Wind Tunnel vs. CFD

So after getting a prototype made up we finally made it to the wind tunnel yesterday up in Charlotte. The A2 wind tunnel is a bit of a commercial wind tunnel, renting out wind tunnel on a time basis. If you read any cycling publications you’ve seen its fans as backdrop for any number of “Aero” tests. It was a really nice facility. It was an open circuit wind tunnel that was sized almost perfectly for bicycles (although maybe a bit small for cars). It was a really professional facility.

We ran our prototype vs a few of the top aero wheels currently in the US with VERY good results, but we can still use a little refinement.

A2 Wind Tunnel, Aero Rim Prototype

Our Uber Lightweight Prototype Rim in the Wind Tunnel

On the way back from the wind tunnel I had some good car time to think about why my CFD was missing some important things that we were seeing in the model. That’s when I stopped at a bike shop and happened to start talking to a bike builder and we got on the topic of CFD and wind tunnels. I mentioned that we did CFD analysis on a bunch of rim designs before heading to the wind tunnel with a prototype, he looked at me incredulously that we would even consider wasting our time at a wind tunnel when we could just model everything in CFD.

I just about threw a chair at him.

Yes computers now are very powerful, and a lot of CFD out there is VERY good at approximating scenarios. But, CFD will never replace a good wind tunnel test, ESPECIALLY with something like bicycle components. There are a few reasons for this.

First of all is Reynolds number similarity in the wind tunnel, which basically means matching accurately simulating flow phenomenon in a wind tunnel. Essentially you want your Reynolds Number and Mach number to be similar between your model in the wind tunnel and real life. For aircraft and rockets, this is very difficult. You cannot put a 1/50 scale aircraft in a wind tunnel and run it at flight speed, that would reduce your Reynolds number by a factor of 50 relative to real world, changing all the flow phenomenon. Your alternative is to increase airspeed by 50 times, this obviously is very difficult to physically do for any flight type air speed, but it will also entirely change the mach regime your model is in, rendering your model useless. Bicycles on the other hand are VERY easy to put in a wind tunnel. You can put full sized models in a relatively small tunnel, then run them at real world air speeds, giving  you essentially real world drag results.

Second is that fluid flow, specifically turbulence is INCREDIBLY complex:

“I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic” – Horice Lamb (1932) British applied Mathematician

 

“Perhaps the biggest fallacy about turbulence is that it can be reliably described (statistically) by a system of equations which is far easier to solve than the full time-dependent three-dimensional Navier-Stokes equation”  – Peter Bradshaw Professor of Engineering @ Standford University

It might seem that bicycles, traveling at a relatively low speed of 20-30 mph are simple things, but the fact of the matter is that there are a ton of very complex things going on in the bike system. Take spokes for instance. They are not simply wires traveling through air, they are rotating, and they are small relative to the rest of the system. This means that they create entirely different types of flows than the rim. There’s also the interface of the rotating wheel and the fork, the stationary ground. Don’t even start on the body of the cyclist (which accounts for 80-90% of all drag anyways).

The solution to this is approximation. In every field of complex engineering we try to break up the model in to manageable parts, then figure out the interactions between these parts. Currently I’m modeling the rim shapes in a 2 dimensional domain. This has some very obvious shortfalls, but to run an accurate model of a 3D rotating wheel (just the front), is beyond the computational power that I, and probably most bike companies, have on hand. It is a light model that allows us to run through a relatively large design space with essentially a souped up gaming computer. That’s one of the reasons why we go to the wind tunnel in the first place, to refine the CFD. Yesterday I found out that my model was predicting the performance of some of the wheels incorrectly, and now that I have other data to reference the CFD against, I can refine the model.

There’s nothing wrong with approximation, it is how design is done. However if you forget that the model within your computer is just a model, you will make missteps or worse. CFD a.k.a Cleverly Forged Data, Colorful Figure Delivery, etc is great for marketing, it shows that you have made the steps to improve your product methodically. However it is very easily altered to suit your needs, I can make a CFD model show that our product is better than brand X easily with the right assumptions and models. You will never have a fully realized fluid model of a bike or any other complex design, in sports or aerospace. In order to close the gap between the simplified CFD world we work in and the real time gains on the road, the wind tunnel will never be replaced.

