The modern aero-engine aims to achieve light weight, higher efficiency, lower initial cost, and maintenance. High-stage loading design is one of the most efficient technologies for high-pressure turbine (HPT). It can reduce weight prominently by the means of increasing the stage loading corresponding to reducing the number of stages. However, the transonic turbine becomes inevitable with the increasing of stage loading in HPT, and this implies a reduction in the efficiency due to the shock losses. The trailing edge shock system is the main characteristic of the transonic turbine cascade. The shock formed on the pressure side propagates towards the suction surface of the adjacent blade. It results in the shock-wave/boundary-layer interaction (SWBLI) on the blade suction surface. Details of the flow characteristics in the SWBLI region must be investigated to explore potential ways to reduce the loss induced by SWBLI. 

In present work, a round jet with inclination angle 135° upstream the throat on the suction surface of the transonic turbine cascade is applied to perform as a variable throat area device, to achieve the adjustment of mass flow matching for the variable cycle engine. The effect of this flow control technique is illustrated in our previous literatures. Application of the jet on suction surface will introduce complicated vortical structures along the suction surface, and the flow within the boundary layer. Moreover the shock wave system will also be different with the no jet case. So the details of the flow near the SWBLI region with suction side jet is appealing for the scholars. In this article, the large eddy simulation results and analysis about the SWBLI  and suction side jet are presented for a transonic turbine cascade with the isentropic outlet Mach number 1.31. three jet velocities, namely 50,150and 250 m/s,  are given to illustrated the effect of the suction side jet on the SWBLI.

The numerical results indicates that for the no jet case, due to the locally high concave curvature on the pressure side profile, this dimple close to the trailing edge will form the double shock system in the turbine passage. The first incident shock does not induce the boundary layer separation, and the base pressure at the trailing edge is increased due to the dimple. But separation bubble appears due to the second strong incident shock.

Due to the complex vortex structures induced by suction side jet, the shock wave system in the passage is different from the baseline, and the flow characteristics in the shock wave boundary layer interaction region is changed. Length of the separation zone on the suction surface is reduced with suction side jet duet to the vortex structures along the suction side. The low momentum fluid within boundary layer is reenergized by the vortices. Length of the separation zone decreases with increasing jet inlet velocity.

The dominant frequency downstream the separation bubble is multi-frequency scale structure for the no jet case, the amplitude arrives peak value close to the frequencies around SL=0.42.  However, the flow unsteadiness caused by SWBLI in the turbine blade surface is weakened by introduction of round jet, the frequencies of the coherent structures dominant the flow unsteadiness downstream the jet flow on the blade suction surface.

The round jet on the suction surface enhances the unsteadiness upstream the SWBLI region, whereas the flow unsteadiness induced by SWBLI decreases significantly close to the SWBLI region. The maximum pressure fluctuation takes up nearly 13% of the local mean pressure in the no jet case in the SWBLI region, but only 8% for the jet case.


Effect of Suction Side Jet on the Shock Wave Boundary Layer Interaction in Transonic Turbine Cascade

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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