Fluent-based small-size oil pool fire temperature field simulation reproduction method

Abstract

The invention discloses a Fluent-based small-size oil pool fire temperature field simulation reproduction method, and belongs to the field of fire safety science and technology, and the method comprises the steps: carrying out a small-size oil pool fire combustion experiment, obtaining the weight loss data of a fuel, and taking the weight loss data as an inlet boundary condition of flow field simulation; on the basis of the Fluent environment, inlet fluid is set as fuel steam, the temperature is set as a fuel boiling point, an EDM combustion model is used for conducting gas-phase combustion large vortex simulation of small-size oil pool fire, temperature stable data of a sampling point are obtained through a thermocouple model and compared with temperature stable data obtained by a thermocouple in the experiment process, the height of an oil pan is adjusted, and the calculation error is reduced. Therefore, simulation reproduction of a small-size oil pool fire temperature field is realized. According to the method, a Fluent-based fire source establishment method reference can be provided for fire disaster and combustion simulation.

Description

Technical Field

[0001] The invention relates to the field of fire safety science and technology, and in particular to a Fluent-based small-size oil pool fire temperature field simulation and reproduction method. Background Art

[0002] Due to the complexity and dynamics of flame structure, the prediction of pool fire behavior has been a hot topic of research in recent years. In order to better understand the behavior of pool fire, a method combining experiments with computational fluid dynamics (CFD) simulations is generally used. In the engineering field, the focus of fire experiments is not the complex structure of the flame, but the impact of its temperature distribution on the surrounding environment. Therefore, excessive pursuit of flow field details will lead to unnecessary waste of computing resources. Compared with refined turbulent combustion simulations, fire source construction methods with good robustness and high computational efficiency have higher application value in this field.

[0003] When faced with fire scenes with highly complex geometries and variable airflow conditions, the traditional fire dynamics simulator (FDS) can provide certain simulation capabilities, but its simulation accuracy is often limited by the limitations of model simplification and calculation algorithms, making it difficult to fully capture the subtle flow characteristics, heat transfer processes, and the interaction between flames and complex structures in the fire scene. In contrast, ANSYS Fluent, as a powerful fluid dynamics simulation software, has shown significant advantages in simulating complex flow fields, multiphase flows, heat transfer, and chemical reactions with its advanced solver technology and rich physical model library. However, although Fluent is widely used in the field of fluid simulation, in the field of fire science, especially the simulation method research for fire source construction is still immature, lacking a systematic methodology and a verified model library, which to a certain extent limits its in-depth application in fire simulation.

[0004] In view of this, it is particularly important to explore and develop a high-efficiency fire source simulation method based on ANSYS Fluent. This method aims to achieve accurate simulation of fire source behavior in complex fire scenarios through sophisticated model construction, reasonable parameter settings and innovative solution strategies. This not only includes the precise setting of the initial conditions of the fire source, such as the type of fuel, initial temperature, combustion rate, etc., but also needs to consider the heat exchange between the fire source and the surrounding environment, the dynamic evolution of the flame morphology, and the complex physical processes such as turbulence and radiation that may be caused. By continuously optimizing and improving the simulation method, it is expected to significantly improve the accuracy of fire simulation and provide more reliable technical support for fire science research, risk assessment and disaster prevention and control. Summary of the invention

[0005] The present invention provides a method for simulating and reproducing the temperature field of a small-scale oil pool fire based on Fluent. Through a small-scale oil pool fire combustion experiment, the weight loss data of the fuel is obtained as the inlet boundary condition of the flow field simulation. Based on the Fluent environment, the inlet fluid is set to fuel vapor, and the temperature is the boiling point of the fuel. The EDM combustion model is used to perform a large eddy simulation of the gas phase combustion of a small-scale oil pool fire. The temperature stability data of the sampling point is obtained through a thermocouple model, and compared with the temperature stability data obtained by the thermocouple during the experiment. The oil pan height is adjusted to reduce the calculation error, thereby realizing the simulation and reproduction of the temperature field of a small-scale oil pool fire. The present invention can provide a reference for a fire source establishment method based on Fluent for fire and combustion simulation, so as to solve the technical problem that Fluent is difficult to establish a fire source in a fire simulation scenario.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] On the one hand, the present invention provides a method for simulating and reproducing the temperature field of a small-scale oil pool fire based on Fluent, and the method for simulating and reproducing the temperature field of a small-scale oil pool fire based on Fluent comprises:

