The analytical expressions was deduced for the inviscid flow field induced by the double vortex filaments that move uniformly and rigidly without change of its form in a cylindrical tube, where the vortex filaments ro...The analytical expressions was deduced for the inviscid flow field induced by the double vortex filaments that move uniformly and rigidly without change of its form in a cylindrical tube, where the vortex filaments rotate around its axial with a constant angular velocity and translates along its axial with a constant transferal velocity. It is a key of solving problem to set up a moving cylindrical coordinate system together with the vortex filaments motion, in which the relative velocity field is presumed to be time-independent and with helical symmetry. The result shows that the absolute velocity field and pressure field are all time-periodic functions, and may degenerate into a time-independent field when the helical vortex filaments slip along the filaments themselves or is immobile. The calculation results at the location of pressure peaks and valleys on pipe wall are accordant with experimental results. When the cylindrical pipe radius tends to infinitely large quantity, it is also concluded that the double helical vortex filaments induce flow field in an unbound space.展开更多
The multipolar velocity field structures are investigated by 2D momentum conservation equation with 3D equilibrium sheared flows in the full toroidal system. Numerical results show that the non-existence of radial vel...The multipolar velocity field structures are investigated by 2D momentum conservation equation with 3D equilibrium sheared flows in the full toroidal system. Numerical results show that the non-existence of radial velocity field in equilibrium surfaces is suitable only for the zero-order term of our 2D simulation. The non-zero-order radial velocity field is still preserved, even when converted to conventional magnetic surface coordinates. The distribution of velocity field vectors of the order of 1, 2, and 3 are presented respectively in 2, 4, and 6 polar fields with the local vortex structure. The excitation mechanisms of these velocity vortices are the coupling effects of the magneto-fluid structure patterns and the toroidal effects. These results can help us understand the complexity of core physics, the transverse transport across magnetic field by the radial plasma flow and the formation of velocity vortices.展开更多
By means of ink trace visualization of the flows in conventional straight, positively curved and negatively curved cascades with tip clearance, and measurement of the aerodynamic parameters in transverse section, and...By means of ink trace visualization of the flows in conventional straight, positively curved and negatively curved cascades with tip clearance, and measurement of the aerodynamic parameters in transverse section, and by appling topology theory, the topological structures and vortex structure in the transverse section of a blade cascade were analyzed. Compared with conventional straight cascade, blade positive curving eliminates the separation line of the upper passage vortex, and leads the secondary vortex to change from close separation to open separation, while blade negative curving effects merely the positions of singular points and the intensities and scales of vortex.展开更多
The details of unsteady flow field in small axial fans are described and the relationship between the internal flow char- acteristics and aerodynamic noise of small axial flow fans are explored in the manuscript. Firs...The details of unsteady flow field in small axial fans are described and the relationship between the internal flow char- acteristics and aerodynamic noise of small axial flow fans are explored in the manuscript. Firstly, the broadband noise model is introduced to calculate the distributions of broadband noise sources in fan’s internal flow field, and further fan’s internal flow characteristics affecting broadband noise sources are analyzed by the main distributions of broad- band noise sources. Secondly, the unsteady characteristics of vortex structure in fan’s internal flow field are analyzed by large eddy simulation, and FH-W acoustic model is introduced to calculate aerodynamic noise affected by the unsteady characteristics of vortex structure. Finally, Monitoring points are set up near and far field of small axial fans, at which sound pressure level and spectral characteristics are analyzed. The results show that broadband noise sources are mainly distributed at the tip clearance close to blade trailing edge and one third of chord length of blade trailing edge of small axial fans. The maximum sound power of broadband noise sources at the tip clearance is greater than that at blade trail- ing edge. Sound power level of broadband noise near one third of blade chord length of blade trailing edge is first in- creasing and then decreasing when the distance between radial planes and the center of fan hub increases. Fan’s internal flow characteristics affecting broadband noise sources are the tip leakage vortex and the trailing edge vortex shedding. The tip leakage vortices at the leading edge of blade tip first integrate and then break down, while vortex cores of the trailing edge vortex shedding gradually move from blade hub to one-third of blade chord length and then move to far field within a one-seventh of the rotation cycle. Within a flow passage of fan rotation period, sound pressure level of the monitoring points is relevant to the unsteady feature of vortex structure and the main bands of aerodynamic noise of monitor points are irrelevant to the unsteady feature of vortex structure, relating to the distance between the monitor points and fan. With the above distance increasing, the main bands of aerodynamic noise are widened and moved from the low bands to high bands. All conclusions in the paper will provide significant references for reducing the noise of small axial flow fans.展开更多
