I am an amateur road cyclist working on improving my speed. This involves not only raw muscle power but many smart tactics as well. Over a period of time, and as a part of my discovery-based learning, I was told that drafting a cyclist can make a big difference in your speed. I had a gut feeling that this is all more of a mind game than actual science and neglected it. I thought considerable effect is only on large objects, and for a small road cycle, it may not make a big difference. However, I was wrong and I realized that it does make a difference to my speed.
Analyst by profession and heart, I decided to check myself so I jumped on one of the Simulation tools that I use, SOLIDWORKS Flow Simulation. It is a Computational Fluid Dynamic (CFD) analysis tool and can help me simulate a cyclist being subjected to a wind force to understand the magnitude of Force to which that he is subjected. I can also simulate multiple cyclists to check the effect of drafting.
I started my hunt for a good bicycle CAD model and found one through my colleague. Did not spend time on a mannequin – Lazy me! Here is an image of that model. Pretty basic but should help us understand the phenomenon.
Got this into SOLIDWORKS Flow Simulation and started off with the Wizard. Just follow through the steps in the Wizard… All settings would be default, except that we select “External Flow analysis;” fluid would be “air” and Velocity of 30 miles per hour. This is relative velocity as we consider the cycle to be a static condition and is resisting the wind.
This creates the basic setup. Now we move on to a few finer things, like simulating the moving ground and rotating wheels. All these are simulated using the Real Wall option in Flow Simulation.
Finally we create goals that are most relevant to us. There are many; however in this case, I will concentrate on the Force that comes on cyclist in this scenario.
That’s it. Trigger the solution, take a break, have a cup of coffee and here come the results.
For a single cycle, the Velocity contour plot would look like this.
The most important value that we are looking for is the Force, and it is around 2.1 lbf. This value in itself may not make much sense so let’s move on to see what happens with two cycles.
The Simulation process remains same, except that we use two cycles. Here are the result plots.
So, here we are. The force has not only decreased by a huge amount on the cyclist who is drafting, but on the leader as well. Typically at higher speeds, all objects subjected to such a wind load experience something called as Drag. When the second cyclist starts drafting, he is not only helping himself but also giving an advantage to the cyclist in the front.
In conclusion, we can see that, indeed drafting helps a lot. Obviously using a mannequin for cyclist and more details, the cycle model should give us more accurate values. This kind of Simulation can also be used for designing an aerodynamic frame and give a phenomenal advantage to the cyclist.
If you want to use Flow Simulation and simulate this phenomenon yourself, watch this detailed video showing the process.