8 Replies Latest reply on Jul 18, 2013 10:59 AM by Jared Conway

# How to define both velocity and pressure in the boundary condition?

Hello Guys,

I have been tryin to do a flow sim on my FSAE project and i'm trying to find my way out through a tricky stuff. I want to simulate my intake(flow sim) for 2 situations.

1) Well I have been able to perform this type of simulation. The boundary conditions for the inlet is pressure(1 atm) and at the runners it varies.

2) This is where i face real trouble. As the car moves along, there would be a velocity of air gushing in through my forward facing intake. But the trouble is i cannot compare the of effect with and without velocity.

Sadly flowsim doesnot allow the defination of more than one type of inlet boundary condition. I would like to know a method in which i can define the inlet boundary condition as both 1 atm and x m/s velocity.

Samioroi

• ###### Re: How to define both velocity and pressure in the boundary condition?

I would imagine with the TB and filter setup you wouldn't have much ram air effect, through with a dome filter at WOT you might.  For that case, can you not just find a stagnation pressure from velocity, and offset all your internal pressures?

Just some thoughts.  Our intake faced rearward, didn't have this issue!

• ###### Re: How to define both velocity and pressure in the boundary condition?

there are a bunch of youtube videos and forum threads on setups for intakes.

are you trying to do this as an internal analysis or external analysis?

for an internal analysis you're bound by the requirements to have one volume flow rate/velocity and a pressure opening or 2 pressure openings.

for external analysis, your intake side could be an environment blowing at X velocity and the pressure would be whatever is at the inlet of your intake.

so let's take a step back, how would you test this in real life? how would you calculate by hand this problem? then what you have to do is back the boundary conditions to the locations on your model.

if there was no ram air, how would you test your model? (justin's comments are important here too, will you really get ram air with a TB and filter at the speeds of FSAE?)

• ###### Re: How to define both velocity and pressure in the boundary condition?

Proven data has shown a FSAE car will go around 30kmph on an average and the average when it comes to throttle postion is 50-60% of WOT.

With that scenario the inlet velocity x- direction vector would be 8.33m/s. I think with a proper bell mouth at the opening of the inlet this can bring about a considerable difference. Well again i have no data to show but all in pursuit of the same.

• ###### Re: How to define both velocity and pressure in the boundary condition?

Also i know teams use surface modelling to make their intake and then thicken them over. Well we have been using regular lofts and other features. Last time we tried making one through surface but were unable to thicken at portions so switched back.

I would like to know if the same level of flexibility can be achieved through regular lofts as surface modelling.

• ###### Re: How to define both velocity and pressure in the boundary condition?

samio regarding the velocity, you can certainly setup your model to be an external analysis with initial conditions of 8.33m/s and see how it goes. then take a look at the pressure at the inlet. setup the same problem as an internal analysis with a velocity input. i suspect that you're going to get the same dP across the system.

on solid loft/sweeps vs surface modeling, is it possible? probably. are surface better and more robust for developing some shapes? yep. probably best to show some pictures of what you're trying to do, post your models and where you are stuck and get them into the appropriate forum for it.

• ###### Re: How to define both velocity and pressure in the boundary condition?

hey Jared,

I have done the simulations for external type and the results show a stagnation pressure pressure of .004 bar which i believe is a very small number.

Thanks for the input. Was of great help.

• ###### Re: How to define both velocity and pressure in the boundary condition?

I am just wondering why there is option for "Pressure" under "Thermodynamics Parameter" if I select an inlet volumetric flow rate boundary condition? Does that mean I can fix both flow rate and pressure for the inlet?

• ###### Re: How to define both velocity and pressure in the boundary condition?

Hi hoi, did you check the help for the definition of that parameter? It is a placeholder only.