[0008] Conduct small-scale oil pool fire combustion experiments to obtain fuel weight loss data as inlet boundary conditions for flow field simulation;

[0009] Based on the Fluent environment, the inlet fluid is set to fuel vapor, the temperature is set to the fuel boiling point, and the EDM combustion model is used to perform large eddy simulation of gas phase combustion of a small-scale oil pool fire.

[0010] The temperature stability data of the sampling point is obtained through the thermocouple model, compared with the temperature stability data obtained by the thermocouple during the experiment, and the oil pan height is adjusted to reduce the calculation error.

[0011] Furthermore, a small-scale oil pool fire combustion experiment was conducted, including:

[0012] You can use a small square or round oil pan, place a certain height of clean water in the oil pan, then pour in a certain amount of fuel and ignite it;

[0013] Multiple thermocouple measuring points are set at equal distances above the oil pan to measure the temperature changes in the gas phase combustion area;

[0014] An electronic balance is placed under the oil pan to measure the mass change of the fuel.

[0015] Furthermore, it is necessary to repeat the experiment several times to reduce the experimental error.

[0016] Furthermore, the fuel weight loss data is obtained as the inlet boundary condition for the flow field simulation, including:

[0017] Based on the fuel mass change monitoring curve, the mass change data in the stable decline phase is selected to calculate the average mass decline rate;

[0018] The average mass drop rate can be used as the mass flow data of the flow inlet boundary condition for flow field simulation.

[0019] Furthermore, based on the Fluent environment, the inlet fluid is set to fuel vapor and the temperature is set to the fuel boiling point, including:

[0020] A suitable three-dimensional computational domain model is established, a computational grid is generated and the boundaries are named. The fuel inlet is set at the oil pan opening, the fuel inlet is set to the mass inlet condition, the outlet is set to the pressure outlet, the inlet fluid is selected as the gas phase fuel vapor, and the fluid temperature is set to the boiling point of the fuel.

[0021] Furthermore, the EDM combustion model is used to perform large eddy simulation of gas phase combustion of small-scale oil pool fire, including:

[0022] First, RANS simulation is performed, the radiation model is the DO model, and the combustion model is the EDM. No ignition operation is required, and the calculation cost is low;

[0023] The turbulence model selected for RANS simulation is the standard k-ε turbulence model, which has a fast calculation speed and good robustness. Although the combustion process of small-sized oil pan fire is not suitable for the description of RANS turbulence model, this model can provide the initial flow field for large eddy simulation, improve the calculation stability and reduce the calculation cost. Steady-state iterative calculation is used, and the number of iteration steps should not be too many. It is sufficient to observe the appearance of high-temperature areas in the calculation domain.

[0024] The RANS calculation results were used as the initial flow field for large eddy simulation, and the turbulence model selected was WALE.

[0025] Furthermore, the temperature stability data of the sampling point is obtained through the thermocouple model, including:

[0026] The temperature data of the sampling points measured by the thermocouple in the combustion experiment cannot be directly compared with the temperature calculated by Fluent. The temperature displayed by the temperature measuring device is its own temperature, that is, the temperature measured by the thermocouple is the temperature of the thermocouple itself. In transient conditions, the temperature data calculated by the software will show obvious jitter;

[0027] Introduce the differential equation describing the thermocouple response, using V tc ρ tc c tc dT tc / dt=A tc [ε tc (I / 4-σ B T tc 4)+h(T f -T tc )] Control the heat exchange between the thermocouple and its surroundings;

[0028] Among them, V tc and A tc are the thermocouple volumes (m 3 ) and surface area (m 2 ), ρ tc and c tc are the densities of the thermocouples (kg / m 3 ) and specific heat (J / kg·K), T tc and T f are the temperature of the thermocouple and the surrounding fluid (K), t is the response time of the thermocouple (s), and I is the incident radiation flux to the thermocouple (W / m 2 ), ε tc is the thermocouple emissivity (0.85), σ B is the Stefan-Boltzmann constant (5.64×10 -8 W / m 2 ·K 4 ), h is the heat transfer coefficient (W / m 2 ·K).

