Method and device for calculating injection ratio of aero-engine test bed

Abstract

The invention discloses an aero-engine test bed injection ratio calculation method. The method comprises the following steps: providing relevant parameters of an engine and a test workshop, and taking a quarter section of an axial normal plane at the tail end of a spray pipe of the test workshop as a calculation section; establishing a two-dimensional N-S equation under the steady flow field; substituting a central value theorem formula into a two-dimensional N-S equation to solve axial speed distribution; according to the method, large-scale commercial calculation software is not needed, the method is simple, the calculation duration of analog calculation is effectively shortened, and the design efficiency of the aircraft engine test bed is improved. The invention further provides a computing device.

Description

Technical Field

[0001] The invention belongs to the field of aeroengines, and in particular relates to a method for calculating the ejection ratio of an aeroengine test bench and a computer system. Background Art

[0002] In the development process of high bypass ratio turbofan aero-engines, indoor whole-machine testing is an important part of the development process. Therefore, it is necessary to provide an aero-engine test bench that meets the requirements for the whole-machine test of the aero-engine. In the aerodynamic design stage of the test bench, the ejection ratio is an important aerodynamic parameter. Only by determining the ejection ratio can the subsequent structural design of the test bench be carried out. At present, when designing an aero-engine test bench, engineers will provide an initial value of the ejection ratio based on experience, and then use large-scale commercial simulation software for simulation, and obtain the final ejection ratio value through multiple rounds of iteration. This process requires a lot of time and computing resources, which greatly prolongs the development cycle of the aero-engine and increases the design cost. Therefore, providing a more efficient ejection ratio calculation method to reduce the amount of parameter iteration calculation is of great practical significance for optimizing the design cost of the aero-engine. Summary of the invention

[0003] The purpose of the present invention is to provide a method for calculating the ejection ratio of an aircraft engine test bench to reduce the workload of simulation calculations. The present invention also provides a calculation device for calculating the ejection ratio of an aircraft engine test bench.

[0004] An embodiment of one aspect of the present invention provides a method for calculating the ejection ratio of an aircraft engine test bench, providing aerodynamic parameters, geometric parameters of the engine and geometric parameters of the test bench, and comprising the following steps:

[0005] Step a): Take the normal plane section of the test workshop at the axial direction where the engine nozzle end is located, and establish the two-dimensional NS equation under the steady flow field;

[0006] Step b): combining the aerodynamic parameters and geometric parameters of the engine and the geometric parameters of the test chamber with the flow field center value theorem formula and the two-dimensional NS equation under the steady flow field to obtain the axial velocity distribution;

[0007] Step c): Calculate the test vehicle flow rate based on the axial velocity distribution, and calculate the estimated value of the ejection ratio in combination with the engine flow rate.

[0008] The above method uses the central value theorem combined with the two-dimensional NS equation to simulate the distribution of axial air flow velocity in a two-dimensional plane. Compared with conventional three-dimensional simulation calculations, it effectively reduces the amount of calculation and can complete the simulation calculation without large-scale commercial software, effectively improving the design efficiency of the engine.

[0009] Furthermore, the calculation process of the axial velocity distribution includes: obtaining a viscous shear stress-velocity function through the two-dimensional NS equation under the steady flow field, and then obtaining the axial velocity distribution through the viscous shear stress function. The main influence of air flow in the test workshop (excluding the engine) is viscous shear stress. Simplifying the NS equation can effectively reduce the computational requirements for solving the numerical solution of the velocity distribution.

[0010] Furthermore, the calculation process of the axial velocity distribution also includes: obtaining a pressure difference-velocity function through the two-dimensional NS equation under the steady flow field, and then using the pressure difference-velocity function to update the axial velocity distribution obtained through the viscous shear stress function, and performing subsequent calculations with the updated axial velocity distribution. During the flow of air between the inner and outer ducts, the pressure difference is the main influencing factor. Therefore, it is necessary to use the pressure difference-velocity function to update the axial velocity distribution.