A vortex electrostatic precipitator （VEP） forms a vortex flow field within a precipitator by means of the vertical staggered layout of the double-vortex collecting plate facing the direction of the gas flow. The ion...A vortex electrostatic precipitator （VEP） forms a vortex flow field within a precipitator by means of the vertical staggered layout of the double-vortex collecting plate facing the direction of the gas flow. The ion concentrations within the precipitator can be significantly increased. Correspondingly, the charging and coagulation rates of fine particles and particle migration velocity are significantly improved within the VEP. Since it can effectively collect fine particles and reduce precipitator size, VEPs represent a new type of electrostatic precipitator with great application potential. In this work the change curve of the external voltage, gas velocity, row spacing and effective collecting area influencing the precipitation efficiency were acquired through a single-factor experiment. Using an orthogonal regression design, attempts were made to analyze the major operating parameters influencing the collecting efficiency of fine particles, establish a multiple linear regression model and analyze the weights of factors and then acquire quantitative rules relating experimental indicators and factors. The regression model was optimized by MATLAB programming, and we then obtained the optimal factor combination which can enhance the efficiency of fine particle collection. The final optimized result is that： when gas velocity is 3.4 m s-1, the external voltage is 18 kV, row spacing is 100 mm and the effective collecting area is 1.13 m2, the rate of fine particle collection is 89.8867%. After determining and analyzing the state of the internal flow field within the VEP by particle image velocimetry （PIV）, the results show that, for a particular gas velocity, a vortex zone and laminar zone are distinctly formed within the VEP, which increases the ion transport ratio as well as the charging, coagulation and collection rates of fine particles within the precipitator, thus making further improvements in the efficiency of fine particle collection.展开更多
In terms of its dynamics, The Tibetan Plateau Vortex （TPV） is assumed to be a vortex in the botmdary layer forced by diabatic heating and friction. In order to analyze the basic characteristics of waves in the vorte...In terms of its dynamics, The Tibetan Plateau Vortex （TPV） is assumed to be a vortex in the botmdary layer forced by diabatic heating and friction. In order to analyze the basic characteristics of waves in the vortex, the governing equations for the vortex were established in column coordinates with the balance of gradient wind. Based on this, the type of mixed waves and their dispersion characteristics were deduced by solving the linear model. Two numerical simulations with triple-nested domains--one idealized large-eddy simulation and one of a TPV that took place on 14 August 2006---were also carried out. The aim of the simulations was to validate the mixed wave deduced from the governing equations. The high-resolution model output data were analyzed and the results showed that the tangential flow field of the TPV in the form of center heating was cyclonic and convergent in the lower levels and anticyclonic and divergent in the upper levels. The simulations also showed that the vorticity of the vortex is uneven and might have shear flow along the radial direction. The changing vorticity causes the formation and spreading of vortex Rossby （VR） waves, and divergence will cause changes to the n^otion of the excitation and evolution of inertial gravity （IG） waves. Therefore, the vortex may contain what we call mixed ：inertial gravity-vortex Rossby （IG-VR） waves. It is suggested that some strongly developed TPVs should be studied in the future, because of their effects on weather in downstream areas.展开更多
Aircraft wake turbulence is an inherent outcome of aircraft flight,presenting a substan-tial challenge to air traffic control,aviation safety and operational efficiency.Building upon data obtained from coherent Dopple...Aircraft wake turbulence is an inherent outcome of aircraft flight,presenting a substan-tial challenge to air traffic control,aviation safety and operational efficiency.Building upon data obtained from coherent Doppler Lidar detection,and combining Dynamic Bayesian Networks(DBN)with Genetic Algorithm-optimized Backpropagation Neural Networks(GA-BPNN),this paper proposes a model for the inversion of wake vortex parameters.During the wake vortex flow field simulation analysis,the wind and turbulent environment were initially superimposed onto the simulated wake velocity field.Subsequently,Lidar-detected echoes of the velocity field are simulated to obtain a data set similar to the actual situation for model training.In the case study validation,real measured data underwent preprocessing and were then input into the established model.This allowed us to construct the wake vortex characteristic parameter inversion model.The final results demonstrated that our model achieved parameter inversion with only minor errors.In a practical example,our model in this paper significantly reduced the mean square error of the inverted velocity field when compared to the traditional algorithm.This study holds significant promise for real-time monitoring of wake vortices at airports,and is proved a crucial step in developing wake vortex interval standards.展开更多
