CN111967201A - Method for analyzing critical icing type based on numerical simulation model - Google Patents
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Abstract
The invention discloses a method for analyzing critical icing type based on a numerical simulation model, which comprises the following steps: establishing a two-dimensional wire geometric model and an air flow field model, and solving to obtain air flow field distribution; establishing a water drop stress balance equation, obtaining a water drop motion equation according to the water drop stress balance equation, obtaining a water drop motion track according to the water drop motion equation and the air flow field distribution, and obtaining a wire collision coefficient according to the water drop motion track; establishing a wire icing heat balance equation, and establishing a wire icing freezing coefficient according to the wire icing heat balance equation; obtaining critical conditions of the rime and the rime, combining the lead collision coefficient and the lead icing freezing coefficient to obtain the change relation of the critical environment temperature and the critical liquid water content along with external environment factors under the critical conditions of the rime and the rime, and judging the icing type according to the change relation and actual weather conditions. The method can be widely applied to the prediction of the icing type of the power transmission line.
Description
Technical Field
The invention relates to the field of power transmission line icing prediction, in particular to a method for analyzing critical icing types based on a numerical simulation model.
Background
The ice coating of the power transmission line seriously affects the safe and stable operation of the power grid, and the occurrence of extreme weather conditions causes the frequent occurrence of large-area ice coating events of the power transmission line, so that accidents such as disconnection, conductor galloping, tower collapse, insulator flashover and the like of the power transmission line are caused, and huge economic and property losses are caused to power grid departments. So far, numerical simulation research on icing of a power transmission line mainly relates to the collision characteristic and the freezing characteristic of a wire, and numerical solving methods are various, but icing growth models corresponding to different icing types are slightly different, so that analysis of the icing types has important reference values for improving the accuracy of icing prediction and preventing icing disasters of power transmission line departments.
Disclosure of Invention
Aiming at some problems existing in the analysis of the icing type of the current power transmission line, the method for analyzing the critical icing type based on the numerical simulation model predicts the icing type on the basis of considering the wire collision coefficient and the wire icing freezing coefficient, and provides an important reference value for the power operation department to realize the icing type prediction.
In order to achieve the above object, the present invention provides a method for analyzing critical icing type based on a numerical simulation model, comprising the steps of:
establishing a two-dimensional wire geometric model and an air flow field model, and solving to obtain air flow field distribution;
establishing a water drop stress balance equation, obtaining a water drop motion equation according to the water drop stress balance equation, obtaining a water drop motion track according to the water drop motion equation and the air flow field distribution, and obtaining a wire collision coefficient according to the water drop motion track;
establishing a wire icing heat balance equation, and establishing a wire icing freezing coefficient according to the wire icing heat balance equation;
obtaining critical conditions of the rime and the rime, combining the lead collision coefficient and the lead icing freezing coefficient to obtain the change relation of the critical environment temperature and the critical liquid water content along with external environment factors under the critical conditions of the rime and the rime, and judging the icing type according to the change relation and actual weather conditions.
Optionally, the step of solving the airflow field distribution includes:
(1) taking a two-dimensional cylindrical section of a cylindrical wire as a research object, placing a two-dimensional wire geometric model in an air flow field to establish a two-dimensional wind tunnel model, wherein the diameter of the section of the wire is D, the distance from a wind speed inlet to the wire is 25D, the distance from a wind speed outlet to the wire is 35D, and the distance from an upper wall surface and a lower wall surface to the wire is 25D;
