Simulink Hydraulic Orifice Equation Questions

Hello,

The Fixed Area Hydraulic Orifice uses an alternative equation that I am unfamiliar with since it differs from the textbook/classic orifice equation. Here are the questions I have:

1. What is the difference between the two?
2. Do the Cds from the classic formulation carry over to the Simulink variation?
3. Does Simulink adjust Cd in relation to the Reynolds number?

Im working on a system level simulink model and need more of an understanding of the orifice inputs to ensure a good engineering model.

Equations used by simulink

Thanks,

Answer 1

[Matteo Pellegri]

Hi.

The orifice equation implemented in the Simulink model is just written in a different form from the standard one and it include the terms required to model the transition from laminar to turbulent flow by looking at the critical dp to reach turbulence (see this link)

https://uk.mathworks.com/help/physmod/hydro/ref/variableorifice.html

In this case, my understanding is that the Cd does not vary since it's defined for fully developed turbulent flow. The transition is instead taken into account by p_cr which is function of the Reynolds number.

I cannot find a source for that specific equation or its derivation but I'm confident that with some googling you can find it!

Best