Piston cylinder with fluid on both sides

rmawsu · October 11, 2017, 20:34

Hi,

I am going to model a hydraulic piston-cylinder while there are fluids on both sides of the piston (preferably two different fluids). The piston should move based on the pressure difference of the fluids on both sides. I have already tried using rigid body solution and immersed solid in CFX, but the fluid moves through the piston even with high momentum scaling factor and considering smooth inside ims= t expert parameter.
The other problem is that I am not able to set two different fluid zones on sides of the piston.

I think this modeling should be similar to what happens in free piston engines but I haven't found any work on those engines using Fluent or CFX.

Does anyone have any idea how I solve these issues?

Any help would be greatly appreciated.

Christophe · October 11, 2017, 23:45

There are two approaches to this. One is create a 3-d solid which overlaps the fluid domain and then simply acts as a source term to restrict the motion of the fluid based on the momentum scaling factor and the velocity differences, which you've tried. The other is to model the piston as a void in the fluid domain and assign those surfaces as rigid body. There's a CFX tutorial to try. Chapter 22 I believe which is a spring loaded pressure relief valve, to introduce the concept.

October 11, 2017, 20:34	Piston cylinder with fluid on both sides	#1
rmawsu New Member Aida Join Date: Sep 2017 Posts: 1 Rep Power: 0	Hi, I am going to model a hydraulic piston-cylinder while there are fluids on both sides of the piston (preferably two different fluids). The piston should move based on the pressure difference of the fluids on both sides. I have already tried using rigid body solution and immersed solid in CFX, but the fluid moves through the piston even with high momentum scaling factor and considering smooth inside ims= t expert parameter. The other problem is that I am not able to set two different fluid zones on sides of the piston. I think this modeling should be similar to what happens in free piston engines but I haven't found any work on those engines using Fluent or CFX. Does anyone have any idea how I solve these issues? Any help would be greatly appreciated.

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October 11, 2017, 23:45		#2
Christophe Member Join Date: Jan 2015 Posts: 62 Rep Power: 11	There are two approaches to this. One is create a 3-d solid which overlaps the fluid domain and then simply acts as a source term to restrict the motion of the fluid based on the momentum scaling factor and the velocity differences, which you've tried. The other is to model the piston as a void in the fluid domain and assign those surfaces as rigid body. There's a CFX tutorial to try. Chapter 22 I believe which is a spring loaded pressure relief valve, to introduce the concept.