MODELLING AND SIMULATION
Simulating the future of cycling
BY USING SIMULATION SOFTWARE, ROAD BIKE MANUFACTURERS CAN DELIVER HIGHER PERFORMANCE PRODUCTS IN LESS TIME AND AT A LOWER COST THAN PREVIOUSLY ACHIEVABLE, AS KEELY PORTWAY DISCOVERS
Tour de France winner Geraint Thomas recently returned to his home town triumphant and rightly
celebrated, but almost as much attention has been paid to the new bikes, components, clothing and other trends to have emerged during the tournament as the riders. Today’s competitive cyclist benefits from more lightweight, aerodynamic and rigid bike models – and, in a similar way, the prototyping process for manufacturers has become less of a heavy load – in terms of both time and cost – thanks to technological advances in simulation software. Looking at aerodynamics, in particular, a
recent simulation undertaken by professor Bert Blocken, from Eindhoven University of Technology in the Netherlands, alongside KU Leuven in Belgium, used some of these technological advances – including computational fluid dynamics (CFD), by Ansys; advanced supercomputers by Cray; alongside wind tunnel testing – to gain a greater understanding of the aerodynamic interactions between the 121 cyclists of a large racing group or ‘peloton’. Researchers carrying out the study used
this combination of computer simulations and wind tunnel measurements to examine two pelotons of 121 riders, where the distance between the rows differed slightly. Computer simulations amounted to three billion cells – which the university cites as a world record for a sports application – and required Cray’s American supercomputers and tens of thousands of software licenses from Ansys.
Centre stage Cyclists push air in front of them while riding, which creates an over pressure and a depression. This air resistance
26 Scientific Computing World August/September 2018
is known as the drag and, because of the aerodynamic interactions with the surrounding cyclists, the rider at the centre of the pack finds his or herself enclosed by the peloton-induced air motion.
Using the Ansys Fluent CFD software
with validated physical modelling capabilities, running on a Cray, Professor Blocken was able to accurately predict the flow pattern between each cyclist, mapping the drag experienced by all riders. ‘These results were so surprising that we also set up a wind tunnel test,’ he explained. The reason being that, compared to the drag of an isolated cyclist, the results showed that the resistance in the core of the peloton is down to five per cent that of an isolated cyclist.
This demonstrated that it is
approximately four times easier to cycle at the centre of the racing group. Whilst it was previously documented that the best position is in the core of a racing group – around row 12 to 14 – the computer models also calculated that the drag experienced by the athletes in this position is 10 to 20 times less than for an isolated cyclist. This is in contrast to the two or three times smaller that was previously believed. The results were validated using a wind tunnel test.
The future of competitive racing The results could have a real impact on competitive racing, as Blocken explained: ‘The calculation models used by race teams to determine the best time to escape are, it turns out, based on the wrong assumptions. This may explain why so few escapes succeed and why the peloton hauls in the riders that do escape. Perhaps these results will lead to more successful escapes.’ Returning to the simulation itself, Thierry
Marchal, global industry director for sports and healthcare at Ansys, agreed that there is much potential in competitive cycling using CFD and wind tunnel simulations in combination: ‘In a time when simulation is crucial to accelerate and amplify innovation for high-tech industries, the peloton project and its surprising results
illustrate that this simulation technology is truly pervasive and can make a huge difference in a popular sport, such as cycling.’ ‘At Ansys, we are developing and
generating simulation, but typically these simulations have been used in the nuclear industry, aerospace, aeronautical and automotive industries to make sure that we can travel safely. Along this line we have seen that the automotive industry and the sport automotive industry, like Formula 1, has been in the driving seat since the 1990s. ‘About 10 years ago the first one-billion
cell simulation was done for a Formula 1 car. Then, later on, Red Bull was going all numerics, gearing up on this kind of wind tunnel testing. But what about the non- motorsport application? We can use wind tunnel analysis in order to understand what’s going on, so why move into simulation? Well, wind tunnel analyses are very important, but they can be expensive, time consuming and you need to have the athlete available. So, although they are extremely important for the validation of the model, a combination of wind analysis and CFD simulation might be extremely useful.’
A winning formula The nod to Formula 1 is echoed by David Power, CTO at vScaler, which has been involved in CFD work. Power explained how the process transfers itself perfectly to non-motor sport: ‘CFD is absolutely used in cycling. It’s about how the air flows over the bike design, the stresses etc that you can see on it. You can understand where the metal is going to flex at which points and at which pressure etc. ‘The resistance that a cyclist encounters
can be greater than 80 per cent, moving the riding positions alone can cut that by 40 per cent using basic maths, but to really limit the resistance needs you to understand the airflow across the bike and the rider in detail and model the most efficient position and components. Also in competitive racing, it helps to avoid any infractions with the rules, which again is so similar to Formula 1.’ vScaler, in partnership with Boston
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