Method for acquiring overtemperature area of oil return pipeline of lubricating oil system

Abstract

The invention provides a method for acquiring an overtemperature area of an oil return pipeline of a lubricating oil system. An oil return pipeline solid domain and a lubricating oil fluid domain are constructed, initial thermal boundary conditions are given, simulation software is used for fluid domain flow thermal coupling calculation, and a first fluid temperature field, a first solid temperature field and a first heat exchange coefficient are obtained; constructing a geometric model solid domain having a heat exchange component with the oil return pipeline, and obtaining a second solid temperature field after heat exchange between the oil return pipeline solid domain and the geometric model solid domain; replacing the first solid temperature field with a second fixed temperature field numerical value, and performing flow thermal coupling calculation again to obtain a second fluid temperature field and a third solid temperature field; the steps are repeated until the difference value between the third solid temperature field and the second solid temperature field meets the iteration requirement; and extracting an over-temperature area in the oil return pipeline solid domain temperature field and / or the lubricating oil fluid domain temperature field meeting iteration requirements. According to the method, the overtemperature area can be accurately judged and captured.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aero-engine, in particular to a simulation method of oil pipeline. BACKGROUND

[0002] The oil system is an important part of the aero-engine, and the bearing cavity where each bearing is located is filled with lubricating oil. The lubricating oil lubricates the bearing and carries away the heat generated by the bearing and the seal, thereby ensuring the stable working temperature of the bearing cavity. Therefore, it is necessary to effectively determine and capture the over-temperature area of the oil return pipeline of the oil system to avoid the influence of the high-temperature area on the normal operation and service life of the engine. SUMMARY

[0003] An object of the present application is to provide an over-temperature area acquisition method of an oil return pipeline of an oil system, which can effectively determine and capture the over-temperature area through thermal simulation.

[0004] To achieve the above-mentioned object, the over-temperature area acquisition method of the oil return pipeline of the oil system comprises the following steps: S101. Constructing a user-defined function, the user-defined function comprising a calculation function and a data transfer function; S102. Constructing a solid domain of the oil return pipeline and a lubricating oil fluid domain, assigning an initial thermal boundary condition, and using a fluid mechanics simulation module of a simulation software to perform fluid-thermal coupling calculation to obtain a first fluid temperature field, a first solid temperature field and a first heat transfer coefficient; S103. Constructing a solid domain of a geometric model of a component in thermal exchange with the oil return pipeline, based on the calculation function, using a heat transfer module of the simulation software to perform thermal-solid coupling calculation to obtain a second solid temperature field after the solid domain of the oil return pipeline and the solid domain of the geometric model exchange heat; S104. Based on the data transfer function, using the second fixed temperature field value to replace the first solid temperature field, and using the fluid mechanics simulation module to perform fluid-thermal coupling calculation again to obtain a second fluid temperature field and a third solid temperature field; S105. Repeating steps S104 and S103 until the difference between the third solid temperature field and the second solid temperature field meets the iteration requirement; S106. Extracting the over-temperature area in the solid domain temperature field of the oil return pipeline and / or the lubricating oil fluid domain temperature field that meets the iteration requirement.

[0005] In one or more embodiments, the calculation function comprises a user-defined function of the variation of the outside air temperature of the oil pipeline, the air flow rate with the rotation speed and time, a user-defined function of the variation of the oil supply amount with the rotation speed and time, and a user-defined function of the variation of the intake amount with the rotation speed and time.

[0006] In one or more embodiments, in step S102, the following steps are further included: dividing the grid of the solid domain of the oil return pipeline and the lubricating oil fluid domain; setting the material properties; selecting the phase; selecting the solution method.

[0007] In one or more embodiments, the first phase air, the second phase oil.

[0008] In one or more embodiments, in step S103, further comprising the following steps: dividing a mesh on the geometric model; setting a thermal radiation condition; setting a thermal convection condition using the calculation function.

[0009] In one or more embodiments, the thermal radiation condition is face-to-face radiation.

[0010] In one or more embodiments, in step S104, the pipe wall surface temperature field of the second solid temperature field is assigned to the pipe wall surface of the oil return pipe solid domain.

