Journal of Advanced Research in Fluid Mechanics and Thermal Sciences, Nov 1, 2023
The present research work is to investigate, how the pulse detonation engine's (PDE) performance ... more The present research work is to investigate, how the pulse detonation engine's (PDE) performance is affected by thermodynamic detonation factors. This analysis deals with the evaluation of PDE by using pure fuels like hydrogen, propane, and butane and a blend of hydrogen (50%) + propane (50%), butane (50%) + hydrogen (50%) and propane (50%) + butane (50%). The performance prediction model method is based on flow paths. Performance loss mechanisms, like the refilling process are recognized and enumerated. Inside flow damage, which mostly results from shock waves inside the PDE combustion tube, is a major factor in the PDE's performance degradation. The novelty of the present analysis is to observe that the Hydrogen fuel displays the maximum specific impulse of 7280 s with a detonation velocity of 2321 m/s at the value of beta 0.17. whereas, the lowest specific impulse is produced by butane with the same beta value.
Journal of Advanced Research in Fluid Mechanics and Thermal Sciences, Jan 19, 2024
In various fields, including rockets, turbines, and engines, the critical role played by nozzles ... more In various fields, including rockets, turbines, and engines, the critical role played by nozzles in achieving optimal performance is underscored. Within the domain of rocketry, particular attention is given to the weight of the nozzle, where even the slightest modifications in weight can lead to a profound impact on rocket performance. In this research, an endeavor is made to comprehensively investigate the intricate interplay of nozzle pressure ratio, nozzle thickness, and Mach number, to unveil the effects of these parameters on nozzle deformation, the development of equivalent stress, and the pivotal factor of safety. Material optimization strategies for a wide array of flow and geometrical parameters are also explored within the framework of this study. With each parameter considered at four levels, an exploration is conducted across Mach numbers of 1.5, 2.0, 2.5, and 3.0, alongside Nozzle Pressure Ratios of 2, 4, 6, and 8. The meticulous analysis of nozzle thicknesses at levels of 1 mm, 2 mm, 3 mm, and 4 mm is carried out. The computational fluid dynamics (CFD) analysis is systematically executed across all cases, with resultant pressure profiles on the internal surfaces of the nozzle serving as essential boundary conditions for static structural analysis. The presentation of findings entails a comprehensive discussion of the factor of safety values for all parameter combinations. Significantly, it is observed from our results that a direct correlation exists between nozzle thickness and factor of safety, with an increase in nozzle thickness corresponding to an enhancement in factor of safety.
International Journal of Innovative Technology and Exploring Engineering, 2019
In this paper, the outcome of the experimental investigation and the flow field development in th... more In this paper, the outcome of the experimental investigation and the flow field development in the duct at supersonic Mach number of 1.2 is presented. The experiments were conducted at various NPR which covers the condition of correct expansion and under expansion. A Convergent-divergent (C-D) nozzle which is connected with the suddenly expanded duct of the diameter of 16 mm of area ratio 2.56. The recirculation zone is controlled by using the microjets of 1 mm of orifice diameter which are placed at 90 degrees interval at 6.5 mm from the central axis of the main jet. The L/D of the duct was used in the investigation was from 1 to 10, and the NPR at which the experiments were conducted considered are in the range from 3, 5, 7, 9 and 11.
In most of the engineering problems, the sudden expansion at the base is encountered in automobil... more In most of the engineering problems, the sudden expansion at the base is encountered in automobile industries, at the base of the fuselage of the aircraft, at the base of the artillery shells, at the base of the unguided rockets and missiles. At transonic Mach numbers, the contribution of the base drag is more than sixty percent. Hence it is mandatory on the part of the researcher to control the base pressure, depending upon the situation. For external aerodynamics, the base pressure should be closed to the ambient pressure to make base drag almost zero. However, for combustion chambers, the base pressure should be very low so that fuel-air mixing is so that the combustor is efficient. With this idea in mind, this study was undertaken. A finite element (FE) method has been used to investigate the effectiveness of the microjets on wall pressure distribution in a convergent-divergent (CD) nozzle with sudden expansion. For control of the base pressure, four microjets of 1 mm orifice diameter placed at 90degree intervals along a pitch circle distance (PCD) of 1.3 in the base region were used as a control mechanism. The variables considered are the Mach number, area ratio, and length-to-diameter ratio (L/D) as 2.2, 2.56, and 8. The simulation was done for nozzle pressure ratio (NPR) 3, 5, 7, 9, and 11 with and without the presence of the microjets. The current results for all the cases of this study indicate that one can identify the Mach number, NPR, and the L/D, which will result in a maximum increase in the pressure. Moreover, the results also proved that the influence of microjet control does not affect the flow field in the duct adversely. The two-dimensional planar CD nozzle with sudden expansion duct has been modelled, and analyses using the K-ε turbulence model independently checked with the ANSYS tool.
The present investigation intends to review the flow control mechanism's effectiveness through a ... more The present investigation intends to review the flow control mechanism's effectiveness through a circular orifice of 1 mm diameter generating sonic flow at the exit even though experiments were conducted for various NPRs and a fixed level of expansion. Tests were conducted at Mach 1.87 for correct and under-expanded cases; for Mach 2.2, investigations were done at design NPR and over-expanded conditions. Lastly, for Mach 2.58, the study was over-expanded alone as the design NPR is 19.3. However, the research focuses on correctly, over, and under-expanded cases. When nozzles face adverse pressure, the control increases the pressure; when the nozzle flow is either ideally expanded or operating at NPR more than the design NPR, the control results in a decrease in pressure. The bare lowest duct size needed for the stream to stay connected is 1D for Mach 1.87 and 2D for the leftover two Mach numbers. Oscillations are observed for pipe size 6D and above, whereas, for short duct length, such fluctuations are not seen.
