The paper considers the results of a study of mutual aerodynamic couplings which give rise to nonstationary aerodynamic interactions between the translational and angular components displacements of neighboring ring blades in the case of variation of attack angle, reduced vibration frequency and the geometric parameters of the blade cascade. The effect of mutual aerodynamic couplings between neighboring blades on the aerodynamic stability of flexural-torsional vibrations of the blades of the peripheral section of the shrouded fan blade ring of gas turbine engine for an attack angle of 15°has been estimated.Introduction. In our earlier work [1], results of determining cross aerodynamic characteristics (CAC) and their effect on the flutter stability of compressor and fan blades were reported. In the case of flexural-torsional vibrations of blades, these characteristics are determined by aerodynamic interaction between translational and angular displacements of their sections. However, during the operation of axial flow turbomachines, mutual aerodynamic couplings also arise from interaction in the stream between the components of displacements of neighboring ring blades. As is pointed out in [2], they may be responsible for the appearance of cascade flutter of blades under the conditions of both attached and separated flow over them. Survey of scientific and technical literature shows that the character of the variation of this type of couplings as a function of flow conditions and blade vibration parameters and their effect on the aerodynamic stability of blade rings have been practically not studied. Therefore, the aim of the present study is to establish the laws governing the variation of mutual aerodynamic couplings as a function of attack angle and reduced vibration frequency for different geometric characteristics (pitch-chord ratio and deflection angle) of blade ring and their effect on its aerodynamic stability. Peculiarities of the Experimental Determination of Mutual Aerodynamic Couplings between Blades.Mutual aerodynamic couplings between blades were determined by using planar blade cascades (Fig. 1) in their tests on an experimental test bench [3]. On the reference blade airfoil (n = 0) vibrating with predetermined amplitudes of translational ( y) and angular (α) displacements and phase angle θ α

We consider the results of investigation of cross aerodynamic characteristics of compressor blades and their dynamic stability under flexural-torsional vibrations for the cases of attached and separated flows in broad ranges of variations of the phase shift, the ratio of amplitudes of the translational and angular components of displacements, the angle of attack, the reduced frequency of vibrations, and the geometry of the blade cascade. Introduction. The principal ideas of the procedure are described and the experimental equipment for the determination of nonstationary aerodynamic characteristics (NAC) of compressor blades in the presence of attached and separated flows are developed in [1] with regard for the aerodynamic cross couplings and mutual aerodynamic couplings based on the application of flat-plate airfoil cascades. The necessity of investigations of this sort is explained by the fact that, as shown in [2-4], the nature and conditions of excitation of the flexural-torsional flutter of blade rims of compressor and fan impellers are determined by the phase shift and the ratio of amplitudes of the translational and angular components of displacements of the blades and depend on the reduced frequency of their vibrations (the Strouhal number) and the angle of attack of the incident airflow.Thus, in what follows, we present the results of evaluation of the cross aerodynamic characteristics (CAC) and their influence on the flutter resistance of blades in the process of flexural-torsional vibrations in the absence of aerodynamic coupling with regard for the parameters of the indicated vibrations, parameters of the incident airflow, and geometry of the rim.Object and Conditions of Experimental Investigations. The CAC are determined by using a straight cascade of blade airfoils whose cross-section is shown in Fig. 1. The values of the parameters of blade airfoils are as follows: