In one way we think a great deal too much of the atomic bomb. ‘How are we to live in an atomic age?’ I am tempted to reply: ‘Why, as you would have lived in the sixteenth century when the plague visited London almost every year, or as you would have lived in a Viking age when raiders from Scandinavia might land and cut your throat at night; or indeed, as you are already living in an age of cancer, an age of syphilis, an age of paralysis, an age of air raids, an age of railway accidents, an age of motor accidents.
In other words, do not let us begin by exaggerating the novelty of our situation. Believe me, dear sir or madam, you and all whom you love were already sentenced to death before the atomic bomb was invented… It is perfectly ridiculous to go about whimpering and drawing long faces because the scientists have added one more chance of painful and premature death to a world which already bristled with such chances and in which death itself was not a chance at all, but a certainty.
If we are all going to be destroyed by an atomic bomb, let that bomb when it comes find us doing sensible and human things—praying, working, teaching, reading, listening to music, bathing the children, playing tennis, chatting to our friends over a pint and a game of darts—not huddled together like frightened sheep and thinking about bombs. They may break our bodies (a microbe can do that) but they need not dominate our minds.
What the atomic bomb has really done is to remind us forcibly of the sort of world we are living in and which, during the prosperous period before, we were beginning to forget. And this reminder is, so far as it goes, a good thing. We have been waked from a pretty dream, and now we can begin to talk about realities.
It is our business to live by our own law not by fears: to follow, in private or in public life, the law of love and temperance even when they seem to be suicidal, and not the law of competition and grab, even when they seem to be necessary to our own survival. For it is part of our spiritual law never to put survival first: not even the survival of our species. We must resolutely train ourselves to feel that the survival of Man on this Earth, much more of our own nation or culture or class, is not worth having unless it can be had by honorable and merciful means.
Nothing is more likely to destroy a species or a nation than a determination to survive at all costs. Those who care for something else more than civilization are the only people by whom civilization is at all likely to be preserved. Those who want Heaven most have served Earth best. Those who love man less than God do most for man.
Let the bomb find you doing well.
C. S. Lewis, On Living In An Atomic Age, 1948.
Mythologists and Theologians
“Mythologists and experimental theologians are needed for the development of a new method of attack”
Telegram to Meyer while in trenches after recovery which was mistranslated from “Meteorologists and experimental physicists,” where Meyer then traveled and met Fritz Haber (german gas warfar pioneer)
Ode to Eddies
Many eddies form a cascade,
Glance with the fresh wind at autumn,
Ere the south wind’s enchanted shade,
O, it stretches toward the water!
Prandtl and Meyer
It would be difficult to create the right mood under the present circumstances, but perhaps by accident another beautiful differential equation will come along again, as it once did when I worked with you.
Letter from Meyer to Prandtl, May 5, 1918. Ref. no. GOAR:2647, DLR-Gottingen Archives
The prediction of cross-spectra from first mode instability waves within high-speed flow over sharp and blunt cones with plasma actuation
Abstract: Leading edge geometries, such as cones, moving at high-speed undergo intense loading due to the growth of instability waves and turbulent transition. These instability waves are highly spatially coherent. Aerodynamic loading related to instability waves and transition cause large-amplitude vibrations within the underlying structure, which may lead to flight-vehicle failure. We examine the effect of plasma actuation on the pressure fluctuations from first mode instability waves on the cone surface via theory with flow-fields predicted by computational fluid dynamics. We present predictions for a seven-degree half-angle cone at free-stream Mach 2.0, 3.5, and 5.0 with varying nose radii. Nose radii range from 0.038 to 38.1 mm and represent both sharp and large leading edge bluntness. For non-actuated flows, we observe that very small radii leading edges do not alter the maximum growth rates. Large radii cones have lower growth rates due to a thicker boundary layer. Spatial coherence of the instability waves decreases with increasing frequency. The growth rates are smaller at higher freestream Mach number. The effect of the simulated plasma actuator adds local heating to the flow-field. Increased nose radii lowers the relative temperature difference between the actuated and base flow-fields. The relative temperature differences are higher at higher freestream Mach number. We find that plasma actuation stabilizes the flow-field and spatial coherence becomes smaller.
- Cheng, J. and Miller, S. A. E., “Cheng, J. and Miller, S. A. E., “The Prediction of Cross-Spectra from First Mode Instability Waves within High-Speed Flow Over Sharp and Blunt Cones with Plasma Actuation,” Aerospace Science and Technology, Vol. 130, No. 107870, 2022. pp. 1-21. DOI: 10.1016/j.ast.2022.107870 [Link via DOI][PDF Preprint]
On Challenges in Turbulent Flow Theory and Experiment
Research in macroscopic classical physics, such as fluid dynamics or aspects of condensed matter physics, continues to confront baffling challenges that are by no means less demanding than those at the post-Newtonian frontiers of physics that have been explored since the beginning of this century. This is so even though the basic equations of macroscopic classical physics are knownindeed, have been known for centuries in many cases. Chaos and nonlinear dynamics are examples of the topics that pose new challenges to our understanding of macroscopic classical systems. Turbulence, a phenomenon related to but distinct from chaos, and having strong roots in engineering, has been increasingly in the focus of physics research in recent years. Turbulence occurs in a very wide variety of flows, ranging from the mixing of cream in a coffee cup to the dispersal of pollutants in the atmosphere, from the formation of galaxies in the early universe to thermal convection in stars, from flows around automobiles, ships and aircraft to combusting flows in turbomachinery.
Uriel Frisch and Steven A. Orszag, DOI: 10.1063/1.881235
On Lift
It’s easy to explain how a rocket works, but explaining how a wing works takes a rocket scientist
Philippe Spalart, Boeing Technical Fellow
Mach Experiment
Syzygy
Would you like to know the best possible method for solving a Syzygy problem? It is this. Having ascertained from your doctor that you are in a state of health to bear, without risk, severe brainwork and keen intellectual excitement, from the most candid of your intimate friends that you are in a pleasant temper, and free from all morbid irritability; and from yourself that you are in the humour for the task seat yourself in an easy-chair, taking care that you have writing materials within reach, and that there are no dictionaries in the room; close your eyes, and paint the two given words on your mental retina.
Lewis Carroll
On the On-Set of Hypersonics
Almost everyone has their own definition of the term hypersonic. If we were to conduct something like a public opinion poll among those present, and asked everyone to name a Mach number above which the flow of a gas should properly be described as hypersonic there would be a majority of answers round about 5 or 6, but it would be quite possible for someone to advocate, and defend, numbers as small as 3, or as high as 12.
Philip Roe, verbal comment at von Karman Institute, 1970.