(2) dividing grids;
(3) the air flow field model is an air flow field established by utilizing a continuity equation and an RANS equation of the air flow field and a standard k-turbulence model, so that the lead is positioned in the air flow field, and the continuity equation and the RANS equation of the air flow field are as follows:
where ρ is the air fluid density, t is time, p is pressure, viAnd vjIs the air velocity component, xiAnd xjFor the coordinate components, the indices i and j respectively denote different coordinate directions in a cartesian coordinate system,
for the reynolds stress component, we assume from Boussinesq vortex-viscosity:
k is the unit mass of the turbulent pulsation kinetic energy of the fluid,ijis a kronecker symbol;
(4) the method adopts a standard k-turbulence model to solve the closing problem of the unsteady incompressible RANS equation, wherein k is respectively as follows:
dissipation ratio, σ, of turbulent pulsating kinetic energy of fluid per unit masskAnd σPrandtl numbers, C corresponding to turbulence kinetic energy k and dissipation ratio, respectively1And C2Constant coefficient, μtIs the coefficient of turbulence viscosity, GkGenerating a term for the kinetic energy of the turbulence;
(5) the boundary conditions are set as follows:
entry boundary conditions: setting the speed inlet, selecting the speed to be consistent with the actual condition, enabling the speed direction to be parallel to the inlet direction, setting the DPM option to be launching (wall-jet), calculating the turbulence intensity and the turbulence characteristic scale according to an empirical formula, and enabling the turbulence intensity I to be 0.16(Re)-1/8The characteristic scale L of the turbulent flow is 0.07L, L is the hydraulic diameter of the wind tunnel pipeline, and Re is the Reynolds number of air;
exit boundary conditions: set as pressure outlet, total pressure (gauge) at outlet set as 0, DPM set as escape;
wall surface: setting the upper wall surface and the lower wall surface and the cylindrical lead wall surface as non-slip boundary conditions, and adopting a standard wall surface function for processing, wherein the DPM of the upper wall surface and the DPM of the lower wall surface are set as escape (escape), and the DPM of the cylindrical lead wall surface is set as collection (trap);
and taking the air velocity and the air pressure as solving variables, establishing a continuous equation of the air flow field and a discrete equation of an RANS equation by using a finite volume method, processing options of airflow momentum, turbulent kinetic energy and turbulent dissipation rate by adopting a second-order windward format, and solving a discrete equation of velocity-pressure coupling by adopting a SIMPLE algorithm so as to obtain the distribution of the airflow field.
Optionally, when the grids are divided, in the area near the wall surface of the wire, the calculation accuracy is improved by adopting local encrypted structural grid division; in the area part far away from the conducting wire, a triangular non-structural grid with low grid resolution is adopted to improve the calculation speed.
Optionally, the step of obtaining the wire collision coefficient includes: if the size of the water drops is less than 10% in volume fraction, the mutual influence among the water drops and the influence of the water drops on the air flow field can be ignored; the water drops do not deform, decompose or participate in the thermal process in the whole process, and the physical properties are kept unchanged; the forces acting on the water drop only take into account the viscous drag, gravity and the air buoyancy, and according to the above assumptions, the equilibrium equation is determined by the water drop force
Obtaining an equation of motion of the supercooled water droplets:
wherein g is the acceleration of gravity, ρpFor supercooled water droplet density, ρ is air fluid density, fdIs the exchange coefficient of air and liquid drop, f is the adhesion mass force vector, v and u areVelocity vectors, R, for air fluid and supercooled water dropletseReynolds number of supercooled water droplet with respect to air flow field, dpIs the diameter (mum) of supercooled water droplets, μ is the kinetic viscosity coefficient of the air fluid, CdIs a coefficient of resistance;
the motion trail of the water drop can be obtained by integrating the formula (6),
according to the motion track of the water drop, setting the distance between infinity and the x-axis of the lead as Y0A water droplet particle moving toward the wire at a velocity v, the wire collision coefficient alpha is obtained1＝Y0and/R, R is the radius of the wire.
