Session: 32-05 Low Pressure Turbines 2

Paper Number: 124285

124285 - Impact of High Freestream Turbulence on LPT Endwall Flow – Part II: Endwall Flow Dynamics 

The flow field surrounding low pressure turbine blades, specifically the endwall vortical structures, are intricate and unsteady. Prior research established that these structures are associated with significant losses in the endwall region. In order to design advanced turbines and implement flow control, a better knowledge of the unsteady flow characteristics is required. The exact location and behavior of the endwall vortical structures is tied to the incoming boundary layer state; therefore, the incoming freestream turbulence is expected to impact their dynamic characteristics and the associated losses. As discussed in Part I, the incoming turbulence intensity was varied between 1% and 8% at three different Reynolds numbers within a linear cascade of high-lift high-work low-pressure turbine blades. The focus of this paper will be on the effect elevated freestream turbulence has on the unsteady dynamics of the endwall flow structures. Three planes of high-speed stereo particle image velocimetry and two planes of high-speed flow visualization were leveraged to gain a more complete understanding of the flow field in the endwall region of the passage. From a detailed flow analysis completed with the SPIV measurements, it was established that elevating the turbulence levels impacted the time-dependent characteristics of the vortices in the endwall region. Differences in temporal characteristics were observed in all planes, however, the bimodal behavior documented by other researchers near the leading edge was still observed. The vortex was observed to intermittently lose coherence at the leading edge and in the passage. The frequency of the loss of coherence events was altered as the freestream turbulence was elevated. Increasing the turbulence levels increased underlying instabilities of the leading edge vortex and dominant vortices in the passage, implying utilizing flow control to disturb the vortex in an unsteady manner at the leading edge or increasing the unsteadiness in the incoming boundary layer is likely to have a similar impact.

Acknowledgements: Distribution Statement A: Approved for Public Release; Distribution is Unlimited. PA# AFRL-2023-4860. This material is based upon work supported by the Air Force Office of Scientific Research under award number FA9550-21RQCOR016 Any opinions, finding, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the United States Air Force.

Presenting Author: Molly Donovan U.S. Air Force Research Laboratory

Presenting Author Biography: Molly completed her both her bachelor's' and masters degrees in Mechanical Engineering from Wright State University in 2018 and 2019. She graduated with her Ph.D. in aerospace engineering from the University of Dayton in the Spring of 2023. Following graduation she began working as a Aerospace Engineering in the Turbine Engine Division at U.S. Air Force Research Laboratory completing experimental research in the aerodynamics of low pressure turbine blades.

Authors:

Molly Donovan U.S. Air Force Research Laboratory
Christopher Marks U.S. Air Force Research Laboratory
Nathan Fletcher US Air Force Research Laboratory
Markus Rumpfkeil University of Dayton