Fluid Mechanics

Ch-8BuoyancyPressure

Flow

Fluids

• Fluids flow and alter shape

• Which states of matter are fluid?

• Liquid• Gas• Plasma

Gasses fill and conform to their container

• Chlorine gas Cl2

Plasma’s conform to magnetic fields

• At PPPL they are experimenting on the fusion of hydrogen plasma

Density

= m/V• “rho” = mass/volume

• Density of Steam = 0.598 kg/m3

• Density of Mercury = 13.6 x 103 kg/m3

Buoyancy

• FB = Fg (of displaced fluid)

• = mog

Archimedes Principle

• Fnet = mfg - mog

Ships are rated as displacing tons of seawater

Fluid Pressure

• P = F/A

• Force/unit area

• Pounds/in2 (Psi)• Or N/m2 (Pascals)

4000 N/m2

• 107 Pascal

Fluid Pressure

• P = F/A

• Force/unit area

• PSI (lbs/insquared)

Pressure increases as area applied decreases

• F1/A1 = F2/A2

Hydraulics at the Dentist

Syringe hydraulic lift

• I raise a 10 N rock with a hydraulic piston that is 13 mm in radius using water connected to a 1.5 mm radius syringe. How much force is necessary for this lift to raise the rock?

Pressure as a Function of Depth

• P = Po + gh

Submarine Ballast Tanks

• The density of the whole device is adjusted by releasing compressed air

WWIII Submarine section

Buoyant force results from differing pressure at depth

FB=A(Po+gh2)-A(Po+gh1)

FB=g(h2-h1)A

FB=gV

FB=mfg That’s Archimedes

Principle

The Coanda Effect

• Fluid adheres to surfaces

• Flowing fluids are directed by curved surfaces

Bernouli’s Principle on Air foils

• Air flowing across and air foil flows faster across the top

• Pressure is lower of the air flows faster

• Fnet is upward

Coanda Effect breaks down at high angles of attack

• The Coanda effect guides the air flow along the surface

• The air flow breaks free and turbulent flow results

• Stall occurs

Coanda Develops First Jet engine aircraft, 1910

It crashes, he loses funding

Lost technologyfor 30 years