Power cabin fire extinguishing agent concentration distribution calculation method

Abstract

The invention relates to helicopter design, in particular to a power cabin fire extinguishing agent concentration distribution calculation method. Numerical calculation is adopted to directly simulate the concentration distribution of the fire extinguishing agent in the power cabin, the calculation period is long, the concentration distribution of the fire extinguishing agent in the power cabin is rapidly obtained, numerical calculation and a theoretical analysis method are combined, the method is used for calculating the concentration distribution of the fire extinguishing agent, an instantaneous point source concentration equation when wind exists is constructed through Matlab, and if other fire extinguishing agents are replaced, the calculation period is short. A new fire extinguishing agent concentration diffusion solution can be established by modifying a diffusion system lamp associated with the fire extinguishing agent. For different models, power cabins and engine accessories are simplified, and after a power cabin model is obtained, fire extinguishing agent concentration distribution can be solved according to the method. The method can be applied to rotor wing or fixed wing fire extinguishing agent concentration solving.

Description

Technical Field

[0001] The invention relates to helicopter design and to a method for calculating the concentration distribution of fire extinguishing agent in a power cabin. Background Art

[0002] As one of the important aircraft, the fire safety performance of helicopters has a great impact on their survivability. Halon 1301 fire extinguishing agent is the preferred fire extinguishing agent in the aviation field. Halon 1301 fire extinguishing agent mainly destroys the chain reaction in the combustion process to achieve the purpose of fire extinguishing. Therefore, Halon 1301 fire extinguishing agent must reach a certain concentration to achieve effective fire extinguishing. The airworthiness CCAR29 clause and HB7879 and other standards stipulate that the volume design concentration of Halon 1301 fire extinguishing agent must not be less than 6% and must be maintained for 0.5 seconds. Therefore, after the fire extinguishing system design is completed, it is very important to quickly evaluate whether the fire extinguishing system design scheme can meet the fire extinguishing agent concentration distribution requirements.

[0003] The existing methods for evaluating whether the fire extinguishing system meets the requirements are mainly through test methods and numerical calculation methods. As a verification method, the test method is very expensive and cannot evaluate the performance of the fire extinguishing system in the scheme design stage. The numerical calculation method is mainly completed by commercial software. Since the power compartment is large and the grid size required for two-phase flow in numerical calculation is small, the calculation cost of calculating the concentration distribution of the fire extinguishing agent in the power compartment through numerical calculation is particularly high, and the calculation cycle is long, which is not conducive to the rapid evaluation of the design of the fire extinguishing system scheme.

[0004] Therefore, it is of great significance to propose a method that can quickly calculate the concentration distribution of fire extinguishing agent in the power compartment and evaluate whether the fire extinguishing system scheme meets the design requirements. Summary of the invention

[0005] Purpose of the Invention

[0006] A method for calculating the concentration distribution of fire extinguishing agent in the power compartment is provided to quickly calculate the concentration distribution of fire extinguishing agent in the power compartment and evaluate whether the fire extinguishing system scheme meets the design requirements.

[0007] Technical Solution

[0008] Due to the complexity of the power cabin structure, the theoretical calculation of the flow field distribution and the fire extinguishing agent concentration distribution in the power cabin cannot be realized. The numerical calculation directly simulates the fire extinguishing agent concentration distribution in the power cabin, and the calculation cycle is long. In order to quickly obtain the fire extinguishing agent concentration distribution in the power cabin, the present invention combines numerical calculation and theoretical analysis methods to propose a method for calculating the fire extinguishing agent concentration distribution in the power cabin:

[0009] 1) Modeling of the power compartment geometry model: According to different models, the power compartment and engine accessories are simplified to obtain the power compartment geometry model;

[0010] 2) Divide the grid. The speed of the fire extinguishing agent near the nozzle changes dramatically. In order to calculate more accurately, the grid scale should be no larger than Δt*U according to the calculation accuracy. Δt is the time accuracy and U is the time precision.

[0011] is the speed magnitude;

[0012] 3) After meshing, the steady-state solution of the power cabin flow field is solved by three-dimensional fluid simulation software:

[0013] After dividing the grid, the steady-state solution model is set up through the three-dimensional fluid simulation software, the boundary conditions and turbulence model required by the specific model are determined, and after the calculation is stable, the steady-state flow field data is exported;

[0014] 4) Point source transport model calculation procedure: Based on the gradient transport theory and Gaussian transient model, the instantaneous point source concentration equation in windy conditions is constructed;

[0015] 5) Using MATLAB, read the steady-state flow field data solved in step 3) to obtain the velocity field of each point in the power cabin;

[0016] 6) Substitute the velocity field in the power cabin into the point source concentration distribution equation in step 4) to solve the concentration distribution of a single fire extinguishing agent injection point source at a certain location at any time;

[0017] 7) Determine the coordinates of the injection points of the fire extinguishing agent concentration, and construct the sum of the concentration distribution of any point in the power cabin after injection from different injection points based on the relative positions of the coordinates;

[0018] 8) Discrete time constant, solve the concentration distribution at any point at different times, and obtain the change of concentration distribution over time.

