[hamed.fg.mech]

hi every one.......i modeled a shock tube problem in cfx v12.1 but its results have many fluctuation.......should i give 0 [atm] for refrence pressure?
problem:
air ideal gas.....high pressure:300kpa low pressure:150kpa
high pressure length:0.5m low pressure length:1.5m total time:0.001
RMS Courant Number:0.01 max Courant Number:0.04
do this value for max Courant Number is Logical?? do you can explain it?
thanks

[ghorrocks]

should i give 0 [atm] for refrence pressure?

No. You should define the reference pressure as the base pressure in the model. Search the forum for further details, this question has been asked a lot.

do this value for max Courant Number is Logical?? do you can explain it?

Do a time step sensitivity check to establish the best time step size.

My PhD thesis has a discussion about things to consider when trying to get accurate shock wave modelling, see http://hdl.handle.net/2100/248

[hamed.fg.mech]

thanks a lot for replay....
You should define the reference pressure as the base pressure in the model. Search the forum for further details, this question has been asked a lot.

do u can explain it for me....i solved my problem with a 0 atm refrence pressure and my results were logical when i use 1atm refrence pressure it didnt give a normal solve......what should i use for my problem as i say above



Do a time step sensitivity check to establish the best time step size?
how do i do it?

[ghorrocks]

Both of these questions have been asked many times on the forum. Do a search to find them.