[0011] Furthermore, the method further comprises a testing step, providing an iteration threshold, and when the global average velocity difference of the axial velocity obtained in step b) exceeds the iteration threshold, step b) is repeated for iteration, and the process is as follows:

[0012] The axial velocity distribution u is obtained by the i-th calculation i , calculate the global average velocity difference

[0013] when If it is less than the iteration threshold, the iteration is terminated and u i as the axial velocity distribution output;

[0014] when If u is greater than the iteration threshold, i Substitute it into the step b) as input and perform the (i+1)th calculation to obtain the axial velocity distribution u i+1 ;

[0015] Repeat the above process, where u_ i According to u i Calculate the average velocity within the cross section.

[0016] The axial velocity distribution obtained by one calculation is not necessarily convergent, so multiple iterative calculations are required until the solution obtained by the differential equation meets the iteration threshold requirement.

[0017] Furthermore, after dimensionless transformation, the iteration threshold is set to 10 -4 -10 -3 The specific value of the iteration threshold determines the accuracy of the calculation results and the overall amount of calculation.

[0018] Furthermore, the step c) further includes a calibration calculation error step:

[0019] If the speed difference between the external outlet and the internal outlet is less than 1%, and Ejection ratio after error correction

[0020] If the speed difference between the external outlet and the internal outlet is less than 1%, and Ejection ratio after error correction

[0021] If the velocity difference between the outer and inner outlets is greater than 1%, and the outer outlet velocity is greater than the inner outlet velocity, the ejection ratio after error correction is

[0022] If the velocity difference between the outer and inner outlets is greater than 1%, and the outer outlet velocity is less than the inner outlet velocity, the ejection ratio after error correction is in is the estimated value of the average flow velocity of the complete section of the test chamber at the upstream of the front end of the engine inlet five times the diameter of the engine inlet, and k is the air specific heat ratio. Based on a large amount of practical engineering experience, the inventor found that it is necessary to correct the error of the results obtained by numerical simulation.

[0023] Furthermore, the method also includes a step of calibrating the ejection tube error: the final ejection ratio Where D' is the diameter of the ejector tube section of equal diameter, and D is the diameter of the engine intake duct. After a lot of engineering practice experience, the inventor found that it is necessary to include the influence of the ejector tube into the ejection ratio calculation and correct the simulation results.

[0024] Furthermore, the characteristic is that, in the calculation process, the ideal gas state equation is used to perform temperature correction on the density of the gas in the inner channel. The temperature of the gas in the inner channel is high, and its density needs to be corrected.

[0025] Furthermore, in the calculation process, according to the principle of symmetry, a quarter of the axial normal plane section of the test vehicle at the end of the engine nozzle is taken as the calculation section. Taking a quarter of the section as the calculation section can effectively reduce the amount of calculation of the simulation calculation.

[0026] According to another embodiment of the present invention, there is provided a computing device which is installed with and capable of executing the method for calculating the ejection ratio of an aircraft engine test bench in any of the aforementioned embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of a calculation cross section in an embodiment;

[0028] Figure 2A schematic diagram of circumferential velocity distribution calculated by MATLAB in one embodiment;

[0029] Figure 3 Schematic diagram of axial velocity distribution contours calculated in one embodiment.

[0030] The purpose of the above drawings is to explain the present invention in detail so that those skilled in the art can understand the technical concept of the present invention, but it is not intended to limit the present invention. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0032] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The phrase appearing in various locations in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive independent or alternative embodiments. Those skilled in the art should be able to understand that the embodiments herein may be combined with other embodiments without causing structural conflicts.

[0033] In the description of this document, terms indicating orientation or positional relationships, such as "up", "down", "left", "right", "horizontal", "vertical", "height", "length", and "width", are intended to accurately describe the embodiments and simplify the description, but are not intended to limit the parts or structures involved to have a specific orientation, be installed or operate in a specific orientation, and should not be construed as a limitation on the embodiments in this document.