[0019] Furthermore, before step 1, a typical working environment in which the fire extinguishing agent is sprayed is determined, and the ventilation volume of each ventilation opening and the position coordinates of each nozzle are determined.

[0020] Furthermore, after completing step 8, a ground simulation test of the fire extinguishing system is used for verification.

[0021] Furthermore, when dividing the grid, the operating speed and calculation accuracy of the computing equipment should be comprehensively considered. According to the computing power of the equipment, the time accuracy Δt should be adjusted to determine the grid size.

[0022] Furthermore, the fire extinguishing agent near the nozzle will undergo a dramatic phase change process instantly, and the velocity field and temperature field will change dramatically. According to the actual calculation situation, the grid should be denser at least 5 cm near the nozzle;

[0023] Furthermore, the three-dimensional fluid simulation software is specifically Fluent or CFX, etc.;

[0024] Furthermore, the method utilizes numerical calculation to simulate the steady-state flow field data of the power cabin.

[0025] Furthermore, the method uses steady-state flow field data to consider the effect of fluid velocity on the diffusion of the fire extinguishing agent.

[0026] The beneficial effects of this application are:

[0027] Avoid the waste of manpower and material resources caused by concentration testing experiments; effectively and quickly evaluate the performance of the fire extinguishing system at the planning stage; and reduce the huge computational cost of using numerical calculations to evaluate the concentration distribution of fire extinguishing agents.

[0028] The present invention can be used in the design process of the power compartment fire extinguishing system, and it has the following characteristics:

[0029] a) Fast calculation speed: Compared with the calculation of fire extinguishing agent concentration through the DPM model in fluent, the instantaneous point source concentration equation method in windy conditions is constructed through Matlab to solve the fire extinguishing agent concentration distribution. The calculation of complex phase change processes through the DPM model of fluent has strict requirements on the number and quality of surrounding grids. At the same time, the calculation process is prone to divergence. When the power cabin is large, the number of grids required is large, and the calculation cost is huge. With this method, only the steady-state flow field needs to be calculated through three-dimensional simulation software, which can greatly reduce the calculation cost;

[0030] b) Strong versatility: This method calculates the concentration distribution of fire extinguishing agent by constructing the instantaneous point source concentration equation in the wind through Matlab. If other fire extinguishing agents are used, the diffusion system lamp related to the fire extinguishing agent can be modified to establish a new fire extinguishing agent concentration diffusion solution. For different models, the power cabin and engine accessories are simplified, and after the power cabin model is obtained, the fire extinguishing agent concentration distribution can be solved according to this method. This method can be applied to the solution of rotor or fixed-wing fire extinguishing agent concentration. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the implementation of the present invention clearer, the technical scheme in the embodiment of the present invention will be described in more detail in combination with the embodiment of the present invention. The same or similar reference numerals throughout represent the same or similar originals or elements with the same or similar functions. The described embodiments are part of the embodiments of the present invention, not all of them. The embodiments described below are exemplary and intended to be used to explain the present invention, and should not be construed as limitations on the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. The embodiments of the present invention are described in detail below.

[0032] Example

[0033] According to the steps of this method, write an implementation example, bring in specific parameters and values, (specific example of a certain model)

[0034] 1) Modeling of the power compartment geometry model: According to different models, the power compartment and engine accessories are simplified to obtain the power compartment geometry model;

[0035] 2) Grid division: The velocity of the extinguishing agent near the nozzle changes dramatically. For more accurate calculation, the grid scale should be no larger than Δt*U according to different calculation accuracy; Δt is the time accuracy, and U is the velocity. To ensure the calculation accuracy, the number of constructed grids is about 2.57 million and the number of nodes is about 452,000.

[0036] 3) After meshing, the steady-state solution of the power cabin flow field is solved by three-dimensional fluid simulation software:

[0037] After dividing the grid, the steady-state solution model is set up through the three-dimensional fluid simulation software, the boundary conditions and turbulence model required by the specific model are determined, and after the calculation is stable, the steady-state flow field data is exported;

[0038] For a certain model, the boundary condition ventilation rate is set to 0.423kg / s, the turbulence model selects the single equation Spalart-Allmaras turbulence model, the solution algorithm selects the SIMPLE method, the discrete format of each variable selects the fluent default setting, and the steady-state flow field data is obtained by solution.

[0039] 4) Point source transport model calculation procedure: Based on the gradient transport theory and Gaussian transient model, the instantaneous point source concentration equation in windy conditions is constructed;

[0040]

[0041] x0=u×(ti)

[0042] y0=v×(ti)

[0043] z0=w×(ti)

[0044] 5) Using MATLAB, read the steady-state flow field data solved in step 3) to obtain the velocity field of each point in the power cabin;

[0045] 6) Substitute the velocity field in the power cabin into the point source concentration distribution equation in step 4) to solve the concentration distribution of a single fire extinguishing agent injection point source at a certain location at any time. By changing the value of t, the fire extinguishing agent concentration value at any location in the power cabin at any time can be solved.

