CN112182988A - CFD software-based crude oil storage tank leakage oil and gas distribution simulation method - Google Patents

CFD software-based crude oil storage tank leakage oil and gas distribution simulation method Download PDF

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CN112182988A
CN112182988A CN202010999606.6A CN202010999606A CN112182988A CN 112182988 A CN112182988 A CN 112182988A CN 202010999606 A CN202010999606 A CN 202010999606A CN 112182988 A CN112182988 A CN 112182988A
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付建民
张新琪
邱深鑫
李震
朱琳
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China University of Petroleum East China
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Abstract

The invention provides a method for simulating the diffusion distribution of evaporated oil gas after crude oil storage tank leakage, which comprehensively considers various factors of meteorological conditions, geographical geometrical environment, historical accident cases, crude oil flowing volatilization characteristics and process control aiming at the arrangement of a crude oil storage tank and a tank set and the leakage characteristics of crude oil. The invention can accurately reflect the distribution state of the liquid pool after crude oil leakage and the diffusion result of volatile oil gas, can analyze the oil gas distribution rule of the same tank set under different leakage scenes and different meteorological conditions, and provides theoretical reference for the layout of the tank set device and the emergency disposal of leakage accidents.

Description

CFD software-based crude oil storage tank leakage oil and gas distribution simulation method
Technical Field
The invention relates to a method for simulating pool flowing and evaporated oil gas diffusion after a crude oil storage tank leaks, in particular to a method for simulating crude oil storage tank leakage based on CFD software Fluent and FLACS, and belongs to the technical field of intelligent simulation.
Background
Crude oil is a hazardous substance, is a viscous oily liquid, has explosive property, and can volatilize toxic gases such as combustible gas, hydrogen sulfide and the like. The crude oil depot is an important place for crude oil storage and transportation, the number of storage tanks is large, the storage capacity is large, the production facilities are large, once the tank body of the storage tank for storing the crude oil leaks, the crude oil flows to the external environment, and poisoning and fire explosion accidents can be caused, so that serious consequences can be caused. The diffusion range of the crude oil liquid pool and the volatile steam after leakage has important influence on accident consequences.
The existing storage tank leakage consequence risk simulation technology is mature, but mostly aims at steady-state leakage large-space flow diffusion, and does not consider the influence of actual process control and storage tank environment barriers on the distribution of a leaked crude oil liquid pool and volatilized steam; secondly, the diffusion characteristic that the crude oil firstly forms a liquid pool on the ground after leaking and then volatilizes oil gas is neglected, and the dynamic analysis can not be carried out on the liquid pool distribution and the volatilization steam diffusion range after the crude oil storage tank leaks.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the problems in the prior art and enhancing the pertinence, the invention provides a crude oil storage tank leakage oil and gas distribution simulation method based on CFD software Fluent and FLACS, which can simulate the crude oil flowing process and the liquid pool finally formed in a partition wall after the crude oil storage tank leaks according to the specific environment arrangement of the crude oil storage tank, calculate the diffusion range of volatile oil and gas and provide a theoretical basis for controlling the risk of the crude oil storage tank leakage accident.
In order to achieve the purpose, the invention adopts the technical scheme that: a CFD software-based crude oil storage tank leakage oil and gas distribution simulation method comprises the following steps:
s1. determining relevant parameters of the crude oil tank field;
s2, determining a high-risk leakage scene comprising a leakage position, a leakage aperture and crude oil viscosity, and calculating the leakage rate of the leakage aperture on the pipe wall;
s3., inputting the leakage rate of the pipe wall leakage hole into Fluent to simulate the flow diffusion process of the leaked crude oil liquid pool of the storage tank, and obtaining the area and the distribution position of the crude oil liquid pool;
s4. calculating the liquid evaporation rate of heat evaporation according to the components of the crude oil and liquid pool, the area and distribution position of the crude oil pool;
s5. inputting crude oil and liquid pool components, the area and distribution position of the crude oil pool and the liquid evaporation rate into FLACS to calculate the diffusion distribution of the evaporated oil gas;
s6. changing atmospheric stability, wind direction and wind speed according to meteorological conditions to obtain the diffusion distribution range of evaporated oil gas under different meteorological conditions and the volume and position of formed flammable vapor cloud.
