Sanjeev Sanghi | Indian Institute of Technology Delhi (original) (raw)
Papers by Sanjeev Sanghi
AIP Conference Proceedings, Dec 31, 2022
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Progress in Computational Fluid Dynamics, 2005
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The two -dimensional, thermally driven f low of air (Pr = 0.71) in a steadily rotating horizontal... more The two -dimensional, thermally driven f low of air (Pr = 0.71) in a steadily rotating horizontal cylinder subject to Boussinesq approximation is investigated numerically. A temperature perturbation in the form of a periodic distribution is imposed over the wall of a steadily rotating cylinder w ith air in a state of solid -body rotation inside it. The relative motion with respect to the solid -body rotation, induced by the combined effect of gravitational and centrifugal buoyancy forces is studied by employing a Cartesian frame rotating with the c ylinder. In addition to these body forces, the fluid motion with respect to the rotating frame also experiences coriolis forces. A semi -explicit pressure correction scheme is employed on a Cartesian colocated mesh to numerically integrate the dimensionles s coupled equations of mass, momentum and energy in time. The dimensionless governing equations involve four dimensionless parameters: 1) Gravitational Rayleigh Number (Ra g) 2) Rotational Rayleigh Number (Ra �) 3) Taylor number (Ta) and 4) Prandtl number ( Pr). The investigation is carried out for Ra g = 10 4 , 10 5 and 10 6 while at each Ra g,
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Physics of Fluids, Jul 1, 2022
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Springer eBooks, 1991
ABSTRACT It is shown here that the dynamics of streamwise rolls of finite length in the wall regi... more ABSTRACT It is shown here that the dynamics of streamwise rolls of finite length in the wall region of a turbulent boundary layer is strongly intermittent. The intermittency is of the heteroclinic type. Streamwise modes participate in explosion events corresponding to a streamwise bursts in physical space. A stability analysis of the systems linearized at fixed points which represent steady rolls is presented in dynamical systems of dimensions as high as 32 and 54 so that bifurcations to intermittency are clearly identified. It is shown that all nonzero streamwise Fourier modes eventually burst, resulting in a streamwise energy cascade during the bursts. The activation of all higher modes is a result of nonlinear phenomena.
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Journal of heat transfer, Aug 15, 2006
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Journal of Sound and Vibration, Dec 1, 2008
A double pendulum with a stopper at the lower joint, as in a mammalian leg, has been studied. The... more A double pendulum with a stopper at the lower joint, as in a mammalian leg, has been studied. The impact has been modelled in a computationally efficient manner using a spring–damper in combination with a logistic function. An estimate of the coefficient of restitution of the impact based on stiffness and the damping coefficient has been developed. The response and
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AIAA Journal, May 1, 2006
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Asia-Pacific Journal of Chemical Engineering, 2011
The proper orthogonal decomposition (POD) has become a very useful tool in the analysis and low‐d... more The proper orthogonal decomposition (POD) has become a very useful tool in the analysis and low‐dimensional modelling of flows. It provides an objective way of identifying the ‘coherent’ structures in a turbulent flow. The application of POD to the case of a thermally driven two‐dimensional flow of air in a horizontal rotating cylinder is presented. The data for the POD analysis are obtained by numerical integrations of the governing equations of mass, momentum and energy. The decomposition based on POD modes or eigenfunctions is shown to converge to within 5% deviation of the computational data for a maximum of 15 modes for the different cases. The presence of degenerate eigenvalues is an indicator of travelling waves in the flow, and this is confirmed by symmetry in both space and time for the corresponding eigenfunctions. Wave speeds are also determined for these travelling waves. Furthermore, low‐dimensional models are constructed employing a Galerkin procedure. The low‐dimensional models yield accurate qualitative as well as quantitative behaviour of the system. Not more than 20 modes are required in the low‐dimensional models to accurately model the system dynamics. The ability of low‐dimensional models to accurately predict the system behaviour for the set of parameters different from the one they were constructed from is also examined. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
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Defence Science Journal, Jul 1, 2004
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Journal of Applied Fluid Mechanics, 2019
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Springer eBooks, 2021
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Lecture notes in mechanical engineering, Sep 21, 2016
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Journal of Fluid Mechanics, Feb 1, 2007
