# Difference between 1D, 2D and 3D Flow

1. Nov 17, 2013

### amck

Hey guys,

I'm new to this forum and was hoping to get a clear answer regarding the difference between 1D, 2D and 3D flows in hydraulics (ex. 2D Numerical Model...) ?

Thanks a bunch!
-A.

2. Nov 18, 2013

It usually refers to the number spatial (or time) dimensions over which the flow variables vary in a given situation or problem.

3. Nov 21, 2013

### amck

Thanks for the response! So if you say 2D flow - it's the flow in a plane whereas 1D would be linear?

4. Nov 21, 2013

Pretty much, though a 1D flow would be awfully uninteresting. A 2-D flow may also arise if, say, the flow is axisymmetric.

5. Nov 21, 2013

### amck

Fair enough. What kind of "real-life" flow would be considered axisymmetric?

6. Nov 21, 2013

The flow around a cone at zero angle of attack, the flow around the Apollo space capsule if it is at zero angle of attack the flow around the front end of a missile, the flow around a non-rotating sphere (in the Stokes limit), and the flow out of a rocket engine would all be examples of axisymmetric flows.

7. Oct 9, 2014

### Sneakatone

so an equation like v=1xt i + 2xt j +6xt k would be 3d

but V= 1xt i +6x j+7 k wouldbe 1D?

8. Oct 10, 2014

### jack action

A 3D flow assumes that a particle of fluid can go either forward or backward, up or down, left or right.

All flows are 3D, but some can be estimated to a 2D or even 1D flow to simplified the calculations without loosing to much accuracy.

For example, you can study an airplane wing section to evaluate its lifting potential in 2D (particles goes from front to rear and can also go up or down):
You can also study flow in a pipe in 1D situation (from inlet to outlet). In the above example, instead of considering the particles moving up and down when entering the enlarged pipe, we can just consider the area change: