Method for analyzing a jet of a fire gun

Abstract

The present application belongs to the technical field of digital computing or data processing equipment or method specially applied to specific application, discloses a method for analyzing the jet flow of a flame gun, establishes a mathematical model and a discrete method for the jet flow of the flame gun, and performs jet flow analysis based on the model; the calculation domain of the jet flow of the flame gun comprises a nozzle part and a jet flow part, the width of the calculation domain below the nozzle of the flame gun is set to 1.5 m, and the width above the nozzle is set to 0.5 m; in the boundary conditions of the calculation domain, the nozzle inlet is set as a velocity inlet, the nozzle pipe boundary is set as a wall surface, the ground is also set as a wall surface, and other boundaries are set as pressure outlets; the Reynolds average method is adopted to model the turbulent flow; the k-ε model is adopted to construct a turbulent flow model, and a two-layer wall surface model is introduced; the VOF model is adopted as a multiphase flow model; and the finite volume method is adopted to disperse the control equations. The present application solves the problem that the jet flow of the flame gun can be conveniently analyzed by constructing a jet flow model of the flame gun.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of digital computing or data processing equipment or method specially applicable to specific applications, and particularly relates to a method for analyzing the jet flow of a flame gun. BACKGROUND

[0002] A flame gun is a device that emits a burning flammable liquid. The flame gun is composed of a backpack and a flame gun. The backpack contains high-pressure inert propellant gas and condensed gasoline. The flame gun includes a small container, a spring valve and a set of ignition devices. When the trigger is pulled, the spring valve will open, the high-pressure flammable liquid will flow through the ignition device, and the nozzle will be ignited at the same time.

[0003] The jet flow generated after ignition is an important standard for the performance of the flame gun, so analyzing the jet flow of the flame gun is a very important link in the development and improvement of the flame gun. Based on this, the inventors have developed a method for analyzing the jet flow of a flame gun, which can realize the analysis of the jet flow of the flame gun. SUMMARY

[0004] The present application aims to provide a method for analyzing the jet flow of a flame gun, and aims to solve the technical problems existing in the prior art.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical scheme, a method for analyzing the jet flow of a flame gun, establishing a jet flow model of the flame gun, and analyzing the jet flow based on the model.

[0006] The jet flow model of the flame gun comprises:

[0007] (1) Calculation domain and boundary conditions

[0008] The jet flow calculation domain of the flame gun includes the nozzle part and the jet flow part. The calculation domain below the nozzle of the flame gun is set to 1.5m in width, and the width above the nozzle is set to 0.5m. In the boundary conditions of the calculation domain, the nozzle inlet is set as a velocity inlet, the nozzle pipe boundary is set as a wall surface, the ground is also set as a wall surface, and the other boundaries are set as pressure outlets.

[0009] (2) Flow control equation

[0010] The Reynolds average method is used to model the turbulent flow, and the flow control equation used is the incompressible Reynolds average equation:

[0011]

[0012] (3) Turbulence model

[0013] The k-ε model is used to construct the turbulence model, and a two-layer wall surface model is introduced. In this model, the entire region is divided into a region with viscous effect and a completely turbulent region.

[0014] (4) Multiphase flow model

[0015] The VOF model is used as the multiphase flow model, and the constraint condition is:

[0016]

[0017] (5) Discrete format

[0018] The finite volume method is used to discretize the control equation, the calculation region is divided into a series of non-repeated control volumes, and there is a control volume around each grid point; the differential equation to be solved is integrated for each control volume to obtain a set of discrete equations, in which the unknown quantity is the value of the dependent variable at the grid point.

[0019] In another preferred embodiment of the present application, quadrilateral grids are generated in the calculation domain, and the specific steps are:

[0020] (1) According to the flow characteristics, the region is divided, and the grid topology in each region is determined;

[0021] (2) Generating boundary layer grid;

[0022] (3) Generating the grid of the boundary line of each region;

[0023] (4) Generating the grid of each sub-domain;

[0024] (5) Optimizing the grid of each sub-domain.

