Wheel Design How-To Part 3

Detailed CFD procedures

Going to go over some details in setting up our computer model for running simulations.

As requested in a previous comment here is the Bontrager white paper that provided some resource in our initial research phase of development.

Mesh Definition

The initial 3D mesh was fraught with convergence and generation issues:InitialQuadMesh

Instead we decided to use a Polyhedral mesh type for simulation. The main concerns were limited computational resources and ease/automation with which we could mesh the components. Polyhedral meshes have a few advantages over more traditional Hex and Tet mesh procedures. Mainly in a comparison of element count and time to convergence is much improved with a poly mesh. This is a result of poly meshes having a higher number of interfaces with other elements per element, thus making the mesh more efficient and robust in resolving to a solution. 

This allowed us to create a script to run several flow cases in sequence for different angles, each of which required a new mesh to be created.

Turbulence Modeling

Given limited time frame and computational resources the run was done as a steady state simulation. It was found by Defraeye that a RANS k-w model provided the most accurate results for a cyclist in a wind tunnel without using a more computationally expensive turbulence model.

Wheel Boundary Layer Mesh

Wheel Boundary Layer Mesh

Overall Wheel Mesh

Overall Wheel Mesh

Boundary Layer Thickness

A boundary layer height of 5 mm was used for wheel

Boundary Layer Thickness estimation

Boundary Layer Thickness estimation

 

Where x is set as depth of rim to obtain a rough general estimation of propagation length (without having to spend excessive time creating BL mesh areas). This 5mm thickness was applied as a 10 element thick BL mesh (expansion ratio set to 1.2).

Speed Selection

CFD domain run speeds were set at 30 mph (13.4 m/s). This was chosen to provide some spread between wheelsets. Reynolds numbers for bicycle wheels range from 11,000-650,000 (20mm rim @ 20mph and Full Disc at 30mph). This is sufficiently high to place wheel aerodynamics in the fully developed turbulent region of air flow (i.e. Re>4000). This means that flow structures remain relatively constant throughout interested flow speeds and Drag will scale directly with a square relation to velocity. It was found at low speeds drag differences between manufacturers only vary slightly, meaning experimental or computational error would make it difficult to determine which wheel design is in fact better. A higher wind speed amplifies This further lent itself to our design theory of creating a wheel based on multiple factors instead of just Aero Performance.

Wheel rotation

Many existing CFD studies neglect rotational effects of the wheel. It is computationally easier to solve for a stationary solution. While we don’t have a lot of computational power on hand, we still achieve rotational modeling by eliminating our spokes. This allows us to set the wheel boundary surfaces with a rotation condition. Eliminating spokes is a safe assumption since their requirement is largely dependent on structural and governing body concerns. Additionally eliminating them will not greatly affect the drag results of a particular rim design. 

Disc Wheel Streamlines

Disc Wheel Streamlines

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Downhill Time Trials

So last week I went to InterBike with Boyd Cycling. It was a pretty cool experience, really a thing I always see on all the bike tech sites out there but finally going there is a totally different experience. First of all, the coverage that all the online venues covering the event combined don’t even begin to scratch the surface of the number of exhibits there. It’s pretty overwhelming. For instance there are foreign sections, China, Japan, Italian “villages” that essentially get no media coverage. There was a HUGE e-bike section of the show as well (which also seemed to be the best funded). However the best section, in my opinion, was the “Urban” village. This encapsulated everything from custom cruisers, fixies, to folding bikes. By far these were the most creative and off the wall exhibits and products.

