[amirbhr]

Hi everyone

I have a cfd problem with changeable boundary condition at outlet of the box. Would anyone please help me to solve the problem with the details below?

The outlet would be as wall until the maximum temperature of the domain reaches 350 (K). Then, the outlet changes to Mass flow outlet until the domain maximum temperature decreases to 330 (K) and once again the outlet converts to wall.

How can I set this boundary condition in Fluent using UDF?

[AlexanderZ]

if you want to change boundary condition type -> you should use scheme language and TUI commands

1. Make *.scm file, here you will define variable (RPVAR) to check your criteria. exhample

(define (make-new-rpvar name default type)(if (not (rp-var-object name))(rp-var-define name default type #f)))
(make-new-rpvar 'my_switch_boundary #f 'boolean)

2. Make UDF to find maximum temperature, use DEFINE_EXECUTE_AT_END
3. Inside UDF compare Tmax with 350k, if Tmax>350 than change flag
4. Get variable from scheme. exhample

cxboolean udf_switch_boundary = False;

if (Tmax>350)
	udf_switch_boundary =True;
else
udf_switch_boundary =False;

5. Send your criteria state to scheme. exhample

if (RP_Variable_Exists_P("my_switch_boundary"))
	{RP_Set_Boolean("my_switch_boundary",udf_switch_boundary);
	Message0("switch was sent to scheme\n");}
	else { Message0("failed to send data to scheme\n");}

6. In Fluent GUI go to Calculation activities -> execute commands
activate command, when -> each timestep
If the wall, you wanna change has name wall-1, than inside command put following:

(if  (%rpgetvar 'my_switch_boundary)
	(begin
		(ti-info "**************SWITCH IS TRUE****************")
		(ti-menu-load-string (format #f "define boundary-conditions modify-zones zone-type wall-1 pressure-outlet"))
	)
	(ti-info "**************SWITCH IS FALSE | NO CHANGE****************")
)

use it as a basis

best regards