In general the word 'model' implies a mathematical construct that mimics the behavior of a real-world experimental or observational system, i.e the experimental or observational data can be generated by the model. Where's the real-world ideal fluid flow? No such systems exist.
> "In principle, if you know the location and velocity of each particle in a fluid, the Euler equations should be able to predict how the fluid will evolve for all time. But mathematicians want to know if that’s actually the case."
At some scale in a real fluid, quantum effects become important, and the notion that it's possible to know both position and momentum falls apart. To quote Peter Atkins:
> "The trouble is when you're dealing with operators, is it turns out you can't always extract explicit information about all of them simultaneously, and this leads to Heisenberg's uncertainty principle, which most people think of as a great confuser of the world and denier of information. I like to think of it as a great clarifier because old-fashioned people, like Newton and Einstein, and Lagrange, and all the people who developed classical mechanics, took it as certain that to specify the state of a particle, you had to specify where it was and how fast it was going."
That's why there are no perfect ideal fluids. Atkins expands:
> "What quantum theory did, through the uncertainty principle, was to clarify - what it said, was discuss the world if you like in terms of positions, or if you prefer, discuss the world in terms of linear momenta, don't try both at once. You get very simple descriptions in terms of positions, you get very simple descriptions in terms of linear momenta, it's only when you - like trying to start a sentence in English and ending in Latin or something, trying to mix the two together, that you get into confusion. So think of the Heisenberg principle as a clarifier - try to think one way, or try to think the other way, but don't try to think like Newton thought."