A concise method of determining critical flutter wind speeds for small damping modes
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摘要: 在低速颤振试验中，小阻尼型颤振模型发生等幅振动的起始风速通常较低，也没有明显的颤振发散现象，采用目测或基于常规模态参数识别的“阻尼法”判定颤振临界风速具有一定的不确定性。针对此问题，根据小阻尼模态颤振试验与抖振试验具有相似的振动现象，提出一种与确定抖振边界类似的“振幅拐点法”来判定颤振临界风速。该方法以振动幅值的均方根值为基础，绘制归一化振动均方根值随风速的变化曲线，以曲线首个拐点对应的风速值为颤振临界风速。将该方法应用于某小阻尼模态颤振试验的发动机挂架变参数据处理，并将处理结果与数值计算结果、阻尼法处理的试验结果进行了对比，结果表明：振幅拐点法与数值计算、阻尼法处理得到的结果规律一致，振幅拐点法得到的结果更接近计算结果，具有简明可靠、稳定性好、适用性强的特点。Abstract: In low speed flutter tests, flutter models with small damping modes start continuous vibration usually at low speeds without obvious flutter divergence. Therefore, it’s of some uncertainty on determing the critical flutter wind speeds by visual inspection or by “damping method （DM）” of modal parameter identification. Considering the similarity between the vibration phenomenon of a small damping modal flutter test and that of a fighter buffet test, a technique named “amplitude turning point method （ATPM）” similarly to that used in identifying buffet boundaries is proposed to determine the critical flutter wind speeds. The method is based on RMS of vibration amplitudes, the curves of normalized vibration RMS changing with wind speeds are drawn, and critical flutter wind speeds are determined according to the first turning points of curves. In a small damping modal flutter test, the method was applied in the test data processing of the engine hangers with variable parameters. Comparing the ATPM results with the DM results and the numerical results, the following conclusions are made: the results of three methods are in agreement, the ATPM results are more similar to the numerical results than the DM results, and the ATPM is concise and reliable, with good stability and applicability.
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图 2 振幅拐点判定依据示意图
Figure 2. Diagram of a criterion on determining amplitude turning point
图 3 某型低速风洞颤振试验全机模型
Figure 3. A full plane model for flutter test in low speed wind tunnel
图 4 基准构型颤振计算v-g图
Figure 4. v-g diagrams for flutter calculation of the basis configuration
图 5 发动机挂架刚度变参试验v–ζ曲线
Figure 5. v–ζ curves for variable parameter test of engine pylon stiffness
图 6 发动机挂架刚度变参试验振幅随风速变化曲线
Figure 6. Curves of amplitudes with v in variable parameter test of engine pylon stiffness
表 1 颤振临界风速计算与试验结果对比
Table 1. Comparison between numerical and test results on determining critical flutter wind speeds
发动机挂架刚度 计算结果/（m·s–1） 试验结果/（m·s–1） Nastran 阻尼法 振幅拐点法 50% 18.8 22.4 21.9 80% 25.9 25.5 25.5 100%（基准） 29.7 28.6 28.6 120% 33.3 30.6 30.6 
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