Large-view flow field measurements using the particle image velocimetry （PIV） technique with high resolution CCD cameras on a rotating 1/8 scale blade model of the NREL UAE phase VI wind turbine are conducted in the...Large-view flow field measurements using the particle image velocimetry （PIV） technique with high resolution CCD cameras on a rotating 1/8 scale blade model of the NREL UAE phase VI wind turbine are conducted in the engineering-oriented q53.2 m wind tunnel. The motivation is to establish the database of the initiation and development of the tip vortex to study the flow structure and mechanism of the wind turbine. The results show that the tip vortex first moves inward for a very short period and then moves outward with the wake expansion, while its vorticity decreases with time after being trailed from the trailing edge of the blade tip, and then increases continuously with the rapid rolling-up to form a strong tip vortex. The measurements also indicate that the downstream movement of the tip vortex is nearly linear in the very near wake under the test condition.展开更多
In this paper, recent measurements of tip vortex flow with and without cavitation carried out in Cavitation Mechanism Tunnel of China Ship Scientific Research Center（CSSRC） are presented. The elliptic hydrofoil with...In this paper, recent measurements of tip vortex flow with and without cavitation carried out in Cavitation Mechanism Tunnel of China Ship Scientific Research Center（CSSRC） are presented. The elliptic hydrofoil with section NACA 662-415 was adopted as test model. High-speed video（HSV） camera was used to visualize the trajectory of tip vortex core and the form of tip vortex cavitation（TVC） in different cavitation situations. Laser Doppler velocimetry（LDV） was employed to measure the tip vortex flow field in some typical sections along the vortex trajectory with the case of cavitation free. Stereo particle image velocimetry（SPIV） system was used to measure the velocity and vorticity distributions with and without cavitation. Series measurement results such as velocity and vorticity distributions, the trajectory of tip vortex core, the vortex core radius, cavity size and cavitation inception number were obtained. The results demonstrated that the minimum pressure coefficient in the vortex core obtained by flow field measurement was quite coincident with the tip vortex cavitation inception number obtained under the condition of high incoming velocity and low air content. And TVC would decrease the vortex strength comparing with the case without cavitation.展开更多
基金Project supported by National Natural Science Foundation of Chi-na (Grant No .50075029) .
文摘The analytical expressions was deduced for the inviscid flow field induced by the double vortex filaments that move uniformly and rigidly without change of its form in a cylindrical tube, where the vortex filaments rotate around its axial with a constant angular velocity and translates along its axial with a constant transferal velocity. It is a key of solving problem to set up a moving cylindrical coordinate system together with the vortex filaments motion, in which the relative velocity field is presumed to be time-independent and with helical symmetry. The result shows that the absolute velocity field and pressure field are all time-periodic functions, and may degenerate into a time-independent field when the helical vortex filaments slip along the filaments themselves or is immobile. The calculation results at the location of pressure peaks and valleys on pipe wall are accordant with experimental results. When the cylindrical pipe radius tends to infinitely large quantity, it is also concluded that the double helical vortex filaments induce flow field in an unbound space.
基金Supported by National Natural Science Foundation of China under Grant No.11575066Domestic ITER under Grant No.2009GB105003
文摘The multipolar velocity field structures are investigated by 2D momentum conservation equation with 3D equilibrium sheared flows in the full toroidal system. Numerical results show that the non-existence of radial velocity field in equilibrium surfaces is suitable only for the zero-order term of our 2D simulation. The non-zero-order radial velocity field is still preserved, even when converted to conventional magnetic surface coordinates. The distribution of velocity field vectors of the order of 1, 2, and 3 are presented respectively in 2, 4, and 6 polar fields with the local vortex structure. The excitation mechanisms of these velocity vortices are the coupling effects of the magneto-fluid structure patterns and the toroidal effects. These results can help us understand the complexity of core physics, the transverse transport across magnetic field by the radial plasma flow and the formation of velocity vortices.
