A rapid prediction method for resistance of metal sponge centrifugal ventilator

Abstract

The present invention discloses a method for quickly predicting the resistance of a metal sponge centrifugal ventilator. The method adopts a porous medium model to replace the metal sponge in the metal sponge centrifugal ventilator, adopts the distributed resistance attached to the porous medium model to replace the resistance caused by the metal sponge, constructs a complete metal sponge centrifugal ventilator model, performs numerical calculation on the model, and obtains a calculation formula for the pressure drop loss of the metal sponge centrifugal ventilator, thereby being able to quickly predict the resistance of the metal sponge centrifugal ventilator. The average error between the calculated resistance value of the metal sponge centrifugal ventilator obtained by the present invention and the experimental value does not exceed 10%, and has good engineering application value.

Description

Technical Field

[0001] The invention belongs to the technical field of aircraft engine ventilators, and in particular relates to a novel ventilator structure - a method for quickly predicting the resistance of a metal sponge centrifugal ventilator. Background Art

[0002] At present, mature aircraft engines widely use mechanical transmission as the main power transmission method. The effectiveness and reliability of their work are heavily dependent on the lubricating oil system. As a subsystem of the lubricating oil system, the ventilation system mainly discharges part of the high-pressure sealing gas in the lubricating oil box and bearing cavity, so that the pressure in each lubricating oil cavity is kept in the normal working range, thereby avoiding the cavity pressure being too high to affect the sealing and oil supply and return performance. In this process, the gas from the lubricating oil cavity will inevitably be mixed with part of the lubricating oil. If the oil-gas mixture is directly discharged into the atmosphere, it will not only cause a certain amount of lubricating oil consumption, but also pollute the atmosphere. Therefore, a ventilator is set at the position where the ventilation pipeline is connected to the outside world to separate and recover the lubricating oil from the oil-gas mixture in each lubricating oil cavity to reduce lubricating oil consumption.

[0003] The metal sponge centrifugal ventilator is a relatively new type of ventilator structure in China. Different from the traditional ventilator, the metal sponge is added to the centrifugal ventilator. Metal sponge is a porous medium material with the characteristics of low density, large specific surface area and high porosity. When the oil-gas mixture enters the ventilator, in addition to the traditional centrifugal separation effect, the porous mesh structure of the metal sponge can also effectively separate the oil droplets for a second time, thereby significantly improving the separation efficiency of the ventilator without increasing the speed, size and weight of the ventilator. However, after the metal sponge is added to the ventilator, it will also have a certain impact on the resistance of the ventilator; the ventilation resistance of the ventilator is generally defined as the pressure drop loss between the inlet and outlet of the ventilator, which is one of the key parameters of the ventilator, and its size will directly affect the reliability of the ventilation system. If the ventilation resistance is too large, the pressure in the bearing cavity will increase and the sealing of the bearing cavity will decrease; if the ventilation resistance is too small, the consumption of lubricating oil will increase. Therefore, it is necessary to obtain the ventilation resistance of the metal sponge centrifugal ventilator.

[0004] In the prior art, the resistance of metal sponge centrifugal ventilators is mainly obtained based on experiments, and the body-centered vertical method is mainly used to simplify the metal sponge model in numerical simulation. However, due to the huge number of structural cells of metal sponge in centrifugal ventilators and their complex structure, most of which are disordered mesh structures, it is very difficult to accurately model the metal sponge. At present, there is no suitable metal sponge processing method that can accurately obtain the resistance of the metal sponge in the actual ventilator. Summary of the invention

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for quickly predicting the resistance of a metal sponge centrifugal ventilator, so as to solve the problems in the prior art such as the high difficulty in accurately modeling the metal sponge and the difficulty in accurately obtaining the actual metal sponge resistance in the ventilator.

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

[0007] A method for quickly predicting the resistance of a metal sponge centrifugal ventilator is disclosed. The method adopts a porous medium model to replace the metal sponge in the metal sponge centrifugal ventilator, and adopts a distributed resistance attached to the inside of the porous medium model to replace the resistance caused by the metal sponge. A complete metal sponge centrifugal ventilator model is constructed, and numerical calculations are performed on the model to obtain a calculation formula for the pressure drop loss of the metal sponge centrifugal ventilator, thereby quickly predicting the resistance of the metal sponge centrifugal ventilator.

