CN114528781A - CFD numerical simulation method combining actual measurement wind-induced snow drift - Google Patents

CFD numerical simulation method combining actual measurement wind-induced snow drift Download PDF

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CN114528781A
CN114528781A CN202210155363.7A CN202210155363A CN114528781A CN 114528781 A CN114528781 A CN 114528781A CN 202210155363 A CN202210155363 A CN 202210155363A CN 114528781 A CN114528781 A CN 114528781A
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李方慧
魏治平
向本军
王程
苏政忠
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Heilongjiang University of Science and Technology
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Abstract

A CFD numerical simulation method combining actual measurement wind-induced snow drift relates to a CFD numerical simulation method of wind-induced snow drift. The method aims to solve the technical problems that relative motion between wind and snow is not considered and accuracy is poor in the existing numerical simulation method. The method comprises the following steps: modeling based on an initial snow distribution form measured by field actual measurement and actually measured snow particle data, considering the relative slip speed of wind phase and snow phase, adopting programming software Visual Studio to write UDF and introduce finite element numerical simulation analysis software Ansys Fluent to simulate the uneven snow distribution of the structure, and utilizing software Tecplot to carry out post-processing on simulated data, thereby establishing a CFD numerical simulation method which combines the actually measured wind-induced snow drift considering the relative movement of wind and snow. The invention improves the accuracy of the numerical simulation method, and can be used in the field of building structure design in cold regions.

Description

CFD numerical simulation method combined with actually measured wind-induced snow drift
Technical Field
The invention belongs to the field of civil engineering, and relates to a CFD numerical simulation method for wind-induced snow drift.
Background
In recent years, snowstorm in cold regions brings great inconvenience to people's trip, communication and production life, and simultaneously greatly threatens the safety of houses and public buildings, wherein wind-induced snow drift easily causes overlarge load of local positions of the buildings, and uneven snow load on the buildings often has an additional effect on the structures, so that the structures are easy to be unstable. The research and prevention of wind and snow is becoming more and more important.
In the early research of wind and snow disasters, the early research is limited by computer conditions, and scholars at home and abroad mainly take actual measurement and experimental research and are gradually adopted by the public along with the continuous progress of society and the rapid development of scientific technology and numerical simulation research based on computational fluid mechanics. The current wind-induced snow drift numerical simulation research adopts the assumption of one-way coupling, the parameter setting adopts empirical values, the one-way coupling is that the influence of snow on the air phase is not considered, the snow phase is regarded as a passively transported solid medium, the deposition and erosion of the snow phase can actually influence the boundary condition of the snow, so that the flow field distribution is further influenced, and the method essentially calculates the diffusion of the snow phase in a stable wind field, which is greatly different from the actual situation, so that the simulation accuracy is reduced.
Disclosure of Invention
The invention provides a CFD numerical simulation method combining actual measurement wind-induced snow drift, aiming at solving the technical problems that relative motion between wind and snow is not considered and accuracy is poor in the existing numerical simulation method. The method considers the relative movement of wind and snow, and optimizes a series of processes from modeling of wind and snow two-phase flow, parameter setting, simulation calculation and the like to obtain a CFD simulation value of wind-induced snow drift.
The CFD numerical simulation method combining the actually measured wind-induced snow drift is carried out according to the following steps:
the method comprises the following steps: collecting basic information required for numerical simulation: collecting the geometric characteristics of the building under study, the geographical position of the building, the geomorphic parameters, the reference height H0Average wind speed V0Wind profile specification, turbulence energy specification, turbulence intensity specification, integral turbulence scale specification and turbulence energy dissipation rate specification; simultaneously measuring the snow particle density and the snow particle diameter d of the accumulated snow at the location of the buildingsAngle of repose, wind speed, wind direction and initial snow depth of the building, calculating threshold friction speed, jump snow speed, ground roughness, building wall roughness, snow roughness and snow settling speed wf；
Step two: establishing a grid model required by numerical simulation: building a model and dividing grids by using the geometric information of the building and the initial snow distribution form collected in the step one to obtain a grid file;
step three: writing air term boundary conditions for numerical simulation: compiling boundary conditions of air phase by using the geographical position information of the place where the building is located, the reference height average wind speed, the wind profile, the turbulence energy, the turbulence intensity, the integral turbulence scale and the turbulence dissipation rate specification information collected in the step one, compiling exponential type wind profile, turbulence energy and turbulence dissipation rate programs based on the C language and Fluent secondary development interfaces in Visual Studio, storing a C language file, and placing the C language file and the grid model file in the step two in the same folder;
step four: writing snow phase boundary conditions for numerical simulation: writing a snow phase volume fraction formula in Visual Studio based on a C language and Fluent secondary development interfaces as an entrance boundary condition of a snow item by using the snow particle density collected in the step one, the gravity acceleration of the place where the building is located and the threshold friction speed and adopting a snow phase movement speed, a snow particle friction speed, jump and suspension layer critical height information adopted in a snow concentration empirical formula and a formula thereof, storing a C language file, and putting the C language file, the model grid file in the step two and the C language file in the step three in the same folder;