[0011] In one or more embodiments, in step S105, the difference between the third solid temperature field and the second solid temperature field is less than 10% of the second solid temperature field as a condition for completing iteration.

[0012] In one or more embodiments, in step S103, the geometric model solid domain includes a casing outer surface sheet solid domain and a bracket solid domain connected to the oil return pipe of the casing.

[0013] In one or more embodiments, the data transfer function is a function of transferring the numerical value calculated by the heat transfer module to the fluid mechanics simulation module.

[0014] The above-mentioned super-temperature region acquisition method considers the heat conduction, heat convection and heat radiation received by the oil return pipe of the aero-engine oil system and the complex physical environment in which the oil return pipe is located, and performs multi-physical field coupling simulation analysis to obtain the internal fluid flow of the oil return pipe, the pipe wall temperature field distribution, the pipe heat exchange capacity and the pipe structure strength, thereby effectively judging and capturing the super-temperature region and providing accurate guidance for the design of the aero-engine. BRIEF DESCRIPTION OF DRAWINGS

[0015] The above-mentioned and other features, properties and advantages of the present application will become more apparent through the following description with reference to the accompanying drawings and embodiments, in which:

[0016] Figure 1 is a schematic diagram of an oil system;

[0017] Figure 2 is a schematic diagram of the flow path of the oil return pipe;

[0018] Figure 3 is a flowchart of a super-temperature region acquisition method for the oil return pipe of the oil system;

[0019] Figure 4This is a flowchart of the simulation analysis method. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments and accompanying drawings. More details are set forth in the following description in order to provide a full understanding of the present invention. However, the present invention can obviously be implemented in many other ways different from those described herein. Those skilled in the art can make similar extensions and derivations based on actual application situations without departing from the spirit of the present invention. Therefore, the scope of protection of the present invention should not be limited by the content of this specific embodiment.

[0021] It should be noted that these and other accompanying drawings are merely examples and are not drawn to scale, and should not be construed as limiting the scope of protection of the present invention.

[0022] Modern aircraft engines often have multiple rotating shafts, and multiple bearings support these rotating shafts. The bearing cavities of each bearing are filled with lubricating oil to achieve the functions of lubrication and heat dissipation.

[0023] The lubricating oil in the bearing cavity flows out of the bearing cavity through the return oil pipe and returns to the oil tank. Because the bearing cavity is connected to the casing and turbine support plate, the return oil pipe passes through high-temperature areas such as the turbine, combustion chamber, and high-pressure compressor outer casing outside the core engine compartment. In these areas, the high ambient temperature leads to a high overall temperature level in the return oil pipe. Direct contact between the pipe and the casing and other areas results in localized high temperatures in these contact areas. The pipe's close proximity to the core engine compartment, containing high-temperature components such as the low-pressure turbine, high-pressure turbine, combustion chamber, and high-pressure compressor, causes localized high temperatures in the pipe due to heat radiation from the nacelle walls. The high external air temperature also affects the pipe's temperature field through convective heat transfer. The pipe is connected to the casing via a support structure, which is also hot, leading to localized high-temperature areas on the pipe wall due to direct heat conduction. Furthermore, the internal fluid flow is a two-phase flow (gas-liquid), and the uneven flow of lubricating oil and air within the pipe, influenced by gravity and preceding flow, results in uneven temperature distribution on the return oil pipe wall.

[0024] like Figure 1 As shown, the lubricating oil system 2 includes a multi-stage process: the lubricating oil starts from the oil tank 201, passes through the pressurization stage 202 of the lubrication component, and enters each stage of heat exchangers for heat exchange. The heat exchangers include an air-lubricating oil radiator 203, a fuel-lubricating oil heat exchanger 204, a servo fuel heater 205, etc. After the lubricating oil is cooled in each heat exchanger, it flows into each bearing cavity 206. The lubricating oil provides lubrication and heat dissipation for the bearing 207 in the bearing cavity 206. The lubricating oil flows out of the bearing cavity 206 from the return oil pipeline 208 and flows back to the return oil stage 209 of the lubrication component, and finally returns to the oil tank 201, completing the circulation of the lubricating oil.