Our booth was tucked into the “Triathlon” section…..yeah yeah. I spent most of my time hand modeling for BikeRadar in the booth:Boyd Eternity Hub
Tubeless Nut

Hand ModelAnd also showing off our one gimmick:

Boyd Cycling Wheelset

Climber’s Wheelset

Yes the most entertaining part of the show for me was to tell people to go pick up our “Climbing Wheelset”. Weighing in at 15 lbs, this thing could serve as a flywheel for an old school steam tractor. There’s a lot of hype around 3D printing right now and a lot of questions were fielded at the show about why we didn’t go that route. The reason is two fold: 3D printing is finite and not continuous. This means that the finish for a curved surface would be stepped surface which would require further finishing (another possibility for imperfections). Additionally 3D printing is typically done with plastics which do not carry high loads well (think spoke tensions and tire pressure).

Why does all that matter? The Aerodynamics of bicycle wheels is converging onto a single (correct, sorry reynolds) design. This means that the variation between the best aerodynamic wheel-sets are getting smaller and smaller. Aerodynamics is VERY sensitive to small variations. Something like 20 psi vs 100 psi in a road tire or low tension (bent) spokes could also greatly alter aerodynamic drag results. So by doing a solid Aluminum wheelset in the wind tunnel we could model a REAL wheel.

Why go through all this trouble anyway? If you see a wheel company showing their slick carbon wheel in the wind tunnel, it means they’re testing a finished product (cough #AeroIsEverything cough). It’s well known carbon molds are very expensive, and if you’ve made the mold, you’re pretty much married to the shape you created, so you’re either wasting money and translating that stupidity to high costs to your customer, or you’re just going with a bad design. This prototyping allows us to make small design changes or evaluate several design at a relatively low cost before making the costly investment in a mold.

Mistakes are how you learn, so it’s better to make i

Bike Wheel Wind Tunnel Testing

Aluminum Prototype in A2 Wind Tunnel

nexpensive small ones than expensive big ones.

Also see my other post (excessive rant) on why Wind Tunnels are absolutely necessary.

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I am done with power meters

I’m done. Power meters suck. Firstly, they dysfunction and break faster than any other product that charges a $2k+ premium aught to. Second they suck the soul out of cycling, just ask Froome dog:

Frooming

Does he look happy? No. An the fact of the matter is that no one’s happy watching their power numbers because they’re always too low. That’s the whole reason you’re looking at your power numbers in the first place: to get better numbers (or to brag about how many watts you did or didn’t put out). It’s all about Marginal Gains, #AeroisEverything, not having any fun, and whatever else it takes to get an edge.

I’m not that type of person. Sure having a power meter taught me a lot about what it really means to do a constant effort. But in all honesty, the only time I genuinely use my power meter now is the handful of times during the year I do intervals (I don’t do intervals), other than that they’re just numbers to tell you you’re going too hard.

I just don’t care enough, I enjoy beers and Krispy Kreme. I always knew that I didn’t want to be a pro cyclist forever, I didn’t want to end up 30 and realize my life was dependent on racing kids for a few hundred bucks (at best). That’s why I applied to grad school, I told my team that I was thinking of going back to grad school and unfortunately that’s why I didn’t get on a team.

I’m super bummed I didn’t get a contract for next year. I applied to grad schools for Engineering for the winter semester, it was sort of a long shot with not a lot of spots available…and I didn’t get in anywhere. Then just as I was wrapping up talking to schools finding out why I didn’t get in I found out that I didn’t get a contract because the possible scheduling conflicts from grad schools. #FirstWorldProblems

I love cycling, I tried to not care one year (I even had a full time big boy job) and I had my best season to date and got a pro contract from that year. Because cycling my passion I think that’s why it’s never really sat well being my job. You’re not really adding any value to anything or anyone’s lives (sponsorship struggles to make sense via dollars), it’s important to admit to yourself you’re a pro cyclist because you’re selfish.

We had long talks in Belgium about what’s the point of all this. Pipe dream for us older folks is to make it to DII teams like UHC. What does that mean? More travel, more obscure races, slightly more money…then if I’m successful there, what next? Getting to be the C team for a DI team? It doesn’t end, so I’m glad the choice was made out of my control because I’m not sure I could have made that choice myself. Fact of the matter is you’re fighting a big uphill battle if you didn’t get into the system when you were a junior. I’m a late entry and I’m done fighting that uphill battle, I’m done having to put the rest of my life on hold for a few bucks and a title that a lot of Cat 1 and some cat 2 riders misuse anyway (and even that doesn’t matter, because to an outside observer, you’re making money therefore you’re a professional).