Compared with the prior art, the invention has the following advantages:
1. based on the arrangement characteristics and the device types of the crude oil storage tanks and the tank groups, a three-dimensional model consistent with an actual tank group can be established, and the simulation calculation result has stronger pertinence and accuracy;
2, the method considers the control characteristics of the actual process, and can simulate the accumulation distribution of the crude oil liquid pool and the diffusion influence range of volatile oil gas after leakage at different accident positions of a specific tank group;
3. the invention considers the influence of different meteorological conditions on oil gas diffusion, can simulate the distribution range under any meteorological conditions, and can more accurately and comprehensively analyze the oil gas diffusion rule and the volume change of combustible steam clouds with burning explosion risks;
the Fluent is used as a mature professional computational fluid mechanics software, and the result reliability is higher and the accuracy is higher due to the abundant computational model; meanwhile, the threshold of a user is reduced, and a formula model does not need to be written by self;
and 5, the FLACS simulation software is verified in a gas diffusion scene calculation model through a large amount of experimental data, so that the application effect on the alkane gas is better, and the calculation result is accurate and credible.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It should be apparent that the drawings in the following description are specific embodiments of the invention, and that other drawings within the scope of the present application can be obtained by those skilled in the art without inventive effort.
FIG. 1 is a flow chart of an embodiment of the present invention;
FIG. 2 is a flow chart of Fluent simulation using the SIMPLE algorithm according to an embodiment of the present invention;
FIG. 3 is a schematic view of a monitor line arrangement according to an embodiment of the present invention;
FIG. 4 is a schematic of a crude oil distribution curve for an example of the present invention.
Detailed Description
The invention will be further explained with reference to the drawings.
Fig. 1 shows a flow chart of an embodiment of the present invention. The invention relates to a CFD software-based crude oil storage tank leakage oil and gas distribution simulation method, which comprises the following steps of:
s1. determining relevant parameters of the crude oil tank field;
the method comprises the following steps: storage tanks (diameter, height, oil content), storage tank walls, bulkheads, fire dams, oil guide tanks, sump parameters (tank farm ground line size), crude oil properties (density and viscosity, boiling point, convective heat transfer coefficient of crude oil), annual average wind speed, annual wind map, atmospheric stability and humidity. Wherein, the oil content is used for calculating the height difference between the crude oil liquid level and the pipe wall leakage hole; the tank size parameters are used for CFD software modeling; the crude oil parameters are used for calculating the leakage rate and the evaporation rate; and the tank area meteorological data are used for calculating the volatile oil gas diffusion distribution in the FLACS.
S2, determining a high-risk leakage scene comprising a leakage position, a leakage aperture and crude oil viscosity, and calculating the leakage rate of the leakage aperture on the pipe wall;
when a high-risk leakage scene needing simulation is determined, risk analysis (risk and operability analysis, fault type and failure analysis) is carried out according to the storage tank accident case and the process flow to determine the leakage position.
In this example, the diameter of a 10-ten-thousand-square large crude oil storage tank reaches 80m, the outflow speed at the leakage hole is much higher than the falling speed of the liquid level in the container, and the kinetic energy of the liquid column in the container can be assumed to be 0.
Determining the initial pressure of the tank top, and solving the parameter conditions at the leakage hole according to an energy conservation equation:
E(Pin,Tin,min％)＝E(Po,To,mo％)+uo 2/2 (1)；
wherein, PinFor back pressure at the leak hole, P0Equal to atmospheric pressure, representing the density of the upper liquid in the storage tank; t is the temperature;
the total energy of the fluid comprises 3 types of kinetic energy, potential energy and pressure energy:
Figure BDA0002691638760000031
according to the small hole outflow model, the leakage rate u of the pipe wall leakage hole0Calculated using the following equation (3):
Figure BDA0002691638760000032
wherein: pinFor back pressure at the leak in the pipe wall, P0Equal to atmospheric pressure, pliquidIs the density of liquid phase medium and has the unit of kg/m3Representing the density of the upper-layer liquid in the storage tank; g is the acceleration of gravity, and the value is 9.8m/s2(ii) a Δ H is liquid level over tube wall leakageThe height of the leak hole is m.
