Transient target mass flow rate

- December 7, 2018 at 8:05 pm
  
  Kamukyo
  Subscriber
  
  Hello,
  
  I would like to set the target mass flow rate for two outlets ( 70% of inlet mass flow rate for outlet 1, 30% of inlet mass flow rate for outlet 2).
  
  I found a example in UDF manual as shown in the attachment.
  
  In this example, the specific mass flow rates were specified (1.00 kg/s when t <0.2, 1.35 kg/s when t>0.2)
  
  However, for my simulation, the inlet mass flow is time-dependent, which means the inlet mass flow rate is changed every 0.001 s that i set as the time step size.
  
  Is there anyway to define the target mass flow rate by using the inlet mass flow rate?
  
  If not, do i have to calculate the inlet mass flow rate every 0.001 s and set 70%, 30% of it for outlets?
  
  Thank you
- December 9, 2018 at 6:38 pm
  
  Raef.Kobeissi
  Subscriber
  
  you can use an outflow boundary condition and specify the ratio for each outlet, there is no guarantee that your ratio will work at all times.
  
  Regards
- December 10, 2018 at 5:12 am
  
  Keyur Kanade
  Ansys Employee
  
  as Raef suggested you may need outflow bc.
  
  or you may go ahead with udf.
  
  please note that as ANSYS employee, we will not able to help to debug udfs.
- December 11, 2018 at 5:01 pm
  
  Kamukyo
  Subscriber
  
  Thank you for your reply.
  
  What you mean is that i can set the mass flow rate for each outlets (Ex 1 kg/s for outlet 1 and 0.5 kg/s for outlet 2) in the target mass flow tab?
  
  Even if Inlet total mass flow rate would vary from 0.6 kg/s to 3 kg/s, once i set the ratio of the mass flow rate such as an example, it may work? or calculate the maximum mass flow rate for the inlet (3 kg/s) and assign (2 kg/s for outlet 1 and 1 kg/s for outlet 2) something like that?
  
  Thank you
- December 11, 2018 at 5:13 pm
  
  Rob
  Forum Moderator
  
  The (old) outflow boundary allows you to set a ratio of flow. So, if you set a flow rate on the inlet you can set the outflow ratio to be 0.5 on each boundary, or 0.3 & 0.7 as desired. I would recommend using a velocity inlet if you do, and note that there are several limitations on the outflow boundary condition: these are covered in the manual.
  
  An alternative is to use a profile (or UDF, look for DEFINE_PROFILE in the UDF manual) using a negative velocity. In this approach you use a pressure inlet and suck the flow out of the domain.
  
  Please can you post the image in the text as ANSYS staff aren't supposed to download files.