The paper presents the results of simulations and experimental investigations on natural frequencies and oscillation modes of pairwise-shrouded cooled turbine blades and their rings with allowance for a possible frequency mistuning and the assured contact of mating surfaces of the root and shroud platform halves. As the research object, the high-pressure turbine wheel of an aircraft bypass turbojet engine has been selected. 3D finite element models of the turbine wheel blades/ period were developed as a system with structural rotational symmetry. The contact interaction between blades over the mating surfaces was modeled on basis of solving the stationary problem. The calculation-and-experimental investigations were performed for two operating conditions of the engine – the non-running engine and the steady-state maximum take-off condition. Results have been cited for individual, isolated blades. The results show a good agreement between calculated and experimental data. The frequency mistuning of those blades is found to be considerably dependent on oscillation mode number, but the mistuning value is practically not affected by the operating condition of the engine. It is confirmed that two oscillation modes are excited in the blade pair as a regular system in the presence of the mistuning of their frequencies, which are close to the inphase and antiphase frequencies. The ratio of natural frequencies of those oscillation modes is dependent on oscillation mode of isolated blades. It is shown that the frequency mistuning of paired blades due to excitation of two oscillation (inphase and antiphase) modes causes doubling of the number of resonant states of the turbine wheel what must be considered when developing methods to ensure their vibrational reliability.

中文翻译：

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成对罩冷却涡轮叶片自然频率和振荡模式的计算和实验研究

本文介绍了成对冷却的涡轮叶片及其环的固有频率和振荡模式的仿真和实验研究结果，并考虑了可能的频率失调以及确保了根部和护罩平台半部的配合表面的可靠接触。作为研究对象，选择了飞机旁路涡轮喷气发动机的高压涡轮。涡轮叶片/周期的3D有限元模型被开发为具有结构旋转对称性的系统。在解决固定问题的基础上，对叶片在配合面上的接触相互作用进行了建模。针对发动机的两个工况进行了计算和实验研究，即非运转发动机和稳态最大起飞工况。已经引用了单个隔离刀片的结果。结果表明计算和实验数据之间的良好一致性。已经发现这些叶片的频率失谐很大程度上取决于振荡模式数，但是该失谐值实际上不受发动机的运行状况的影响。可以确定的是，在叶片对中有两个振荡模式作为常规系统在它们的频率不平衡的情况下被激发，这些频率接近于同相和反相频率。这些振荡模式的固有频率的比率取决于隔离叶片的振荡模式。