Optionally, the step of establishing the freezing coefficient of the wire icing includes: short wave radiation qnThe heat gain is very low, usually negligible, and the stationary wire or the low-speed rotating cylinder conducts the heat loss qiThe value is small and negligible, unless in the initial stage of wire icing, the icing degree is very low and cannot be ignored, and the volume and mass of the water drop are small, the collision kinetic energy q of the water drop is smallkAnd the heat balance equation of the ice coating of the obtained lead is not considered:
qf+qv+qa+qR＝qc+qe+ql+qs+qr (10)
wherein q isfThe latent heat released during freezing of water droplets when they collide with the wire, qf＝α1α2α3ωvDLf；qvFor heating the wire by air, qv＝hrcv2D/(2Ca)；qkIs the collision kinetic energy of water drops; q. q.saThe heat energy released after the water drops freeze to ice, qa＝-α1α2α3ωvDCits；qnEnergy obtained for short wave radiation; q. q.sRFor transmitting electric current Joule heat, qR＝I2r0D/(2R)；qcFor convective heat losses, qc＝πDh(ts-ta)；qeLoss of latent heat for evaporation or sublimation, qe＝πDhχ[e(ts)-e(ta)]；qlHeat absorbed by water droplets impinging on the wire surface, ql＝-α1ωvCwDta；qsHeat lost by long-wave radiation, qs＝4π1σRD(273.15+ta)3(ts-ta)；qrThe quantity of heat taken away when the unfrozen part of the supercooled water drops leaves the ice surface; q. q.siTo conduct heat loss, qr＝α1ωvCwD(1-α3)(ts-ta)，
Each heat is brought into formula (10) to obtain a freezing coefficient alpha3Comprises the following steps:
order to
Then
The saturated water vapour pressure e (t) at the water or ice surface of the ice-coated surface at a temperature t may be expressed as:
wherein h is the convective heat transfer coefficient, rcCoefficient of restitution for locally viscous heating of the surface of a cylindrical conductor, CaIs the specific heat capacity of air, I is the current magnitude, r0Resistivity per unit length of wire (omega. m)-1) R is the radius of the wire, alpha1To collect the coefficients, CωIs the specific heat capacity of water, LfTo coefficient of latent heat of vaporization, CiIs the specific heat capacity of ice, taIs the ambient temperature, tsIs the surface temperature of the wire, chi is the evaporation or sublimation coefficient, e (t) is the saturated vapor pressure (kPa) of the water surface or ice surface of the ice-coated surface at the temperature t,1is the emissivity of the outer surface of the ice layer, σRStefan-Boltzman constant.
Optionally, the solving step of the change relationship between the environmental temperature and the liquid water content under the critical conditions of the rime and the rime along with the external environmental factors is as follows: according to the physical significance of different ice coating types of the lead, the critical conditions of rime and rime are as follows:
from the equation (12), the freezing coefficient is related to the collision coefficient, the ambient temperature, the wind speed, the liquid water content in the air, the current, the water droplet diameter and the wire radius, so the critical condition for the transformation between rime and rime can be expressed as:
equation (15) is a multivariable equation including environmental factors and collision coefficients, i is the magnitude of current, dpIs the diameter of the water drop, D is the diameter of the wire, alpha1Is the wire impact coefficient;
on the basis of the critical condition of rime conversion of rime to rime, the wire collision coefficient alpha is calculated according to a numerical simulation method1And under the critical condition of the wire icing type, bringing the critical condition value into a formula (15), wherein the relation between the critical environment temperature and the external environment factors is expressed as follows:
in the formula (f)1(ta) Is the critical ambient temperature, V is the wind speed (m/s), LfIs the latent heat of evaporation coefficient;
according to equation (14), the relationship between the critical liquid water content and the external environmental factors is expressed as:
where ω represents the critical liquid water content.
Optionally, the ice coating type is determined according to the variation relationship and the actual weather condition, and the specific determination method is as follows:
according to the change relation, the freezing coefficient is reduced due to the fact that the liquid water content of the air is increased; in order to maintain the freezing coefficient of the wire ice coating unchanged, the environment temperature needs to be reduced to reduce the latent heat released in the freezing process of water drops; along with the increase of the liquid water content of the air, the influence of the wind speed on the critical environment temperature is more obvious, so that under the ice coating condition, the wind speed, the environment temperature and the liquid water content in the air are increased, and the formation of the rime is facilitated, otherwise, the ice coating is facilitated to form the rime; meanwhile, under the ice coating condition, the diameter of the supercooled water drops is increased to be beneficial to ice coating to form rime, and on the contrary, the diameter of the supercooled water drops is increased to be beneficial to ice coating to form rime.
Compared with the prior art, the invention can realize the following beneficial effects:
the method calculates the external airflow flow field distribution and the water drop movement locus of the cylindrical lead based on the Fluent discrete phase model, obtains the lead collision coefficients in different environments, and provides a method for deducing the external conditions corresponding to the types of rain and rime based on numerical simulation according to the definitions of the ice-coated rain and rime growth and the lead ice-coated heat balance equation. Conducting wire icing numerical simulation and analysis are carried out, and the result shows that: the type of the ice coating on the lead is related to the collision characteristic and the freezing characteristic, the ambient temperature, the diameter of water drops, the content of the water drops, the wind speed, the current and the diameter of the lead can influence the type of the ice coating, and the type of the ice coating can be accurately judged according to the curves and the environmental parameters. The icing growth models corresponding to different icing types are slightly different, so that the icing type is accurately judged, and the corresponding icing growth model can be selected according to the judged icing type, so that the result accuracy can be effectively improved.