[0029] Furthermore, h is the heat transfer coefficient obtained by the formula h = kNu / D, where:

[0030] k is the thermal conductivity (W / m·K), and D is the characteristic size of the thermocouple head (m). For a spherical thermocouple, D is the diameter. For a cylindrical head, D requires its diameter and height to be calculated, so that V tc / A tc =D / 6;

[0031] Nu is the Nusselt number, which is expressed as a combination of the Prandtl number Pr and the Reynolds number Re. Nu = 0.42Pr 0.2 +0.57Pr 0.33 Re 0.5 , Pr=μc p / k, Re = ρuD / μ.

[0032] Furthermore, by comparing the temperature stability data obtained by the thermocouple during the experiment, the oil pan height was adjusted to reduce the calculation error, including:

[0033] The increase in the height of the oil pan sidewall slows down the lateral diffusion of fuel vapor during the simulation, promoting gas phase combustion and heat release;

[0034] Reasonable adjustment of the oil pan height can reduce the difference between the calculated and experimental values ​​of the temperature at the measuring point, thereby constructing a more accurate temperature field of a small-sized oil pool fire.

[0035] Based on the experimental results of small-scale oil fire combustion, the present invention proposes a method for constructing the temperature field of the gas phase combustion area based on Fluent, which can quickly and efficiently obtain relatively accurate temperature data distribution, thereby providing a reference for fire source construction based on Fluent for the field of fire safety science and technology.

[0036] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects:

[0037] 1. Utilizing ANSYS Fluent's advanced fluid dynamics technology, it is possible to break through the simulation accuracy limitations of traditional fire dynamics simulators (FDS) in complex fire scenarios. Fluent's rich physical model library and efficient solver enable it to more precisely simulate the subtle flow, heat transfer, and the interaction between flames and complex structures in a fire scene, thereby significantly improving the accuracy and reliability of simulation results. This advantage provides strong technical support for in-depth research on fire science and optimization of fire prevention and control strategies.

[0038] 2. In view of the shortcomings of fire source construction simulation methods in the field of fire science, this study is committed to developing a high-efficiency fire source simulation method based on ANSYS Fluent. Through sophisticated model construction, reasonable parameter settings and innovative solution strategies, accurate simulation of fire source behavior is achieved, including complex physical processes such as accurate setting of fire source initial conditions, heat exchange between fire source and environment, and dynamic evolution of flame morphology. The development of this method not only fills the gap in existing technology, but also provides an efficient and accurate fire source establishment method for the field of fire simulation, which helps to improve the scientificity and effectiveness of fire risk assessment and disaster prevention and control. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0040] Figure 1 It is a schematic diagram of the execution flow of a method for simulating and reproducing temperature field of a small-sized oil pool fire based on Fluent provided in an embodiment of the present invention;

[0041] Figure 2 is a schematic diagram of thermocouple arrangement provided by an embodiment of the present invention;

[0042] Figure 3 is a point-line graph of fuel weight reduction data obtained from repeated experiments provided by an embodiment of the present invention;

[0043] Figure 4It is a schematic diagram of the calculation domain, grid and boundary conditions set for the simulation calculation provided by the embodiment of the present invention;

[0044] Figure 5 is a temperature cross-section cloud diagram of a simulation result provided by an embodiment of the present invention;

[0045] Figure 6 is a comparison diagram of the calculation results and experimental results of the thermocouple stable temperature under different grid sizes provided by an embodiment of the present invention;

[0046] Figure 7 It is a temperature difference diagram between the experiment and the simulation under different oil pan height increases provided by the embodiment of the present invention. DETAILED DESCRIPTION

[0047] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0048] First of all, it should be noted that in the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "exemplary" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the word "exemplarily" is intended to present the concept in a concrete way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or it can be either of the two.

[0049] Moreover, in the embodiments of the present invention, "image" and "picture" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they want to express are the same. "of", "corresponding, relevant" and "corresponding" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they want to express are the same.

