State-of-the-art centrifugal compressors for turbocharger applications are required to provide broad compressor maps, high pressure ratios and high ef ciency levels. Usually these requirements are perceived as contradictory and represent challenging design targets. Various techniques for map width enhancements have been reported since the early 1980s. ABB Turbo Systems Limited has adopted a simple bleed system for internal ow recirculation to a high owrate, high ef ciency, pressure ratio 4.2 centrifugal compressor stage. After initial test runs had proved the effectiveness of the bleed system, computational uid dynamics (CFD) calculations were performed in order to gain insight into the ow pattern in both the compressor stage and the bleed system. The simulations explain the effectiveness by comparing them with simulations without the bleed channel. Selected streamline and iso-surface plots show the effect of the bleed channel ow on the main ow through the impeller. Four more variants of bleed channels have been modelled and investigated by CFD in order to optimize the bleed slot location and dimension. The most promising con guration, which showed a signi cant improvement in map width without a loss in ef ciency, was subsequently built and tested. This test con rmed the validity of the CFD simulation results.

A casing treatment with axial and radial skewed slots ending in a plenum chamber has experimentally been investigated at a highly subsonic axial compressor stage. The aim was to investigate the physical phenomenon of this treatment family that is responsible for the stabilization of the blade passage flow and the drop in efficiency mostly observed. The experimentally gained performance results of this configuration showed an extension of the operating range by approximately 50%, while the efficiency for design conditions is reduced by 1.4%. Apart from this, operating points at part load conditions have been observed nearly without any loss in efficiency. The detailed flow analysis is performed by means of results from a 3D pneumatic probe with temperature sensor and a dynamic total pressure probe. The focus of the investigations is on the incidence flow to the compressor rotor, the tip clearance vortex flow in combination with the wall stall separation region and the blade stall due to suction side separation. The casing treatment configuration is investigated with a special interest in detecting those effects which have an impact on the stability and the compressor overall efficiency, including the interaction of the rotor and the stator flow fields.

A casing treatment with axial and radial skewed slots ending in a plenum chamber has numerically been investigated at a highly subsonic axial compressor stage. The aim was to understand the physical phenomena of this treatment family that are responsible for the stabilization of the blade passage flow and the drop in efficiency mostly observed. Unsteady 3D Reynolds-averaged simulations were performed with the commercial CFD Code TASCflow 2.12. The closure problem was faced with a standard k-ε high Reynolds turbulence model and a logarithmic wall function. Two configurations with solid casing and casing treatment were investigated at the operating points with maximum efficiency and on the stability line. The experimentally gained performance results of this configuration show an extension of the operating range of approximately 50% based on the operating range at nominal speed, while the efficiency for design conditions falls by 1.4%. Apart from this, measurements at part load conditions show operating points without any loss in efficiency. The numerical simulations predict this efficiency drop as well. The detailed analysis is performed for the solid casing and casing treatment configuration at the operating point on the stability line. Influences of the incidence flow, the tip clearance vortex and the blade suction side separation were investigated. Special interest is directed towards the interaction of the casing treatment with the blade passage flow field and a detailed analysis of the flow inside the casing treatment, the effect of the plenum chamber and the interaction with the treatment slot flow is performed.

A casing treatment with axial and radial skewed slots ending in a plenum chamber has experimentally been investigated at a highly subsonic axial compressor stage. The aim was to investigate the physical phenomenon of this treatment family that is responsible for the stabilization of the blade passage flow and the drop in efficiency mostly observed. The experimentally gained performance results of this configuration showed an extension of the operating range by approximately 50%, while the efficiency for design conditions is reduced by 1.4%. Apart from this, operating points at part load conditions have been observed nearly without any loss in efficiency. The detailed flow analysis is performed by means of results from a 3D pneumatic probe with temperature sensor and a dynamic total pressure probe. The focus of the investigations is on the incidence flow to the compressor rotor, the tip clearance vortex flow in combination with the wall stall separation region and the blade stall due to suction side separation. The casing treatment configuration is investigated with a special interest in detecting those effects which have an impact on the stability and the compressor overall efficiency, including the interaction of the rotor and the stator flow fields.

An industrial axial compressor has to meet a wide range of operation requirements and therefore must run within the whole compressor map without restrictions at an overall high level of efficiency. Additionally a robust design is required allowing a continuous operation of up to five years under industrial boundary conditions without inspection. These requirements led the industrial turbomachinery market to be generally conservative and sensitive to every single change through modern compressor development. The consequence for industrial compressor designs are, that these have made only moderate development steps during the last 50 years. This paper deals with a novel hybrid axial flow compressor, which combines the advantages of an conventional industrial compressor, such as good operating range and efficiency, with the advantages of gas turbine compressors, mainly the higher power density resulting in a higher stage pressure ratio. Furthermore, the surge robustness of the novel compressor blading has been strongly improved. Starting from scratch, the development began with comprehensive matrix studies in all areas of the design, taking into account aerodynamics, mechanics, rotor dynamics and power density in order to ascertain the overall optimum for this new hybrid generation. State of the art CFD analysis has been intensively used to optimize the compressor blading as well as the flow behavior of inlet and exit for the specified requirements and different compressor control mechanisms. The novel hybrid compressor is designed for a volume flow of 930 000 m3/h and allows a scaling from 100 000 up to 1 500 000 m3/h of air. To verify the design, a rig — downscaled by the factor of 3 — was tested. The rig was intensively instrumented with thermocouples and pressure probes, a torquemeter, strain gauges, tip-timing probes, and transient pressure transducers. Besides the measurement of blading performance, inlet and exit flange-to-flange instrumentation has been used to collect performance data under a variety of industrial operating conditions. The compressor behavior will be presented with a focus on aerodynamic aspects. The analytical and experimental data will be discussed in detail.