s3., inputting the leakage rate of the pipe wall leakage hole into Fluent to simulate the flow diffusion process of the leaked crude oil liquid pool of the storage tank, and obtaining the area and the distribution position of the crude oil liquid pool;
the steps of simulating the flow diffusion process of the leaked crude oil pool of the storage tank by using Fluent are as follows:
s3.1, establishing a Fluent tank group model, and establishing a storage tank, a pipe wall leakage hole, a separation dike and an oil guide groove model by using 3D modeling software (design model in workbench) according to the scene size in a ratio of 1: 1;
s3.2, adopting Meshing software to perform unstructured grid division on the model, and encrypting grids at the pipe wall leakage hole by modifying the size of a surface grid according to the actual size of the pipe wall leakage hole;
s3.3, simulating the flow diffusion process of the crude oil leakage pool of the storage tank, guiding the grid file into a Fluent solver, checking the size torsion rate and the angle torsion rate of the grid by utilizing Fluent (qualified if the size torsion rate and the angle torsion rate are lower than 0.85), setting the size torsion rate and the angle torsion rate as transient calculation, opening gravity, setting the gravity acceleration, and setting components, boundary conditions, a solving model and a solving algorithm thereof;
the method solves the crude oil flowing problem through Fluent, and because mass transfer or heat transfer process does not exist in the flowing process, the control equation to be considered comprises a continuity equation and a momentum equation, and the conservation forms of the equations are respectively as follows:
Figure BDA0002691638760000041
wherein ρ is density;
Figure BDA0002691638760000042
is the rate of change of the density of the material over time;
Figure BDA0002691638760000043
is a vector differential operator;
Figure BDA0002691638760000044
is speedA vector; smIs a quality source item;
Figure BDA0002691638760000045
wherein p is a static pressure,
Figure BDA0002691638760000046
in order to be the stress tensor,
Figure BDA0002691638760000047
and
Figure BDA0002691638760000048
are an attraction force item and an external force item,
Figure BDA0002691638760000049
is a vector differential operator.
The gravity acceleration is set according to the local actual gravity acceleration, the Fluent simulation components are air and crude oil, the crude oil components are set to be liquid water because the Fluent has no crude oil components, and then the viscosity and the density of the liquid water are modified to be the viscosity and the density of the crude oil so as to replace the crude oil components;
the boundary conditions are as follows:
setting the leakage hole on the pipe wall as mass flow inlet with leakage rate u0Is determined by formula (1); setting the wall of the storage tank, the partition wall and the fire bank as wall boundary conditions, wherein an outlet of the oil guide groove is communicated with the atmosphere and is set as a pressure outlet with the pressure equal to 0;
the solution model is:
in the crude oil flow solving process, in addition to the conservation equation, the crude oil flow state needs to be considered, the flow velocity of the crude oil leaking from the storage tank is very high, the flow process is complex (the complex flow behaviors such as splashing, impact, diffusion and the like can occur after the crude oil leaks), and the process is regarded as a turbulent flow process, so a realizable k-turbulent flow model is adopted for calculation and solving, and the realizable k-turbulent flow model is as follows:
Figure BDA00026916387600000410
Figure BDA00026916387600000411
Figure BDA00026916387600000412
in the formula, Gk、GbIs the generation term of turbulent kinetic energy, respectively generated by mean velocity gradient and buoyancy, YMRepresents the effect on the overall dissipation ratio, caused by the fluctuating expansion in compressible turbulence; sk、SAs source term, σkIs the Plantt constant, σ, of turbulent energyPrandtl constant for dissipation ratio, μ is flow viscosity, turbulent dissipation ratio, C1、C2Is an empirical constant;
fluent simulation adopts a SIMPLE algorithm, and each sub-item adopts the following discrete format: the gradient adopts a least square unit, the pressure adopts a second-order format, and the momentum, the turbulent kinetic energy, the turbulent dissipation rate and all components adopt a second-order windward format;
the Fluent simulation adopts the SIMPLE algorithm with the following specific steps:
a. assuming a distribution V of the initial velocity field0Distribution P of the pressure field0；
b. Solving a momentum dispersion equation;
c. solve to obtain a new velocity field V*；
d. Solving a pressure correction equation according to the new velocity field to obtain P';
e. correcting the pressure field and the speed field according to the P';
f. solving the discretization equation by using the corrected velocity field to obtain new pressure, velocity and other variables;
g. judging whether the calculation result is converged (if the calculation residual value tends to be stable or is lower than the set residual value, judging that the calculation result is converged), if not, substituting the result and turning to the step d, and if so, turning to the next step;
h. the calculation is completed.
