The present study aims to investigate the role of injector geometry, particularly injector tube l... more The present study aims to investigate the role of injector geometry, particularly injector tube length to diameter ratio (L/D) in liquid jet stability and breakup in presence of crossflow. Water is injected into a crossflow of air. Aerodynamic Weber number (We) and liquid Reynolds number (Rel) are systematically varied to observe various breakup modes. Bag breakup and surface stripping is observed for different operating conditions. Timeresolved jet trajectory images are processed using Proper Orthogonal Decomposition (POD) algorithm. POD mode shapes and corresponding Power Spectral Density (PSD) plots are analyzed to study breakup process and probe role of injector geometry effects. Further, high-resolution images are captured for the near-nozzle region. Detailed comparison is made for various cases. It is observed that with increase in (L/D), the jet surface becomes more turbulent and unstable. This results in early breakup and lower jet penetration
Journal of Loss Prevention in the Process Industries
The present study reports a modular engineering model for predicting peak pressure in vented expl... more The present study reports a modular engineering model for predicting peak pressure in vented explosions. Modelling assumptions are explained in detail and model components are validated against experimental and computational results. A basic version of this model is reported in our earlier paper (Sinha et al. [1]). Previous experimental and modelling efforts on vented explosion have primarily focussed on idealized condition of empty container with uniformly mixed fuel. However, in real accidents, there are often obstacles in flame path, and a leaked fuel may not get enough time to mix uniformly. These realistic accidental scenarios are accounted for in this extended model. The model is further simplified, and a final equation is proposed which depend on two fuel related parameters and two geometric parameters. Fuel parameters are pre-tabulated, and geometric parameters are easy to compute. Procedure to compute pressure generated by external explosion and internal pressure are outlined in detail. Experimental results available in open literature are used to evaluate model prediction capabilities. The model, in principle should be applicable for any gaseous fuel. However, the focus of the present investigation is to assess it for hydrogen explosions. In parallel to the modelling effort, a dedicated in-house solver HyFOAM is developed utilizing OpenFOAM platform. The HyFOAM predictions are validated against experimental results from the recently published test data involving hydrogen explosion in a 20-feet ISO container (Skjold et al. [2-4]). Moreover, as experimental investigations are expensive and require significant testing and safety infrastructure, a limited number of scenarios can be tested experimentally. In 2 addition to the experimental results, few more cases are simulated using HyFOAM and engineering model results are compared with the CFD results, and a reasonably good match is observed.
The authors presented a basic mathematical model for estimating peak overpressure attained in ven... more The authors presented a basic mathematical model for estimating peak overpressure attained in vented explosions of hydrogen in a previous study (Sinha et al. [1]). The model focussed on idealized cases of hydrogen, and was not applicable for realistic accidental scenarios like presence of obstacles, initial turbulent mixture, etc. In the present study, the underlying framework of the model is reformulated to overcome these limitations. The flame shape computations are simplified. A more accurate and simpler formulation for venting is also introduced. Further, by using simplifying assumptions and algebraic manipulations, the detailed model consisting of several equations is reduced to a single equation with only four parameters. Two of these parameters depend only on fuel properties and a standard table provided in the Appendix can be used. Therefore, to compute the overpressure, only the two parameters based on enclosure geometry need to be evaluated. This greatly simplifies the model and calculation effort. Also, since the focus of previous investigation was hydrogen, properties of hydrocarbon fuels, which are much more widely used, were not accounted for. The present model also accounts for thermophysical properties of hydrocarbons and provides table for fuel parameters to be used in the final equation for propane and methane. The model is also improved by addition of different sub-models to account for various realistic accidental scenarios. Moreover, no adjustable parameters are used; the same equation is used for all conditions and all gases. Predictions from this simplified model are compared with experimentally measured values of overpressure for hydrogen and hydrocarbons and found to be in good agreement. First the results from experiments focussing on idealized conditions of uniformly mixed fuel in an empty enclosure under quiescent conditions are considered. Further the model applicability is also tested for realistic conditions of accidental explosion consisting of obstacles inside the enclosure, non-uniform fuel distribution, initial turbulent mixture, etc. For all the cases tested, the new simple model is found to produce reasonably good predictions.
The present investigation is focused on experimental studies on the structure of airblast spray i... more The present investigation is focused on experimental studies on the structure of airblast spray in crossflow. Atomizer is at a higher pressure than ambient and the airblast gas is expected to exhibit features generally found in under-expanded gas jets. High-speed images are captured using shadowgraphy technique. Certain wave-like structures observed in the near-nozzle region are attributed to shock-vortex interactions, generally observed in under-expanded gas jets. Proper Orthogonal Decomposition (POD) analysis has been carried out using these images. POD mode shapes clearly show signatures of shock-vortex oscillations and frequencies close to the screeching frequency observed in under-expanded jets. The POD modes are compared for different conditions and the significance of dynamic structures and their temporal behavior is discussed. Finally, a regime map is also proposed to characterize spray behavior in crossflow.
Please refer to published version for the most recent bibliographic citation information. If a pu... more Please refer to published version for the most recent bibliographic citation information. If a published version is known of, the repository item page linked to above, will contain details on accessing it.
The present study focuses on the jet break-up and spray formation of a jet in a cross-flow config... more The present study focuses on the jet break-up and spray formation of a jet in a cross-flow configuration under atmospheric conditions. A water jet is subjected to air cross flow and the resulting spray structure is studied. The cross flow air velocity and jet momentum both are varied to obtain a set of momentum ratios. Different regimes of breakup are observed. Bag breakup is quantified in terms of bag breakup frequency and is found to increase with both Q and We. The penetration length of water jet is found to increase with Q. High speed images have shown details about the various stages of bag breakup, such as inception, growth and rupture.
The present study is aimed at numerical investigation of the various operating conditions for a l... more The present study is aimed at numerical investigation of the various operating conditions for a laminar premixed methane/air flame impinging normal to a flat plate. The effect of variation of operating parameters on the flame structure and heat transfer characteristics has been evaluated using commercial Computational Fluid Dynamics (CFD) software Fluent. The effect of variation of exit velocity profile, equivalence ratio (Φ), Reynolds number and burner to plate separation distance has been simulated on flame structure and heat transfer. It was observed that for plug flow the pressure dropped at the stagnation point on the plate resulting in poor heat flux at the central region. While varying Reynolds number keeping other variables fixed, it was found that the inner reaction zone of peak temperature became broader and heat flux increases owing to increase in mass flow. Another case of varying Φ revealed the effect of entrainment of ambient oxygen in rich flames and its effect on int...
The focus of the present article is to study the effect of liquid jet injection velocity profile ... more The focus of the present article is to study the effect of liquid jet injection velocity profile on the structure of liquid jet in crossflow (JICF). The experiments are conducted over a range of liquid-to-air momentum ratios (Q ~ 3-100) and aerodynamic Weber numbers (We = 17 -89). Control over the velocity profile of the injected liquid is achieved through the usage of different L/D ratios of the nozzle of the plain-orifice atomizer. The geometrical parameter L/D is varied between 10 and 100 in order to obtain fully-developed laminar flow, transition and turbulent flow. High-speed imaging and Shadowgraphy are used to study the trajectory, dropsizing and transient behavior of the resultant spray. It is observed that the dependence of trajectory of the spray is not just limited to the momentum ratio, Q, but also requires correction factors with respect to the injection velocity profiles, which are in turn related to L/D. The trajectory for the turbulent jet is found to be lower at all times when compared to that of a laminar jet for the corresponding conditions. This behavior may be attributed to the inherent instabilities present in a turbulent jet as opposed to a perfectly laminar jet. Further, we also investigate the transient phenomena of the liquid jet breakup at different conditions with the aid of Proper Orthogonal Decomposition (POD) analysis. Distinct modes of breakup are captured for the laminar and turbulent cases.
Experimental investigation of the structure of spray from an air-blast atomizer emerging into a c... more Experimental investigation of the structure of spray from an air-blast atomizer emerging into a cross flowing air stream is carried out. The resultant spray dispersion and trajectory are studied with the aid of optical diagnostics. Various combinations of cross-flow air velocities and air-blast spray parameters are analysed. The shadowgraphy technique incorporating laser-induced backlighting is used to study penetration for various conditions. The resulting images are then processed and analysed for effect of various parameters on spray penetration. Decrease of cross-flow velocity and increasing of Gas to Liquid Ratio (GLR) is found to increase the penetration.
This study reports results of an experimental investigation of airblast spray of water and ethano... more This study reports results of an experimental investigation of airblast spray of water and ethanol in crossflow. Laser shadowgraphy and Particle / Droplet Imaging Analysis (PDIA) are used to derive spray trajectory and drop size information while Particle Tracking Velocimetry (PTV) is used to measure drop velocities. A new phenomenon of spray bifurcation is observed for low Gas to Liquid Ratio (GLR) cases and is attributed to the bimodal nature of drop size distribution in the resultant airblast spray. A novel correlation for spray trajectory is proposed incorporating the momentum ratio and liquid surface tension. This correlation is shown to be effective in predicting the non-linear spray trajectory over a large range of conditions for not only water but ethanol and Jet-A also. The droplet Sauter Mean Diameter (SMD) is found to increase with height from the injector wall and decrease along the crossflow direction. The effect of drag is assessed by comparing velocity of different sizes of droplets at various locations. Smaller droplets are entrained into the crossflow at much lower elevations, whereas larger droplets tend to penetrate further into the crossflow. The larger drops are found predominantly on the windward periphery of the airblast spray.
The present investigation is focused on modeling of spray in crossflow using Large Eddy Simulatio... more The present investigation is focused on modeling of spray in crossflow using Large Eddy Simulations (LES). The modeling efforts are supported by experiments which are used both to provide accurate boundary and initial conditions and to evaluate droplet shapes in the near nozzle region. The droplets are modeled as Lagrangian parcels in an Eulerian continuum. The objective is to use experiments and simulations in conjugation and assess various modeling assumptions for such configurations; and provide guidelines for future modeling efforts. Droplets in such configuration have been found to be distorted and not in perfect spherical shape from experimental results of our previous study. The effort has been to examine the effect of drag law used and the effect of this distortion on the droplet sizes produced in the flow field. Spray wind-ward trajectory and droplet sizes obtained from simulations are compared with the experimental results available. Although computational spray trajectory shows a reasonable match with experimental values, droplet sizes using the standard Taylor-Analogy Breakup (TAB) model are found to be larger than that form experimental observation. To account for this distortion and its role in early breakup of droplets, constants of the TAB model are modified and the droplet sizes are found to be in good agreement with the experimental data.
The present study focuses on an airblast spray of ethanol injected into a crossflow of preheated ... more The present study focuses on an airblast spray of ethanol injected into a crossflow of preheated air. Air temperature is varied from 295 to 418 K. Correlation for the spray trajectory is derived for the wind-ward spray edge. All previously reported studies have emphasized on the role of momentum ratio on the spray trajectory, whereas the importance of air density on spray atomization has not been addressed, possibly due to lack of experimental data. In this study, for a constant momentum ratio at different crossflow temperatures, the spray trajectory has been measured. From this data, a general correlation is derived which accounts for the density of the crossflow air by adding a correction factor to the correlation. This correlation is found to be in reasonable agreement with experimental results.
Liquid jet in cross flow has been a widely studied subject although most of the experimental work... more Liquid jet in cross flow has been a widely studied subject although most of the experimental work has been carried out at ambient conditions. The present study involves the investigation of the behavior of an ethanol jet injected into a cross flowing air at elevated temperatures up to 428 K. Spray parameters such as the trajectory and drop size distributions are measured and compared for cold and hot flow conditions. Experiments are conducted for a range of liquid-to-air momentum ratios (Q) ~ 4 -13 and for Aerodynamic Weber numbers (We) ~ 15. Though most of the existing literature attributes the effect of elevated temperature on the effective change in Q due to density variation, the present study shows interesting observations where the results vary in spite of maintaining similar magnitudes of Q between cold and hot flow conditions. It is observed that a higher trajectory is consistently manifested by the ethanol jet at elevated temperatures as compared to that found at ambient temperatures. It is proposed that the physical parameter, density ratio, needs to be considered as an additional parameter to account for these differences. Therefore, a new trajectory correlation is proposed which is observed to match experimental data at different temperatures. The drop size measurements indicate considerable amount of evaporation of the fine droplets formed at the leeward portion of the resultant spray of ethanol jet in cross flow.
Experimental data on evaporation of droplets of decane, Jet-A1, and Jet-A1 surrogate are generate... more Experimental data on evaporation of droplets of decane, Jet-A1, and Jet-A1 surrogate are generated using a spray in crossflow configuration. The advantage of a crossflow configuration is that it enables us to study droplet evaporation under forced convective conditions involving droplet diameters of size relevant in practical combustors. Specifically, spray form an airblast atomizer is injected into a preheated crossflow of air and the resulting spray structure is characterized along with droplet size and velocity measurements. An existing correlation for the spray trajectory is modified to incorporate the effect of elevated temperature, and is found to be in good agreement with the experimental data. Droplet sizes and velocities are measured at different locations along the crossflow direction to assess droplet evaporation. Specifically, droplets having size less than 25-µm are selected for further analysis since these droplets are observed to exhibit velocities which are aligned with the crossflow. By comparing the droplet diameter profiles at upstream and downstream locations, the evaporation constant k for the d 2 -law is obtained iteratively. To assess the efficacy of the values of k obtained,the calculated droplet size distribution using the proposed k values at the downstream location is 3 compared with the measured droplet size distribution at that location. A reasonably good match is found for all the three liquids confirming the validity of the analysis.
The present study is aimed at numerical investigation of the various operating conditions for a l... more The present study is aimed at numerical investigation of the various operating conditions for a laminar premixed methane/air flame impinging normal to a flat plate. The effect of variation of operating parameters on the flame structure and heat transfer characteristics has been evaluated using commercial Computational Fluid Dynamics (CFD) software Fluent. The effect of variation of exit velocity profile, equivalence ratio (Φ), Reynolds number and burner to plate separation distance has been simulated on flame structure and heat transfer. It was observed that for plug flow the pressure dropped at the stagnation point on the plate resulting in poor heat flux at the central region. While varying Reynolds number keeping other variables fixed, it was found that the inner reaction zone of peak temperature became broader and heat flux increases owing to increase in mass flow. Another case of varying Φ revealed the effect of entrainment of ambient oxygen in rich flames and its effect on intermediate species formation. This case also exhibited how the heat flux increases and how temperature varied with Φ. The last case considered was that of varying separation distance between burner and target plate (H). Cases are considered with very small to large (H/d) ranging from 1 to 7. It was observed that the larger (H/d) ratios resulted in poorer heat flux owing to heat lost to ambient air.
Experimental investigation of the structure of spray from an air-blast atomizer emerging into a c... more Experimental investigation of the structure of spray from an air-blast atomizer emerging into a cross flowing air stream is carried out. The resultant spray dispersion and trajectory are studied with the aid of optical diagnostics. Various combinations of cross-flow air velocities and air-blast spray parameters are analysed. The shadowgraphy technique incorporating laser-induced backlighting is used to study penetration for various conditions. The resulting images are then processed and analysed for effect of various parameters on spray penetration. Decrease of cross-flow velocity and increasing of Gas to Liquid Ratio (GLR) is found to increase the penetration.
The present work is on spray in cross flow to be used for a cavity combustor. Three airblast atom... more The present work is on spray in cross flow to be used for a cavity combustor. Three airblast atomizers (A,B and C) with different spray properties are characterized for spray structure and droplet diameters using shadowgraphy. Their suitability is assessed for spray in crossflow studies and one among them (atomizer A) is used for crossflow studies. A set up is designed and fabricated to have spray injection in transverse direction to air flow. The air velocity profile is characterized and uniformity and low level of turbulence are ensured. The spray is subjected to air cross flow and images of the structure is taken by using shadowgraphy. The effect of Weber Number and Momentum ratio is discussed on spray penetration and dispersion.
