Zero mass flow rate and non converging solution during fan simulation

Bisht · June 2, 2015, 16:29

Hi, I am simulating a fan at 6000 rpm using Moving reference frame but it's showing 0.0001 L/s mass flow rate at inlet though the experimental result is around 10 L/s. My result is also not converging properly.
I have tested it for both coupled implicit and segregated flow model, Lowered the Courant no., underrelaxation factor but still my solution is not correct. Although coupled implicit showing better convergence than segregated flow at Courant no. =2

I am using following physics model for my simulations:
Constant density, realizable k-epsilon two layer, steady, Stagnation inlet, pressure outlet

The inlet velocity is zero so I am using stagnation Inlet. The mesh is refined and have more than a million cells. Velocity plot is showing a velocity of 0.35 m/s just below the inlet plane.

Kindly suggest me in this regard.
here are the Images of my simulations.
https://mail.google.com/mail/?ui=2&i...2&disp=safe&zw
https://mail.google.com/mail/?ui=2&i...3&disp=safe&zw

fluid23 · June 3, 2015, 15:42

Don't setup reports on your boundaries. You need a derived part or something that is offset. It depends somewhat on your geometry, but measuring engineering parameters at a boundary condition is usually not advised.

As for convergence issues, this could be anything. Most likely its a mesh issue. What do your y+ values look like? Is your mesh appropriate? Usually its just a bad mesh.

I am unable to open your images. It could be that a stagnation inlet is the wrong choice. This is a better choice for a pipe flow problem where you are given pressure and want to allow the flow to devlop. Stagnation inlet is zero velocity yes, but it isn't going to give you a zero velocity everywhere (if the fan were off). You probably should use a velocity inlet and set that to zero.

Bisht · June 4, 2015, 07:48

Thanks Matt for your suggestion. Yeah I think it's something to do with my mesh, I checked it's not fine enough near fan. Can I take pressure outlet as inlet because I want to setup the same value of pressure at Inlet and Outlet?
you can see the image here
http://i58.tinypic.com/1253qbn.jpg

fluid23 · June 4, 2015, 08:42

Still can't get to the image. Firewall.

Is this a ducted fan? (fan in pipe)

Bisht · June 4, 2015, 09:11

It's a fan over a motor

fluid23 · June 4, 2015, 09:11

Still nothing.

Bisht · June 4, 2015, 09:20

I think you firewall is blocking the image to get display. Anyway, I will try to simulate it keeping in mind your suggestions.

June 2, 2015, 16:29	Zero mass flow rate and non converging solution during fan simulation	#1
Bisht Member Kamal Bisht Join Date: Jun 2015 Location: Germany Posts: 57 Rep Power: 10	Hi, I am simulating a fan at 6000 rpm using Moving reference frame but it's showing 0.0001 L/s mass flow rate at inlet though the experimental result is around 10 L/s. My result is also not converging properly. I have tested it for both coupled implicit and segregated flow model, Lowered the Courant no., underrelaxation factor but still my solution is not correct. Although coupled implicit showing better convergence than segregated flow at Courant no. =2 I am using following physics model for my simulations: Constant density, realizable k-epsilon two layer, steady, Stagnation inlet, pressure outlet The inlet velocity is zero so I am using stagnation Inlet. The mesh is refined and have more than a million cells. Velocity plot is showing a velocity of 0.35 m/s just below the inlet plane. Kindly suggest me in this regard. here are the Images of my simulations. https://mail.google.com/mail/?ui=2&i...2&disp=safe&zw https://mail.google.com/mail/?ui=2&i...3&disp=safe&zw Last edited by Bisht; June 3, 2015 at 02:54. Reason: New image

June 3, 2015, 15:42		#2
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	Don't setup reports on your boundaries. You need a derived part or something that is offset. It depends somewhat on your geometry, but measuring engineering parameters at a boundary condition is usually not advised. As for convergence issues, this could be anything. Most likely its a mesh issue. What do your y+ values look like? Is your mesh appropriate? Usually its just a bad mesh. I am unable to open your images. It could be that a stagnation inlet is the wrong choice. This is a better choice for a pipe flow problem where you are given pressure and want to allow the flow to devlop. Stagnation inlet is zero velocity yes, but it isn't going to give you a zero velocity everywhere (if the fan were off). You probably should use a velocity inlet and set that to zero.

June 4, 2015, 07:48		#3
Bisht Member Kamal Bisht Join Date: Jun 2015 Location: Germany Posts: 57 Rep Power: 10	Thanks Matt for your suggestion. Yeah I think it's something to do with my mesh, I checked it's not fine enough near fan. Can I take pressure outlet as inlet because I want to setup the same value of pressure at Inlet and Outlet? you can see the image here http://i58.tinypic.com/1253qbn.jpg

June 4, 2015, 08:42		#4
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	Still can't get to the image. Firewall. Is this a ducted fan? (fan in pipe)

June 4, 2015, 09:11		#5
Bisht Member Kamal Bisht Join Date: Jun 2015 Location: Germany Posts: 57 Rep Power: 10	It's a fan over a motor

June 4, 2015, 09:20		#7
Bisht Member Kamal Bisht Join Date: Jun 2015 Location: Germany Posts: 57 Rep Power: 10	I think you firewall is blocking the image to get display. Anyway, I will try to simulate it keeping in mind your suggestions.