Fig. 2 is a flow chart of the Fluent simulation using the SIMPLE algorithm according to the embodiment of the present invention.
The interaction of crude oil and air components is also involved in the flow, generally, the crude oil and the air are not mixed and dissolved, so a VOF two-phase flow model is adopted, the fluid modeling is carried out on the crude oil-air by solving a momentum equation set and tracking the volume fraction of each fluid in the whole domain, and the transient tracking of a crude oil-air interface is realized; the following formula is followed:
Figure BDA0002691638760000051
Figure BDA0002691638760000052
wherein q represents the number of phases, FqU, v represent the linear velocity of the fluid in the direction of flow, as the volume fraction of the corresponding term.
S3.4, arranging crude oil volume fraction monitoring lines in the earth surface area for monitoring the concentration distribution of crude oil on the ground, and setting the density of the monitoring lines according to the size of a crude oil tank area, wherein the number of the monitoring lines is not less than 10 to ensure the data accuracy, and the monitoring lines are parallel to the leakage direction;
fig. 3 is a schematic view of a monitor line according to an embodiment of the present invention.
And S3.5, setting the residual value to be 0.0001, wherein the residual value is a convergence criterion, and considering that the calculated result residual under the simple algorithm is lower than the residual value to achieve convergence. Initializing a model (initializing the volume fraction of crude oil components in the crude oil storage tank cavity model to 0), setting a time step and calculation time (in order to ensure better convergence, the time step can be set to 0.01s, the calculation steps can be 120000, and 120s can be calculated), and starting to perform calculation analysis;
and S3.6, after the calculation is finished, performing post-processing by using Fluent to obtain the flowing dynamic process of the crude oil liquid pool, finally, judging indexes according to the volume fraction of 0.1% in the coverage range (namely the leakage condition) of the liquid pool stabilized in the bank, obtaining the part with the volume fraction higher than 0.1% on each monitoring line and a specific coordinate range, fitting a function distribution formula of the crude oil by adopting Matlab according to the coordinates, and calculating the area and the distribution position of the crude oil liquid pool. The calculation formula is as follows:
A＝∫f(x)dx (11)；
wherein A is the area of the liquid pool, and x is a coordinate value.
FIG. 4 is a schematic illustration of a crude oil distribution curve according to an embodiment of the present invention.
s4. calculating the liquid evaporation rate of heat evaporation according to the components of the crude oil and liquid pool, the area and distribution position of the crude oil pool;
rate of evaporation v of liquid2Determined by equation (12):
Figure BDA0002691638760000061
in the formula T0Is ambient temperature, in units of K; t isdIs the boiling point of the liquid under normal pressure and has the unit of K; l is the length of the liquid pool and the unit is m; h is the heat of vaporization of the liquid in m; a is thermal diffusivity in m2S; k is the ground thermal conductivity, with the unit W/(m.k); t is the evaporation time in units of s; nu is the nussel number, calculated as in formula (13):
Nu＝hD/k (13)；
wherein h is the convective heat conductivity of the fluid and has the unit W/(m)2K); d is the geometrical characteristic length of the heat transfer surface, and the unit is m; k is the thermal conductivity of the stationary fluid, in W/(m)2K); the ground condition has certain influence on heat evaporation, and the ground parameter K of cement is 1.1W/(m.k), and a is 1.29 x 10^ (-7).
s5. inputting crude oil and liquid pool components, the area and distribution position of the crude oil pool and the liquid evaporation rate into FLACS to calculate the diffusion distribution of the evaporated oil gas; the FLACS considers the congestion of a real geometric environment, is suitable for the influence analysis of the diffusion of inflammable and toxic substances, can simulate the multi-component diffusion of the oil gas evaporated from the full-size crude oil in a tank field, obtains a large amount of test verification of calculation results, and has high accuracy.
