Does Static Pressure Equal Total Pressure in All Fluid Scenarios?

[su214]

static and total pressure !

hello :)
i'm new here and it is the 1st time i post a thread here ...

now please correct me if I'm wrong...
1-static pressure is equal to the total pressure if the gas is static (V=0)
2- total pressure is always equal or bigger than the static pressure
3-as the velocity increases the static pressure decrease

if these statements are correct then

1- is the ambient pressure is equal to total pressure and the total pressure is constant at same altitude for any given moving flow
-ex:at sea level-?

2-if the above statement is correct ,then in case of increasing of fluid velocity will its static pressure will equal zero at certain velocity ?

3-
here :http://img801.imageshack.us/img801/7098/29329605.jpg

the underlined lines confused me very much the author say that " the static P and T remain UNCHANGED "??
and the stagnation reference depend on the frame of reference?
i can't understand the underline lines...

 

[AIR&SPACE]

STAGNATION pressure is the pressure of a gas if it is brought to zero velocity.

 

[Saladsamurai]

now please correct me if I'm wrong...

1-static pressure is equal to the total pressure if the gas is static (V=0)

No this is incorrect and is a common mistake. In Aerodynamics, when we use the word static we are not implying that the fluid is at rest. The static pressure and static temperature are those values that we would measure if we were riding along with the flow.

2- total pressure is always equal or bigger than the static pressure

Using the correct definition of static pressure given above: yes. Total pressure (or stagnation pressure) is a reference value of pressure used for convenience. It is the value that the pressure would take on if the fluid is brought (isentropically, i.e. reversibly) to rest.

3-as the velocity increases the static pressure decrease

Correct.


So, from the definition of stagnation pressure, we can see that if the fluid is actually at rest, the stagnation pressure and static pressure take on the same value.