The accumulation of pollutants in the recirculation zone can worsen ventilation.It is critical to reduce recirculation zones to improve the ventilation efficiency of buildings.However,the variation rule of the recircu...The accumulation of pollutants in the recirculation zone can worsen ventilation.It is critical to reduce recirculation zones to improve the ventilation efficiency of buildings.However,the variation rule of the recirculation zone in a cylindrical confined space(CCS)is unclear,and there are few solutions to suppress or eliminate the recirculation zone at present.In this paper,an annular deflector orifice plate for suppressing the recirculation zone was developed based on the structural characteristics of the CCS.This device is simple in structure and can be used flexibly.Through experiments and numerical simulations,the variation rule of the recirculation zone length and the influence of structural parameters of the device on the vortex suppression were explored.Firstly,empirical formulas for calculating the length of the recirculation zone in the CCS were obtained.In addition,it was proved that placing the annular orifice plate inside the CCS effectively reduced the recirculation zone and improved the ventilation efficiency.Compared to the system without the annular orifice plate,the dimensionless length of the recirculation zone was decreased by 76.3%,and the time to completely discharge the pollutants from the CCS was decreased by 16.7%.Finally,parameters of the annular orifice plate that form the best vortex suppression effect were proposed:the porosity range was 40%–50%,uniform in shape with equal ring spacing,and placed more than one inlet diameter away from the inlet.The results help guide the ventilation design of CCS.展开更多
A coupled system simulating both firebox and reactor is established to study the naphtha pyrolysis in an industrial tubular furnace.The firebox model is based on zone method including combustion,radiation,and convecti...A coupled system simulating both firebox and reactor is established to study the naphtha pyrolysis in an industrial tubular furnace.The firebox model is based on zone method including combustion,radiation,and convection to simulate heat transfer in the furnace.A two-dimensional recirculation model is proposed to estimate the flow field in furnace.The reactor model integrates the feedstock reconstruction model,an auto-generator of detail kinetic schemes,and the reactor simulation model to simulate the reaction process in the tubular coil.The coupled simulation result is compared with industrial process and shows agreement within short computation time.展开更多
The characteristics of swirler flow field, including cold flow field and combustion flow field, in gas tur- bine combustor with two-stage swirler are studied by using particle image velocimetry （PIV）. Velocity compo...The characteristics of swirler flow field, including cold flow field and combustion flow field, in gas tur- bine combustor with two-stage swirler are studied by using particle image velocimetry （PIV）. Velocity compo- nents, fluctuation velocity, Reynolds stress and recirculation zone length are obtained, respectively. Influences of geometric parameter of primary hole, arrangement of primary hole, inlet air temperature, first-stage swirler an- gle and fuel/air ratio on flow field are investigated, respectively. The experimental results reveal that the primary recirculation zone lengths of combustion flow field are shorter than those of cold flow field, and the primary reeir- culation zone lengths decrease with the increase of inlet air temperature and fuel/air ratio. The change of the geo- metric parameter of primary hole casts an important influence on the swirler flow field in two-stage swirler com- bustor.展开更多
When the frigate moves forward,due to the ship motion such as pitching and rolling,the flow over the flight deck becomes very complex,which may seriously threaten the taking off and landing of the ship-borne helicopte...When the frigate moves forward,due to the ship motion such as pitching and rolling,the flow over the flight deck becomes very complex,which may seriously threaten the taking off and landing of the ship-borne helicopter.The flow fields over the different modified simple frigate shape(SFS)models,consisting of the hangar and flight deck,were numerically studied by changing the ratio of hangar height and length in the static state and pitching state.For different models,the contours of velocity and pressure above the flight deck,as well as the variations of velocity components of the observation points and line in static state and pitching state were compared and analyzed.The results show that the size of recirculation zone and the location of the reattachment point have distinct differences for diverse models,and reveal the tracks of recirculation zone’s center and reattachment position in a pitching period.In addition,the velocity components at two observation positions also change periodically with the periodic motion.Furthermore,the deviations of the velocity components in static state and pitching state are relatively large,therefore,the flow fields in static state cannot be used to simulate that in pitching state correctly.展开更多