The procedure for calculating the diffusion distribution of the boil-off gas using FLACS is as follows:
s5.1, constructing a three-dimensional model of the tank group according to the actual size of the tank group and a ratio of 1:1, wherein the three-dimensional model comprises a storage tank, a separation dike, a fire dike, an oil guide groove, an escalator and pipeline facilities;
s5.2, setting a calculation scene as dispersion AND entrainment, inputting the area AND the distribution position of a crude oil pool, setting no initial kinetic energy leakage in leak, inputting the evaporation rate of liquid, AND setting the volatile components of crude oil in GAS COMPOSITION AND VOLUME;
s5.3, dividing a calculation grid, dividing a 1m uniform fine grid at the position of the liquid pool, and widening the periphery according to the scale of 1: 1.2;
the method adopts a finite volume method to solve a compressible Reynolds average equation in a three-dimensional Cartesian coordinate system:
Figure BDA0002691638760000071
in the formula, psi is mass, momentum, energy and material variables; mu.seffEffective turbulent viscosity in pa · s; rho is the density of crude oil evaporation gas and has the unit of kg/m3；SψIs an energy term; x is the number ofiIs the coordinate of the i direction; u. ofiRepresenting the velocity item in the same direction, and the unit is m/s;
and S5.4, setting a gas monitoring area to meet all positions containing possible gas diffusion, setting calculation time, and simulating to obtain the diffusion process and distribution range of the evaporated oil gas and the volume and position of the combustible steam cloud reaching the explosion concentration.
s6. changing atmospheric stability, wind direction and wind speed according to meteorological conditions to obtain the diffusion distribution range of evaporated oil gas under different meteorological conditions and the volume and position of formed flammable vapor cloud.
The above example is only a result of calculation performed under one meteorological condition for a certain leakage position, and the diffusion distribution range of the leaked oil gas under different meteorological states and the volume and the position of the flammable vapor cloud which is possibly subjected to fire and explosion accidents can be obtained by changing the settings such as atmospheric stability, wind direction and wind speed according to the meteorological conditions, and the volatile oil gas diffusion distribution rule can be obtained by classification and comparison.
Finally, it is to be noted that: the above examples are only specific embodiments of the present invention, and are not intended to limit the technical solutions of the present invention, and the scope of the present invention is not limited thereto. Those skilled in the art will understand that: any person skilled in the art can modify or easily conceive the technical solutions described in the foregoing embodiments or equivalent substitutes for some technical features within the technical scope of the present disclosure; such modifications, changes or substitutions do not depart from the spirit and scope of the embodiments of the present invention, and they should be construed as being included therein.

Claims (10)

1. A CFD software-based crude oil storage tank leakage oil and gas distribution simulation method is characterized by comprising the following steps:
s1. determining relevant parameters of the crude oil tank field;
s2, determining a high-risk leakage scene comprising a leakage position, a leakage aperture and crude oil viscosity, and calculating the leakage rate of the leakage aperture on the pipe wall;
s3., inputting the leakage rate of the pipe wall leakage hole into Fluent to simulate the flow diffusion process of the leaked crude oil liquid pool of the storage tank, and obtaining the area and the distribution position of the crude oil liquid pool;
s4. calculating the liquid evaporation rate of heat evaporation according to the components of the crude oil and liquid pool, the area and distribution position of the crude oil pool;
s5. inputting crude oil and liquid pool components, the area and distribution position of the crude oil pool and the liquid evaporation rate into FLACS to calculate the diffusion distribution of the evaporated oil gas;
s6. changing atmospheric stability, wind direction and wind speed according to meteorological conditions to obtain the diffusion distribution range of evaporated oil gas under different meteorological conditions and the volume and position of formed flammable vapor cloud.
2. The method for simulating crude oil storage tank leakage oil and gas distribution based on CFD software as claimed in claim 1, wherein the step s1 of determining relevant parameters of crude oil tank field comprises: the system comprises a storage tank, a storage tank wall, a separation dike, a fire dike, an oil guide groove, a liquid collecting pool parameter, crude oil physical property, annual average wind speed, an annual wind diagram, atmospheric stability and humidity.
3. The method for simulating crude oil storage tank leakage oil and gas distribution based on CFD software as claimed in claim 1, wherein the high risk leakage scenario determined in step s2 is risk analyzed according to accident case and process flow to determine the leakage position.