[0025] In another preferred embodiment of the present application, when generating quadrilateral grids, based on the index of grid liquid volume fraction gradient, the area where the grid needs to be encrypted is marked, and the grid is encrypted.

[0026] In another preferred embodiment of the present application, the grid encryption rule is that the liquid volume fraction gradient is greater than 0.5, the roughening rule is that the liquid volume fraction gradient is less than 0.2, the highest encryption level is 3 layers, and the checking and encryption are performed once every 20 time steps.

[0027] In another preferred embodiment of the present application, when establishing the turbulence model, the specific processing in different regions is:

[0028] (1) In the fully turbulent region The k-ε model will be used;

[0029] (2) In the near-wall region with viscous effect A one-equation model is used.

[0030] In another preferred embodiment of the present application, the equation discretized in a given cell is:

[0031]

[0032] In another preferred embodiment of the present application, the spatial discretization is performed by using a second-order upwind scheme, and the calculation equation of the surface value φ f is: In another preferred embodiment of the present application, the time discretization scheme is as follows: the expression of the variable φ changing with time is:

[0033] The beneficial effects of the present application are:

[0034] (1) In the present application, when generating the quadrilateral mesh, the local adjustment is automatically performed according to the distribution of the jet flow, so that the calculation accuracy and efficiency can be improved.

[0035] (2) By increasing the mesh density at the position where the flow field feature changes, the calculation accuracy in these regions can be ensured, while the mesh in other regions can be as coarse as possible, so that the calculation efficiency can be improved.

[0036] (3) The appearance of the Reynolds stress term makes the Reynolds equation not closed, so that the mathematical model can be closed by the additional given turbulence model.

[0037] (4) The standard k-ε model is effective only for fully developed turbulence, and can only be used to solve the flow in the turbulence core region, and is not suitable for the flow in the near-wall region. Based on this, the two-layer wall model is introduced in the present application.

[0038] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter in the description of embodiments of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0039] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, including the appended drawings.

[0040] Figure 1 is a schematic diagram of the jet flow range simulation calculation domain and boundary conditions of the embodiment of the present application.

[0041] Figure 2 is the jet flow range simulation calculation domain mesh division and adaptive mesh of the embodiment of the present application. DETAILED DESCRIPTION

[0042] Embodiments of the present application will be described in detail below, examples of which are shown in the accompanying drawings, in which the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application.

[0043] In the description of the present application, it needs to be understood that the terms "longitudinal", "transverse", "vertical", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0044] In the description of the present application, unless otherwise specified and limited, it needs to be explained that the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be mechanical connection or electrical connection, it can be the communication between two elements, it can be direct connection or indirect connection through intermediate medium, and the specific meaning of the above terms can be understood by the person skilled in the art according to the specific circumstances.

[0045] The present application provides a flame gun jet analysis method, establishes a flame gun jet analysis model, and performs jet analysis based on the model. The flame gun jet analysis model specifically includes a calculation domain and boundary conditions, flow control equations, turbulence models, multiphase flow models and discrete formats.

[0046] I. Calculation domain and boundary conditions

[0047] As shown in Figure 1 , the nozzle height of the flame gun is 1.5 m, so the width of the calculation domain below the nozzle is 1.5 m, and the width above the nozzle is set to 0.5 m. In the boundary conditions of the calculation domain, the nozzle inlet is set as a velocity inlet, the nozzle pipe boundary is set as a wall surface, and the ground is also set as a wall surface. Other boundaries are set as pressure outlets.

[0048] Generate quadrilateral grids in the calculation domain, and control the maximum size of the grid to be within 1 mm. The steps of generating the jet simulation grid are as follows:

[0049] (1) According to the flow characteristics, divide into zones and determine the grid topology in each zone;

[0050] (2) Generate boundary layer grid;

[0051] (3) Generate the interface grid of each zone;

[0052] (4) Generate the grid of each subdomain;

[0053] (5) Optimize the grid of each subdomain.

