Both objects are identical exept nose area. Meaning of this is just to see how air acts around those two shapes. Enviromental settings are for both models: 20m/s air speed, surface roughness of 10um.
Force that moving air produces is shown in Newtons. Since air and its behaviour is scalable, object size is not relevant. Only magnitude of differencies rule in this study.
First, air is directional to objects Z-axis which is air direction. In this picture you are able to see pressure map of the objects. On round nose simulation high pressure area shows up in front, higher air drag is present. Sharp nose model has very moderate pressure area causing less drag. By numbers: sharp 0.5N, round 1.3N, so more than twice of force.
Next test is highly interesting. Side wind of 3m/s is present in axis Y and at the same time 20m/s air is moving in Z axis (direction of movement).
What happens now is that Z-axis directional force remains at level of 0.65N on sharp nose, and 1.6N on round nose. But when looking at the Y axis force, round nose gives a results of 0.44N and sharp gives 0.51N. Colors represent air velocity, scale is between 10 - 25 m/s.
So this tells us what was obvious, round shapes do help on sidewinds, but they cause lot of drag up front. Choosing right shapes could help to maximize efficiency in certain circumstances. This would mean that you should have shape to match every wind conditions, otherways you need to choose which parameters are most important for you, fast movement and less stability in windy conditions or, less fast but better stability. That allways leads into compromise. Whether you choose to run only 200 meters straight line in a calm weather, I'd go with the sharp one. When ride is longer say 6 hours and stability is required to match the enviromental changes, I'd go with something more round shape. Fact is that you can't have both in one packet.
hi
ReplyDeletethanks
ReplyDelete