So now I’m back to a clean slate with literally no commitments for next year or even next month.

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Belgium Part 1

We’ve now been in Belgium over 2 weeks and have done 4 races.  We flew in a day before our first Pro Kermesse, got promptly lost on our first day riding around Aarchot. We lined up in downtown Buggenhout (don’t worry none of the town names make any sense) still very much jet lagged not knowing what to expect. Giddy with excitement and nerves my heart rate was pegged at 160 just sitting on the start line from adrenaline. I’m not sure if it was the jet lag, the different riding style, course itself or combination of everything, but I only made it 60 of the 100 miles.

It was a little disheartening to only make it halfway through the first race here in Belgium but I reserved judgement knowing that a continental flight the day before at least had SOME factor to do with it. The next race on the docket was the UCI 1.2 Havenpijl Antwerpen race. But that was nearly a week after our first race, so we had some time to overcome the Jet Lag and get acclimated to the country.

Matt Green took us on our first legitimate ride around the Belgian countryside without getting lost. My first reaction was how crazy the riding is here. There’s no Froome-ing it riding around here in Belgium, if you put your head down for a second you’ll catch a gutter, hit a car, slide out on cow turds, you name it. There’s almost no steady riding, you’re continuously turning and hopping curbs (just on a ride!); a ride around here is more like an alley cat race.

I did my first big solo ride a few days later and decided to get really lost and figure my way back home eventually. To my suprise it’s really easy to get around here. The trick is this: If you have particular roads or a route you want to ride, you WILL get lost, but if you just head in a general direction you’ll be fine. There are no dead ends in the Belgian road system, ever road leads to Rome, or um Aarschot. Also there are literally bike routes every where you go. This not only includes paths along canals and rail-trails, but touring routes. All you have to do it pick up a numbered sign that are usually zip tied to traffic signs and follow a given route.Pave IMG_3233

Back to Havenpijl Antwerpen, our second race. By that point we had started to get the hang of cleaning our bikes and washing our shoes every day (it rains a lot). The 170km race did two large 50km circuits then a bunch of small 17km circuits. There was also a large storm that was the remnant of a hurricane that almost hit America, decided to head East instead, and rain on our race. This meant 20mph wind and torrential rain. Also this was the first race with cobbles! I know I was nervous at the start, I had pictures of Roubaix and Flanders in my head, with pave splitting the field. We rolled out got to the first cobbled section and things, um, slowed down. I thought, whatever, it’s early in the race, not a decisive moment. The decisive moment, it turned out, was to happen 20 km later because of….corners. Running into the last 2km there were 6 corners on some very tame brick roads, however it had started raining. I was probably in the top 50 guys (not bad in a field of 200), and when we hit the corners, guys were dropping wheels in the corner like it was their job, the Belgians were bad at cornering.

I’m not sure where the difference came from, maybe it’s that in America every dude is willing to crash in every freaking corner not to drop a wheel, or the fact that they’re all running at least 120psi in their tires at all times (long story), but the Belgians were taking the wet corners very gingerly. So the field split, and the winning move of 25 got away because a guy dropped a wheel in the corners. The thing the Belgians are VERY good at is positioning, there is NO space to move around in the field, you’re always bumping guys in the field but not in a dangerous way. Because of this they don’t do the whole leaving space in front of you before a corner thing, or take a good line through a corner, they just do this:

Marching Band Turn

Since this sort of field split thing has happened to us several times, I’ll address it, we are flying totally blind in these races. I mean we know generally what teams are good and where the decisive sections SHOULD be, but it’s easy to underestimate how big a factor knowing the course and riders around you have. I mean in the US we race every weekend with the same guys, but here it’s 90 race days out of the year, and they’ve all been racing since before they could walk and know the courses inside and out. To us, ever attack is just another bunch of huge Belgian dudes going up the road.IMG_3329

The rain really started coming down after that point, we attacked and chased to try to get the break back, the field split a bunch of times, but in the end it stayed away.

