Rotor Wake Generated Unsteady Aerodynamic Response of a Compressor Stator

Abstract

An experimental investigation was conducted to determine the fluctuating pressure distribution on a stationary vane row, with the primary source of excitation being the wakes from the upstream rotor blades. This was accomplished in a large scale, low speed, single stage research compressor. The forcing function, the velocity defect created by the rotor wakes, was measured with a crossed hot-wire probe. The aerodynamic response on the vanes was measured by means of flush mounted high response dynamic pressure transducers. The dynamic data were analyzed to determine the chordwise distribution of the dynamic pressure coefficient and aerodynamic phase lag as referenced to a transverse gust at the vane leading edge. Vane suction and pressure surface data as well as the pressure difference across the vane were obtained for reduced frequency values ranging from 3.65 to 16.80 and for an incidence angle range of 35.5 deg. The pressure difference data were correlated with a state-of-the-art aerodynamic cascade transverse gust analysis. The correlation was quite good for all reduced frequency values for small values of incidence. For the more negative incidence angle data points, it was shown that a convected wake phenomena not modeled in the analysis existed. Both the first and second harmonic unsteady pressure differential magnitude data decrease in the chordwise direction. The second harmonic magnitude data attains a value very nearly zero at the vane trailing edge transducer location, while the first harmonic data is still finite, albeit small, at this location. That the magnitude of the unsteady pressure differential data approaches zero near to the trailing edge, particularly the second harmonic data which has reduced frequency values to 16.8, is significant in that it reflects upon the validity of the Kutta condition for unsteady flows.

Navier-Stokes and Potential Calculations of Axial Spacing Effect on Vortical and Potential Disturbances and Gust Response in an Axial Compressor

“…Many researchers have undertaken the study of gust and gust response in axial compressors, e.g., Whitehead (1970), Goldstein and Atassi (1976), Fleeter et al (1978Fleeter et al ( , 1980, Gallus et al (1980), Capece et al (1986 and1987), Lewis et al (1987), Rai (1987), Rai et al (1990), Giles (1988), Hall and Crawley (1987), Hall and Verdon (1989), Hardin et al (1987), Manwaring and Fleeter (1989, 1990, 1991, Scott and Atassi (1990), Verdon and Hall (1990), Fang (1991), Korakianitis (1991), Henderson and Fleeter (1993), and others. Kielb and Chiang (1992) provided a summary of recent advances in forced response analyses.…”

Discussion: “The Time-Variant Aerodynamic Response of a Stator Row Including the Effects of Airfoil Camber” (Fleeter, S., Bennett, W. A., and Jay, R. L., 1980, ASME J. Eng. Power, 102, pp. 334–342)

“…Of the several useful aspects of this paper, I am particularly interested in the authors' conclusions related to convected wake segment (rotor wake segment in the present case) transport through a chopping blade row (stater row in the present case). They have shown in this and an earlier paper [8], that the convection of chopped wake segments along a chopping blade section, suction and pressure surfaces occurs at different velocities; they also suggested that this kind of wake action may be important enough to consider if more accurate analytical predictions of the unsteady effects involved are desired. An approproximate description of the wake chopping and transport process in a turbo-machine has been proposed by several investigators [9][10][11][12][13][14] and detailed measurements including fluid velocities and particle pathlines seem to support the general model involved.…”

Unsteady flows in a single-stage transonic axial-flow fan stator row

“…The effects of blade-row interactions on blade loading have been studied by Fleeter et al [21] Blade row interactions have also been demonstrated to be a source of acoustic excitation in turbomachines. In 1977, Schmidt and Okiishi [27] found that the level of discrete frequency noise at the inlet of a multistage compressor could be varied appreciably by relative positioning of the stationary blade rows.…”