[0054] In the calculation process, the adaptive grid technology is used to encrypt the grid in real time. In the specific operation, the local adjustment is automatically carried out according to the jet distribution, the area needing encryption is marked based on the grid liquid volume fraction gradient index, and the grid is directly encrypted by using the Cartesian method; the encryption rule is that the liquid volume fraction gradient is greater than 0.5, and the coarsening rule is that the liquid volume fraction gradient is less than 0.2. The highest encryption level is 3 layers, and the checking and encryption are carried out once every 20 time steps, that is, every 20 time steps are completed in the iteration, the local grid encryption is carried out once.

[0055] The area where the jet liquid column moves away is also reflected in the index of the proportion of liquid water in the calculation domain, and it is not necessary to use a smaller grid to calculate. The areas which have been encrypted before and do not need to be concerned about subsequently will adopt the way of merging the grid, so that the grid returns to the original grid to reduce the calculation amount of the simulation solution.

[0056] As shown in combination with 2, by automatically carrying out local adjustment, the grid density is increased at the position where the flow field characteristics change, so that the calculation accuracy in these areas can be ensured, and the grid in other areas can be as coarse as possible, thereby improving the calculation efficiency.

[0057] II. Flow control equation

[0058] The turbulence measurement results show that the turbulence fluctuation frequency is between 10 2 and 10 5 , and the amplitude is generally not more than 10% of the average amount. Based on this, the instantaneous amount can be decomposed into the average amount and the fluctuation amount. In actual problems, it is not necessary to know the details of the turbulence fluctuation, and the average characteristics of the turbulence are more valuable, so the average value of the turbulence needs to be calculated.

[0059] The principle of the Reynolds average method is as follows: the velocity, pressure and other physical quantities of any point in the turbulent flow change irregularly with time.

[0060] The Reynolds average method is used to model the turbulence, and the Reynolds equation can be obtained by Reynolds averaging the NS equation. The flow control equation used in the jet simulation process of the embodiment is the incompressible Reynolds average equation:

[0061]

[0062] III. Turbulence model

[0063] The k-ε model is adopted, and the definitions of the turbulent kinetic energy k and the turbulent dissipation rate ε in the k-ε model are as follows:

[0064]

[0065] The transport equation of the turbulent kinetic energy k is:

[0066]

[0067] where μ is the dynamic viscosity; μ t is the turbulent viscosity; G k is the turbulent energy production term due to the mean velocity gradient; σ k ,σ ε is the Prandtl number corresponding to the turbulent energy and dissipation rate, where σ k = 1.0, σ ε = 1.3; C 1ε ,C 2ε are empirical coefficients, C 1ε = 1.44, C 2ε = 1.92.

[0068] The eddy viscosity μ t is given by:

[0069]

[0070] The formula for the Reynolds stress is:

[0071]

[0072] Since the standard k-ε model is valid only for fully developed turbulence, it can only be used to solve the flow in the core region of turbulence and is not applicable to the flow in the near-wall region. Therefore, a two-layer wall model is introduced. In this model, the entire region is divided into a region with viscous effect and a fully turbulent region, and the division of the two regions is determined by the wall distance and the turbulent Reynolds number Re y .

[0073] where Re y is defined as:

[0074]

[0075] where y is the vertical distance from the wall to the center of the cell.

[0076] The specific processing in different regions is as follows:

[0077] (1) In the fully turbulent region the k-ε model will be used;

[0078] (2) In the near-wall region with viscous effect a one-equation model is used. The momentum equation and the k equation of this model are the same as those of the k-ε model, except that the eddy viscosity μ t and the turbulent energy dissipation rate ε t are calculated by the following formulas:

[0079]

[0080] Among them, l μ and l ε It is a length scale:

[0081]

[0082] The constants in the formula: A μ =70, A ε =2c l

[0083] To make the μ defined in the two-layer model t,2layer Capable of being related to μ defined by the outer high Reynolds number t Smooth transition, introducing an improved eddy viscosity coefficient:

[0084] μ t,enh =λ ε μ t +(1-λ ε )μ t,2layer

[0085] Where μ t λ is the eddy viscosity coefficient defined for the k-ε model. ε It is a mixed function, equal to 1 when far from the wall and equal to 0 when close to the wall, as specified in the following formula:

[0086]

[0087] The constant A determines the width of the mixing function, by defining... λ ε The value will be in △Re y Within 1% of the change. Generally, △Re y The assignment will be Between 5% and 20%.

