A bit of a preface:
I’m a dabbling ultracyclist and, ahem, ‘bicycle inventor’, not an engineer per se, so I could use some sanity checks.
I’m desining a fully faired ‘utilitatrian’ recumbent bicycle - not for setting records, but for ultracycling events (200+ km, and I really want to attend 1200km PBP next year) and just having fun.
I have very severe size constraints however - it must fit into a cargo elevator 2200mm by 1400mm with about 1m wide door, so a velomobile is out of a question and simply slapping together an airofoil shape to fit my (considerable, unfortunately) girth is not an option as well, and making a very blunt nose and severely cammed tail negate much of streamlining benefits, so I need to get creative
I’ve read in an article on bicycle aerodynamcs that channeling air from high-pressure zone to low-pressure zones by a hose should result in a net benefit… so theoretically. making ‘scoop’ in front of the bike fairing, running the air thought a frame tube (2" id) and dumping it out into separation zone in cammed tail should result in less of an aero penalty. (This concept is also used in ‘boundary air blowing’, where such air channeling into a zone of separation in an airfoil is supposed to eliminate it entirely).
I’ve also read that about an experiment in aero tube with a hole in a sphere center that resulted in half the drag… unfortunately, there were no concerete numbers or even desription of exprimental conditions (Hole size? Re?)
So, I’ve tried getting my fairing model and running a tube throught it:
I’ve made a few experiments varying size of scoop, ‘exahaust’, center pipe width… got slightly MORE drag in all cases compared to a simple kamm tail :(.
I’ve tried to replicate a ‘sphere with a hole’ setup and indeed got a bit less drag, but much less than halfing it!
So, what gives? I don’t want to waste my efforts to make my bicycle slower, but I’m not sure that using ‘default settings’ is an optiomal way to solve that case, yet I have no idea where even to begin to start changing the conditions.
Can anyone provide some pointers?