Ishita Shrivastava | IIT Bombay (original) (raw)

Papers by Ishita Shrivastava

Bulletin of the American Physical Society, Nov 23, 2015

Submitted for the DFD15 Meeting of The American Physical Society CFD simulation of boundary effec... more Submitted for the DFD15 Meeting of The American Physical Society CFD simulation of boundary effects on closely spaced jets ISHITA SHRIVASTAVA, ERIC ADAMS, Massachusetts Inst of Tech-MIT-In coastal areas characterized by shallow water depth, industrial effluents are often diluted using multiple closely spaced jets. Examples of such effluents include brine from desalination plants, treated wastewater from sewage treatment plants and heated water from thermal power plants. These jets are arranged in various orientations, such as unidirectional diffusers and rosette groups, to maximize mixing with ambient water. Due to effects of dynamic pressure, the jets interact with each other leading to mixing characteristics which are quite different from those of individual jets. The effect of mutual interaction is exaggerated under confinement, when a large number of closely spaced jets discharge into shallow depth. Dilution through an outfall, consisting of multiple jets, depends on various outfall and ambient parameters. Here we observe the effects of shoreline proximity, in relation to diffuser length and water depth, on the performance of unidirectional diffusers discharging to quiescent water. For diffusers located closer to shore, less dilution is observed due to the limited availability of ambient water for dilution. We report on the results of Computational Fluid Dynamics (CFD) simulations and compare the results with experimental observations.

Journal of Hydraulic Engineering, Apr 1, 2019

AbstractThis paper analyzes the mixing of a tee diffuser discharging in shallow water with curren... more AbstractThis paper analyzes the mixing of a tee diffuser discharging in shallow water with currents. Experiments are conducted for tee diffusers with different designs discharging in a crossflow. M...

Journal of Hydraulic Engineering, Dec 1, 2019

AbstractThe effect of receiving water depth on the dilution of a unidirectional diffuser discharg... more AbstractThe effect of receiving water depth on the dilution of a unidirectional diffuser discharging dense effluent in quiescent conditions is analyzed. Dilution measurements from previous studies ...

Journal of Hydraulic Engineering

Pathways and Challenges for Efficient Desalination

Recently proposed options for desalination brine management involve blending of brine with a ligh... more Recently proposed options for desalination brine management involve blending of brine with a lighter effluent or concentrating the brine prior to discharge, either of which can significantly alter the discharge concentrations of contaminants. We evaluate the effect of these brine management strategies on the design of submerged outfalls used to discharge brine. Optimization of outfall design is considered such that adequate mixing can be provided with minimum cost. Designs with submerged and surfacing plume are considered for outfalls located in shallow coastal regions with small currents (quiescent receiving water is assumed). Pre-dilution with treated wastewater is shown to reduce the outfall cost, whereas pre-dilution with seawater or pre-concentration are shown to result in higher costs than the discharge of brine alone. The effect of bottom slope is also explored and the results suggest that multiport diffusers are better suited than single jets at locations with a mild bottom ...

Bulletin of the American Physical Society, 2015

Submitted for the DFD15 Meeting of The American Physical Society CFD simulation of boundary effec... more Submitted for the DFD15 Meeting of The American Physical Society CFD simulation of boundary effects on closely spaced jets ISHITA SHRIVASTAVA, ERIC ADAMS, Massachusetts Inst of Tech-MIT-In coastal areas characterized by shallow water depth, industrial effluents are often diluted using multiple closely spaced jets. Examples of such effluents include brine from desalination plants, treated wastewater from sewage treatment plants and heated water from thermal power plants. These jets are arranged in various orientations, such as unidirectional diffusers and rosette groups, to maximize mixing with ambient water. Due to effects of dynamic pressure, the jets interact with each other leading to mixing characteristics which are quite different from those of individual jets. The effect of mutual interaction is exaggerated under confinement, when a large number of closely spaced jets discharge into shallow depth. Dilution through an outfall, consisting of multiple jets, depends on various outfall and ambient parameters. Here we observe the effects of shoreline proximity, in relation to diffuser length and water depth, on the performance of unidirectional diffusers discharging to quiescent water. For diffusers located closer to shore, less dilution is observed due to the limited availability of ambient water for dilution. We report on the results of Computational Fluid Dynamics (CFD) simulations and compare the results with experimental observations.

The effect of receiving water depth on the mixing characteristics of shallow water outfalls in qu... more The effect of receiving water depth on the mixing characteristics of shallow water outfalls in quiescent conditions is analyzed with an emphasis on negatively buoyant discharges. Dilution measurements for submerged jets from previous studies are analyzed to determine the effect of "shallowness" on the mixing of single port outfalls. For a unidirectional multiport diffuser, the width of the effluent plume is observed to contract in shallow water. A model is proposed relating the dilution of a unidirectional multiport diffuser to the dilution of a single port outfall using the contracted width. Measurements of the contracted width in shallow water are made to complement the proposed model, which is verified by additional measurements of dilution. It is shown that the effect of shallowness on single and multiple port outfalls is similar, and three regimes, namely, "deep", "shallow" and "wellmixed," can be identified for both types of outfalls bas...

