Detailed measurements of complex flow fields within the NASA Low Speed Centrifugal Compressor (LSCC) have been acquired. The measurement data provide insight into the fundamental physics of flow in centrifugal compressors, and can be used to assess computational fluid dynamics codes and to develop flow-physics models. The resultant benefit is better predictive computational tools and shorter design cycle times.

Centrifugal compressors are widely used in auxiliary power-unit turbochargers, small gas turbine engines, gas-processing plants, and other applications. However, in comparison with their axial-flow counterparts, centrifugal compressors have generally been investigated in less detail.

The LSCC was designed to be representative of conventional high-speed subsonic compressors typically employed in small gas turbine engines. However, the measurements were acquired in the LSCC at low subsonic speeds, where the flowing air behaves as though it were essentially incompressible. As such, the measurements are reasonably representative of what would be found in many centrifugal pumps. The measurement data can therefore be used to validate any aerodynamical computer code that is applicable to centrifugal pumps.

Figure 1. The Dots Indicate Locations, most within the passages between rotor blades, where flow velocities were measured by a laser anemometer.

The large size and low speed of the LSCC enable the detailed measurement, by use of a laser anemometer, of all three components of velocity within passages between rotor blades, with a spatial resolution unparalleled in investigations of high-speed compressors. For example, three-dimensional viscous flows that occur very near the surfaces of blades were measured in detail. Complementary measurements of static pressures on blade and shroud surfaces, pressure measurements by pneumatic probes at various positions across inlet and exit surfaces were acquired, and flow-visualization tracings were also acquired. Collectively, the results of the experiments in the LSCC constitute a benchmark set of high-quality data for assessing the predictive capabilities of state-of-the-art three-dimensional viscous-flow computer codes.

Figure 2. Selected Results of Velocity Measurements illustrate the general nature of the data acquired. "PS" and "SS" denote the pressure and suction surface, respectively, of a rotor blade. For clarity, different vector scales are used in the main and detail plots of velocity vectors, and the pitchwise spatial resolution of the main plot is 1/3 that of the detail plots.

Figure 1 illustrates the LSCC impeller and the locations of laser-anemometer measurements. The upper part of Figure 2 shows results of velocity measurements taken at the 64-percent meridional chord position, indicating the extent of the through-flow-velocity deficit characteristic of centrifugal-compressor flow fields. The lower part of Figure 2 illustrates the nature of secondary flow measurements at the same location, along with some details that demonstrate the resolution of measurements acquired in viscous-flow regions near blade surfaces.

This work was done by Randall M. Chriss, Anthony J. Strazisar, and Jerry R. Wood of Lewis Research Center and Michael D. Hathaway of the U. S. Army Research Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com under the Machinery/Automation category.

Inquiries concerning rights for the commercial use of this invention should be addressed to

NASA Lewis Research Center
Commercial Technology Office
Attn: Tech Brief Patent Status
Mail Stop 7 — 3
21000 Brookpark Road
Cleveland
Ohio 44135.

Refer to LEW-16417.


NASA Tech Briefs Magazine

This article first appeared in the July, 1998 issue of NASA Tech Briefs Magazine.

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