This paper addresses the necessity to make a physical interpretation of a highly complex three-dimensional tip clearance flow field study for high-speed mixed-flow compressor having stage exit static pressure to inlet...This paper addresses the necessity to make a physical interpretation of a highly complex three-dimensional tip clearance flow field study for high-speed mixed-flow compressor having stage exit static pressure to inlet total pressure ratio of 3.8 with 39,836 rpm rotor speed.The four different tip configurations namely the constant(l Z 0.016 and 0.019)and variable(l Z 0.011(inlet)-0.019(exit)and 0.019(inlet)-0.022(exit))tip clearances were numerically analysed using available experimental data-set.The numerical investigation reveals that in contrast to the classic jet-wake pattern,two anomalous velocity profiles formed at the impeller exit which results in pressure losses in the vaneless diffuser.Near the impeller inlet,the tip leakage flow rolls up to discrete tip leakage vortex structure for each tip clearance configuration.This results in the formation of a region of momentum deficit,recirculation zone,which gets weakened as it moves downstream.The tip clearance configuration is observed to profoundly influence the extent and vorticity of the tip leakage vortex.In the splitter blade passage,the tip leakage flow and Coriolis flow interact with passage flow,resulting in the formation of two secondary passage vortices that move downstream along the pressure and suction surface of the splitter blade.The tip clearance configuration directly influences the impeller exit jetwake pattern by modulating the secondary passage vortices trajectory and vorticity.Moreover,off-design analysis for tip clearances l Z 0.016 and l Z 0.019,depict distinctive tip leakage vortex characteristics.When operating near the stall conditions(80%of design mass flow rate),l Z 0.019 exhibits bubble shape tip leakage vortex breakdown occurring near the impeller inlet.This result in a substantial change in the tip leakage vortex nature;expansion of the recirculation zone and early weakening of the vorticity in the tip leakage vortex.It is observed that vortex breakdown plays a vital role in characteristics of the passage flow field structure and compressor performance near the stall conditions.展开更多
In this paper,the flow field characteristics of a double-swirl low-emission combustor were analyzed by using Particle Imaging Velocimetry(PIV)technology in an optical three-sector combustor test rig.The interactions b...In this paper,the flow field characteristics of a double-swirl low-emission combustor were analyzed by using Particle Imaging Velocimetry(PIV)technology in an optical three-sector combustor test rig.The interactions between sectors and the flow field structure were explained.The results illustrated that there was a big difference between the flow field structures of the middle sector and the side sector under the same pressure drop,which was mainly induced by the interactions between sectors.The interactions made the swirl intensity of the middle sector weaker than that of the side sector,which made the recirculation zone of the middle sector be smaller than that of the side sector.With the increase of swirler pressure drop,the jet velocity at the exit of the swirler,the jet expansion angle,the width of the recirculation zone and the recirculating speed of the central axis became larger,enhancing the interactions between air streams from middle sector and side sector.The flow velocity in the central plane between sectors was small,especially the radial velocity,mainly because of the loss of the swirl intensity by the interactions between flow field of adjacent sectors.The expansion angle determined the position of the vortex in the primary recirculation zone;the axial and radial position of the vortex move downstream and radial outward with the increase of the jet expansion angle.The results of the mechanism of flow field organization in this study can be used to support the design of new low-emission combustor.展开更多
Effect of venturi angle and main stage swirl intensity on flow field and interactions were investigated using PIV.The results showed the difference between the side sector and the middle sector was caused by interacti...Effect of venturi angle and main stage swirl intensity on flow field and interactions were investigated using PIV.The results showed the difference between the side sector and the middle sector was caused by interactions.The interactions were stronger with the rise of the main stage swirl intensity.When the swirl intensity was 0.7 and 0.9,there was little difference of the width of the recirculation zone.But the flow field had a great difference when the swirl intensity was 0.5 and 0.7,which means that when the swirl intensity was small,the swirl intensity had a great influence on the flow field.Venturi angle had a great influence on the flow field structure and interactions when the venturi angle was big,such as 90°.The venturi angle just had a small influence on the width of the recirculation zone when the venturi angle was relatively small,such as 28°and 52°.The velocity of the center plane between two sectors(plane 3)was small.There was a recirculation zone at upstream of the center plane between two sectors(plane 3)when the swirl intensity was 0.7 and 0.9,whereas not one when the swirl intensity was 0.5.The above was induced by interactions.In addition,the velocity of plane 1,plane 3,and plane 5 when the venturi angle was 52°was smaller than that of 28°and 90°.展开更多