step five: numerically simulating the required program access, specifically operating as follows: opening an Ansys-Fluent interface to select 2D/3D, double precision and parallelism, selecting a folder Directory containing a grid file in the second step, a C language file in the third step and a C language file in the fourth step under a General Options-Working Directory, and selecting Set up compatibility Environment for UDF interface opening software under the Environment; selecting User Defined-Functions-completed under the Ansys-Fluent main menu, and selecting the C language files in the third step and the fourth step for loading and compiling to obtain the inlet speeds and volume fractions of the air phase and the snow phase;
step six: adopting Ansys-Fluent software, firstly setting model, material and solver parameters, then introducing the grid model obtained in the step two and the inlet speed and volume fraction of the air phase and the snow phase obtained in the step five, and carrying out wind-snow two-phase flow simulation to obtain a convergence file of wall surface shearing force, the speed and volume fraction of the air phase and the snow phase;
step seven: and (5) performing post-processing on the wall surface shearing force and the wall surface shearing force by using the convergence file calculated in the step six: storing the convergence file calculated by Ansys-Fluent in a Tecplot support format, performing post-processing calculation by using the Tecplot, and making a cloud map and a contour map of pressure, speed and wall shear force in a calculation domain range by extracting components of speed, pressure and wall shear force in x, y and z directions in a calculated three-dimensional space and using a Tecplot custom function specificity Equations;
step eight: post-processing calculation of numerically simulated snow deposit erosion: extracting the wall shear force on the bottom surface of the model or the horizontal and vertical center lines of the bottom surface through Tecplot based on the wall shear force obtained by the calculation in the step seven, and obtaining the wall shear force through a formula
Figure BDA0003512306240000021
Converting the wall surface shearing force into the wall surface friction speed, wherein tau is the wall surface shearing force, and rho is the air density; comparing the wall surface friction speed with a threshold friction speed, and when the wall surface friction speed is greater than the threshold friction speed, corroding the accumulated snow; when the wall surface friction speed is lower than the threshold friction speed, the accumulated snow is deposited; and respectively calculating the erosion amount and the deposition amount, calculating the snow accumulation change thickness, finally superposing the snow accumulation change thickness and the initial snow accumulation depth of the building to obtain the final distribution form of the snow accumulation, and completing the CFD numerical simulation combining the actually measured wind-induced snow drift.
Furthermore, the solving process of the mesh file in the step two is as follows: determining a model calculation domain according to the geometric characteristics of a building in the Ansys-Ican, setting the calculation domain to meet the requirement that the blocking rate is less than 3%, then establishing a grid model in the Ican according to the model, setting reasonable grid size according to the model size to ensure the smooth convergence of the calculation and the accuracy of the simulation, regulating and controlling the triangle and the tetrahedron of the grid deflection rate (Skewness) to be not more than 0.95, regulating and controlling the Aspect Ratio (Aspect Ratio) of the grid, regulating and controlling the flattening degree (Squish) of the grid to be between 0 and 1, and finally outputting a solved grid file in an Ansys-Fluent format.
Further, wherein reasonable mesh size means: the grid model controls the quality of the structured grid to be 0.6-1, and the quality of the unstructured grid to be 0.3-1; the grid aspect ratio is: the grid aspect ratio in the flow core area is less than 5:1, and the boundary layer grid aspect ratio is less than 10: 1.
Further, the empirical formula of snow concentration described in step four is an empirical formula of snow concentration proposed by pomroy & Gray, 1990, 1992, pomroy & Male.
Furthermore, the wind-snow two-phase flow simulation in the step six comprises the following specific processes:
1) adopting Ansys-Fluent software to select Transient in the column of Time under General;
2) selecting a texture model in one column of multiple streams of Multiphase under the model Models, selecting a Realizable k-epsilon model in a k-epsilon two-equation model in one column of Viscous under the model Models, selecting a Phase Interaction-slip in one column of multiple streams of Multiphase under the model Models, and setting a sliding speed algebraic equation;
3) selecting Fluid under material Materials, adding air phase, setting Viscosity Viscosity and Density Density, creating material snow phase, setting the Viscosity Viscosity to be consistent with air phase, and setting Density Density and particle size according to the first step;
4) setting the required fluid and Solid solution in the grid calculation domain under the volume grid Cell Zone Conditions, and setting the Boundary Conditions in Boundary Conditions: the entrance boundary is a speed entrance, the two sides and the top of the calculation domain are symmetrical boundaries, the ground and the model surface are non-slip wall surfaces, and the exit boundary is a free exit;
5) and (3) accessing the air phase Boundary condition in step three in a Boundary Conditions-inlet (entrance): setting wind section, turbulence energy and dissipation rate, and accessing the Volume Fraction of the snow phase in the fourth step by Volume Fraction in the Boundary Conditions-inlets-snow phase-Multiphase; the Fluent-texture model is calculated by adopting a finite volume method, and as the wind and snow flows only have two phases and the integral fraction sum of the two phases is 1, the volume fraction of the snow phase is only required to be given, and the air phase is calculated by software without setting;
6) selecting a SIMPLE algorithm in a selection method under the Solution set by a solver;
7) in the selection monitor-resolution under the solver setting Solution, the continuity equation, the momentum equation and the convergence accuracy of k-epsilon are set, wherein the convergence accuracy of k-epsilon is set to 1e-6Precision;
8) in the Initialization under the Solution set by the solver, the Standard Initialization is selected and initialized at the entrance;
9) and finally, setting the calculated time step length and the calculated step number in Run Calculation, and starting Calculation to obtain a convergence file of the wall shear force, the air phase and snow phase speed and the volume fraction.
