Hockey Puck Aerodynamics
This blog has been in the works for about a year. I think it was worth the wait. Let me explain, as a number of things were at play here. First, I had just attended a Siemens NX CAD system training in advance of our release of FloEFD for NX last year. So I was looking for an application I could cut my teeth on for my first FloEFD for NX analysis. Something with CAD requirements that were simple enough that I could create with my beginner NX CAD skills. Also, I had just done a presentation at PTC world on CFD in sports, basically going over some of our customers FloEFD analysis on their sporting equipment, like this company that analyzed their sail boats http://www.mentor.com/products/mechanical/success/wb-sails .
Now with this being one year ago, it was in the heart of hockey playoff season, and my team, the San Jose Sharks were battling with Vancouver in the conference finals for a spot in the Stanley cup. So I was struggling to figure out something related to hockey that I could do a CFD analysis on. Then one night I was throwing around the football, and remembered some show about the history of football and how the football was originally pretty round, but over time became enlongated to allow for accurate forward passes. Basically the shape of the football was determined by its aerodynamics. That made me think about hockey pucks. Hockey pucks can reach speeds of 110 mph on the fastest slap shots. The shape of the puck though has stayed constant for 100 years I bet. It’s flat surfaces are needed to keep the puck flat on the ice and not bounce during passes, but no thought has been given to it’s aerodynamics.
So I had my idea, to analyze the hockey puck. But then, the sharks lost in the conference finals, and really, I didn’t want to think about hockey after that heartbreaking defeat. It was my plan to wait till the San Jose Sharks made it to the cup this year for this blog, but unfortunately they lost in the first round to St Louis. Not wanting to wait another year, I decided to finish this off now.
My specific focus on this analysis was the grip pattern around the puck. I’m guessing it helps with keeping the puck on the stick, but what is the consequence on the drag on the puck? I mean, hockey players switched in droves to the composite hockey sticks for the better performance on their shots, so why wouldn’t the NHL be interested in better puck performance. Now, I found a NX CAD part where someone had made a knurled pattern on a shaft. I simply swished the shaft down to the dimensions of a puck, and adjusted the knurl pattern to the spacing on a puck. Now, as a Canadian, I have a hockey puck on my desk at all times, so I did see that the grip pattern is a bit different then the knurling pattern, in that knurling is cutting the cross hatching into the object, where the puck has the cross hatch pattern raised. My CAD skills were beginner, so I went with what I had.
Below are some images and animations of the results for the knurled hockey puck at 100 mph. I utilized FloEFD’s solution adaptive mesh, as I figured the drag results would be very sensitive to accurately capturing the low speed wake. You can see the mesh in the one image, and how the mesh flows the wake downstream. The main thing I wanted was the drag, which I found to be 1.18 N. Very small amount of force.
Then I analyzed with no knurling/smooth sides, to see whether the knurling is like the dimpling on a golf ball, helping the boundary layer reattach sooner and reduce the drag on the ball. Below are some images of the results. For the most part the results seem the same. You can see the wake though seems more a-symmetric (lower speed on one side). This indicates that now there is a oscillation in the shed vortex so this lower speed air would move back and forth. As this analysis was run steady state, this is just a snapshot in time, so the low speed area happened to be on that side when the analysis stopped. The isosurface to me, seems to be smaller (not as wide and tapers more downstream compared to previously), an indication of less drag. And sure enough, FloEFD says the drag is 0.9 N, again a small amount, but a full 23.7% improvement!
Now, to be a true aerodynamic characterization, I would need to solve at different angles of attack, and I’m not sure what kind of spin a hockey player imparts on his shot, but I’m sure that would influence the results. Still, I hope this opens the NHL’s eyes to looking into the important aspects aerodynamics play in their sport. 23.7% faster shots would make it harder on goalies and increase scoring, which is always a good thing.