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Quebec Update

It’s been a few important races since I’ve updated: US Pro, Philly, and the first stage of GP Saguenay.

Pro Nationals wen’t a little worse than expected. Going into it I felt like I was just getting over some allergies or a cold or something, but felt alright at the race start. However as the race wore on and the strange tactics of the day played out I felt progressively worse. A large group got away in literally the first 2 km of the race and got a 6 minute lead in about 6 minutes. The group rode fairly easy, except for the climb, when Garmin blew all their riders setting pace for no one up the climb, then sitting up on the flats again (no idea what this tactic accomplished except disrupting any chase). I made it 3 big laps of the race, which is about the same as last year, however since I felt great last year I’ll call it progress.

Philly was an awesome race, and has the biggest spectator fanfare of nearly any race out there. I was tasked with following early stuff in hopes of a breakaway, but was a little too active and missed the actualbreak some 3 laps in. Fortunately Clay jumped across to it. I was feeling ok but a little blown on the last lap when Brecht got a flat on the final downhill of the race and I had to give him my wheel. There was no hope of chasing back on so I pedaled in pretty easy, having at least 3 beers between Lemon Hill and the Manayunk Wall.LemonHillPhilly

After that it was a flight up to Quebec City and then transfer to Saguenay for the GP Saguenay a UCI 2.2 race. We spent a few days in Quebec City….which is friggin awesome btw.

GP Saggy is a bunch of circuit road races with one crit thrown in. Yesterday was the first RR 11 laps around the town of La Baie. The race started right up the climb, which peaked out at 20%. The first time over I got into a group of 38 riders with Stephen and Matt. It was a little too big of a group and a few too many people just sitting on, and we were brought back by lap 3.

The counter attack over the climb stayed away for a few more laps, but got back with 3 laps to go. Nothing serious got away after that. The 3 of us that were left got it lined up pretty good with 3km to go but we got pinched and separated.photo 1 photo 5

Today’s more  of the same, 21 km laps, about 177km total on tap for today.

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Wilmington Grand Prix

It’s been a little while since I’ve had a post. Speedweek was a whirlwind of racing with our team coming into the second step on the podium (I also genuinely felt shitty most of speedweek due to allergies or a cold or something that did not allow be to breath without turning on a faucet of phlegm).

Astellas Cycling Speedweek

2nd Overall Team at Speedweek 2014

This past weekend was the NCC Teir 1 race: the Wilmington Grand Prix. I had never done the race and never been to Delaware. Katie and I hitched a ride up with Thomas up the Thursday before in hopes of doing the Monkey Hill Time Trial: an 8 minute TT that had a cobbled finishing climb. It sounded awesome, but heavy storms cancelled the race. It was just as well since our 5 our second part of the drive took 8 hours, barely giving us enough time to do our pre-race openers in Wilmington.

This was my first time at Wilmington and it definitely won’t be my last, this was my kind of course: 8 technical corners and two hills per lap really sifted the race out. We only had 4 guys there, Thomas, Brandon, Michael Pincus, and myself. Brandon just won the Collegiate Nationals D1 Crit and Thomas and I were both fresh off Speedweek so we felt pretty good about just being a reduced squad.

I got a call-up for being awesome, which helped out a lot due to the technical nature of the course. It wasn’t a long race so aggression started early. Pincus got into an early split that was brought back after a few laps. There was a counter with 2 riders that dangled for a few laps. I attacked across to the two along with another rider. Eventually our group swelled to 10+ riders including UHC and our meager gap suddenly exploded to 30 seconds. One of the UHC guys dropped back to I guess help chase our group of now 10 back, leaving Brad White to just sit on the back of the group.

Our group was working not great but well enough together that UHC was unable to chase us down. Their efforts were further hampered by their chase train crashing in corner 1 with 8 laps to go.

