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I'd like to start off by saying that I'm new to StackOverflow and to Modelica.

My goal is to simulate the injector system of a Rotating Detonation Engine. Essentially this is a piping system from a tank to a rocket engine. This system will change depending on the experimental setup, so I chose Modelica (specifically OpenModelica) because of the re-usability of components. The flows encountered will be at high pressures and high flow rates (sustaining a detonation requires this), and choked flow will occur.

My question is this: does the standard "Fluid" library in Modelica allow for choked flow? I understand that a few valves model this, but will the current library be able to capture "choking" in a long rough pipe, or the small end of a converging pipe (basically anywhere choking can happen, despite it not being the design location for a choke)?

If yes, excellent. If not, is there a non-standard library available? Should I be looking at something other than Modelica? I am happy to work on making a new library, but before going through that work I thought I would check to see if anything already existed.

I have read through most of the "Media" and the basics of the "Fluid" libraries and I get the feeling that compressible flow is modeled as a means of increasing accuracy over in-compressible flow, but not to actually handle choked flow.

Thank you for your time. I hope everyone is keeping safe!

Thomas
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  • Since this has not been answered for one week, feel free to directly ask the developers by creating a new issue at https://github.com/modelica/ModelicaStandardLibrary/issues/new – tbeu Jun 16 '20 at 05:34

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The pipe model in the Modelica library does not handle choked flows. Adding a standard orifice in series with the pipe should help provided the 'zeta' value is adjusted to make the velocity at the orifice match with the speed of sound in the gas. In other words Modelica library does not provide a valid mean of modeling choked flows in pipes. However, I found a very interesting library called FreeFluids (https://github.com/CarlosTrujilloGonzalez/FreeFluidsModelica) who does have a very good model for choked pipes. An example is provided with the library for a choked air flow in a 10m long diam. 50mm circular pipe. The model returns correct values for air.

Laurent
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