[0088] IV. Multiphase Flow Model

[0089] The jet range simulation involves a water-air two-phase flow problem. This embodiment uses the VOF model as the multiphase flow model. In the VOF model, different fluid components share a common set of momentum equations. By introducing the variable of phase volume fraction, the phase interface of each computational unit is tracked. Within each control volume, the sum of all phase volume fractions is 1. All variables and their properties are shared by all phases within the control volume and represent the volume average. Therefore, the variables and their properties within any given control volume purely represent a single phase or a mixture of phases and are determined by the phase volume fraction.

[0090] In a unit, if the volume fraction of the q-th phase fluid is α q Then there are three possible scenarios:

[0091] (1)α q = 0: No qth phase fluid exists in the cell.

[0092] (2)α q = 1: The cell is full of qth phase fluid.

[0093] (3) 0 < α < 1 q < 1: The cell contains an interface between the qth phase fluid and other one or more phases.

[0094] For n-phase flow, based on the basic flow governing equations, the VOF model gives the following additional constraint conditions according to the mass conservation principle:

[0095]

[0096] In the study of the jet of the torch, n = 2, water as the main phase, air as the secondary phase, and the water phase volume fraction at the velocity inlet is set to 1.

[0097] V. Discrete scheme

[0098] The finite volume method is used to discretize the governing equations, and the calculation region is divided into a series of non-repeating control volumes, and there is a control volume around each grid point; the differential equation to be solved is integrated for each control volume, and a set of discrete equations is obtained, in which the unknowns are the values of the dependent variables at the grid points.

[0099] The steady-state conservation equation considering the transport of scalar φ can easily explain the discretization of the control volume. The following is the equation written in the integral form for the control volume V:

[0100]

[0101] Where: ρ is the density, v is the velocity vector, A is the surface area vector, is the diffusion coefficient of φ, is the gradient of φ, is the source term per unit volume .

[0102] The above equation is applied to each control volume or cell in the region.

[0103] The discretized equation in a given cell is:

[0104]

[0105] Where: N faces is the area of the grid cell, φ f is the flow rate through the surface f, v f φ fA f - the mass flow through the surface f, A f is the area of the surface φ, is the component of the velocity in the direction normal to the face f, V is the volume of the grid cell.

[0106] The spatial discretization is performed using a second order upwind scheme. When using a second order upwind scheme, the surface value φ f is calculated using the following equation:

[0107]

[0108] where φ and φ f are the cell center value and the gradient value of the upwind cell, respectively, and ΔS is the displacement vector from the center of the upwind cell to the center of the surface. In this case, the gradient φ f within each cell needs to be determined. We use the divergence theorem to calculate this gradient, whose discrete form is as follows:

[0109]

[0110] Here, the value φ f at the surface is calculated from the average of φ of the two cells adjacent to the surface. Finally, the gradient φ f is limited to ensure that no new maximum and minimum values are introduced.

[0111] In addition, the time discretization scheme needs to be considered. Let the expression of the variable φ as a function of time be:

[0112]

[0113] where F represents the spatial direction discrete term.

[0114] The second order time discretization is performed as follows:

[0115]

[0116] After the time derivative is discretized, the second order accuracy implicit estimate

[0117]

[0118] The iterative scheme is:

[0119]

[0120] In the description of the specification, the description of the terms "preferred embodiment", "one embodiment", "some embodiments", "example", "specific example" or "some examples" etc. means that the particular feature, structure, material or characteristic being described in connection with the embodiment or example is included in at least one embodiment or example of the application. The illustrative appearance of the above-mentioned terms in various places in the specification are not necessarily referred to the same embodiment or example. Moreover, the particular features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0121] Although embodiments of the present application have been shown and described, it would be appreciated by those skilled in the art that changes, modifications, alternatives and variations to these embodiments could be made without departing from the principles and spirit of the application, the scope of which is defined by the claims and their equivalents.

