Scale down the model

shahid nadeem · August 22, 2014, 02:56

Hello Dear Friends can anyone tell me how to specify the inlet and outlet boundary conditions when i have scalwd down the model to some smaller dimensions. Please guide me on this

RodriguezFatz · August 22, 2014, 08:48

1) Why did you scale it down?
2) What kind of inlet and outlet b.c. do you have?

shahid nadeem · August 23, 2014, 00:35

Dear Sir, the thing is that i have a long 1.5 m * 20 m pipe through which compressible flow enters and exits in the vaccum vessel maintained at 0.01 milibar. i was thinking if i could scale the model to 25 % then i will get the results fast. i have pressure inlet condition as 0.4 bar and pressure exit as 0.01milibar. so can i scale down the model i such a way that i could scale down my boundary conditions also and do you think the pressure drop of scale down model will be of use for the original model?

Thanks in advance.

RodriguezFatz · August 25, 2014, 07:44

I don't understand the benefit of scaling a simulation down. If you don't keep the Reynoldsnumber constant during scaling, your results will be useless. And if you do so, you don't save any computational time.

virendra_p · September 9, 2014, 03:33

i think the scaling rule for your problem will be Mach no. similarity (not 100% sure) and applying it you will reduce your dimensions (saving lot of time) and other variables (pressure, velocity etc.) will be adjusted by the similarity equation. Please refer standard books, papers for accurate details. Good luck.

August 22, 2014, 02:56	Scale down the model	#1
shahid nadeem Member Nazim Join Date: Oct 2013 Posts: 93 Rep Power: 12	Hello Dear Friends can anyone tell me how to specify the inlet and outlet boundary conditions when i have scalwd down the model to some smaller dimensions. Please guide me on this

August 22, 2014, 08:48		#2
RodriguezFatz Senior Member Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 26	1) Why did you scale it down? 2) What kind of inlet and outlet b.c. do you have? __________________ The skeleton ran out of shampoo in the shower.

August 25, 2014, 07:44		#4
RodriguezFatz Senior Member Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 26	I don't understand the benefit of scaling a simulation down. If you don't keep the Reynoldsnumber constant during scaling, your results will be useless. And if you do so, you don't save any computational time. __________________ The skeleton ran out of shampoo in the shower.

September 9, 2014, 03:33	hi shahid	#5
virendra_p Member Virendrasingh Pawar Join Date: Jun 2013 Posts: 47 Rep Power: 12	i think the scaling rule for your problem will be Mach no. similarity (not 100% sure) and applying it you will reduce your dimensions (saving lot of time) and other variables (pressure, velocity etc.) will be adjusted by the similarity equation. Please refer standard books, papers for accurate details. Good luck. shahid nadeem likes this.

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August 23, 2014, 00:35		#3
shahid nadeem Member Nazim Join Date: Oct 2013 Posts: 93 Rep Power: 12	Dear Sir, the thing is that i have a long 1.5 m * 20 m pipe through which compressible flow enters and exits in the vaccum vessel maintained at 0.01 milibar. i was thinking if i could scale the model to 25 % then i will get the results fast. i have pressure inlet condition as 0.4 bar and pressure exit as 0.01milibar. so can i scale down the model i such a way that i could scale down my boundary conditions also and do you think the pressure drop of scale down model will be of use for the original model? Thanks in advance.