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Now showing items 1 - 5 of 5

  • Sensitivity of Turbine Efficiency and Flow Structures to Varying Purge Flow

    Schuepbach, P.   Abhari, R. S.   Rose, M. G.   Gier, J.  

    In many turbines, a small amount of air is ejected at the hub rim seal to prevent ingestion of hot gases into the cavity between the stator and the disk. This paper presents an experimental and computational investigation on the sensitivity of a 1.5-stage high-work axial turbine to varying purge flow rates equipped with nonaxisymmetric end walls. The paper gives a correlation of the total-to-total efficiency for different rates of purge flow injection while providing a physical explanation of the responsible mechanisms. The experimental data revealed a transitional behavior of the hub passage vortex when the purge flow injection rate reached 0.9% of the main mass flow. The increase of purge flow caused a lifting off of the rotor passage vortex. The result of this event was an unstable passage vortex resulting in a lower streamwise vorticity and higher unsteadiness. Additionally, a number of subharmonic frequencies appeared at an injection rate of 0.9% that were absent in the other injection rate cases. From the computations it could be seen that the injection created additional normal vorticity at the rotor leading edge. Through turning around the rotor leading edge, a streamwise vorticity component was introduced. The sensitivity to injection in terms of created vorticity was much larger below an injection rate of 0.9% than above.
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  • Influence of Rim Seal Purge Flow on the Performance of an Endwall-Profiled Axial Turbine

    Schuepbach, P.   Abhari, R. S.   Rose, M. G.   Gier, J.  

    Nonaxisymmetric endwall profiling is a promising method to reduce secondary losses in axial turbines. However, in high-pressure turbines, a small amount of air is ejected at the hub rim seal to prevent the ingestion of hot gases into the cavity between the stator and the rotor disk. This rim seal purge flow has a strong influence on the development of the hub secondary flow structures. This paper presents time-resolved experimental and computational data for a one-and-1/2-stage high work axial turbine, showing the influence of purge flow on the performance of two different nonaxisymmetric endwalls and the axisymmetric baseline case. The experimental total-to-total efficiency assessment reveals that the nonaxisymmetric endwalls lose some of their benefit relative to the baseline case when purge is increased. The first endwall design loses 50% of the efficiency improvement seen with low suction, while the second endwall design exhibits a 34% deterioration. The time-resolved computations show that the rotor dominates the static pressure field at the rim seal exit when purge flow is present. Therefore, the purge flow establishes itself as jets emerging at the blade suction side corner. The jet strength is modulated by the first vane pressure field. The jets introduce circumferential vorticity as they enter the annulus. As the injected fluid is turned around the rotor leading edge, a streamwise vortex component is created. The dominating leakage vortex has the same sense of rotation as the rotor hub passage vortex. The first endwall design causes the strongest circumferential variation in the rim seal exit static pressure field. Therefore, the jets are stronger with this geometry and introduce more vorticity than the other two cases. As a consequence the experimental data at the rotor exit shows the greatest unsteadiness within the rotor hub passage with the first endwall design. [DOI: 10.1115/1.4000578]
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  • Effects of Suction and Injection Purge-Flow on the Secondary Flow Structures of a High-Work Turbine

    Schuepbach, P.   Abhari, R. S.   Rose, M. G.   Germain, T.   Raab, I.   Gier, J.  

    In high-pressure turbines, a small amount of air is ejected at the hub rim seal to cool and prevent the ingestion of hot gases into the cavity between the stator and the disk. This paper presents an experimental study of the flow mechanisms that are associated with injection through the hub rim seal at the rotor inlet. Two different injection rates are investigated: nominal sucking of -0.14% of the main massflow and nominal blowing of 0.9%. This investigation is executed on a one-and-1/2-stage axial turbine. The results shown here come from unsteady and steady measurements, which have been acquired upstream and downstream of the rotor. The paper gives a detailed analysis of the changing secondary flow field, as well as unsteady interactions associated with the injection. The injection of fluid causes a very different and generally more unsteady flow field at the rotor exit near the hub. The injection causes the turbine efficiency to deteriorate by about 0.6%.
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  • [ASME ASME Turbo Expo 2009: Power for Land, Sea, and Air - Orlando, Florida, USA (June 8–12, 2009)] Volume 7: Turbomachinery, Parts A and B - Influence of Rim Seal Purge Flow on Performance of an Endwall-Profiled Axial Turbine

    Schuepbach, P.   Abhari, R. S.   Rose, M. G.   Gier, J.  

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  • [ASME ASME Turbo Expo 2008: Power for Land, Sea, and Air - Berlin, Germany (June 9–13, 2008)] Volume 6: Turbomachinery, Parts A, B, and C - Improving Efficiency of a High Work Turbine Using Non-Axisymmetric Endwalls: Part II—Time-Resolved Flow Physics

    Schuepbach, P.   Abhari, R. S.   Rose, M. G.   Germain, T.   Raab, I.   Gier, J.  

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