Fluid mechanics/ aerodynamics buoyancy and aerostatixa
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Course
Thermodynamics And Fluid Mechanics 1 (MMME1030)
Institution
The University Of Nottingham (UON)
Lecture notes based on buoyancy and aerostatics covering aerostats and aerodynes, applications, equations, gas balloons and hot air balloons, neutral buoyancy
Aerostatics refers to the static buoyancy of any body immersed in the atmosphere.. ≈ the study of
gases not in motion i gas equivalent of hydrostatics (static buoyancy of a body in waters
Aerostats
= 'Lighter-than-air' vehicles ie He. H,not air
* use buoyancy to float in the air
* Characteristics = large low density gas-filled canopy which is less dense than surrounding air
↳ lunpowered) balloon ↳ (powered) airship
Aerodynes
= heavier-than-air vehicles
* use N 3L → must push gas lair ↓ to push aircraft ↑
☆ Use lift to fly in air
↳ aerodynamic lift (generated by a wing): fixed-wing aircraft; rotorcraft
→ powered lift (in form of engine thrust): VTOL aircraft; rocket
Application of aerostats:
* Transport/recreational → Hot air balloon coldest successful human-carrying flight craft)
→ Airship (not used for transport today)
* survailance → Blimp (non-rigid airship used for surveillance a video imaging)
* weather balloon → carries instruments to transmit info
Long Endurance multi-Intelligence vehicle (LEMV) = a hybrid military airship for surveillance,
intelligence and reconnaissance support up to 20,000ft. can take off as conventional aeroplane,
uses He to remain airborne and manoeuvre whilst airborne using on-board engines
gradient =#
in absolute form, the hydrostatic equation → p=pgh where we
÷
p-pressure,p-density, g- grav acceleration, n = distance measured
☒•
vertically down from free surface. In relative form. p, =p.-pgh
where h-vertical distance between points I and 2 (as shown)
÷
""%, gradient:-#
pressure. p
Net buoyancy force = hydrostatic force-weight Pepsea-level
using relative form ↗ and letting height = H: FB = Apg H-W-pug-W where v. volume of the body
.
The buoyancy force acting on a body → FB = Vg/pair-pbody)
This equation shows:
A body will produce net up thrust due to buoyancy if p body <p of surrounding fluid
* magnitude of lift force is increased by: ↑/pair-p body/ difference
: ↑ volume of the body
contain
Gas balloons a gas of lower molecular weight than air to achieve buoyancy lie Hel.The gas is
typically at a higher pressure than the surrounding air but at the same temp. net buoyancy force
is same eq as for solid body (different process 1. in practice, p of gas in and outside balloon
changes with height but the eq is only valid for the opposite (however, the as are small and
have negligible effect compared to pressure so doesn't really matters
Buoyancy is independant of balloon pressure but from e.Os: She = 1¥ } ⇒"↑↑dePnressisty"r⇒e↓inbsuidoeyancy
with hot air balloons, ↑ temp of fluid inside balloon ⇒ ↓ density of that fluid)
Hydrostatic
FB = AGH/p cold air-photair) - W -: from gas e.0.5, we can see that ↑ temp of gas at constant force, FH
pressure decreases the density: increases the buoyancy
Neutral buoyancy is when a balloon neither rises or sinks. As net buoy (FB) = FH-W and
(for neutral buoy) Fn-W . FB = 0 so:
balloon mass = structure + payload mg p balloon =p c-ph weight.w
= FH-W → 0 = Agh Pcoid-phot)-ing → mg = Vg (Pcoid-phot) #=P)
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