[0025] Furthermore, such as Figure 2 As shown, the lubricating oil return line 208 extends from the bearing cavity 206, passes through the low-pressure turbine support plate 301 of the aero-engine, and extends out of the aero-engine casing 302. The return line outside the casing is close to the outer casing of the aero-engine, passes near the low-pressure turbine 303, high-pressure turbine 304, and combustion chamber 305, and then connects to the lubrication assembly return stage 209. The flowing medium in the return line is heated lubricating oil and air leaking from the bearing cavity.

[0026] The low-pressure turbine support plate 301, low-pressure turbine 303, high-pressure turbine 304, and outer casing of combustion chamber 305 have high temperatures, which will exert strong heat radiation on the nearby oil return line 208. The lubricating oil flows through the bearing cavity and the bearing cavity wall heated by the high-temperature gas in the booster chamber, and has a high temperature when it flows out of the bearing cavity.

[0027] Therefore, the return oil pipe of the aero-engine lubricating oil system passes through multiple high-temperature regions, presenting several high-temperature risk points. Inside the return oil pipe, due to the uneven flow of the gas-liquid two-phase flow, a certain temperature difference exists between the pipe walls. These high-temperature risk points affect lubricating oil coking, while the temperature difference between the pipe walls affects the overall thermal deformation and strength of the pipeline. Based on this, accurate identification and detection of lubricating oil overheating areas are crucial when optimizing and improving the engine. Thermal simulation analysis of the lubricating oil pipeline and its internal lubricating oil is particularly important, as it allows for risk identification before failures occur and the development of corresponding corrective and optimization measures.

[0028] This invention provides a method for obtaining the overheated area of ​​the return oil pipeline of a lubricating oil system, which can accurately capture dangerous areas and predict pipeline coking before actual testing and application of aero-engines, and provide guidance for engine design.

[0029] Reference Figure 3 and Figure 4The method, as understood, includes the following steps: S101. Constructing a custom function, which includes a calculation function and a data transfer function; S102. Constructing the solid domain and lubricating oil fluid domain of the return oil pipeline, assigning initial thermal boundary conditions, and using the fluid dynamics simulation module of the simulation software to perform fluid-thermal coupling calculations to obtain the first fluid temperature field, the first solid temperature field, and the first heat transfer coefficient; S103. Constructing the geometric model solid domain of the components that exchange heat with the return oil pipeline, and based on the calculation function, using the heat transfer module of the simulation software to perform thermo-solid coupling calculations to obtain the return oil pipeline... S104. The second solid temperature field after heat exchange between the solid domain of the pipeline and the solid domain of the geometric model; S105. Based on the data transfer function, the second fixed temperature field value is used to replace the first solid temperature field, and the fluid dynamics simulation module is used again to perform fluid-thermal coupling calculation to obtain the second fluid temperature field and the third solid temperature field; S106. Repeat steps S107 and S108 until the difference between the third solid temperature field and the second solid temperature field meets the iteration requirements; S107. Extract the over-temperature region in the solid domain temperature field and / or lubricating oil fluid domain temperature field of the return oil pipeline that meets the iteration requirements.

[0030] Specifically, in step S101, the custom function is code that implements specific functions, used to extend and customize functionality. Custom functions include calculation functions and data transfer functions. Calculation functions include custom functions based on the oil supply rate calculated by the lubricating oil system and the intake air rate calculated by the air system, varying with rotational speed and time; and custom functions based on the external nacelle's external air temperature and air velocity, varying with rotational speed and time. The data transfer function is a function that transfers the values ​​calculated by the heat transfer module to the fluid dynamics simulation module, aiming to transfer the values ​​and data from the heat transfer module to the fluid dynamics simulation module.

