[hitzhwan]

How to write an expression in CFD-POST?
the down is the errors.

[vinerm]

Your expression is correct. The problem most likely is with the name; CFDPost is case-sensitive. Wall and wall are different.

[hitzhwan]

Originally Posted by vinerm

Your expression is correct. The problem most likely is with the name; CFDPost is case-sensitive. Wall and wall are different.

Thanks, but I do not understand your meaning. You mean I should use "Wall" but not " wall", but this is now written by me, but just use the right click to get it. Additionally , what is PM?

[vinerm]

The error is Temperature. CFDPost uses only T and not Temperature.

PM implies private message within cfd-online.

[hitzhwan]

Originally Posted by vinerm

The error is Temperature. CFDPost uses only T and not Temperature.

PM implies private message within cfd-online.

No， it is not the problem, the Temperature is just the list of variable in the CFDPOST, both T and Temperature is Ok. Because I tried it successfully. The most problem I think it the 300[K], why the K is italic？

[vinerm]

Units are always italic.

Click on More... when it shows the error. See it shows something useful though I doubt that.

[vinerm]

It appears you do not have a space between 300 and [K]. Space is must.

[hitzhwan]

Originally Posted by vinerm

It appears you do not have a space between 300 and [K]. Space is must.

But what is the reason? Can you try it by yourself?

[vinerm]

It works perfectly at my end, with T as well as with Temperature. With or without space. So, the only remaining portion is boundary name. Check it against the names it shows in the Tree in Outline Tab.

[hitzhwan]

Originally Posted by vinerm

It works perfectly at my end, with T as well as with Temperature. With or without space. So, the only remaining portion is boundary name. Check it against the names it shows in the Tree in Outline Tab.

Yes , you are right. It cannot be defined as wall name, when it changes ,it works. Thanks .I have a another question, why I can not find the static pressure in the CFD post, I only can use the pressure variable. Why?

[hitzhwan]

Originally Posted by hitzhwan

Yes , you are right. It cannot be defined as wall name, when it changes ,it works. Thanks .I have a another question, why I can not find the static pressure in the CFD post, I only can use the pressure variable. Why?

What's more, the static temperature also can not find.

[vinerm]

The names of the variables are defined to ensure that there is no ambiguity. For static values, just the regular names are enough. So, static temperature is just Temperature and static pressure is just Pressure. For total or absolute, Total or Absolute are used as first word.

[hitzhwan]

Originally Posted by vinerm

The names of the variables are defined to ensure that there is no ambiguity. For static values, just the regular names are enough. So, static temperature is just Temperature and static pressure is just Pressure. For total or absolute, Total or Absolute are used as first word.

I find that the total temperature is equal to static temperature for the imcompressible flow. But the total pressure is not equal to the static pressure. The total pressure should add the dynamic pressure.

[vinerm]

Both, total temperature and total pressure, are functions of velocity and have got nothing to do with compressibility. Both are equal to their static counterparts only when the velocity is 0. Otherwise, total values are always sum of static and dynamic values.

[hitzhwan]

Originally Posted by vinerm

Both, total temperature and total pressure, are functions of velocity and have got nothing to do with compressibility. Both are equal to their static counterparts only when the velocity is 0. Otherwise, total values are always sum of static and dynamic values.

But I cannot find the total pressure or total temperature in the CFD POST

[vinerm]

Total Pressure and Total Temperature are always there. Variables are listed alphabetically in CFDPost.

[hitzhwan]

Originally Posted by vinerm

Total Pressure and Total Temperature are always there. Variables are listed alphabetically in CFDPost.

As you can see, we can not see the total pressure or total temperature in the list, I also search in the other option, it also does not have. Moreover， we cannot find the phase fraction ,too. Do you know why？

[vinerm]

Since total values are velocity dependent, those are specific to each phase, i.e., total pressure for Phase 1 is different from that for Phase 2. All these would be available under Phases. Same is true for phase (volume) fraction.

[hitzhwan]

Originally Posted by vinerm

Since total values are velocity dependent, those are specific to each phase, i.e., total pressure for Phase 1 is different from that for Phase 2. All these would be available under Phases. Same is true for phase (volume) fraction.

You see， in the phase interface， we can not see those variables. Why?

[vinerm]

It appears that you are using either VOF or Mixture model. That implies there is single set of Navier-Stokes equation. In this case, there would be single velocity field, hence, single total pressure and total temperature. So, ignore my previous post. About the unavailability of total values, it is strange. However, it is possible that you wrote selected variables. If you loaded Fluent data file, then total values should be there. However, you can just create total values yourself using expressions.