DESIGN
Initially, the four separate turbine blades were created in SolidWorks based on the parameters displayed in Table 1.
Table 1: Blade design specifications
The chord length to achieve the desired solidity was determined using the following equation
Once the blades were completed a set of center pieces were designed to connect all three of the blades together. This center piece will slide over a rod that will act as an axis for the turbine to revolve around. The assembled version of the four designs can be viewed in Figure 1.
Figure 1: Four VAWT designs
PRINTING
There were then two rounds of test prints performed using two different printers, print material and support material. These prints are described in the following table.
Table 2: Description of two test prints
The Ultimaker was used to print a total of 6 parts (Figure 2) and the Statasys F370 was used to print three (Figure 3).
Figure 2: Parts printed with Ultimaker 3
Figure 3: Parts printed with Statasys F370
There were several visible differences between the two printing methods. When comparing the larger strait blades, it was seen that the blade printed with the Statasys F370 better maintained its airfoil cross-sectional shape.
Figure 4: A comparison of the two rounds of printing in ABS (left) and PLA (left)
There was also considerable amount of warpage along the edge of the PLA parts, which were not seen on the ABS parts.
Figure 5: Warpage on PLA (top) part compared to ABS (bottom)
This was an unexpected result because it was previously deteremined that PLA would be used because it was less likely to warp when compared to ABS. This was perhaps because of the orientation at which the part was printed or possibly the heat and airflow settings of the Ultimaker itself.
The top surface finish of the ABS was systematically rough due to the 3 times higher layer thickness. As for the PLA parts, the side that was facing up felt smooth to the touch. The bottom side however, from which the support material was removed, turned out chaotically rough. The support material used by the Statasys F370 was QRS which was dissolved off of the parts, removing the risk of ruining the surface finish. Due to the small over all thickness of the parts, this surface roughness had a large affect on the over cross-section of the PLA blades, as well. The effect of this and warpage was again noticeable in the smaller strait blades that were printed in PLA.
Figure 6: Effect of warpage and surface roughness on cross-section of VAWT blades
Lastly, when printing the smaller helical blades, the Statasys F370 was used because, due to the curvature and very small thickness, it was determined that attempting to physically remove the support structure would result in breaking the part. Ultimately, the print was successful, but the larger layer thickness and curved shape caused the part to have somewhat jagged edges.
Figure 7: Rough edges due to layer thickness and curvature of the smaller helical blades
UP NEXT
From these two rounds of printing it was determined that it would be possible to print all of the parts designed using the Statasys F370 with some adjustments to the resolution settings. However, it is preferred that adjustments be made to the designs and print process to make the Ultimaker 3’s prints successful. Some adjustment considerations include increase the minimum chord length of the blades to increase part thicknesses and re-arranging the printing orientation of the blades. Additionally, some changes to the printing setting will be explored to hopefully better maintain the desired cross-sectional shape of the blades.