Oblique detonation wave(ODW)has been investigated widely for application in ramjet-type engines,but there are less works concerning its instability in a confined space.Recently,a wave complex induced by ODW decoupling...Oblique detonation wave(ODW)has been investigated widely for application in ramjet-type engines,but there are less works concerning its instability in a confined space.Recently,a wave complex induced by ODW decoupling has been observed,and this study investigates the instability of this wave complex featuring a recirculation zone.Numerical results show that the wave complex with recirculation zone oscillates,but the oscillations are found to be periodic rather than random,never reported before.The dependence of the period and frequency on the corner location and angle are analyzed in detail,with very irregular motion tracks of recirculation zone cores.Further quantitative analysis by Fast Fourier transformation reveals two origins of instability:one is the basic oscillation of the recirculation zone associated with the movement of surrounding wave complex;the other is self-excitation inside the recirculation zone,which makes its motion tracks more complicated than the external wave configuration.展开更多
The interaction of bodies like spheres and disks in rotating fluids leads to novel flow structures. The primary swirling flow in circumferential direction is superimposed by a secondary motion in the meridional plane....The interaction of bodies like spheres and disks in rotating fluids leads to novel flow structures. The primary swirling flow in circumferential direction is superimposed by a secondary motion in the meridional plane. The flow is visualized by introducing ink through a hole in the center of the axes and distributed radially in the central plane between the interacting bodies. The flow structure depends on the shape of the bodies, their geometrical arrangement and the Reynolds number given by the rotational speed. The observed flow structures gave rise to further investigations with PIV-measurcments and numerical simulations.展开更多
Reverse-swirl(RS)burner which has been industrialized couples reverses jet and swirl flow for the stabilization of flame.Using Dantec multichannel constant-temperature anemometer,experiments on airflow characteristics...Reverse-swirl(RS)burner which has been industrialized couples reverses jet and swirl flow for the stabilization of flame.Using Dantec multichannel constant-temperature anemometer,experiments on airflow characteristics were implemented on a 1:2 scaled burner model with different values in terms of reverse primary air(RPA)ratio and swirl inner secondary air(SISA)ratio.It was found that the shape of annular coupled recirculation zone(ACRZ)had stayed symmetrical all the time.The RPA ratio was the main factor that had an impact on the values of axial and RMS velocity as well as the radial velocity direction of ACRZ.Both RPA ratio and SISA ratio had a great impact on the area of ACRZ,relative reverse flow rate,mixing between SISA and outer secondary air(OSA)as well as swirling ability of the airflow.The area of ACRZ reached its peak when the RPA ratio was 11.92%or SISA ratio was 17.03%;however,when the RPA ratio and SISA ratio reached 14.86%and 28.41%respectively,the combination of RPA and SISA became relatively favorable;besides,ACRZ area,relative reverse flow and swirling ability became suitable and the mixing between SISA and OSA was relatively delayed.The research was of great practical and theoretical importance to the design and operation of RS burner.展开更多
A new type of swirl burner has been developed to stabilize pulverized\|coal combustion by burning different types of coal at different loads and to reduce NO x formation during combustion. The burner uses a device to...A new type of swirl burner has been developed to stabilize pulverized\|coal combustion by burning different types of coal at different loads and to reduce NO x formation during combustion. The burner uses a device to concentrate the coal powder in the primary\|air tube that divides the primary coal\|air into two streams with different pulverized\|coal concentrations. This paper reports the measurement of gas\|particle flows at the exit of the different swirl burners using a 3\|D Phase Doppler Particle Anemometer (PDPA). The effect of different geometrical configurations on the two\|phase flow field is studied. The results that give the two\|phase flow fields and particle concentrations show the superiority of the new swirl burner.展开更多
基金financially sponsored by the Collaborative Innovation Foundation of the Shaanxi Provincial Department of Education (No.20JY035).
