GB941343A - Improvements in or relating to impeller blading for centrifugal compressors - Google Patents

Abstract

941,343. Controlling boundary layer air. R. BIRMANN. Aug. 29, 1961, No. 31059/61. Heading F2R. [Also in Division F1] A compressor comprises an impeller hub carrying blades, each of which comprises two spaced sections, the inlet edge 67 of the trailing section 66 projecting beyond the inlet edge 69 of the leading section 68 in a direction opposite to the direction of flow. The inlet edges 67 lie on an imaginary cone coaxial with the impeller, while the inlet edges 69 are radial (or more nearly radial), both inlet edges of each blade being orthogonal to the flow reaching it. In addition to the main flow between the blades, an auxiliary flow takes place through each blade, entering at 117 and discharging at 118, whereby the boundary layers along the initial portion of the concave side of the trailing section 66 are energized by being sucked away. This prevents separation of flow from the blades and permits the main flow to enter smoothly the passages between the blades under abnormal conditions in which the relative velocity is more or less at right angles to the blades. The outlet edge 66<1> of each trailing section 66 terminates short of the outlet edge 681 of the corresponding leading section 68 in the direction of flow, whereby the auxiliary flow is discharged slightly upstream of the impeller outer diameter in such a manner that the boundary layers that tend to form on the trailing side of each blade are energized and blown away and the discharge velocity is made uniform around the impeller periphery. Where the compressor operates over part of its range of operation as an expander or turbine rather than a compressor, good efficiency under these conditions can be obtained by having a large inlet eye, the mean square value of the inner and outer inlet diameters of the impeller being made approximately 55 to 60% of the discharge diameter. Specification 941,342 is referred to.