Prediction of stability against subsonic flutter for axial turbine machine compressor blade assemblies

The developed method for prediction of their dynamic stability limit is described for the first flexural and torsional modes of vibrations against subsonic flutter. It involves the use of the database of the critical reduced frequencies of the blade vibrations as a dynamic stability limit within the wide range of variations of the following characteristics: phase angle of flexural, torsional and flexural-torsional vibrations of the adjacent blades; attack angle; reduced vibration frequency; geometric parameters for the airfoil and cascade; law of motion for blade airfoils. The algorithm realized as the numerical software assumes the determination of the critical reduced frequencies in the most loaded section of the full-scale blade assembly via the analysis of the distribution of the relative flow rate, attack angle, amplitudes of vibrations over the blade height and the subsequent comparison with the functional defining its critical value for different attack angles. The results of practical implementation of the developed procedure are given for the assessment of the stability of the blade assemblies of axial compressors in some modern aircraft gas-turbine engine at the first flexural mode of vibrations. It is implied that the proposed method allows one to select the optimal reduced frequency of vibrations of the blade assembly for the specified geometry of its peripheral sections and attack angle of the mainstream flow upon the condition of subsonic flutter at the engine design state.