The present study aims to investigate the role of injector geometry, particularly injector tube l... more The present study aims to investigate the role of injector geometry, particularly injector tube length to diameter ratio (L/D) in liquid jet stability and breakup in presence of crossflow. Water is injected into a crossflow of air. Aerodynamic Weber number (We) and liquid Reynolds number (Rel) are systematically varied to observe various breakup modes. Bag breakup and surface stripping is observed for different operating conditions. Timeresolved jet trajectory images are processed using Proper Orthogonal Decomposition (POD) algorithm. POD mode shapes and corresponding Power Spectral Density (PSD) plots are analyzed to study breakup process and probe role of injector geometry effects. Further, high-resolution images are captured for the near-nozzle region. Detailed comparison is made for various cases. It is observed that with increase in (L/D), the jet surface becomes more turbulent and unstable. This results in early breakup and lower jet penetration
Journal of Loss Prevention in the Process Industries
The present study reports a modular engineering model for predicting peak pressure in vented expl... more The present study reports a modular engineering model for predicting peak pressure in vented explosions. Modelling assumptions are explained in detail and model components are validated against experimental and computational results. A basic version of this model is reported in our earlier paper (Sinha et al. [1]). Previous experimental and modelling efforts on vented explosion have primarily focussed on idealized condition of empty container with uniformly mixed fuel. However, in real accidents, there are often obstacles in flame path, and a leaked fuel may not get enough time to mix uniformly. These realistic accidental scenarios are accounted for in this extended model. The model is further simplified, and a final equation is proposed which depend on two fuel related parameters and two geometric parameters. Fuel parameters are pre-tabulated, and geometric parameters are easy to compute. Procedure to compute pressure generated by external explosion and internal pressure are outlined in detail. Experimental results available in open literature are used to evaluate model prediction capabilities. The model, in principle should be applicable for any gaseous fuel. However, the focus of the present investigation is to assess it for hydrogen explosions. In parallel to the modelling effort, a dedicated in-house solver HyFOAM is developed utilizing OpenFOAM platform. The HyFOAM predictions are validated against experimental results from the recently published test data involving hydrogen explosion in a 20-feet ISO container (Skjold et al. [2-4]). Moreover, as experimental investigations are expensive and require significant testing and safety infrastructure, a limited number of scenarios can be tested experimentally. In 2 addition to the experimental results, few more cases are simulated using HyFOAM and engineering model results are compared with the CFD results, and a reasonably good match is observed.
The authors presented a basic mathematical model for estimating peak overpressure attained in ven... more The authors presented a basic mathematical model for estimating peak overpressure attained in vented explosions of hydrogen in a previous study (Sinha et al. [1]). The model focussed on idealized cases of hydrogen, and was not applicable for realistic accidental scenarios like presence of obstacles, initial turbulent mixture, etc. In the present study, the underlying framework of the model is reformulated to overcome these limitations. The flame shape computations are simplified. A more accurate and simpler formulation for venting is also introduced. Further, by using simplifying assumptions and algebraic manipulations, the detailed model consisting of several equations is reduced to a single equation with only four parameters. Two of these parameters depend only on fuel properties and a standard table provided in the Appendix can be used. Therefore, to compute the overpressure, only the two parameters based on enclosure geometry need to be evaluated. This greatly simplifies the model and calculation effort. Also, since the focus of previous investigation was hydrogen, properties of hydrocarbon fuels, which are much more widely used, were not accounted for. The present model also accounts for thermophysical properties of hydrocarbons and provides table for fuel parameters to be used in the final equation for propane and methane. The model is also improved by addition of different sub-models to account for various realistic accidental scenarios. Moreover, no adjustable parameters are used; the same equation is used for all conditions and all gases. Predictions from this simplified model are compared with experimentally measured values of overpressure for hydrogen and hydrocarbons and found to be in good agreement. First the results from experiments focussing on idealized conditions of uniformly mixed fuel in an empty enclosure under quiescent conditions are considered. Further the model applicability is also tested for realistic conditions of accidental explosion consisting of obstacles inside the enclosure, non-uniform fuel distribution, initial turbulent mixture, etc. For all the cases tested, the new simple model is found to produce reasonably good predictions.
