Why do some high speed trains like the Shinkansen E5 and E6, have really long noses while other trains, like the Eurostar and Javelin, have shorter noses?
How does the shape of the nose affect the train?
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1$\begingroup$ Have you made a table of, say, max speed vs. nose profile? or carriage cross-section (rail gauge and body height)? $\endgroup$– Carl WitthoftCommented Feb 6, 2017 at 14:00
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2$\begingroup$ Somehow I suspect that the answer will end up being that it's a stylistic choice on the part of the design team. Possibly with a strong cultural influence of what a fast train is though to look like. A chart of nose profile Vs company building it or Vs countries in use may end up being more meaningful than Vs max speed. $\endgroup$– AndrewCommented Feb 6, 2017 at 15:22
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$\begingroup$ Are you sure they're long noses and not long tails? Most HSTs can run in both directions, and the turbulence at the back can be more important (think about aero cycling helmets, and the shape of airliners) $\endgroup$– Chris HCommented Jun 7, 2017 at 9:32
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2 Answers
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It all depends on the level of efficiency you seek.
A train, given its size, has a ridiculously small cross section. This small frontal area footprint is being 'pushed' by the inertia of hundreds of tonnes of metal.
All high speed train have aerodynamic noses, but some will tend to be pedantic about how many thousandths of a percent efficiency they can squeeze out of an aerodynamic profile.
There are a couple of other factors that come into play with the design of the nose and that is the pressure pulse that is generated as a train passes another object, generally another train going in the opposite direction or a tunnel. It's why passengers are told to stay away from the platform edge as fast trains pass by, its not that you'll be blown away, but may sucked towards the train by the low pressure.
Two high speed trains passing each other can generate a huge amount of suction between them at the nose, because of the low pressures there, so having a longer nose helps spread this out a bit and reduce the area of minimum pressure. If not the trains could be pulled towards each other, or some instability set up by the rapid sideways pressure pulse. The nose of the E5 Series, at 15 metres, is a massive 9 metres longer than the previous incarnation of the bullet train (Shinkansen), the E2 Series. This, according to its designers at JR East, will help eliminate the phenomena of "tunnel boom".
Japan's rail tunnels are somewhat narrower than their European counterparts, so when the Shinkansen enters a tunnel at speeds above 200 kilometres per hour, the sudden increase in air pressure can cause a loud "boom" at the other end of the tunnel. In some cases, such shock waves are thought to have damaged tunnels in Japan, ripping chunks of material from tunnel ceilings.
The shape of the front car has evolved gradually to combat this danger, and the striking "Long Nose" design of the E5 Series is the result.
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In high speeds the impact of aerodynamic forces need to be included in analysis. Recall from the formula for aerodynamics
$$F_a = 1/2 \rho v^2 C_d A$$
Where $\rho , v, C_d,A$ are air density, speed of the vehicle , drag coefficient and contact area with air. The drag coeffient has other components. The viscous effect has an impact on the aerodynamics forces.
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1$\begingroup$ We expect answers here to be better than just throwing out equations. This also doesn't answer the question about why different nose shapes were chosen to solve what appear to be similar problems. $\endgroup$ Commented Feb 6, 2017 at 12:24
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$\begingroup$ The different shapes have different shape coefficient. I gave a simple answer i dont have time to give a lecture here im sorry $\endgroup$– Payam30Commented Feb 7, 2017 at 6:25
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$\begingroup$ @Payam30 In that case, you might want to write a comment instead of an answer. $\endgroup$– KarloCommented Jun 6, 2017 at 17:01