3 Replies Latest reply on Jun 27, 2017 9:43 AM by Bill McEachern

    Utilizing Flow Simulation To Calculate RPM in a Impeller, Torque maybe? Not typical to other examples..

    Mike Tkachuk

      Hi to all the members of the SolidWorks community!

       

      I'll try to make this as short and simple as possible, as it has been taking me for a loop the past bit.

       

      Background: I am currently finishing off my last year as a Mechanical Engineer. I have an Internship and have been challenged with the task to find the RPM of an Impeller which has been designed. I have done LOTS of research on this matter, I have seen multiple propellers utilizing "External"  analysis with both "Excluded cavities without flow conditions" and "Exclude internal space" checked as well as Rotation checked and ran multiple times with different combinations of Local regions averaging/ sliding and Global Regions ran as simulations. I have also researched and tried multiple ways of Rotating Regions and Flow Trajectories when comparing to other impellers, Turbines/windmills, props, blowers, heat-exchangers, tutorials etc.... and have come up empty handed.

       

      The Problem:   When comparing to other examples such as props and Turbines. The RPM is always known, which allows you to utilize the Rotating Regions features. However I do not know the RPM as that is what I am trying to figure out. I do know fluid properties which can allow me to use the Boundary Conditions and set Goals from there. I am thinking one possibility would be to find Torque generated by the fluid acting on the impeller, and through formulas and an excel spread sheets, & further utilizing the Newtonian method, to cross reference with Solid works data and hopefully come up with a realistic numbers. I am not 100% sure of what analysis type I should be using as well ( Internal or External) or possibly motion/ fans. as I have yet to find an example that uses the fluid properties and goals to accurately depict the RPM of the object being rotated by the fluid.

       

      I do have a target RPM of 200 and an inlet and outlet pressure as well as volume flow, fluid rotating will be water.

       

      I look forward to hearing back from everyone whom maybe able to help or make any suggestions, maybe I am just over thinking/ analyzing this but I am at a standstill and thought i'd try to get some feed back!

       

      Regards

       

      Mike Tkachuk

        • Re: Utilizing Flow Simulation To Calculate RPM in a Impeller, Torque maybe? Not typical to other examples..
          Bill McEachern

          I would read and try the example problems for impellers. What kind of rotor are you trying to analyze? Is it a propeller or an impeller? Flow simulation can give a decent approximation using the rotating frame approximation for impellers and a bit of a rougher one for a propeller, at least in my experience. A propeller/axial flow turbine for me is defined as a low solidity axial flow lift actuated rotor. An impeller is a high solidity (solid) rotor that turns the flow 90° - it is not typically a lift based device (like a centrifugal pump) but people might argue that one - just to put some sort of references down. So for an impeller you can set pressures and speeds and compute torque and flow rates. On an propeller it gets a bit trickier with the advance ratio. You can typically build a momentum code for a decent approximation. PROP PC by NREL is a good one for wind turbines, that you may have access to. I don't do this sort of thing much and certainly not in awhile but you can make a momentum code with a spreadsheet. I could give you a rough outline if there is any interest (its not that difficult but the tip does present some challenges).

          In either case, with flow simulation, you set up the conditions and compute torque over a given set of rotor speeds. Your answer/estimate is lying on that line for a given set of conditions - typically you know something else that defines the actual point. Typically at some maximum where it works best is the target. A free RPM problem is not that useful typically but it is where the rotational drag is equal to the torque.

            • Re: Utilizing Flow Simulation To Calculate RPM in a Impeller, Torque maybe? Not typical to other examples..
              Mike Tkachuk

              Mr. McEachern

               

              I would first like to thank you for your time and response, I have done 1 impeller tutorial (is there any others) and I modeled a propeller and did multiple "tutorials" off YouTube, to further gain an understanding/ practice on the flow simulator.

               

              The design is for an Impeller, as it will be contained within a casing/housing system. My intentions was to utilize the radial flow of the fluid (water) induced by the vanes to to make a 360 degree "jet stream" circumferentially & perpendicular to the hosing & impeller. 

              I would greatly appreciate any and all reference materially you could provide me, such as a spread sheet, I will message you privately with email address.

               

              I have attached some photos of the design, I have designed such part that the "Outlet" can be adjusted (shorter/longer) as needed, the reasoning is that I could utilize the interrupted flow by lengthening or shortening to control the velocity, Low speed= High Torque mentality, and further adjust such length to produce 200 RPM in order to produce desired Turbulence and Cavitation properties. Knowing fluid properties, such as volume flow, pressures, density, dynamic viscosity etc.. with respect to  response 'for an impeller you can set pressures and speeds and compute torque and flow rate' would your study be a Transient analysis or Static? From what I understand/ researched, if you wanted to calculate the true RPM of the impeller (or any object) it needs to be Transient, as SolidWorks calculates everything based on the "impeller" being rotated as compared to Static, were the fluid is being rotated around the impeller.

               

              I have attached some photos to further illustrate what I have going on. keeping in mind that this is just the impeller, does not include the housing/casing where it will be seated. All photos have same Inlet and Outlet Locations. I look forward to hearing back from you and thank you once again for your time and advice!

               

              Regards

               

              Mike Tkachuk

               

              IMP-Design 1.GIF

              Description/Legend of Design 1

               

               

               

              IMP-Design 1.2.GIF

              Design 1, Body Transparent, Lids on

               

               

               

              IMP-Flow Channels.GIF

              Design 1,Body hidden, Channels where fluid flow will occur, Orange highlight is the outermost surface where the fluid will be in conntact

               

              IMP- Design 2.GIF

              Design 2,

               

               

              IMP-3.GIF

              Design 3,