Further, in step eight, the erosion amount is calculated by the formula:
Figure BDA0003512306240000041
wherein A iseroIs a constant coefficient of u*As inlet friction speed, u*tIs the threshold speed.
Further, in the eighth step, the deposition amount is calculated by the following formula:
Figure BDA0003512306240000042
wherein wfThe speed of sedimentation of the snow in the middle, phisIs the mass concentration of snow, phis＝ρsf, f is the volume fraction of snow, psIs the snow particle density.
Further, in the eighth step, the calculation formula of the snow-accumulated-snow-thickness-changing is as follows:
Figure BDA0003512306240000043
wherein q issIs qero or qdepγ is the maximum volume fraction of accumulated snow, ρsIs the snow particle density.
The method of the invention uses Imem CFD software to establish a model, applies the cube and peripheral snow distribution measured by actual measurement to the establishment of the model, considers the initial snow distribution of wind-induced snow drift, and uses Ansys Fluent to carry out numerical simulation analysis. The simulation result is compared with a classical wind-induced snow drift experiment and compared with a method which is not combined with actual measurement, so that the accuracy of the simulation method is verified. The invention considers the relative movement between the wind and the snow and combines the relative movement with the actual measurement, thereby improving the accuracy of the wind-induced snow drift numerical simulation.
The overall flow of the CFD numerical simulation method in combination with actual measured wind-induced snow drift of the present invention is schematically shown in fig. 1, and the numerical simulation method in combination with actual measured wind-induced snow drift of the present invention has the following advantages:
1. the relative slip velocity between the wind phase and the snow phase is considered, and the effect between the two phases is considered by solving the relative velocity between the two phases.
2. The snow distribution form of wind blowing snow obtained by actual measurement is applied to the establishment of the model, and the influence of the deposition and erosion of the snow phase on the flow field distribution in the calculation domain is considered.
3. Various data based on local conditions are measured by using an experimental tool and are applied to numerical simulation, so that a simulation result is more fit with the reality and is more accurate.
The method of the invention is helpful for knowing the law of wind and snow movement, preventing building collapse and reducing casualties and economic loss. The method can be used in the field of building structure design in cold regions.
Drawings
FIG. 1 is a schematic overall flow diagram of the CFD numerical simulation method of the present invention incorporating measured wind-induced snow drift;
FIG. 2 is a diagram of the meshing and calculation domains of embodiment 1;
FIG. 3 is a graph showing the distribution of accumulated snow obtained through step seven in example 1;
fig. 4 is a graph showing the comparison of the snow flux per unit time obtained in example 1, the snow flux per unit time obtained in the classical experiment, and the snow flux per unit time obtained in example 2, i.e., a method not combined with the actual measurement.
Detailed Description
The following examples are used to demonstrate the beneficial effects of the present invention:
example 1: the embodiment is a numerical simulation method combining actual measurement of wind-induced snow drift, and the method is carried out according to the following steps:
the method comprises the following steps: collecting basic information required for numerical simulation: the geometric features of the building under study were collected: a cube model with side length of 1m, the geographic position and geomorphic parameter of the building is 0.16, the average wind speed at the position with reference height of 10m is 5m/s, and the wind profileUsing a formula
Figure BDA0003512306240000051
z0And v0Respectively representing the height (1m) of a reference point and the corresponding reference average wind speed (5m/s), and z represents any height; alpha represents a landform parameter, and for B-class landforms, the value of alpha is 0.16; the kinetic energy of turbulence is expressed by formula
Figure BDA0003512306240000052
The energy dissipation rate of the turbulence adopts a formula
Figure BDA0003512306240000053
Wherein, CμTaking 0.09 as an empirical constant; i and l are the turbulence intensity and turbulence length scales, respectively, where:
the intensity of the turbulent kinetic energy adopts a formula
Figure BDA0003512306240000054
Integral turbulence scale using formula
Figure BDA0003512306240000055
Wherein z isG、zbAnd alpha' are landform parameters, in the specification of Japanese AIJ, class B landforms correspond to class II flat lands, and the values of the three landform parameters are 5m, 350m and 0.15 respectively.
The particle diameter of the local Snow is measured to be 0.00015m, the repose angle is measured to be 45 degrees and the Snow density is measured to be 145kg/m by adopting a sample separating sieve, a cone funnel, a Snow Fork and an HOBO small meteorological station instrument3Calculating the threshold friction speed to be 0.2m/s, the jump snow particle speed to be 0.2m/s, the ground roughness coefficient to be 0.25 and the snow particle settling speed to be 0.2 m/s.
Step two: establishing a grid model required by numerical simulation: establishing a model and dividing grids in an Ansys-Imem CFD according to the geometric information of the building and the initial snow distribution form of the building collected in the step one, determining a model calculation domain, wherein the length, the width and the height are respectively 20m, 10m and 8m, the set blocking rate of the calculation domain is 1.25%, then establishing a grid model in the Imem CFD according to the model, and the number of the grids is 360 ten thousand according to the size of the model. And controlling the quality of the structured grid to be 0.8 and the quality of the unstructured grid to be 0.8 by the grid model, and finally outputting the solved grid file in an Ansys-Fluent format. A graph of the grid partitioning and computational domains is shown in fig. 2; in fig. 2, 1 is a symmetric boundary, 2 is a free-development boundary, 3 is a velocity inlet, and 4 is a non-slip wall.