[0008] The present invention also includes the following technical features:

[0009] Specifically, the following steps are included:

[0010] Step 1, constructing a metal sponge centrifugal ventilator model: establishing a metal sponge centrifugal ventilator model according to an actual ventilator structure, the metal sponge centrifugal ventilator model comprising a mass flow inlet, a metal sponge region and a pressure outlet; the metal sponge region is a porous medium model constructed using a Kelvin structure as a unit cell;

[0011] Step 2, constructing a metal sponge centrifugal ventilator model calculation domain and meshing the calculation domain, importing the divided metal sponge centrifugal ventilator model mesh into the fluid simulation software Fluent, and combining the viscous resistance coefficient and inertial resistance coefficient of the metal sponge area to perform numerical calculation to obtain the inlet and outlet pressure drop loss value of the metal sponge centrifugal ventilator;

[0012] Step 3: Compare the inlet and outlet pressure drop loss values ​​of the metal sponge centrifugal ventilator obtained by numerical calculation in step 2 with the test values ​​of the actual ventilator. If the pressure drop loss values ​​obtained by numerical calculation are consistent with the change trends of the actual test values ​​with the rotation speed, it is reliable to use the porous medium model to replace the metal sponge region, and continue with the following steps:

[0013] Step 4: Use the orthogonal design method to design the calculation conditions: the factors affecting the ventilator resistance include speed, ventilation volume, outlet pressure, temperature, porosity and PPI; select five levels for each influencing factor, and use the six-factor five-level orthogonal design table to obtain the calculation conditions. Based on the range, determine the order of influence of each factor on the ventilator resistance within the given working condition range;

[0014] Step 5: Use the metal sponge centrifugal ventilator model and grid in step 2 to calculate the working condition in step 4. Change the boundary conditions in Fluent according to the data in the orthogonal design table of the calculated working condition to obtain the pressure drop loss under different working conditions. Then, according to the order of the influence of each factor on the ventilator resistance obtained in step 4, use the π theorem to fit the pressure drop loss under different working conditions, and obtain the preliminary prediction formula of the pressure drop loss of the metal sponge centrifugal ventilator model:

[0015]

[0016] In the above formula, n is the rotation speed, Q is the flow rate of the incoming flow, p0 is the outlet pressure, ρ is the density of the incoming flow, μ is the viscosity, B is the pore density of the metal sponge, e is the porosity, c1, c2, c3, c4 are unknown coefficients;

[0017] Step 6: Use the least squares method to fit and solve the undetermined coefficients of the preliminary prediction formula for pressure drop loss to obtain the final calculation formula for pressure drop loss of the metal sponge centrifugal ventilator:

[0018]

[0019] In the above formula, n is the rotation speed, Q is the flow rate, p0 is the outlet pressure, ρ is the density, μ is the viscosity, B is the PPI, ΔP is the inlet and outlet pressure difference, which is used to measure the resistance of the ventilator. The porosity e represents the ratio of the empty volume of the metal sponge to the total volume; PPI represents the number of holes per unit foot.

[0020] Specifically, the method for calculating the viscous drag coefficient and the inertial drag coefficient of the metal sponge area includes: placing the metal sponge area in the middle of a rectangular flow domain, performing Boolean difference between the rectangular flow domain and the metal sponge area to obtain a calculation domain, and meshing the calculation domain. After the meshing is completed, the mesh is imported into the fluid simulation software Fluent, and the calculation domain of the metal sponge area is calculated to obtain the viscous drag coefficient and the inertial drag coefficient of the metal sponge area.

[0021] Compared with the prior art, the present invention has the following technical effects:

[0022] The resistance correlation formula obtained by the method of the present invention can quickly predict the resistance of the metal sponge centrifugal ventilator, and the average error between the calculated value of the metal sponge centrifugal ventilator resistance obtained by using the correlation formula and the experimental value does not exceed 10%, which has good engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart of the method of the present invention;

[0024] Figure 2 It is a schematic diagram of the actual structure of a metal sponge centrifugal ventilator;

[0025] Figure 3 The metal sponge centrifugal ventilator model of the present invention and its computational domain and grid division; (a) is the metal sponge centrifugal ventilator model; (b) is the computational domain grid division of the metal sponge centrifugal ventilator;

[0026] Figure 4 It is the metal sponge area replaced by the porous medium model of the present invention; (a) is a single cell; (b) is the Kelvin structure metal sponge model;

[0027] Figure 5 The calculation domain and grid division of the metal sponge region of the present invention; (a) is the metal sponge calculation domain; (b) is the metal sponge calculation domain grid division;

[0028] Figure 6 The comparison result between the change trend of the ventilator resistance with the speed obtained by numerical calculation and the test value;