[0031] In step S102, the specific steps are as follows: Mesh the solid domain and lubricating oil fluid domain of the return oil pipeline using mesh generation software. The fluid domain portion uses a structured hexahedral mesh and boundary layers are defined. Boundary conditions are set and output to the CFD software. In the CFD software, the mesh generation is checked for correctness, and the mesh is optimized and smoothed, with units set according to the actual dimensions. A fluid simulation model is selected. In some embodiments, the implicit VOF model in the transient multiphase flow model is used, and the volume force equations are enabled. The two-phase interface option is set to Sharp type. The turbulence model is selected as the k-epsilon Realizable model, and the near-wall surface uses Scalable Wall. The process involves: using the Functions method; opening the energy equation; importing the aforementioned custom function; setting material properties, including the physical parameters of air and lubricating oil based on the actual lubricating oil and operating temperature of the aero-engine, and setting the physical parameters of the pipe wall material; selecting phases, choosing air as the first phase and oil as the second phase, and setting the corresponding surface tension coefficients; setting domain conditions: defining the internal region of the pipe as the fluid domain and the external region as the solid domain; setting boundary conditions, such as setting inlet and outlet boundary conditions and pipe wall boundary conditions; selecting the solution method, such as selecting the coupled mode for pressure-velocity coupling, and selecting the second-order upwind finite difference scheme for each equation; finally, setting calculation parameters, such as setting the step size to 0.001s and setting 1000 time steps for calculation. Ultimately, the first fluid temperature field, the first solid temperature field, and the first heat transfer coefficient are obtained, along with initial values ​​for the pipe inner wall temperature field and heat transfer coefficient.

[0032] Step S103 specifically includes the following steps: dividing the geometric model in the heat transfer module into a mesh, the geometric model in the heat transfer module including but not limited to the outer surface sheet of the casing, the support connecting the casing and the pipeline, and the pipeline solid domain; assigning the initial parameters such as the first fluid temperature field, the first solid temperature field, the pipeline inner wall temperature field, and the first heat transfer coefficient to the pipeline inner wall in the heat transfer module; setting thermal radiation conditions, adding the casing to the pipeline thermal radiation boundary in the heat transfer module, selecting face-to-face radiation as the type, and selecting the radiation heat transfer coefficient according to the actual situation; setting thermal convection conditions, setting thermal convection conditions on the pipeline outer wall through the calculation function in the user-defined function, the value of which is related to the wind speed and temperature; setting temperature conditions, setting temperature conditions on the outer surface of the casing according to the actual temperature of the casing; finally running steady-state thermal analysis to perform thermo-solid coupling calculations and obtain the second solid temperature field after heat exchange between the return oil pipeline solid domain and the geometric model solid domain.

[0033] In step S104, the second solid temperature field obtained in step S103 is used to open the energy equation and assign the pipe wall temperature field to the pipe wall of the return oil pipe solid domain in the fluid dynamics simulation module. Boundary conditions, step size and solution method are set in the fluid dynamics simulation module to perform flow-heat transient analysis. The fluid dynamics simulation module is used again to perform flow-heat coupling calculation to obtain the second fluid temperature field and the third solid temperature field.

[0034] In step S105, the third solid temperature field and the second solid temperature field are compared. If the difference between the second solid temperature field and the third solid temperature field exceeds 10%, the data of the second solid temperature field is replaced with the data of the third solid temperature field, and the data is substituted into steps S103 and S104 for recalculation. The iteration continues until the difference between the third solid temperature field and the second solid temperature field is less than 10% of the second solid temperature field, which is the condition for the iteration to be completed.

[0035] After the final iteration is completed, step S106 is performed to extract the over-temperature region in the solid domain temperature field and / or lubricating oil fluid domain temperature field of the return oil pipeline that meets the iteration requirements, so as to guide the solution of problems such as pipeline coking prediction and pipeline strength positioning.