[0050] In addition, in the embodiments of the present invention, sometimes a subscript (such as W1) may be mistakenly written as a non-subscript form (such as W1). When the difference is not emphasized, the meanings to be expressed are consistent.

[0051] Example

[0052] This embodiment provides a method for simulating and reproducing the temperature field of a small-scale oil pool fire based on Fluent, which can be implemented by an electronic device, which can be a terminal or a server. The execution flow of the method for simulating and reproducing the temperature field of a small-scale oil pool fire based on Fluent is shown in the figure, including:

[0053] S1, conduct small-scale oil pool fire combustion experiments;

[0054] Specifically, in this embodiment, the implementation process of the above S1 is as follows:

[0055] S11, use a small square or round oil pan, place a certain height of clean water in the oil pan, then pour a certain amount of fuel and ignite it;

[0056] S12, multiple thermocouple measuring points are set at equal distances above the oil pan to measure the temperature change in the gas phase combustion area;

[0057] S13, an electronic balance is placed under the oil pan to measure the mass change of the fuel.

[0058] The above operation needs to be repeated several times to reduce experimental errors.

[0059] S2, obtain the fuel weight loss data as the inlet boundary condition for flow field simulation;

[0060] Specifically, in this embodiment, the implementation process of the above S2 is as follows:

[0061] S21, based on the fuel mass change monitoring curve, selecting the mass change data in the stable decline stage to calculate the average mass decline rate;

[0062] S22, the average mass drop rate can be used as mass flow data of the flow inlet boundary condition for flow field simulation.

[0063] S3, based on the Fluent environment, the inlet fluid is set to fuel vapor and the temperature is the fuel boiling point;

[0064] Specifically, in this embodiment, the implementation process of the above S3 is as follows:

[0065] S31, establishing a suitable three-dimensional computational domain model, generating a computational grid and naming the boundaries, wherein a fuel inlet is set at an oil pan opening;

[0066] S32, setting the fuel inlet to a mass inlet condition and the outlet to a pressure outlet;

[0067] S33, the inlet fluid is selected to be fuel vapor in gas phase, and the fluid temperature is set to the boiling point of the fuel.

[0068] S4, large eddy simulation of gas phase combustion of small-scale oil pool fire using EDM combustion model;

[0069] Specifically, in this embodiment, the implementation process of the above S4 is as follows:

[0070] S41, first perform RANS simulation, the radiation model is DO model, the combustion model is EDM, no ignition operation is required, and the calculation cost is low;

[0071] S42, the turbulence model selected in RANS simulation is the standard k-ε turbulence model, which has a fast calculation speed and good robustness. Although the combustion process of small-sized oil pan fire is not suitable for description by RANS turbulence model, this model can provide the initial flow field for large eddy simulation, improve the calculation stability and reduce the calculation cost;

[0072] S43, use steady-state iterative calculation, the number of iterations should not be too many, and it is sufficient to observe the appearance of high-temperature areas in the calculation domain;

[0073] S44, using the RANS calculation results as the initial flow field for large eddy simulation calculation, the selected turbulence model is WALE.

[0074] S5, obtaining temperature stability data of the sampling point through a thermocouple model;

[0075] Specifically, in this embodiment, the implementation process of the above S5 is as follows:

[0076] S51, the temperature data of the sampling point measured by the thermocouple in the combustion experiment cannot be directly compared with the temperature calculated by Fluent. The temperature displayed by the temperature measuring device is its own temperature, that is, the temperature measured by the thermocouple is the temperature of the thermocouple itself. In transient conditions, the temperature data calculated by the software will show obvious jitter;

[0077] S52, introduce the differential equation describing the thermocouple response, using V tc ρ tc c tc dT tc / dt=A tc [ε tc (I / 4-σ B T tc 4 )+h(T f -T tc )] Control the heat exchange between the thermocouple and its surroundings;

[0078] Among them, V tc and A tc are the thermocouple volumes (m 3 ) and surface area (m 2 ), ρ tc and c tc are the densities of the thermocouples (kg / m 3 ) and specific heat (J / kg·K), T tc and T f are the temperature of the thermocouple and the surrounding fluid (K), t is the response time of the thermocouple (s), and I is the incident radiation flux to the thermocouple (W / m 2 ), ε tc is the thermocouple emissivity (0.85), σB is the Stefan-Boltzmann constant (5.64×10 -8 W / m 2 ·K 4 ), h is the heat transfer coefficient (W / m 2 ·K).