4. The method for simulating crude oil storage tank leakage oil and gas distribution based on CFD software of claim 3, wherein in step s2, the tube wall leakage hole leakage rate u is determined according to the small hole outflow model0Calculated using the following equation (3):
Figure FDA0002691638750000011
wherein: pinFor back pressure at the leak in the pipe wall, P0Equal to atmospheric pressure, pliquidIs the density of liquid phase medium and has the unit of kg/m3Representing the density of the upper-layer liquid in the storage tank; g is the acceleration of gravity, and the value is 9.8m/s2(ii) a Δ H is the height in m of the liquid level above the leak hole in the pipe wall.
5. The method for simulating crude oil tank leakage oil and gas distribution based on CFD software according to claim 1, wherein the step of simulating tank leakage crude oil pool flow diffusion process using Fluent in step s3 is as follows:
s3.1, establishing a Fluent tank group model, and establishing a storage tank, a pipe wall leakage hole, a separation dike and an oil guide groove model according to the scene size by using 3D modeling software according to a ratio of 1: 1;
s3.2, carrying out unstructured gridding division on the model, and encrypting grids at the pipe wall leakage hole by modifying the size of a surface grid according to the actual size of the pipe wall leakage hole;
s3.3, simulating the flow diffusion process of the crude oil leakage pool of the storage tank, introducing the grid file into a Fluent solver, checking the size torsion rate and the angle torsion rate of the grid by utilizing the Fluent, setting transient calculation, setting gravity acceleration, setting components, boundary conditions, a solving model and a solving algorithm thereof;
s3.4, arranging crude oil volume fraction monitoring lines in the ground surface area for monitoring the concentration distribution of crude oil on the ground, and setting the density of the monitoring lines according to the size of the crude oil tank area, wherein the number of the monitoring lines is not less than 10, and the monitoring lines are parallel to the leakage direction;
s3.5, setting a residual value to be 0.0001, initializing a model, setting a time step length and calculation time, and starting to perform calculation analysis;
and S3.6, after the calculation is finished, performing post-processing by using Fluent to obtain the flowing dynamic process of the crude oil liquid pool and the coverage range of the liquid pool which is finally stabilized in the dam, fitting a function distribution formula of the crude oil by using Matlab according to coordinates, and calculating the area and the distribution position of the crude oil liquid pool.
6. The method for simulating crude oil storage tank leakage oil and gas distribution based on CFD software according to claim 5, wherein in step s3.3, the control equation includes a continuity equation and a momentum equation, and the conservation forms of the equations are respectively:
Figure FDA0002691638750000021
wherein ρ is density;
Figure FDA0002691638750000022
is the rate of change of the density of the material over time;
Figure FDA0002691638750000023
is a vector differential operator;
Figure FDA0002691638750000024
is a velocity vector; smIs a quality source item;
Figure FDA0002691638750000025
wherein p is a static pressure,
Figure FDA0002691638750000026
in order to be the stress tensor,
Figure FDA0002691638750000027
and
Figure FDA0002691638750000028
are an attraction force item and an external force item;
the gravity acceleration is set according to the local actual gravity acceleration, the Fluent simulation components are air and crude oil, the crude oil components are set to be liquid water, and the viscosity and the density of the liquid water are modified to be the viscosity and the density of the crude oil;
the boundary conditions are as follows:
setting the leakage hole on the pipe wall as mass flow inlet with leakage rate u0As determined by equation (3); setting the wall of the storage tank, the partition wall and the fire bank as wall boundary conditions, wherein an outlet of the oil guide groove is communicated with the atmosphere and is set as a pressure outlet with the pressure equal to 0;
the solution model is:
firstly, a realizable k-turbulence model is adopted for calculation and solution, and the realizable k-turbulence model is as follows:
Figure FDA0002691638750000029
Figure FDA0002691638750000031
Figure FDA0002691638750000032
in the formula, Gk、GbIs the generation term of turbulent kinetic energy, respectively generated by mean velocity gradient and buoyancy, YMRepresents the effect on the overall dissipation ratio, caused by the fluctuating expansion in compressible turbulence; sk、SAs source term, σkIs the Plantt constant, σ, of turbulent energyPrandtl constant for dissipation ratio, μ is flow viscosity, turbulent dissipation ratio, C1、C2Is an empirical constant;
fluent simulation adopts a SIMPLE algorithm, and each sub-item adopts the following discrete format: the gradient adopts a least square unit, the pressure adopts a second-order format, and the momentum, the turbulent kinetic energy, the turbulent dissipation rate and all components adopt a second-order windward format;
thirdly, performing fluid modeling on the crude oil-air by solving a momentum equation set and tracking the volume fraction of each fluid in the whole domain by adopting a VOF two-phase flow model to realize transient tracking on a crude oil-air interface; the following formula is followed:
Figure FDA0002691638750000033
Figure FDA0002691638750000034
wherein q represents the number of phases, FqU, v represent the linear velocity of the fluid in the direction of flow, as the volume fraction of the corresponding term.