Step three: writing air term boundary conditions for numerical simulation: compiling boundary conditions of air phase by using the geographical position information of the building collected in the step one, reference height average wind speed, wind profile, turbulence energy, turbulence intensity, integral turbulence scale and turbulence dissipation rate specification information, compiling exponential wind profile, turbulence energy and turbulence dissipation rate in Visual Studio on the basis of C language and Fluent secondary development interfaces, storing a C language file, and putting the C language file and the grid model file in the step two in the same folder;
step four: writing snow phase boundary conditions for numerical simulation: the density of the snow particles collected by the first step is 145kg/m3Local gravity acceleration of 9.81m/s2A threshold rubbing speed of 0.2m/s, using Pomeroy&Gray(1990)、Pomeroy&Empirical formula for snow concentration, i.e. formula, proposed by Male (1992)
Figure BDA0003512306240000061
Where ρ issThe density of the snow particles is shown, g is the acceleration of gravity, and 9.81m/s is taken2，upAverage speed of snow particles in jump layer up＝2.8u*t，u*Is the inlet friction speed; the friction speed and the wind speed u at the height of 10m are obtained according to actual measurement fitting of Beyers and the like10Is determined in accordance with the relationship (c) of (c),
Figure BDA0003512306240000062
the snow phase movement speed is 5m/s, the snow particle friction speed is 0.15m/s, u*tIs a threshold speed; taking 0.15 m/s; h issIs the critical height of the jump layer and the suspension layer,
Figure BDA0003512306240000063
snow phase movement speed of 5m/s and snow particle friction speed0.15m/s, compiling a snow phase volume fraction formula as an entry boundary condition of the snow item in Visual Studio on the basis of a C language and Fluent secondary development interface, storing a C language file, and putting the C language file, the model grid file in the step two and the C language file in the step three in the same folder;
step five: numerically simulating the required program access, specifically operating as follows: and opening an Ansys-Fluent interface to select 3D, double-precision and parallel. And selecting a folder Directory containing the grid file in the step two and the self-defined program in the step three and the step four under the General Options-Working Directory, and selecting the Set up compatibility Environment for the UDF interface to open the software under the Environment. Selecting C language files of the third step and the fourth step under User-Defined-Functions-completed under the Ansys-Fluent main menu for loading and compiling to obtain the inlet speeds and volume fractions of the air phase and the snow phase;
step six: adopting Ansys-Fluent software, firstly setting model, material and solver parameters, then introducing the grid model obtained in the step two and the inlet speed and volume fraction of the air phase and the snow phase obtained in the step five, and carrying out wind-snow two-phase flow simulation to obtain a convergence file of wall surface shearing force, the speed and volume fraction of the air phase and the snow phase, wherein the specific steps are as follows:
1) selecting Transient under General on the Time column;
2) selecting a texture model in one column of the multi-stream Multiphase under the model Models, selecting a readable k-epsilon model in one column of the Viscous under the model Models and under a k-epsilon two-equation model, selecting a Phase Interaction-slip in one column of the multi-stream Multiphase under the model Models, and setting a relative slip speed to be 0.25 m/s;
3) selecting Fluid under Materials, adding air phase, setting Viscosity Viscosity and Density Density, creating material snow phase, setting snow phase Viscosity Viscosity to be consistent with air, setting Density Density to be 145kg/m according to step one3(by Snow Fork Snow characteristics analyzer), particle size 0.00015m (by sample screen);
4) setting required fluid and Solid solution in a grid calculation domain under the volume grid Cell Zone Conditions, and setting Boundary Conditions in Boundary Conditions: the entrance boundary is a speed entrance, the two sides and the top of the calculation domain are symmetrical boundaries, the ground and the model surface are non-slip wall surfaces, and the exit boundary is a free exit;
5) and (3) accessing the air phase Boundary condition in step three in a Boundary Conditions-inlet (entrance): setting wind section, turbulence energy and dissipation rate, and accessing the Volume Fraction of the snow phase in the fourth step by Volume Fraction in the Boundary Conditions-inlets-snow phase-Multiphase; the Fluent-texture model is calculated by adopting a finite volume method, and as the snowstorm flow only has two phases and the integral fraction sum of the two phases is 1, the volume fraction of the snow phase is only required to be given, and the air phase is calculated by software and does not need to be set.
6) A SIMPLE algorithm is selected in a method under the condition that a solver is set to solve.
7) Under the Solution set by the solver, the convergence accuracy of the continuity equation, the momentum equation and the k-epsilon is set in the selection of the Monitors-Residual, and the convergence accuracy is set to be 1e in the embodiment-6And (4) precision.
8) And selecting Standard Initialization Standard Initialization in Initialization under solver setting Solution to initialize at an entrance.
9) Finally, the step number set for Calculation in Run Calculation is 1000 steps, and the precision is 10-6And starting to calculate to obtain a convergence file of the wall shear force, the velocities and the volume fractions of the air phase and the snow phase.
Step seven: and (5) post-processing the wall shear force and the wall shear speed by using the convergence file calculated in the step six: storing the convergence file calculated by Ansys-Fluent in a Tecplot support format, performing post-processing calculation by using the Tecplot, and making a cloud map and a contour map of pressure, speed and wall shear force in a calculation domain range by extracting components of speed, pressure and wall shear force in x, y and z directions in a calculated three-dimensional space and using a Tecplot custom function specificity Equations; the distribution pattern of snow is shown in FIG. 3.
