裂纹参数变化对叶片低阶弯曲振动特性的影响

Effect of Variation in Crack Parameters on the Characteristics of Blades Low-order Flexural Vibration

目的研究叶盘叶片进气及出气边萌生的横向贯穿型裂纹的分布位置及深度变化对叶片一阶弯曲振动特性的影响。方法根据叶片尺寸及工况建模,得到正常叶片在静止及不同旋转速度下的一阶振动频率,并进行拟合。在正常叶片模型的基础上,通过布尔运算建立裂纹模型,研究横向贯穿型裂纹在不同分布位置及不同深度下对一阶弯曲振动频率的影响,并进行拟合。针对裂纹深度变化采集的定时信号通过DFT变换,得到正常及含有不同深度裂纹叶片的一阶频率,对建模结论进行验证。结果一阶弯曲振动频率先减小后增大,在距离叶根4.23 mm时为最小值801.16 Hz;当裂纹距叶根的距离大于35 mm时,振动频率先接近后大于正常叶片,振幅先接近后小于正常叶片,最终将35 mm设定为位置的阈值;裂纹深度的增加使振动频率单调减小,且速率不断增大。采集的信号经DFT变换得到的一阶弯曲振动频率与建模结果的误差分别为1.9%,2.0%,1.5%,0.6%。结论当叶片进气或出气边位置阈值内出现裂纹萌生及扩展时,一阶弯曲振动频率会小于正常值,此时叶片的一阶弯曲共振区域会增大,需要对旋转机械进行严格的工况监测,同时裂纹深度的增加可提高叶尖定时监测的准确性。

Objective To research the effect of the location and depth of the lateral and penetrating cracks initiating at the leading or trailing edge of the disk blades on the frequency of the first-order flexural vibration of the blades. Methods The frequencies of normal blades in static and rotation were calculated through modeling according to the size and working condition,then the models for lateral and penetrating cracks were built by Booleans operation on the basis of normal blades to research the variation of frequencies affected by location and depth of the lateral and penetrating cracks and all the data was fitted. The modeling results were verified by the frequencies of the first-order flexural vibration of normal blades and those with different crack depth through DFT analysis of BTT signals. Results The results showed that the frequency decreased at first and then increased. The minimum frequency of 801. 16 Hz was got at the distance of 4. 23 mm. When the distance to the root was greater than 35 mm,the frequency became close to and then greater than the normal value,so the distance of 35 mm was set as the threshold of location. In addition,the frequency decreased with the increase of the crack depth,and the speed of changing kept increasing. The measurement errors of BTT signals with the results of FEM were 1. 9%,2. 0%,1. 5% and 0. 6%,respectively. Conclusion When cracks initiate at the leading or trailing edge within the location threshold,the frequencies of the first-order flexural vibration are lower than the normal values,and the resonance region of first-order flexural vibration will expend so that the working condition needs to be monitored seriously. Meanwhile,the increase of the crack depth can improve the accuracy of BTT data.