[0046] 7) Determine the coordinates of the injection point of the fire extinguishing agent concentration, and construct the sum of the concentration distribution of any point in the power cabin after injection from different injection points according to the relative position of the coordinates; by solving the fire extinguishing agent concentration value C of any nozzle at any position in the power cabin at time t1t , C 2t , C 3t

[0047] etc. 1t represents the fire extinguishing agent concentration value formed by nozzle No. 1 at time t), the fire extinguishing agent concentration value of all nozzles at time t is added up to obtain the fire extinguishing agent concentration value at any position.

[0048] 8) Discrete time constant, solve the concentration distribution at any point at different times, and obtain the change of concentration distribution over time.

[0049] A method for calculating the concentration distribution of fire extinguishing agent in a power compartment. The invention uses a transient point source transport model to calculate the diffusion process of the fire extinguishing agent.

[0050] Preferably, the fire extinguishing agent concentration distribution is solved by gradient transport theory and Gaussian model.

[0051] Preferably, the steady-state flow field data calculated by three-dimensional fluid simulation software is used as the influencing parameter of fluid velocity on the diffusion of fire extinguishing agent concentration.

[0052] Preferably, the fire extinguishing agent concentration distribution in the power compartment is calculated by combining numerical calculation and theoretical calculation.

[0053] Matlab explanation: ① Read the three-dimensional flow field data to obtain the steady-state flow field data in the power cabin; ② According to the gradient transport theory and Gaussian transient model, construct the instantaneous point source concentration equation when there is wind. ③ Substitute the steady-state flow field data into the instantaneous point source concentration equation when there is wind to solve the fire extinguishing agent concentration distribution value.

[0054] It is understood by those skilled in the art that, unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as the general understanding of ordinary technicians in the field to which the present invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and unless defined as here, will not be interpreted with idealized or overly formal meanings. The specific implementation methods described above further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Within the spirit and principle of the present invention, any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment of equivalent changes for application in other fields, but any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the technical solution content of the present invention, any modification, equivalent replacement, improvement, etc., made according to the technical essence of the present invention, should be included in the protection scope of the present invention.

Claims

1. A method for calculating the concentration distribution of fire extinguishing agent in a power compartment, characterized in that: The steps include: 1) Power compartment geometry modeling: Simplify the power compartment and engine accessories according to different models. Obtain the power cabin geometric model; 2) Divide the grid. The speed of the fire extinguishing agent near the nozzle changes dramatically. In order to calculate more accurately, the grid scale should be no larger than Δt*U according to the calculation accuracy. Δt is the time accuracy and U is the speed. 3) After meshing, use three-dimensional fluid simulation software to solve the steady-state solution of the power cabin flow field: After meshing, use three-dimensional fluid simulation software to set the steady-state solution model, the boundary conditions required by the specific model, the turbulence model, and after the calculation is stable, export the steady-state flow field data; 4) Point source transport model calculation procedure: Based on the gradient transport theory and Gaussian transient model, the instantaneous point source concentration equation in windy conditions is constructed; 5) Using MATLAB, read the steady-state flow field data solved in step 3) to obtain the velocity field of each point in the power cabin; 6) Substitute the velocity field in the power cabin into the point source concentration distribution equation in step 4) to solve the concentration distribution of a single fire extinguishing agent injection point source at a certain location at any time; 7) Determine the coordinates of the injection points of the fire extinguishing agent concentration, and construct the sum of the concentration distribution of any point in the power cabin after injection from different injection points based on the relative positions of the coordinates; 8) Discrete time constant, solve the concentration distribution at any point at different times, and obtain the change of concentration distribution over time.

2. The method according to claim 1, characterized in that Prior to 1), determine the typical working environment in which the fire extinguishing agent is sprayed, determine the ventilation volume of each ventilation port and the position coordinates of each nozzle.

3. The method according to claim 2, characterized in that After completing 8), conduct a ground simulation test of the fire extinguishing system for verification.

4. The method according to claim 3, characterized in that When dividing the grid, the operating speed and calculation accuracy of the computing equipment should be comprehensively considered. According to the computing power of the equipment, the time accuracy Δt should be adjusted to determine the size of the grid.

5. The method according to claim 4, characterized in that The fire extinguishing agent near the nozzle will undergo a dramatic phase change process instantly, and the velocity field and temperature field will change dramatically. According to the actual calculation situation, the grid should be encrypted at least 5 cm near the nozzle.

6. The method according to claim 5, characterized in that The three-dimensional fluid simulation software is specifically fluent or CFX.

7. The method according to claim 6, characterized in that This method uses numerical calculation to simulate the steady-state flow field data of the power cabin.

8. The method according to claim 7, characterized in that This method uses steady-state flow field data to consider the effect of fluid velocity on the diffusion of fire extinguishing agent.

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