Multimethod aerodynamic research of engine-realistic turbine rear structures

Doctoral thesis, 2024

Despite the significant advancements in aircraft engine technology over the past years, the aerodynamics of engine-realistic turbine rear structures (TRS) remain largely unexplored. The TRS, a structural and aerodynamic component situated downstream of the low-pressure turbine (LPT), plays a pivotal role in engine aerodynamic performance, deswirling the LPT flow to maximize the engine thrust. However, there is a significant gap in available experimental aerodynamic data on state-of-the-art TRS configurations under engine-relevant conditions.

The thesis closes this critical knowledge gap and provides the first comprehensive aerodynamic analysis of the latest and most advanced TRS configurations. Prior studies on the TRS were limited to simplified models. In contrast, this thesis is focused on two TRS types used in all state-of-the-art turbofan engines: with radial and leaned outlet guide vanes (OGVs). For the first time, aerodynamic tests of engine-realistic TRSs have been carried out under engine-relevant Reynolds numbers and flow coefficients, facilitated by a unique annular 1.5 stage LPT-OGV facility at Chalmers University of Technology, established in 2015.

For the experimental investigation of the TRS flow, a multimethod approach was applied and involved an array of advanced measurement techniques to provide insights into various aspects of TRS flow. This included the use of pressure probes and static pressure taps for acquiring total and static pressure distributions, crucial for estimating pressure losses. The oil-film method was employed to capture flow-visualization patterns, serving to indicate laminar-turbulent transition and loss-generating structures. Moreover, for the first time in the context of TRS flow, hot-wire anemometry (HWA) and PIV techniques were employed to provide time-resolved and instantaneous velocity field data, effectively capturing the unsteady phenomena.

The central focus of this thesis is detailed examination of pressure loss mechanisms within TRS, focusing on the impact of different OGV designs and operating conditions on TRS aerodynamics. This involves an in-depth aerodynamic evaluation of multiple OGV types commonly found in real engines, such as regular OGVs, those with increased thickness, and OGVs with integrated engine mount recesses (bumps). For the first time, this study aerodynamically evaluated and compared two engine-realistic TRSs with simultaneously mounted OGVs of different types. The experimental data for the radial TRS was compared with preliminary CFD results, obtained using current industrial tools. The insights obtained from the PIV and HWA campaign were instrumental, allowing for a thorough examination of the structure and propagation of LPT rotor and stator wakes into TRS.