[0034] In the process of designing an engine test bench, the ejection ratio of the test bench must be determined first. If experimental testing or large-scale commercial software is used for calculation and simulation, it will incur high costs and consume a lot of man-hours. Whether using the experimental method or using commercial software for three-dimensional simulation calculations, the required man-hours are more than 120 (hours*man), and the cost is high, which seriously restricts the efficiency of aircraft engine development and design.

[0035] In order to solve the above problem, an embodiment of one aspect of the present invention provides a method for calculating the ejection ratio of an aircraft engine test bench.

[0036] When conducting the engine test, the engine is placed at the center of the cross section of the test chamber. In a preferred embodiment, according to the principle of symmetry, Figure 1As shown, a quarter section of the axial normal plane of the test chamber at the position of the engine nozzle end is intercepted as a calculation section and a coordinate system is established, wherein the x direction (not shown) is the engine axial direction, the yz plane is the axial normal plane, and the calculation section includes the engine inner duct 1, outer duct 2 and test chamber 3. At the same time, the aerodynamic parameters of the engine (including inner and outer duct temperatures, air flow velocity), geometric parameters (inlet duct, inner and outer duct diameters) and geometric parameters of the test chamber are provided as basic parameters for starting calculation. Unless otherwise specified, the numerical values ​​involved in the embodiments are dimensionless when performing calculations.

[0037] Step a): Couple the global flow field through viscous shear force.

[0038] According to the two-dimensional NS equation:

[0039]

[0040] Among them, u is the axial velocity, τ is the shear stress, f is the volume force, and the other symbols are in accordance with the general mathematical expression standards. When solving the steady flow field, can be simplified to

[0041] Step b): According to the flow field center value theorem formula, if Δu = 0 (where Δ is the Laplace operator), the rectangular coordinate system is converted into a cylindrical coordinate system:

[0042]

[0043] Where ω is the angular velocity, n is a natural number, B(x, r) is the surface for loop integral calculation, and the remaining symbolic expressions conform to general mathematical specifications.

[0044] For the air flow within the test room 3, the main influence is the viscous shear stress. According to the NS equation, there is a viscous shear stress-velocity function relationship:

[0045]

[0046] Where μ is the viscosity coefficient, v is the y-speed, and the other symbols conform to general mathematical specifications.

[0047] The aerodynamic parameters, geometric parameters of the engine and the geometric parameters of the test chamber are substituted into the flow field center value theorem formula, the viscous shear stress is added to the test chamber flow field and the axial velocity center value theorem is applied to solve it, and the axial velocity distribution u' is obtained.

[0048] Furthermore, for the air flow within the inner duct 1 and the outer duct 2, the main influencing factor is the pressure difference. According to the NS equation, there is a pressure difference-velocity function relationship:

[0049]

[0050] Where ρ is the air density, P is the pressure, and the rest of the expressions conform to general mathematical standards.

[0051] The influence of the pressure difference on the air flow in the inner duct 1 and the outer duct 2 is superimposed on the fluid equation dominated by the viscous shear stress to update the axial velocity distribution u' and obtain the updated axial velocity distribution u.

[0052] In a preferred embodiment, since the temperature in the inner channel 1 is relatively high, the gas density in the inner channel 1 needs to be temperature corrected using the ideal gas state equation: ρ = P / RT, where R is the gas constant and T is the temperature.

[0053] Step c): For a given aircraft engine operating condition, the air flow m1 is determined; based on the axial velocity distribution u, the flow m2 within the test bench 3 section can be calculated, and thus the estimated value of the aircraft engine test bench ejection ratio can be calculated.

[0054] Since the analytical solution of the NS equation cannot be obtained in general, in a preferred embodiment, the above calculation process can be solved by numerical solution using computing software such as MATLAB.