I was feeling pretty good and thought the group could split, I countered some of Bobby Lea’s attacks but things were brought back (Guys….LET THE UHC dude chase people back, CMON!!!!). Anyway we went into the last lap as a single group and were diddling around to the point where the field was bearing down on us.

On the back side of the course Champ Sys were the only team to lead out since they were the only team with 2 riders. The back side of the course was a gradual downhill leading into the second to last corner (which had a car sized pothole), then lots of traffic furniture, before a brick laden final corner to a long long uphill drag to the finish.

I did a decent job jockeying into the 2nd to last corner but got a little pinched by the Champ Sys lead-out guy swinging off. I got around him before the corner, but the gap had already opened. I dodged some traffic furniture and opened up my sprint. While I have a decent sprint that can bean non-sprinters, my sprint is not enough to beat many real sprinters. The order coming out of the last corner did not change. I kept the same 5 meter gap from Bobby Lea’s rear wheel all the way to the finish line for 4th, a decent result, but no podium.

My consolation prize was getting drug tested by USADA right after the finish. I’d never gotten tested before and it was a fairly interesting experience. I chugged about 8 bottles of water to the point of getting light headed in order to pea. In the end it took me an hour and a half to pee in front of USADA officials and finally head off (they were really super nice, if only those waters were beer!).

After Wilmington the girlfriend and I met up with my old Purdue roommate Dave and headed up to his place in Philly, which was at the top of the Manyunk Wall (Oh em Gee, Philly). Manyunk is a huge bar district so we had to um…scout things out that night:

The next day Dave and I rode parts of the Philly Classic course, I was pretty much just losing my shit the entire time (every time we’d get on Kelly Drive, I’d get on my super deep announcer voice: “Back on Kelly Drive”).

After that it was MegaBus up to NYC to visit my Bro and Parents, my

Best Race Flyer Ever

Best Race Flyer Ever

Bro’s graduating from Columbia’s Journalisim school with a Masters degree. We missed mos to the ceremony for work and what not but it was cool to hang around NYC and see the family.

Litterally the only existing picture of me in the race

My recovery day Monday consisted of renting CitiBikes and doing a lap around Central Park before the 30 minute time limit ran out (we failed miserably).meandtheGF

The Brains and The Brawn

The Brains and The Brawn

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Winston Salem Classic Recap

It was a big weekend of racing this past weekend up in Winston Salem NC. On tap were a repeat of last years Winston Salem classic kicked up a notch. In it’s first year of the event, our Smart Stop team got pretty dusted in the crit, but Dan Patten and I went 1-2 in the Road Race.

However this year the Crit was bumped up to NCC/USA Crits and the Road Race was elevated to international status as a UCI 1.2 race in addition to being NRC. This meant that all the Pro teams were going to be in attendance.

Friday kicked off with a road race following the same course as the previous year’s. However last years race only completed 12 laps of the brutal 7.2 mile course (with only 9 finishers out of 150+ starters), this years edition did 15.

You can watch the entire thing here, but to get a jist of things the race was full gas for the first 2 hours. Astellas was well represented in nearly every move. Only after 2 hours of continuous attacking did a breakaway get off the front. Luckily Matt Green was in there for us and gave us a chance to take a break.

A few laps later, everyone had apparently rested up enough and the group really started splitting on the difficult Pilot View climb. I had just followed some small attacks and was gassed when the group went up the road (poor tactical choice on my part). Fortunately Brecht got up into the lead group going over the top of the climb. The large group had all the teams represented and the remaining field became groupetto. Matt dropped back after a hard day in the break and Brecht managed to hold on for 11th.

I rode off the front of the field because everyone was finished racing in the last lap and came in 24th.

The next day was the twilight crit in downtown Winston Salem.

The race last year was pretty easy to control and ride at the front…not the case this year. What would seem like a relatively open course that would be easy to move around was the course with one of the worst whip lash effects I’ve experienced all year, just watch the vide of the race:

There is literally no point in this race where the field isn’t strung out single file, I remember passing the big billboard some 100 meters after the finish line and still seeing guys coming out of the final corner nearly every lap.

