Optimize Your Blade Design
What a year it’s been! Kids are running around with boxes on their heads and writing on walls. Great White sharks are confusing us for seals at an alarming rate, and we are now storing large quantities of fertilizer in Tupperware…..oh, and did I mention a virus?
Here at TPM, it seems our engineering challenges of 2020 have been just as mind boggling as the rest of the events in the world. Take for instance, Composite Airfoil Blades. They perform one task. They move fluid molecules from point A to point B, while capturing and directing the energy along the way. As engineers, we must do this as efficiently as possible.
To calculate all the inducible factors that go into this in a single study would be maddening! AF (Axial Force), Cd (Drag), Cl (Lift), and all the other rotational forces that occur. Recall, the space shape of an airfoil is a complex three-dimensional object.
To achieve this in today’s high-performance turbine/propeller designs, we have adopted use of Blade Element & Moment Theory. This “2D” approach allows me to optimize the span wise 3D shape by dividing the blade into smaller sections, or elements along the span of the airfoil. Chord Length (C), and twist (Angle of Attack or Alpha), are in turn calculated at each element or section. This is then transposed to be used in calculating the energy efficiency coefficient for that particular element. This can be accomplished in many programs, such as matlab, etc. See below Figures 1&2: Mathematical Modeling & Explanation of Terms.
Figure 1
Figure 2
In preparation for importing this data into SOLIDWORKS, some formatting is required. Remember, we now have a bunch of discrete two-dimensional points that are present in any NACA airfoil. I will typically run these elements through a coordinate transformation to generate the “Z” or 3D discrete points locations. This is then exported through .txt file and imported into SOLIDWORKS for further refinement and analysis. See Figures 3&4: Raw Data. See Figure 5: Displacement Distribution and Figure 6: Transpose Data.
Figure 3
Figure 4
Figure 5
Figure 6
Now that the pre-processing has been accomplished, we can begin to utilize the SOLIDWORKS Simulation suite to further understand our conceptual design. For this airfoil, we were interested in capturing the pressure profile as seen on the leading edge and trailing surfaces. We went about setting up our goals and environment in SOLIDWORKS Flow. See Figure 7: Test Parameters.
Figure 7
As with any Simulation study, I would approach the results with the question “Why does this make sense?” Interrogate the surface quality, look for weak points in your meshing and be sure to understand what the colors are telling you. Many times, I will confirm results simply by looking at other types of plots. For instance, does temperature, velocity and pressure coincide with each other? In this example I have an Iso plot combined with pressure gradients. See Figure 8: SOLIDWORKS CFD.
Figure 8
As I mentioned earlier, this airfoil may work, but is it the best design? Further refinement is usually required. However, I now have a deep understanding of how the blade reacts to the air. I can now make small changes to my blade element parameters in Matlab and repeat the process. When I begin to diverge from my goals, I take a step back, and will most likely utilize the last iteration. Following this workflow can provide a quick, reliable means to designing not only a blade that works, but a shape that is extremely efficient, suitable for its environment and will last for years…unless fatigue gets you…but that’s another blog post!
In conclusion and slightly off topic, I want to give all my American manufacturing buddies a pat on the back. During an unprecedented time, manufacturing never wavered. We kept creating and building no matter what obstacle we ran into (with very little complaining). You all…. are a very impressive group of individuals indeed! Please let us know here at TPM how we can help you achieve your goals!
By: Rob Stoklosa, Technical Solutions Consultant, TPM Inc.