Computational Study of the Effects of Protruding Studs Casing Treatment on the Performance of an Axial Transonic Turbofan

A Dissertation Presented for the Doctor of Philosophy in Computational Engineering, The University of Tennessee at Chattanooga

Max David Collao, May 2017


Turbo-compressors play crucial roles in the operation of air-breathing engines and special attention is given to the compressor's ability to withstand adverse operating conditions. Various methods have been devised in order to enhance compressor stability and increase compressor stall margin, usually with some sacrifice of performance and efficiency. Active methods make use of external devices injecting and/or bleeding air from the compressor duct. Passive methods are primarily based on casing treatments, often involving protrusions into the rotor casing, to affect the behavior of the flow in favorable ways. In either case, it is desirable that the stability enhancing method be as simple as possible and that it keep performance and/or efficiency degradation to a minimum. 

The present work consists of a CFD analysis performed to evaluate the impact of a novel form of passive stability control on the operation of an axial flow compression system. The casing treatment consists of ``studs,'' which are solid structures protruding from the casing into the duct. These structures are located slightly downstream of the fan rotor. The compression system that is studied in this investigation is the NASA SDT2-R4 transonic turbofan stage. The simulation software used is ``Tenasi,'' the UTC-SimCenter developed flow solver. 

Various simulations were conducted of the turbofan operation with and without casing treatment. Measures of performance and efficiency of the turbofan stage with no casing treatment were computed, and the results showed good agreement with available experimental data. The computed results from simulation with casing treatment suggest that protruding studs have the potential of improving the stability of the turbofan. The computed stall margin increase using an initial configuration of protruding studs is about 5.4% of mass flow rate, with a decrease in efficiency of about 1.6%. The flow-field was investigated through visualizations of flow features in order to understand the mechanisms of flow instabilities and stability enhancement. Other simulations were also carried out using modifications of the original studs to assess further changes in performance.

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