Shock oscillation mechanisms of highly separated transitional shock-wave/boundary-layer interactions
type: CreativeWork
description: In business jet and defence applications, cruise altitudes typically range from 15 to 16 km, significantly higher than the 10 to 13 km common for commercial aircraft. At these higher altitudes, the atmosphere is quieter, air density is lower, and engine sizes are smaller than those of commercial aircraft. These conditions result in a low chord Reynolds number on the transonic fan – the first bladed component at the engine inlet of the turbofan engine. Consequently, a laminar boundary layer persists on the suction side of the transonic fan during cruise. Additionally, the trend in compressor design is higher blade loading, leading to larger separations. These conditions combined induce a shock oscillation with frequencies approximately matching the blade's natural structural frequencies. This resonance causes excitation and vibrations, which, if not mitigated, can lead to fatigue and potential structural failure. This dissertation explores the dynamics of this shock oscillation mechanism in transitional shock-wave/boundary-layer interactions (SBLIs) with the work arising from the occurrence and mitigation of shock oscillation-induced unsteadiness in transonic fans operating at low Reynolds numbers. The focus of the study is to investigate a particular shock oscillation mechanism. The study uses experimental and numerical approaches, and demonstrates that a canonical research configuration can replicate the shock oscillation mechanism observed in highly loaded transonic cascades. Using Large Eddy Simulations (LES) and experimental methods such as high-speed Schlieren imaging, spark light shadowgraphy, and particle image velocimetry (PIV), the research identifies a specific mechanism driven by the interplay of natural laminar separation growth, transition through shear layer instabilities, and separation suppression through turbulence. Reynolds-averaged methods typically used in industry cannot be used to resolve the oscillation mechanism. The oscillation mechanism of …
abstract: In business jet and defence applications, cruise altitudes typically range from 15 to 16 km, significantly higher than the 10 to 13 km common for commercial aircraft. At these higher altitudes, the atmosphere is quieter, air density is lower, and engine sizes are smaller than those of commercial aircraft. These conditions result in a low chord Reynolds number on the transonic fan – the first bladed component at the engine inlet of the turbofan engine. Consequently, a laminar boundary layer persists on the suction side of the transonic fan during cruise. Additionally, the trend in compressor design is higher blade loading, leading to larger separations. These conditions combined induce a shock oscillation with frequencies approximately matching the blade's natural structural frequencies. This resonance causes excitation and vibrations, which, if not mitigated, can lead to fatigue and potential structural failure. This dissertation explores the dynamics of this shock oscillation mechanism in transitional shock-wave/boundary-layer interactions (SBLIs) with the work arising from the occurrence and mitigation of shock oscillation-induced unsteadiness in transonic fans operating at low Reynolds numbers. The focus of the study is to investigate a particular shock oscillation mechanism. The study uses experimental and numerical approaches, and demonstrates that a canonical research configuration can replicate the shock oscillation mechanism observed in highly loaded transonic cascades. Using Large Eddy Simulations (LES) and experimental methods such as high-speed Schlieren imaging, spark light shadowgraphy, and particle image velocimetry (PIV), the research identifies a specific mechanism driven by the interplay of natural laminar separation growth, transition through shear layer instabilities, and separation suppression through turbulence. Reynolds-averaged methods typically used in industry cannot be used to resolve the oscillation mechanism. The oscillation mechanism of …
author: Nel, Philipp
language: en
license: https://creativecommons.org/licenses/by/4.0/
date published: 2025
date modified: 2026-07-27T21:28:29Z
provider: Technische Universität Berlin
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Technische Universität Berlin

PropertyValue
property ID: DOI
value: 10.14279/depositonce-24824