An experimental study has been carried out to assess the effectiveness of the active control in t... more An experimental study has been carried out to assess the effectiveness of the active control in the form of micro jets to control the base pressure in a suddenly expanded axi-symmetric duct. Four micro jets of 1mm orifice diameter located at 90 intervals along a pitch circle diameter of 1.3 times the nozzle outlet diameter in the base region are employed as active controls. The Mach numbers of the present study are 2.5 and 3.0. The jets are expanded suddenly into an axi-symmetric circular tube with four cross-sectional area 2.56, 3.24, 4.84 and 6.25 times that of nozzle exit area. The Length to Diameter ratio of the suddenly expanded duct is varied from 10 to 1 and experiments are conducted for Nozzle Pressure Ratio (NPR) from 3 to 11. Since the jets remain over expanded for all the NPRs of the present study, even though, with increase in the NPR, the level of over expansion will decrease. It is well known that for over expanded nozzles an oblique shock will be formed at the nozzle lip, which in turn will result in the increase of the base pressure once it passes through the shock wave. From the results it is observed that for the NPRs 3 and 5 there is no appreciable gain in the base pressure, and hence, control employed in the form of micro jets is not effective, however, at NPR 7, 9, and 11 there is remarkable change in the base pressure values. This clearly indicates that the level of expansion plays a significant role to decide on the value of the base pressure and the control effectiveness of the micro jets. It is found that the micro jets can serve as an effective controller of base pressure in a suddenly expanded duct. The micro jets do not adversely influence the wall pressure flow field in the enlarge duct.
A method for evaluating the performance of micro jets, in a flow behind a highly expanded nozzle ... more A method for evaluating the performance of micro jets, in a flow behind a highly expanded nozzle is presented. In the process, the pressure distribution of the flow behind the nozzle outlet is calculated for a defined range of Mach numbers. The outcome shows the existence of oblique shock, Mach waves, and expansion fan in the investigation depending upon the expansion level of the shear layer at the nozzle lip. The height of the backward facing step is 2.5. The range of NPRs chosen for this case is within 3 and 11.Since very small jets are used as active control method, four jets of one millimeter hole diameter are installed for flow control. It is observed that the control effectiveness is quite good for the entire range of L/D at around Mach 2.0. For L/D ranging from 10 to 2, the decrements in the suction at the base exhibits thirty per cent increase in base pressure with micro jets. The final argument is that efficacy of the flow regulation is case sensitive and to arrive at the optimum flow variable lot of runs are needed to draw the conclusions. Also, the efficacy of very small jets is improved for suitable pressure gradient. For over expanded jets the dynamic effectiveness is minimum. The nature of flow in the abruptly expanded duct, in the presence and absence of the flow manipulator is unaltered and hence, remains identical for most of the cases.
Three-way catalytic converters are utilized to minimize exhaust emissions. The efficient working ... more Three-way catalytic converters are utilized to minimize exhaust emissions. The efficient working of catalytic converter depends upon the flow field developed inside the converter. Due to the prevailing stringent norms, such as Bharat stage-VI, it is essential to create and design a high performing converter having uniform flow distribution within the converter to meet these norms. An easy way to gain an almost sufficiently homogeneous stream circulation is to compose the diffuser inclination minimally and correspondingly to manufacture the cone angle length long enough. The objective of the study is to examine an automobile catalytic convertor to present a detail and comprehensive report on the key parameters affecting the flow uniformity inside the converter and thus attempting to achieve minimum pressure drop across the converter to reduce the backpressure. They are modifying the existing geometry of the catalytic converter to have more uniform flow within the convertor. The analysis had been carried out with varying diffuser angles-57.3, 52.3, and 45 degrees separately. Simulation program using computational fluid dynamics (CFD) software package STAR CCM + 11.02 was used. The monolith design with a 52.3º cone angle evaluated with computations provides an actual parabolic curve, which gives a laminar flow within the catalytic converter, which in turn will increase the conversion efficiency of the converter by 1.060 %. The pressure drop within the monolith is also reduced by 3.7 Pa. This accounts to be a reduction in backpressure up to 5%, thus reduces brake specific fuel consumption of automobiles. The results are validated with the literature. The result shows the overall pressure drop augments with velocity. The temperature effect on light-off performance also studied.
International journal of engineering & technology, Aug 24, 2018
This investigation presents the outcome of the tests conducted to control the pressure in the re-... more This investigation presents the outcome of the tests conducted to control the pressure in the re-circulation zone. Also, the efficiency of the flow controllers to govern the pressure at the base in a rapidly expanded pipe has been investigated. Tiny jets our in number of 1 mm diameter are positioned at the interval of 90 degrees at 6.5 mm from the central axis of the main jet. The Mach numbers of the abruptly expanded flows studied for base pressure range from 1.1 to 3 and the obtained wall pressure distribution is depicted for Mach number 1.6 and 1.8 respectively. Axi-symmetric round brass tubes were used to join jets; and cross-sectional area of those tubes are 2.56. L/D ratio of the broadened pipe was differed from 1 to 10 and NPR was shifted from 3 to 11. Notwithstanding, the outcomes displayed were for Low L/D values of 4, 3, 2 and 1 individually. Also, when the stream was released to the pipes of the given area ratios, it stayed connected with the channel divider for all the inertial levels and the NPRs tried in the present case. Further it is understood that level of expansion assumes a noteworthy part to choose the pressure at the base and its control adequacy. At whatever point, the stream is over expanded, it leads to the formation of an oblique shock at the nozzle lip, prompting improvement of the pressure in the base locale. Shock waves formation, reflection and recombination proceeded till the pressure winds up noticeably environmental and seen that the stream stays intact for low L/D ratio of 4. Very small scale (micro) jets proved to fit in as controllers for the base pressure.