[0055] In some embodiments, the axial velocity distribution u obtained by a single calculation is often not convergent and needs to be iteratively calculated. In a preferred embodiment, step b) also includes a test step, providing an iteration threshold d, calculating the global average velocity difference of the axial velocity distribution u when It is necessary to substitute the axial velocity distribution u as the input into the NS equation and re-execute step b) until the calculated value is The specific process is as follows:

[0056] The axial velocity distribution u is obtained by the i-th calculation i , calculate the global average velocity difference

[0057] when The iteration ends and u i as the axial velocity distribution output;

[0058] when will u i Substitute it into the step b) as input and perform the (i+1)th calculation to obtain the axial velocity distribution u i+1 ;

[0059] Repeat the above process until the iteration ends, According to u iCalculate the average velocity within the cross section.

[0060] In the preferred embodiment, the iteration threshold d is set to 10 -4 ~10 -3 .

[0061] In one embodiment, the final axial velocity distribution u calculated using MATLAB is as follows: Figure 2 The calculated axial velocity distribution contour map is shown in Figure 3 shown.

[0062] The inventors have found in a large number of engineering practices that under some working conditions, there is a certain error between the ejection ratio calculated by the above process and the actual ejection ratio of the test bench. In a preferred embodiment, after step c), a step of calibrating the calculated error is also included to correct the ejection ratio:

[0063] If the speed difference between the external outlet and the internal outlet is less than 1%, and Ejection ratio after error correction

[0064] If the speed difference between the external outlet and the internal outlet is less than 1%, and Ejection ratio after error correction

[0065] If the velocity difference between the outer and inner outlets is greater than 1%, and the outer outlet velocity is greater than the inner outlet velocity, the ejection ratio after error correction is

[0066] If the velocity difference between the outer and inner outlets is greater than 1%, and the outer outlet velocity is less than the inner outlet velocity, the ejection ratio after error correction is

[0067] in is an estimated value of the average flow velocity of the complete cross section of the test workshop at a position five times the engine inlet diameter upstream of the front end of the engine inlet, which can be obtained by integrating u in the entire cross section, and k is the air specific heat ratio.

[0068] In engineering practice, an ejector is also installed in the engine ground test workshop to guide and silence the gas ejected by the engine and then discharge it into the atmosphere. The ejector will also have a significant impact on the airflow in the test workshop. Therefore, in the preferred embodiment, it also includes a step of calibrating the ejector error, introducing the ejector geometric parameters to calibrate the ejection ratio: the final ejection ratio Where D' is the ejector tube diameter and D is the engine intake duct diameter.

[0069] Through the above method, the amount of calculation for simulating the ejection ratio of the engine test bench can be effectively reduced, reducing the approximately 120 (hours * people) required for three-dimensional simulation with the help of large-scale commercial software to 2 (hours * people), effectively improving the design efficiency of the engine test bench and shortening the overall engine development cycle.

[0070] In other embodiments, the above calculation process can also be performed within the entire cross-section of the test workshop, but the calculation results are equivalent and the amount of calculation is greater.

[0071] Another embodiment of the present invention further provides a computing device, which is installed with and can run a program for executing the method for calculating the ejection ratio of an aircraft engine test bench provided in any of the above embodiments. In different embodiments, the computing device can be configured as a general-purpose computer, server or cloud computing device installed with a computing program, or can be configured as a specially designed computing device such as a single-chip microcomputer that can execute the relevant computing program.

[0072] The purpose of the above embodiments is to further explain the present invention in detail in conjunction with the accompanying drawings so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the claims of the present invention, the optimization or equivalent replacement of the method steps involved, or the combination of the implementation methods in different embodiments without any conflict of principles, all fall within the protection scope of the present invention.

