A Low Pressure Turbine at Extreme Off-Design Operation

Abstract

In a cooperative project between the Institute of Aircraft Propulsion Systems and MTU Aero Engines GmbH, a two-stage low pressure turbine with integrated 3D airfoil and endwall contouring is tested. The experimental data taken in the altitude test-facility study the effect of high incidence in off-design operation. Steady measurements are covering a wide range of Reynolds numbers between 40,000 and 180,000. The results are compared with steady multistage CFD predictions with a focus on the stator rows. A first unsteady simulation is taken into account as well. The CFD simulations include leakage flow paths with disk cavities modeled. Compared to design operation the extreme off-design high-incidence conditions lead to a different flow-field Reynolds number sensitivity. Airfoil lift data reveals changing incidence with Reynolds number of the second stage. Increased leading edge loading of the second vane indicates a strong cross channel pressure gradient in the second stage leading to larger secondary flow regions and a more three-dimensional flow-field. Global characteristics and area traverse data of the second vane are discussed. The unsteady CFD approach indicates improvement in the numerical prediction of the predominating flow-field.

Effect of Free-Stream Turbulence on Endwall Flow of Highly Loaded Turbine Cascades in a Wide Range of Incidence

“…Tsujita et al (Tsujita & Yamamoto, 2010) found the horseshoe vortex and the passage vortex increase the secondary loss in the cascade passage at positive incidence angle (i = +5°). Equivalent conclusions were proposed by Benner et al (Benner et al, 2004) and Lipfert et al (Lipfert et al, 2013). The incidence angle influences turbine flow characteristics and requires more comprehensive research in extremely off-design incidence conditions.…”

“…Based on this research, numerous studies on off-design operation (Gao et al, 2020;Kiran & Anish, 2017; have been conducted; NASA Fundamental Aeronautics Program (Variable Speed Power Turbines, VSPT) presented that the high turbine efficiency over a large (40° to 60°) incidence variation and low Reynolds numbers are the key aerodynamic challenges (Welch, 2010). Low Reynolds number operation has been widely studied (Lipfert et al, 2013;Liu et al, 2018;Qu et al, 2020). Nevertheless, the high loaded and transition flow may increase sensitivity to the incidence angle; the underlying coupling mechanism of incidence and FSTI remains to be further investigated.…”

Effects of incidence angle on a low-pressure turbine blade boundary layer evolution through large eddy simulation

“…Zoric et al 8 indicated that because of the adverse pressure gradient, the suction side boundary layer separation and transition processes are strongly affected by the incidence angle. Lipfert et al 9 demonstrated that the high incidence causes an overspeed zone at the front of the suction side. As a consequence, the suction side loading increases largely and the passage vortex gains more strength.…”

“…Lipfert et al. 9 demonstrated that the high incidence causes an overspeed zone at the front of the suction side. As a consequence, the suction side loading increases largely and the passage vortex gains more strength.…”