Experimental-numerical investigation of the dynamic stability of flexural-torsional vibrations of compressor blades under conditions of attached and separated flow. Part 1. Procedure and equipment for the determination of nonstationary aerodynamic characteristics

Abstract

We present the results of investigations of the aerodynamic stability of flexural-torsional vibrations of compressor blades under conditions of attached and separated flow with regard for the cross and mutual aerodynamic links of the blades in a broad range of variations of the phase shift, the ratio of the amplitudes of translational and angular components of their displacements, and the angle of attack. A procedure and equipment used for the experimental determination of the nonstationary aerodynamic characteristics of the blades are described on the basis of the model of flat-plate airfoil cascades.Statement of the Problem. In trying to get the highest possible specific parameters of the aircraft gas-turbine engines (AGTE), we inevitably encounter the problems of vibrations of blades in the rotors of these engines. Thus, one of the methods used to make turbomachines more compact and decrease their weight is based on the application of blades with high aspect ratios. This leads, on the one hand, to a shift of the spectrum of natural frequencies of vibrations of the blades to the region of lower frequencies and, on the other hand, to the excitation of of high-frequency flexural-torsional modes of vibrations of the blades characterized by the presence of a phase shift between the translational and angular components of displacements of the sections and different values of the ratio of their amplitudes.It is known [1] that the role of decisive factor in the loss of the stability of a wing in the case of classical flutter is played by the phase shift between the translational and the angular components of displacements of the wing responsible for the formation of aerodynamic crosslinks and the supply of energy from the flow. The principal features of the classical flutter of airplane wings are also typical of the loss of aerodynamic stability of the analyzed blades [2]. However, this process is complicated by the mutual influence of neighboring blades in the blade ring. A similar phenomenon is also typical of the lightened blade rings of fan and compressor stages containing either compliant disks or damping (antivibration) shroud platforms. The self-excited vibrations of these rings are realized in the form of running strain waves with various numbers of the nodal diameters and circles. Note that the phase shift between the translational and rotational components of displacements in the sections of blades located near the shroud 200 0039-2316/07/3902-0200

Experimental-numerical investigation of the dynamic stability of flexural-torsional vibrations of compressor blades under conditions of attached and separated flow. part 3. mutual aerodynamic couplings

“…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…”

“…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 y between them, the components of nonstationary aerodynamic forces L and moments M were measured in the case of sequential excitation of vibrations of airfoils which were upstream (n = −1) and downstream (n = +1).…”

“…The experimental study of mutual aerodynamic couplings was carried out in the same ranges of blade cascade parameters, conditions of flow over blade airfoils and vibration characteristics as earlier [1] using the methodological approaches and means presented in [3]. The center of twist did not change during tests, it was in the middle of the chord of the airfoils.…”

Experimental Validation of Numerical Blade Flutter Prediction

“…IV.E, we will give an example of a blade whose overall stability prediction does not coincide with the prediction obtained through the 2-D cross section taken at 90% of the blade span. At the present day, the 2-D approach is verified by tests of cylindrical blades (i.e., blades whose cross section is constant along the span) [18][19][20][21][22][23][24]. A study [25] is devoted to the comparison of energy and modal methods based on a quasi-3-D approach.…”