Step eight: post-processing calculation of numerical simulation snow deposit erosion: and calculating the obtained wall surface shearing force based on the step seven: based on the seven steps of calculationExtracting the wall shear force of the bottom surface of the model through Tecplot, converting the wall shear stress into the friction speed of the wall through a custom function, comparing the wall friction speed with a threshold friction speed, and adopting a formula to realize erosion when the wall friction speed is greater than the threshold friction speed
Figure BDA0003512306240000081
Calculating the amount of erosion, wherein AeroTaking 7.0 × 10 as constant coefficient-4(ii) a When the wall friction speed is less than the threshold friction speed, the deposition is carried out by adopting a formula
Figure BDA0003512306240000082
Calculating the deposition amount, wherein wfIs the sedimentation velocity of snow, phisIs the mass concentration of snow, phis＝ρsf, f is the volume fraction of snow, psIs the snow particle density; then using the formula
Figure BDA0003512306240000083
Calculating the snow change thickness, wherein qsIs qeroOr qdepGamma is the maximum volume fraction of the accumulated snow, and is taken as 0.62; and finally, overlapping the changed thickness of the accumulated snow with the initial accumulated snow depth of the building in the first step to obtain the final distribution form of the accumulated snow, and finishing the CFD numerical simulation combining the actually measured wind-induced snow drift.
Example 2: in this embodiment, the wind-induced snow drift value is simulated without actually measuring and without considering the relative slip velocity of the wind phase and the snow phase, and the specific method is performed according to the following steps:
the method comprises the following steps: collecting basic information required by numerical simulation: the geometry of the specifically studied buildings: the side length of the cube model is 1m, the geographic position and geomorphic parameter of the building is 0.16, the average wind speed at the position of 10m of the reference height is 5m/s, and the wind profile adopts a formula
Figure BDA0003512306240000084
z and v0Respectively representing the height (1m) of the reference point and the corresponding reference meanWind speed (5 m/s); alpha represents a landform parameter, and for B-type landforms, the value of alpha is 0.16; the kinetic energy of turbulence is expressed by formula
Figure BDA0003512306240000085
The energy dissipation rate of the turbulence adopts a formula
Figure BDA0003512306240000086
Wherein, CμTaking 0.09 as an empirical constant; i and l are respectively turbulence intensity and turbulence length scale, and the turbulence energy intensity adopts a formula
Figure BDA0003512306240000087
Integral turbulence scale using formula
Figure BDA0003512306240000088
Wherein z isG、zbAnd alpha' are topographic parameters, in the Japanese AIJ specification, class B topography corresponds to class II flat ground, and the values of the three topographic parameters are 5m, 350m and 0.15 respectively.
The relevant values are taken empirically: the diameter of the snow particles is 0.00015m, the angle of repose is not considered, and the snow density is 150kg/m3Calculating the threshold friction speed to be 0.2m/s, the jump snow particle speed to be 0.2m/s, the ground roughness coefficient to be 0.25 and the snow particle settling speed to be 0.2 m/s.
Step two: establishing a grid model required by numerical simulation: establishing a model and dividing grids in an Ansys-Imem CFD according to the geometric information of the building and the initial snow distribution form of the building collected in the step one, determining a model calculation domain, wherein the length, the width and the height are respectively 20m, 10m and 8m, the set blocking rate of the calculation domain is 1.25%, then establishing a grid model in the Imem CFD according to the model, and the number of the grids is 360 ten thousand according to the size of the model. And controlling the quality of the structured grid to be 0.8 and the quality of the unstructured grid to be 0.8 by the grid model, and finally outputting the solved grid file in an Ansys-Fluent format.
