Reversed Flow in Outlet

JSped · January 12, 2016, 23:40

Hi guys,

My simulation uses pipes with "mass flow inlet" at the inlet and "flow-split" outlet at the outlet. Are these appropriate inlet/outlet boundary types for fluid flowing into and out of a pipe?

The reason I ask is that I've been getting two faces of 'reversed flow' at the outlet. How would I remedy this?

I appreciate any help.

Deranda · January 20, 2016, 03:20

Hi,

in all my simulations, I used a pressure out as boundary conditions and I think thats a common way...
However, if u have reversed flow at your outlet, u have to enlarge the outletarea. For example, if u have a turbulent flow through a pipe and u get reversed flow at the pipes end, u can extrude the pipe by 1m (dont have to be very fine mesh) so the flow can turn into a moderate laminar flow.

By using the extruder in the mesh options u have an easy way to get an enlarged outlet.
The extruder just takes the outlet mesh an extrude the cells.
You have to select your outlet boundary -> extrusion type -> constant normal rate. Then a new tab appears where you can choose your parameters like length, stretching etc...

fluid23 · January 20, 2016, 10:59

Only use flow-split if you have two (or more) outlets to the system, pressure outlet if you only have one. A mass flow or velocity inlet is appropriate depending on what you are analyzing. As Deranda says, extrude the inlet/outlets. You are seeing re-circulation because your boundary conditions are too close to the rest of your geometry.

January 12, 2016, 23:40	Reversed Flow in Outlet	#1
JSped New Member James Join Date: Jan 2016 Posts: 3 Rep Power: 10	Hi guys, My simulation uses pipes with "mass flow inlet" at the inlet and "flow-split" outlet at the outlet. Are these appropriate inlet/outlet boundary types for fluid flowing into and out of a pipe? The reason I ask is that I've been getting two faces of 'reversed flow' at the outlet. How would I remedy this? I appreciate any help.

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January 20, 2016, 03:20		#2
Deranda Member Nils Join Date: Nov 2015 Posts: 59 Rep Power: 10	Hi, in all my simulations, I used a pressure out as boundary conditions and I think thats a common way... However, if u have reversed flow at your outlet, u have to enlarge the outletarea. For example, if u have a turbulent flow through a pipe and u get reversed flow at the pipes end, u can extrude the pipe by 1m (dont have to be very fine mesh) so the flow can turn into a moderate laminar flow. By using the extruder in the mesh options u have an easy way to get an enlarged outlet. The extruder just takes the outlet mesh an extrude the cells. You have to select your outlet boundary -> extrusion type -> constant normal rate. Then a new tab appears where you can choose your parameters like length, stretching etc...

January 20, 2016, 10:59		#3
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	Only use flow-split if you have two (or more) outlets to the system, pressure outlet if you only have one. A mass flow or velocity inlet is appropriate depending on what you are analyzing. As Deranda says, extrude the inlet/outlets. You are seeing re-circulation because your boundary conditions are too close to the rest of your geometry.