Showing papers by "Dilip K. Maiti published in 2011"

Dependence of flow characteristics of rectangular cylinders near a wall on the incident velocity

Abstract: Numerically simulated results are presented for a family of rectangular cylinders with aspect ratios r 1 (=b/a with height a and width b) ranging from 0.1 to 1.0 (square cylinder) to gain a better insight into the dependency of the aerodynamic characteristics on the operational dimensionless parameters, namely Reynolds number Re and aspect ratio r 1. This work describes the flow from a long cylinder of rectangular cross-section placed parallel to a wall and subjected to a uniform shear flow. The flow is investigated in the laminar Reynolds number range (based on the incident stream at the cylinder upstream face and the height of the cylinder) at cylinder to wall gap height 0.5 times the cylinder height. The governing unsteady Navier–Stokes equations are solved numerically through a finite volume method on a staggered grid system using QUICK scheme for convective terms. The resulting equations are then solved by an implicit, time-marching, pressure correction-based SIMPLE algorithm for Reynolds number up to 1,000. The critical Reynolds numbers at which vortex shedding from the cylinder is started are specified for both the cases: far from the wall and near to the wall. It is reported that the vortex shedding from the rectangular cylinder of lower aspect ratio r 1 (≤ 0.25) becomes regular and insensitive to the Reynolds number, while the aerodynamic characteristics of the rectangular cylinders with higher aspect ratio r 1 (≥ 0.5) are strongly dependent on the Reynolds number.

Numerical study on heat/mass transfer by shear/thermal/solutal-convection in a cavity under counteracting buoyancies

Abstract: This study provides physical insights into a lid-driven square cavity filled with a mixture of a solvent vapor and non-condensable gas, subjected to the vertically parallel thermal and solutal gradients. The top lid is maintained at constant speed while bottom lid and the other two walls are kept fixed. Zero heat and mass fluxes are imposed on the vertical side walls. The transport equations are solved numerically through a pressure-correction-based iterative algorithm (SIMPLE) with the QUICK scheme for convective terms. The diffusivities of heat and salt are assumed to be equal throughout this investigation. The essential details of flow, temperature and concentration fields are presented for the opposing buoyancy forces ratio (B < 0) with special attention being given for the values of parameters for which either the flow inside the cavity is operated by the mechanically induced convection; or the flow structure inside the cavity is akin to a single-diffusive thermal or solutal convection. The variations of average rates of heat and mass transfer are uniform with the Reynolds number, while the variations of these quantities against the solutal Richardson number (RiC) and thermal Richardson number (RiT) point to the existence of the local minimum/maximum. Finally, two linear relations between RiC and RiT at a constant sliding speed are proposed to identify the above points of high and low transport phenomena and justified with the exhibition of the flow structures inside the cavity.

Addition of Halide to π‐Bond Directly from Aqueous NaX Solution: A General Strategy for Installation of Two Different Functional Groups.

Abstract: Activation of π-bonds with organic Lewis acid and cationic surfactant mediates direct transfer of halides to alkynes (I) and alkenes (III), (V), (VII) and (IX) and affords α,α-dihaloketones (II) and 1,2-halohydrins (IV), (VI), (VIII) and (X), resp., with high regio- and stereoselectivity.

First Synthesis of Fused-Δ1-pyrrolines via Intramolecular 1,3-Dipolar Cycloaddition of Ketoimine: A Complete Diastereoselective Approach.

Abstract: Aldimines (V) and (VII) undergo intermolecular formal cycloaddition of an azomethine ylide to the imine moiety to produce imadazole structures.