[0029] Figure 7 and Figure 8 It is the comparison result between the resistance of the metal sponge centrifugal ventilator calculated by the resistance correlation formula and the test value. DETAILED DESCRIPTION

[0030] The present invention adopts a porous medium model to replace the metal sponge in the metal sponge centrifugal ventilator, and adopts the distributed resistance attached to the fluid to replace the resistance caused by the metal sponge; because the porous medium model requires a viscous resistance coefficient and an inertial resistance coefficient, a simplified structural model of the metal sponge is established based on the key structural parameters of the actual metal sponge, and a numerical method is used to calculate and obtain the resistance data of the metal sponge, and its viscous resistance coefficient and inertial resistance coefficient are calculated; after the metal sponge in the ventilator is processed, a complete metal sponge centrifugal ventilator resistance calculation model can be formed, and the model is numerically calculated to obtain a metal sponge centrifugal ventilator resistance calculation correlation formula; the correlation formula can well predict the resistance size of the metal sponge centrifugal ventilator, and solves the problems existing in the prior art.

[0031] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0032] Embodiment 1:

[0033] like Figures 1 to 5 As shown, this embodiment provides a method for quickly predicting the resistance of a metal sponge centrifugal ventilator, comprising the following steps:

[0034] Step 1: Construct a metal sponge centrifugal ventilator model: According to the actual ventilator structure (such as Figure 2) Establish a metal sponge centrifugal ventilator model (such as Figure 3 a), the metal sponge centrifugal ventilator model includes a mass flow inlet, a metal sponge region and a pressure outlet; the metal sponge region is a porous medium model constructed using a Kelvin structure as a unit cell;

[0035] The Kelvin structure is a tetradecahedron structure including six quadrilaterals and eight hexagons; the length and width of the porous medium model can be adjusted according to the porosity e and pore density (PPI) B of the metal sponge structure parameters; Figure 4 As shown, Figure 4 a is a single cell structure. Figure 4 b is the Kelvin structure porous media model;

[0036] Step 2: construct the calculation domain of the metal sponge centrifugal ventilator model and divide the calculation domain into grids (such as Figure 3 b) Import the divided metal sponge centrifugal ventilator model grid into the fluid simulation software Fluent, and combine the viscous drag coefficient and inertial drag coefficient of the metal sponge area to perform numerical calculation to obtain the inlet and outlet pressure drop loss value of the metal sponge centrifugal ventilator;

[0037] The method for calculating the viscous resistance coefficient and inertial resistance coefficient of the metal sponge region includes: placing the metal sponge region in the middle of a rectangular parallelepiped flow domain (such as Figure 5 ), the rectangular flow domain and the metal sponge region are Boolean-subtracted to obtain the calculation domain, and the calculation domain is meshed, that is, the control equation is discretized in the spatial region for subsequent calculation; after the meshing is completed, the mesh is imported into the fluid simulation software Fluent, and the calculation domain of the metal sponge region is calculated to obtain the viscous resistance coefficient and inertial resistance coefficient of the metal sponge region;

[0038] Viscous drag coefficient and the inertial drag coefficient C F The calculation is done using the following formula:

[0039]

[0040] In the formula C F are the viscous drag coefficient and inertial drag coefficient of the metal sponge respectively; p1, v1 and p2, v2 are two different sets of pressure and velocity parameters at the inlet of the computational domain; p0, v0 are the pressure and velocity parameters at the outlet of the computational domain; L is the length of the entire computational domain (from the inlet to the outlet); μ is the aerodynamic viscosity coefficient; R is the gas constant; T is the air temperature;

[0041] In this embodiment, it is calculated that the viscous resistance coefficient of the Kelvin structure metal sponge with a porosity of 92% and a PPI of 25 is 6.669×10 7 , the inertial drag coefficient is 3147.

[0042] Step 3: Compare the inlet and outlet pressure drop loss values ​​of the metal sponge centrifugal ventilator obtained by numerical calculation in step 2 with the test values ​​of the actual ventilator. If the pressure drop loss values ​​obtained by numerical calculation are consistent with the change trends of the actual test values ​​with the rotation speed, it is reliable to use the porous medium model to replace the metal sponge region, and continue with the following steps:

[0043] Keep the boundary conditions consistent with the actual ventilator test values, and use compressible gas as the flow medium in the ventilator. Figure 6 The numerical calculation and experimental results of the resistance of the metal sponge centrifugal ventilator with a flow rate of 16±4g / s and different speeds, and with the installation of e92p25 (porosity of 92%, number of holes per unit foot is 25). Figure 6 It can be seen that the change trend of the ventilator resistance with the speed obtained by numerical calculation is consistent with the experimental value. After calculation, the average error of the resistance is 11.436%. Therefore, the porous medium model adopted in this scheme to replace the metal sponge processing method and the ventilator pressure drop loss calculated by Fluent have certain reliability and can meet the requirements of studying the resistance characteristics of metal sponge centrifugal ventilators.

