# Primitive variables in Fluid Mechanics

hanson
Hello!
I know that the primitive variables in fluid mechanics are velocity and pressure. But why?
I don't see how "primitive" these variables are...What does it mean by a "primitive variable"? Is that all other variables in a fluid flow can be derived from velocity and pressure? Is there any other set of primitive variable? Lastly, how do you know velocity and pressure are primituve variables?

hanson

quark
I am not aware of such terminology but they are the main variables. You can manage any fluid flow problem if you know these two things.

hanson
quark, thanks! I was afarid that no one is going to help me out. Why can we manage all flow problems if we know these 2 things?

Rocketa
hanson said:
Hello!
I know that the primitive variables in fluid mechanics are velocity and pressure. But why?
I don't see how "primitive" these variables are...What does it mean by a "primitive variable"? Is that all other variables in a fluid flow can be derived from velocity and pressure? Is there any other set of primitive variable? Lastly, how do you know velocity and pressure are primituve variables?

Try this ...
When you try to solve a fluid field without energy equation (heat transfer)? Conservation of mass and Conservation of momentum (Derived from Newton's Second law) are sufficient. You will find the main variables are pressure and velocity. With pressure and velocity information you can find the fluid field. BESIDES all the properties.

abhaythermax
QUOTE=hanson;752113]Hello!
I know that the primitive variables in fluid mechanics are velocity and pressure. But why?
I don't see how "primitive" these variables are...What does it mean by a "primitive variable"? Is that all other variables in a fluid flow can be derived from velocity and pressure? Is there any other set of primitive variable? Lastly, how do you know velocity and pressure are primituve variables?[/QUOTE][/FONT][/SIZE]

abhaythermax
what is primitive variable? i know it is velocity and pressure,but why it is? Is that all other variables in a fluid flow can be derived from velocity and pressure?