This question is different from What is the optimal streamlined shape?. That question is probably about an ideal situation of flowing through space with no gravity in a fluid with zero viscosity and infinite bulk modulus. This one is about a real bullet train which is not an ideal situation like that. https://www.youtube.com/watch?v=7ccoEmlxlks shows a video of a Shinkansen 800 bullet train. It looks like a shape that will not produce much turbulence at the back end. That's based on my guess that that would be a kind of streamlined shape. My question is
Is it known for different speeds, what the force of air resistance divided by the density of air, divided by the crossectional area of the train, divided by the square of the speed of the train is when it is on rails?
I know that if atoms were infinitely small and air had the same density but with an infinite bulk modulus and zero viscosity and the train had an infinite strength and shear modulus and bulk modulus as well, that number would be constant because the laws of flow of a fluid in an ideal situation like that are preserved under a slowing down or speeding up of the process. However even if the laws allow it, we could not in general reverse the process of flowing through a fluid with turbulence because there is a forwards arrow of time because there was a beginning of time, just like if you call one heptagon in a hyperbolic heptagonal tiling the central point and start there doing a random walk, where you will be next give where you are will always be random but where you were last given where you are now and where you started will never be fully random.
12:00 into the video https://www.youtube.com/watch?v=5zI9sG3pjVU, you see the flow of air around a smooth sphere. It appears to have a jet of air a little behind the sphere nearly stationary in the frame of reference of the sphere. And the kinetic energy of the air in that jet in the frame of reference of the rest of the flowing air probably converts into kinetic energy of the eddies. So for speeds large enough to have a high enough Reynold number to be turbulent and a low enough speed to not be a high fraction of the speed of sound, for that sphere, the force of air resistance divided by the density of air, divided by the crossectional area of the sphere, divided by the square of the speed of the sphere should be very close to 1. I believe an ideal shape similar to the shape of the Shinkansen 800 in an ideal situation of going through a fluid would have zero resistance. However if it's flowing through space without gravity or real wheels like a train and no opposing gravity against a normal force like a real bullet train, there might be exponential growth in the fluid pushing it out of its original orientation.
I know almost nothing about engineering. I'm looking for a simple answer that can just satisfy me with knowledge. Then I'll leave it to other people to invest in new research based on the answer if they want to. I'm not trying to design anything myself. However, I cannot figure out an algorithm for determining in advance given what the answer is, whether it will satisfy me. When somebody is working on something, they don't propose a concrete algorithmic plan from the start. They feed themselves ideas and trust themselves to think for themselves later how to use them. Similarly, a good answer to this question would come from somebody who can function as if they are a future self of me and uses their discretion to figure out what type of answer will probably be a good answer that satisfies me.