[HN Gopher] Into The Tunnel: The secret life of wind tunnels
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Into The Tunnel: The secret life of wind tunnels
Author : iamwil
Score : 46 points
Date : 2025-05-23 17:17 UTC (5 hours ago)
(HTM) web link (jordanwtaylor2.substack.com)
(TXT) w3m dump (jordanwtaylor2.substack.com)
| pomian wrote:
| Great article. Nice review... Helps to see the mathematical
| equations and numbers, like Bernoulli and Reynolds's, compared to
| graphs and flow tunnel simulations.
| zh3 wrote:
| Having spend some time there, I really like the R J Mitchell
| (designer of the Spitfire) wind tunnel - used to be at
| Farnborough until they took a section of it to Southampton Uni.
| Real sense of history using it!
|
| Most of our use is validating sensors for use outside wind
| tunnels, that is showing our on-bike drag sensors match wind
| tunnel measurements (it's for serious cyclists and triathletes).
| Watching live drag (more accurately, CdA) change with body
| position is fascinating - and tells me my back can't handle the
| most aero position for more than a few tens of seconds.
| sandworm101 wrote:
| There is a third type of tunnel not really discussed here:
| hypersonic wind tunnels. They are closed but not looped. At one
| end are giant tanks of compressed and chilled air, almost liquid.
| At the other, even bigger expansion tanks filled with vacuum.
| Tests last only seconds and are more like explosions than wind.
|
| https://asiatimes.com/2023/06/chinas-jf-22-hypersonic-wind-t...
|
| In the western world, hypersonic testing has been traditionally
| done live. For groups like NASA, it was always a tossup between
| biulding a monster tunnel, or just strapping the test articles to
| the sharp end of a rocket and letting the upper atmosphere be the
| tunnel.
| Animats wrote:
| The article also references another article by the same author
| about cavitation and propellors, which is studied with water
| tunnels.[1]
|
| The water tunnel was invented by Sir Charles Parsons. Parsons had
| invented the compound steam turbine, the long shaft of finned
| wheels seen inside all modern turbo devices, in 1884. The first
| turbine product was turbo-generators for power stations. It took
| a while for demand to build up, since this was only five years
| after Edison's light bulb demo.
|
| So Parsons decided to try ship propulsion. A prototype boat was
| built with one turbine and one propeller. Too much power was
| available, and the propeller was cavitating, spinning in its own
| self-created vacuum and going nowhere. A demo for the British
| Admiralty was an embarrassing flop.
|
| This was unexpected. Before Parsons' turbine, nobody had enough
| engine power to force a propeller into cavitation. Parsons had to
| start studying propeller design.
|
| So Parsons built the first water tunnel, in Newcastle.[2] There
| was a closed loop of water, maybe two meters around, and a window
| to look in at the propeller. Parsons could see the cavitation
| bubbles.
|
| Having built a debugging tool, Parsons was able to try out
| propeller designs, and came up with some workable high-speed
| propellers. So it was time to rebuild the test boat.
|
| That was Turbinia, version 2. One boiler, three turbines, three
| long propeller shafts, and three propellers on each shaft, spaced
| over a meter apart. Way overpowered. First boat with serious
| vroom. Turbinia was far faster than anything else on the water.
|
| Turbinia's public demo went down in history. The British Navy had
| prepared a huge parade of warships for Queen Victoria's Diamond
| Jubilee fleet review. The might of the British Empire was shown
| off to the rest of the world. Everybody who was anybody,
| including the Queen, was there. Parsons brought Turbinia up
| behind the fleet and went to full power, turbines screaming.
| Turbinia zoomed through the columns of ships and disappeared into
| the distance. Some Navy patrol boats gave chase, but couldn't
| possibly catch Turbinia.
|
| The British Admiralty wasn't pleased with this. But they couldn't
| do much. Sir Charles Parsons, son of an Irish lord, was a peer of
| the realm. He could only be tried by the House of Lords, which
| was more concerned about British naval superiority than the
| Admiralty being embarrassed. Also, there's a story that when the
| Admiralty sent some people over to Parsons' offices to chew him
| out, the Prussian naval attache was just leaving. Within a few
| years, Parsons turbines powered two new destroyers, and after
| that, the entire next generation of naval vessels.
|
| [1] https://jordanwtaylor2.substack.com/p/killer-bubbles
|
| [2]
| https://research.ncl.ac.uk/marinepropulsion/resources/fundam...
|
| [3] https://en.wikipedia.org/wiki/Turbinia
| Scramblejams wrote:
| Such a fun topic. And then there are some things tunnels can't
| do, or can only do in the most limited form, like analyse post-
| stall behavior. You can't very well have your model tumbling free
| in your flow, it might crash and make a mess. (Well, there have
| been attempts, some of them successful, but also quite limited in
| their parameters.)
|
| So you have to resort to a free flight model, scaled down to
| simulate the parameters required. There's a (fascinating, for
| those so inclined) treatise on it here[0].
|
| [0]
| https://ntrs.nasa.gov/api/citations/20110012492/downloads/20...
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