Step three: writing air term boundary conditions for numerical simulation: compiling boundary conditions of air phase by using the geographical position information of the building collected in the step one, reference height average wind speed, wind profile, turbulence energy, turbulence intensity, integral turbulence scale and turbulence dissipation rate specification information, compiling exponential wind profile, turbulence energy and turbulence dissipation rate on the basis of C language and Fluent secondary development interfaces in Visual Studio in the prior art, storing C language files, and putting the C language files and the grid model files in the step two in the same folder;
step four: writing snow phase boundary conditions for numerical simulation: the density of the snow particles collected in the first step is 150kg/m3Local gravity acceleration of 9.81m/s2A threshold rubbing speed of 0.2m/s, using Pomeroy&Gray(1990)、Pomeroy&Empirical formula for snow concentration, i.e. formula, proposed by Male (1992)
Figure BDA0003512306240000091
Where ρ issThe density of the snow particles is shown, g is the acceleration of gravity, and 9.81m/s is taken2，upAverage speed of snow particles in jump layer up＝2.8u*t，u*As the entrance friction speed, the friction speed obtained by actual measurement fitting according to Beyers and the like and the wind speed u at the height of 10m10Is determined in accordance with the relationship (c) of (c),
Figure BDA0003512306240000092
the snow phase movement speed is 5m/s, the snow particle friction speed is 0.15m/s, u*tIs a threshold speed; taking 0.15 m/s; h issIs the critical height of the jump layer and the suspension layer,
Figure BDA0003512306240000093
the snow phase movement speed is 5m/s, the snow particle friction speed is 0.15m/s, a snow phase volume fraction formula is compiled in Visual Studio on the basis of a C language and Fluent secondary development interface to serve as an entrance boundary condition of a snow item, a C language file is stored, and the C language file, the model grid file in the step two and the C language file in the step three are placed in the same folder;
step five: numerically simulating the required program access, specifically operating as follows: and (4) storing the grid files in the step two and the self-defined programs in the step three and the step four into the same folder, and opening an Ansys-Fluent interface to select 3D, double-precision and parallel. The folder Directory is selected under the General Options-Working Directory, and the Set up compatibility Environment for UDF interface opening software under the selection Environment. User-Defined-Functions under the Ansys-Fluent main menu is selected
-selecting the C language files of the third and fourth steps under complied to load and compile to obtain the inlet velocities and volume fractions of the air phase and the snow phase;
step six: specifically setting the model, the material and the solver parameters of the numerical simulation software, introducing the Ansys-Fluent into the grid model, and simulating the wind-snow two-phase flow based on the secondary development programming introduced in the fifth step, wherein the method specifically comprises the following steps:
1) selecting Transient in the Time column under General;
2) selecting a texture model in one column of the multi-Phase flow under the model Models, selecting a readable k-epsilon model in one column of the Viscous under the model Models and selecting a k-epsilon two-equation model in one column of the Viscous under the model Models, and selecting a Phase Interaction-slip in one column of the multi-Phase flow under the model Models, wherein the relative slip speed of the wind Phase and the snow Phase is not considered;
3) selecting Fluid under Materials, adding air phase, setting Viscosity Viscosity and Density Density, creating material snow phase, setting snow phase Viscosity Viscosity to be consistent with air, setting Density Density to be 150kg/m according to step one3A particle diameter of 0.00015 m;
4) setting required fluid and Solid solution in a grid calculation domain under the volume grid Cell Zone Conditions, and setting Boundary Conditions in Boundary Conditions: the entrance boundary is a speed entrance, the two sides and the top of the calculation domain are symmetrical boundaries, the ground and the model surface are non-slip wall surfaces, and the exit boundary is a free exit;
5) and (3) accessing the air phase Boundary condition in step three in a Boundary Conditions-inlet (entrance): setting a wind section, turbulent kinetic energy and dissipation rate, and accessing the Volume Fraction of the snow phase in the fourth step in the Volume Fraction accessing step under Boundary Conditions-inlets-snow phase-Multiphase; the Fluent-texture model is calculated by adopting a finite volume method, and as the wind and snow flows only have two phases and the integral fraction sum of the two phases is 1, the volume fraction of the snow phase is only required to be given, and the air phase is calculated by software without setting;
6) a SIMPLE algorithm is selected in a method under the condition that a solver is set to solve.
7) Under the Solution set by the solver, the convergence accuracy of the continuity equation, the momentum equation and the k-epsilon is set in the selection of the Monitors-Residual, and the convergence accuracy is set to be 1e in the embodiment-6And (4) precision.
8) And selecting Standard Initialization Standard Initialization in Initialization under solver setting Solution to initialize at an entrance.
9) And finally, calculating the Calculation step number set in the Run Calculation with the Calculation step number of 1000 steps and the precision of 10-6And (5) starting to calculate to obtain a convergence file of the wall shear force, the velocities and the volume fractions of the air phase and the snow phase.
Step seven: and (5) performing post-processing on the wall surface shearing force and the wall surface shearing force by using the convergence file calculated in the step six: after the Ansys-Fluent calculation converges, the file is saved in a Tecplot supported format. And performing post-processing calculation by using Tecplot, and making a cloud map and a contour map of the pressure, the speed and the wall shear force within the calculation domain range by using a Tecplot custom function specificity Equations by extracting the calculated components of the speed, the pressure and the wall shear force of x, y and z.
Step eight: post-processing calculation of numerically simulated snow deposit erosion: extracting the wall shear force on the bottom surface of the model through Tecplot based on the wall shear force obtained by the calculation in the step seven, converting the wall shear stress into the friction speed of the wall through a custom function, comparing the wall friction speed with a threshold friction speed, and corroding when the wall friction speed is greater than the threshold friction speed by adopting a formula
Figure BDA0003512306240000111
Wherein A iseroTaking 7.0 × 10 as constant coefficient-4(ii) a When the wall friction speed is less than the threshold friction speed, the deposition is carried out by adopting a formula
Figure BDA0003512306240000112
WhereinwfThe speed of sedimentation of the snow in the middle, phisIs the mass concentration (phi) of snows＝ρsf, f is the volume fraction of snow, ρsSnow particle density) calculating erosion amount and deposition amount; based on the initial snow depth of the step one, a formula is adopted
Figure BDA0003512306240000113
Calculating the accumulated snow change thickness and the accumulated snow change amount (wherein q is used uniformlysIn place of qeroAnd q isdepAnd gamma is the maximum volume fraction of the accumulated snow, and is taken as 0.62), the final distribution form of the accumulated snow is obtained, and the numerical simulation of wind-induced snow drift is completed.
