14th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
Variable inlet guide vanes (VIGVs) are most commonly used as the major control unit of integrally geared multi-shaft compressors. Accordingly, the performance of the VIGV is crucial for both an efficient and wide operation range of the compressor. In order to consider design improvements, the loss mechanisms and utilisation limits of common VIGVs need to be better understood. Experimental investigations in the wake of a typical, commercially used VIGV configurations were therefore conducted at the swirl generator wind tunnel of the Bundeswehr University Munich. The particular design of the test facility allows full field traverses in the wake of annular cascades at application oriented subsonic flow conditions. The traverses were carried out by a cranked five-hole probe at varied stagger angles of the VIGV between a range of 50° and 90° in steps of 10°, covering the low loss operating range as well as its limits defined by an open flow separation at the blades. Furthermore, local inflow inhomogeneities, mainly caused by a distinct turbulent inflow velocity profile, are considered during the data processing. In addition to previous research efforts, not only profile losses but also local secondary flow loss effects generated by the three-dimensional vane geometry are resolved in full detail and are hence considered in the loss characterisation. Thus, a precise and more comprehensive local and total loss assessment is acquired. Besides the pure profile losses dominating the region downstream of the blade at mid height, considerable loss generated by the interaction of the flow with the wall is identified at the outer region of the cross section. As to be expected, this effect increases with decreasing stagger angles. Furthermore, the formation of a blade tip vortex is observed downstream of the blade tip. With decreasing stagger angles, however, this effect is superimposed by flow separation effects at the suction side of the blades as will be shown in the full paper.