8 Replies Latest reply on Nov 21, 2014 12:05 PM by Jared Conway

    Transonic flow simulation

    Amit Katz

      This question is more about the abilities of Flow Simulation, and not about a specific setup. I have a compressed air supply (60 psig) and I'm curious if Flow Sim could help me design a de Laval nozzle to increase the mass flow rate. Just dumping out 60 psig to ambient through a tube would choke the flow, and I want to maximize my mass flow rate. I know it's possible to simulate low Mach numbers (<.3) and supersonic flow separately, but how does the software do with compressible flow right at the sonic regime? Would I get reliable numbers for the expansion through the nozzle?

        • Re: Transonic flow simulation
          Peter Dr. Giese

          Hello Amit,

          Flowsimulation is well designed to calculate supersonic flow with compressible fluids. I have calculated several times the nozzles for fluid cells which are feeded by pressurized hydrogen with 8 bar = 116 psig.

          The calculated values fitted really well with measured one.

          I have heard too, that Flowsimulation delivers better results than eg. CFD codes from ANSIS

          • Re: Transonic flow simulation
            Jared Conway

            hi amit, shouldn't be an issue, this is well defined in the software documentation and also the swx website. are you able to access that information? i'm not sure if you have the software or not.

            • Re: Transonic flow simulation
              Amit Katz

              I am running into a slight problem with this. My overall design is a simple conical diffuser, since my flow would be coming out of a pressurized air tank through a tube there is no need to use a converging section to bring it to a choked state. The way I have the simulation set up is I set the total pressure at the inlet to the pressure in the tank (60 psig) and the outlet is set to ambient conditions. The issue is that if I set the "high mach number flow" option, then I get a warning that the mach numbers are too low (the max is Mach 1.8 or so.) If I turn off the "high mach number flow" then I get a warning that the flow is supersonic in too many cells and "use of stopping is recommended".

              • Re: Transonic flow simulation
                Amit Katz

                I'm having some trouble quantifying the efficiency of a nozzle like this. As you can see from the screenshots the fluid domain is small, including only the nozzle and the hose immediately before and afterwards. My boundary conditions are a set total pressure at the inlet (to simulate the supply of compressed air) and ambient conditions at the outlet. The problem is that since the thermodynamic state of the air is set at the inlet and the outlet, those values will always be the same no matter how I change the geometry of the nozzle.

                 

                The inlet and outlet hose diameters are a set size, all I'm doing is changing the angle on the nozzle. What I'd like to find out is how to expand the air in the most efficient way possible. I thought initially of taking the enthalpy difference across the domain, but since this is a state variable it will always be the same no matter what I do to the nozzle. Any ideas?

                  • Re: Transonic flow simulation
                    Jared Conway

                    can you elaborate on your analysis setup and explain how you would test this in the physical world and then explain how you want to quantify efficiency?

                     

                    flow simulation is pretty straight forward, i have a feeling that the issue here is that you haven't thought through the goals so that you can set the BCs appropriately. i think with some more info i can help out. remember that flow can either be setup as pressure pressure or flow pressure (inlet/outlet conditions). what you get out of these 2 cases is the flow rate or the pressure at the flow end respectively.