[0079] h is the heat transfer coefficient obtained by the formula h = kNu / D, where:

[0080] k is the thermal conductivity (W / m·K), and D is the characteristic size of the thermocouple head (m). For a spherical thermocouple, D is the diameter. For a cylindrical head, D requires its diameter and height to be calculated, so that V tc / A tc =D / 6;

[0081] Nu is the Nusselt number, which is expressed as a combination of the Prandtl number Pr and the Reynolds number Re. Nu = 0.42Pr 0.2 +0.57Pr 0.33 Re 0.5 , Pr=μc p / k, Re = ρuD / μ.

[0082] S6, compared with the temperature stability data obtained by the thermocouple during the experiment, the oil pan height was adjusted to reduce the calculation error;

[0083] Specifically, in this embodiment, the implementation process of the above S6 is as follows:

[0084] S61, the increase in the height of the oil pan sidewall slows down the lateral diffusion of fuel vapor during the simulation, promoting gas phase combustion and heat release;

[0085] S62, reasonable adjustment of the oil pan height can reduce the difference between the calculated and experimental values ​​of the temperature at the measuring point, thereby constructing a more accurate temperature field of a small-sized oil pool fire.

[0086] Below, this embodiment uses a practical application scenario to illustrate the application process of the method of the present invention.

[0087] This example uses n-heptane liquid as fuel, and constructs a small-scale n-heptane oil pool fire temperature field based on combustion experiments and Fluent simulation environment. The ambient temperature of this example is 14°C, the boiling point of n-heptane is 98°C, and a square oil pan is used, with a side length of 30 cm and a height of 5 cm. Based on this, the specific implementation process of the method of the present invention is as follows:

[0088] (1) Preparation for small-scale n-heptane oil pool fire experiment

[0089] First, place a certain height of clean water in the oil pan (the specific height is determined according to the experimental design, usually used to stabilize combustion and reduce overheating at the bottom of the oil pool). Then, slowly pour in an appropriate amount of n-heptane fuel, ensuring that the fuel layer is even and does not exceed the edge of the oil pan;

[0090] Set up multiple thermocouple measuring points at equal distances above the oil pan. These measuring points should cover the main part of the gas phase combustion area so as to accurately measure the temperature change. Connect the thermocouples to the temperature recording equipment to ensure that the temperature change data can be recorded in real time and accurately. Figure 2 As shown;

[0091] Place a high-precision electronic balance under the oil pan, ensure that the balance is stable and in good contact with the oil pan, and record the initial mass of the oil pan (including clean water and fuel) before igniting the fuel.

[0092] (2) Conduct a small-scale n-heptane combustion experiment and derive fuel loss data and thermocouple temperature data.

[0093] First, ignite the n-heptane fuel with a safe ignition device (such as an ignition gun), make sure to operate at a safe distance, and pay attention to the combustion situation;

[0094] Based on the fuel quality change monitoring curve obtained from multiple experiments (such as Figure 3 ), select the data of the stable descent stage for analysis, and calculate the average descent rate of the fuel mass, which is usually achieved by dividing the mass change in this stage by time. The average mass descent rate can be used as the mass flow data of the flow inlet boundary condition of the flow field simulation;

[0095] Export temperature data of multiple thermocouple measurement points based on temperature recording equipment.

[0096] (3) Perform Fluent simulation calculations.