Drawings
Fig. 1 is a flow chart of a method for analyzing critical icing type based on a numerical simulation model.
Fig. 2 is a built two-dimensional wire geometric model.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
Referring to fig. 1, the present embodiment provides a method for analyzing critical icing type based on a numerical simulation model, which includes the following steps:
step 1: and establishing a two-dimensional wire geometric model and an air flow field model, and solving to obtain air flow field distribution.
The two-dimensional wire model refers to a geometric model established by taking a two-dimensional cylindrical section of a wire as a research object, and the air flow field model refers to an air flow field established by utilizing a continuity equation and an RANS equation of the air flow field and a standard k-turbulence model, so that the wire is positioned in the air flow field.
In detail, the airflow field distribution is solved through a Fluent discrete phase model, and the solving steps are as follows:
(1) taking a two-dimensional cylindrical section of a cylindrical wire as a research object, adding an air flow field to establish a two-dimensional wind tunnel model containing a two-dimensional wire geometric model; as shown in fig. 2, a two-dimensional wire is placed in an air flow field to establish a two-dimensional wind tunnel model, wherein the diameter of the cross section of the wire is D, the distance from a wind speed inlet to the wire is 25D, the distance from a wind speed outlet to the wire is 35D, and the distance from an upper wall surface to a lower wall surface to the wire is 25D;
(2) dividing grids, wherein in order to take account of calculation precision and calculation speed when the grids are divided, in the area near the wall surface of the lead, the calculation precision is improved by mainly adopting partial encrypted structural grid division; in the area part far away from the conducting wire, a triangular non-structural grid with low grid resolution is adopted to improve the calculation speed.
(3) The air flow field model is an air flow field established by utilizing a continuity equation and an RANS equation of the air flow field and a standard k-turbulence model, so that the lead is positioned in the air flow field, and the continuity equation and the RANS equation of the air flow field are as follows:
where ρ is the air fluid density, t is time, p is pressure, viAnd vjIs the air velocity component, xiAnd xjFor the coordinate components, the indices i and j respectively denote different coordinate directions in a cartesian coordinate system,
for the reynolds stress component, we assume from Boussinesq vortex-viscosity:
k is the unit mass of the turbulent pulsation kinetic energy of the fluid,ijis a kronecker symbol;
(4) the method adopts a standard k-turbulence model to solve the closing problem of the unsteady incompressible RANS equation, wherein k is respectively as follows:
dissipation ratio, σ, of turbulent pulsating kinetic energy of fluid per unit masskAnd σPrandtl numbers, C corresponding to turbulence kinetic energy k and dissipation ratio, respectively1And C2Constant coefficient, μtIs the coefficient of turbulence viscosity, GkGenerating a term for the kinetic energy of the turbulence;
(5) the boundary conditions are set as follows:
entry boundary conditions: setting speed inlet, selecting speed in the direction parallel to inlet direction, setting DPM option as emitting (wall-jet), turbulence intensity and turbulenceThe flow characteristic scale is calculated according to an empirical formula, the turbulence intensity I is 0.16(Re)-1/8The characteristic scale L of the turbulent flow is 0.07L, L is the hydraulic diameter of the wind tunnel pipeline, and Re is the Reynolds number of air;
exit boundary conditions: set as pressure outlet, total pressure (gauge) at outlet set as 0, DPM set as escape;
wall surface: setting the upper wall surface and the lower wall surface and the cylindrical lead wall surface as non-slip boundary conditions, and adopting a standard wall surface function for processing, wherein the DPM of the upper wall surface and the DPM of the lower wall surface are set as escape (escape), and the DPM of the cylindrical lead wall surface is set as collection (trap);
the method comprises the steps of establishing a discrete equation of a control equation by using an air speed and pressure as solving variables and using a finite volume method, wherein the control equation is a formula (1) and a formula (2), options of airflow momentum, turbulent kinetic energy and turbulent dissipation rate are processed by adopting a second-order windward format, and a discrete equation of speed-pressure coupling is solved by adopting a SIMPLE algorithm, so that airflow field distribution is obtained.
Step 2: and establishing a water drop stress balance equation, obtaining a water drop motion equation according to the water drop stress balance equation, obtaining a water drop motion track according to the water drop motion equation and the air flow field distribution, and obtaining a wire collision coefficient according to the water drop motion track.