The present investigation is focused on experimental studies on the structure of airblast spray i... more The present investigation is focused on experimental studies on the structure of airblast spray in crossflow. Atomizer is at a higher pressure than ambient and the airblast gas is expected to exhibit features generally found in under-expanded gas jets. High-speed images are captured using shadowgraphy technique. Certain wave-like structures observed in the near-nozzle region are attributed to shock-vortex interactions, generally observed in under-expanded gas jets. Proper Orthogonal Decomposition (POD) analysis has been carried out using these images. POD mode shapes clearly show signatures of shock-vortex oscillations and frequencies close to the screeching frequency observed in under-expanded jets. The POD modes are compared for different conditions and the significance of dynamic structures and their temporal behavior is discussed. Finally, a regime map is also proposed to characterize spray behavior in crossflow.
Please refer to published version for the most recent bibliographic citation information. If a pu... more Please refer to published version for the most recent bibliographic citation information. If a published version is known of, the repository item page linked to above, will contain details on accessing it.
The present study focuses on the jet break-up and spray formation of a jet in a cross-flow config... more The present study focuses on the jet break-up and spray formation of a jet in a cross-flow configuration under atmospheric conditions. A water jet is subjected to air cross flow and the resulting spray structure is studied. The cross flow air velocity and jet momentum both are varied to obtain a set of momentum ratios. Different regimes of breakup are observed. Bag breakup is quantified in terms of bag breakup frequency and is found to increase with both Q and We. The penetration length of water jet is found to increase with Q. High speed images have shown details about the various stages of bag breakup, such as inception, growth and rupture.
The present study is aimed at numerical investigation of the various operating conditions for a l... more The present study is aimed at numerical investigation of the various operating conditions for a laminar premixed methane/air flame impinging normal to a flat plate. The effect of variation of operating parameters on the flame structure and heat transfer characteristics has been evaluated using commercial Computational Fluid Dynamics (CFD) software Fluent. The effect of variation of exit velocity profile, equivalence ratio (Φ), Reynolds number and burner to plate separation distance has been simulated on flame structure and heat transfer. It was observed that for plug flow the pressure dropped at the stagnation point on the plate resulting in poor heat flux at the central region. While varying Reynolds number keeping other variables fixed, it was found that the inner reaction zone of peak temperature became broader and heat flux increases owing to increase in mass flow. Another case of varying Φ revealed the effect of entrainment of ambient oxygen in rich flames and its effect on int...
The focus of the present article is to study the effect of liquid jet injection velocity profile ... more The focus of the present article is to study the effect of liquid jet injection velocity profile on the structure of liquid jet in crossflow (JICF). The experiments are conducted over a range of liquid-to-air momentum ratios (Q ~ 3-100) and aerodynamic Weber numbers (We = 17 -89). Control over the velocity profile of the injected liquid is achieved through the usage of different L/D ratios of the nozzle of the plain-orifice atomizer. The geometrical parameter L/D is varied between 10 and 100 in order to obtain fully-developed laminar flow, transition and turbulent flow. High-speed imaging and Shadowgraphy are used to study the trajectory, dropsizing and transient behavior of the resultant spray. It is observed that the dependence of trajectory of the spray is not just limited to the momentum ratio, Q, but also requires correction factors with respect to the injection velocity profiles, which are in turn related to L/D. The trajectory for the turbulent jet is found to be lower at all times when compared to that of a laminar jet for the corresponding conditions. This behavior may be attributed to the inherent instabilities present in a turbulent jet as opposed to a perfectly laminar jet. Further, we also investigate the transient phenomena of the liquid jet breakup at different conditions with the aid of Proper Orthogonal Decomposition (POD) analysis. Distinct modes of breakup are captured for the laminar and turbulent cases.