With all the big teams sticking around from the UCI race the previous day, we knew it was going to be fast. I managed to get into an early move of 4 that was a little too early, we got chased down in short order.1908261_675083375861372_1995002056913752458_n Thankfully Brecht got into a move right afterwards of 3 riders that built up a 20 second advantage fairly quickly. Thomas and I spent most the rest of the race covering and killing, the rest of the team being taken out in a large crash early in the race (go to 1:58 to see nearly the entire field getting pushed back into the race), and Ryan getting taken out by a 24 hr flu bug.

I got in some bad swarms and got shuffled back when UHC started chasing. Due to the tight nature of the course (and huge downhill headwind), they had a hard time bringing things back, however the break of 3 were in the cross hairs going into 1 to go. They actually got caught at the uphill on the backside of the crouse, that’s when Brecht attacked and provided us with the biggest victory of the year:Brecht Winning Winston Salem for Astellas Cycling10245564_835115283168844_3066675718220017947_nThis is a pretty big upset for us. I’d like to say that Brecht had a lot of help from us, but he had a phenomenal ride Saturday and timed his attack perfectly. The upset of UHC is a big deal, even if the like’s of Cycling Illustrated call it “Unhearalded”

It’s time to keep the momentum rolling as our team splits up to tackle Joe Martin and SpeedWeek. I’ll be doing Athens Twilight, which is definitely a bucket list race for me.

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Del Ray Twilight Criterium

First race of the year is in the bag…with both good and weird results (watch the entire replay below!!).

The USA Crits season kicked off this past weekend in Del Ray Beach Flo-Rida. Del Ray is a super fancy bar district right on the Atlantic coast. I mean fancy as in “I’ve seen more Masaratti’s, Ferrari’s, Tesla’s, and Bentley’s in the past two days than in the rest of my life” fancy.

The Del Ray Crit itself was pretty much your standard 4 corner Crit with a very narrow alleyway between turns 3 and 4. The tricky part about this race would be the power vacuum left by UHC. Not only was it the first race of the year, but the dominating team from last year was absent due to a change in race calendars.

It was also a first real run for our Astellas Crit squad. We went into it with pretty open expectations, being the first time most of us had ridden together (except Me and Thomas). We had Hogan, Justin, Stephen, Michael, and Thomas there.

Astellas Team Photo

The race kicked off and from the gun Stephen was in a 3 man breakaway. Hogan, Stephen and Michael had first shift in covering moves so we were pretty happy we were represented. Stephen in particular had a nasty knee injury in the off season and said before the race he would only be useful in the first hour.

The break built up a half lap lead pretty quickly. Hogan and I went to the front and tried to slow things up. The break got REALLY close to lapping the field, Thomas even went to the back in anticipation of the eventual catch. However thanks to some poorly timed primes the gap fell back down to half a lap. Then Stephen got popped off the break after turning himself inside out to stick on. I was feeling probably a little too antsy and started rallying Hogan and Michael to start chasing. We brought back some time, then after some more primes the field started to split up a little bit. All this action brought the breakaway BACK to within 15 seconds…but we just never were able to close it down.

We kept trying to bring things back, but oddly enough the other big teams that weren’t represented (Champion System, Jamis and InCycle) didn’t really contribute to chasing (or riding in the field split for that matter), so the break went back up to 20 seconds and stayed away to the finish.

Thomas and Justin were riding for the sprint but had some miscommunication about shooting gaps and got separated.

Overall though I’d say it was a successful race. We raced as a team and did a great job controlling the race as much as we could. We had some obvious kinks that are fairly easily fixable. I know I  was feeling pretty nervous about my form going into the race (especially after my shoulder surgery). I definitely rode too much and should’ve both saved some legs till later in the race, and attacked a lot more instead of drilling the front. However any doubts about my legs are pretty well buried after the weekend, so next weekend will be a different story.

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