Standard Configurations for Unsteady Flow Through Vibrating Axial-Flow Turbomachine-Cascades (STCF)

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Standard configurations

First standard configuration (compressor cascade in low subsonic flow)

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The first standard configuration, included by the courtesy of Dr. Frank Carta at the United Technologies Research Center [Carta 1982a,b; 1984], and its 15 recommended aeroelastic sample cases, gives an overview of different steady-state and time- dependent flow conditions at low Mach numbers (see Fig. 3.1.1, Tables 3.1.1-2). Most prediction models give good agreement with the data, but some minor differences between the different models became apparent.

Maximum thickness at x=0.5 Vibration in pitch around (xa,ya)=(0.5,0.0115) Thickness / chord = 0.06 span=0.254 m c=0.1524m t=0.75 g=55o camber=10o i=variable (2o, 6o) Working fluid: Air a = 0.5o, 2o (=0.0087, 0.0349 rad) k=variable Fig. 3.1.1: First standard configuration: Cascade geometry [Bölcs and Fransson, 1986, p. 58] All results (experimental as well as predictions) presented on this standard configuration have been (as the flow velocity is very low) non-dimensionalized with the incompressible dynamic pressure, (r-_•v-_2/2). The most important conclusion from this standard configuration is that the detailed blade surface pressures, and thus the flutter limits, can be fairly accurately predicted for low incidence flows on this type of cascades. The reader is referred to section 7.1 in the original report on the standard configurations [Bölcs and Fransson, 1986] for details. It is however of importance to note that although the results obtained are positive, the agreement between the data and the predictions, or between the different predictions, is not as good as would be wished from a theoretical point of view. It should especially be mentioned that, in several cases, a flat plate model gives as good agreement, or better, with the data as some prediction models that consider the blade thickness.
The aeroelastic sample cases originally defined have proven their value and are thus presently kept in the data-base. It is however important to point out that some uncertainties as regards to the exact value of the inlet flow angle still exist. It has been found by different researchers that a better agreement with the steady-state blade surface pressure distribution is obtained if the inlet flow angle is modified about 2o [Bölcs and Fransson, 1986, p. 61], or if a stream-tube variation is introduced. Results on this standard configuration have been presented by Chiang and Fleeter [1989b] and Huff [1989]. These authors have, as other researchers, found a good agreement with the experimental data.