Analytical Approach for Quantifying the Working Potential of Blading with and without Casing Treatments

Abstract

To improve the understanding of casing treatments and their working principle, performance and detailed ow measurements were carried out in a transonic compressor. For this purpose an axial slot casing treatment was applied to a datum con guration (Darmstadt Rotor-1). Both are additionally compared to a rotor having the same number of blades and identical blade angles but a tip section enhancement with a slight forward sweep and a smaller tip-gap. For each case corrected, lossless compressor maps are derived from the performance measurements. It shows that a reduction of blockage and the associated redistribution of mass ow increases the work input. In particular, this holds true for the casing treatment con guration at massive throttled mass ows. Additionally the test rig was analytically modeled to derive an ideal compressor map. Theses curves are compared against the experimental, corrected data. It is found that curve gradients match very well for the whole working range and di erent speedlines in the suband transonic regime. In contrast, total pressure ratio and work input are over predicted, whereby deviation is quite negligible. This is seen as an indication that also a real but idealized lossless blading does not use the full theoretical potential of work input. Consequently the quality of a blading is not only determined by the e ciency but also by the rate of actual to theoretical work input, especially in terms of blockage. In some cases the potential of conventional blading could even be exceeded by the use of casing treatments.