The catalytic converter is a device which converts harmful exhaust gases from internal combustion... more The catalytic converter is a device which converts harmful exhaust gases from internal combustion engine into harmless gases. Global warming and air pollution are a buzz in today's scenario. Greenhouse gasses are responsible for global warming. Carbon dioxide, which contributes to being the single most significant greenhouse gasses emission, comes from the exhaust of an automobile. Catalytic converter plays a vital role in the reduction of such greenhouse gasses. The objective of the present study is to examine an automobile catalytic convertor to present a detail and comprehensive report on the key parameters affecting the flow uniformity inside the converter and thus attempting to achieve minimum pressure drop across the converter to reduce the backpressure. The catalytic converter geometry is modified to increase the conversion efficiency of the converter. The results reported in the latter part of this paper gives a good insight about the recirculation zones created in the base and also velocity and pressure plots to find a solution for uniform flow within the monolith and also achieved a reduction in pressure drop of 3.7 Pa.
This paper presents the outcome of the experimental investigation conducted to control the base p... more This paper presents the outcome of the experimental investigation conducted to control the base pressure for suddenly expanded flow for a fairly high area ratio of non-dimensional backward facing step height of 2.2. The Mach number range of the study were from 1.25 to 3.0 and the NPRs in the range from 3 to 11. The length-to-diameter ratio of the present study was varied from 1 to 10. It is seen that, the relief and L/D combination results in control effectiveness at various Mach numbers taking the base pressure above or below the value of the without case. This shows that the level of base pressure is sensitive to the combination of parameters under study. If base drag reduction is the aim, NPR 11 and L/D range from 10 to 5 seem to be the choice for that. If base suction enhancement is desired, Mach number in the range 2.5 to 3.0 and L/D 10 to 4 seem to be the choice.
Journal of Advanced Research in Fluid Mechanics and Thermal Sciences, Dec 25, 2020
The ballistic research has introduced the requirements for obtaining aerodynamic data including b... more The ballistic research has introduced the requirements for obtaining aerodynamic data including base and wall pressures over a very wide range of Mach number, Reynolds number, and manipulation of these forces by applying both active and passive control strategies. The manipulation of base and wall pressure plays a significant role in bluff body aerodynamics and control of aerodynamic forces is essential in the reduction of drag and improving the overall performance of such bodies. In this study, an experimental investigation was conducted in sudden expansion axis-symmetric passage for controlling wall pressure. Micro jets constituting four micro-holes around base and symmetric to nozzle axis are used as active control to manipulate the wall pressure. Wall pressure distribution is depicted for Mach numbers 1.25 and 1.3 respectively. Length-to-diameter (L/D) ratios of current investigation range from 10 to 5 with area ratios of 2.56. It is found that wall pressure is highly impacted by the microjet flow control at certain Mach numbers and geometrical parameters like the area ratio and L/D ratio also play a significant role in flow control and 50 % to 60% increase in the wall pressure is found at L/D = 10. It is also shown that the nozzle pressure ratio (NPR) also influences the wall pressure. However, the wall pressure distribution of the ducts is found fluctuating in nature in case of correctly expanded flows and remains ineffective even with microjet control
In this study, experiments were conducted to control the base pressure and wall pressure in the w... more In this study, experiments were conducted to control the base pressure and wall pressure in the wake at considerably high Mach numbers for a duct diameter of 25 mm. Tests were done at Mach 1.87 and 2.2. The Nozzle Pressure Ratios considered are 3 to 11 at different expansion levels. These experiments were conducted to evaluate the flow mechanism's efficacy while the nozzle is under the impact of favorable and adverse pressure. The control mechanism was positioned at 6.5 mm from the central axis of the main jet. Results reveal that the minimum pipe length required for the flow to remain attached with the duct is L = 2D. When the duct is L = 2D or 3D, the flow pattern is erratic due to the incident's excessive interaction of the reflected shock waves, and the impact of the ambient pressure. Because of the high duct diameter, the control is not efficient even though nozzles are under-expanded. For a larger area ratio, the reattachment length will be large, hence control becomes marginally effective. For over-expanded jets, the control results to reduce the pressure inside the duct. When nozzles encounter high-intensity adverse pressure results in high wall pressure compared to the lower nozzle pressure ratio due to the decline in the strength of the wave. When nozzles are under-expanded, the control effectiveness is optimum. The control mechanism is employed is able to suppress oscillations for large ducts compared to the short duct, where the flow is oscillatory. The control mechanism also results in the reduction of jet noise for some selected cases.