文摘The accumulation of pollutants in the recirculation zone can worsen ventilation.It is critical to reduce recirculation zones to improve the ventilation efficiency of buildings.However,the variation rule of the recirculation zone in a cylindrical confined space(CCS)is unclear,and there are few solutions to suppress or eliminate the recirculation zone at present.In this paper,an annular deflector orifice plate for suppressing the recirculation zone was developed based on the structural characteristics of the CCS.This device is simple in structure and can be used flexibly.Through experiments and numerical simulations,the variation rule of the recirculation zone length and the influence of structural parameters of the device on the vortex suppression were explored.Firstly,empirical formulas for calculating the length of the recirculation zone in the CCS were obtained.In addition,it was proved that placing the annular orifice plate inside the CCS effectively reduced the recirculation zone and improved the ventilation efficiency.Compared to the system without the annular orifice plate,the dimensionless length of the recirculation zone was decreased by 76.3%,and the time to completely discharge the pollutants from the CCS was decreased by 16.7%.Finally,parameters of the annular orifice plate that form the best vortex suppression effect were proposed:the porosity range was 40%–50%,uniform in shape with equal ring spacing,and placed more than one inlet diameter away from the inlet.The results help guide the ventilation design of CCS.
基金Supported by the National Natural Science Foundation of China(U1462206)
文摘A coupled system simulating both firebox and reactor is established to study the naphtha pyrolysis in an industrial tubular furnace.The firebox model is based on zone method including combustion,radiation,and convection to simulate heat transfer in the furnace.A two-dimensional recirculation model is proposed to estimate the flow field in furnace.The reactor model integrates the feedstock reconstruction model,an auto-generator of detail kinetic schemes,and the reactor simulation model to simulate the reaction process in the tubular coil.The coupled simulation result is compared with industrial process and shows agreement within short computation time.
基金Supported by the National Natural Science Foundation of China(50906040)the Nanjing University of Aeronautics and Astronautics Research Funding(NZ2012107,NS2010052)~~
文摘The characteristics of swirler flow field, including cold flow field and combustion flow field, in gas tur- bine combustor with two-stage swirler are studied by using particle image velocimetry （PIV）. Velocity compo- nents, fluctuation velocity, Reynolds stress and recirculation zone length are obtained, respectively. Influences of geometric parameter of primary hole, arrangement of primary hole, inlet air temperature, first-stage swirler an- gle and fuel/air ratio on flow field are investigated, respectively. The experimental results reveal that the primary recirculation zone lengths of combustion flow field are shorter than those of cold flow field, and the primary reeir- culation zone lengths decrease with the increase of inlet air temperature and fuel/air ratio. The change of the geo- metric parameter of primary hole casts an important influence on the swirler flow field in two-stage swirler com- bustor.
基金supported by the Fundamental Research Funds for the Central Universities(No. NS2019006)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘When the frigate moves forward,due to the ship motion such as pitching and rolling,the flow over the flight deck becomes very complex,which may seriously threaten the taking off and landing of the ship-borne helicopter.The flow fields over the different modified simple frigate shape(SFS)models,consisting of the hangar and flight deck,were numerically studied by changing the ratio of hangar height and length in the static state and pitching state.For different models,the contours of velocity and pressure above the flight deck,as well as the variations of velocity components of the observation points and line in static state and pitching state were compared and analyzed.The results show that the size of recirculation zone and the location of the reattachment point have distinct differences for diverse models,and reveal the tracks of recirculation zone’s center and reattachment position in a pitching period.In addition,the velocity components at two observation positions also change periodically with the periodic motion.Furthermore,the deviations of the velocity components in static state and pitching state are relatively large,therefore,the flow fields in static state cannot be used to simulate that in pitching state correctly.
文摘This paper addresses the necessity to make a physical interpretation of a highly complex three-dimensional tip clearance flow field study for high-speed mixed-flow compressor having stage exit static pressure to inlet total pressure ratio of 3.8 with 39,836 rpm rotor speed.The four different tip configurations namely the constant(l Z 0.016 and 0.019)and variable(l Z 0.011(inlet)-0.019(exit)and 0.019(inlet)-0.022(exit))tip clearances were numerically analysed using available experimental data-set.The numerical investigation reveals that in contrast to the classic jet-wake pattern,two anomalous velocity profiles formed at the impeller exit which results in pressure losses in the vaneless diffuser.Near the impeller inlet,the tip leakage flow rolls up to discrete tip leakage vortex structure for each tip clearance configuration.This results in the formation of a region of momentum deficit,recirculation zone,which gets weakened as it moves downstream.The tip clearance configuration is observed to profoundly influence the extent and vorticity of the tip leakage vortex.In the splitter blade passage,the tip leakage flow and Coriolis flow interact with passage flow,resulting in the formation of two secondary passage vortices that move downstream along the pressure and suction surface of the splitter blade.The tip clearance configuration directly influences the impeller exit jetwake pattern by modulating the secondary passage vortices trajectory and vorticity.Moreover,off-design analysis for tip clearances l Z 0.016 and l Z 0.019,depict distinctive tip leakage vortex characteristics.When operating near the stall conditions(80%of design mass flow rate),l Z 0.019 exhibits bubble shape tip leakage vortex breakdown occurring near the impeller inlet.This result in a substantial change in the tip leakage vortex nature;expansion of the recirculation zone and early weakening of the vorticity in the tip leakage vortex.It is observed that vortex breakdown plays a vital role in characteristics of the passage flow field structure and compressor performance near the stall conditions.
基金supported by the Project 91641109 and the Project 51406202 of National Natural Science Foundation of China
文摘In this paper,the flow field characteristics of a double-swirl low-emission combustor were analyzed by using Particle Imaging Velocimetry(PIV)technology in an optical three-sector combustor test rig.The interactions between sectors and the flow field structure were explained.The results illustrated that there was a big difference between the flow field structures of the middle sector and the side sector under the same pressure drop,which was mainly induced by the interactions between sectors.The interactions made the swirl intensity of the middle sector weaker than that of the side sector,which made the recirculation zone of the middle sector be smaller than that of the side sector.With the increase of swirler pressure drop,the jet velocity at the exit of the swirler,the jet expansion angle,the width of the recirculation zone and the recirculating speed of the central axis became larger,enhancing the interactions between air streams from middle sector and side sector.The flow velocity in the central plane between sectors was small,especially the radial velocity,mainly because of the loss of the swirl intensity by the interactions between flow field of adjacent sectors.The expansion angle determined the position of the vortex in the primary recirculation zone;the axial and radial position of the vortex move downstream and radial outward with the increase of the jet expansion angle.The results of the mechanism of flow field organization in this study can be used to support the design of new low-emission combustor.
