Hydrogen filled shock-tube open to the atmosphere

tomhcosta · August 6, 2020, 13:03

Hi,

I'm trying to modulate a shock tube with gas in the driver section, hydrogen and air in the driven section in fluent.
I am studying if the length and diameter of the tube affects the pressure and temperature of the gas in order to see If there can be ignition. I have a rectangle with 2 sections, high-pressure hydrogen in the driver section separated by a diaphragm and atmospheric air in the driven section with 0 pressure gauge on the outlet. I am trying to do a pressure and temperature analysis but it seems to be giving wrong results because of the 2 different gases in the same structure.

Can anybody help?

AlexanderZ · August 7, 2020, 05:48

why do you think, you have wrong results?
pressure as well as concentration you are applying using PATCH tool
so the difference with this model will be only concentrations of gases in specified regions

edward3600 · August 10, 2020, 21:18

Quote:

Originally Posted by tomhcosta

Hi,

I'm trying to modulate a shock tube with gas in the driver section, hydrogen and air in the driven section in fluent.
I am studying if the length and diameter of the tube affects the pressure and temperature of the gas in order to see If there can be ignition. I have a rectangle with 2 sections, high-pressure hydrogen in the driver section separated by a diaphragm and atmospheric air in the driven section with 0 pressure gauge on the outlet. I am trying to do a pressure and temperature analysis but it seems to be giving wrong results because of the 2 different gases in the same structure.

Can anybody help?

Tomás. I just noticed you defined an outlet? If you want to define an outlet, you cannot just define it as 0 Pa. You need to develop a bigger region to represent a "room" where that pressure is also atmospheric (i.e. 101325 Pa). Defining a wall at the end of the shock tube as "outlet" with 0 Pa means you are sucking air in Driven Section out of tube from that wall, which is incorrect. Try keeping things simple, and just blocking both ends of tube first with all walls (or symmetry). Let it reflect within the tube for simplicity. After you have resolved this issue, you can build on this with an ambient room space for example, if you want to define an open shock tube.

Cheers,
Edward

tomhcosta · August 11, 2020, 14:19

I ended up by not doing the 0 pressure gauge because I thought it would happen what you are saying, the problem now is that when I run with 10 bar everything is ok and results print like expected from the calculated values but when i run with 20 bar on the driver section, i run it and the results print like i have to pressure in the driver or driven section as it appear as 0 Pa.

August 6, 2020, 13:03	Hydrogen filled shock-tube open to the atmosphere	#1
tomhcosta New Member Tomás Costa Join Date: Aug 2020 Posts: 4 Rep Power: 6	Hi, I'm trying to modulate a shock tube with gas in the driver section, hydrogen and air in the driven section in fluent. I am studying if the length and diameter of the tube affects the pressure and temperature of the gas in order to see If there can be ignition. I have a rectangle with 2 sections, high-pressure hydrogen in the driver section separated by a diaphragm and atmospheric air in the driven section with 0 pressure gauge on the outlet. I am trying to do a pressure and temperature analysis but it seems to be giving wrong results because of the 2 different gases in the same structure. Can anybody help?

August 7, 2020, 05:48		#2
AlexanderZ Senior Member Alexander Join Date: Apr 2013 Posts: 2,363 Rep Power: 34	why do you think, you have wrong results? pressure as well as concentration you are applying using PATCH tool so the difference with this model will be only concentrations of gases in specified regions __________________ best regards ****************************** press LIKE if this message was helpful

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August 11, 2020, 14:19		#4
tomhcosta New Member Tomás Costa Join Date: Aug 2020 Posts: 4 Rep Power: 6	I ended up by not doing the 0 pressure gauge because I thought it would happen what you are saying, the problem now is that when I run with 10 bar everything is ok and results print like expected from the calculated values but when i run with 20 bar on the driver section, i run it and the results print like i have to pressure in the driver or driven section as it appear as 0 Pa.