Experimental investigation of the structure of spray from an air-blast atomizer emerging into a c... more Experimental investigation of the structure of spray from an air-blast atomizer emerging into a cross flowing air stream is carried out. The resultant spray dispersion and trajectory are studied with the aid of optical diagnostics. Various combinations of cross-flow air velocities and air-blast spray parameters are analysed. The shadowgraphy technique incorporating laser-induced backlighting is used to study penetration for various conditions. The resulting images are then processed and analysed for effect of various parameters on spray penetration. Decrease of cross-flow velocity and increasing of Gas to Liquid Ratio (GLR) is found to increase the penetration.
This study reports results of an experimental investigation of airblast spray of water and ethano... more This study reports results of an experimental investigation of airblast spray of water and ethanol in crossflow. Laser shadowgraphy and Particle / Droplet Imaging Analysis (PDIA) are used to derive spray trajectory and drop size information while Particle Tracking Velocimetry (PTV) is used to measure drop velocities. A new phenomenon of spray bifurcation is observed for low Gas to Liquid Ratio (GLR) cases and is attributed to the bimodal nature of drop size distribution in the resultant airblast spray. A novel correlation for spray trajectory is proposed incorporating the momentum ratio and liquid surface tension. This correlation is shown to be effective in predicting the non-linear spray trajectory over a large range of conditions for not only water but ethanol and Jet-A also. The droplet Sauter Mean Diameter (SMD) is found to increase with height from the injector wall and decrease along the crossflow direction. The effect of drag is assessed by comparing velocity of different sizes of droplets at various locations. Smaller droplets are entrained into the crossflow at much lower elevations, whereas larger droplets tend to penetrate further into the crossflow. The larger drops are found predominantly on the windward periphery of the airblast spray.
The present investigation is focused on modeling of spray in crossflow using Large Eddy Simulatio... more The present investigation is focused on modeling of spray in crossflow using Large Eddy Simulations (LES). The modeling efforts are supported by experiments which are used both to provide accurate boundary and initial conditions and to evaluate droplet shapes in the near nozzle region. The droplets are modeled as Lagrangian parcels in an Eulerian continuum. The objective is to use experiments and simulations in conjugation and assess various modeling assumptions for such configurations; and provide guidelines for future modeling efforts. Droplets in such configuration have been found to be distorted and not in perfect spherical shape from experimental results of our previous study. The effort has been to examine the effect of drag law used and the effect of this distortion on the droplet sizes produced in the flow field. Spray wind-ward trajectory and droplet sizes obtained from simulations are compared with the experimental results available. Although computational spray trajectory shows a reasonable match with experimental values, droplet sizes using the standard Taylor-Analogy Breakup (TAB) model are found to be larger than that form experimental observation. To account for this distortion and its role in early breakup of droplets, constants of the TAB model are modified and the droplet sizes are found to be in good agreement with the experimental data.
The present study focuses on an airblast spray of ethanol injected into a crossflow of preheated ... more The present study focuses on an airblast spray of ethanol injected into a crossflow of preheated air. Air temperature is varied from 295 to 418 K. Correlation for the spray trajectory is derived for the wind-ward spray edge. All previously reported studies have emphasized on the role of momentum ratio on the spray trajectory, whereas the importance of air density on spray atomization has not been addressed, possibly due to lack of experimental data. In this study, for a constant momentum ratio at different crossflow temperatures, the spray trajectory has been measured. From this data, a general correlation is derived which accounts for the density of the crossflow air by adding a correction factor to the correlation. This correlation is found to be in reasonable agreement with experimental results.
Liquid jet in cross flow has been a widely studied subject although most of the experimental work... more Liquid jet in cross flow has been a widely studied subject although most of the experimental work has been carried out at ambient conditions. The present study involves the investigation of the behavior of an ethanol jet injected into a cross flowing air at elevated temperatures up to 428 K. Spray parameters such as the trajectory and drop size distributions are measured and compared for cold and hot flow conditions. Experiments are conducted for a range of liquid-to-air momentum ratios (Q) ~ 4 -13 and for Aerodynamic Weber numbers (We) ~ 15. Though most of the existing literature attributes the effect of elevated temperature on the effective change in Q due to density variation, the present study shows interesting observations where the results vary in spite of maintaining similar magnitudes of Q between cold and hot flow conditions. It is observed that a higher trajectory is consistently manifested by the ethanol jet at elevated temperatures as compared to that found at ambient temperatures. It is proposed that the physical parameter, density ratio, needs to be considered as an additional parameter to account for these differences. Therefore, a new trajectory correlation is proposed which is observed to match experimental data at different temperatures. The drop size measurements indicate considerable amount of evaporation of the fine droplets formed at the leeward portion of the resultant spray of ethanol jet in cross flow.
