how to put resistance in ansys

marauder · September 5, 2014, 04:44

Why don't you just give Boundary Conditions as Mass Flow inlet or Velocity inlet and a Pressure outlet at 0 pressure. Create plane before inlet and outlet of the fan. The static pressure difference between these two planes will be your head generated.

chaudhry_hashim · September 5, 2014, 07:46

I already tried it but i didnt get results so I searched one of the paper in which he put resistance just before the outlet and plot the curve by choking the resistance let say its 25 percent open. He put the same pressure boundary cond. at the inlet and outlet. But I dont understand about resistance which type of resistance he used in his cfd model.

marauder · September 5, 2014, 08:42

Ok here's what I understand.
You have a Y and X on your plot as Pressure rise & Flow rate. Now what I earlier suggested was give X(flow rate) as input variable and calculate Y to plot.

Another way would be (as your paper suggests) to keep a flow regulating element at outlet or inlet, leave the openings to atmosphere. As you operate the fan at constant RPM, current and keep increasing the resistance, then the flow will start decreasing and pressure rise will be increasing. You can plot Pressure rise vs Flow by changing the resistance.
Either way if you have set up your problem correctly the value of the resistance is of no importance as it is only used to vary the flow so as to arrive at different X & Y values. So you shouldn't worry about the resistance as long as it is within the limits.

Correct me if I'm wrong. Anyways I'm checking my with a small example myself :P

chaudhry_hashim · September 5, 2014, 09:32

Yes Sir, this is what I am trying to do. So I stick to the same radiator boundary cond. which you suggest me. I have to plot pressure rise vs. flowrate. I am giving 0 Pa at both inlet and outlet, and I am running the fan at a constant RPM . what I wanted to do is to just play with the resistance and get the fan curve.
Is my model is correct?
I have total three interfaces
1- interface between upstream and fan inlet
2- interface between downstream 1 and fan outlet
3- interface between downstream 1 and downstream 2

I have uploaded the sketch of cfd model in which I also mentioned the interior face on which I am giving Radiator BC.

Thankyou so much for helping me out

marauder · September 5, 2014, 09:56

There's nothing wrong with your model or boundary conditions then.
For cross checking your model you must be using some data or formulae. Are you saying this is not matching with your analysis?
Can you post a static pressure contour of your run, just to check.

chaudhry_hashim · September 5, 2014, 12:31

Sure I am trying to do it again with improve mesh then I will send you the contour of static pressure.

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September 5, 2014, 04:44		#21
marauder Member Anonymous Join Date: Mar 2014 Posts: 84 Rep Power: 12	Why don't you just give Boundary Conditions as Mass Flow inlet or Velocity inlet and a Pressure outlet at 0 pressure. Create plane before inlet and outlet of the fan. The static pressure difference between these two planes will be your head generated.

September 5, 2014, 07:46	hi	#22
chaudhry_hashim Member hashim chaudhry Join Date: Jun 2014 Location: turkey Posts: 46 Rep Power: 11	I already tried it but i didnt get results so I searched one of the paper in which he put resistance just before the outlet and plot the curve by choking the resistance let say its 25 percent open. He put the same pressure boundary cond. at the inlet and outlet. But I dont understand about resistance which type of resistance he used in his cfd model.

September 5, 2014, 08:42		#23
marauder Member Anonymous Join Date: Mar 2014 Posts: 84 Rep Power: 12	Ok here's what I understand. You have a Y and X on your plot as Pressure rise & Flow rate. Now what I earlier suggested was give X(flow rate) as input variable and calculate Y to plot. Another way would be (as your paper suggests) to keep a flow regulating element at outlet or inlet, leave the openings to atmosphere. As you operate the fan at constant RPM, current and keep increasing the resistance, then the flow will start decreasing and pressure rise will be increasing. You can plot Pressure rise vs Flow by changing the resistance. Either way if you have set up your problem correctly the value of the resistance is of no importance as it is only used to vary the flow so as to arrive at different X & Y values. So you shouldn't worry about the resistance as long as it is within the limits. Correct me if I'm wrong. Anyways I'm checking my with a small example myself :P

September 5, 2014, 09:56		#25
marauder Member Anonymous Join Date: Mar 2014 Posts: 84 Rep Power: 12	There's nothing wrong with your model or boundary conditions then. For cross checking your model you must be using some data or formulae. Are you saying this is not matching with your analysis? Can you post a static pressure contour of your run, just to check.

September 5, 2014, 12:31	hi	#26
chaudhry_hashim Member hashim chaudhry Join Date: Jun 2014 Location: turkey Posts: 46 Rep Power: 11	Sure I am trying to do it again with improve mesh then I will send you the contour of static pressure.