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  • Articles  (5)
  • Cambridge University Press  (5)
  • 2005-2009  (5)
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  • Articles  (5)
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  • 1
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    Suppression of vortex shedding behind a circular cylinder by another control cylinder at low Reynolds numbers (2007)
    Cambridge University Press
    Details
    Publication Date: 2007-02-01
    Description: Vortex shedding behind a cylinder can be controlled by placing another small cylinder behind it, at low Reynolds numbers. This has been demonstrated experimentally by Strykowski & Sreenivasan (J. Fluid Mech. vol. 218, 1990, p. 74). These authors also provided preliminary numerical results, modelling the control cylinder by the innovative application of boundary conditions on some selective nodes. There are no other computational and theoretical studies that have explored the physical mechanism. In the present work, using an over-set grid method, we report and verify numerically the experimental results for flow past a pair of cylinders. Apart from providing an accurate solution of the Navier-Stokes equation, we also employ an energy-based receptivity analysis method to discuss some aspects of the physical mechanism behind vortex shedding and its control. These results are compared with the flow picture developed using a dynamical system approach based on the proper orthogonal decomposition (POD) technique. © 2007 Cambridge University Press.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 2
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    Subcritical instability on the attachment-line of an infinite swept wing (2005)
    Cambridge University Press
    Details
    Publication Date: 2005-04-25
    Description: The leading-edge contamination (LEC) problem of an infinite swept wing is shown here as vortex-induced instability. The governing equation for receptivity is presented for LEC in terms of disturbance energy based on the Navier-Stokes equation. The unperturbed shear layer given by the swept Hiemenz boundary-layer solution is two-dimensional and an exact solution of incompressible the Navier-Stokes equation. Thus, the LEC problem is solved numerically by solving the full two-dimensional Navier Stokes equation. The contamination at the attachment-line is shown by solving a receptivity to a convecting vortex moving outside the attachment-line boundary layer, which triggers subcritical spatio-temporal instability. The mechanism of LEC is shown to be due es sentially to a convecting counter-clockwise rotating vortex, whereas a clockwise rotating vortex displays much weaker receptivity. These results are consistent with experimental results for the bypass mechanism. The role of linear and n onlinear mechanisms in the contamination problem is discussed as interactions between vorticity and velocity terms of the developed receptivity equation. The computed temporal growth rates reveal pattern formation during such instabilities. Proper orthogonal decomposition (POD) of the numerical solution shows the structure of the leading eigenvector as the coherent eddy excited during the bypass transition. © 2005 Cambridge University Press.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 3
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    Accelerated flow past a symmetric aerofoil: experiments and computations (2007)
    Cambridge University Press
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    Publication Date: 2007-10-30
    Description: Accelerated flow past a NACA 0015 aerofoil is investigated experimentally and computationally for Reynolds number Re = 7968 at an angle of attack α = 30°. Experiments are conducted in a specially designed piston-driven water tunnel capable of producing free-stream velocity with different ramp-type accelerations, and the DPIV technique is used to measure the resulting flow field past the aerofoil. Computations are also performed for other published data on flow past an NACA 0015 aerofoil in the range 5200 ≤ Re ≤ 35000, at different angles of attack. One of the motivations is to see if the salient features of the flow captured experimentally can be reproduced numerically. These computations to solve the incompressible Navier-Stokes equation are performed using high-accuracy compact schemes. Load and moment coefficient variations with time are obtained by solving the Poisson equation for the total pressure in the flow field. Results have also been analysed using the proper orthogonal decomposition technique to understand better the evolving vorticity field and its dependence on Reynolds number and angle of attack. An energy-based stability analysis is performed to understand unsteady flow separation. © 2007 Cambridge University Press.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 4
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    Fragmented landholding, productivity, and resilience management (2006)
    Cambridge University Press
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    Publication Date: 2006-07-13
    Description: The operation of a number of non-contiguous parcels of land as a single farming unit is known as land fragmentation. It is a widespread and persistent phenomenon and, at the same time, widely criticized by development agencies. Available evidence clearly suggests that the unqualified faith in the merit of consolidation is not justified; fragmentation may have some rationale. This paper substantiates the latter position with a case study of an irrigated agricultural system. Thereafter, it locates fragmentation within the broader context and analyses its role within a hierarchy of phenomena in the linked social and ecological local system. For this analysis an evolutionary game model is used. It is shown that fragmentation increases the resilience of the system of cooperation. The study concludes by suggesting an appropriate strategy for resilience management.
    Print ISSN: 1355-770X
    Electronic ISSN: 1469-4395
    Topics: Economics
    Published by Cambridge University Press
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  • 5
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    Optimal time for investment to regulate emissions of particulate matter in Indian thermal power plants (2007)
    Cambridge University Press
    Details
    Publication Date: 2007-12-01
    Description: This study aims to find the optimal switching point for the Indian coal-based power plants to switch to a cost-effective technology and reduce particulate emissions. Regulation in the form of an emission standard, an emissions tax, an ash tax, or a coal tax provides an incentive for the power plants to abate. We have taken a period of 40 years to show the pattern of abatement in a sample of 40 power plants. Linear programming using GAMS has been used for the analysis to determine when the plants will shift to cost-efficient technology. We have first done the analysis on a firm-to-firm basis and then we have aggregated to show the variability of our results.
    Print ISSN: 1355-770X
    Electronic ISSN: 1469-4395
    Topics: Economics
    Published by Cambridge University Press
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