A proper orthogonal decomposition (POD) analysis and low-dimensional modelling of thermally drive... more A proper orthogonal decomposition (POD) analysis and low-dimensional modelling of thermally driven two-dimensional flow of air in a horizontal rotating cylinder, subject to the Boussinesq approximation, is considered. The problem is unsteady due to the harmonic nature of the gravitational buoyancy force with respect to the rotating observer and is characterized by four dimensionless numbers: gravitational Rayleigh number (Rag), the rotational Rayleigh number (RaΩ), the Taylor number (Ta) and Prandtl number (Pr). The data for the POD analysis are obtained by numerical integration of the governing equations of mass, momentum and energy. The POD is applied to the computational data for RaΩ varying in the range 102–106 while Rag and Pr are fixed at 105 and 0.71 respectively. The ratio of Ta to RaΩ is fixed at 100 so that the results apply to physically realistic situations. A new criterion, in the form of appropriately defined error norms, for assessing the truncation error of the POD expansion is proposed. It is shown that these error norms reflect the accuracy of the POD-based reconstructions of a given data ensemble better than the widely employed average energy criterion. The translational symmetry in both space and time of the pair of modes having degenerate (equal) eigenvalues confirms the presence of travelling waves in the flow for several different RaΩ values. The shifts in space and time of the structure of the degenerate modes are utilized to estimate the wave speeds in a given direction. The governing equations for the fluctuations are derived and low-dimensional models are constructed by employing a Galerkin procedure. For each of the five values of RaΩ, the low-dimensional models yield accurate qualitative as well as quantitative behaviour of the system. Sufficient modes are included in the low-dimensional models so that the modelling of the unresolved scales of motion is not needed to stabilize their solution. Not more than 20 modes are required in the low-dimensional models to accurately model the system dynamics. The ability of low-dimensional models to accurately predict the system behaviour for a set of parameters different from those from which they were constructed is also examined.
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PhDT, Sep 1, 1992
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Progress in Computational Fluid Dynamics, 2015
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Journal of Fluid Mechanics, Aug 23, 2021
We present an experimental and numerical investigation of electrokinetic instability (EKI) in mic... more We present an experimental and numerical investigation of electrokinetic instability (EKI) in microchannel flow with streamwise conductivity gradients, such as those observed during sample stacking in capillary electrophoresis. A plug of a low-conductivity electrolyte solution is initially sandwiched between two high-conductivity zones in a microchannel. This spatial conductivity gradient is subjected to an external electric field applied along the microchannel axis, and for sufficiently strong electric fields an instability sets in. We have explored the physics of this EKI through experiments and numerical simulations, and supplemented the results using scaling analysis. We performed EKI experiments at different electric field values and visualised the flow using a passive fluorescent tracer. The experimental data were analysed using the proper orthogonal decomposition technique to obtain a quantitative measure of the threshold electric field for the onset of instability, along with the corresponding coherent structures. To elucidate the physical mechanism underlying the instability, we performed high-resolution numerical simulations of ion transport coupled with fluid flow driven by the electric body force. Simulations reveal that the non-uniform electroosmotic flow due to axially varying conductivity field causes a recirculating flow within the low-conductivity region, and creates a new configuration wherein the local conductivity gradients are orthogonal to the applied electric field. This configuration leads to EKI above a threshold electric field. The spatial features of the instability predicted by the simulations and the threshold electric field are in good agreement with the experimental observations and provide useful insight into the underlying mechanism of instability.
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Motivated by a developmental approach of using micro-actuated surface protrusions to control/mane... more Motivated by a developmental approach of using micro-actuated surface protrusions to control/maneuver slender bodies in supersonic flight, this paper presents a detailed study of a two dimensional laminar supersonic flow over a flat plate with a surface protrusion. The flow field is computed by solving the Navier-Stokes equations using the finite difference method with the particle velocity upwinding scheme (PVUS) for spatial discretization, and the explicit Mac Cormack scheme for temporal integration. A range of free stream Mach numbers (2.0 4.5), Reynolds numbers (1000 - 100000) and protrusion heights (0.866% to 8.66% of the characteristic length) has been considered for a thorough parametric study. The parametric study indicates that the oblique shock structure and strength are influenced by all the variables to varying extents. However, the shock location is substantially altered by the protrusion height, Reynolds number, and protrusion shape, while the influence of Mach number is only marginal. An increase in the protrusion height results in an increased wall pressure as well as increased separation lengths on both sides of the protrusion. In contrast, an increase in Mach number increases the wall pressure, but moves the separation point marginally towards the protrusion. Increase in Reynolds number and protrusion bluffness (triangular → trapezoidal → rectangular) increases separation lengths on both sides of the protrusion. In addition to taking a close look at the flow physics, particularly in the protrusion vicinity, considerable attention has also been devoted to important design parameters such as wall pressure, skin friction and the overall normal and tangential force coefficients.