2ND INTERNATIONAL CONFERENCE ON ADVANCED RESEARCH IN MECHANICAL ENGINEERING (2ND ICARME – 21), 2022
The present investigation intends to review the flow control mechanism's effectiveness through a ... more The present investigation intends to review the flow control mechanism's effectiveness through a circular orifice of 1 mm diameter generating sonic flow at the exit even though experiments were conducted for various NPRs and a fixed level of expansion. Tests were conducted at Mach 1.87 for correct and under-expanded cases; for Mach 2.2, investigations were done at design NPR and over-expanded conditions. Lastly, for Mach 2.58, the study was over-expanded alone as the design NPR is 19.3. However, the research focuses on correctly, over, and under-expanded cases. When nozzles face adverse pressure, the control increases the pressure; when the nozzle flow is either ideally expanded or operating at NPR more than the design NPR, the control results in a decrease in pressure. The bare lowest duct size needed for the stream to stay connected is 1D for Mach 1.87 and 2D for the leftover two Mach numbers. Oscillations are observed for pipe size 6D and above, whereas, for short duct length, such fluctuations are not seen.
In this paper results reported are the outcome of investigation carried to regulate the suddenly ... more In this paper results reported are the outcome of investigation carried to regulate the suddenly expanded flow through a converging-diverging nozzle at high supersonic Mach numbers and at lower length to diameter ratios. The geometrical and the flow variables assessed in this investigation are the diameter ratio, length to diameter (L/D) ratio, expansion level, and the Mach number. The step heights of the present case are 1.6, 1.8, 2.2 and 2.5. The tests were conducted for P0/Patm in the range of 3 to 11. The (L/D) ratio of the suddenly expanded duct of the test was from 10 to 1, however, the outcome are presented for L/D 4, 3, 2, and 1. The Mach numbers tested in the investigation are 1.9, 2.1, 2.4, and 2.8. The results show that the efficacy of the active control is considerable in regulating the base pressure. Further, it found that for Mach numbers 1.9 and 2.1 the control is very effective for NPRs 9 and 11 but, for NPRs 3, 5, and 7 the control efficiency is only marginal. At NP...
Article history: Received 26 June 2019 Received in revised form 11 October 2019 Accepted 14 Octob... more Article history: Received 26 June 2019 Received in revised form 11 October 2019 Accepted 14 October 2019 Available online 10 November 2019 In most of the engineering problems, the sudden expansion at the base is encountered in automobile industries, at the base of the fuselage of the aircraft, at the base of the artillery shells, at the base of the unguided rockets and missiles. At transonic Mach numbers, the contribution of the base drag is more than sixty percent. Hence it is mandatory on the part of the researcher to control the base pressure, depending upon the situation. For external aerodynamics, the base pressure should be closed to the ambient pressure to make base drag almost zero. However, for combustion chambers, the base pressure should be very low so that fuel-air mixing is so that the combustor is efficient. With this idea in mind, this study was undertaken. A finite element (FE) method has been used to investigate the effectiveness of the microjets on wall pressure di...
A method for evaluating the performance of micro jets, in a flow behind a highly expanded nozzle ... more A method for evaluating the performance of micro jets, in a flow behind a highly expanded nozzle is presented. In the process, the pressure distribution of the flow behind the nozzle outlet is calculated for a defined range of Mach numbers. The outcome shows the existence of oblique shock, Mach waves, and expansion fan in the investigation depending upon the expansion level of the shear layer at the nozzle lip. The height of the backward facing step is 2.5. The range of NPRs chosen for this case is within 3 and 11.Since very small jets are used as active control method, four jets of one millimeter hole diameter are installed for flow control. It is observed that the control effectiveness is quite good for the entire range of L/D at around Mach 2.0. For L/D ranging from 10 to 2, the decrements in the suction at the base exhibits thirty per cent increase in base pressure with micro jets. The final argument is that efficacy of the flow regulation is case sensitive and to arrive at the ...
This paper presents the outcome of the experimental investigation conducted to control the base p... more This paper presents the outcome of the experimental investigation conducted to control the base pressure for suddenly expanded flow for a fairly high area ratio of non-dimensional backward facing step height of 2.2. The Mach number range of the study were from 1.25 to 3.0 and the NPRs in the range from 3 to 11. The length-to-diameter ratio of the present study was varied from 1 to 10. It is seen that, the relief and L/D combination results in control effectiveness at various Mach numbers taking the base pressure above or below the value of the without case. This shows that the level of base pressure is sensitive to the combination of parameters under study. If base drag reduction is the aim, NPR 11 and L/D range from 10 to 5 seem to be the choice for that. If base suction enhancement is desired, Mach number in the range 2.5 to 3.0 and L/D 10 to 4 seem to be the choice.
An experimental study has been carried out to assess the effectiveness of the active control in t... more An experimental study has been carried out to assess the effectiveness of the active control in the form of micro jets to control the base pressure in a suddenly expanded axi-symmetric duct. Four micro jets of 1mm orifice diameter located at 90 intervals along a pitch circle diameter of 1.3 times the nozzle outlet diameter in the base region are employed as active controls. The Mach numbers of the present study are 2.5 and 3.0. The jets are expanded suddenly into an axi-symmetric circular tube with four cross-sectional area 2.56, 3.24, 4.84 and 6.25 times that of nozzle exit area. The Length to Diameter ratio of the suddenly expanded duct is varied from 10 to 1 and experiments are conducted for Nozzle Pressure Ratio (NPR) from 3 to 11. Since the jets remain over expanded for all the NPRs of the present study, even though, with increase in the NPR, the level of over expansion will decrease. It is well known that for over expanded nozzles an oblique shock will be formed at the nozzle...