Just two days later we raced a Kermesse that was formerly the world Kermesse championship (totally unofficial, I think). By this point we were actually starting to get the hang of Belgian style racing, plus the short 7km circuit was the closest thing to a crit we were probably ever going to get.

We stayed super active in the first part of the race. I eventually made it into a move of 14 some guys and we rotated through, and it was hard. We got a minute fairly quickly, then we all got Ice Bucket challenged by a 5 minute torrential freezing cold rain storm, but our gap just stayed up there at one minute. Here’s another difference: there’s apparently no sitting on in the breakaway here, you ride until you’re cross eyed and then just get dropped from the break (it’s a noble death). I was rolling through pretty good for most of the race but most the guys had a foot and 20 kilos on me and I was really starting to hurt, so I started skipping pulls. This prompted all sorts of, what I assume were Flemish curse words, hip slings, and even a poke in the butt (not on the side by the way although he may have also just thought I was cute).

Breakaway

We eventually got caught, and I noticed ANOTHER particularity of Belgian racing. In America, when you get dropped almost EVERYONE applaudes you: “Good job”, “You gave it your best”, etc. Maybe this is because cycling isn’t an American pastime, or it’s just a cultural thing. However in Belgium, when you drop out, all the old people just stair at you like this:

I couldn’t help it, I really felt embarrassed rolling around the course after getting dropped. Although it could have also been caused by the fact that at one point I had 20/6 odds on me to win at the bookies and they just lost their money…

We had a few days off before our next race so we took a couple rest days and train-ed it up to Amsterdam for a night so see the sighs, have a few beers, etc.

Amsterdam

Once back we did a little bit more training and a day trip to Brussels before our next race the UCI 1.1 Zottegem (could you imagine a UCI 1.1 race just being on a Tuesday in America??).

Zottegem was a 190km race in the Flanders region. We even did a climb from the actual Ronde. I wasn’t feeling super this race, we missed the break, chased, didn’t catch it, the usual. There were cross winds and actual climbs this time. I flatted and had the pleasure of going through the caravan…which is WAY more enjoyable than doing it in the US (more experienced caravan drives I think here).

Anyway we walked away with no results there as well, but had a good race as a team (we tried hard).

Today we’re racing the Dutch Food Valley Classic complete with not just one World Tour team but 3: Belkin, Cannondale, and Movistar, NBD.

I THINK there’s also a live stream to watch the race (although you might have to be in Belgium…no idea):

http://www.arnhemveenendaalclassic.nl/profkoers/live-stream/

Race starts at 9am EST and should finish around 2pm EST

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First Belgian Race Today

So we’ve gotten into our Belgian house here in Aarshot Friday morning. It’s a super nice house, and looks like it’s right out of an IKEA show room. We had our first legitimate ride that afternoon and promptly got VERY lost, stopping at least 10 times to check our saved maps on our phones. Belgium has the 3rd highest road density in the world. This isn’t even counting the endless network of bike paths and random goat paths. So basically there’s roads everywhere you go in every direction you could want…but none of the roads are longer than a km (only slight exaggeration). It generally makes for very confusing and and heads up riding with all the pedestrian and car traffic: think of doing an Alley Cat race on every single ride, forget the idea of zoning out in a ride.

Toe-ing up for a Pro Kermesse race today. It’s going to be 20 laps of an 8 km course.

I’ll be sure to have a good write up on the race come Monday or whatever, so in the meantime enjoy this video I finally put together from the GoPro I had at Athens Twilight, complete with sweet music track and more importantly: Audio from our self neutralization:

 

 

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