Jagadeesh Gopalan - Academia.edu (original) (raw)

Papers by Jagadeesh Gopalan

i-manager's Journal on Electrical Engineering, 2014

Physics of Fluids, 2007

Experimental results on the effect of energy deposition using an electric arc discharge, upstream... more Experimental results on the effect of energy deposition using an electric arc discharge, upstream of a 60° half angle blunt cone configuration in a hypersonic flow stream is reported. Investigations involving drag measurements and high speed Schlieren flow visualization have been carried out in a hypersonic shock tunnel using air and argon as the test gases; and an unsteady drag reduction of about 50% (maximum reduction) has been observed in the energy deposition experiments done in argon environment. These studies also show that the effect of discharge on the flow field is more pronounced in argon environment as compared to air, which confirms that thermal effects are mainly responsible for flow alteration with discharge. It has also been observed that the interaction of the hypersonic flow with the discharge filament results in the development of an unsteady flow field.

International Journal of Hypersonics, 2010

This paper presents the results of numerical and experimental investigations on sonic jet (nitrog... more This paper presents the results of numerical and experimental investigations on sonic jet (nitrogen) injections into a hypersonic cross-flow of air. The simulations aim at finding suitable injection conditions consistent with the experimental facility at IISc from the viewpoint of combustion. Numerical results under predicted the measured jet penetration depth for normal injection. It is found from numerical simulations that the total pressure loss in case of oblique injection is less than the normal injection.

Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, 2013

The study of detonations and their interactions are vital for the understanding of the highspeed ... more The study of detonations and their interactions are vital for the understanding of the highspeed flow physics involved and the ultimate goal of controlling their detrimental effects. However, producing safe and repeatable detonations within the laboratory can be quite challenging, leading to the use of computational studies which ultimately require experimental data for their validation. It is the objective of the current study to examine the induced flow field from the interaction of a shock front and accompanying products of combustion, produced from the detonation taking place within a non-electrical tube lined with explosive material, with porous plates with varying porosities, 0.7% to 9.7%. State of the art high-speed schlieren photography alongside high resolution pressure measurements are used to visualise the induced flow field and examine the attenuation effects which occur at different porosities. The detonation tube is placed at different distances from the plates' surface, 0 mm to 30 mm, and the pressure at the rear of the plate is recorded and compared. The results indicate that depending on the level of porosity and the Mach number of the precursor shock front secondary reflected and transmitted shock waves are formed through the coalescence of compression waves. With reduced porosity, the plates act almost as a solid surface, therefore the shock propagates faster along its surface.

42nd AIAA Aerospace Sciences Meeting and Exhibit, 2004

This paper deals with the effect of electrical energy deposition on the wave drag experienced by ... more This paper deals with the effect of electrical energy deposition on the wave drag experienced by a 120° apex angle blunt cone flying at Mach 5.75. The experiments are conducted in the Indian Institute of Science (IISc) hypersonic shock tunnel HST-2. The electrical energy is deposited along the stagnation streamline of the model using a spark discharge system powered by a DC power supply. Drag is measured using a single component accelerometer balance mounted inside the blunt cone model. Illustrative numerical simulations are also carried out by solving the 3-D compressible Navier-Stokes equations, for complimenting the experiments. Results from the parametric numerical studies indicate a substantial reduction in drag (20%~65%) as a result of electrical energy deposition (~ 1 kw; source volume ~ 8e−8m3)8e-8m^3)8e−8m3). Preliminary experimental measurements show ~15% reduction in aerodynamic drag around the reentry body whereas ~45% reduction in drag is predicted by the CFD studies for a similar energy source configuration as used in the experiments.

