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A. Sameen

Bio: A. Sameen is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Reynolds number & Vortex. The author has an hindex of 12, co-authored 44 publications receiving 454 citations. Previous affiliations of A. Sameen include Indian Institute of Science & Jawaharlal Nehru Centre for Advanced Scientific Research.

Papers
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Proceedings ArticleDOI
10 Jul 2005
TL;DR: In this article, a variable ejector system is applied to a hydrogen fuel-cell system to economize the fuel consumption, and detailed experimental and numerical studies have been carried out and the characteristic curves are generated to understand the effects of the ejector throat area ratio and operating pressure ratio on the entrainment of secondary stream.
Abstract: An ejector is a pumping device which exchanges energy between a high energy primary fluid and a relatively low energy secondary fluid to produce a discharge of intermediate specific energy level but higher mass flow rate. The present study addresses a new method to control the performance of a variable ejector system which is applied to a hydrogen fuel-cell system to economize the fuel consumption. Although the variable ejector concept had been proved, its flow characteristics have not yet been established for meeting the industrial demands. Towards achieving this objective, in this paper, detailed experimental and numerical studies have been carried out and the characteristic curves are generated to understand the effects of the ejector throat area ratio and the operating pressure ratio on the entrainment of secondary stream. In the experimentation a movable cylinder, inserted into a conventional ejector-diffuser system, is used to change the ejector throat area ratio, which controls the mass flow rate of the suction flow. In the numerical study, a fully implicit finite volume scheme of the compressible, Reynolds-Averaged, Navier-Stokes equations employed. The results show that the variable ejector can control the recirculation ratio by changing the throat area ratio and the operating pressure ratio.

17 citations

Journal ArticleDOI
TL;DR: In this paper, the effects of compressibility on the local streamline topology and vortical structure of high-speed mixing layers of turbulent flows were investigated. But the connection between vortex orientation and kinetic energy production was not investigated.
Abstract: Direct numerical simulations of high-speed mixing layers are used to characterize the effects of compressibility on the basis of local streamline topology and vortical structure. Temporal simulations of the mixing layers are performed using a finite volume gas-kinetic scheme for convective Mach numbers ranging from wherein larger angles with streamwise direction are preferred. The connection between vortex orientation and kinetic energy production is also investigated. The findings lead to improved insight into turbulence suppression dynamics in high Mach number turbulent flows.

17 citations

Journal ArticleDOI
01 Apr 2009-EPL
TL;DR: In this article, the specific non-Boussinesq roles played by various fluid properties in thermal convection were demonstrated by allowing each of them to possess, one at a time, a temperature dependence that could be either positive or negative.
Abstract: We demonstrate the specific non-Boussinesq roles played by various fluid properties in thermal convection by allowing each of them to possess, one at a time, a temperature dependence that could be either positive or negative. The negative temperature dependence of the coefficient of thermal expansion hinders effective thermal convection and reduces the Nusselt number, whereas the negative dependence of fluid density enhances the Nusselt number. Viscosity merely smears plume generation and has a marginal effect on heat transport, whether it increases or decreases with temperature. At the moderate Rayleigh number examined here, the specific heat capacity shows no appreciable effect. On the other hand, the conductivity of the fluid near the hot surface controls the heat transport from the hot plate to the fluid, which suggests that a less conducting fluid near the bottom surface will reduce the Nusselt number and the bulk temperature.

16 citations

Journal ArticleDOI
TL;DR: In this paper, a boundary layer flow over a porous laminated flat plate is analyzed and the porosity of the porous region is modeled as an array of circular cylinders kept in the span-wise direction of the flow.

