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.

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