Claims

1. A method for calculating the ejection ratio of an aircraft engine test bench, characterized in that: Provide engine aerodynamic parameters, geometric parameters and test workshop geometric parameters, and include the following steps: Step a): Take the normal plane section of the test chamber at the axial direction where the engine nozzle end is located, and establish the two-dimensional NS equation under the steady flow field; Step b): combining the aerodynamic parameters and geometric parameters of the engine and the geometric parameters of the test chamber with the flow field center value theorem formula and the two-dimensional NS equation under the steady flow field to obtain the axial velocity distribution; Step c): Calculate the test vehicle flow rate based on the axial velocity distribution, and calculate the estimated value of the ejection ratio in combination with the engine flow rate.

2. The method for calculating the ejection ratio of an aircraft engine test bench according to claim 1, characterized in that: The calculation process of the axial velocity distribution includes: obtaining a viscous shear stress-velocity function through the two-dimensional NS equation under the steady flow field, and then obtaining the axial velocity distribution through the viscous shear stress function.

3. The method for calculating the ejection ratio of an aircraft engine test bench according to claim 2, characterized in that: The calculation process of the axial velocity distribution also includes: obtaining a pressure difference-velocity function through the two-dimensional NS equation under the steady flow field, and then using the pressure difference-velocity function to update the axial velocity distribution obtained through the viscous shear stress function, and performing subsequent calculations with the updated axial velocity distribution.

4. The method for calculating the ejection ratio of an aircraft engine test bench according to claim 1 or 2, characterized in that: It also includes a testing step, providing an iteration threshold, when the global average velocity difference of the axial velocity obtained in step b) exceeds the iteration threshold, repeating step b) for iteration, the process is as follows: The axial velocity distribution u is obtained by the i-th calculation i , calculate the global average velocity difference when If it is less than the iteration threshold, the iteration is terminated and u i as the axial velocity distribution output; when If u is greater than the iteration threshold, i Substitute it into the step b) as input and perform the (i+1)th calculation to obtain the axial velocity distribution u i+1 ; Repeat the above process, where According to u i Calculate the average velocity within the cross section.

5. The method for calculating the ejection ratio of an aircraft engine test bench according to claim 4, characterized in that: After dimensionless transformation, the iteration threshold is set to 10. -4 -10 -3 .

6. The method for calculating the ejection ratio of an aircraft engine test bench according to claim 1 or 2, characterized in that: The step c) also includes a calibration calculation error step: If the speed difference between the external outlet and the internal outlet is less than 1%, and Ejection ratio after error correction If the speed difference between the external outlet and the internal outlet is less than 1%, and Ejection ratio after error correction If the velocity difference between the outer and inner outlets is greater than 1%, and the outer outlet velocity is greater than the inner outlet velocity, the ejection ratio after error correction is If the velocity difference between the outer and inner outlets is greater than 1%, and the outer outlet velocity is less than the inner outlet velocity, the ejection ratio after error correction is in is the estimated value of the average flow velocity of the complete cross section of the test vehicle at a position five times the diameter of the engine inlet duct upstream of the front end of the engine inlet duct, and k is the air specific heat ratio.

7. The method for calculating the ejection ratio of an aircraft engine test bench according to claim 6, characterized in that: It also includes the steps for calibrating the ejector tube error: Final ejection ratio Where D' is the ejector tube diameter and D is the engine intake duct diameter.

8. The method for calculating the ejection ratio of an aircraft engine test bench according to claim 1 or 2, characterized in that: In the calculation process, the ideal gas state equation is used to make temperature correction for the density of the internal gas.

9. The method for calculating the ejection ratio of an aircraft engine test bench according to claim 1 or 2, characterized in that: During the calculation process, according to the principle of symmetry, one quarter of the axial normal plane section of the test workshop at the end of the engine nozzle is taken as the calculation section.

10. A computing device, characterized in that: The computing device is installed with and can run a program for executing the method for calculating the ejection ratio of an aircraft engine test bench as claimed in any one of claims 1 to 9.

Images