文摘By means of ink trace visualization of the flows in conventional straight, positively curved and negatively curved cascades with tip clearance, and measurement of the aerodynamic parameters in transverse section, and by appling topology theory, the topological structures and vortex structure in the transverse section of a blade cascade were analyzed. Compared with conventional straight cascade, blade positive curving eliminates the separation line of the upper passage vortex, and leads the secondary vortex to change from close separation to open separation, while blade negative curving effects merely the positions of singular points and the intensities and scales of vortex.
文摘The details of unsteady flow field in small axial fans are described and the relationship between the internal flow char- acteristics and aerodynamic noise of small axial flow fans are explored in the manuscript. Firstly, the broadband noise model is introduced to calculate the distributions of broadband noise sources in fan’s internal flow field, and further fan’s internal flow characteristics affecting broadband noise sources are analyzed by the main distributions of broad- band noise sources. Secondly, the unsteady characteristics of vortex structure in fan’s internal flow field are analyzed by large eddy simulation, and FH-W acoustic model is introduced to calculate aerodynamic noise affected by the unsteady characteristics of vortex structure. Finally, Monitoring points are set up near and far field of small axial fans, at which sound pressure level and spectral characteristics are analyzed. The results show that broadband noise sources are mainly distributed at the tip clearance close to blade trailing edge and one third of chord length of blade trailing edge of small axial fans. The maximum sound power of broadband noise sources at the tip clearance is greater than that at blade trail- ing edge. Sound power level of broadband noise near one third of blade chord length of blade trailing edge is first in- creasing and then decreasing when the distance between radial planes and the center of fan hub increases. Fan’s internal flow characteristics affecting broadband noise sources are the tip leakage vortex and the trailing edge vortex shedding. The tip leakage vortices at the leading edge of blade tip first integrate and then break down, while vortex cores of the trailing edge vortex shedding gradually move from blade hub to one-third of blade chord length and then move to far field within a one-seventh of the rotation cycle. Within a flow passage of fan rotation period, sound pressure level of the monitoring points is relevant to the unsteady feature of vortex structure and the main bands of aerodynamic noise of monitor points are irrelevant to the unsteady feature of vortex structure, relating to the distance between the monitor points and fan. With the above distance increasing, the main bands of aerodynamic noise are widened and moved from the low bands to high bands. All conclusions in the paper will provide significant references for reducing the noise of small axial flow fans.
基金sponsored by the National Natural Science Foundation of China(grant no.51278229)the Six Talent Peak Project of Jiangsu Province(grant no.JNHB-018)
文摘A vortex electrostatic precipitator （VEP） forms a vortex flow field within a precipitator by means of the vertical staggered layout of the double-vortex collecting plate facing the direction of the gas flow. The ion concentrations within the precipitator can be significantly increased. Correspondingly, the charging and coagulation rates of fine particles and particle migration velocity are significantly improved within the VEP. Since it can effectively collect fine particles and reduce precipitator size, VEPs represent a new type of electrostatic precipitator with great application potential. In this work the change curve of the external voltage, gas velocity, row spacing and effective collecting area influencing the precipitation efficiency were acquired through a single-factor experiment. Using an orthogonal regression design, attempts were made to analyze the major operating parameters influencing the collecting efficiency of fine particles, establish a multiple linear regression model and analyze the weights of factors and then acquire quantitative rules relating experimental indicators and factors. The regression model was optimized by MATLAB programming, and we then obtained the optimal factor combination which can enhance the efficiency of fine particle collection. The final optimized result is that： when gas velocity is 3.4 m s-1, the external voltage is 18 kV, row spacing is 100 mm and the effective collecting area is 1.13 m2, the rate of fine particle collection is 89.8867%. After determining and analyzing the state of the internal flow field within the VEP by particle image velocimetry （PIV）, the results show that, for a particular gas velocity, a vortex zone and laminar zone are distinctly formed within the VEP, which increases the ion transport ratio as well as the charging, coagulation and collection rates of fine particles within the precipitator, thus making further improvements in the efficiency of fine particle collection.