Journal of Advanced Research in Fluid Mechanics and Thermal Sciences, Nov 1, 2023
The present research work is to investigate, how the pulse detonation engine's (PDE) performance ... more The present research work is to investigate, how the pulse detonation engine's (PDE) performance is affected by thermodynamic detonation factors. This analysis deals with the evaluation of PDE by using pure fuels like hydrogen, propane, and butane and a blend of hydrogen (50%) + propane (50%), butane (50%) + hydrogen (50%) and propane (50%) + butane (50%). The performance prediction model method is based on flow paths. Performance loss mechanisms, like the refilling process are recognized and enumerated. Inside flow damage, which mostly results from shock waves inside the PDE combustion tube, is a major factor in the PDE's performance degradation. The novelty of the present analysis is to observe that the Hydrogen fuel displays the maximum specific impulse of 7280 s with a detonation velocity of 2321 m/s at the value of beta 0.17. whereas, the lowest specific impulse is produced by butane with the same beta value.
Journal of Advanced Research in Fluid Mechanics and Thermal Sciences, Jan 19, 2024
In various fields, including rockets, turbines, and engines, the critical role played by nozzles ... more In various fields, including rockets, turbines, and engines, the critical role played by nozzles in achieving optimal performance is underscored. Within the domain of rocketry, particular attention is given to the weight of the nozzle, where even the slightest modifications in weight can lead to a profound impact on rocket performance. In this research, an endeavor is made to comprehensively investigate the intricate interplay of nozzle pressure ratio, nozzle thickness, and Mach number, to unveil the effects of these parameters on nozzle deformation, the development of equivalent stress, and the pivotal factor of safety. Material optimization strategies for a wide array of flow and geometrical parameters are also explored within the framework of this study. With each parameter considered at four levels, an exploration is conducted across Mach numbers of 1.5, 2.0, 2.5, and 3.0, alongside Nozzle Pressure Ratios of 2, 4, 6, and 8. The meticulous analysis of nozzle thicknesses at levels of 1 mm, 2 mm, 3 mm, and 4 mm is carried out. The computational fluid dynamics (CFD) analysis is systematically executed across all cases, with resultant pressure profiles on the internal surfaces of the nozzle serving as essential boundary conditions for static structural analysis. The presentation of findings entails a comprehensive discussion of the factor of safety values for all parameter combinations. Significantly, it is observed from our results that a direct correlation exists between nozzle thickness and factor of safety, with an increase in nozzle thickness corresponding to an enhancement in factor of safety.
International Journal of Innovative Technology and Exploring Engineering, 2019
In this paper, the outcome of the experimental investigation and the flow field development in th... more In this paper, the outcome of the experimental investigation and the flow field development in the duct at supersonic Mach number of 1.2 is presented. The experiments were conducted at various NPR which covers the condition of correct expansion and under expansion. A Convergent-divergent (C-D) nozzle which is connected with the suddenly expanded duct of the diameter of 16 mm of area ratio 2.56. The recirculation zone is controlled by using the microjets of 1 mm of orifice diameter which are placed at 90 degrees interval at 6.5 mm from the central axis of the main jet. The L/D of the duct was used in the investigation was from 1 to 10, and the NPR at which the experiments were conducted considered are in the range from 3, 5, 7, 9 and 11.
In most of the engineering problems, the sudden expansion at the base is encountered in automobil... more In most of the engineering problems, the sudden expansion at the base is encountered in automobile industries, at the base of the fuselage of the aircraft, at the base of the artillery shells, at the base of the unguided rockets and missiles. At transonic Mach numbers, the contribution of the base drag is more than sixty percent. Hence it is mandatory on the part of the researcher to control the base pressure, depending upon the situation. For external aerodynamics, the base pressure should be closed to the ambient pressure to make base drag almost zero. However, for combustion chambers, the base pressure should be very low so that fuel-air mixing is so that the combustor is efficient. With this idea in mind, this study was undertaken. A finite element (FE) method has been used to investigate the effectiveness of the microjets on wall pressure distribution in a convergent-divergent (CD) nozzle with sudden expansion. For control of the base pressure, four microjets of 1 mm orifice diameter placed at 90degree intervals along a pitch circle distance (PCD) of 1.3 in the base region were used as a control mechanism. The variables considered are the Mach number, area ratio, and length-to-diameter ratio (L/D) as 2.2, 2.56, and 8. The simulation was done for nozzle pressure ratio (NPR) 3, 5, 7, 9, and 11 with and without the presence of the microjets. The current results for all the cases of this study indicate that one can identify the Mach number, NPR, and the L/D, which will result in a maximum increase in the pressure. Moreover, the results also proved that the influence of microjet control does not affect the flow field in the duct adversely. The two-dimensional planar CD nozzle with sudden expansion duct has been modelled, and analyses using the K-ε turbulence model independently checked with the ANSYS tool.
The present investigation intends to review the flow control mechanism's effectiveness through a ... more The present investigation intends to review the flow control mechanism's effectiveness through a circular orifice of 1 mm diameter generating sonic flow at the exit even though experiments were conducted for various NPRs and a fixed level of expansion. Tests were conducted at Mach 1.87 for correct and under-expanded cases; for Mach 2.2, investigations were done at design NPR and over-expanded conditions. Lastly, for Mach 2.58, the study was over-expanded alone as the design NPR is 19.3. However, the research focuses on correctly, over, and under-expanded cases. When nozzles face adverse pressure, the control increases the pressure; when the nozzle flow is either ideally expanded or operating at NPR more than the design NPR, the control results in a decrease in pressure. The bare lowest duct size needed for the stream to stay connected is 1D for Mach 1.87 and 2D for the leftover two Mach numbers. Oscillations are observed for pipe size 6D and above, whereas, for short duct length, such fluctuations are not seen.