[0097] According to the actual size of the experimental oil pan and the surrounding environment, use CAD software or Fluent's own modeling tools to establish a suitable three-dimensional computational domain model. The model should include the oil pan, the fuel vapor area, and sufficient external space to simulate the airflow generated by combustion; use meshing tools (such as Fluent Meshing, ANSYS Meshing, etc.) to mesh the computational domain. The mesh should be fine enough to capture the details of the combustion process while considering the computational cost; name each boundary of the computational domain (such as fuel inlet, outlet, wall, etc.), such as Figure 4 As shown, it is convenient to set boundary conditions later;

[0098] The opening of the oil pan is set as the fuel inlet and set as the mass inlet condition, the mass flow rate of the fuel vapor is determined according to the experimental data, the inlet fluid is set as the gas phase vapor of n-heptane, and the fluid temperature is set as the boiling point of n-heptane; one or more suitable boundaries are selected as the outlet and set as the pressure outlet condition;

[0099] In Fluent, set the radiation model to DO (Discrete Ordinates) model and the combustion model to EDM (EddyDissipation Model). There is no need to perform ignition operations because the EDM model can automatically handle the ignition process. Select the standard k-ε turbulence model for RANS simulation. Although this model may not be accurate enough in describing the combustion process of small-scale oil pool fires, it can quickly provide the initial flow field and provide a basis for subsequent large eddy simulations. Set the calculation type to steady state and select an appropriate solver (such as a pressure-based solver). Set a reasonable number of iterations based on the size of the calculation domain and the fineness of the grid. Since this is only a preliminary calculation, the number of iterations should not be too many. It is sufficient to observe the presence of high-temperature areas in the calculation domain. During the iteration process, monitor the changes in key parameters such as the temperature field and velocity field to ensure that the calculation process is stable.

[0100] The results of RANS simulation are used as the initial flow field and imported into the calculation settings of large eddy simulation. In large eddy simulation, the turbulence model is replaced with WALE (Wall-Adapting Local Eddy-viscosity) model, which is more suitable for capturing large-scale vortex structures in the combustion process. The corresponding parameters, such as grid size, time step, etc., and the temperature sampling points are set, and the large eddy simulation calculation is started to observe the dynamic changes of airflow, temperature distribution, fuel consumption, etc. in the combustion process. The calculated temperature cloud map is shown in Figure 1. Figure 5 shown.

[0101] (5) Post-process the temperature data using the thermocouple model.

[0102] Using V tc ρ tc c tc dT tc / dt=A tc [ε tc (I / 4-σ B T tc 4 )+h(T f -T tc )] Control the heat exchange between the thermocouple and its surroundings;

[0103] Among them, V tc and A tc are the thermocouple volumes (m3 ) and surface area (m 2 ), ρ tc and c tc are the densities of the thermocouples (kg / m 3 ) and specific heat (J / kg·K), T tc and T f are the temperature of the thermocouple and the surrounding fluid (K), t is the response time of the thermocouple (s), and I is the incident radiation flux to the thermocouple (W / m 2 ), ε tc is the thermocouple emissivity (0.85), σ B is the Stefan-Boltzmann constant (5.64×10 -8 W / m 2 ·K 4 ), h is the heat transfer coefficient (W / m 2 ·K); h is the heat transfer coefficient obtained by the formula h=kNu / D, where k is the thermal conductivity (W / m·K) and D is the characteristic size of the thermocouple head (m). For spherical thermocouples, D is the diameter. For cylindrical heads, D requires its diameter and height for calculation, so that V tc / A tc =D / 6, Nu is the Nusselt number, which is expressed by the combination of Prandtl number Pr and Reynolds number Re, Nu = 0.42Pr 0.2 +0.57Pr 0.33 Re 0.5 , Pr=μc p / k, Re = ρuD / μ;

[0104] The temperature sampling instrument used in the experiment is a WRN-191K thermocouple, which is a shell-connected thermocouple. The protection tube has a diameter of 5 mm and is made of 304 stainless steel. The temperature measuring material is nickel-chromium-nickel-silicon. The thermal response time is t 0.5 The time interval is 1.2s, that is, 1.2s can output 50% of the total temperature step between the thermocouple temperature and the ambient temperature. The temperature increase of each time step can be obtained according to the simulation time step and the dynamic response time curve of the thermocouple temperature sensor. However, the acquisition of the dynamic response curve of the thermocouple temperature sensor requires higher experimental conditions and experimental costs. The increase range of each time step is delineated according to the experimentally obtained thermocouple temperature records. Of course, the fuzzy delineation of the increase range will cause deviations in the prediction of the thermocouple temperature rise curve, but this method only cares about the temperature distribution after the combustion reaches a stable state, and it is not very meaningful to study the temperature rise curve of the thermocouple, so the subsequent analysis only compares the final temperature of the thermocouple.

