A Note on Critical Thinking

Miller, S. A. E., “Note on Critical Thinking,” NASA Alumni Association Magazine, Dec., 2022. pp 5. (one-page)

One might visit any leading university campus in the United States and ask the graduate faculty training future researchers one question, “what is the purpose of educating students?” One of the most frequent answers is to create critical thinkers. An obvious follow-up question is, “how do you create critical thinkers?” More opinions are presented than there are graduate faculty.

We live in a marvelous time where the majority of knowledge is accessible within a minute. Using a pocket computer (cell phone), we can query any question and have the answer almost immediately. We are able to create artwork, essays, poetry, and simple mathematical proofs with emergent machine learning technology.

Often today, when students are faced with problems in the university classroom such as design, mathematics, religious studies, fluid dynamics, economics, art, English, or even creating a poem, students almost unanimously and immediately reach for their pocket computer.

But what does the growing mind do when faced with an ill-posed problem or one that is well-posed but without a solution? In my own experience teaching students, there is often a range of human reactions that have included confusion, frustration, anger, fear, humiliation, and many others. These are emotions to be celebrated, because they represent a reaction from the student of being pushed outside their boundaries and intellectual comfort zone.

Here, students are no longer in the K-12 or early university environment, which lay out lesson plans in carefully constructed curriculums where problems and answers are well-defined. Educated wise minds should be fortunate to be in the position of not knowing or understanding something. As it represents an opportunity to define and solve a problem that challenges us as a people.

If our goal is to create a society where ideas are openly discussed, debated, and used for the benefit of our people, then training critical thinkers are essential. We cannot have a ‘mob’ mentality where ideas are repeated without being criticized.

The computer and Internet are a miracle of our age. These technologies have advanced the world civilization beyond all recent predictions and comprehension. However, we have come to be addicted to these tools as a people. They have created an intellectual handicap and have limited our creativity and critical thinking. It is no wonder that in recent years scores nationwide in mathematics have dropped significantly [1]. As students are using online groups and past homework solutions to ‘ace’ their courses.

I continually ask students in my own research group and classes to perform analyses on their own. They are required to close their laptop, turn off their phone, find a quiet room alone, define the problem, and attempt a solution on a blank piece of paper with a pen. I ask that they write down the laws of motion and examine the variation of a physical phenomenon.

Often a student will use every technique and manipulative emotion to not use their own mind. Instead of presenting their own ideas and analyses, they return to an unfortunate habit of seeking answers online that do not exist.

This is the core beginning of training critical thinkers – to overcome their fear of being wrong, to present their ideas with welcome criticism, and to challenge the status quo. The idea of critical thought is completely foreign to students, as no one has demanded they think critically.

Technology should allow us to enhance critical thinking, but not replace it. We must teach students to use technology in conjunction with their most useful resource, which is their own mind. The solution is simple – first, use our minds to think critically and independently without technology, and use technology for what it is – a tool.

References

[1] Mervosh, S. and Wu, A., “Math Scores Fell in Nearly Every State, and Reading Dipped on National Exam,” New York Times, Oct. 24, 2022.

Viscosity Coefficients

Often viscosity is isotropic, meaning that it is the same in all directions. In such a case, only two of the six components of the strain rate tensor are independent, so two coefficients of viscosity can be used to describe the viscous behavior of the fluid. These two coefficients are related by -2/3. This relationship arises because the strain rate tensor has a simple form for isotropic fluids, and the viscosity is proportional to the magnitude of the rate of deformation of the fluid. Viscosity is multiplied by the strain rate tensor in the Navier-Stokes equations because viscosity is a scalar that describes the internal friction within a fluid and the strain rate tensor describes the rate of change of velocity in the fluid. The use of two coefficients of viscosity in the Navier-Stokes equations is a result of the symmetric form of the strain rate tensor and the isotropic nature of viscosity in many fluids.

AIAA SciTech 2023

This year, some of my students and collaborators are going to the AIAA SciTech conference in the DC area in the National Harbor, MD. We are presenting two particular papers. The first involves hypersonic flow-fields and the second involves acoustics and aerodynamic experiments. The citations, papers, and presentations are:

  • King, C. and Miller, S. A. E., “Fully Parabolic Prediction of the Hypersonic Near-Field About Slender Axisymmetric Bodies,” AIAA SciTech, National Harbor, MD, Jan. 23-27, AIAA 2023-1424, 2023. DOI: 10.2514/6.2023-1424 [Link via DOI][PDF Preprint][PDF Presentation]
  • Goldschmidt, J., Tingle, H., Ifju, P., Miller, S. A. E., Ukeiley, L., Goldman, B., Droandi, G., and Lee, K., “Acoustics and Forces from Isolated and Installed Tandem eVTOL Rotor Configurations,” AIAA SciTech, National Harbor, MD, Jan. 23-27, AIAA 2023-0791, 2023. DOI: 10.2514/6.2023-0791 [Link via DOI][PDF Preprint]

MLK Day 2023

Well, I don’t know what will happen now. We’ve got some difficult days ahead. But it doesn’t matter with me now. Because I’ve been to the mountaintop. And I don’t mind. Like anybody, I would like to live a long life. Longevity has its place. But I’m not concerned about that now. I just want to do God’s will. And He’s allowed me to go up to the mountain. And I’ve looked over. And I’ve seen the promised land. I may not get there with you. But I want you to know tonight, that we, as a people, will get to the promised land. And I’m happy, tonight. I’m not worried about anything. I’m not fearing any man. Mine eyes have seen the glory of the coming of the Lord.

