INVESTIGATIONS OF THREE-DIMENSIONAL CASCADES

摘要

The actual flow conditions within the passages of a 14-inch diameter, four-bladed impeller of a mixed flow compressor have been investigated and compared with design values, which were based on axial symmetry and incom¬pressible, nonviscous flow. The blades were designed as bound-vortex sheets, having a zero tangential component of vorticity, i.e., the velocity distribution in meridional planes is not disturbed by the blades. Flow surveys at the impeller outlet from hub to shroud and from blade to blade were made with a three-dimensional, spherical pitot probe mounted on the impeller. This probe and also mercury seals for transferring the pressure signals from the rotating shaft to stationary manometers were especially developed for this investigation. Test runs conducted in the range from 1500 to 3000 rpm and from 8.7 to 44.1 cubic feet per second showed that the shape of the meridional velocity distribution between hub and shroud agrees essentially with the theory. However, in the blade-to-blade direction the distribution curves for the meridional velocity are displaced as much as 20% above and 10% below the average. Variations in the cone angle of the relative velocity are only in the order of 2° and 3°, i.e., the flow does not "twist" away much from surfaces of revolution. The median impeller slip factor was 0.57 within the test range.