Aero-engine turbine moving blade resonance point alternating stress prediction method

Abstract

The invention discloses an aero-engine turbine moving blade resonance point alternating stress prediction method, which comprises the following steps of: 1, generating a grid required by CFD (computational fluid dynamics) calculation according to geometric files of a turbine guide blade and a moving blade; 2, the resonance rotating speed of the movable blades is determined; step 3, carrying out grid steady CFD analysis under the resonance rotating speed; 4, carrying out grid non-full-ring unsteady calculation under the resonance rotating speed to obtain the modal force of the moving blade; 5, calculating the alternating stress of the turbine moving blade; 6, adjusting the static pressure of the outlet of the movable blade, and carrying out calculation again to obtain alternating stress; 7, changing the axial distance between the moving blade and the guide blade, and carrying out calculation again to obtain alternating stress; and 8, drawing a curve according to the alternating stress in the step 6 and the alternating stress in the step 7. The method has the beneficial effects that complex and long-time-consuming unsteady simulation does not need to be carried out on the turbine part, the method is convenient to use in the preliminary design stage of engineering, and the working efficiency is high.

Description

Technical Field

[0001] The invention relates to the technical field of aerodynamic elasticity mechanics of aircraft engine turbine components, and in particular to a method for predicting alternating stress at a resonance point of an aircraft engine turbine rotor blade. Background Art

[0002] Forced response is the vibration response of the blade after it is subjected to periodic aerodynamic excitation (wake, potential interference, inlet distortion, shock wave, etc.) from the upstream and downstream blade rows. When the external excitation frequency is the same as a certain natural frequency of the blade, resonance is induced. Once the alternating stress exceeds the limit value, it may lead to high-cycle fatigue failure of the blade. Usually, the turbine blades are subjected to the wake excitation of the upstream guide vanes, causing the alternating stress to exceed the limit. Designers predict the dangerous speed at which resonance occurs through the intersection of the blade natural frequency and the aerodynamic excitation line on the Campbell diagram, and avoid the resonance danger point within the operating speed by adjusting the blade natural frequency (such as changing the maximum thickness of the blade and the position of the maximum thickness, etc.). However, in actual work, it is difficult for designers to avoid all resonance points, especially the resonance points corresponding to high-order modes. Therefore, predicting the vibration response of the blade at the resonance point is critical for evaluating its high-cycle fatigue life.

[0003] In the prior art, the vibration response of the blade at the resonance point is predicted by forced response prediction based on the CFD (computational fluid dynamics) method. The principle is to simulate the movement of the fluid by numerically solving the control equations of fluid flow, such as the Navier-Stokes equations. In the forced response prediction, the effect of external excitation on the fluid and the structure is mainly considered. Although the existing forced response prediction based on the CFD method can deeply understand the interaction between the fluid and the structure and provide an important reference for design and optimization, the calculation of the forced response prediction based on the CFD method is time-consuming, which is inconvenient to use in the design stage, and seriously reduces the prediction efficiency.

[0004] Therefore, a method that can quickly predict alternating stress is urgently needed. Summary of the invention

[0005] In order to solve the above problems, especially to address the deficiencies in the prior art, the present invention provides a method for predicting alternating stress at the resonance point of a turbine blade of an aero-engine, which can solve the above problems.

[0006] To achieve the above purpose, the present invention adopts the following technical means:

[0007] A method for predicting alternating stress at a resonance point of a turbine rotor blade of an aero-engine comprises the following steps:

[0008] Step 1: Based on the geometry geomturbo file of the turbine guide vanes and turbine rotor blades, use the software to generate the mesh required for CFD calculation;

[0009] Step 2: Use software to perform modal analysis, calculate the natural frequency, vibration mode and corresponding maximum modal stress of the turbine blades at different speeds, and draw the Campbell diagram of the turbine blades to determine the resonant speed;

[0010] Step 3: Based on the resonant speed in step 2, specify the static pressure at the turbine blade outlet, and use the software to perform steady-state CFD calculations on the grid in step 1 to obtain steady-state results;

[0011] Step 4: Using the steady result obtained in step 3 as the initial field, use the software to perform the non-full-ring unsteady CFD calculation of the grid in step 1, obtain the unsteady pressure of the turbine blade at the blade passing frequency, and dot-product it with the corresponding vibration mode to obtain the modal force;

[0012] Step 5: Based on the modal stress obtained from the modal analysis in step 2 and the modal force obtained in step 4, assuming that the damping coefficient is a constant, calculate the alternating stress of the turbine blade;

[0013] Step 6: Adjust the static pressure at the rotor blade outlet, repeat steps 1 to 5, and obtain the alternating stress of the turbine rotor blade under different turbine guide vane pressure ratios;

[0014] Step 7: changing the axial spacing between the turbine moving blades and the turbine guide vanes, repeating steps 1 to 6, and obtaining a series of dimensionless alternating stresses under the axial spacing between the turbine moving blades and the turbine guide vanes;

[0015] Step 8: Draw a curve based on the alternating stress in step 6 and the alternating stress in step 7.