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AIP Conference Proceedings, Dec 31, 2022
Bookmarks Related papers MentionsView impact
Progress in Computational Fluid Dynamics, 2005
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The two -dimensional, thermally driven f low of air (Pr = 0.71) in a steadily rotating horizontal... more The two -dimensional, thermally driven f low of air (Pr = 0.71) in a steadily rotating horizontal cylinder subject to Boussinesq approximation is investigated numerically. A temperature perturbation in the form of a periodic distribution is imposed over the wall of a steadily rotating cylinder w ith air in a state of solid -body rotation inside it. The relative motion with respect to the solid -body rotation, induced by the combined effect of gravitational and centrifugal buoyancy forces is studied by employing a Cartesian frame rotating with the c ylinder. In addition to these body forces, the fluid motion with respect to the rotating frame also experiences coriolis forces. A semi -explicit pressure correction scheme is employed on a Cartesian colocated mesh to numerically integrate the dimensionles s coupled equations of mass, momentum and energy in time. The dimensionless governing equations involve four dimensionless parameters: 1) Gravitational Rayleigh Number (Ra g) 2) Rotational Rayleigh Number (Ra �) 3) Taylor number (Ta) and 4) Prandtl number ( Pr). The investigation is carried out for Ra g = 10 4 , 10 5 and 10 6 while at each Ra g,
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Physics of Fluids, Jul 1, 2022
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Springer eBooks, 1991
ABSTRACT It is shown here that the dynamics of streamwise rolls of finite length in the wall regi... more ABSTRACT It is shown here that the dynamics of streamwise rolls of finite length in the wall region of a turbulent boundary layer is strongly intermittent. The intermittency is of the heteroclinic type. Streamwise modes participate in explosion events corresponding to a streamwise bursts in physical space. A stability analysis of the systems linearized at fixed points which represent steady rolls is presented in dynamical systems of dimensions as high as 32 and 54 so that bifurcations to intermittency are clearly identified. It is shown that all nonzero streamwise Fourier modes eventually burst, resulting in a streamwise energy cascade during the bursts. The activation of all higher modes is a result of nonlinear phenomena.
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Journal of heat transfer, Aug 15, 2006
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Journal of Sound and Vibration, Dec 1, 2008
A double pendulum with a stopper at the lower joint, as in a mammalian leg, has been studied. The... more A double pendulum with a stopper at the lower joint, as in a mammalian leg, has been studied. The impact has been modelled in a computationally efficient manner using a spring–damper in combination with a logistic function. An estimate of the coefficient of restitution of the impact based on stiffness and the damping coefficient has been developed. The response and
Bookmarks Related papers MentionsView impact
AIAA Journal, May 1, 2006
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Asia-Pacific Journal of Chemical Engineering, 2011
The proper orthogonal decomposition (POD) has become a very useful tool in the analysis and low‐d... more The proper orthogonal decomposition (POD) has become a very useful tool in the analysis and low‐dimensional modelling of flows. It provides an objective way of identifying the ‘coherent’ structures in a turbulent flow. The application of POD to the case of a thermally driven two‐dimensional flow of air in a horizontal rotating cylinder is presented. The data for the POD analysis are obtained by numerical integrations of the governing equations of mass, momentum and energy. The decomposition based on POD modes or eigenfunctions is shown to converge to within 5% deviation of the computational data for a maximum of 15 modes for the different cases. The presence of degenerate eigenvalues is an indicator of travelling waves in the flow, and this is confirmed by symmetry in both space and time for the corresponding eigenfunctions. Wave speeds are also determined for these travelling waves. Furthermore, low‐dimensional models are constructed employing a Galerkin procedure. The low‐dimensional models yield accurate qualitative as well as quantitative behaviour of the system. Not more than 20 modes are required in the low‐dimensional models to accurately model the system dynamics. The ability of low‐dimensional models to accurately predict the system behaviour for the set of parameters different from the one they were constructed from is also examined. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.