[0036] The aforementioned method employs multiphysics flow-thermal-structure interaction (MPF) simulation to analyze the return oil pipe of an aero-engine lubricating oil system and its complex physical environment. It comprehensively considers heat conduction, convection, and radiation within the pipe, performing MPF simulation analysis to obtain information on the internal fluid flow, pipe wall temperature distribution, heat exchange capacity, and structural strength. CFD software is used to calculate the internal flow within the fluid domain. The flow pattern characteristics are then substituted into the steady-state thermal analysis model of the heat transfer module, strictly distinguishing between gas and liquid flows through the wall. Steady-state thermal analysis calculations are performed in the heat transfer module to obtain the temperature field. The pipe wall temperature is then substituted into the solid domain of the CFD software to calculate the fluid domain CFD thermal analysis, obtaining the fluid temperature field. This process is iterated repeatedly to ultimately obtain the fluid flow characteristics, pipe temperature field, and fluid temperature field. This method can accurately identify hazardous areas before actual aero-engine testing and application, providing detailed guidance data for engine design and problem-solving.

[0037] It should be noted that the use of terms such as "first" and "second" to define the components in the above content is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this application.

[0038] Furthermore, this application uses specific terms to describe embodiments of the application. For example, "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic related to at least one embodiment of the application. Therefore, it should be emphasized and noted that "an embodiment," "one embodiment," or "an alternative embodiment" mentioned twice or more in different locations in this specification do not necessarily refer to the same embodiment. In addition, certain features, structures, or characteristics in one or more embodiments of the application can be appropriately combined.

[0039] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any variations and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the invention, fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for obtaining the over-temperature zone of the return oil pipeline in a lubricating oil system, characterized in that, Includes the following steps: S101. Construct a user-defined function, which includes a calculation function and a data transfer function; S102. Construct the solid domain and lubricating oil fluid domain of the return oil pipeline, assign initial thermal boundary conditions, and use the fluid dynamics simulation module of the simulation software to perform fluid domain flow-thermal coupling calculations to obtain the first fluid temperature field, the first solid temperature field, and the first heat transfer coefficient. S103. Construct a geometric model solid domain that has heat exchange components with the return oil pipeline. Based on the calculation function, use the heat transfer module of the simulation software to perform thermo-solid coupling calculation to obtain the second solid temperature field after the return oil pipeline solid domain and the geometric model solid domain exchange heat. S104. Based on the data transfer function, the first solid temperature field is replaced by the second fixed temperature field value, and the fluid dynamics simulation module is used again to perform fluid-thermal coupling calculation to obtain the second fluid temperature field and the third solid temperature field. S105. Repeat steps S104 and S103 until the difference between the third solid temperature field and the second solid temperature field meets the iteration requirements; S106. Extract the over-temperature region within the solid domain temperature field and / or the lubricating oil fluid domain temperature field of the return oil pipeline that meets the iteration requirements.

2. The method as described in claim 1, characterized in that, The calculation functions include custom functions for the changes in external air temperature and air velocity in the lubricating oil pipeline with rotational speed and time, custom functions for the changes in oil supply with rotational speed and time, and custom functions for the changes in intake air volume with rotational speed and time.

3. The method as described in claim 1, characterized in that, Step S102 further includes the following steps: The solid domain and the lubricating oil fluid domain of the return oil pipeline are meshed; material properties are set; phase selection is performed; and a solution method is selected.

4. The method as described in claim 3, characterized in that, The first phase is air, and the second phase is oil.

5. The method as described in claim 1, characterized in that, Step S103 further includes the following steps: The geometric model is meshed; thermal radiation conditions are set; and thermal convection conditions are set using the calculation function.

6. The method as described in claim 5, characterized in that, Make the thermal radiation conditions face-to-face radiation.

7. The method as described in claim 1, characterized in that, In step S104, the pipe wall temperature field of the second solid temperature field is applied to the pipe wall of the solid domain of the return oil pipeline.

8. The method as described in claim 1, characterized in that, In step S105, the difference between the third solid temperature field and the second solid temperature field is less than 10% of the second solid temperature field as a condition for the iteration to be completed.

9. The method as described in claim 1, characterized in that, In step S103, the geometric model solid domain includes the outer surface sheet solid domain of the casing and the support solid domain connecting the casing to the oil return pipeline.

10. The method as described in claim 1, characterized in that, The data transfer function is a function that transfers the values ​​calculated by the heat transfer module to the fluid dynamics simulation module.

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