42nd AIAA Aerospace Sciences Meeting and Exhibit, 2004

A new free floating internally mountable balance system that ensures unrestrained motion of the m... more A new free floating internally mountable balance system that ensures unrestrained motion of the model exposed to hypersonic flow in the shock tunnel has been designed, fabricated and tested. The drag force acting on a blunt leading edge flat plate has been measured using the new balance system. The model acceleration in the axial direction is measured using an accelerometer by ensuring unrestrained model motion during testing in the hypersonic shock tunnel. The balance has been calibrated by an impulse hammer. To measure the drag force, normal force and pitching moment of a typical hypersonic vehicle, another free floating balance configuration has been designed, fabricated and tested. Finite element modeling (FEM) and CFD are exhaustively used in the design and calibration of the two balances. The experimentally measured drag force on the blunt leading edge flat plate at nominal Mach number of 5.75 matches well with FEM results. The details of the study are described in this paper.

24th International Congress on High-Speed Photography and Photonics, 2001

ABSTRACT

This paper describes the implementation of Background oriented Schlieren (BOS) technique to captu... more This paper describes the implementation of Background oriented Schlieren (BOS) technique to capture the density field of a blast wave generated through a micro-explosion. The three dimensional density field was reconstructed using the filtered back projection technique. This was carried out at several instants of time in order to capture the evolution of the density field. The reconstructed density field revealed the internal structure of the flow field. The results show that there is a significant variation in density between the forward and rearward propagating parts of the shock wave. This implies that these micro-explosions possess some characteristics similar to a muzzle blast rather than a true point source. PIV measurements were also attempted at several instants of time. However, the alumina particles expelled from the tube had very high S/N ratio resulting in saturation of the CCD. Hence no useful velocity field data could be obtained. The density fields generated in this study helps to understand the flow physics associated with blast waves generated using controlled micro-explosions. The findings can be used to scale laboratory experiments to real life explosions.

SSRN Electronic Journal, 2014

Agriculture is the sector most vulnerable to climate change due to its high dependence on climate... more Agriculture is the sector most vulnerable to climate change due to its high dependence on climate and weather conditions. Climate change is a main challenge for agriculture, food security and rural livelihoods for millions of people in India. Among India's population of more than one billion people, about 68% are directly or indirectly involved in the agricultural sector. This sector is particularly vulnerable to present-day climate variability. In this paper an attempt is made to map and analyze the vulnerability to climate change in different districts of four south Indian states: Andhra Pradesh, Karnataka, Tamil Nadu and Kerala. We have taken five sources of vulnerability indicators: socio-demographic, climatic, agricultural, occupational and common property resources vulnerabilities to compute the composite vulnerability index. The composite vulnerability index suggests that, Adilabad, Chamarajanagar, Thiruvarur and Kasaragod are the most vulnerable districts of Andhra Pradesh, Karnataka, Tamil Nadu and Kerala respectively, whereas Hyderabad, Belgaum, Thoothukkudi, Kottayam are the least vulnerable districts.

Materials Science and Engineering: A, 2015

The AA5086 aluminum alloy sheets with different starting textures were subjected to shock wave de... more The AA5086 aluminum alloy sheets with different starting textures were subjected to shock wave deformation with an input impulse of $ 0.2 Ns. Microstructural examination indicate no significant change in grain size; however, the evolution of substructure manifesting intra-granular misorientation was evident. The improvement in hardness indicates the absence of recovery and strain hardening during shock deformation. Shock deformed samples show characteristic texture evolution with high Brass {110}〈112〉 component. The study demonstrates the viability of high velocity forming of AA5086 aluminum alloy sheet using shock wave.

Shock Waves, 2009

NONEL tube finds vast applications in civil and military because of its safe and confined explosi... more NONEL tube finds vast applications in civil and military because of its safe and confined explosion technique. Spectroscopic and chemical analysis of a NONEL tube with an uniform mixture of HMX and Al is reported here. Peak temperature obtained at the open end of the ...

