9 Replies Latest reply on Feb 23, 2015 7:12 PM by Jared Conway

Cfd of fsae intake

Dhruv Malhotra Feb 13, 2015 1:45 PM

I require some technical help on the cfd of an fsae intake manifold, regarding specifying the boundary conditions. According to flow simulation, specifying outlet boundary condition mean flow is exiting the manifold to that condition. I don't understand why in case of intake manifold most people and solidworks tutorial has specified environmental pressure(101325Pa) at the outlet of runners, as the flow here enters the engine of the car and not atmosphere. Rather env.pressure should be given at the inlet as the flow is entering through the environment considering ambient conditions. I just want to check the pressure loss till the air reaches the engine. And taking the bc's as provided in tutorial( inlet velocity, outlet env.pressure), solver shows pressure at inlet above the ambient pressure! Please help and provide some technical understanding about this!! (As in cfd of c-d nozzle the selection of boundary conditions is straight forward.) I am not doing time dependent transient analysis, but the simple analysis.

Values for boundary conditions in cfd of c-d nozzle-

inlet env.pressure- 101325Pa

mass flow rate- 0.075kg/s (reference max.)

Re: Cfd of fsae intake

Jared Conway Feb 13, 2015 2:57 PM (in response to Dhruv Malhotra)

flow simulation works best in one of 2 ways

2 pressures > determine the flow rate
an inlet volume flow rate and a pressure > determine the pressure at the inlet side

you can use outlet volume flow rate but it is not recommended by the developers due to the assumption made about the velocity profile

from a physical perspective, an outlet volume flow rate of your intake at the engine side and then a pressure opening where it meets with the throttle body makes sense to me.

but another way you could think of it is to look at how you will test in your flow bench and just match that.
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- Re: Cfd of fsae intake
  
  Dhruv Malhotra Feb 14, 2015 5:01 PM (in response to Jared Conway)
  
  Env. pressure at inlet will work fine.Volume flow rate at outlet mean either providing some value from some previous cfd for flow rate goals, or by taking one fourth of the value that is theoretically found at choke conditions. Will that provide accurate results? Wouldn't that account for too much assumption as you said that it is not recommended by the developers to use volume flow rate at outlet?
  
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Re: Cfd of fsae intake

Amit Katz Feb 13, 2015 2:57 PM (in response to Dhruv Malhotra)

Typically for a manifold I would just model the part itself and set environmental pressure at the outlet, and a set inlet volume/mass flow. The reason being is that I am simply interested in the pressure difference from inlet to outlet, and not the actual pressure readings at either end. This also explains why there is positive pressure above ambient at the inlet, because the outlet's boundary is set at the ambient.
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- Re: Cfd of fsae intake
  
  Dhruv Malhotra Feb 14, 2015 4:45 PM (in response to Amit Katz)
  
  Even I have in mind to set mass/volume flow rate at inlet instead of inlet velocity, as that might be more accurate. Because the velocity i am putting is taken from value of surface goal of c-d nozzle at inlet conditions rather volume flow rate was calculated at choke conditions(20mm restrictor) and considered to be reference maximum.
  
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  - Re: Cfd of fsae intake
    
    Amit Katz Feb 16, 2015 8:56 AM (in response to Dhruv Malhotra)
    
    In the case of choked and supersonic flow, I would go with mass flow rate, just to be on the safe side.
    
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    - Re: Cfd of fsae intake
      
      Dhruv Malhotra Feb 23, 2015 11:37 AM (in response to Amit Katz)
      
      Thank you for your support Amit.
      
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  - Re: Cfd of fsae intake
    
    Jared Conway Feb 17, 2015 5:19 PM (in response to Dhruv Malhotra)
    
    how are you going to test this in the real world?
    
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    - Re: Cfd of fsae intake
      
      Dhruv Malhotra Feb 23, 2015 11:35 AM (in response to Jared Conway)
      
      Just through a manifold air pressure(MAP) sensor placed approximately at the end of runners. The pressure of air entering the intake will be known.
      
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      - Re: Cfd of fsae intake
        
        Jared Conway Feb 23, 2015 7:12 PM (in response to Dhruv Malhotra)
        
        so pressure opening at the inlet
        
        and flow rate out seems like a good fit
        
        however most people would test this on a flow bench, but that would be tested in a similar fashion
        
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