Experimental data on evaporation of droplets of decane, Jet-A1, and Jet-A1 surrogate are generate... more Experimental data on evaporation of droplets of decane, Jet-A1, and Jet-A1 surrogate are generated using a spray in crossflow configuration. The advantage of a crossflow configuration is that it enables us to study droplet evaporation under forced convective conditions involving droplet diameters of size relevant in practical combustors. Specifically, spray form an airblast atomizer is injected into a preheated crossflow of air and the resulting spray structure is characterized along with droplet size and velocity measurements. An existing correlation for the spray trajectory is modified to incorporate the effect of elevated temperature, and is found to be in good agreement with the experimental data. Droplet sizes and velocities are measured at different locations along the crossflow direction to assess droplet evaporation. Specifically, droplets having size less than 25-µm are selected for further analysis since these droplets are observed to exhibit velocities which are aligned with the crossflow. By comparing the droplet diameter profiles at upstream and downstream locations, the evaporation constant k for the d 2 -law is obtained iteratively. To assess the efficacy of the values of k obtained,the calculated droplet size distribution using the proposed k values at the downstream location is 3 compared with the measured droplet size distribution at that location. A reasonably good match is found for all the three liquids confirming the validity of the analysis.
The present study is aimed at numerical investigation of the various operating conditions for a l... more The present study is aimed at numerical investigation of the various operating conditions for a laminar premixed methane/air flame impinging normal to a flat plate. The effect of variation of operating parameters on the flame structure and heat transfer characteristics has been evaluated using commercial Computational Fluid Dynamics (CFD) software Fluent. The effect of variation of exit velocity profile, equivalence ratio (Φ), Reynolds number and burner to plate separation distance has been simulated on flame structure and heat transfer. It was observed that for plug flow the pressure dropped at the stagnation point on the plate resulting in poor heat flux at the central region. While varying Reynolds number keeping other variables fixed, it was found that the inner reaction zone of peak temperature became broader and heat flux increases owing to increase in mass flow. Another case of varying Φ revealed the effect of entrainment of ambient oxygen in rich flames and its effect on intermediate species formation. This case also exhibited how the heat flux increases and how temperature varied with Φ. The last case considered was that of varying separation distance between burner and target plate (H). Cases are considered with very small to large (H/d) ranging from 1 to 7. It was observed that the larger (H/d) ratios resulted in poorer heat flux owing to heat lost to ambient air.
Experimental investigation of the structure of spray from an air-blast atomizer emerging into a c... more Experimental investigation of the structure of spray from an air-blast atomizer emerging into a cross flowing air stream is carried out. The resultant spray dispersion and trajectory are studied with the aid of optical diagnostics. Various combinations of cross-flow air velocities and air-blast spray parameters are analysed. The shadowgraphy technique incorporating laser-induced backlighting is used to study penetration for various conditions. The resulting images are then processed and analysed for effect of various parameters on spray penetration. Decrease of cross-flow velocity and increasing of Gas to Liquid Ratio (GLR) is found to increase the penetration.
The present work is on spray in cross flow to be used for a cavity combustor. Three airblast atom... more The present work is on spray in cross flow to be used for a cavity combustor. Three airblast atomizers (A,B and C) with different spray properties are characterized for spray structure and droplet diameters using shadowgraphy. Their suitability is assessed for spray in crossflow studies and one among them (atomizer A) is used for crossflow studies. A set up is designed and fabricated to have spray injection in transverse direction to air flow. The air velocity profile is characterized and uniformity and low level of turbulence are ensured. The spray is subjected to air cross flow and images of the structure is taken by using shadowgraphy. The effect of Weber Number and Momentum ratio is discussed on spray penetration and dispersion.
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Papers by Anubhav Sinha