An experimental study has been carried out to assess the effectiveness of the active control in t... more An experimental study has been carried out to assess the effectiveness of the active control in the form of micro jets to control the base pressure in a suddenly expanded axi-symmetric duct. Four micro jets of 1mm orifice diameter located at 90 intervals along a pitch circle diameter of 1.3 times the nozzle outlet diameter in the base region are employed as active controls. The Mach numbers of the present study are 2.5 and 3.0. The jets are expanded suddenly into an axi-symmetric circular tube with four cross-sectional area 2.56, 3.24, 4.84 and 6.25 times that of nozzle exit area. The Length to Diameter ratio of the suddenly expanded duct is varied from 10 to 1 and experiments are conducted for Nozzle Pressure Ratio (NPR) from 3 to 11. Since the jets remain over expanded for all the NPRs of the present study, even though, with increase in the NPR, the level of over expansion will decrease. It is well known that for over expanded nozzles an oblique shock will be formed at the nozzle lip, which in turn will result in the increase of the base pressure once it passes through the shock wave. From the results it is observed that for the NPRs 3 and 5 there is no appreciable gain in the base pressure, and hence, control employed in the form of micro jets is not effective, however, at NPR 7, 9, and 11 there is remarkable change in the base pressure values. This clearly indicates that the level of expansion plays a significant role to decide on the value of the base pressure and the control effectiveness of the micro jets. It is found that the micro jets can serve as an effective controller of base pressure in a suddenly expanded duct. The micro jets do not adversely influence the wall pressure flow field in the enlarge duct.
A method for evaluating the performance of micro jets, in a flow behind a highly expanded nozzle ... more A method for evaluating the performance of micro jets, in a flow behind a highly expanded nozzle is presented. In the process, the pressure distribution of the flow behind the nozzle outlet is calculated for a defined range of Mach numbers. The outcome shows the existence of oblique shock, Mach waves, and expansion fan in the investigation depending upon the expansion level of the shear layer at the nozzle lip. The height of the backward facing step is 2.5. The range of NPRs chosen for this case is within 3 and 11.Since very small jets are used as active control method, four jets of one millimeter hole diameter are installed for flow control. It is observed that the control effectiveness is quite good for the entire range of L/D at around Mach 2.0. For L/D ranging from 10 to 2, the decrements in the suction at the base exhibits thirty per cent increase in base pressure with micro jets. The final argument is that efficacy of the flow regulation is case sensitive and to arrive at the optimum flow variable lot of runs are needed to draw the conclusions. Also, the efficacy of very small jets is improved for suitable pressure gradient. For over expanded jets the dynamic effectiveness is minimum. The nature of flow in the abruptly expanded duct, in the presence and absence of the flow manipulator is unaltered and hence, remains identical for most of the cases.
Three-way catalytic converters are utilized to minimize exhaust emissions. The efficient working ... more Three-way catalytic converters are utilized to minimize exhaust emissions. The efficient working of catalytic converter depends upon the flow field developed inside the converter. Due to the prevailing stringent norms, such as Bharat stage-VI, it is essential to create and design a high performing converter having uniform flow distribution within the converter to meet these norms. An easy way to gain an almost sufficiently homogeneous stream circulation is to compose the diffuser inclination minimally and correspondingly to manufacture the cone angle length long enough. The objective of the study is to examine an automobile catalytic convertor to present a detail and comprehensive report on the key parameters affecting the flow uniformity inside the converter and thus attempting to achieve minimum pressure drop across the converter to reduce the backpressure. They are modifying the existing geometry of the catalytic converter to have more uniform flow within the convertor. The analysis had been carried out with varying diffuser angles-57.3, 52.3, and 45 degrees separately. Simulation program using computational fluid dynamics (CFD) software package STAR CCM + 11.02 was used. The monolith design with a 52.3º cone angle evaluated with computations provides an actual parabolic curve, which gives a laminar flow within the catalytic converter, which in turn will increase the conversion efficiency of the converter by 1.060 %. The pressure drop within the monolith is also reduced by 3.7 Pa. This accounts to be a reduction in backpressure up to 5%, thus reduces brake specific fuel consumption of automobiles. The results are validated with the literature. The result shows the overall pressure drop augments with velocity. The temperature effect on light-off performance also studied.
International journal of engineering & technology, Aug 24, 2018
This investigation presents the outcome of the tests conducted to control the pressure in the re-... more This investigation presents the outcome of the tests conducted to control the pressure in the re-circulation zone. Also, the efficiency of the flow controllers to govern the pressure at the base in a rapidly expanded pipe has been investigated. Tiny jets our in number of 1 mm diameter are positioned at the interval of 90 degrees at 6.5 mm from the central axis of the main jet. The Mach numbers of the abruptly expanded flows studied for base pressure range from 1.1 to 3 and the obtained wall pressure distribution is depicted for Mach number 1.6 and 1.8 respectively. Axi-symmetric round brass tubes were used to join jets; and cross-sectional area of those tubes are 2.56. L/D ratio of the broadened pipe was differed from 1 to 10 and NPR was shifted from 3 to 11. Notwithstanding, the outcomes displayed were for Low L/D values of 4, 3, 2 and 1 individually. Also, when the stream was released to the pipes of the given area ratios, it stayed connected with the channel divider for all the inertial levels and the NPRs tried in the present case. Further it is understood that level of expansion assumes a noteworthy part to choose the pressure at the base and its control adequacy. At whatever point, the stream is over expanded, it leads to the formation of an oblique shock at the nozzle lip, prompting improvement of the pressure in the base locale. Shock waves formation, reflection and recombination proceeded till the pressure winds up noticeably environmental and seen that the stream stays intact for low L/D ratio of 4. Very small scale (micro) jets proved to fit in as controllers for the base pressure.
