Next week: Joseph Nichols, 28-Apr-26, 12:20pm Central
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Ellad Tadmor
Apr 20, 2026, 9:10:47 PM (5 days ago) Apr 20
to aem-solid...@umn.edu
AEM Mechanics Research Seminar
Tuesday 28-Apr-2026, 12:20pm Central
Prof. Joseph Nichols
Department of Aerospace Engineering and Mechanics, University of Minnesota
Title: Large-Scale Input/Output Analysis of Boundary Layer Flows
Abstract: Understanding how and predicting when a boundary layer flow will transition to turbulence is crucial to the design of safe and performant aerospace vehicles. A boundary layer is a thin zone of highly sheared flow close to a solid surface caused by the fact that flow past the wall must match the wall’s velocity at the point of contact (the “no-slip” condition). Boundary layers at high Mach numbers (such as those encountered during atmospheric reentry) support multiple instabilities that may cause an initially smooth, laminar boundary layer flow to transition to turbulence, at which point both the drag and the wall heat flux increase significantly. These include oblique Mack 1st mode instability, Mack 2nd mode instability, crossflow instability, and entropy layer instability -- all of which may occur simultaneously and interact with one another to precipitate transition. The presence of complex geometry, such as fins and flaps, complicates the physics of boundary layer transition yet further. Finally, while many studies focus on these various instabilities in canonical configurations, less attention has been paid to the receptivity problem of how these instabilities are triggered by environmental disturbances.
This talk will present our research group’s recent work on Input/Output (I/O) analysis as a tool to study instability and receptivity of boundary layer flows. As a global method, I/O analysis captures effects of complex geometry directly and provides a way to decompose multiple instabilities into separate components. By restricting inputs to realizable disturbances in the freestream, I/O analysis also reveals how instabilities are triggered by the environment. As freestream disturbances must pass through bow-shock of a high-speed vehicle before they can boundary layer instabilities, accurate shock-perturbation models are essential, for which we propose a novel shock-kinematic boundary condition.
As a global method, computational expense remains a pacing challenge for I/O analysis. We will discuss our recent advances addressing this challenge, including high-order discontinuous Galerkin methods using adaptive curved elements, hierarchical I/O analysis, and graph-based rank-reduced interface preconditioning. As physics-based techniques to accelerate solution of large-scale linear systems, our methods generalize to a wide range of problems involving wave propagation near interfaces. For example, we show how I/O analysis can be used to understand experimental measurements of fully turbulent low-speed boundary layers past embedded cylinders.
Tuesday 28-Apr-2026, 12:20pm Central
In-person: Room 321, Mechanical Engineering, University of Minnesota
Online: Webinar registration link
Department of Aerospace Engineering and Mechanics, University of Minnesota
Title: Large-Scale Input/Output Analysis of Boundary Layer Flows
Abstract: Understanding how and predicting when a boundary layer flow will transition to turbulence is crucial to the design of safe and performant aerospace vehicles. A boundary layer is a thin zone of highly sheared flow close to a solid surface caused by the fact that flow past the wall must match the wall’s velocity at the point of contact (the “no-slip” condition). Boundary layers at high Mach numbers (such as those encountered during atmospheric reentry) support multiple instabilities that may cause an initially smooth, laminar boundary layer flow to transition to turbulence, at which point both the drag and the wall heat flux increase significantly. These include oblique Mack 1st mode instability, Mack 2nd mode instability, crossflow instability, and entropy layer instability -- all of which may occur simultaneously and interact with one another to precipitate transition. The presence of complex geometry, such as fins and flaps, complicates the physics of boundary layer transition yet further. Finally, while many studies focus on these various instabilities in canonical configurations, less attention has been paid to the receptivity problem of how these instabilities are triggered by environmental disturbances.
This talk will present our research group’s recent work on Input/Output (I/O) analysis as a tool to study instability and receptivity of boundary layer flows. As a global method, I/O analysis captures effects of complex geometry directly and provides a way to decompose multiple instabilities into separate components. By restricting inputs to realizable disturbances in the freestream, I/O analysis also reveals how instabilities are triggered by the environment. As freestream disturbances must pass through bow-shock of a high-speed vehicle before they can boundary layer instabilities, accurate shock-perturbation models are essential, for which we propose a novel shock-kinematic boundary condition.
As a global method, computational expense remains a pacing challenge for I/O analysis. We will discuss our recent advances addressing this challenge, including high-order discontinuous Galerkin methods using adaptive curved elements, hierarchical I/O analysis, and graph-based rank-reduced interface preconditioning. As physics-based techniques to accelerate solution of large-scale linear systems, our methods generalize to a wide range of problems involving wave propagation near interfaces. For example, we show how I/O analysis can be used to understand experimental measurements of fully turbulent low-speed boundary layers past embedded cylinders.
For more information, visit the AEM Mechanics Research Seminar website:
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Ellad B. Tadmor, Ph.D.
Russell J. Penrose Professor
Department of Aerospace Engineering and Mechanics
University of Minnesota
https://dept.aem.umn.edu/~tadmor/
Russell J. Penrose Professor
Department of Aerospace Engineering and Mechanics
University of Minnesota
https://dept.aem.umn.edu/~tadmor/
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