基金supported by the National Key Basic Research and Development Project of China(Grant No.2012CB417202)the National Nature Science Fund of China(Grant No.41175045)+1 种基金the Special Fund for Meteorological Research in the Public Interest(Grant Nos.GYHY201006014,GYHY201206042 and GYHY201106003)the Sichuan Meteorological Bureau Fund for Young Scholars(Grant No.2011YOUTH02)
文摘In terms of its dynamics, The Tibetan Plateau Vortex （TPV） is assumed to be a vortex in the botmdary layer forced by diabatic heating and friction. In order to analyze the basic characteristics of waves in the vortex, the governing equations for the vortex were established in column coordinates with the balance of gradient wind. Based on this, the type of mixed waves and their dispersion characteristics were deduced by solving the linear model. Two numerical simulations with triple-nested domains--one idealized large-eddy simulation and one of a TPV that took place on 14 August 2006---were also carried out. The aim of the simulations was to validate the mixed wave deduced from the governing equations. The high-resolution model output data were analyzed and the results showed that the tangential flow field of the TPV in the form of center heating was cyclonic and convergent in the lower levels and anticyclonic and divergent in the upper levels. The simulations also showed that the vorticity of the vortex is uneven and might have shear flow along the radial direction. The changing vorticity causes the formation and spreading of vortex Rossby （VR） waves, and divergence will cause changes to the n^otion of the excitation and evolution of inertial gravity （IG） waves. Therefore, the vortex may contain what we call mixed ：inertial gravity-vortex Rossby （IG-VR） waves. It is suggested that some strongly developed TPVs should be studied in the future, because of their effects on weather in downstream areas.
基金supported by the National Natural Science Foundation of China (No.U2133210).
文摘Aircraft wake turbulence is an inherent outcome of aircraft flight,presenting a substan-tial challenge to air traffic control,aviation safety and operational efficiency.Building upon data obtained from coherent Doppler Lidar detection,and combining Dynamic Bayesian Networks(DBN)with Genetic Algorithm-optimized Backpropagation Neural Networks(GA-BPNN),this paper proposes a model for the inversion of wake vortex parameters.During the wake vortex flow field simulation analysis,the wind and turbulent environment were initially superimposed onto the simulated wake velocity field.Subsequently,Lidar-detected echoes of the velocity field are simulated to obtain a data set similar to the actual situation for model training.In the case study validation,real measured data underwent preprocessing and were then input into the established model.This allowed us to construct the wake vortex characteristic parameter inversion model.The final results demonstrated that our model achieved parameter inversion with only minor errors.In a practical example,our model in this paper significantly reduced the mean square error of the inverted velocity field when compared to the traditional algorithm.This study holds significant promise for real-time monitoring of wake vortices at airports,and is proved a crucial step in developing wake vortex interval standards.
基金Project supported by the National Basic Research Program of China (973 Program) (No. 2007CB714600)
文摘Large-view flow field measurements using the particle image velocimetry （PIV） technique with high resolution CCD cameras on a rotating 1/8 scale blade model of the NREL UAE phase VI wind turbine are conducted in the engineering-oriented q53.2 m wind tunnel. The motivation is to establish the database of the initiation and development of the tip vortex to study the flow structure and mechanism of the wind turbine. The results show that the tip vortex first moves inward for a very short period and then moves outward with the wake expansion, while its vorticity decreases with time after being trailed from the trailing edge of the blade tip, and then increases continuously with the rapid rolling-up to form a strong tip vortex. The measurements also indicate that the downstream movement of the tip vortex is nearly linear in the very near wake under the test condition.
基金Project supported by the Key Project of National Natural Science Foundation of China(Grant No.11332009)
文摘In this paper, recent measurements of tip vortex flow with and without cavitation carried out in Cavitation Mechanism Tunnel of China Ship Scientific Research Center（CSSRC） are presented. The elliptic hydrofoil with section NACA 662-415 was adopted as test model. High-speed video（HSV） camera was used to visualize the trajectory of tip vortex core and the form of tip vortex cavitation（TVC） in different cavitation situations. Laser Doppler velocimetry（LDV） was employed to measure the tip vortex flow field in some typical sections along the vortex trajectory with the case of cavitation free. Stereo particle image velocimetry（SPIV） system was used to measure the velocity and vorticity distributions with and without cavitation. Series measurement results such as velocity and vorticity distributions, the trajectory of tip vortex core, the vortex core radius, cavity size and cavitation inception number were obtained. The results demonstrated that the minimum pressure coefficient in the vortex core obtained by flow field measurement was quite coincident with the tip vortex cavitation inception number obtained under the condition of high incoming velocity and low air content. And TVC would decrease the vortex strength comparing with the case without cavitation.
