振动下传对T型叶根三联叶片模态阶序的影响

The Influence of Root-Wards Infiltrated Vibration on its Mode Order in Case of Interconnected Blade Triplets with "T" Roots

采用三维8节点非协调单元有限元模型,对汽轮机调节级T型叶根三联叶片在静止和工作状态下的振动特性进行了计算分析。计算中考虑了工作状态下温度的影响和离心力作用使得轮缘周向尺寸增大,造成叶根松动,导致振动延伸到叶根部分的情况。计算结果表明:振动下传不仅导致旋转状态下的固有频率小于相应的静止状态下的值,而且由于叶片参振结构和质量的重新组合,导致叶片模态阶序发生了转移和变化。在静止时,叶片的第1阶固有振动为切向振动,第2阶固有振动为轴向振动,而旋转状态下,第1阶固有振动变成了轴向振动,第2阶固有振动变成了切向振动。

The vibration characteristics of governing stages＇ blade triplets with ＂T＂ roots are being mathematically analyzed for static as well as operating conditions by using three dimensional incompatible elements with 8 nodes. The fact that the temperature and centrifugal forces effect an increase of the disc rim＇ s dimensions, cause the blade roots to slacken and thereby induce vibration to infiltrate into the blades＇ root part. Calculation resuhs indicate that the downwards infiltration of vibration not only causes natural vibration frequencies, under rotating conditions, to get lower, compared with those under static conditions, but because of variation of the blade＇ s rigidity and mass collocation, the modal order of vibration undergoes a shifting as well. Under static conditions the blade＇ s 1 ^st order natural vibration is tangential and the 2^nd order axial, but under rotating conditions the 1^ storder changes to axial and the 2^nd order to tangential. Figs 6, table I and refs 5.