基金supported by National Natural Science Foundation of China(Grant No.51306182 and 61827802)。
文摘Effect of venturi angle and main stage swirl intensity on flow field and interactions were investigated using PIV.The results showed the difference between the side sector and the middle sector was caused by interactions.The interactions were stronger with the rise of the main stage swirl intensity.When the swirl intensity was 0.7 and 0.9,there was little difference of the width of the recirculation zone.But the flow field had a great difference when the swirl intensity was 0.5 and 0.7,which means that when the swirl intensity was small,the swirl intensity had a great influence on the flow field.Venturi angle had a great influence on the flow field structure and interactions when the venturi angle was big,such as 90°.The venturi angle just had a small influence on the width of the recirculation zone when the venturi angle was relatively small,such as 28°and 52°.The velocity of the center plane between two sectors(plane 3)was small.There was a recirculation zone at upstream of the center plane between two sectors(plane 3)when the swirl intensity was 0.7 and 0.9,whereas not one when the swirl intensity was 0.5.The above was induced by interactions.In addition,the velocity of plane 1,plane 3,and plane 5 when the venturi angle was 52°was smaller than that of 28°and 90°.
基金supported by the National Natural Science Foundation of China(Grant Nos.12002041 and 11822202)。
文摘Oblique detonation wave(ODW)has been investigated widely for application in ramjet-type engines,but there are less works concerning its instability in a confined space.Recently,a wave complex induced by ODW decoupling has been observed,and this study investigates the instability of this wave complex featuring a recirculation zone.Numerical results show that the wave complex with recirculation zone oscillates,but the oscillations are found to be periodic rather than random,never reported before.The dependence of the period and frequency on the corner location and angle are analyzed in detail,with very irregular motion tracks of recirculation zone cores.Further quantitative analysis by Fast Fourier transformation reveals two origins of instability:one is the basic oscillation of the recirculation zone associated with the movement of surrounding wave complex;the other is self-excitation inside the recirculation zone,which makes its motion tracks more complicated than the external wave configuration.
文摘The interaction of bodies like spheres and disks in rotating fluids leads to novel flow structures. The primary swirling flow in circumferential direction is superimposed by a secondary motion in the meridional plane. The flow is visualized by introducing ink through a hole in the center of the axes and distributed radially in the central plane between the interacting bodies. The flow structure depends on the shape of the bodies, their geometrical arrangement and the Reynolds number given by the rotational speed. The observed flow structures gave rise to further investigations with PIV-measurcments and numerical simulations.
基金China Coal Research Institute Company of Energy Conservation Project(No.11021-ZC)for the support to our research.
文摘Reverse-swirl(RS)burner which has been industrialized couples reverses jet and swirl flow for the stabilization of flame.Using Dantec multichannel constant-temperature anemometer,experiments on airflow characteristics were implemented on a 1:2 scaled burner model with different values in terms of reverse primary air(RPA)ratio and swirl inner secondary air(SISA)ratio.It was found that the shape of annular coupled recirculation zone(ACRZ)had stayed symmetrical all the time.The RPA ratio was the main factor that had an impact on the values of axial and RMS velocity as well as the radial velocity direction of ACRZ.Both RPA ratio and SISA ratio had a great impact on the area of ACRZ,relative reverse flow rate,mixing between SISA and outer secondary air(OSA)as well as swirling ability of the airflow.The area of ACRZ reached its peak when the RPA ratio was 11.92%or SISA ratio was 17.03%;however,when the RPA ratio and SISA ratio reached 14.86%and 28.41%respectively,the combination of RPA and SISA became relatively favorable;besides,ACRZ area,relative reverse flow and swirling ability became suitable and the mixing between SISA and OSA was relatively delayed.The research was of great practical and theoretical importance to the design and operation of RS burner.
文摘A new type of swirl burner has been developed to stabilize pulverized\|coal combustion by burning different types of coal at different loads and to reduce NO x formation during combustion. The burner uses a device to concentrate the coal powder in the primary\|air tube that divides the primary coal\|air into two streams with different pulverized\|coal concentrations. This paper reports the measurement of gas\|particle flows at the exit of the different swirl burners using a 3\|D Phase Doppler Particle Anemometer (PDPA). The effect of different geometrical configurations on the two\|phase flow field is studied. The results that give the two\|phase flow fields and particle concentrations show the superiority of the new swirl burner.
