Session: 31-01 Tandem Design

Paper Number: 151868

Experimental and Numerical Evaluation of a Highly-Loaded Multistage Low-Speed Axial Compressor Featuring Tandem Stator Vanes: Part 1 — Operational Behavior and Steady-State Flow Field 

An increase of aerodynamic loading of today's traditionally designed compressors is strongly limited as the geometry of the aerofoils used is already highly optimized. However, fundamental research has shown that a significantly higher loading can be achieved using tandem aerofoil configurations. This enabling innovative technology opens up new opportunities for increasing the specific work per stage beyond that of traditionally designed compressors whilst maintaining a high level of efficiency. For a given compressor pressure ratio, the tandem vane concept can be expected to significantly reduce the length and stage count of a compressor, with corresponding benefits for the architecture and cycle of future aircraft engines. New blading concepts are therefore investigated numerically and experimentally on a 3.5-stage low-speed compressor design, simulated in CFD and validated on the FRANCC research test rig. The design of the research compressor is targeted at rear stages of axial high-pressure compressors, consisting of an inlet guide vane and three stages with conventional rotors and tandem stator vanes. This paper series presents results of an investigation of the operational behavior, the steady-state and time-resolved flow field at design and degraded total pressure inlet profile conditions.

Part 1 of this paper series investigates the operational behavior and steady-state flow field throughout the multistage compressor. Results of experimental investigations are presented alongside with those of numerical simulations.

The research compressor is equipped with extensive instrumentation permanently installed in the compressor for measuring the operational overall and stagewise performance. The flow field is captured using 5-hole probes, which are traversed downstream of each blade row at four different operating points.

The numerical model consists of 3.5 stages including the stator cavity geometry and real-geometry features such as tip clearances, fillet radii and sealing gaps. The numerical work was performed using steady-state 3D RANS simulations. To obtain a valid comparison of prediction and experiment, the simulations were performed post-test with inlet conditions derived from the measurement.

The operational behavior shows a wide operating range of the compressor with a stall limit at approx. 82% of the design mass flow. The efficiency characteristic shows a wide plateau at the level of state-of-the-art designs. Towards throttled operation, the efficiency only drops slightly, showing the capability of the tandem stators to withstand high aerodynamic loading. The CFD simulations capture the major performance characteristics and the stall limit well, but show some systematic offset.

The rotor flow field investigations show consistent trends of the CFD and the experiment but with a slight systematic difference in the pressure rise and flow angle. Downstream of the tandem stators, the measurements resolve the flow structures of the tandem configuration. Here a very good agreement of experiment and simulation is observed.

This work presented here proves, that compressor stages with tandem stator vanes are capable of high aerodynamic loading with a good overall efficiency and a wide operating range. Furthermore, it is shown that 3D numerical simulations are capable of resolving the flow structures and operating behavior obtained from the experiment properly, but some misalignment in remained. Further work carried out on the low-speed compressor is presented in parts 2 and 3 of the paper series.

Presenting Author: Daniel Jäger Technical University of Munich, Institute of Turbomachinery and Flight Propulsion

Presenting Author Biography: Daniel Jäger studied mechanical engineering at the Technical University Munich. He got
engaged with flight propulsion systems during his Bachelor’s and Master’s thesis.
Following that, he joined the Institute of Turbomachinery and Flight Propulsion at Technical
University Munich as a researcher. There, he was responsible for the buildup of the new
low-speed axial compressor test rig “FRANCC” at the institute. Since the commissioning of
the rig, he is conducting experimental investigations of tandem stators. His research focus
lies on the investigation of the multistage behavior and unsteady flow phenomena of these
stators.
Besides his research activities, he supports a lecture on the fundamentals of
turbomachinery for undergraduate students and supervises a student group performing
research on small flight propulsion systems.

Authors:

Daniel Jäger Technical University of Munich, Institute of Turbomachinery and Flight Propulsion
Patrick Steudel Technical University of Munich, Institute of Turbomachinery and Flight Propulsion
Volker Gümmer Technical University of Munich, Institute of Turbomachinery and Flight Propulsion