[0105] (6) Adjust the oil pan height to reduce calculation errors.

[0106] The thermocouple temperature stability data obtained by simulation under different grid sizes are compared with the experimental data, such as Figure 6 As shown in the figure, the temperature values ​​obtained by simulation calculation are significantly different from the experimental values, and reducing the grid size cannot effectively solve the problem of large calculation errors;

[0107] After confirming that the oil pan height is an important factor affecting the temperature calculation value, the oil pan height was adjusted. According to the comparison between the experimental data and the simulation results, the oil pan height was gradually adjusted and the simulation calculation was repeated;

[0108] By adjusting the oil pan height and recalculating the simulation results for multiple iterations, the difference between the calculated value and the experimental value of the temperature at the measuring point can be gradually reduced; after each iteration, the degree of agreement between the simulation results and the experimental data is carefully analyzed, and the oil pan height or other related parameters are further adjusted as needed;

[0109] After multiple iterations of optimization, when the temperature field obtained by simulation is highly consistent with the experimental data, such as Figure 7 As shown in the figure, it can be considered that a relatively accurate temperature field of a small-scale oil pool fire has been constructed. At this point, the simulation results can be used to further analyze the combustion characteristics and heat transfer laws of the oil pool fire.

[0110] In summary, this embodiment provides a method for simulating and reproducing the temperature field of a small-scale oil pool fire based on Fluent. By conducting a small-scale oil pool fire combustion experiment, the weight loss data of the fuel is obtained as the inlet boundary condition of the flow field simulation. Based on the Fluent environment, the inlet fluid is set to fuel vapor and the temperature is set to the boiling point of the fuel. The EDM combustion model is used to perform a large eddy simulation of the gas phase combustion of a small-scale oil pool fire. The temperature stability data of the sampling point is obtained through the thermocouple model, and compared with the temperature stability data obtained by the thermocouple during the experiment. The oil pan height is adjusted to reduce the calculation error, thereby realizing the simulation and reproduction of the temperature field of a small-scale oil pool fire.

[0111] Finally, it should be noted that the above is a preferred embodiment of the present invention. It should be noted that although the basic creative concept of the present invention has been described, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention. Therefore, the attached claims are intended to be interpreted as including the preferred embodiment and all changes and modifications that fall within the scope of the embodiments of the present invention.

Claims

1. A method for simulating and reproducing temperature field of small-scale oil pool fire based on Fluent, characterized in that: The Fluent-based small-scale oil pool fire temperature field simulation and reproduction method includes: Conduct small-scale oil pool fire combustion experiments to obtain fuel weight loss data as inlet boundary conditions for flow field simulation; Based on the Fluent environment, the inlet fluid is set to fuel vapor, the temperature is set to the fuel boiling point, and the EDM combustion model is used to perform large eddy simulation of gas phase combustion of a small-scale oil pool fire. The temperature stability data of the sampling point is obtained through the thermocouple model, compared with the temperature stability data obtained by the thermocouple during the experiment, and the oil pan height is adjusted to reduce the calculation error.

2. The method for simulating and reproducing temperature field of small-scale oil pool fire based on Fluent according to claim 1, characterized in that: Conduct small-scale oil pool fire experiments, including: You can use a small square or round oil pan, place a certain height of clean water in the oil pan, then pour in a certain amount of fuel and ignite it; Multiple thermocouple measuring points are set at equal distances above the oil pan to measure the temperature changes in the gas phase combustion area; An electronic balance is placed under the oil pan to measure the mass change of the fuel.

3. The method for simulating and reproducing temperature field of small-scale oil pool fire based on Fluent according to claim 2, characterized in that: The experiment needs to be repeated several times to reduce the experimental error.

4. The method for simulating and reproducing temperature field of small-scale oil pool fire based on Fluent according to claim 1, characterized in that: Obtain fuel weight loss data as inlet boundary conditions for flow field simulation, including; Based on the fuel mass change monitoring curve, the mass change data in the stable decline phase is selected to calculate the average mass decline rate; The average mass drop rate can be used as the mass flow data of the flow inlet boundary condition for flow field simulation.

