Could this "plain Jane flat cardboard" be the best design? All the professional wind tunnel designs were more elegant and looked more scientific. So I began my improvements. Not so much for velocity but for the "looks".
Since the idea is to use the standard KW wind tunnel for regular KW Challenge testing and then add on the shroud for some "serious fun" testing at higher wind speeds after the main KW challenge I needed to keep the same dimensions inside the standard KW tunnel when the radius shroud was in place. A 3/4" plywood with a 32" diameter hole was hinged to the entrance of the standard KW wind tunnel. It was hinged on one side to allow it to be swung open so teams could get inside and set their turbine for testing. 2x6 extensions were added to hold the radius portion of the design.
2X6 extensions and plywood hinged in place. You can see the turbine inside through the 32" diameter opening.
Important to note is the tight fit of the 3/4" plywood to the opening of the standard KW wind tunnel as shown here. No gaps mean fewer losses in wind speed.