Valentin Vikhorev, Division of Fluid Dynamics, defends his PhD thesis

Doctoral student: Valentin Vikhorev
Main supervisor: Valery Chernoray
Examiner: Valery Chernoray
Faculty opponent: Lars Ellbrant, PhD från Chalmers 2014, Technology Demonstrator Director på GKN Aerospace

Abstract

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 further 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.

Keywords: turbine rear structure, turbine rear frame, engine-realistic, outlet guide vanes,
engine-mount recess, bump, vane lean, low-pressure turbine, experimental, multimethod approach,
multi-hole probe, pressure taps, oil-film visualization, hot-wire anemometry, particle image
velocimetry, computational fluid dynamics.

Link to Teams meeting.