Adolf Hamster
Supporters
- Feb 1, 2018
- 7,057
- 2,229
ok so bit of an update to this
due to the boredom of lockdown figured i'd have a crack at seeing if the drag crisis has any significant effect on our bb's and as far as i can tell the answer seems to be no.
in the chart above the drag crisis starts around Re<10^5.
for a sphere moving in air Re is given as Re=pvd/u (there's meant to be greek symbols of rho and mu but i cba typing them out properly)
where p=the density of air (~1.225kg/m³), v is the velocity of the fluid (or very loosely approximated the velocity of the bb in m/s), d is the characteristic length (again loosely approximated to 6mm) and u is the viscousity of air (~18.5*10^-6 Pas)
so if you run the numbers for an 0.2g bb at 2.5j you get Re=62818 which is well below the transition point.
in fact you need to be over 6j before you get to the region where the the drag crisis starts to become an effect of note.
of course this is very approximate, and as with all calculation based approaches it's entirely possible i done goofed.
due to the boredom of lockdown figured i'd have a crack at seeing if the drag crisis has any significant effect on our bb's and as far as i can tell the answer seems to be no.
in the chart above the drag crisis starts around Re<10^5.
for a sphere moving in air Re is given as Re=pvd/u (there's meant to be greek symbols of rho and mu but i cba typing them out properly)
where p=the density of air (~1.225kg/m³), v is the velocity of the fluid (or very loosely approximated the velocity of the bb in m/s), d is the characteristic length (again loosely approximated to 6mm) and u is the viscousity of air (~18.5*10^-6 Pas)
so if you run the numbers for an 0.2g bb at 2.5j you get Re=62818 which is well below the transition point.
in fact you need to be over 6j before you get to the region where the the drag crisis starts to become an effect of note.
of course this is very approximate, and as with all calculation based approaches it's entirely possible i done goofed.
Last edited by a moderator:
