A new transonic compressor test rig for gas turbine front stages was commissioned at the Technical University of Darmstadt in 2018. In the first measurement campaign numerous transient stall maneuvers were conducted by throttling the compressor beyond its stability limit. Several distinct phenomena can be observed during in-stall operation. This work gives an overview of those different manifestations of stall with focus on classification and characterization. For this purpose, detailed post-processing and unsteady data analysis are conducted providing information in terms of operating points, propagation speeds of disturbances, structural behavior of the rotor as well as unsteady wall pressure fields. The authors propose explanations for the different phenomena and possible influences of the rig on the in-stall behavior are discussed. Finally, an overview of the occurrence of the detected phenomena is given.
In this paper we give insight into characteristics of a 1.5-stage transonic axial compressor rig with focus on surge during a stalled operating point. The new compressor rig at TU Darmstadt is representative for the front stage of an industrial gas turbine. Transient throttling maneuvers were conducted for multiple operating points during the first test campaign of the TCD 2 (Transonic Compressor Darmstadt 2), providing an extensive set of unsteady structural and aerodynamic data beyond the stability limit. Enhanced analytical methods allow detailed studies including aerodynamic spectral analysis as well as determination of propagation speed and size of disturbances. The results differ from observations at comparable test rigs, revealing an interesting manifestation of stall: In a wide range of the stability limit it shows a periodicity. The stall emerges and vanishes recurrently, causing strong oscillations of the pressure ratio. Additional unsteady measurements of the mass flow indicate a surge. Regarding the compressor map, this results in staggering operating points, showing a hysteresis. However, due to a rather small plenum and experience with a similar test rig the TCD 2 was not expected to surge. Comprehensive analyses are carried out to characterize this phenomenon.
In this paper we give insight into characteristics of a 1.5-stage transonic axial compressor rig with focus on surge during a stalled operating point. The new compressor rig at TU Darmstadt is representative for the front stage of an industrial gas turbine. Transient throttling maneuvers were conducted for multiple operating points during the first test campaign of the TCD 2 (Transonic Compressor Darmstadt 2), providing an extensive set of unsteady structural and aerodynamic data beyond the stability limit. Enhanced analytical methods allow detailed studies including aerodynamic spectral analysis as well as determination of propagation speed and size of disturbances. The results differ from observations at comparable test rigs, revealing an interesting manifestation of stall: In a wide range of the stability limit it shows a periodicity. The stall emerges and vanishes recurrently, causing strong oscillations of the pressure ratio. Additional unsteady measurements of the mass flow indicate a surge. Regarding the compressor map, this results in staggering operating points, showing a hysteresis. However, due to a rather small plenum and experience with a similar test rig the TCD 2 was not expected to surge. Comprehensive analyses are carried out to characterize this phenomenon.
In this study the aerodynamic impacts of inlet distortions caused by a gas turbine inlet manifold are analyzed experimentally. The investigation is performed at the new transonic compressor test rig at Technical University of Darmstadt, that features high modularity and extensive instrumentation. The existing axial air inlet system of the test rig is replaced by a scaled inlet manifold. Analog to the design of a real gas turbine intake, bearing support struts are integrated in the experimental setup to investigate their interaction with the inlet distortions. For the detailed analysis of compressor performance, the measurement systems were extended to resolve the flow over the whole circumference at three different axial positions. At the stage inlet a traversable rake with radially distributed five hole probes allows the quantification of the inflow conditions. To determine global compressor characteristics and analyze the propagation of inlet distortions through the compressor, a fully traversable instrumentation at the stage exit is installed. Additionally, a 360°-traversable rotor casing ring, instrumented with unsteady measurement systems, enables the analysis of the effects of non-uniform inflow conditions on the unsteady flow field of the rotor.
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