Search

CN-116305542-B - Engine blade multi-order dynamic stress measurement design method based on strain gauge

CN116305542BCN 116305542 BCN116305542 BCN 116305542BCN-116305542-B

Abstract

The multi-order dynamic stress measurement design method for the engine blade based on the strain gauge comprises the steps of S1, S2, analyzing the intensity of the blade and analyzing the blade vibration according to the vibration range of the blade, S3, determining the vibration monitoring order of the blade, the patch position and the patch direction of the strain gauge, S4, calculating the limit value of the strain gauge according to the vibration principle and based on the maximum vibration risk factor, S5, calculating the multi-order conversion coefficient and the multi-order limit value of the strain gauge, and S6, determining the vibration order which can be monitored by the strain gauge simultaneously through sensitivity analysis. The use of a reduced number of strain gages was tested.

Inventors

  • LIU XIANG
  • ZENG YAWEI
  • WU MIANMIAN
  • Lei Xinliang
  • WANG CHUNJIAN
  • CHEN GUANFENG

Assignees

  • 中国航发四川燃气涡轮研究院

Dates

Publication Date
20260505
Application Date
20230224

Claims (8)

  1. 1. The design method for measuring the multi-order dynamic stress of the engine blade based on the strain gauge is characterized by comprising the following steps of: S1, determining the vibration range of a blade, wherein the blade is a compressor rotor, a stator blade or a turbine rotor or a stator blade, and the vibration range is represented by the upper frequency limit f s , so that the requirements are met: f s =n max /60 J max S (1) Wherein n max is the maximum working rotation speed of the blade, J max is the maximum main excitation order of the blade, and S margin is provided; The highest vibration order corresponding to the upper limit of the blade frequency f s can be determined according to vibration calculation; S2, analyzing the strength and vibration of the blade according to the vibration range of the blade; S3, determining the vibration monitoring order of the blade, and the patch position and the patch direction of the strain gauge, wherein, The patch position and the patch direction of the strain gauge in the S3 comprise: Patch position, a foil gage monitoring multistage vibration synthesizes the vibration result of multistage and confirms the patch position of foil gage, includes: Determining the position of a patch capable of monitoring multi-order vibration at the same time according to the multi-order vibration stress distribution; When the ratio of the multi-order vibration stress to the maximum vibration stress of each order is larger than a preset value, the multi-order vibration stress is used as the patch position of the strain gauge, when the stress gradient at the position of the maximum mode vibration stress of the design monitoring order is smaller or smaller than the preset value, the strain gauge can be stuck at the maximum vibration stress, when the maximum vibration stress point of the design monitoring order is at the position where the round, sharp angle position or the stress gradient of the stress cannot be stuck with the strain gauge is larger, the sticking position of the strain gauge is selected at the position of the next largest stress point where the gradient is smaller than the preset value, when a strain gauge is designed and the multi-order vibration of the blade is monitored, the positions where the multi-order vibration stress is larger than the preset value are selected as patch positions according to the mode vibration stress distribution of the vibration monitoring order; patch orientation, comprising: The patch position of a strain gauge can be monitored simultaneously when the multi-stage blade vibrates according to the mode vibration stress distribution, and as the main stress directions of different-order vibration at the same position can be different, the patch direction of the strain gauge needs to be further determined after the patch position is primarily determined, and the requirements are met: a) If a strain gauge is designed to monitor only certain first-order vibration, the patch direction of the strain gauge can be determined as the first/third main strain direction of the modal vibration of the first-order vibration at the patch position; b) If the strain gauge is designed preliminarily and the multi-order vibration is monitored simultaneously, taking a certain direction in the middle as the patch direction according to the vibration principal stress direction of the multi-order vibration at the patch position, and the included angle between the vibration principal stress direction of each order monitored by the preliminary design and the determined patch direction is not more than 30 degrees, the strain gauge can monitor the corresponding multi-order vibration simultaneously; c) If the strain gauge is primarily designed to monitor multi-order vibration at the same time, but the included angle between the vibration principal stress direction of certain order vibration at the patch position and the principal stress direction of other orders of vibration is larger than 40 degrees, the strain gauge cannot monitor the order vibration at the same time; S4, calculating a limit value of the strain gauge according to the vibration principle and based on the maximum vibration risk factor; S5, calculating a multi-order conversion coefficient and a multi-order limit value of the strain gauge; and S6, determining the vibration order which can be monitored simultaneously by the strain gauge through sensitivity analysis.
  2. 2. The design method according to claim 1, wherein S2 includes: Establishing a finite element model of an aeroengine blade, and carrying out strength analysis and modal analysis under the working condition of the maximum rotation speed of the engine or the maximum state of the test, wherein the vibration order of the modal analysis is determined by the upper frequency limit f s ; The intensity analysis and the mode analysis adopt the same finite element model, the mode under different rotation speeds is calculated to obtain the dynamic frequency f D of the blade, and the mode of the blade without considering the rotation speed, aerodynamic force and temperature field load is calculated to obtain the static frequency f of the blade.