In detail, the water drop stress balance equation is
The steps of obtaining the wire impact coefficient are as follows: if the size of the water drops is less than 10% in volume fraction, the mutual influence among the water drops and the influence of the water drops on the air flow field can be ignored; the water drops do not deform, decompose or participate in the thermal process in the whole process, and the physical properties are kept unchanged; the acting force acting on the water drop only considers viscous resistance, gravity and air buoyancy, and according to the assumption, the motion equation of the supercooled water drop is obtained by the water drop stress balance equation:
wherein g is the acceleration of gravity, ρpFor supercooled water droplet density, ρ is air fluid density, fdIs the exchange coefficient of air and liquid drops, f is the adhering mass force vector, v and u are the velocity vectors of the air fluid and supercooled water drops, respectively, ReReynolds number of supercooled water droplet with respect to air flow field, dpIs the diameter (mum) of supercooled water droplets, μ is the kinetic viscosity coefficient of the air fluid, CdIs a coefficient of resistance;
the motion trail of the water drop can be obtained by integrating the formula (6),
according to the motion track of the water drop, setting the distance between infinity from the conducting wire and the x axis as Y0A water droplet particle moving toward the wire at a velocity v, the wire collision coefficient alpha is obtained1＝Y0and/R, R is the radius of the wire.
And step 3: and establishing a wire icing heat balance equation, and establishing a wire icing freezing coefficient according to the wire icing heat balance equation.
In detail, short-wave radiation qnThe heat gain is very low, usually negligible, and the stationary wire or the low-speed rotating cylinder conducts the heat loss qiThe value is small and negligible, unless in the initial stage of wire icing, the icing degree is very low and cannot be ignored, and the volume and mass of the water drop are small, the collision kinetic energy q of the water drop is smallkAnd the heat balance equation of the ice coating of the obtained lead is not considered:
qf+qv+qa+qR＝qc+qe+ql+qs+qr (10)
wherein the content of the first and second substances,qflatent heat released during freezing of water droplets when colliding with the wire; q. q.svHeating the wire for air; q. q.skIs the collision kinetic energy of water drops; q. q.saThe heat energy released after the water drops are frozen into ice; q. q.snEnergy obtained for short wave radiation; q. q.sRJoule heat for transmitting current; q. q.scHeat loss by convection; q. q.seLatent heat loss for evaporation or sublimation; q. q.slHeat absorbed by water droplets impinging on the wire surface; q. q.ssHeat lost to long wave radiation; q. q.srThe quantity of heat taken away when the unfrozen part of the supercooled water drops leaves the ice surface; q. q.siFor conduction of heat loss, the expression of the heat is shown in table 1;
TABLE 1
Each heat is brought into formula (10) to obtain a freezing coefficient alpha3Comprises the following steps:
order to
Then
Wherein h is the convective heat transfer coefficient, rcCoefficient of restitution for locally viscous heating of the surface of the cylindrical conductor, caIs the specific heat capacity of air, I is the current magnitude, r0Resistivity per unit length of wire (omega. m)-1) R is the radius of the wire, alpha1To collect the coefficients, CωIs the specific heat capacity of water, LfTo coefficient of latent heat of vaporization, CiIs the specific heat capacity of ice, taIs the ambient temperature, tsIs the surface temperature of the wire, chi is the evaporation or sublimation coefficient, and e (t) is the water on the ice-coated surface at the temperature tSaturated water vapor pressure (kPa) of the surface or ice,1is the emissivity of the outer surface of the ice layer, σRStefan-Boltzman constant.
The saturated water vapour pressure e (t) at the water or ice surface of the ice-coated surface at a temperature t may be expressed as:
t may represent all temperatures, and tsIn particular to the surface temperature, t, of the wireaIn particular the ambient temperature, in terms of tsAnd taIn order to distinguish the temperature of the wire from the ambient temperature, e (t) is a function of temperature, where t may be tsOr ta。
And 4, step 4: obtaining critical conditions of the rime and the rime, combining the lead collision coefficient and the lead icing freezing coefficient to obtain the change relation of the critical environment temperature and the critical liquid water content along with external environment factors under the critical conditions of the rime and the rime, and judging the icing type according to the change relation and actual weather conditions.