28th International Symposium on Shock Waves, 2012

A gene is a unit of heredity in a living organism. It normally resides on a stretch of DNA that c... more A gene is a unit of heredity in a living organism. It normally resides on a stretch of DNA that codes for a type of protein or for an RNA chain that has a function in the organism. All living things depend on genes, as they specify all proteins and functional RNA chains. Genes hold the information to build and maintain an organism’s cells and pass genetic traits to offspring. The gene has to be transferred to bacteria or eukaryotic cells for basic and applied molecular biology studies. Bacteria can uptake exogenous genetic material by three ways: conjugation, transduction and transformation. Genetic material is naturally transferred to bacteria in case of conjugation and transferred through bacteriophage in transduction. Transformation is the acquisition of exogenous genetic material through cell wall. The ability of bacteria of being transformed is called competency and those bacteria which have competency are competent cells. Divalent Calcium ions can make the bacteria competent and a heat shock can cause the bacteria to uptake DNA. But the heat shock method cannot be used for all the bacteria. In electroporation, a brief electric shock with an electric field of 10-20kV/cmmakes pores in the cell wall, facilitates the DNA to enter into the bacteria. Microprecipitates, microinjection, liposomes, and biological vectors are also used to transfer polar molecules like DNA into host cells.

Shock Waves, 2009

Experimental results on the effect of energy deposition using an electric arc discharge, upstream... more Experimental results on the effect of energy deposition using an electric arc discharge, upstream of a 60° half angle blunt cone configuration in a hypersonic flow is reported.Investigations involving drag measurements and high speed schlieren flow visualization have been carried out in hypersonic shock tunnel using air and argon as the test gases; and an unsteady drag reduction of about 50% (maximum reduction) has been observed in the energy deposition experiments done in argon environment. These studies also show that the effect of discharge on the flow field is more pronounced in argon environment as compared to air, which confirms that thermal effects are mainly responsible for flow alteration in presence of the discharge.

Shock Waves, 2009

A waverider is a lifting body configuration whose upper surface is parallel to the free stream, a... more A waverider is a lifting body configuration whose upper surface is parallel to the free stream, and the lower surface aerodynamically so designed, that the resulting shock at the design Mach number, is always attached with the leading edge of the vehicle. This prevents spillage from high pressure (lower) surface to the low pressure (upper) surface.In the present study a

Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, 2011

The use of high-velocity sheet-forming techniques where the strain rates are in excess of 102/s c... more The use of high-velocity sheet-forming techniques where the strain rates are in excess of 102/s can help us solve many problems that are difficult to overcome with traditional metal-forming techniques. In this investigation, thin metallic plates/foils were subjected to shock wave loading in the newly developed diaphragmless shock tube. The conventional shock tube used in the aerodynamic applications uses a metal diaphragm for generating shock waves. This method of operation has its own disadvantages including the problems associated with repeatable and reliable generation of shock waves. Moreover, in industrial scenario, changing metal diaphragms after every shot is not desirable. Hence, a diaphragmless shock tube is calibrated and used in this study. Shock Mach numbers up to 3 can be generated with a high degree of repeatability (±4 per cent) for the pressure jumps across the primary shock wave. The shock Mach number scatter is within ±1.5 per cent. Copper, brass, and aluminium pla...

Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, 2011

This article reports experimental results on supersonic combustion in a new facility. The facilit... more This article reports experimental results on supersonic combustion in a new facility. The facility is a combustion-driven shock tunnel, which is cheaper to build than the facilities in which such experiments are carried out conventionally. The observation region is a zone between two parallel flat plates with a 33° wedge attached to the upstream end of the bottom plate. Gaseous hydrogen is injected at an angle of 45° into an oncoming supersonic flow of Mach 2 (approximate) from a port on the bottom plate. The resulting flow field is visualized by a high speed camera in a dark background. Three different test gases, namely nitrogen, air, and oxygen-rich air are used, and the results are compared. A distinct luminosity due to combustion for oxygen-containing test gases is observed. Heat-transfer rates on a probe placed at the downstream end of the observation region and midway between the parallel plates are measured and compared for the three cases. Wall static pressure at 28 mm down...