Processes, 2021

Confined plunging jets are investigated as potential outfalls for the discharge of desalination b... more Confined plunging jets are investigated as potential outfalls for the discharge of desalination brine. Compared to offshore submerged outfalls that rely on momentum to induce mixing, plunging jets released above the water surface utilize both momentum and negative buoyancy. Plunging jets also introduce air into the water column, which can reduce the possibility of hypoxic zones. In contrast to unconfined plunging jets, confined plunging jets include a confining tube, or downcomer, around the jet, which increases the penetration depth of the bubbles and can provide better aeration. However, the presence of this downcomer can hinder mixing with surrounding water. Therefore, laboratory measurements of dilution are reported here and compared to the dilution of unconfined plunging jets. In addition, qualitative observations of bubble penetration depth are also used to discuss aeration potential. For designs that increase the bubble penetration depth as compared to unconfined plunging jet...

Processes, 2020

Laboratory experiments were conducted to measure entrained air bubble penetration depth and dilut... more Laboratory experiments were conducted to measure entrained air bubble penetration depth and dilution of a dense vertical unconfined plunging jet to evaluate its performance as an outfall to dilute brine from desalination plants as well as a means to aerate water column. Experiments involved neutrally buoyant or dense plunging jets discharging in quiescent receiving water. The density difference between effluent and receiving water, the plunging jet length (height above water surface), and the receiving water salinity were varied in the experiments. Observed penetration depth for neutrally buoyant jets was somewhat greater than previously reported, and increased modestly with jet density. Increasing density also resulted in an increasing number of fine bubbles descending together with the dense plume. These observations can help guide the design of plunging jets to mitigate anoxic conditions in the water column when brine is introduced to a receiving water body, as with seawater desa...

Journal of Hydraulic Engineering, 2019

AbstractThe effect of receiving water depth on the dilution of a unidirectional diffuser discharg... more AbstractThe effect of receiving water depth on the dilution of a unidirectional diffuser discharging dense effluent in quiescent conditions is analyzed. Dilution measurements from previous studies ...

Journal of Hydro-environment Research, 2019

High discharge salinity of reject brine from desalination plants necessitates the use of submerge... more High discharge salinity of reject brine from desalination plants necessitates the use of submerged jets which induce mixing with ambient water and lead to reduction in concentrations of salt and other contaminants. Predilution, in which brine is blended with a lighter effluent prior to discharge, can also cause reduction in contaminant concentrations. Condenser cooling water from a co-located power plant, treated wastewater effluent from a treatment plant and seawater can be used for pre-dilution. The effect of pre-dilution on shallowness and contaminant concentrations in the diluted effluent is examined for discharge using single port and multiport outfalls. The density difference between the effluent and ambient seawater is lower for the discharge of prediluted brine, which leads to shallow conditions. Pre-dilution also results in lower concentrations of contaminants in the diluted effluent by reducing the discharge concentrations as well as increasing outfall dilution in deep water by increasing the densimetric Froude number. This helps in satisfying regulatory requirements on contaminant concentrations with small discharge velocity or using outfalls with small number of ports. While discharge of pre-diluted brine using an existing outfall helps save on the capital cost, it can cause a significant increase in pumping cost. For a new outfall, design parameters can be adjusted such that pumping cost stays constant.

Journal of Hydraulic Engineering, 2019

AbstractThis paper analyzes the mixing of a tee diffuser discharging in shallow water with curren... more AbstractThis paper analyzes the mixing of a tee diffuser discharging in shallow water with currents. Experiments are conducted for tee diffusers with different designs discharging in a crossflow. M...

Journal of Fluid Mechanics, 2015

We report upon laboratory experiments and numerical simulations examining the evolution of an int... more We report upon laboratory experiments and numerical simulations examining the evolution of an interfacial internal solitary wave incident upon a triangular ridge whose peak lies below the interface. If the ridge is moderately large, the wave is observed to shoal and break similar to solitary waves shoaling upon a constant slope, but interfacial waves are also observed to transmit over and reflect from the ridge. In laboratory experiments, by measuring the interface displacement as it evolves in time, we measure the relative transmission and reflection of available potential energy after the incident wave has interacted with the ridge. The numerical simulations of laboratory- and ocean-scale waves measure both the available potential and kinetic energy to determine the partition of incident energy into that which is transmitted and reflected. From shallow-water theory, we define a critical amplitude, AcA_{c}Ac, above which interfacial waves are unstable. The transmission is found to de...