The catalytic converter is a device which converts harmful exhaust gases from internal combustion... more The catalytic converter is a device which converts harmful exhaust gases from internal combustion engine into harmless gases. Global warming and air pollution are a buzz in today's scenario. Greenhouse gasses are responsible for global warming. Carbon dioxide, which contributes to being the single most significant greenhouse gasses emission, comes from the exhaust of an automobile. Catalytic converter plays a vital role in the reduction of such greenhouse gasses. The objective of the present study is to examine an automobile catalytic convertor to present a detail and comprehensive report on the key parameters affecting the flow uniformity inside the converter and thus attempting to achieve minimum pressure drop across the converter to reduce the backpressure. The catalytic converter geometry is modified to increase the conversion efficiency of the converter. The results reported in the latter part of this paper gives a good insight about the recirculation zones created in the base and also velocity and pressure plots to find a solution for uniform flow within the monolith and also achieved a reduction in pressure drop of 3.7 Pa.
This paper presents the outcome of the experimental investigation conducted to control the base p... more This paper presents the outcome of the experimental investigation conducted to control the base pressure for suddenly expanded flow for a fairly high area ratio of non-dimensional backward facing step height of 2.2. The Mach number range of the study were from 1.25 to 3.0 and the NPRs in the range from 3 to 11. The length-to-diameter ratio of the present study was varied from 1 to 10. It is seen that, the relief and L/D combination results in control effectiveness at various Mach numbers taking the base pressure above or below the value of the without case. This shows that the level of base pressure is sensitive to the combination of parameters under study. If base drag reduction is the aim, NPR 11 and L/D range from 10 to 5 seem to be the choice for that. If base suction enhancement is desired, Mach number in the range 2.5 to 3.0 and L/D 10 to 4 seem to be the choice.
Journal of Advanced Research in Fluid Mechanics and Thermal Sciences, Dec 25, 2020
The ballistic research has introduced the requirements for obtaining aerodynamic data including b... more The ballistic research has introduced the requirements for obtaining aerodynamic data including base and wall pressures over a very wide range of Mach number, Reynolds number, and manipulation of these forces by applying both active and passive control strategies. The manipulation of base and wall pressure plays a significant role in bluff body aerodynamics and control of aerodynamic forces is essential in the reduction of drag and improving the overall performance of such bodies. In this study, an experimental investigation was conducted in sudden expansion axis-symmetric passage for controlling wall pressure. Micro jets constituting four micro-holes around base and symmetric to nozzle axis are used as active control to manipulate the wall pressure. Wall pressure distribution is depicted for Mach numbers 1.25 and 1.3 respectively. Length-to-diameter (L/D) ratios of current investigation range from 10 to 5 with area ratios of 2.56. It is found that wall pressure is highly impacted by the microjet flow control at certain Mach numbers and geometrical parameters like the area ratio and L/D ratio also play a significant role in flow control and 50 % to 60% increase in the wall pressure is found at L/D = 10. It is also shown that the nozzle pressure ratio (NPR) also influences the wall pressure. However, the wall pressure distribution of the ducts is found fluctuating in nature in case of correctly expanded flows and remains ineffective even with microjet control
In this study, experiments were conducted to control the base pressure and wall pressure in the w... more In this study, experiments were conducted to control the base pressure and wall pressure in the wake at considerably high Mach numbers for a duct diameter of 25 mm. Tests were done at Mach 1.87 and 2.2. The Nozzle Pressure Ratios considered are 3 to 11 at different expansion levels. These experiments were conducted to evaluate the flow mechanism's efficacy while the nozzle is under the impact of favorable and adverse pressure. The control mechanism was positioned at 6.5 mm from the central axis of the main jet. Results reveal that the minimum pipe length required for the flow to remain attached with the duct is L = 2D. When the duct is L = 2D or 3D, the flow pattern is erratic due to the incident's excessive interaction of the reflected shock waves, and the impact of the ambient pressure. Because of the high duct diameter, the control is not efficient even though nozzles are under-expanded. For a larger area ratio, the reattachment length will be large, hence control becomes marginally effective. For over-expanded jets, the control results to reduce the pressure inside the duct. When nozzles encounter high-intensity adverse pressure results in high wall pressure compared to the lower nozzle pressure ratio due to the decline in the strength of the wave. When nozzles are under-expanded, the control effectiveness is optimum. The control mechanism is employed is able to suppress oscillations for large ducts compared to the short duct, where the flow is oscillatory. The control mechanism also results in the reduction of jet noise for some selected cases.