5. The method for simulating and reproducing temperature field of small-scale oil pool fire based on Fluent according to claim 1, characterized in that: Based on the Fluent environment, the inlet fluid is set to fuel vapor and the temperature is set to the fuel boiling point, including: Establish a suitable three-dimensional computational domain model, generate computational meshes and name the boundaries, where the fuel inlet is set at the oil pan opening; Set the fuel inlet to mass inlet condition and the outlet to pressure outlet; The inlet fluid is selected to be fuel vapor in gas phase, and the fluid temperature is set to the boiling point of the fuel.

6. The method for simulating and reproducing temperature field of small-scale oil pool fire based on Fluent according to claim 1, characterized in that: Use the EDM combustion model to perform large eddy simulation of gas phase combustion of small-scale oil pool fires, including: First, RANS simulation is performed, the radiation model is the DO model, and the combustion model is the EDM. No ignition operation is required, and the calculation cost is low; The turbulence model selected in RANS simulation is the standard k-ε turbulence model, which has a fast calculation speed and good robustness. Although the combustion process of small-sized oil pan fire is not suitable for description by RANS turbulence model, this model can provide the initial flow field for large eddy simulation, improve the calculation stability and reduce the calculation cost; Use steady-state iterative calculations. The number of iterations should not be too many. It is sufficient to observe the appearance of high-temperature areas in the calculation domain. The RANS calculation results were used as the initial flow field for large eddy simulation, and the turbulence model selected was WALE.

7. The method for simulating and reproducing temperature field of small-scale oil pool fire based on Fluent according to claim 1, characterized in that: Thermocouple models are used to obtain temperature stability data at the sampling point, including: The temperature data of the sampling points measured by the thermocouple in the combustion experiment cannot be directly compared with the temperature calculated by Fluent. The temperature displayed by the temperature measuring device is its own temperature, that is, the temperature measured by the thermocouple is the temperature of the thermocouple itself. In transient conditions, the temperature data calculated by the software will show obvious jitter; Introduce the differential equation describing the thermocouple response, using V tc ρ tc c tc dT tc / dt=A tc [ε tc (I / 4-σ B T tc 4 )+h(T f -T tc )] Control the heat exchange between the thermocouple and its surroundings; Among them, V tc and A tc are the thermocouple volumes (m 3 ) and surface area (m 2 ), ρ tc and c tc are the densities of the thermocouples (kg / m 3 ) and specific heat (J / kg·K), T tc and T f are the temperature of the thermocouple and the surrounding fluid (K), t is the response time of the thermocouple (s), and I is the incident radiation flux to the thermocouple (W / m 2 ), ε tc is the thermocouple emissivity (0.85), σ B is the Stefan-Boltzmann constant (5.64×10 -8 W / m 2 ·K 4 ), h is the heat transfer coefficient (W / m 2 ·K).

8. The method for simulating and reproducing temperature field of small-scale oil pool fire based on Fluent according to claim 7, characterized in that: h is the heat transfer coefficient obtained by the formula h = kNu / D, where: k is the thermal conductivity (W / m·K), and D is the characteristic size of the thermocouple head (m). For a spherical thermocouple, D is the diameter. For a cylindrical head, D requires its diameter and height to be calculated, so that V tc / A tc =D / 6; Nu is the Nusselt number, which is expressed as a combination of the Prandtl number Pr and the Reynolds number Re. Nu = 0.42Pr 0.2 +0.57Pr 0.33 Re 0.5 , Pr=μc p / k, Re = ρuD / μ.

9. The method for simulating and reproducing temperature field of small-scale oil pool fire based on Fluent according to claim 1, characterized in that: Compare the temperature stability data obtained by the thermocouple during the experiment and adjust the oil pan height to reduce the calculation error, including: The increase in the height of the oil pan sidewall slows down the lateral diffusion of fuel vapor during the simulation, promoting gas phase combustion and heat release; Reasonable adjustment of the oil pan height can reduce the difference between the calculated and experimental values ​​of the temperature at the measuring point, thereby constructing a more accurate temperature field of a small-sized oil pool fire.

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