Does Static Pressure Equal Total Pressure in All Fluid Scenarios?

In summary: However, as the flow velocity increases, the stagnation pressure increases while the static pressure decreases. This is because the stagnation pressure is a reference value and does not take into account the effects of velocity. As for the underlined lines in the image, the author is stating that the static pressure and temperature do not change as the flow frame of reference changes. This is because they are reference values and do not depend on the frame of reference. In summary, static pressure and total pressure are not the same, with static pressure being the value measured while riding along with the flow and total pressure being a reference value used for convenience. As the flow velocity increases, the static pressure decreases while the total pressure increases. The static pressure and temperature do not change
  • #1
su214
3
0
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...
 
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  • #2


STAGNATION pressure is the pressure of a gas if it is brought to zero velocity.
 
  • #3


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.
 

1. What is the difference between static pressure and total pressure?

Static pressure is the force per unit area exerted by a fluid at rest, while total pressure is the sum of static pressure and dynamic pressure (the pressure created by the motion of a fluid).

2. How is static pressure measured?

Static pressure is typically measured using a manometer, which consists of a U-shaped tube filled with a liquid (such as water or mercury). The difference in fluid levels in the two sides of the tube is directly proportional to the static pressure.

3. What is the importance of static pressure in fluid dynamics?

Static pressure is essential in understanding the behavior of fluids, as it is a key component in determining fluid flow and pressure distribution in a system. It is also necessary for calculating other important variables such as velocity and density.

4. How does total pressure affect the performance of a fluid system?

Total pressure has a significant impact on the efficiency and performance of a fluid system, particularly in applications such as gas turbines and jet engines. It is used to measure the work done by a fluid and is a crucial factor in determining the amount of power that can be extracted from a fluid flow.

5. Can static and total pressure ever be equal?

Yes, in certain situations where a fluid is not in motion, or is moving at a constant velocity, the static pressure and total pressure can be equal. This is known as a stagnation point, where the fluid comes to a complete stop and all of its kinetic energy is converted to potential energy.

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