# Tag Info

Accepted

### Why does rainwater form moving waves on the ground? Is there a name for this effect?

These waves are called "roll waves." They are due to an instability in shallow shear flows. The analysis is much too complex for a short answer, but if you google "Roll Wave" you will find more ...
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### Why are aerodynamic / streamlined shapes always stumpy at the front?

You are correct if your boat will only travel in a straight line. In real life the motion of the boat will often have a yaw angle, so that it is moving slightly "sideways" relative to the ...
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### Turbulent spacetime from Einstein equation?

Gravity can, of course, become turbulent if it is coupled to a turbulent fluid. The interesting question is thus, as John Rennie points out, whether a vacuum solution can be "turbulent". As far as I'...
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### Turbulent spacetime from Einstein equation?

The fluid-gravity correspondence that Thomas referred to in his answer is a very concrete set-up where we can import intuition from fluid dynamics to suggest how we might get turbulence in vacuum GR (...
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### Pressure loss in an infinite pipe

What comes first? Pressure or flow? Without potential, a pressure differential, there is no flow. It's pressure that needs to be there first. So rather than ask what pressure drop you get, it's ...
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### Why does rainwater form moving waves on the ground? Is there a name for this effect?

I think that the explanation is that waves of different size run with different speeds. This makes the faster waves run up to the slower which make them stack up, or constructively interfere.
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### Why are aerodynamic / streamlined shapes always stumpy at the front?

One way of looking at the problem is to consider the pressures over the surface. Streamlines curling outwards tend to indicate high pressure pushing water away, streamlines curling inwards indicate ...
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### Concept behind Reynolds number

I think your handout is written in quite a confusing way. The main point of the Reynolds number is similarity. You can show that flows around a geometrically identical shape, but with different size, ...
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### Benefits of rear spoiler in cars

From Wikipedia: A spoiler is an automotive aerodynamic device whose intended design function is to 'spoil' unfavorable air movement across a body of a vehicle in motion, usually described as ...

### How to estimate the Kolmogorov length scale

Here's an empirical way to roughly estimate ε for a natural stream. You need: an audio recorder a thermometer a buoyant object tape measure a stopwatch freeware audio software (like Audacity) 1. In ...
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### What is the physical application of Navier-Stokes existence and smoothness?

IANAFD but I'll stick my neck out and say this: resolving the Clay problem one way or another won't cause people doing CFD to lose any more sleep than they already do. First of all, Jean Leray ...
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### What do the differences between spatial and temporal spectra imply about the structure of turbulence?

Thanks for posing a great question. I would love for Taylor's hypothesis to be uniformly valid! It would mean my dissertation would be finished immediately. Let me take on your cluster of questions ...
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