Restrictor Design

[lyons5959]

To model the restrictor accurately I use an orifice and a PID controller. I attach a sensor to the orifice to measure mass flow. Also attached to the orifice is an actuator controlling the orifice diameter. The PID controller uses the mass flow sensor as the target and outputs the orifice diameter. Just make sure to set the maximum diameter close to your real restrictor size.

Result: Airflow through the resrictor increases until it reaches the target and will then be limited by the PID controller decreasing the orifice diameter.

[Charlie]

Are you sure you've reached steady state?

WAVE begins with a static system, it takes runs to generate steady flow. The restrictor is an abnormal thing for an intake system, in my experience you need additional cycles to reach the point where the restrictor has an effect.

If you have a big plenum you might just be feeding from that.

[samphlett]

A controlled orifice can interact with the wave dynamics if it's varying rapidly w.r.t. crank angle. Be aware.

[lyons5959]

Yes, the controller is tuned to steady state. The pressure signal is filtered to reduce the effect of cyclic variation and pressure waves. The controller is also filtered to prevent any interaction with the pressure waves. If I knew how to post a picture or attachment I would post a plot of air flow vs. engine speed. It steadily increases until it chokes at ~ 244 kg/hr=68g/s (19mm restrictor). I have also modeled the restrictor and run it with CD-ADAPCO's STAR-CCM interacting with WAVE and it produced VERY similar results, it just takes a lot more time to simulate.

[EPMAl]

As said previously, if your restrictor chokes (which is probably the case), that means you've attained a sonic flow and whatever geometry you're using, it won't make a big difference. I've done CFD (Fluent) on different geometry and since they almost all got to sonic flow, the mass flows were really close to one another (something around 74g/s). At that point, the only thing that your geometry is influencing is if and where you'll get recirculation along the walls of your divergent cone which may cause turbulence in your plenum (more than there already is).

[autocratz]

participating first time in FSAE need some idea on restrictor design so that it would not much affect the power output of engine

[Drew Price]

Originally posted by autocratz:
....need some idea on restrictor design so that it would not much affect the power output of engine

When you figure out how to do that, please let us know.



Best,
Drew

[Nishant Jain]

I talked to the Ricardo guys about this in Detroit a few years ago and they said restrictors wouldn't model properly. I don't remember exactly what the solution was, but it was something along the lines of modeling your restrictor so that your pressure drop is correct even if the geometry is wrong.

@Matt: So in the case of the restrictor, we're basically not modeling on Wave but testing on a flowbench for pressure drop and then recreating that on Wave. Is that correct?

@lyons5959: Can you tell me a bit more about the PID Controller method for restrictor design? We're using Wave for the first time this semester, and I haven't gotten round to figuring out the sensors and controllers yet. Why would you want the controller to actually decrease the diameter at any point?