A detailed experimental comparison of axial compressor blades designed for free vortex flow and equivalent untwisted and twisted constant section blades

Abstract

As a contribution to the knowledge of the performance of potentially cheap compressor blades, six stages of both twisted and untwisted constant section or' strip ' blades were tested at a low speed in the 106 compressor. The performance is compared with that of six stages of equivalent free vortex blades, and interstage flow traverses provide the more detailed flow information. In terms of maximum stage efficiency, the twisted constant section blades are half a per cent better than the free vortex blades and the untwisted blades are one and a half per cent worse. Both twisted and untwisted 'strip' blades have a higher surge flow than the free vortex blades, but there is very little difference in the temperature rise characteristics. At values of flow coefficient greater than the design flow, the performance of the three sets of blades becomes almost identical and the application of 'strip' blades at a diameter ratio of 0.75 involves no sacrifice in performance. Incidental tests on the relation between pressure coefficient and Reynolds number show that the maximum pressure coefficient falls to about half its original value for a change in Re from 1.3 x 10power5 to 0.023 x 10power5 and this is accompanied by a reduction in the surge point flow coefficient.