[0044] Step 4: Use the orthogonal design method to design the calculation conditions: the factors affecting the ventilator resistance include speed, ventilation volume, outlet pressure, temperature, porosity and PPI; select five levels for each influencing factor, and use the six-factor five-level orthogonal design table to obtain the calculation conditions. Based on the range, determine the order of influence of each factor on the ventilator resistance within the given working condition range;

[0045] The level selection corresponding to each factor is shown in the following table:

[0046]

[0047] The orthogonal design table for calculation conditions is as follows:

[0048]

[0049]

[0050] Through the calculated results and based on the range, it is determined that under the given operating conditions, the order of influence of each factor on the ventilator resistance is speed, ventilation volume, porosity, PPI, temperature, and outlet pressure.

[0051]

[0052] Step 5: Use the metal sponge centrifugal ventilator model and grid in step 2 to calculate the working condition in step 4. Change the boundary conditions in Fluent according to the data in the orthogonal design table of the calculated working condition to obtain the pressure drop loss under different working conditions. Then, according to the order of the influence of each factor on the ventilator resistance obtained in step 4, use the π theorem to fit the pressure drop loss under different working conditions, and obtain the preliminary prediction formula of the pressure drop loss of the metal sponge centrifugal ventilator model:

[0053]

[0054] In the above formula, n is the rotation speed, Q is the flow rate of the incoming flow, p0 is the outlet pressure, ρ is the density of the incoming flow, μ is the viscosity, B is the pore density of the metal sponge, e is the porosity, c1, c2, c3, c4 are unknown coefficients;

[0055] Specifically, the π theorem is used to fit the pressure drop loss under different working conditions, including:

[0056] Select p0, ρ, and B as the basic physical quantities for dimensionless processing. The dimensions of the three basic physical quantities include all the dimensions involved. Use the π theorem to process the remaining parameters dimensionlessly. After calculation, the three dimensionless numbers obtained are:

[0057]

[0058] Where n, p0, Q, μ, and ρ represent the rotation speed, outlet pressure, flow rate, viscosity, and airflow density, respectively; the porosity e is a dimensionless quantity. The four dimensionless quantities are combined into the resistance correlation formula (2):

[0059]

[0060] The left side of the equation is the dimensionless formula of the prediction parameter, which is the relative resistance size in the present invention; the right side of the equation is the dimensionless number obtained by dimensionlessly converting each factor, which is combined into a power function type to establish a preliminary prediction formula (3) for the pressure drop loss of the metal sponge centrifugal ventilator.

[0061] Step 6: Use the least squares method to fit and solve the undetermined coefficients of the preliminary prediction formula for pressure drop loss to obtain the final calculation formula for pressure drop loss of the metal sponge centrifugal ventilator:

[0062]

[0063] In the above formula, n is the speed, Q is the flow rate, p0 is the outlet pressure, ρ is the density, μ is the viscosity, B is the PPI, ΔP is the inlet and outlet pressure difference, which is used to measure the resistance of the ventilator, the porosity e represents the ratio of the empty volume of the metal sponge to the total volume; PPI represents the number of holes per unit foot;

[0064] More specifically, the meanings of the parameters in the above formula are shown in the following table:

[0065]

[0066] When the working parameters of the metal sponge ventilator are given, the resistance of the ventilator can be quickly predicted using the above resistance correlation formula.

[0067] The comparison between the test value of the ventilator with a porosity of 92% and a PPI of 25 and the resistance calculated by the resistance correlation formula is as follows: Figure 7 As shown in the figure, the test value of the ventilator with a porosity of 94% and PPI45 is compared with the resistance calculated by the resistance correlation formula. Figure 8 As shown in the figure, it can be seen that the maximum error of the calculated resistance value of the ventilator compared with the experimental value is less than 15%, and the average error is about 10%. At higher flow and speed, the resistance value calculated by the resistance correlation formula has a further reduced error compared with the experimental value, and its maximum error is less than 10%. This shows that the metal sponge centrifugal ventilator resistance rapid prediction method of the present invention is effective.