7. The method for simulating the distribution of the leakage oil and gas of the crude oil storage tank based on the CFD software as claimed in claim 6, wherein the Fluent simulation in the step II adopts a SIMPLE algorithm as the specific steps:
a. assuming the distribution of an initial velocity field and the distribution of a pressure field;
b. solving a momentum dispersion equation;
c. solving to obtain a new speed field;
d. solving a pressure correction equation according to the new velocity field to obtain P';
e. correcting the pressure field and the speed field according to the P';
f. solving the discretization equation by using the corrected velocity field to obtain new pressure, velocity and other variables;
g. judging whether the calculation result is converged, if not, substituting the result and converting the result into d, and if so, converting the result into the next step;
h. the calculation is completed.
8. The method for simulating the leakage oil and gas distribution of the crude oil storage tank based on the CFD software as claimed in claim 5, wherein the calculation formula in step s3.6 is as follows:
A＝∫f(x)dx (11)；
wherein A is the area of the liquid pool, and x is a coordinate value.
9. The CFD software-based crude oil storage tank leakage oil and gas distribution simulation method according to claim 1, wherein the liquid evaporation rate v 4 in the step s42Determined by equation (12):
Figure FDA0002691638750000041
in the formula T0Is ambient temperature, in units of K; t isdIs the boiling point of the liquid under normal pressure and has the unit of K; l is the length of the liquid pool and the unit is m; h is the heat of vaporization of the liquid in m; a is thermal diffusivity in m2S; k is the ground thermal conductivity, with the unit W/(m.k); t is the evaporation time in units of s; nu is the nussel number, calculated as in formula (13):
Nu＝hD/k (13)；
wherein h is the convective heat conductivity of the fluid and has the unit W/(m)2K); d is the geometric characteristic length of the heat transfer surfaceThe unit is m; k is the thermal conductivity of the stationary fluid, in W/(m)2K); taking cement ground parameters K as 1.1W/(m.k) and a as 1.29 x 10^ (-7).
10. The method for simulating crude oil storage tank leakage oil and gas distribution based on CFD software according to claim 1, wherein in step s5, the calculation of the diffusion distribution of boil-off oil and gas by using FLACS is as follows:
s5.1, constructing a three-dimensional model of the tank group according to the actual size of the tank group and a ratio of 1:1, wherein the three-dimensional model comprises a storage tank, a separation dike, a fire dike, an oil guide groove, an escalator and pipeline facilities;
s5.2, setting a calculation scene into dispersion and entrainment, and inputting the area and the distribution position of the crude oil pool and the evaporation rate of liquid;
s5.3, dividing a calculation grid, dividing a 1m uniform fine grid at the position of the liquid pool, and widening the periphery according to the scale of 1: 1.2;
solving a compressible Reynolds average equation in a three-dimensional Cartesian coordinate system by adopting a finite volume method:
Figure FDA0002691638750000042
in the formula, psi is mass, momentum, energy and material variables; mu.seffEffective turbulent viscosity in pa · s; rho is the density of crude oil evaporation gas and has the unit of kg/m3；SψIs an energy term; x is the number ofiIs the coordinate of the i direction; u. ofiRepresenting the velocity item in the same direction, and the unit is m/s;
and S5.4, setting a gas monitoring area to meet all positions containing possible gas diffusion, setting calculation time, and simulating to obtain the diffusion process and distribution range of the evaporated oil gas and the volume and position of the combustible steam cloud reaching the explosion concentration.
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