Dr. and Rev. MLK, Mason Temple in Memphis, TN on April 3, 1968.

Spring 2023 Semester

It’s the start of a new semester, and I’m excited to welcome a new group of students to the Theoretical Fluid Dynamics and Turbulence Group. This semester, we have a diverse group of students working on a range of interesting projects.

Christian King, who joined us in May 2021 as a Ph.D. student, is studying hypersonic aerodynamics. Albert Lin, another Ph.D. student who joined us in August 2021, is focused on hypersonic stability and transition with roughness. Gustavo Resende Coelho, a master’s student who started with us in January 2021, is investigating eVTOL aerodynamics and aeroacoustics.

In addition to our Ph.D. and master’s students, we also have a number of talented undergraduate students. Kaiana L. Kibler, who started with us in January 2022 as a B.S. student in Aerospace, is working on supersonic exhaust double sonic boom shock radiation. Jason Matthew Rosenblum, another B.S. student in Aerospace who joined us in January 2022, is focusing on wave rotor nozzle technology. Colton Shepard and Sean Skowron, both B.S. students in Aerospace who started with us in January and August 2022, respectively, are studying transonics and sonic boom prediction and validation, respectively.

I’m looking forward to a productive and exciting semester with this talented group of students. As always, we are grateful for the support of organizations like DARPA, which help make our research possible.

Acoustical Society of America – December 2022

This year my research group had a good showing at the Acoustical Society of America, Dec. 2022. I was happy to give a 20 minute talk myself on jet and rocket coherence and loading. My student, Dr. Alex Carr, who is now a Research Aerospace Engineering at NASA reported on his sonic boom predictions. My M.S. student, Mr. Coelho, presented on his predictions of eVTOL configurations using reduced order modeling and the famous Ffowcs-Williams and Hawkings equation. My students presented a few short reseach papers. The presentations, abstracts, and citations are:

  • Carr, A. N., Lonzaga, J. B., and Miller, S. A. E., “Split-Step Simulations of Sonic Boom Propagation Beyond the Lateral Cutoff in a Turbulent Atmosphere,” 183rd Meeting of the Acoustical Society of America, Nashville, TN, Dec. 5-9, 2022. [Abstract PDF][Presentation PDF]
  • Carr, A. N., Lonzaga, J. B., and Miller, S. A. E., “Non-Normality of Sonic Boom Loudness Metrics in the Turbulent Atmospheric Boundary Layer at Large Lateral Distances from the Flight Path,” 183rd Meeting of the Acoustical Society of America, Nashville, TN, Dec. 5-9, 2022. [Abstract PDF][Presentation PDF]
  • Coelho, G. R., Goldschmidt, J., Tingle, H., Ifju, P., Ukeiley, L., Goldman, B., Secchi, M., and Miller, S. A. E., “Aeroacoustic and Aerodynamic Interaction Effects Between eVTOL Rotors,” 183rd Meeting of the Acoustical Society of America, Nashville, TN, Dec. 5-9, 2022. [Abstract PDF][Presentation PDF]
  • Miller, S. A. E., “Simplified Prediction of Near-field Jet Coherence using the Cross-Power Spectral Density Acoustic Analogy,” 183rd Meeting of the Acoustical Society of America, Nashville, TN, Dec. 5-9, 2022. (Invited) [Abstract PDF][Presentation PDF]

Chairing Turbulence Theory at APS Division of Fluid Dynamics – Highlight of the year

All our presenters were present and traveled internationally. DNS is the tool of choice for numerical simulations. Theory emerged from results, and I hope that new relations will guide those making turbulence models today.

High-order inertial range scaling exponents in incompressible turbulence using generalized extended self-similarity
Presenter: Sualeh Khurshid, Massachusetts Institute of Technology, Author: Sualeh Khurshid, Massachusetts Institute of Technology

Temporal large-scale intermittency and its impact on flow statistics
Presenter: Lukas Bentkamp, University of Bayreuth, Germany, Author: Lukas Bentkamp, University of Bayreuth, Germany, Author: Michael Wilczek, University of Bayreuth, Germany

Non-locality and scaling of extreme events in fluid turbulence
Presenter: Alain Pumir, Ecole Normale Superieure de Lyon, Author: Alain J Pumir, Ecole Normale Superieure de Lyon, Author: Dhawal Buaria, New York University (NYU)

Probability density functions of dissipation rate and enstrophy in turbulence
Presenter: Toshiyuki Gotoh, Nagoya Inst of Tech, Author: Toshiyuki Gotoh, Nagoya Inst of Tech, Author: Takeshi Watanabe, Nagoya Institute of Technology, Author: Izumi Saito, Nagoya Institute of Technology

