3 Replies Latest reply on Nov 29, 2015 1:56 AM by David Paulson

    How to create a simulation of a water jet hitting an object

    Graham Rigby

      Hi. So I'm trying to simulate a pelton wheel turbine using SolidWorks flow simulation. I am only looking at one stationary bucket, just to measure that the forcing is accurate to the hand calculations. For those unfamiliar with the pelton wheel, essentially high pressure water is sent through a nozzle out into ambient air. This now fast moving jet of water is shot at a bucket which redirects the flow. The change in momentum of the water jet gives the bucket a force.

       

      My issue is that I do not know how to go about this problem. I have the diameter and speed of the jet already from nozzle calculations. All I want is a jet of water flying through an air medium. The air actually isn't that important but I'm not sure if I can just have nothing there at all. I'm doing it in external flow. Usually what SolidWorks thinks I want is for this scenario to happen under water. Sure I have my jet of water going at 40 m/s, but it's carrying a lot of surrounding water with it. I can't figure out how to get the simulation to not care about the medium fluid and to just care about the water jet.

       

      This is my test setup, a simple "nozzle" and a plate. Essentially I want a stream of water emanating from the face at the narrow end of the nozzle at 40 m/s directed at the plate. I then measure the force on the plate.

      CFD setup.png

      This is what I'm able to get. Notice the streamlines emanating from the far left, in addition to the ones given by the nozzle (hard to see but they're there at the correct speed).

      CFD problem.png

      I do not want there to be fluid anywhere else but the jet, or air if a medium is required. Any help? I am using SolidWorks 2015.

        • Re: How to create a simulation of a water jet hitting an object
          Angelo De Dominicis

          Hello

           

          Solving such a problem with SWFS could be done only if you're prepared to do a workaround and some assumptions. On paper, it is not supported since Flow Simulation can't handle multiphase flows, being the jet stream the liquid phase and surrounding air the gaseous one.

           

          Take this with a grain of salt, though: If you model the problem with a wall boundary around the stream, and prescribe a "sliding condition" on it, it could resemble the real thing rather well. This boundary should be modelled with certain degree of outward draft, just enough to minimize pressure readings on walls since the real thing is not radially constrained.

           

          The thing is, a real jet stream does not cross the distance towards the vane undisturbed. Friction with surrounding still air slows down its outer layers creating a velocity profile which is not quite constant from jet axis.

           

          Vane forces on Pelton´s depend almost entirely on fluid momentum changes so i think this could sort of work. Test it and show us how it went.

           

          Regards.

          Angelo

          • Re: How to create a simulation of a water jet hitting an object
            David Paulson

            Graham,

             

            If all you are looking for is the force on a Pelton turbine bucket a manuall calculation miohgt be the best place to start, if only to have a good estimate of the magnitude of the force.  When modeling with Flow,  start with a simplistic model that cannot fail so that you do not get too tied up with two phase flow which the solver cannot resolve.  In other words,  you may not be able to directly model a condition that involves two phase flow, but the proportion of the phase distributioon may not be significant (?). 

             

            Just start with a simple model and then increase the complexity until the "wheels fall off".  Simplify the model to make the analysis work, and thenadd the complexity until the program no longer can provide a reasonable result.