The critical conditions of rime and rime are as follows:
from the equation (12), the freezing coefficient is related to the collision coefficient, the ambient temperature, the wind speed, the liquid water content in the air, the current, the water droplet diameter and the wire radius, so the critical condition for the transformation between rime and rime can be expressed as:
equation (15) is a multivariable equation including environmental factors and collision coefficients, i is the magnitude of current, dpIs the diameter of the water drop, D is the diameter of the wire, alpha1Is the wire impact coefficient;
in the rime of the rimeOn the basis of converting critical conditions, the wire collision coefficient alpha is calculated according to a numerical simulation method1The wire freezing coefficient is related to the coefficient of impact, ambient temperature, wind speed, air liquid water content, current, water droplet diameter and wire radius. According to the boundary conditions of the rime and the rime, the relation between the critical environment temperature, the critical liquid water content and other factors can be expressed as a function related to the wire collision coefficient, namely a formula (16) and a formula (17), and the ice coating type can be judged according to the function.
Under the critical condition of the wire icing type, bringing the critical condition value into a formula (15), wherein the relation between the critical environment temperature and the external environment factors is expressed as follows:
in the formula (f)1(ta) Is the critical ambient temperature, V is the wind speed (m/s), LfIs the latent heat of evaporation coefficient;
according to equation (14), the relationship between the critical liquid water content and the external environmental factors is expressed as:
where ω represents the critical liquid water content.
From the equations (16) and (17), the relationship between the critical ambient temperature and the current at different wind speeds and the relationship between the critical ambient temperature and the liquid water content at different water droplet diameters can be known. According to the relation curve, the freezing coefficient is reduced due to the increase of the liquid water content of the air; in order to maintain the freezing coefficient of the wire ice coating unchanged, the environment temperature needs to be reduced to reduce the latent heat released in the freezing process of water drops; as the liquid water content of the air increases, the wind speed has a more pronounced effect on the critical ambient temperature. Therefore, under the ice coating condition, the wind speed, the ambient temperature and the liquid water content in the air are increased, which is beneficial to the formation of the rime, and on the contrary, the rime is beneficial to the formation of the ice coating. Meanwhile, under the ice coating condition, the diameter of the supercooled water drops is increased to be beneficial to ice coating to form rime, and on the contrary, the diameter of the supercooled water drops is increased to be beneficial to ice coating to form rime.
In summary, in the embodiment, by obtaining the wire collision coefficient and the freezing coefficient, and combining the critical conditions of rime and rime, the change relationship between the critical environment temperature and the critical liquid water content along with the external environment factors is obtained, whether the current ice coating is rime or rime can be accurately judged according to the change relationship and by combining the actual weather conditions (such as wind speed, environment temperature, liquid water content in the air, and the like), and after the ice coating type is accurately judged, a corresponding ice coating growth model can be conveniently and specifically selected subsequently, so that people can conveniently predict the growth condition of future wire ice coating.
The above description is only an example of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can substitute or change the technical solution of the present invention and the inventive concept thereof within the scope of the present invention.
Claims (7)
1. A method for analyzing critical icing type based on a numerical simulation model is characterized by comprising the following steps:
establishing a two-dimensional wire geometric model and an air flow field model, and solving to obtain air flow field distribution;
establishing a water drop stress balance equation, obtaining a water drop motion equation according to the water drop stress balance equation, obtaining a water drop motion track according to the water drop motion equation and the air flow field distribution, and obtaining a wire collision coefficient according to the water drop motion track;
establishing a wire icing heat balance equation, and establishing a wire icing freezing coefficient according to the wire icing heat balance equation;
obtaining critical conditions of the rime and the rime, combining the lead collision coefficient and the lead icing freezing coefficient to obtain the change relation of the critical environment temperature and the critical liquid water content along with external environment factors under the critical conditions of the rime and the rime, and judging the icing type according to the change relation and actual weather conditions.