  3. 3. The design method according to claim 2, wherein the determining the vibration monitoring order of the blade in S3, because there may be more resonance orders of the blade in the working rotation speed range, the determining the vibration order of the blade to be monitored in the test, the vibration order of the blade to be focused on, includes: a) Front third-order bending vibration, front second-order torsional vibration and front second-order string bending vibration of the fan/compressor rotor blade; b) Front two-order bending vibration, front two-order torsional vibration and front first-order string bending vibration of the fan/compressor stator blade; c) Front fourth-order Liang Motai of unobvious chord-bending characteristics of the turbine buckets and front two-order plate modes representing the chord-bending characteristics; d) A spanwise bending mode of the single turbine vane; e) Exciting factors excite resonance orders near an important rotating speed; In order to determine the monitoring order of the blade, resonance analysis needs to be performed on the blade, and two determination modes exist on a frequency line in a resonance rotating speed diagram of the blade: a) Connecting the static frequency of the blade and the dynamic frequency at different rotating speeds into a frequency line of the blade changing along with the rotating speed; b) Calculating the static frequency f of the blade and the dynamic frequency of one rotating speed n, then reversely solving a dynamic frequency coefficient B according to the relation between the dynamic frequency and the static frequency, calculating the dynamic frequency of the blade at different rotating speeds by the formula (2), finally drawing a frequency line of the blade, calculating the rotating speed of the dynamic frequency, and selecting the rotating speed of the blade under the highest working condition or the maximum working rotating speed, wherein the relation between the dynamic frequency and the static frequency satisfies the following conditions: (2)。
  4. 4. a design method according to claim 3, wherein calculating the limit value of the strain gauge in S4 includes: Allowable vibration stress calculations for each node include: according to the stable equivalent stress of the ith node in the blade static strength calculation result Minimum value of stretching limit of material at i-th node working temperature And fatigue limit at the i-th node operating temperature at stress ratio of-1 From the formula shown in (3), the allowable vibration stress of the ith node on the blade can be obtained Fatigue limit Taking a fatigue limit test value of a component, taking a fatigue limit test value of a component with the same performance or function if the component has no fatigue limit, taking a fatigue limit-3σ value of a material if the component has no fatigue limit, taking a fatigue limit of a fatigue life N f =1×10 7 for a blade made of stainless steel, taking a fatigue limit of a fatigue life N f =3×10 7 for a blade made of nonferrous metal alloy, taking a fatigue limit of a fatigue life N f =1×10 9 for a blade made of titanium alloy, and taking a fatigue limit of a fatigue life N f =3×10 7 if the component has no fatigue limit; (3); maximum vibration risk factor calculation, comprising: vibration stress of any node on blade body of blade in test Not greater than the corresponding allowable vibration stress I.e. When the blade generates certain-order resonance, the node of the vibration stress on the blade, which exceeds the allowable vibration stress, is the most dangerous point of the high cycle fatigue of the blade, and the high cycle fatigue risk of any node on the blade depends on the vibration stress of the node and the allowable vibration stress value, and the allowable vibration stress of any node on the blade is calculated And modal vibration stress Defining a vibration risk factor K of a node as shown in a formula (4), wherein the node is more dangerous under the resonance of the order as the K value is larger, the maximum value of the vibration risk factor in the blade body node is Kmax as shown in a formula (5), the corresponding node is Kmax, and the Kmax is the most dangerous point of the high cycle fatigue of the blade under the vibration of the order; (4) K max =max(K i )(5); The calculation of dynamic stress limit value includes ensuring that the vibration stress of all nodes on the blade is not greater than the corresponding allowable vibration stress when the blade generates certain order resonance, and ensuring that the vibration stress of other nodes on the blade is the maximum vibration stress allowed by the node under the order resonance when the vibration stress of Kmax point is equal to the allowable vibration stress At this time, at any node Can be stressed by the mode vibration of the node And Kmax is obtained according to formula (6), and the maximum allowable vibration stress of any node obtained by formula (6): a) For Kmax point, its maximum allowable vibration stress Equal to its allowable vibration stress ; B) For other nodes than the Kmax point, the maximum allowable vibration stress Less than its allowable vibration stress ; Obtaining the maximum allowable vibration stress corresponding to the node at the patch position of the strain gauge according to the formula (5), namely a dynamic stress limit value of the strain gauge under the vibration of the order; Conversion of dynamic strain limit values, comprising: since the strain gauge actually measures the dynamic strain at the patch position in the test, converting the dynamic stress limit value into a dynamic strain limit value includes: a) For the isotropic material blade, when the stress state at the position of the strain gauge is close to the unidirectional stress state, obtaining a corresponding dynamic strain limit value according to Hooke's law by the dynamic stress limit value; b) The patch position of the strain gauge of the blade is not in a unidirectional stress state under the service condition, and the dynamic strain limit value Can be directly strained by the relative vibration at the patch position of the strain gauge The result is obtained according to the formula (7), (7); The multi-order limit value calculation of the strain gauge comprises the following steps: Establishing a local coordinate system, extracting modal vibration stress and strain components of each-order vibration in the direction of the strain gauge patch to determine the maximum relative vibration stress and strain of the blade in one period, and obtaining the strain components of each-order vibration in the monitoring direction of the strain gauge at the position of the strain gauge patch Then, the dynamic strain limit value of each-order vibration is calculated by using the formula (8), Limit value = (8); A) Because the strain value is generally small, the strain value is inconvenient to monitor and use in the test, and the dynamic strain limit value is converted into micro-strain mu epsilon for use; b) Because of the difference of the patch error, the actual vibration and the calculation result and the actual engine working process factors, in order to ensure the test safety, the dynamic strain limiting value needs to be considered for a certain reserve N, and the reserve coefficient N can be selected by referring to the following different situations, namely, the selection range of the reserve coefficient N: 1, if the effective value is measured by the strain gauge in the test process, N is 2.5; 2, if the amplitude value is measured by the strain gauge in the test process, N is 1.67; 3, since the calculation limit value uses the-3σ value of the fatigue limit, in the dynamic stress special measurement test, N is 1.0.