Analyzing energy cascade of filtered vortices using a novel turbulence database framework
Presenter: Hanxun Yao, Johns Hopkins University, Author: Hanxun Yao, Johns Hopkins University, Author: Michael Schnaubelt, Johns Hopkins University, Author: Alex Szalay, Johns Hopkins University, Author: Tamer A Zaki, Johns Hopkins University, Author: Charles Meneveau, Johns Hopkins University

Statistical equilibrium of large scales in three-dimensional hydrodynamic turbulence
Presenter: Eric Falcon, Université Paris Cité, MSC, CNRS, Author: Jean-Baptiste Gorce, Université Paris Cité, MSC, CNRS, Author: Eric Falcon, Université Paris Cité, MSC, CNRS

Detailed kinetic energy dynamics of turbulent fluids
Presenter: Justin Beroz, Massachusetts Institute of Technology MI, Author: Justin Beroz, Massachusetts Institute of Technology MI, Author: Steven G Johnson, Massachusetts Institute of Technology MI, Author: John W Bush, Massachusetts Institute of Technology MI

Lagrangian curvature statistics from Gaussian sub-ensembles in turbulent von-Kármán flow
Presenter: Yasmin Hengster, Univ of Edinburgh, Author: Yasmin Hengster, Univ of Edinburgh, Author: Daniel Schanz, German Aerospace Center, Institute of Aerodynamics and Flow Technology, Department of Experimental Methods, Göttingen, Germany, Author: Florian Huhn, German Aerospace Center, Institute of Aerodynamics and Flow Technology, Department of Experimental Methods, Göttingen, Germany, Author: Daniel Garaboa Paz, Group of Nonlinear Physics, University of Santiago de Compostela, Spain, Author: Eberhard Bodenschatz, Max Planck Institute for Dynamics and Self-Organization, Author: Moritz Linkmann, School of Mathematic, University of Edinburgh

Scaling of Lagrangian acceleration in isotropic turbulence at high Reynolds numbers
Presenter: Katepalli R Sreenivasan, New York University (NYU), Author: Dhawal Buaria, New York University (NYU), Author: Katepalli R Sreenivasan, New York University (NYU)

Dynamic Phase Alignment in Navier-Stokes Turbulence
Presenter: Lucio M Milanese, Massachusetts Institute of Technology MI, Author: Lucio M Milanese, Massachusetts Institute of Technology MI, Author: Nuno F Loureiro, MIT PSFC, Author: Stanislav A Boldyrev, University of Wisconsin – Madison

Characteristics of significant and insignificant regions in isotropic turbulence
Presenter: Miguel P Encinar, Univ Politecnica de Madrid, Author: Miguel P Encinar, Univ Politecnica de Madrid, Author: Javier Jimenez, Universidad Politecnica de Madrid

Isotropy, super-isotropy, and the extension of von Karman-Howarth equation: a Lundgren-equation based probability density function approach and its solution to homogeneous isotropic turbulence
Presenter: Simon Goertz, Technische Universität Darmstadt, Chair of Fluid Dynamics, Otto-Berndt-Str. 2, 64287 Darmstadt, Germany, Author: Dominik Plümacher, Technische Universität Darmstadt, Chair of Fluid Dynamics, Otto-Berndt-Str. 2, 64287 Darmstadt, Germany, Author: Simon Goertz, Technische Universität Darmstadt, Chair of Fluid Dynamics, Otto-Berndt-Str. 2, 64287 Darmstadt, Germany, Author: Martin Oberlack, Technische Universität Darmstadt, Chair of Fluid Dynamics, Otto-Berndt-Str. 2, 64287 Darmstadt, Germany

APS Presentation – Alternative Analytical Solution for Planar Oblique Shock Waves

Abstract: One now famous analytical solution for shock waves was developed by Dr. Theodore Meyer within his Ph.D. dissertation under advisement of Professor Ludwig Prandtl. The original solution relies on analysis via control volume of the equations of motion. This approach has limited future development of analytical solutions for more complex flow-fields. In this presentation, we recover the classic solution of Meyer for the planar oblique shock wave via a new approach. We recast the Navier-Stokes equations in terms of generalized functions and an arbitrary surface that evolves in space and time. A closed-form solution for the density field is found, which depends on the integration of a Green’s function and source. The source is a function of the ambient fluid properties and surface shape. The surface shape is constructed with the use of the product of multiple Heaviside functions. The integral is evaluated for the planar oblique shock wave. The newly derived approach yields exactly the same solution as presented by Meyer. The new method represents a possible avenue to attack unsolved canonical fluid flow problems.

Acknowledgements: Research was sponsored by the Defense Advance Research Project Agency (DARPA) and the Army Research Office and was accomplished under Grant Number W911NF-21-1-0342. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Office or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein.

Miller, S. A. E., “Alternative Analytical Solution for Planar Oblique Shock Waves,” 75th Annual Meeting of the American Physical Society Division of Fluid Dynamics, Indianapolis, IN, Nov. 20-22, 2022. [Abstract PDF]