velocity profile and production of friction factor and Reynolds number (¦¢Re) are investigated. The results show the strong effect of viscoelastic parameters on the velocity profile. The results also show that ¦¢Re decreases with increasing fluid elasticity and radius ratio.

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%

The objective of this article is to study gas temperature estimation in a partially filled Rotating cylinder. From the measured temperatures on the shell, an inverse analysis is presented for estimating the gas temperature in an arbitrary cross-section of the aforementioned system. A finite-volume method is employed to solve the direct problem. By minimizing the objective function, a hybrid effective algorithm, which contains a local optimization algorithm, is adopted to estimate the unknown parameter. The measured data are simulated by adding random errors to the exact solution. The effects of measurement errors on the accuracy of the inverse analysis are investigated. Two optimization algorithms are used in determination of the gas temperature. The conjugate gradient method is found to be better than the Levenberg-Marquardt method, since the former produces more accurate results for the same measurement errors. A good agreement between the exact value and the estimated result has been observed for both algorithms.

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.

Flow and thermal characteristics of mixed convection in a nanofluid filled wavy conduit were numerically investigated in this study. The conduit was considered to contain a pair of Rotating cylinders. It was heated and cooled from its lower and upper wavy surfaces, respectively. The Rotating cylinders were placed along the centerline of the wavy conduit. It was also permeated by an external magnetic field. Finite element method was employed to simulate the conservation equations. Based on the current investigation, a new model was developed to improve the thermal conductivity of nano fluids inside a wavy conduit. In addition, a detailed parametric study was conducted to visualize the effects of dimensionless key parameters on the flow structure and temperature field in the conduit. The numerical results indicated that the physical parameters could noticeably affect both fluid flow using streamlines and temperature distributions using isotherm contours and average Nusselt number. The Rotating cylinders, wavy surfaces, and inclined magnetic field were found to have the most significant effects on the heat transfer mechanism. Maximum heat transfer occurred when placing the magnetic field at an angle of 90o.