Articles written in Sadhana

    • Convective transport around two rotating tandem circular cylinders at low Reynolds numbers


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      The convective transport around two rotating circular cylinders kept in a tandem configuration to an unconfined flow of an incompressible fluid (Prandtl number, Pr = 0.717) is investigated through two-dimensional numerical simulation. The flow Reynolds number is considered constant at Re = 100. Four different gapspacings between the tandem cylinders such as 0.2, 0.7, 1.5 and 3.0 are chosen for simulation. The cylinders are rotating about their centroidal axes for a range of dimensionless speed (0<=W<=2.75). The rotation to the objects causes the unsteady periodic flow around them to become stabilized and at some critical rotational speed, the vortex shedding stops completely resulting in a steady flow pattern. The critical speed of rotation at which the vortex shedding completely stops is a function of the cylinder spacing. Overall, it is observed that increasing the gap increases the critical rotation rate. The thermal fields are also strongly stabilized as a result of the cylinder rotation. The rotating cylinders actually create a zone in their proximity which acts like a buffer to the convective transport. The conduction mode of heat transfer predominates in these regions causing the heat transfer rate to assume a decaying pattern with increasing the rotational speed at all cylinder spacings.

    • Estimation of critical rotation rates for suppression of steady separation bubble behind a circular cylinder


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      An effort has been made in this paper to numerically estimate the critical rotational speeds for which the steady separation bubble completely disappears behind a circular cylinder. The cylinder is subjected to an unconfined free stream flow, however, fictitious confining boundaries are considered for computationalconvenience. The Reynolds numbers computed from the free stream flow velocity are considered in the range of 10–40. In this range of Reynolds number, the flow around a stationary circular cylinder remains steady and separated with the formation of a recirculation zone through counter-rotating vortices (separation bubble) behind the body. Rotational motion is provided to the cylinder that causes stabilization of the flow field. The separation bubble vanishes and an attached type flow feature is observed. The rotational speeds at which the recirculating zone behind the cylinder completely vanishes in the said range of Reynolds number are considered as the critical rotation rates. The aerodynamic coefficients are obtained for the specific operating conditions and a regimediagram is produced depicting the separated and the attached flows.

    • Effect of blockage on fluid flow past a square cylinder at low Reynolds numbers


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      A channel confined flow around a bluff object is significantly different from its unconfined counterpart. A confined flow is presumably more stabilized due to the presence of the confinement. This causes a delay in the onset of flow separation and vortex shedding in comparison to the unconfined flow. While the abovefacts have been reported for the confined flow around a circular object in a channel, the same for a square object is infrequent. The present study focuses on the steady flow past a stationary square cylinder placed in a channelat low Reynolds numbers (1≤Re≤30). The behavior of the flow is observed through numerical simulation for various channel confinements (0:01≤B≤0:9, blockage ratio). The steady state laminar two-dimensional incompressible flow equations are solved using a finite volume based technique. An effort is made to find the separation critical Reynolds number at all blockages. It is observed that the separation critical Reynolds number increases with an increase in the blockage ratio. Unsteady flow characteristics at various blockages are alsostudied at Re = 100. In the unsteady regime, the frequency of vortex shedding increases with an increase in the blockage.

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