# Fluent-Boundary Conditions

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 January 10, 2009, 13:26 Fluent-Boundary Conditions #1 Vijay Guest   Posts: n/a Sponsored Links let us assume a flow in simple pipe (air). Step 1: I used mass flow rate boundary condition at inlet and outflow boundary condition at outlet. I calculated pressure values at inlet and outlet in post processing step from pressure contours. In step 2 , I used the above obtained pressure values (Total pressure values at inlet and Static Pressure value at outlet)as my pressure inlet and outlet boundary conditions respectively for the same model. Now question is I am not getting the same mass flow rate at inlet as in step no. 1

 January 10, 2009, 14:34 Re: Fluent-Boundary Conditions #2 John S. Guest   Posts: n/a Massflow, as you know, is a function of density, velocity and area. In the model, the area of the inlet is set and cannot vary, leaving only density and massflow as variables, with density being a function of pressure and temperature. So when you specify massflow at a boundary it will calculate the area directly from the model and set pressure, temperature and velocity in order to achieve it. Similarly, when you specify pressure at the boundary it will vary massflow and velocity to set the boundary condition. Also consider aerodynamic blockage caused by boundary layer buildup. As the boundary layer is resolved, it has the effect of reducing the "effectiveness" of the inlet, causing it to flow as if it were restricted, i.e. the area the flow sees is less than the physical area of the geometry. So in order to truly equate these two analyses you would either have to take the aerodynamic blockage into consideration with the massflow-specified model or apply some kind of loss coefficient with the pressure specified model.

 January 10, 2009, 18:05 Re: Fluent-Boundary Conditions #3 Vijay Guest   Posts: n/a what parameter should I consider to introduce the loss coefficient. Thank you for your help.

 January 19, 2009, 18:30 Re: Fluent-Boundary Conditions #4 Vijay Guest   Posts: n/a Can you get back to me to the last question. I appreciate the help that you are doing. It would be very helpful if can extend our discussion.

March 20, 2016, 12:12
#5
Member

Join Date: Oct 2014
Location: beijing
Posts: 53
Rep Power: 4
Quote:
 Originally Posted by John S. ;155902 Massflow, as you know, is a function of density, velocity and area. In the model, the area of the inlet is set and cannot vary, leaving only density and massflow as variables, with density being a function of pressure and temperature. So when you specify massflow at a boundary it will calculate the area directly from the model and set pressure, temperature and velocity in order to achieve it. Similarly, when you specify pressure at the boundary it will vary massflow and velocity to set the boundary condition. Also consider aerodynamic blockage caused by boundary layer buildup. As the boundary layer is resolved, it has the effect of reducing the "effectiveness" of the inlet, causing it to flow as if it were restricted, i.e. the area the flow sees is less than the physical area of the geometry. So in order to truly equate these two analyses you would either have to take the aerodynamic blockage into consideration with the massflow-specified model or apply some kind of loss coefficient with the pressure specified model.
Dear expert.. I have to use Superficial gas velocity 0.0016 m/s. But In fluent we have to put Velocity Magnitude at VELOCITY INLET boundary conditions.( INLET VELOCITY) How can I calculate INLET GAS VELOCITY form superficial gas velocity??? ( Reactor dimensions are 20*5*50 cm W*D*L and inlet dimensions are 2.4*1.2 L*D )

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Ankan Kumar FLUENT 5 November 9, 2016 04:44 Novice FLUENT 5 March 20, 2016 12:10 ABM FLUENT 2 February 17, 2009 12:41 Vijay FLUENT 3 January 9, 2009 12:42 Arturo Ortiz FLUENT 0 January 25, 2001 18:52