Bulletin of the American Physical Society, Nov 23, 2015

Submitted for the DFD15 Meeting of The American Physical Society CFD simulation of boundary effec... more Submitted for the DFD15 Meeting of The American Physical Society CFD simulation of boundary effects on closely spaced jets ISHITA SHRIVASTAVA, ERIC ADAMS, Massachusetts Inst of Tech-MIT-In coastal areas characterized by shallow water depth, industrial effluents are often diluted using multiple closely spaced jets. Examples of such effluents include brine from desalination plants, treated wastewater from sewage treatment plants and heated water from thermal power plants. These jets are arranged in various orientations, such as unidirectional diffusers and rosette groups, to maximize mixing with ambient water. Due to effects of dynamic pressure, the jets interact with each other leading to mixing characteristics which are quite different from those of individual jets. The effect of mutual interaction is exaggerated under confinement, when a large number of closely spaced jets discharge into shallow depth. Dilution through an outfall, consisting of multiple jets, depends on various outfall and ambient parameters. Here we observe the effects of shoreline proximity, in relation to diffuser length and water depth, on the performance of unidirectional diffusers discharging to quiescent water. For diffusers located closer to shore, less dilution is observed due to the limited availability of ambient water for dilution. We report on the results of Computational Fluid Dynamics (CFD) simulations and compare the results with experimental observations.

Journal of Hydraulic Engineering, Apr 1, 2019

AbstractThis paper analyzes the mixing of a tee diffuser discharging in shallow water with curren... more AbstractThis paper analyzes the mixing of a tee diffuser discharging in shallow water with currents. Experiments are conducted for tee diffusers with different designs discharging in a crossflow. M...

Journal of Hydraulic Engineering, Dec 1, 2019

AbstractThe effect of receiving water depth on the dilution of a unidirectional diffuser discharg... more AbstractThe effect of receiving water depth on the dilution of a unidirectional diffuser discharging dense effluent in quiescent conditions is analyzed. Dilution measurements from previous studies ...

Journal of Hydraulic Engineering

Pathways and Challenges for Efficient Desalination

Recently proposed options for desalination brine management involve blending of brine with a ligh... more Recently proposed options for desalination brine management involve blending of brine with a lighter effluent or concentrating the brine prior to discharge, either of which can significantly alter the discharge concentrations of contaminants. We evaluate the effect of these brine management strategies on the design of submerged outfalls used to discharge brine. Optimization of outfall design is considered such that adequate mixing can be provided with minimum cost. Designs with submerged and surfacing plume are considered for outfalls located in shallow coastal regions with small currents (quiescent receiving water is assumed). Pre-dilution with treated wastewater is shown to reduce the outfall cost, whereas pre-dilution with seawater or pre-concentration are shown to result in higher costs than the discharge of brine alone. The effect of bottom slope is also explored and the results suggest that multiport diffusers are better suited than single jets at locations with a mild bottom ...

Bulletin of the American Physical Society, 2015

Submitted for the DFD15 Meeting of The American Physical Society CFD simulation of boundary effec... more Submitted for the DFD15 Meeting of The American Physical Society CFD simulation of boundary effects on closely spaced jets ISHITA SHRIVASTAVA, ERIC ADAMS, Massachusetts Inst of Tech-MIT-In coastal areas characterized by shallow water depth, industrial effluents are often diluted using multiple closely spaced jets. Examples of such effluents include brine from desalination plants, treated wastewater from sewage treatment plants and heated water from thermal power plants. These jets are arranged in various orientations, such as unidirectional diffusers and rosette groups, to maximize mixing with ambient water. Due to effects of dynamic pressure, the jets interact with each other leading to mixing characteristics which are quite different from those of individual jets. The effect of mutual interaction is exaggerated under confinement, when a large number of closely spaced jets discharge into shallow depth. Dilution through an outfall, consisting of multiple jets, depends on various outfall and ambient parameters. Here we observe the effects of shoreline proximity, in relation to diffuser length and water depth, on the performance of unidirectional diffusers discharging to quiescent water. For diffusers located closer to shore, less dilution is observed due to the limited availability of ambient water for dilution. We report on the results of Computational Fluid Dynamics (CFD) simulations and compare the results with experimental observations.

The effect of receiving water depth on the mixing characteristics of shallow water outfalls in qu... more The effect of receiving water depth on the mixing characteristics of shallow water outfalls in quiescent conditions is analyzed with an emphasis on negatively buoyant discharges. Dilution measurements for submerged jets from previous studies are analyzed to determine the effect of "shallowness" on the mixing of single port outfalls. For a unidirectional multiport diffuser, the width of the effluent plume is observed to contract in shallow water. A model is proposed relating the dilution of a unidirectional multiport diffuser to the dilution of a single port outfall using the contracted width. Measurements of the contracted width in shallow water are made to complement the proposed model, which is verified by additional measurements of dilution. It is shown that the effect of shallowness on single and multiple port outfalls is similar, and three regimes, namely, "deep", "shallow" and "wellmixed," can be identified for both types of outfalls bas...

