AE 451

Aeroelasticity

Class overview

Introduction

Welcome to the exciting world of aeroelasticity! This is a class about how aerodynamic structures interact with surrounding air flow, and learning to assess whether these interactions will lead to airplane failure or not. This interplay belongs to a broader category of behavior referred to as fluid-structure interaction (FSI) -- fluid flow affects the dynamics of an immersed structure (in our case, an airplane), and the structure can respond to and in turn affect the surrounding flow. This FSI can sometimes be desirable -- for example, some renewable energy harvesing devices involve immersing flexible structures in a flow and extracting electrical energy from the structural motion that arises from the FSI dynamics. In other cases (and in most cases we care about in aeroelasticity), FSI is remarkably dangerous -- see, e.g., the videos below of an airplane wing that is induced into motion by the surrounding flow, leading to spectacular failure.

So how do we, as aeroelasticians, avoid these FSI-driven catasrophic failures? The answer is to understand how to represent these FSI dynamics simply but with sufficient accuracy, and to use these representations to predict whether failure will occur or not. That is what we will do in this class -- we will review how represent the aerodynamic structures and the flow forces on these structures using relatively simple expressions. We will then explore some of the most important ways in which these structural- and aero-dynamics can interact, and how to characterize whether these interactions are safe or dangerous.

One important note: we will be learning some important, useful, and beautiful content in this class. At the same time, this class is by no means the end of the story -- aeroelasticity (and FSI more generally) involves nonlinear interactions between fluid and structural dynamics, each of which constitutes of nonlinear, high dimensional system. This subject is challenging and remains a captivating (and often frustrating!) area of study. For example, my research groups and those of Profs. Bodony, Freund, Wissa, and Chamorro (to name a few) take on various FSI problems. So for those who get hooked on this material, look for ways to explore further!

Some motivating videos


Here are some examples of aeroelastic behavior that we want to avoid: in both cases, an airplane wing is driven into motion by surrounding flow stimuli, and this wing motion leads to catastrophic failure! But notice something interesting -- the way the wings fail in the different videos is distinct. In the top video the wing is pushed in a purely upward motion, whereas in the bottom video the wing oscillates up and down. These distinct behaviors are indicative of two different types of instabilities that can arise in aeroelastic systems. In this class, we will learn about these (and other!) important instabilities -- how to characterize them, predict them, and design systems to avoid them!

Learning outcomes

By the end of this class, you will be able to:

  1. Understand the key types of aeroelastic instabilities (divergence and flutter).

  2. Be able to recognize which simplified structural and aerodynamic models are appropriate for different situations, and how to combine these into a coupled FSI dynamical system.

  3. Be able to analyze the above FSI system and determine whether instabilities will occur or not.

  4. Have some knowledge about where these simplified models lose their meaning.

  5. Have an improved ability to be able to solve challenging problems that you haven't seen before through (i) demonstrating a willingness to try an answer even if it isn't right, (ii) identifying what features of the answer aren't right and use this to modify your approach, (iii) repeating the process until you arive at a meaningful answer.

  6. Be able to communicate technical content in a succinct and compelling manner through a report that is well written and supported by meaningfully designed, visually resplendent figures.

Andres, circa some time before COVID-19

About me

My name is Andres Goza (feel free to call me either "Andre" or "Andres"), and I have happily been an Assistant Professor in AE since January 2019. My group's research focuses on developing computational methods to understand fluid-structure interaction (though unlike in aeroelasticity, in the systems we focus on fluid-structure interaction is often something we seek to exploit). I am passionate about fluid mechanics, numerical methods, fluid-structure interaction, advising, Harry Potter, Christopher Nolan movies (no Tenet spoilers!), and listening to good audiobooks on runs.

I got into teaching because I fell in love with an applied math course I took in college (the equivalent of AE 370 here), and was inspired to share the beauty and power of course material with future students. I am really looking forward to taking this AE 451 journey together!