Question regarding stagnation state and process

In summary: This is a bit tricky to explain. Essentially, when you are moving with a fluid, there is a certain frame of reference that is used to measure thermodynamic properties. This is usually referred to as the velocity reference frame. In the velocity reference frame, the fluid is moving at a constant velocity. The stagnation state is defined as the thermodynamic state which would exist if the fluid were brought to zero velocity and zero potential. To determine the stagnation state, you must reach the state without any energy exchange (Q=0 and W=0). This is usually accomplished by bringing the fluid to a standstill. Another way to think of stagnation properties is to think of what the fluid properties would be if you were moving with the fluid. In
  • #1
jason.bourne
82
1
question regarding stagnation state and process!

stagantion state: it is reference state defined as the thermodynamic state which would exist if the fluid were brought to zero velocity and zero potential.

this is the definition from the textbook fundamentals of gas dynamics b Zucker R.D.

and in order to accomplish stagnation process, the stagnation state must be reached

1) without any energy exchange (Q=0 and W=0)

2) without losses

that is the process has to be reversible.

how do i check whether the process is reversible or not?
is entropy the only way to determine whether the process is reversible or not?
why the process has to be reversible in case of determining the stagnation state?
suppose we consider aircrafts which has pitot static tubes, which helps in determining the stagnation state, but the flow before it, is it reversible? i don't think so then how does pitot tube help in determining the stagnation state?

please help to understand this stagnation state and process. Can you explain me it clearly?
 
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  • #2


Another way to think of stagnation properties is to think of what the fluid properties would be if you were moving with the fluid. In that sense I think you can see that the zero relative velocity has to be accomplished without changing the properties themselves.

The entropy aspect is an approximation in practice. There is no way to completely eliminate its production when you look at something like a pitot tube. The engineering comes in when you design a tube in an effort to reduce the losses as much as possible and keep your measurement as true as you can to the actual value.

A process is reversible if there are a few things:
- No delta T or heat transfer across the system boundary
- Usually small changes in state must be made
- The changes happen slowly
- Friction can not be present
 
  • #3


FredGarvin said:
Another way to think of stagnation properties is to think of what the fluid properties would be if you were moving with the fluid. In that sense I think you can see that the zero relative velocity has to be accomplished without changing the properties themselves.


can you please explain this frame of reference part. m not geting it. coz all i know is suppose if m traveling with the fluid and if i have a pressure measuring device(pressure gauge) and a temperature prob they will give me the value of static properties rather than the stagnation properties. So what reference frame has to be chosen so that i can determine the stagnation state?
 

1. What is a stagnation state?

A stagnation state is a thermodynamic state in which a fluid is brought to rest and all its kinetic energy is converted to internal energy. This state is often used as a reference point for analyzing fluid flow.

2. How is stagnation state different from other thermodynamic states?

Unlike other thermodynamic states, a stagnation state is not a state of equilibrium. It is a non-equilibrium state in which the fluid is brought to rest but still has internal energy due to its temperature.

3. What is a stagnation process?

A stagnation process is a thermodynamic process in which a fluid is brought to a stagnation state. This can be achieved by slowing down the fluid's velocity, increasing its temperature, or both.

4. How is stagnation state used in aerodynamics?

In aerodynamics, stagnation state is often used as a reference point for measuring pressure and temperature changes in a fluid flowing around an object. It is also used to determine the efficiency of an aircraft's engine.

5. Can stagnation state be achieved in real-world scenarios?

Yes, stagnation state can be achieved in real-world scenarios through processes such as shock waves, adiabatic compression, and isentropic expansion. It is also commonly used in wind tunnel testing and in the study of gas dynamics.

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