3 Replies Latest reply on Oct 31, 2014 5:56 PM by Jamil Snead

    Lofting airfoil sections with twist and changing chord length

    Shane Smith

      Hello,

       

      For my senior design project my group is designing a wind turbine. I've been trying to model the turbine blades in solidworks but I've been having issues getting the loft to work without weird twists happening. I have tried guide curves, and everything I can think of, but nothing is working. I don't understand why the loft doesn't work, the shape slowly changes along the root of the blade, and I've introduced as gradual changes as I can to try to minimize stress concentrations. I'm trying to get an accurate model of my design so I can do FEA on the finished shape with loads determined by BEMT analysis, and if the testing is successful, 3-D print the blade design.

       

      I have defined airfoil curves at 19 sections of the blade, with it morphing from a circle to an ellipse, then the three different airfoils with varying twist and chord length. I have not been able to get the loft to work without it applying additional twist to the shape which would hurt the performance.

       

      Solidworks screenshot.jpg

        • Re: Lofting airfoil sections with twist and changing chord length
          Jamil Snead

          One key to a smooth loft is when you are clicking each section in order, try to click on the same part of every section so that the green dots (connectors) follow the flow of the loft. I tried it by clicking on the leading edges and the loft tuned out pretty good. You can always adjust the position of those green connectors after you have selected the profiles. Another thing you can do if part of the loft away from the green connectors is being funky is you can right click on another part of one of the profiles and select "add connector" and it will put a new series of cyan dots. Move those around to make another flow line. The connectors are sort of like guide curves. They don't control the path in between profiles but they tell the loft which parts of each profile to connect. So I made a second set of connectors to join the trailing edges, and it improved the loft even more. I didn't need to use the guide curve. Check out my example.

          blade1.PNG

          blade2.PNG

            • Re: Lofting airfoil sections with twist and changing chord length
              Shane Smith

              Ok, I had been trying that exact same thing, except I was putting the points on the trailing edge, not sure why that didn't work and the leading edge did, but thanks. I guess I was hoping for a more precise way to do a loft, since the connectors can be off by even a little and over the full shape the twist will change quite a bit. Is there a better way to do this that will be more exact, or do I just need to play with the loft until it looks okay?

               

              It seems like the loft works fine for simple shapes, but for this many profiles and the complicated shapes it is difficult to get the exact shape you want.

                • Re: Lofting airfoil sections with twist and changing chord length
                  Jamil Snead

                  One obvious thing that is more precise is to use guide curves. I am not sure why your guide curve didn't work, maybe you needed another one on the opposite edge. But sometimes guide curves are tricky because you have to know how you want the loft to go between profiles.

                   

                  Another option is to split each profile at the point where you want the connectors to be. It's easy to locate connectors on endpoints of segments.