Session: 40-07 Turbine Secondary Flows and Interactions

Paper Number: 128243

128243 - LES Analysis of Loss Anomaly of a Turbine Blade With Large Trailing Edge Radius 

There is great interest in the usage of Ceramic Matrix Composites (CMC) as a turbine blade material. CMCs can tolerate higher temperatures than alloyed metallic blades, resulting in better thermal efficiency of gas turbine engines. The unique manufacturing process of the CMC blades may result in a larger trailing edge thickness. The design space therefore needs to be updated due to the resulting relevant flow physics. It is critical to fully understand the aerodynamic performance of the CMC blades using experimental and numerical simulations.

Recently, experimental results acquired at NASA Glenn Transonic Turbine Blade Cascade Rig show that a loss measure increases with increasing trailing edge thickness and monotonically decrease as the Reynolds number (Re) increases [1]. However, it was observed that the losses locally peak at a Re ~1.2x10⁶ and then subsequently drop. A similar observation may be made when investigating the data reported by Kerestes et al. [2]. They experimentally and numerically investigated the various designs of low-pressure turbine (LPT) blades. The experimental data showed that the losses suddenly increase at the high exit Re (~140,000) which was not captured by their numerical simulations. A possible cause of this intriguing phenomenon is transonic vortex shedding, which is the mechanism of vortex shedding promoted by reflected shed shockwaves at the trailing edge at a relatively high Re [3]. Recently, Rossiter et al. [4] performed Large Eddy simulation (LES) over a large range of Re (1.5x10⁵ < Re < 2.5x10⁶) to investigate the aerodynamics of a single blade in the context of transonic vortex shedding and reported that there is a transitional regime in the kinematic energy loss coefficient profile in the range of 8x10⁵ < Re < 1.0x10⁶. The blade shapes in [4] are different from the ones in [1] and the loss profiles plateau in the large Reregime unlike the one reported in [1] which shows a peak. 

A RANS analysis or a low-resolution LES does not produce this apparent anomaly and thus it is worth performing a high-resolution LES to investigate the aerodynamics of the CMC blade in the light of these recent studies. To this end, we generated a very fine mesh by significantly refining the mesh resolution at the suction and pressure sides as well as near the trailing edge region which yielded a grid with the total mesh count of ~200 million cells, which is comparable to what was investigated in [4]. 

In the final paper, we will discuss numerical challenges of the simulation at the high-Re number in the presence of strong free-stream turbulence and we will offer a physical explanation of the local increase in the losses for the CMC blade occurring at Re ~1.2x10⁶.

Presenting Author: Kenji Miki NASA Glenn Research Center

Presenting Author Biography: Georgia Institute of Technology —Atlanta, GA, 2003-2008– Ph.D. Program, Aerospace Engineering
Institute for Computational Engineering and Sciences (ICES), The University of Texas at Austin - 2008-2012, Title: Postdoctoral Researcher
General Electric (GE), Global Research Center 2012-2014- Title: Lead Engineer
Then I joined NASA, Glenn Research Center (GRC) 2014-present as a civil servant.

My specialty is about numerical modeling using LES or RANS for application of turbomachinery, combustor-turbine interaction, and rotating detonation engines. I am the AIAA associate fellow and serve on the AIAA Gas Turbine Engines Technical Committee.

Authors:

Kenji Miki NASA Glenn Research Center
Ali Ameri The Ohio State University / NASA Glenn Research Center
Paul Giel HX5 LLC / NASA Glenn Research Center