  5. 5. The design method according to claim 4, wherein calculating the multi-order conversion coefficient of the strain gauge in S5 includes: The vibration stress relation between the measuring position and the preset position of the strain gauge is established, and the following conditions are satisfied: In which, in the process, -Modal vibration equivalent stress values at preset positions; -an actual measured vibration equivalent stress value at a preset position; -patch position strain gage directional modal vibration stress values; -a patch position strain gauge direction measured vibration stress value; The patch angle sensitivity analysis method comprises the steps of setting the actual patch angle and the designed patch angle to be different as beta when the patch angle sensitivity analysis is carried out, respectively obtaining the corresponding limit value of the strain gauge by the angles after deviation of the designed patch position, wherein the deviation angle beta=3 degrees of the strain gauge adhered to the front edge and the rear edge of the blade, and the alpha=5 degrees of the rest analysis is carried out; Setting the offset distance between the actual patch position and the designed patch position as R when carrying out strain sheet position sensitivity analysis, selecting 4 points on a circle with the radius of R as the radius of the patch design position on the surface of the blade as the offset position of the strain sheet, respectively obtaining corresponding limit values of the strain sheet at the offset position according to the designed patch angle, and taking R=2mm for a fan blade for sticking the strain sheet at normal temperature; for the turbine blade attached with the high-temperature strain gauge, reference may be made to r=1mm; The sensitivity quantification index comprises a deviation delta between a limit value after calculating the angle or position deviation of the strain gauge and a patch design result limit value in a quantification mode according to a formula (10), and the deviation delta meets the following conditions: The limit value after deviation is recalculated by adopting the formula 8, and the angle and the position after deviation are determined and then are extracted again 。
  6. 6. The design method according to claim 5, wherein the method in S6 comprises: For a solid blade, the conversion coefficient of the maximum vibration stress point of the strain gauge design monitoring order is not more than 3; The conversion coefficient of the maximum vibration stress point of the strain gauge design monitoring order is between 3 and 5 for the hollow blade and the adjustable blade; sensitivity bias requirements, including: the sensitivity quantification index deviation delta is larger than 33%, the influence of the pasting position and the angle of the strain gauge on the limiting value is extremely large, the dynamic stress limiting value is greatly changed due to errors in the artificial patch, the vibration monitoring and the test result analysis are not facilitated, and the strain gauge is not suitable for monitoring the vibration of the order; when the measured signal in the test is the maximum transient value, the reserve coefficient is 1.67.
  7. 7. A design method for determining the reliability priority of a strain gauge measurement, characterized in that the reliability priority of a strain gauge measurement can be determined according to the size of a conversion coefficient by using the method of any one of claims 1 to 6, comprising: And calculating the limit value and conversion coefficient of the strain gauge under each-order vibration of the blade, monitoring the same-order vibration by a plurality of strain gauges at different positions, and measuring the result by the strain gauge with the minimum conversion coefficient in actual analysis.
  8. 8. A method for identifying vibration orders, wherein the method according to any one of claims 1 to 6 is used, and the method is applicable to identifying vibration orders corresponding to actual measurement response frequencies of blades according to multi-order limit value design results, and comprises the following steps: For strain gauges at different positions on the same blade, actually measuring response values of the strain gauges at different positions under a certain response frequency, and determining interval orders of blade vibration corresponding to the response frequency, wherein the interval orders comprise a first order point and a second order point; defining response values of strain gauges at different positions on the same blade under the response frequency as response vectors; The limiting values of the strain gauges at different positions of the blade corresponding to the first order point are defined as a first order point limiting value vector, and the limiting values of the strain gauges at different positions of the blade corresponding to the second order point are defined as a second order point limiting value vector; And respectively obtaining the included angle between the response vector and the first order point limit value vector, and the included angle between the response vector and the second order point limit value vector, wherein the vibration order corresponding to the smaller included angle is used as the blade vibration order corresponding to a certain response frequency, and/or after the actual measurement response frequency is determined to vibrate for a certain specific order according to the vibration analysis result, calculating the included angle between the response vector and the lower limit value vector of the order, if the included angle is smaller than 10 degrees, the actual measurement vibration mode and the modal vibration mode are better combined, and if the included angle is larger than 20 degrees, the actual measurement vibration mode and the modal vibration mode are obviously different.