13 citations

Journal ArticleDOI
TL;DR: In this article, the flow over a porous laminated flat plate is investigated from a flow control perspective through experiments and computations, where a square array of circular cylinders is used to model the porous lamination and the velocities at the fluid-porous interface by solving the Navier-Stokes and the continuity equations using a staggered flow solver and using LDV in experiments.
Abstract: The flow over a porous laminated flat plate is investigated from a flow control perspective through experiments and computations. A square array of circular cylinders is used to model the porous lamination. We determine the velocities at the fluid–porous interface by solving the two-dimensional Navier–Stokes and the continuity equations using a staggered flow solver and using LDV in experiments. The control parameters for the porous region are porosity, $$\phi $$ and Reynolds number, Re, based on the diameter of the circular cylinders used to model the porous lamination. Computations are conducted for $$0.4< \phi < 0.9$$ and $$25< Re < 1000$$ , and the experiments are conducted for $$\phi = 0.65$$ and 0.8 at $$Re \approx 391,\ 497$$ and 803. The permeability of the porous lamination is observed to induce a slip velocity at the interface, effectively making it a slip wall. The slip velocity is seen to be increasing functions of $$\phi $$ and Re. For higher porosities at higher Re, the slip velocity shows non-uniform and unsteady behavior and a breakdown Reynolds number is defined based on this characteristic. A map demarcating the two regimes of flow is drawn from the computational and experimental data. We observe that the boundary layer over the porous lamination is thinner than the Blasius boundary layer and the shear stress is higher at locations over the porous lamination. We note that the porous lamination helps maintain a favorable pressure gradient at the interface which delays separation. The suitable range of porosities for effective passive separation control is deduced from the results.

13 citations


Cited by
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Book ChapterDOI
01 Jan 1997
TL;DR: The boundary layer equations for plane, incompressible, and steady flow are described in this paper, where the boundary layer equation for plane incompressibility is defined in terms of boundary layers.
Abstract: The boundary layer equations for plane, incompressible, and steady flow are $$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

2,598 citations

Journal ArticleDOI
TL;DR: Key emphasis is given to the physics and structure of the thermal and velocity boundary layers which play a key role for the better understanding of the turbulent transport of heat and momentum in convection at high and very high Rayleigh numbers.
Abstract: Recent experimental, numerical and theoretical advances in turbulent Rayleigh-Benard convection are presented. Particular emphasis is given to the physics and structure of the thermal and velocity boundary layers which play a key role for the better understanding of the turbulent transport of heat and momentum in convection at high and very high Rayleigh numbers. We also discuss important extensions of Rayleigh-Benard convection such as non-Oberbeck-Boussinesq effects and convection with phase changes.

630 citations

Journal ArticleDOI
TL;DR: A review of linear instability analysis of flows over or through complex 2D and 3D geometries is presented in this article, where the authors make a conscious effort to demystify both the tools currently utilized and the jargon employed to describe them, demonstrating the simplicity of the analysis.
Abstract: This article reviews linear instability analysis of flows over or through complex two-dimensional (2D) and 3D geometries. In the three decades since it first appeared in the literature, global instability analysis, based on the solution of the multidimensional eigenvalue and/or initial value problem, is continuously broadening both in scope and in depth. To date it has dealt successfully with a wide range of applications arising in aerospace engineering, physiological flows, food processing, and nuclear-reactor safety. In recent years, nonmodal analysis has complemented the more traditional modal approach and increased knowledge of flow instability physics. Recent highlights delivered by the application of either modal or nonmodal global analysis are briefly discussed. A conscious effort is made to demystify both the tools currently utilized and the jargon employed to describe them, demonstrating the simplicity of the analysis. Hopefully this will provide new impulses for the creation of next-generation algorithms capable of coping with the main open research areas in which step-change progress can be expected by the application of the theory: instability analysis of fully inhomogeneous, 3D flows and control thereof.

599 citations

Journal ArticleDOI
TL;DR: In this article, a review highlights the profound and unexpected ways in which viscosity varying in space and time can affect flow and the most striking manifestations are through alterations of flow stability, as established in model shear flows and industrial applications.
Abstract: This review highlights the profound and unexpected ways in which viscosity varying in space and time can affect flow. The most striking manifestations are through alterations of flow stability, as established in model shear flows and industrial applications. Future studies are needed to address the important effect of viscosity stratification in such diverse environments as Earth's core, the Sun, blood vessels, and the re-entry of spacecraft.

231 citations