[0068] When the rotation speed n, the incoming flow rate Q, the outlet pressure p0, the incoming flow density ρ and viscosity μ, the pore density B and the porosity e of the metal sponge centrifugal ventilator are known, the resistance can be calculated by using the resistance correlation formula obtained in the present invention, thus avoiding complicated and tedious test procedures, saving manpower and material resources, and providing an efficient method for predicting the resistance of a metal sponge centrifugal ventilator.

Claims

1. A method for quickly predicting the resistance of a metal sponge centrifugal ventilator, characterized in that: The method adopts a porous medium model to replace the metal sponge in the metal sponge centrifugal ventilator, adopts the distributed resistance attached to the porous medium model to replace the resistance caused by the metal sponge, constructs a complete metal sponge centrifugal ventilator model, performs numerical calculation on the model, and obtains the calculation formula of the pressure drop loss of the metal sponge centrifugal ventilator, so as to quickly predict the resistance of the metal sponge centrifugal ventilator. The following steps are involved: Step 1, constructing a metal sponge centrifugal ventilator model: establishing a metal sponge centrifugal ventilator model according to an actual ventilator structure, the metal sponge centrifugal ventilator model comprising a mass flow inlet, a metal sponge region and a pressure outlet; the metal sponge region is a porous medium model constructed using a Kelvin structure as a unit cell; Step 2, constructing a metal sponge centrifugal ventilator model calculation domain and meshing the calculation domain, importing the divided metal sponge centrifugal ventilator model mesh into the fluid simulation software Fluent, and combining the viscous resistance coefficient and inertial resistance coefficient of the metal sponge area to perform numerical calculation to obtain the inlet and outlet pressure drop loss value of the metal sponge centrifugal ventilator; Step 3, comparing the inlet and outlet pressure drop loss value of the metal sponge centrifugal ventilator obtained by numerical calculation in step 2 with the test value of the actual ventilator. If the pressure drop loss value obtained by numerical calculation is consistent with the change trend of the actual test value with the rotation speed, it is reliable to use the porous medium model to replace the metal sponge region, and continue with the following steps; Step 4: Use the orthogonal design method to design the calculation conditions: the factors affecting the ventilator resistance include speed, ventilation volume, outlet pressure, temperature, porosity and PPI; select five levels for each influencing factor, and use the six-factor five-level orthogonal design table to obtain the calculation conditions. Based on the range, determine the order of influence of each factor on the ventilator resistance within the given working condition range; Step 5: Use the metal sponge centrifugal ventilator model and grid of step 2 to calculate the working condition of step 4, change the boundary conditions in Fluent according to the data in the orthogonal design table of the calculated working condition, and obtain the pressure drop loss of different working conditions. Then, according to the order of the influence of various factors on the ventilator resistance obtained in step 4, use the π theorem to fit the pressure drop loss of different working conditions, and obtain the preliminary prediction formula of the pressure drop loss of the metal sponge centrifugal ventilator model; Step 6: Use the least squares method to fit and solve the unknown coefficients of the preliminary prediction formula for pressure drop loss to obtain the final calculation formula for the pressure drop loss of the metal sponge centrifugal ventilator.

2. The method for rapid prediction of resistance of a metal sponge centrifugal ventilator according to claim 1, characterized in that: The preliminary prediction formula for the pressure drop loss of the metal sponge centrifugal ventilator model is: （3） In the above formula, is the speed, Q is the flow rate, is the outlet pressure, is the incoming flow density, is the viscosity, B is the pore density of the metal sponge, is the porosity, c1, c2, c3, c4 are unknown coefficients; The calculation formula for the pressure drop loss of the metal sponge centrifugal ventilator is: In the above formula, n is the speed, Q is the flow rate, is the outlet pressure, is the density, is viscosity, B is PPI, The inlet and outlet pressure difference is used to measure the resistance of the ventilator and the porosity. It represents the ratio of the empty volume of the metal sponge to the total volume; Indicates the number of holes per foot.

3. The method for rapid prediction of resistance of a metal sponge centrifugal ventilator according to claim 2, characterized in that: The method for calculating the viscous drag coefficient and the inertial drag coefficient of the metal sponge area includes: placing the metal sponge area in the middle of a rectangular flow domain, performing Boolean difference between the rectangular flow domain and the metal sponge area to obtain a calculation domain, and meshing the calculation domain. After the meshing is completed, the mesh is imported into the fluid simulation software Fluent, and the calculation domain of the metal sponge area is calculated to obtain the viscous drag coefficient and the inertial drag coefficient of the metal sponge area.

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