[0016] A further solution of the present invention is that in step 1, the grid required for CFD calculation is generated using Autogrid software.

[0017] A further solution of the present invention is that in step 1, the required grid is a single-channel two-row grid.

[0018] A further solution of the present invention is that in step 2, modal analysis is carried out using Ansys Mechanical software.

[0019] A further solution of the present invention is that in step 2, the natural frequency, vibration mode and corresponding maximum modal stress of the turbine blades at different rotation speeds are calculated taking into account the prestress.

[0020] A further solution of the present invention is that in the step 2, a modal Campbell diagram of the turbine blade is drawn based on the number of blades N of the turbine guide vane and the natural frequency of the vibration mode of the turbine blade.

[0021] A further solution of the present invention is that in step three, a mixing surface model of CFX software is used to carry out steady-state CFD calculation of the grid in step one.

[0022] A further solution of the present invention is that in step 4, the time tilt method of CFX software is used to carry out the unsteady CFD calculation of the non-full ring of the grid in step 1.

[0023] A further solution of the present invention is that in step 5, the calculation formula of the alternating stress of the turbine blade is:

[0024]

[0025] Among them, σ is the alternating stress, σ0 is the modal stress, is the modal force, Q is the damping coefficient, and ω is the natural frequency.

[0026] Beneficial effects of the present invention:

[0027] The method proposed in the present invention does not require complex and time-consuming unsteady simulation of turbine components. It only needs to use steady calculation to design the pressure drop ratio of the guide vanes and the dimensionless axial spacing of the guide vanes to quickly evaluate the magnitude of the alternating stress at the resonance point of the turbine blades when excited by the upstream guide vane wake. This method is convenient for use in the preliminary design stage of the project and has high work efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A flow chart for drawing a standard turbine rotor blade resonance point alternating stress prediction curve for the present invention;

[0029] Figure 2 It is a schematic diagram of the Campbell diagram of the turbine rotor blade of the present invention;

[0030] Figure 3 A schematic diagram of a standard turbine guide vane and moving blade provided by the present invention;

[0031] Figure 4 It is a curve diagram for predicting the modal alternating stress at the resonance point of the standard turbine moving blade of the present invention. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Example

[0034] like Figure 1As shown, a method for predicting alternating stress at a resonance point of a turbine rotor blade of an aero-engine comprises the following steps:

[0035] Step 1: Based on the geometry geomturbo file of the turbine guide vanes and turbine rotor blades, use Autogrid software to generate the single-channel two-row grid required for CFD calculation;

[0036] Step 2: Specify multiple speeds and the temperature field of the turbine blades at the speeds, use Ansys Mechanical software to perform modal analysis, calculate the natural frequency ω, vibration mode Φ and corresponding maximum modal stress σ0 of the turbine blades at different speeds while considering prestress, and draw the modal Campbell diagram of the turbine blades according to the number of blades N of the turbine guide vane and the natural frequency ω of the vibration mode of the turbine blades to determine the resonant speed, such as Figure 2 As shown;

[0037] Step 3: Based on the resonant speed of step 2, specify the static pressure at the turbine blade outlet, and use the mixing surface model of CFX software to carry out the steady-state CFD calculation of the single-channel two-row grid in step 1 to obtain the steady-state result;

[0038] Step 4: Using the steady results obtained in step 3 as the initial field, the time tilt method of CFX software is used to carry out the non-full-ring unsteady CFD calculation of the single-channel two-row grid in step 1 to obtain the unsteady pressure of the turbine blade at the blade passing frequency. And dot product it with the corresponding vibration shape Φ to obtain the modal force

[0039] Step 5: Based on the modal stress σ0 obtained from the modal analysis in step 2 and the modal force obtained in step 4 Assuming the damping coefficient Q is a constant, calculate the alternating stress σ of the turbine blades.

