Fluid-structure interaction in compressible flows

Traditional methods of analyzing fluid-structure interaction problems in compressible flows have focused on simplified fluid models that allow to predict linear instabilities. Two main shortcomings of these efforts have been the neglect of pre-existing, viscous fluid instabilities as well as the limitation due to the underlying inviscid flow assumption. This thesis describes and reports results from two analyses that directly include the effects of viscosity and flow inhomogeneities. First, a local linear analysis of instabilities of a laminar boundary layer grazing a thermo- mechanically compliant panel is carried out. Relevant parameter combinations for the panel result in two distinctly different system behaviors, which approximately correspond to a quasi-one- dimensional motion of the panel and a synchronization of the fluid instability with flexural panel modes. For the latter, the interaction between boundary layer instability and the panel shows a gradual phase shift between wall-normal velocity and pressure perturbation at the interface, resulting in non-zero power transfer and thus altering of stability properties. For the quasi-one- dimensional motion, the phase remains constant and the boundary layer instability is altered due to an effective change in boundary condition, from a no-slip wall to zero pressure perturbation in the free limit. Comparisons with a local Piston theory model show phase changes between the wall-normal velocity and the interface pressure that are not accurately captured by Piston theory, emphasizing its inadequacy to resolve viscous fluid-structure interaction instabilities in super- and hypersonic flows. Second, a non-linear Navier–Stokes solver coupled to a linear beam model is used to evaluate flutter boundaries—a fluid-structural instability that can cause structural failure. Common limitations such as an inviscid flow assumption to leverage simplified fluid models—most popularly Piston Theory—or an imposed solution ansatz are lifted by solving for global eigenvalues of the fluid-structure system including viscous and boundary condition effects. The analyses show a substantial stabilizing effect due to the presence of the boundary layer, which has been reported in transonic and very low supersonic flows but lacking the higher super- and hypersonic regime. While the thickness of the grazing boundary layer has a substantial effect on the magnitude of the stabilization, Reynolds number effects are relatively small. Most interestingly, however, Mach number effects are minor, with critical parameters for the onset of flutter aligning across three different Mach numbers considered, making a simplified model that captures viscous effects to complement existing inviscid flutter analyses a possibility.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Aerospace Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Dettenrieder, Fabian Stefan

Contributors dc:contributor

• Bodony, Daniel J
• Goza, Andres
• Elliott, Gregory
• Masud, Arif

• Fluid-structure Interaction
• Flutter Instability
• Laminar Boundary Layer
• Linear Stability Theory

Statement dc:rights

• Copyright 2024 Fabian Dettenrieder

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/127220

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F127220