How to create a time delay for inlets?

danny21 · July 5, 2015, 12:19

Hello,
I am having some trouble with a simulation that I am running. I am running a multi element wing for a Formula One style car in a fluid domain with the obvious Inlet, outlet, symmetry planes, and ground plane. However, I also have a small cut in the bottom of the main plane that I want to be an inlet. The thought behind the design is that if you can get air moving faster out of the inlet, you can lower the pressure which creates more downforce.
The problem that I am running into is that I am getting reversed flow even though the air is flowing in the same direction as the fluid domain inlet. I looked towards the streamlines to find some answers. The only idea I saw was that it started flowing before the fluid domain inlet reached it.

Any ideas?

Thanks,
Danny

kguntur · July 6, 2015, 02:09

Hi Danny,

Could you be a little more specific? Where is this 2nd inlet? Are you running transient or steady state? How long are you getting the reversed flow?

From your title I assume you want to the inlet velocity to be 0 initially and then at a perticular time or iteration you want to increase the velocity. You can use field function to achive this.

Hope this helps.

-Krishna.

danny21 · July 9, 2015, 21:27

Hi Kirshna,
Thank you for the reply.
I am running a steady state simulation and I am getting flow reversal and the conjugate gradient is unable to converge. The second inlet is on the under side of the wing. I made a cut in the bottom so that the inlet would point tangent to the wing.

I would like the air from the 2nd inlet (under the wing) to be delayed until the air from the front of the fluid domain reaches it so that it simulates the interaction between the two. For example the car driving along at a steady state and the air coming out from under the wing. I've uploaded some pictures that I hope will help.

I have not dealt with field functions and I was wondering if you could either explain how you would go about doing that or point me towards a tutorial that would explain it? I've found a lot that explain how to refine surfaces.

Best Regards,
Danny

danny21 · July 14, 2015, 19:02

Bump for attention

ggulgulia · July 16, 2015, 08:29

Hi Danny

I am curious to know the relative locations of the two inlets and the outlet. Is the 2nd inlet opposite to the first one, at the tail of the wing? What exactly is the boundary condition at both the inlets?

Also you should try converting the 2nd inlet as outlet and monitor how much mass flows out of the boundary, the pressure there. The values that need input when using the same as inlet boundary should be more than what you get when you run trial with outlet boundary.

Where exactly are you getting Reversed Flow? (CCM+ output window will give the name of the boundary that has reversed flow)

Thirdly you will have to resort to transient simulation if you want to introduce a delay b/w the inlets of the two boundaries

Hope this was helpful

July 5, 2015, 12:19	How to create a time delay for inlets?	#1
danny21 New Member Danny Join Date: Jul 2015 Posts: 3 Rep Power: 10	Hello, I am having some trouble with a simulation that I am running. I am running a multi element wing for a Formula One style car in a fluid domain with the obvious Inlet, outlet, symmetry planes, and ground plane. However, I also have a small cut in the bottom of the main plane that I want to be an inlet. The thought behind the design is that if you can get air moving faster out of the inlet, you can lower the pressure which creates more downforce. The problem that I am running into is that I am getting reversed flow even though the air is flowing in the same direction as the fluid domain inlet. I looked towards the streamlines to find some answers. The only idea I saw was that it started flowing before the fluid domain inlet reached it. Any ideas? Thanks, Danny

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July 6, 2015, 02:09		#2
kguntur Member kris Join Date: May 2014 Posts: 73 Rep Power: 11	Hi Danny, Could you be a little more specific? Where is this 2nd inlet? Are you running transient or steady state? How long are you getting the reversed flow? From your title I assume you want to the inlet velocity to be 0 initially and then at a perticular time or iteration you want to increase the velocity. You can use field function to achive this. Hope this helps. -Krishna.

July 14, 2015, 19:02		#4
danny21 New Member Danny Join Date: Jul 2015 Posts: 3 Rep Power: 10	Bump for attention

July 16, 2015, 08:29		#5
ggulgulia Senior Member Gajendra Gulgulia Join Date: Apr 2013 Location: Munich Posts: 144 Rep Power: 13	Hi Danny I am curious to know the relative locations of the two inlets and the outlet. Is the 2nd inlet opposite to the first one, at the tail of the wing? What exactly is the boundary condition at both the inlets? Also you should try converting the 2nd inlet as outlet and monitor how much mass flows out of the boundary, the pressure there. The values that need input when using the same as inlet boundary should be more than what you get when you run trial with outlet boundary. Where exactly are you getting Reversed Flow? (CCM+ output window will give the name of the boundary that has reversed flow) Thirdly you will have to resort to transient simulation if you want to introduce a delay b/w the inlets of the two boundaries Hope this was helpful