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Defence Science Journal, Jul 1, 2004
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Journal of Applied Fluid Mechanics, 2019
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Springer eBooks, 2021
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Lecture notes in mechanical engineering, Sep 21, 2016
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Journal of Fluid Mechanics, Feb 1, 2007
A proper orthogonal decomposition (POD) analysis and low-dimensional modelling of thermally drive... more A proper orthogonal decomposition (POD) analysis and low-dimensional modelling of thermally driven two-dimensional flow of air in a horizontal rotating cylinder, subject to the Boussinesq approximation, is considered. The problem is unsteady due to the harmonic nature of the gravitational buoyancy force with respect to the rotating observer and is characterized by four dimensionless numbers: gravitational Rayleigh number (Rag), the rotational Rayleigh number (RaΩ), the Taylor number (Ta) and Prandtl number (Pr). The data for the POD analysis are obtained by numerical integration of the governing equations of mass, momentum and energy. The POD is applied to the computational data for RaΩ varying in the range 102–106 while Rag and Pr are fixed at 105 and 0.71 respectively. The ratio of Ta to RaΩ is fixed at 100 so that the results apply to physically realistic situations. A new criterion, in the form of appropriately defined error norms, for assessing the truncation error of the POD expansion is proposed. It is shown that these error norms reflect the accuracy of the POD-based reconstructions of a given data ensemble better than the widely employed average energy criterion. The translational symmetry in both space and time of the pair of modes having degenerate (equal) eigenvalues confirms the presence of travelling waves in the flow for several different RaΩ values. The shifts in space and time of the structure of the degenerate modes are utilized to estimate the wave speeds in a given direction. The governing equations for the fluctuations are derived and low-dimensional models are constructed by employing a Galerkin procedure. For each of the five values of RaΩ, the low-dimensional models yield accurate qualitative as well as quantitative behaviour of the system. Sufficient modes are included in the low-dimensional models so that the modelling of the unresolved scales of motion is not needed to stabilize their solution. Not more than 20 modes are required in the low-dimensional models to accurately model the system dynamics. The ability of low-dimensional models to accurately predict the system behaviour for a set of parameters different from those from which they were constructed is also examined.
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PhDT, Sep 1, 1992
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Progress in Computational Fluid Dynamics, 2015
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Journal of Fluid Mechanics, Aug 23, 2021
We present an experimental and numerical investigation of electrokinetic instability (EKI) in mic... more We present an experimental and numerical investigation of electrokinetic instability (EKI) in microchannel flow with streamwise conductivity gradients, such as those observed during sample stacking in capillary electrophoresis. A plug of a low-conductivity electrolyte solution is initially sandwiched between two high-conductivity zones in a microchannel. This spatial conductivity gradient is subjected to an external electric field applied along the microchannel axis, and for sufficiently strong electric fields an instability sets in. We have explored the physics of this EKI through experiments and numerical simulations, and supplemented the results using scaling analysis. We performed EKI experiments at different electric field values and visualised the flow using a passive fluorescent tracer. The experimental data were analysed using the proper orthogonal decomposition technique to obtain a quantitative measure of the threshold electric field for the onset of instability, along with the corresponding coherent structures. To elucidate the physical mechanism underlying the instability, we performed high-resolution numerical simulations of ion transport coupled with fluid flow driven by the electric body force. Simulations reveal that the non-uniform electroosmotic flow due to axially varying conductivity field causes a recirculating flow within the low-conductivity region, and creates a new configuration wherein the local conductivity gradients are orthogonal to the applied electric field. This configuration leads to EKI above a threshold electric field. The spatial features of the instability predicted by the simulations and the threshold electric field are in good agreement with the experimental observations and provide useful insight into the underlying mechanism of instability.
Bookmarks Related papers MentionsView impact
Motivated by a developmental approach of using micro-actuated surface protrusions to control/mane... more Motivated by a developmental approach of using micro-actuated surface protrusions to control/maneuver slender bodies in supersonic flight, this paper presents a detailed study of a two dimensional laminar supersonic flow over a flat plate with a surface protrusion. The flow field is computed by solving the Navier-Stokes equations using the finite difference method with the particle velocity upwinding scheme (PVUS) for spatial discretization, and the explicit Mac Cormack scheme for temporal integration. A range of free stream Mach numbers (2.0 4.5), Reynolds numbers (1000 - 100000) and protrusion heights (0.866% to 8.66% of the characteristic length) has been considered for a thorough parametric study. The parametric study indicates that the oblique shock structure and strength are influenced by all the variables to varying extents. However, the shock location is substantially altered by the protrusion height, Reynolds number, and protrusion shape, while the influence of Mach number is only marginal. An increase in the protrusion height results in an increased wall pressure as well as increased separation lengths on both sides of the protrusion. In contrast, an increase in Mach number increases the wall pressure, but moves the separation point marginally towards the protrusion. Increase in Reynolds number and protrusion bluffness (triangular → trapezoidal → rectangular) increases separation lengths on both sides of the protrusion. In addition to taking a close look at the flow physics, particularly in the protrusion vicinity, considerable attention has also been devoted to important design parameters such as wall pressure, skin friction and the overall normal and tangential force coefficients.
Bookmarks Related papers MentionsView impact