2ND INTERNATIONAL CONFERENCE ON ADVANCED RESEARCH IN MECHANICAL ENGINEERING (2ND ICARME – 21), 2022
The present investigation intends to review the flow control mechanism's effectiveness through a ... more The present investigation intends to review the flow control mechanism's effectiveness through a circular orifice of 1 mm diameter generating sonic flow at the exit even though experiments were conducted for various NPRs and a fixed level of expansion. Tests were conducted at Mach 1.87 for correct and under-expanded cases; for Mach 2.2, investigations were done at design NPR and over-expanded conditions. Lastly, for Mach 2.58, the study was over-expanded alone as the design NPR is 19.3. However, the research focuses on correctly, over, and under-expanded cases. When nozzles face adverse pressure, the control increases the pressure; when the nozzle flow is either ideally expanded or operating at NPR more than the design NPR, the control results in a decrease in pressure. The bare lowest duct size needed for the stream to stay connected is 1D for Mach 1.87 and 2D for the leftover two Mach numbers. Oscillations are observed for pipe size 6D and above, whereas, for short duct length, such fluctuations are not seen.
In this paper results reported are the outcome of investigation carried to regulate the suddenly ... more In this paper results reported are the outcome of investigation carried to regulate the suddenly expanded flow through a converging-diverging nozzle at high supersonic Mach numbers and at lower length to diameter ratios. The geometrical and the flow variables assessed in this investigation are the diameter ratio, length to diameter (L/D) ratio, expansion level, and the Mach number. The step heights of the present case are 1.6, 1.8, 2.2 and 2.5. The tests were conducted for P0/Patm in the range of 3 to 11. The (L/D) ratio of the suddenly expanded duct of the test was from 10 to 1, however, the outcome are presented for L/D 4, 3, 2, and 1. The Mach numbers tested in the investigation are 1.9, 2.1, 2.4, and 2.8. The results show that the efficacy of the active control is considerable in regulating the base pressure. Further, it found that for Mach numbers 1.9 and 2.1 the control is very effective for NPRs 9 and 11 but, for NPRs 3, 5, and 7 the control efficiency is only marginal. At NP...
Article history: Received 26 June 2019 Received in revised form 11 October 2019 Accepted 14 Octob... more Article history: Received 26 June 2019 Received in revised form 11 October 2019 Accepted 14 October 2019 Available online 10 November 2019 In most of the engineering problems, the sudden expansion at the base is encountered in automobile industries, at the base of the fuselage of the aircraft, at the base of the artillery shells, at the base of the unguided rockets and missiles. At transonic Mach numbers, the contribution of the base drag is more than sixty percent. Hence it is mandatory on the part of the researcher to control the base pressure, depending upon the situation. For external aerodynamics, the base pressure should be closed to the ambient pressure to make base drag almost zero. However, for combustion chambers, the base pressure should be very low so that fuel-air mixing is so that the combustor is efficient. With this idea in mind, this study was undertaken. A finite element (FE) method has been used to investigate the effectiveness of the microjets on wall pressure di...
A method for evaluating the performance of micro jets, in a flow behind a highly expanded nozzle ... more A method for evaluating the performance of micro jets, in a flow behind a highly expanded nozzle is presented. In the process, the pressure distribution of the flow behind the nozzle outlet is calculated for a defined range of Mach numbers. The outcome shows the existence of oblique shock, Mach waves, and expansion fan in the investigation depending upon the expansion level of the shear layer at the nozzle lip. The height of the backward facing step is 2.5. The range of NPRs chosen for this case is within 3 and 11.Since very small jets are used as active control method, four jets of one millimeter hole diameter are installed for flow control. It is observed that the control effectiveness is quite good for the entire range of L/D at around Mach 2.0. For L/D ranging from 10 to 2, the decrements in the suction at the base exhibits thirty per cent increase in base pressure with micro jets. The final argument is that efficacy of the flow regulation is case sensitive and to arrive at the ...
This paper presents the outcome of the experimental investigation conducted to control the base p... more This paper presents the outcome of the experimental investigation conducted to control the base pressure for suddenly expanded flow for a fairly high area ratio of non-dimensional backward facing step height of 2.2. The Mach number range of the study were from 1.25 to 3.0 and the NPRs in the range from 3 to 11. The length-to-diameter ratio of the present study was varied from 1 to 10. It is seen that, the relief and L/D combination results in control effectiveness at various Mach numbers taking the base pressure above or below the value of the without case. This shows that the level of base pressure is sensitive to the combination of parameters under study. If base drag reduction is the aim, NPR 11 and L/D range from 10 to 5 seem to be the choice for that. If base suction enhancement is desired, Mach number in the range 2.5 to 3.0 and L/D 10 to 4 seem to be the choice.
An experimental study has been carried out to assess the effectiveness of the active control in t... more An experimental study has been carried out to assess the effectiveness of the active control in the form of micro jets to control the base pressure in a suddenly expanded axi-symmetric duct. Four micro jets of 1mm orifice diameter located at 90 intervals along a pitch circle diameter of 1.3 times the nozzle outlet diameter in the base region are employed as active controls. The Mach numbers of the present study are 2.5 and 3.0. The jets are expanded suddenly into an axi-symmetric circular tube with four cross-sectional area 2.56, 3.24, 4.84 and 6.25 times that of nozzle exit area. The Length to Diameter ratio of the suddenly expanded duct is varied from 10 to 1 and experiments are conducted for Nozzle Pressure Ratio (NPR) from 3 to 11. Since the jets remain over expanded for all the NPRs of the present study, even though, with increase in the NPR, the level of over expansion will decrease. It is well known that for over expanded nozzles an oblique shock will be formed at the nozzle...
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