Description

Engine blade multi-order dynamic stress measurement design method based on strain gauge Technical Field The invention belongs to the technical field of aeroengines, and particularly relates to a strain gauge-based multi-order dynamic stress measurement design method for an engine blade. Background The working speed range of the aeroengine is wide, direct excitation factors of the blade are many, resonance points are unavoidable, the resonance of the blade can generate larger vibration so as to influence the high cycle fatigue life of the blade, and even the high cycle fatigue failure of the blade can be caused. Therefore, in the test process, the dynamic stress of the blade is required to be monitored, so that the test is ensured to be carried out safely and smoothly, and meanwhile, the vibration characteristic of the blade is obtained. Currently widely used strain gages remain the primary means for monitoring the vibration characteristics and high cycle fatigue of aircraft engine blades. In order to ensure that the blade does not experience high cycle fatigue failure due to resonance during the test, it is necessary to ensure that the vibratory stress of the blade does not continue to exceed the allowable vibratory stress of the blade. It is therefore desirable to give steady state vibration stress limits for the strain gage. And in the test, the vibration stress of the blade is not exceeded or is not continuously exceeded by a steady-state vibration stress limit value, so that the blade cannot be subjected to high-cycle fatigue damage, and the test is ensured to be carried out safely. Because the number of the blade stages of the aeroengine is more, resonance points of each stage of blade in the working rotation speed range are more, if each stage of resonance point of each stage of blade is designed with one strain gauge for monitoring (the damage of the strain gauge in the test and the reliability of measured dynamic stress data are considered, a plurality of blades are actually selected to be pasted with the strain gauge in the circumferential direction), a large number of strain gauges are required to be pasted, but the number of the strain gauges which are actually pasted in one test and used for monitoring the dynamic stress of the blade is limited due to factors such as test requirements, test equipment, follow-up staff, economy and the like, and at the moment, the multi-stage vibration of the blade can be completely designed, and the purpose of monitoring more blade vibration orders by using the strain gauges with limited number is realized. The engine is provided with a plurality of multi-stage blades, each stage of blade is provided with a plurality of strain gauges, and the method in the prior art is used for pasting the patch on the engine, so that the test cost is high. Disclosure of Invention In view of the above, the invention provides a design method for measuring multi-order dynamic stress of an engine blade based on a strain gauge, which solves the technical problem of higher cost in the engine test of the prior art method. An engine blade multi-order dynamic stress measurement design method based on a strain gauge, the method comprising: s1, determining the vibration range of the blade; S2, analyzing the strength and vibration of the blade according to the vibration range of the blade; s3, determining the vibration monitoring order of the blade, and the patch position and the patch direction of the strain gauge; S4, calculating a limit value of the strain gauge according to the vibration principle and based on the maximum vibration risk factor; S5, calculating a multi-order conversion coefficient and a multi-order limit value of the strain gauge; and S6, determining the vibration order which can be monitored simultaneously by the strain gauge through sensitivity analysis. The invention has the beneficial effects that: In the test of the aero-engine, a resistance strain gauge (hereinafter referred to as strain gauge) is generally adopted to monitor the vibration stress of the blade, but the number of the blade stages to be monitored of the aero-engine in the test is more, and the resonance points of each stage of the blade in the working rotation speed range are more, so that the problem of how to monitor more-order vibration of the blade by using a limited/less strain gauge is solved, the design method provided by the invention can be used for determining the patch position and the patch direction of the dynamic stress monitoring strain gauge of the blade in an aeroengine test, can realize that one strain gauge monitors the vibration of the multi-stage blade at the same time, can assist in judging the vibration order by comparing the response of different strain gauges on the same blade with the relation of the limiting value, and can verify the accuracy of the adopted modal analysis method. Drawings In order to more clearly illustrate the technical solutions of the embodiments of the p