Measurement, 2009

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright

i-manager's Journal on Electrical Engineering, 2014

Physics of Fluids, 2007

Experimental results on the effect of energy deposition using an electric arc discharge, upstream... more Experimental results on the effect of energy deposition using an electric arc discharge, upstream of a 60° half angle blunt cone configuration in a hypersonic flow stream is reported. Investigations involving drag measurements and high speed Schlieren flow visualization have been carried out in a hypersonic shock tunnel using air and argon as the test gases; and an unsteady drag reduction of about 50% (maximum reduction) has been observed in the energy deposition experiments done in argon environment. These studies also show that the effect of discharge on the flow field is more pronounced in argon environment as compared to air, which confirms that thermal effects are mainly responsible for flow alteration with discharge. It has also been observed that the interaction of the hypersonic flow with the discharge filament results in the development of an unsteady flow field.

International Journal of Hypersonics, 2010

This paper presents the results of numerical and experimental investigations on sonic jet (nitrog... more This paper presents the results of numerical and experimental investigations on sonic jet (nitrogen) injections into a hypersonic cross-flow of air. The simulations aim at finding suitable injection conditions consistent with the experimental facility at IISc from the viewpoint of combustion. Numerical results under predicted the measured jet penetration depth for normal injection. It is found from numerical simulations that the total pressure loss in case of oblique injection is less than the normal injection.

Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, 2013

The study of detonations and their interactions are vital for the understanding of the highspeed ... more The study of detonations and their interactions are vital for the understanding of the highspeed flow physics involved and the ultimate goal of controlling their detrimental effects. However, producing safe and repeatable detonations within the laboratory can be quite challenging, leading to the use of computational studies which ultimately require experimental data for their validation. It is the objective of the current study to examine the induced flow field from the interaction of a shock front and accompanying products of combustion, produced from the detonation taking place within a non-electrical tube lined with explosive material, with porous plates with varying porosities, 0.7% to 9.7%. State of the art high-speed schlieren photography alongside high resolution pressure measurements are used to visualise the induced flow field and examine the attenuation effects which occur at different porosities. The detonation tube is placed at different distances from the plates' surface, 0 mm to 30 mm, and the pressure at the rear of the plate is recorded and compared. The results indicate that depending on the level of porosity and the Mach number of the precursor shock front secondary reflected and transmitted shock waves are formed through the coalescence of compression waves. With reduced porosity, the plates act almost as a solid surface, therefore the shock propagates faster along its surface.

42nd AIAA Aerospace Sciences Meeting and Exhibit, 2004

This paper deals with the effect of electrical energy deposition on the wave drag experienced by ... more This paper deals with the effect of electrical energy deposition on the wave drag experienced by a 120° apex angle blunt cone flying at Mach 5.75. The experiments are conducted in the Indian Institute of Science (IISc) hypersonic shock tunnel HST-2. The electrical energy is deposited along the stagnation streamline of the model using a spark discharge system powered by a DC power supply. Drag is measured using a single component accelerometer balance mounted inside the blunt cone model. Illustrative numerical simulations are also carried out by solving the 3-D compressible Navier-Stokes equations, for complimenting the experiments. Results from the parametric numerical studies indicate a substantial reduction in drag (20%~65%) as a result of electrical energy deposition (~ 1 kw; source volume ~ 8e−8m3)8e-8m^3)8e−8m3). Preliminary experimental measurements show ~15% reduction in aerodynamic drag around the reentry body whereas ~45% reduction in drag is predicted by the CFD studies for a similar energy source configuration as used in the experiments.

