Bernd Becker

Future aero engine designs must address environmental challenges and meet noise and emissions regulations. To increase efficiency and reduce size, axial compressors require higher pressure ratios and a more compact design, leading to necessary modifications in the variable stator vanes, especially in the stator hub region. This study examines the impact of a variable cantilevered stator on the performance and aerodynamics of a 1.5-stage transonic compressor, representative of a high-pressure compressor front stage. Experimental tests at the transonic compressor test rig at Technical University of Darmstadt involved two variable stators with identical airfoil designs but different hub configurations, using the same inlet guide vane and rotor. Detailed aerodynamic analysis was conducted using steady and unsteady instrumentation. The cantilevered stator achieved a 2% increase in efficiency and a 1% increase in total pressure ratio, due to higher aerodynamic loading and reduced pressure losses. The primary performance gain comes from the reduction of the hub blockage area. The cantilevered stator also performed well at near stall conditions, unlike the shrouded stator. Time-resolved measurements indicated that loss mechanisms are closely linked to the rotor wake phase. Overall, variable cantilevered stators outperformed shrouded stators in this compressor stage.

The aerodynamic impact of hub gap leakage on the performance characteristics of an axial compressor rotor in conventional design (no blisk) with a high hub-to-tip ratio has been investigated using three-dimensional steady-state Reynolds-averaged Navier–Stokes simulations. The inclusion of circumferential hub gaps in front of the leading edge and after the trailing edge, as well as inter-platform leakage, reduced the total pressure ratio and the polytropic efficiency of the rotor by as much as 3.74% and 3.97%, respectively, compared to a design case with clean endwalls. Potential design recommendations in terms of improved aerodynamic robustness against leakage effects were derived from the separate sealing of each hub gap. Six geometry modifications were assessed, which based on these results. In a throttled operating condition, large edge radii in the front gap on the disk and platform partially recovered the initial losses of both the total pressure ratio (17.7%) and polytropic efficiency (19.6%). A circular lateral platform shape with the opening pointing toward the blade’s pressure side showed superior loss recovery capabilities at a dethrottled operating point. The combination of both features did not reduce the losses further. However, the circular lateral platform shape combined with smaller front gap chamfers proved more beneficial in a throttled state.

This paper experimentally investigates a highly-loaded 1.5-stage transonic axial compressor, which comprises a variable inlet guide vane, a BLISK rotor, and a variable stator in tandem arrangement. A detailed comparison between the newly designed compressor stage and a reference stage with a conventional stator design was conducted by using extensive instrumentation. Thus, steady and unsteady phenomena—focusing on the aerodynamic and aeroelastic behavior—were analyzed. Due to the new stator vane design, a higher aerodynamic stator vane loading was pursued, while the vane count was reduced. This, in turn, allowed a rotor design with an increased work coefficient. This experimental study revealed several effects of the optimized compressor stage in terms of both performance and the corresponding aerodynamics, as well as the aeroelastic behavior.

This study investigates the aerodynamic and aeroelastic characteristics of a transonic axial compressor, focusing on blade count reduced rotor behavior. The analysis is based on experiments, conducted at the Transonic Compressor Darmstadt test rig at Technical University of Darmstadt and compulsory simulations. In order to obtain measurement data for the detailed aerodynamic and aeroelastic investigation, extensive steady and unsteady instrumentation was applied. Besides transient measurements at the stability limit to determine the operating range and limiting phenomena, performance measurements were performed, presenting promising results with respect to the capabilities of blade count reduced rotors. Close to the stability limit, aerodynamic disturbances like radial vortices were detected for both rotors, varying in size, count, speed and trajectory. Comparing the rotor configurations results in different stability limits along the compressor map as well as varying aeromechanical behavior. Those effects can partially be traced to the variation in blade pitch and associated aerodynamics.

The paper presents numerical and experimental results for a low speed compressor cascade with bleed air removal at the endwall. The aerofoil design is representative for a stator blade in a modern high pressure compressor near the casing wall. Secondary air is commonly supplied by simple bleed geometries downstream of stator rows. The focus of the present investigation was the systematic development of a passage integrated bleed configuration. With the assumption of an invariable bleed mass flow rate it should be designed to provide an advantageous effect on the main flow. Furthermore, a high pressure recovery in the bleed flow was aspired. Steady 3D RANS simulations were performed using the Spalart-Allmaras turbulence model. In both numerical simulations and experiments, an improved performance was found. Beside reduced losses and increased pressure rise, the wake flow downstream of the customized bleed geometry was found to be more homogeneous with decreased deviations due to a favorable influence on the secondary flow.