Processes, 2021

Confined plunging jets are investigated as potential outfalls for the discharge of desalination b... more Confined plunging jets are investigated as potential outfalls for the discharge of desalination brine. Compared to offshore submerged outfalls that rely on momentum to induce mixing, plunging jets released above the water surface utilize both momentum and negative buoyancy. Plunging jets also introduce air into the water column, which can reduce the possibility of hypoxic zones. In contrast to unconfined plunging jets, confined plunging jets include a confining tube, or downcomer, around the jet, which increases the penetration depth of the bubbles and can provide better aeration. However, the presence of this downcomer can hinder mixing with surrounding water. Therefore, laboratory measurements of dilution are reported here and compared to the dilution of unconfined plunging jets. In addition, qualitative observations of bubble penetration depth are also used to discuss aeration potential. For designs that increase the bubble penetration depth as compared to unconfined plunging jet...

Processes, 2020

Laboratory experiments were conducted to measure entrained air bubble penetration depth and dilut... more Laboratory experiments were conducted to measure entrained air bubble penetration depth and dilution of a dense vertical unconfined plunging jet to evaluate its performance as an outfall to dilute brine from desalination plants as well as a means to aerate water column. Experiments involved neutrally buoyant or dense plunging jets discharging in quiescent receiving water. The density difference between effluent and receiving water, the plunging jet length (height above water surface), and the receiving water salinity were varied in the experiments. Observed penetration depth for neutrally buoyant jets was somewhat greater than previously reported, and increased modestly with jet density. Increasing density also resulted in an increasing number of fine bubbles descending together with the dense plume. These observations can help guide the design of plunging jets to mitigate anoxic conditions in the water column when brine is introduced to a receiving water body, as with seawater desa...

Journal of Hydraulic Engineering, 2019

AbstractThe effect of receiving water depth on the dilution of a unidirectional diffuser discharg... more AbstractThe effect of receiving water depth on the dilution of a unidirectional diffuser discharging dense effluent in quiescent conditions is analyzed. Dilution measurements from previous studies ...

Journal of Hydro-environment Research, 2019

High discharge salinity of reject brine from desalination plants necessitates the use of submerge... more High discharge salinity of reject brine from desalination plants necessitates the use of submerged jets which induce mixing with ambient water and lead to reduction in concentrations of salt and other contaminants. Predilution, in which brine is blended with a lighter effluent prior to discharge, can also cause reduction in contaminant concentrations. Condenser cooling water from a co-located power plant, treated wastewater effluent from a treatment plant and seawater can be used for pre-dilution. The effect of pre-dilution on shallowness and contaminant concentrations in the diluted effluent is examined for discharge using single port and multiport outfalls. The density difference between the effluent and ambient seawater is lower for the discharge of prediluted brine, which leads to shallow conditions. Pre-dilution also results in lower concentrations of contaminants in the diluted effluent by reducing the discharge concentrations as well as increasing outfall dilution in deep water by increasing the densimetric Froude number. This helps in satisfying regulatory requirements on contaminant concentrations with small discharge velocity or using outfalls with small number of ports. While discharge of pre-diluted brine using an existing outfall helps save on the capital cost, it can cause a significant increase in pumping cost. For a new outfall, design parameters can be adjusted such that pumping cost stays constant.

Journal of Hydraulic Engineering, 2019

AbstractThis paper analyzes the mixing of a tee diffuser discharging in shallow water with curren... more AbstractThis paper analyzes the mixing of a tee diffuser discharging in shallow water with currents. Experiments are conducted for tee diffusers with different designs discharging in a crossflow. M...

Journal of Fluid Mechanics, 2015

We report upon laboratory experiments and numerical simulations examining the evolution of an int... more We report upon laboratory experiments and numerical simulations examining the evolution of an interfacial internal solitary wave incident upon a triangular ridge whose peak lies below the interface. If the ridge is moderately large, the wave is observed to shoal and break similar to solitary waves shoaling upon a constant slope, but interfacial waves are also observed to transmit over and reflect from the ridge. In laboratory experiments, by measuring the interface displacement as it evolves in time, we measure the relative transmission and reflection of available potential energy after the incident wave has interacted with the ridge. The numerical simulations of laboratory- and ocean-scale waves measure both the available potential and kinetic energy to determine the partition of incident energy into that which is transmitted and reflected. From shallow-water theory, we define a critical amplitude, AcA_{c}Ac, above which interfacial waves are unstable. The transmission is found to de...