42nd AIAA Aerospace Sciences Meeting and Exhibit, 2004

A new free floating internally mountable balance system that ensures unrestrained motion of the m... more A new free floating internally mountable balance system that ensures unrestrained motion of the model exposed to hypersonic flow in the shock tunnel has been designed, fabricated and tested. The drag force acting on a blunt leading edge flat plate has been measured using the new balance system. The model acceleration in the axial direction is measured using an accelerometer by ensuring unrestrained model motion during testing in the hypersonic shock tunnel. The balance has been calibrated by an impulse hammer. To measure the drag force, normal force and pitching moment of a typical hypersonic vehicle, another free floating balance configuration has been designed, fabricated and tested. Finite element modeling (FEM) and CFD are exhaustively used in the design and calibration of the two balances. The experimentally measured drag force on the blunt leading edge flat plate at nominal Mach number of 5.75 matches well with FEM results. The details of the study are described in this paper.

24th International Congress on High-Speed Photography and Photonics, 2001

ABSTRACT

This paper describes the implementation of Background oriented Schlieren (BOS) technique to captu... more This paper describes the implementation of Background oriented Schlieren (BOS) technique to capture the density field of a blast wave generated through a micro-explosion. The three dimensional density field was reconstructed using the filtered back projection technique. This was carried out at several instants of time in order to capture the evolution of the density field. The reconstructed density field revealed the internal structure of the flow field. The results show that there is a significant variation in density between the forward and rearward propagating parts of the shock wave. This implies that these micro-explosions possess some characteristics similar to a muzzle blast rather than a true point source. PIV measurements were also attempted at several instants of time. However, the alumina particles expelled from the tube had very high S/N ratio resulting in saturation of the CCD. Hence no useful velocity field data could be obtained. The density fields generated in this study helps to understand the flow physics associated with blast waves generated using controlled micro-explosions. The findings can be used to scale laboratory experiments to real life explosions.

SSRN Electronic Journal, 2014

Agriculture is the sector most vulnerable to climate change due to its high dependence on climate... more Agriculture is the sector most vulnerable to climate change due to its high dependence on climate and weather conditions. Climate change is a main challenge for agriculture, food security and rural livelihoods for millions of people in India. Among India's population of more than one billion people, about 68% are directly or indirectly involved in the agricultural sector. This sector is particularly vulnerable to present-day climate variability. In this paper an attempt is made to map and analyze the vulnerability to climate change in different districts of four south Indian states: Andhra Pradesh, Karnataka, Tamil Nadu and Kerala. We have taken five sources of vulnerability indicators: socio-demographic, climatic, agricultural, occupational and common property resources vulnerabilities to compute the composite vulnerability index. The composite vulnerability index suggests that, Adilabad, Chamarajanagar, Thiruvarur and Kasaragod are the most vulnerable districts of Andhra Pradesh, Karnataka, Tamil Nadu and Kerala respectively, whereas Hyderabad, Belgaum, Thoothukkudi, Kottayam are the least vulnerable districts.

Materials Science and Engineering: A, 2015

The AA5086 aluminum alloy sheets with different starting textures were subjected to shock wave de... more The AA5086 aluminum alloy sheets with different starting textures were subjected to shock wave deformation with an input impulse of $ 0.2 Ns. Microstructural examination indicate no significant change in grain size; however, the evolution of substructure manifesting intra-granular misorientation was evident. The improvement in hardness indicates the absence of recovery and strain hardening during shock deformation. Shock deformed samples show characteristic texture evolution with high Brass {110}〈112〉 component. The study demonstrates the viability of high velocity forming of AA5086 aluminum alloy sheet using shock wave.

Shock Waves, 2009

NONEL tube finds vast applications in civil and military because of its safe and confined explosi... more NONEL tube finds vast applications in civil and military because of its safe and confined explosion technique. Spectroscopic and chemical analysis of a NONEL tube with an uniform mixture of HMX and Al is reported here. Peak temperature obtained at the open end of the ...