Comparing the accumulated snow flux per unit time shown by the simulation result of example 1, the accumulated snow flux per unit time obtained by example 2 without combining with the actual measurement and without considering the relative slip speeds of the wind phase and the snow phase, and the accumulated snow flux per unit time of the classical experiment, as shown in fig. 4, it can be seen from fig. 4 that the accumulated snow flux per unit time obtained by example 2 without combining with the actual measurement and without considering the relative slip speeds of the wind phase and the snow phase greatly differs from the curve obtained by the classical experiment method, while the simulation result of example 1 is well consistent with the result of the classical experiment, which indicates that the simulation method of example 1 has high accuracy.

Claims (8)

1. A CFD numerical simulation method combined with actually measured wind-induced snow drift is characterized by comprising the following steps of:
the method comprises the following steps: collecting basic information required for numerical simulation: collecting the geometric characteristics of the building under study, the geographical position of the building, the geomorphic parameters, the reference height H0Average wind speed V0Wind profile specification, turbulence energy specification, turbulence intensity specification, integral turbulence scale specification and turbulence energy dissipation rate specification; simultaneously measuring the snow particle density and the snow particle diameter d of the accumulated snow at the location of the buildingsAngle of repose, wind speed, wind direction and initial snow depth of building, calculating threshold friction speed, speed of jumping snow particles, and ground roughnessRoughness of building wall surface, roughness of snow surface and sedimentation velocity w of snow particlesf；
Step two: establishing a grid model required by numerical simulation: building a model and dividing grids by using the geometric information of the building and the initial snow distribution form collected in the step one to obtain a grid file;
step three: writing air term boundary conditions for numerical simulation: compiling boundary conditions of air phase by using the geographical position information of the place where the building is located, the reference height average wind speed, the wind profile, the turbulence energy, the turbulence intensity, the integral turbulence scale and the turbulence dissipation rate specification information collected in the step one, compiling exponential type wind profile, turbulence energy and turbulence dissipation rate programs based on the C language and Fluent secondary development interfaces in Visual Studio, storing a C language file, and placing the C language file and the grid model file in the step two in the same folder;
step four: writing snow phase boundary conditions for numerical simulation: writing a snow phase volume fraction formula in Visual Studio based on a C language and Fluent secondary development interfaces as an entrance boundary condition of a snow item by using the snow particle density collected in the step one, the gravity acceleration of the place where the building is located and the threshold friction speed and the snow phase motion speed, the snow particle friction speed, the jump and the critical height information of a suspension layer adopted in a snow concentration empirical formula and a formula thereof, storing a C language file, and putting the C language file, the model grid file in the step two and the C language file in the step three in the same folder;
step five: numerically simulating the required program access, specifically operating as follows: opening an Ansys-Fluent interface to select 2D/3D, double precision and parallelism, selecting a folder Directory containing a grid file in the second step, a C language file in the third step and a C language file in the fourth step under a General Options-Working Directory, and selecting Set up compatibility Environment for UDF interface opening software under the Environment; selecting User Defined-Functions-completed under the Ansys-Fluent main menu, and selecting the C language files in the third step and the fourth step for loading and compiling to obtain the inlet speeds and volume fractions of the air phase and the snow phase;
step six: adopting Ansys-Fluent software, firstly setting model, material and solver parameters, then introducing the grid model obtained in the step two and the inlet speed and volume fraction of the air phase and the snow phase obtained in the step five, and carrying out wind-snow two-phase flow simulation to obtain a convergence file of wall surface shearing force, the speed and volume fraction of the air phase and the snow phase;
step seven: and (5) performing post-processing on the wall surface shearing force and the wall surface shearing force by using the convergence file calculated in the step six: storing the convergence file calculated by Ansys-Fluent in a Tecplot support format, performing post-processing calculation by using the Tecplot, and making a cloud map and a contour map of pressure, speed and wall shear force in a calculation domain range by extracting components of speed, pressure and wall shear force in x, y and z directions in a three-dimensional space of a calculation domain and using a Tecplot custom function specificity Equations;
step eight: post-processing calculation of numerically simulated snow deposit erosion: extracting the wall shear force on the bottom surface of the model or the horizontal and vertical center lines of the bottom surface through Tecplot based on the wall shear force obtained by the calculation in the step seven, and obtaining the wall shear force through a formula
Figure FDA0003512306230000021
Converting the wall surface shearing force into the wall surface friction speed, wherein tau is the wall surface shearing force, and rho is the air density; comparing the wall surface friction speed with a threshold friction speed, and when the wall surface friction speed is greater than the threshold friction speed, corroding the accumulated snow; when the wall surface friction speed is lower than the threshold friction speed, the accumulated snow is deposited; and respectively calculating erosion amount and deposition amount, calculating the snow accumulation change thickness, finally superposing the snow accumulation change amount and the initial snow accumulation depth of the building to obtain the final distribution form of the snow accumulation, and completing the CFD numerical simulation combining the actually measured wind-induced snow drift.
2. A CFD numerical simulation method in combination with measured wind-induced snow drift according to claim 1, characterized in that the solving step of the grid file in step two is: determining a model calculation domain according to the geometric characteristics of a building in the Ansys-Ican, setting the calculation domain to meet the requirement that the blocking rate is less than 3%, then establishing a mesh model in the Ican according to the model, setting reasonable mesh size according to the size of the model, regulating and controlling the mesh skewness to be that a triangle and a tetrahedron are not more than 0.95, regulating and controlling the aspect ratio of the mesh, regulating and controlling the mesh flattening degree to be between 0 and 1, and finally outputting a solved mesh file in an Ansys-Fluent format.