2. The method for analyzing the critical icing type based on the numerical simulation model as claimed in claim 1, wherein the air flow field distribution is solved through a Fluent discrete phase model, and the solving step is as follows:
(1) taking a two-dimensional cylindrical section of a cylindrical wire as a research object, placing a two-dimensional wire geometric model in an air flow field to establish a two-dimensional wind tunnel model, wherein the diameter of the section of the wire is D, the distance from a wind speed inlet to the wire is 25D, the distance from a wind speed outlet to the wire is 35D, and the distance from an upper wall surface and a lower wall surface to the wire is 25D;
(2) dividing grids;
(3) the air flow field model is an air flow field established by utilizing a continuity equation and an RANS equation of the air flow field and a standard k-turbulence model, so that the lead is positioned in the air flow field, and the continuity equation and the RANS equation of the air flow field are as follows:
where ρ is the air fluid density, t is time, p is pressure, viAnd vjIs the air velocity component, xiAnd xjFor the coordinate components, the indices i and j respectively denote different coordinate directions in a cartesian coordinate system,
for the reynolds stress component, we assume from Boussinesq vortex-viscosity:
k is fluid turbulence per unit massThe kinetic energy of the pulsation is changed,ijis a kronecker symbol;
(4) the method adopts a standard k-turbulence model to solve the closing problem of the unsteady incompressible RANS equation, wherein k is respectively as follows:
dissipation ratio, σ, of turbulent pulsating kinetic energy of fluid per unit masskAnd σPrandtl numbers, C corresponding to turbulence kinetic energy k and dissipation ratio, respectively1And C2Constant coefficient, μtIs the coefficient of turbulence viscosity, GkGenerating a term for the kinetic energy of the turbulence;
(5) the boundary conditions are set as follows:
entry boundary conditions: setting the speed inlet, selecting the speed to be consistent with the actual condition, enabling the speed direction to be parallel to the inlet direction, setting the DPM option to be launching (wall-jet), calculating the turbulence intensity and the turbulence characteristic scale according to an empirical formula, and enabling the turbulence intensity I to be 0.16(Re)-1/8The characteristic scale L of the turbulent flow is 0.07L, and L is the hydraulic diameter of the wind tunnel pipeline; re is the Reynolds number of air;
exit boundary conditions: set as pressure outlet, total pressure (gauge) at outlet set as 0, DPM set as escape;
wall surface: setting the upper wall surface and the lower wall surface and the cylindrical lead wall surface as non-slip boundary conditions, and adopting a standard wall surface function for processing, wherein the DPM of the upper wall surface and the DPM of the lower wall surface are set as escape (escape), and the DPM of the cylindrical lead wall surface is set as collection (trap);
and taking the air velocity and the air pressure as solving variables, establishing a continuous equation of the air flow field and a discrete equation of an RANS equation by using a finite volume method, processing options of airflow momentum, turbulent kinetic energy and turbulent dissipation rate by adopting a second-order windward format, and solving a discrete equation of velocity-pressure coupling by adopting a SIMPLE algorithm so as to obtain the distribution of the airflow field.
3. The method for analyzing the critical icing type based on the numerical simulation model as claimed in claim 2, wherein when the grids are divided, the calculation accuracy is improved by adopting partial encrypted structural grid division in the near-wall surface area of the wire; in the area part far away from the conducting wire, a triangular non-structural grid with low grid resolution is adopted to improve the calculation speed.
4. The method for analyzing critical icing type based on numerical simulation model according to claim 1, wherein the step of obtaining the wire impact coefficient comprises: if the size of the water drops is less than 10% in volume fraction, the mutual influence among the water drops and the influence of the water drops on the air flow field can be ignored; the water drops do not deform, decompose or participate in the thermal process in the whole process, and the physical properties are kept unchanged; the forces acting on the water drop only take into account the viscous drag, gravity and the air buoyancy, and according to the above assumptions, the equilibrium equation is determined by the water drop force
Obtaining an equation of motion of the supercooled water droplets:
wherein g is the acceleration of gravity, ρpFor supercooled water droplet density, ρ is air fluid density, fdIs the exchange coefficient of air and liquid dropletsF is the adhering mass force vector, v and u are the velocity vectors of the air fluid and supercooled water droplets, respectively, ReReynolds number of supercooled water droplet with respect to air flow field, dpIs the diameter (mum) of supercooled water droplets, μ is the kinetic viscosity coefficient of the air fluid, CdIs a coefficient of resistance;
the motion trail of the water drop can be obtained by integrating the formula (6),
according to the motion track of the water drop, setting the distance between infinity and the x-axis of the lead as Y0A water droplet particle moving toward the wire at a velocity v, the wire collision coefficient alpha is obtained1＝Y0and/R, R is the radius of the wire.
5. The method for analyzing critical icing type based on numerical simulation model according to any one of claims 1-4, wherein the establishing step of the wire icing freezing coefficient is as follows: short wave radiation qnThe heat gain is very low, usually negligible, and the stationary wire or the low-speed rotating cylinder conducts the heat loss qiThe value is small and negligible, unless in the initial stage of wire icing, the icing degree is very low and cannot be ignored, and the volume and mass of the water drop are small, the collision kinetic energy q of the water drop is smallkAnd the heat balance equation of the ice coating of the obtained lead is not considered:
qf+qv+qa+qR＝qc+qe+ql+qs+qr (10)
wherein q isfThe latent heat released during freezing of water droplets when they collide with the wire, qf＝α1α2α3ωvDLf；qvFor heating the wire by air, qv＝hrcv2D/(2Ca)；qkIs the collision kinetic energy of water drops; q. q.saThe heat energy released after the water drops freeze to ice, qa＝-α1α2α3ωvDCits；qnEnergy obtained for short wave radiation; q. q.sRFor transmitting electric current Joule heat, qR＝I2r0D/(2R)；qcFor convective heat losses, qc＝πDh(ts-ta)；qeLoss of latent heat for evaporation or sublimation, qe＝πDhχ[e(ts)-e(ta)]；qlHeat absorbed by water droplets impinging on the wire surface, ql＝-α1ωvCwDta；qsHeat lost by long-wave radiation, qs＝4π1σRD(273.15+ta)3(ts-ta)；qrThe quantity of heat taken away when the unfrozen part of the supercooled water drops leaves the ice surface; q. q.siTo conduct heat loss, qr＝α1ωvCwD(1-α3)(ts-ta)，
Each heat is brought into formula (10) to obtain a freezing coefficient alpha3Comprises the following steps:
order to
Then
Wherein h is the convective heat transfer coefficient, rcCoefficient of restitution for locally viscous heating of the surface of a cylindrical conductor, CaIs the specific heat capacity of air, I is the current magnitude, r0Resistivity per unit length of wire (omega. m)-1) R is the radius of the wire, alpha1To collect the coefficients, CωIs the specific heat capacity of water, LfTo coefficient of latent heat of vaporization, CiIs the specific heat capacity of ice, taIs the ambient temperature, tsIs the surface temperature of the wire, chi is the evaporation or sublimation coefficient, e (t) is the saturated vapor pressure (kPa) of the water surface or ice surface of the ice-coated surface at the temperature t,1is the emissivity of the outer surface of the ice layer, σRStefan-Boltzman constant;
the saturated water vapour pressure e (t) at the water or ice surface of the ice-coated surface at a temperature t may be expressed as:
e (t) is a function of temperature, where t may be tsOr ta。
6. The method for analyzing critical icing type based on the numerical simulation model according to claim 5, wherein the critical conditions of rime and rime are as follows:
from the equation (12), the freezing coefficient is related to the collision coefficient, the ambient temperature, the wind speed, the liquid water content in the air, the current, the water droplet diameter and the wire radius, so the critical condition for the transformation between rime and rime can be expressed as:
equation (15) is a multivariable equation including environmental factors and collision coefficients, i is the magnitude of current, dpIs the diameter of the water drop, D is the diameter of the wire, alpha1Is the wire impact coefficient;
calculating the lead collision coefficient alpha on the basis of the critical condition of rime interconversion of rimes1，
Under the critical condition of the wire icing type, bringing the critical condition value into a formula (15), wherein the relation between the critical environment temperature and the external environment factors is expressed as follows:
in the formula (f)1(ta) Is the critical ambient temperature, V is the wind speed (m/s), LfIs the latent heat of evaporation coefficient;
according to equation (15), the relationship between the critical liquid water content and the external environmental factors is expressed as:
where ω represents the critical liquid water content.
7. The method for analyzing critical icing type based on numerical simulation model as claimed in claim 6, wherein the icing type is judged according to the variation relation and the actual meteorological conditions by the following specific judgment method:
according to the change relation, the freezing coefficient is reduced due to the fact that the liquid water content of the air is increased; in order to maintain the freezing coefficient of the wire ice coating unchanged, the environment temperature needs to be reduced to reduce the latent heat released in the freezing process of water drops; along with the increase of the liquid water content of the air, the influence of the wind speed on the critical environment temperature is more obvious, so that under the ice coating condition, the wind speed, the environment temperature and the liquid water content in the air are increased, and the formation of the rime is facilitated, otherwise, the ice coating is facilitated to form the rime; meanwhile, under the ice coating condition, the diameter of the supercooled water drops is increased to be beneficial to ice coating to form rime, and on the contrary, the diameter of the supercooled water drops is increased to be beneficial to ice coating to form rime.
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