28th International Symposium on Shock Waves, 2012

A gene is a unit of heredity in a living organism. It normally resides on a stretch of DNA that c... more A gene is a unit of heredity in a living organism. It normally resides on a stretch of DNA that codes for a type of protein or for an RNA chain that has a function in the organism. All living things depend on genes, as they specify all proteins and functional RNA chains. Genes hold the information to build and maintain an organism’s cells and pass genetic traits to offspring. The gene has to be transferred to bacteria or eukaryotic cells for basic and applied molecular biology studies. Bacteria can uptake exogenous genetic material by three ways: conjugation, transduction and transformation. Genetic material is naturally transferred to bacteria in case of conjugation and transferred through bacteriophage in transduction. Transformation is the acquisition of exogenous genetic material through cell wall. The ability of bacteria of being transformed is called competency and those bacteria which have competency are competent cells. Divalent Calcium ions can make the bacteria competent and a heat shock can cause the bacteria to uptake DNA. But the heat shock method cannot be used for all the bacteria. In electroporation, a brief electric shock with an electric field of 10-20kV/cmmakes pores in the cell wall, facilitates the DNA to enter into the bacteria. Microprecipitates, microinjection, liposomes, and biological vectors are also used to transfer polar molecules like DNA into host cells.

Shock Waves, 2009

Experimental results on the effect of energy deposition using an electric arc discharge, upstream... more Experimental results on the effect of energy deposition using an electric arc discharge, upstream of a 60° half angle blunt cone configuration in a hypersonic flow is reported.Investigations involving drag measurements and high speed schlieren flow visualization have been carried out in hypersonic shock tunnel using air and argon as the test gases; and an unsteady drag reduction of about 50% (maximum reduction) has been observed in the energy deposition experiments done in argon environment. These studies also show that the effect of discharge on the flow field is more pronounced in argon environment as compared to air, which confirms that thermal effects are mainly responsible for flow alteration in presence of the discharge.

Shock Waves, 2009

A waverider is a lifting body configuration whose upper surface is parallel to the free stream, a... more A waverider is a lifting body configuration whose upper surface is parallel to the free stream, and the lower surface aerodynamically so designed, that the resulting shock at the design Mach number, is always attached with the leading edge of the vehicle. This prevents spillage from high pressure (lower) surface to the low pressure (upper) surface.In the present study a

Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, 2011

The use of high-velocity sheet-forming techniques where the strain rates are in excess of 102/s c... more The use of high-velocity sheet-forming techniques where the strain rates are in excess of 102/s can help us solve many problems that are difficult to overcome with traditional metal-forming techniques. In this investigation, thin metallic plates/foils were subjected to shock wave loading in the newly developed diaphragmless shock tube. The conventional shock tube used in the aerodynamic applications uses a metal diaphragm for generating shock waves. This method of operation has its own disadvantages including the problems associated with repeatable and reliable generation of shock waves. Moreover, in industrial scenario, changing metal diaphragms after every shot is not desirable. Hence, a diaphragmless shock tube is calibrated and used in this study. Shock Mach numbers up to 3 can be generated with a high degree of repeatability (±4 per cent) for the pressure jumps across the primary shock wave. The shock Mach number scatter is within ±1.5 per cent. Copper, brass, and aluminium pla...

Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, 2011

This article reports experimental results on supersonic combustion in a new facility. The facilit... more This article reports experimental results on supersonic combustion in a new facility. The facility is a combustion-driven shock tunnel, which is cheaper to build than the facilities in which such experiments are carried out conventionally. The observation region is a zone between two parallel flat plates with a 33° wedge attached to the upstream end of the bottom plate. Gaseous hydrogen is injected at an angle of 45° into an oncoming supersonic flow of Mach 2 (approximate) from a port on the bottom plate. The resulting flow field is visualized by a high speed camera in a dark background. Three different test gases, namely nitrogen, air, and oxygen-rich air are used, and the results are compared. A distinct luminosity due to combustion for oxygen-containing test gases is observed. Heat-transfer rates on a probe placed at the downstream end of the observation region and midway between the parallel plates are measured and compared for the three cases. Wall static pressure at 28 mm down...

Measurement, 2009

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright