Committee Chair

Webster, Robert S.

Committee Member

Sreenivas, Kidambi; Newman, James C., III; Matthews, Matt


Dept. of Computational Engineering


College of Engineering and Computer Science


University of Tennessee at Chattanooga

Place of Publication

Chattanooga (Tenn.)


Turbo-compressors play a crucial role 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 flow paths 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 fan stage. 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 trailing edge. The stage that is studied in this investigation is the NASA SDT2 R4 transonic turbofan. The simulation software used is “Tenasi,” an in-house 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 to improve the stability of the turbofan. The computed stall margin increase using an initial configuration of protruding studs is about 5.4% in terms 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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Ph. D.; A dissertation submitted to the faculty of the University of Tennessee at Chattanooga in partial fulfillment of the requirements of the degree of Doctor of Philosophy.




Compressors; Turbomachines


Turbofan; Compression system; Stability enhancing method; CFD; Simulations; SDT2-R4

Document Type

Doctoral dissertations




xvi, 126 leaves