# mass flow outlet???

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 March 27, 2007, 00:59 mass flow outlet??? #1 davy Guest   Posts: n/a I'm trying to model a suction through a hole on a wing surface. I could model a injection easily by setting the assigned surface as a mass flow inlet. However, i couldn't find any function that would allow me to do a suction through mass flow outlet (just no such fucntion?) and it wouldn't allow me to assign a negative value for mass flow rate nor placing a -1 value in the flow vector would do the job...PLEASE HELP ME (starting to go a lil insane)

 March 27, 2007, 08:46 Re: mass flow outlet??? #2 Gernot Guest   Posts: n/a 2 possibillties : 1.) If you have incompressible flow you can try a `negative velocity inlet īmeans take a velocity inlet and set the velocity negative. 2.) at the pressure outlet panel thereīs a button Target mass flow rate. Iīve never worked with option #2 but maybe itīll help you.

 August 18, 2010, 07:18 hi #3 Senior Member     Morteza Join Date: May 2010 Location: Iran,Islamic Republic of Posts: 159 Rep Power: 7 hi I am trying to model suction over an airfoil in fluent and gambit. but i encountered some problems that i can not find the solutions for since 2 weeks ago. first:: i have read many articles that model continous suction or suction using a synthetic jet. all of the articles give us the suction velocity ,but when i choose the outer boundary as pressure far field ,i see some warnings. some body tolds me that i have to use the pressure outlet boundary condition for suction hole... but i can not calculate the pressure for my low renolds number model... in other words when i am trying to re-do an earlier numerical work in fluent that used velocity inlet for suction,i also have tobe able to do it.. 2; the drag coefficient is negative in nearly all cases and the lift coefficient has a big variation with the exact value..and sometimes has a negative value. 3.i have modeled more than 7 different cases in gambit with differen meshes. i do not know where do the problems come from? please answer these questions : a: which type of mesh is better for modelling a base airfoil and suction-including airfoil.. C-H grid....O-grid....boundary layer mesh or .... please send me a dbs file of mesh over a base airfoil and a dbs file of mesh over a sutioned airfoil... b: please tell me which boundary conditions i have touse in gambit... pressure far field,symmetry,wall or ...... for a typical C-H grid over airfoil please express the boundary cond. detailed. c: which solver and discretization schemes is better to model a base airfoil and suctioned airfoil. tell me the appropriate turbulance model and any other things you things is good to better model an airfoil. d: to calculatethe darg and lift coefficients in fluent , is it needed to change the default value of area in refrence value? elease send me by email useful file(tyrorial,mesh file,dbs file ,case and data file or..) thatcan help me to do this...thanks i am ready to send you my works to tell me my faults.. but it isan emergency ..please sooner... thanks f:: please answer me,,,,,, i'm stock...

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