3. The method according to claim 2, wherein the reasonable grid size is: the grid model controls the quality of the structured grid to be 0.6-1, and the quality of the unstructured grid to be 0.3-1.
4. A CFD numerical simulation method incorporating measured wind induced snow drift according to claim 2, characterised in that the grid aspect ratio is: the grid aspect ratio in the flow core area is less than 5:1, and the boundary layer grid aspect ratio is less than 10: 1.
5. A CFD numerical simulation method combining measured wind-induced snow drift according to claim 1, 2, 3 or 4, characterized in that the wind-snow two-phase flow simulation in the sixth step is as follows:
1) adopting Ansys-Fluent software to select Transient in the column of Time under General;
2) selecting a texture model in one column of the multi-stream multi-Phase under the model Models, selecting a Rearizable k-epsilon model in a k-epsilon two-equation model in one column of the Viscous under the model Models, selecting a Phase Interaction-slip in one column of the multi-stream multi-Phase under the model Models, and setting a slip speed algebraic equation;
3) selecting Fluid under material Materials, adding air phase, setting Viscosity Viscosity and Density Density, creating material snow phase, setting the Viscosity Viscosity to be consistent with air phase, and setting Density Density and particle size according to the first step;
4) setting the required fluid and Solid solution in the grid calculation domain under the volume grid Cell Zone Conditions, and setting the Boundary Conditions in Boundary Conditions: the entrance boundary is a speed entrance, the two sides and the top of the calculation domain are symmetrical boundaries, the ground and the model surface are non-slip wall surfaces, and the exit boundary is a free exit;
5) air phase Boundary Conditions at Boundary Conditions-inlet access step three: setting a wind section, turbulent kinetic energy and dissipation rate, and accessing the Volume Fraction of the snow phase in the fourth step under Boundary Conditions-inlets-snow phase-Multiphase; the Fluent-texture model is calculated by adopting a finite volume method, and as the wind and snow flows only have two phases and the integral fraction sum of the two phases is 1, the volume fraction of the snow phase is only required to be given, and the air phase is calculated by software without setting;
6) selecting a SIMPLE algorithm in a selection method under the Solution set by a solver;
7) in the selection monitor-resolution under the solver setting Solution, the continuity equation, the momentum equation and the convergence accuracy of k-epsilon are set, wherein the convergence accuracy of k-epsilon is set to 1e-6Precision;
8) in the Initialization under the Solution set by the solver, the Standard Initialization is selected and initialized at the entrance;
9) and finally, setting the calculated time step length and the calculated step number in Run Calculation, and starting Calculation to obtain a convergence file of the wall shear force, the air phase and snow phase speed and the volume fraction.
6. A CFD numerical simulation method in combination with measured wind-induced snow drift according to claim 1, 2, 3 or 4, characterized in that in step eight, the erosion amount is calculated by the formula:
Figure FDA0003512306230000031
wherein A iseroIs a constant coefficient of u*As inlet friction speed, u*tIs the threshold speed.
7. A CFD numerical simulation method in combination with measured wind-induced snow drift according to claim 1, 2, 3 or 4, characterised in thatIn step eight, the calculation formula of the deposition amount is as follows:
Figure FDA0003512306230000032
wherein wfThe speed of sedimentation of the snow in the middle, phisIs the mass concentration of snow, phis＝ρsf, f is the volume fraction of snow, ρsIs the snow particle density.
8. A CFD numerical simulation method in combination with measured wind-induced snow drift according to claim 1, 2, 3 or 4, characterized in that in step eight, the calculation formula of the snow change thickness is:
Figure FDA0003512306230000033
wherein q issIs q iseroOr qdepγ is the maximum volume fraction of accumulated snow, ρsIs the snow particle density.
CN202210155363.7A 2022-02-21 2022-02-21 CFD numerical simulation method combining actual measurement wind-induced snow drift Pending CN114528781A (en)

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Cited By (3)

* Cited by examiner, † Cited by third party
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CN115186569A (en) * 2022-07-07 2022-10-14 中科三清科技有限公司 Floating object drift simulation method and device, storage medium and electronic equipment
CN118261020A (en) * 2024-05-31 2024-06-28 北京航空航天大学 Method, device, medium and product for predicting falling off of ice crystal ice deposit in high altitude
CN118364554A (en) * 2024-05-17 2024-07-19 哈尔滨工业大学 Integrated wind-induced snow drift numerical simulation method for early stage of building design

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115186569A (en) * 2022-07-07 2022-10-14 中科三清科技有限公司 Floating object drift simulation method and device, storage medium and electronic equipment
CN115186569B (en) * 2022-07-07 2023-01-31 中科三清科技有限公司 Floating object drift simulation method and device, storage medium and electronic equipment
CN118364554A (en) * 2024-05-17 2024-07-19 哈尔滨工业大学 Integrated wind-induced snow drift numerical simulation method for early stage of building design
CN118261020A (en) * 2024-05-31 2024-06-28 北京航空航天大学 Method, device, medium and product for predicting falling off of ice crystal ice deposit in high altitude
CN118261020B (en) * 2024-05-31 2024-07-23 北京航空航天大学 Method, device, medium and product for predicting falling off of ice crystal ice deposit in high altitude

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