[0040] Step 6: Adjust the static pressure at the rotor blade outlet, repeat steps 1 to 5, and re-carry out steady and unsteady calculations to obtain different turbine guide vane pressure ratios K p The alternating stress σ of turbine blades under the condition of K p =P t，inlet / P s，outlet , where P t，inlet is the total inlet pressure, P s，outlet is the outlet static pressure;

[0041] Step 7: Change the axial spacing d between the turbine moving blades and the turbine guide vanes, repeat steps 1 to 6, re-carry out steady and unsteady calculations, and obtain a series of dimensionless alternating stresses σ under the axial spacing d between the turbine moving blades and the turbine guide vanes, where: gap is the axial distance between the guide vane and the moving blade, ls is the axial chord length of the guide vane, such as Figure 3 As shown;

[0042] Step 8: Draw a curve based on the alternating stress σ in step 6 and the alternating stress σ in step 7, such as Figure 4 shown.

[0043] The examples given in the present invention are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here, and the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for predicting alternating stress at a resonance point of a turbine blade of an aero-engine, characterized in that: The following steps are involved: Step 1: Based on the geometry geomturbo file of the turbine guide vanes and turbine rotor blades, use the software to generate the mesh required for CFD calculation; Step 2: Use software to perform modal analysis, calculate the natural frequency, vibration mode and corresponding maximum modal stress of the turbine blades at different speeds, and draw the Campbell diagram of the turbine blades to determine the resonant speed; Step 3: Based on the resonant speed in step 2, specify the static pressure at the turbine blade outlet, and use the software to perform steady-state CFD calculations on the grid in step 1 to obtain steady-state results; Step 4: Using the steady result obtained in step 3 as the initial field, use the software to perform the non-full-ring unsteady CFD calculation of the grid in step 1, obtain the unsteady pressure of the turbine blade at the blade passing frequency, and dot-product it with the corresponding vibration mode to obtain the modal force; Step 5: Based on the modal stress obtained from the modal analysis in step 2 and the modal force obtained in step 4, assuming that the damping coefficient is a constant, calculate the alternating stress of the turbine blade; Step 6: Adjust the static pressure at the rotor blade outlet, repeat steps 1 to 5, and obtain the alternating stress of the turbine rotor blade under different turbine guide vane pressure ratios; Step 7: changing the axial spacing between the turbine moving blades and the turbine guide vanes, repeating steps 1 to 6, and obtaining a series of dimensionless alternating stresses under the axial spacing between the turbine moving blades and the turbine guide vanes; Step 8: Draw a curve based on the alternating stress in step 6 and the alternating stress in step 7.

2. The method for predicting alternating stress at resonance point of turbine rotor blades of an aircraft engine according to claim 1, characterized in that: In the step 1, the grid required for CFD calculation is generated using Autogrid software.

3. The method for predicting alternating stress at resonance point of turbine blades of an aircraft engine according to claim 2, characterized in that: In the step 1, the required grid is a single-channel two-row grid.

4. The method for predicting alternating stress at resonance point of turbine rotor blades of an aircraft engine according to claim 1, characterized in that: In the step 2, modal analysis is performed using Ansys Mechanical software.

5. The method for predicting alternating stress at resonance point of turbine rotor blades of an aircraft engine according to claim 4, characterized in that: In the step 2, the natural frequency, vibration mode and corresponding maximum modal stress of the turbine rotor blade at different rotation speeds are calculated taking the prestress into consideration.

6. The method for predicting alternating stress at resonance point of turbine rotor blades of an aircraft engine according to claim 5, characterized in that: In the step 2, a modal Campbell diagram of the turbine blade is drawn according to the number of blades N of the turbine guide vane and the natural frequency of the vibration mode of the turbine blade.

7. The method for predicting alternating stress at resonance point of turbine rotor blades of an aircraft engine according to claim 1, characterized in that: In step three, the mixing surface model of CFX software is used to carry out steady-state CFD calculation of the grid in step one.

8. The method for predicting alternating stress at resonance point of turbine rotor blades of an aircraft engine according to claim 1, characterized in that: In the step 4, the time tilt method of CFX software is used to carry out the unsteady CFD calculation of the non-full ring of the grid in step 1.

9. The method for predicting alternating stress at resonance point of turbine rotor blades of an aircraft engine according to claim 1, characterized in that: In step 5, the calculation formula of the alternating stress of the turbine blade is: Among them, σ is the alternating stress, σ0 is the modal stress, is the modal force, Q is the damping coefficient, and ω is the natural frequency.

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