Claims

1. A method of analyzing a jet of a flamethrower, characterized by: A jet model of the flame gun is established, and jet analysis is performed based on the model; The jet model of the flame gun comprises: (1) Calculation domain and boundary conditions The jet calculation domain of the flame gun comprises a nozzle part and a jet part, the calculation domain width below the nozzle of the flame gun is set to 1.5 m, and the width above the nozzle is set to 0.5 m; in the boundary conditions of the calculation domain, the nozzle inlet is set as a velocity inlet, the nozzle pipe boundary is set as a wall surface, the ground is also set as a wall surface, and other boundaries are set as pressure outlets; (2) Flow control equation The Reynolds average method is adopted to model the turbulent flow, and the flow control equation adopted is the incompressible Reynolds average equation: (3) Turbulence model The k-ε model is adopted to construct the turbulence model, and a two-layer wall surface model is introduced, in which the entire region is divided into a region with viscous influence and a completely turbulent region; The specific processing in different regions is as follows: model;​​ (ii) in the near-wall region where the viscous effects are important, i.e. , a one-equation model is used; the momentum equation and the equation of this one-equation model are the same as in the k-ε model, except that the eddy viscosity and the turbulent kinetic energy dissipation rate are calculated from the following equations: wherein, and is a length scale: Constants in the formulas: , , To make the two-layer model definition of able to smoothly transition with the outer high Reynolds number definition of , an improved eddy viscosity coefficient is introduced: where is the eddy viscosity coefficient defined for the k-ε model, is a blending function that is 1 far from the wall and 0 near the wall, defined as constant determines the width of the blending function by defining , the value of will vary by ; the assignment of will vary between and ; (4) Multiphase flow model The VOF model is adopted as the multiphase flow model, and the constraint condition is: (5) Discrete format The finite volume method is adopted to discretize the control equation, the calculation region is divided into a series of non-repeated control volumes, and each grid point has a control volume around it; the differential equation to be solved is integrated for each control volume, and a set of discrete equations is obtained, in which the unknown quantity is the value of the dependent variable at the grid point.

2. The jet analysis method of a flamethrower according to claim 1, characterized in that: Quadrilateral grids are generated in the calculation domain, and the specific steps are as follows: (1) According to the flow characteristics, the region is divided, and the grid topology in each region is determined; (2) Boundary layer grid is generated; (3) Interzone grid is generated; (4) Subdomain grid is generated; (5) Optimize the subdomain grid.

3. The method of claim 2, wherein: When generating the quadrilateral grid, based on the grid liquid volume fraction gradient index, the region which needs to be encrypted is marked, and the grid is encrypted.

4. The method of claim 3, wherein: The grid encryption rule is that the liquid volume fraction gradient is greater than 0.5, the coarsening rule is that the liquid volume fraction gradient is less than 0.2, the highest encryption level is 3 layers, and the check and encryption are performed every 20 time steps.

5. The method of claim 4, wherein: The discrete equation in a given cell is: where: N faces is the area of the grid cell, is the pair flux through surface f, is the mass flux through surface f, is the area of surface f, is the component of V normal to face f, V is the grid cell volume.

6. The method of jet analysis of a flamethrower according to claim 5, characterized in that: The spatial discretization is performed using a second order upwind scheme, and the surface value of the governing equation is given by: where and are the cell center value and the gradient value of the upwind cell, respectively, is the displacement vector from the upwind cell center to the surface center.

7. The method of jet analysis of a flamethrower according to claim 6, characterized in that: Time-discrete format, set variables The expression over time is: ; F represents the discrete term in the spatial direction.

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