Learning Forum

[jose monteiro]

 

hello, i think i know the problem and i have some questions about it to. I think is because the total termperature, that is requeried in mass flow and pressure inlets. 

In my problem im simulating the filling of an hydrogen tank, and when i check the static temperature it comes down to values below what i input(to 275 from 293 Temp constant that i input for example) and then whith some time like 40 seconds of real time simulated it comes close to what i input. My velocity decreases with the time as it should in a real experiment and i check my mach number and was above 0.5 in the first second of real time simulated. My questions are:

1- what is the number that fluent uses as limit to compressible flow, i have seen some sources saying it considers compressible above 0.3 of mach number, so between 0.3 and 1 is compressible but subsonic that is my case, so i expect differences exist between total and static temperature and on a incompressibles dont. 

2- if what i said above is true, how can we input static temperature inlet (on pressure or mass flow inlets) or its impossible. Because i want to use a temperature profile inUDF that i found on a article and i suspect it is static temperature because most of sensors measure static temperature. 

3- if my input was a pressure profile and subsonic how can i do to an UDF with absolute pressure since is a static pressure and fluent only uses stagnation for pressure subsonic inlets.

More informations about my model: K-e standart, scalable wall functions, transient , pressure based, simple, inlet tube adiabatic and walls are couple (aluminium and fiber walls), mass flow rate of 0.008 kg/s, that gives me a velocity of 750 and 0.5 approximately, (important: im getting this conclusions because when i do contours of total temp in the inlet the values that i input are equal and if i do static the values decrease as mentionated but in the surface of the tube are correct since in that zone is no slip condition and adiabatic so the fluid rests adiabtic and in that case total and static temperature are the same, it is why i think is the problem above).