2.2.4 FLUID DYNAMICS

What does fluid dynamics help calculate for aircraft? A) Aerodynamic forces and moments B) Only aircraft mass C) Only engine temperature

A) Aerodynamic forces and moments

Which properties are used in fluid-dynamics calculations? A) Mass force work and power only B) Velocity pressure density and temperature C) Torque and angular momentum only

B) Velocity pressure density and temperature

What drives downhill fluid flow? A) A decrease in mass B) Gyroscopic rigidity C) Gravitational potential energy

C) Gravitational potential energy

What drives flow caused by pressure differences? A) An imbalance between forces at different locations B) Equal pressure everywhere C) A change in colour

A) An imbalance between forces at different locations

Which materials are fluids? A) Solids and metals only B) Liquids and gases C) Only gases

B) Liquids and gases

How do fluid molecules differ from solid molecules in the notes? A) They are fixed in a lattice B) They have no motion C) They are constantly moving and occupy available volume

C) They are constantly moving and occupy available volume

How are pressures within a confined fluid transmitted? A) In all directions and equally throughout the fluid B) Only downward C) Only along the pipe axis

A) In all directions and equally throughout the fluid

Which aircraft system uses directed hydraulic pressure? A) Fuel tanks only B) Control actuators C) Cabin windows only

B) Control actuators

What is density? A) Volume per unit mass B) Mass multiplied by volume C) Mass per unit volume

C) Mass per unit volume

Which equation gives density? A) ρ = m/V B) ρ = V/m C) ρ = mV

A) ρ = m/V

What is the SI unit of density? A) m³/kg B) kg/m³ C) N/m²

B) kg/m³

Which density conversion is stated? A) 1 g/cm³ = 1 kg/m³ B) 1 g/cm³ = 0.001 kg/m³ C) 1 g/cm³ = 1000 kg/m³

C) 1 g/cm³ = 1000 kg/m³

Which volume relation is correct? A) 1 ml = 1 cm³ B) 1 ml = 100 cm³ C) 1 ml = 0.001 cm³

A) 1 ml = 1 cm³

Why are solids generally denser than fluids? A) Their particles cannot move B) More particles are packed into a smaller volume C) They always have greater temperature

B) More particles are packed into a smaller volume

Why is air relatively light? A) It has no volume B) It is a solid C) It has little mass in the same volume

C) It has little mass in the same volume

What happens to most fluid densities when temperature increases? A) Volume increases and density decreases B) Volume decreases and density increases C) Both remain fixed

A) Volume increases and density decreases

What happens to density when pressure compresses a fluid? A) Volume increases and density decreases B) Volume decreases and density increases C) Mass becomes zero

B) Volume decreases and density increases

How is density related to pressure in the notes? A) Inversely proportional B) Independent C) Directly proportional

C) Directly proportional

How is density related to temperature in the notes? A) Inversely proportional B) Directly proportional C) Independent

A) Inversely proportional

Why should temperature and pressure be quoted with a density? A) Density has no units B) Density varies with temperature and pressure C) Pressure changes mass

B) Density varies with temperature and pressure

What temperature does the stated ISA use? A) 0°C B) 100°C C) 15°C

C) 15°C

What pressure does the stated ISA use? A) 760 mmHg B) 76 mmHg C) 7600 mmHg

A) 760 mmHg

Which listed fluid has density about 1000 kg/m³? A) Air B) Water C) Hydrogen

B) Water

Which listed gas has the lowest density? A) Air B) Helium C) Hydrogen

C) Hydrogen

What is specific gravity? A) Density of a substance divided by density of water B) Mass divided by pressure C) Volume divided by mass

A) Density of a substance divided by density of water

What is the usual symbol for specific gravity? A) ρ B) SG C) V

B) SG

Does specific gravity have units? A) Yes kg/m³ B) Yes N/m² C) No it is a ratio

C) No it is a ratio

Why should temperatures be specified for specific gravity? A) Volume of a given mass varies with temperature B) Water has no density C) Mass changes with gravity

A) Volume of a given mass varies with temperature

For equal container volumes how can specific gravity be compared? A) Mass of water divided by mass of liquid B) Mass of liquid divided by mass of water C) Volume divided by mass

B) Mass of liquid divided by mass of water

What is a hydrometer used to measure? A) Gas temperature only B) Fluid velocity only C) Density or specific gravity of a liquid

C) Density or specific gravity of a liquid

What supports a common hydrometer while it floats? A) A weighted float with graduations B) A rotating rotor C) A pressure pump

A) A weighted float with graduations

What principle allows a hydrometer to float? A) Bernoulli principle only B) Archimedes principle C) Newton third law only

B) Archimedes principle

What must a hydrometer displace to float? A) No liquid B) The entire container volume C) A volume of liquid equal to its mass requirement

C) A volume of liquid equal to its mass requirement

In a dense liquid how does the hydrometer sink? A) It displaces a smaller volume and sinks less B) It displaces a larger volume and sinks more C) It cannot float

A) It displaces a smaller volume and sinks less

In a less dense liquid how does the hydrometer sink? A) It displaces no volume B) It must displace a greater volume and sinks deeper C) It rises above the liquid

B) It must displace a greater volume and sinks deeper

What makes a hydrometer stem more sensitive? A) A thicker stem B) A shorter scale C) A thinner stem

C) A thinner stem

Why is a thinner stem more sensitive? A) A small density change gives greater movement B) It has no graduations C) It prevents displacement

A) A small density change gives greater movement

What determines hydrometer range? A) Mass of the liquid only B) Length of the stem and number of graduations C) Colour of the fluid

B) Length of the stem and number of graduations

What is viscosity? A) Density divided by volume B) Pressure due to height C) Resistance of a fluid to flow

C) Resistance of a fluid to flow

What causes internal fluid friction? A) Relative motion between molecular layers B) Gravity alone C) A lack of molecules

A) Relative motion between molecular layers

Where is river water slowest in the example? A) At the river centre B) Immediately beside the stationary bank C) Above the river

B) Immediately beside the stationary bank

Where is river water fastest in the example? A) At the stationary bank B) Below the river bed C) Away from the bank after the velocity increases

C) Away from the bank after the velocity increases

Which fluid has higher viscosity? A) Tar B) Air C) Water

A) Tar

What does high viscosity cause? A) Zero shear stress B) Greater resistance to flow C) Higher compressibility only

B) Greater resistance to flow

What is shear stress in the notes? A) Mass per unit volume B) Pressure per unit time C) Force required to slide one unit area over another

C) Force required to slide one unit area over another

What occurs within a boundary layer? A) Velocity changes across the fluid near a surface B) Density becomes zero C) Pressure stops acting

A) Velocity changes across the fluid near a surface

Where is the greatest rate of velocity change? A) Farthest from every boundary B) Closest to the stationary boundary C) At the centre of a vacuum

B) Closest to the stationary boundary

What makes a boundary layer thicker? A) Lower viscosity only B) Zero velocity change C) Greater velocity change or greater viscosity

C) Greater velocity change or greater viscosity

In airflow over a wing what is the stationary boundary? A) The wing skin B) The air far from the wing C) The aircraft centre of gravity

A) The wing skin

How does air velocity change away from the wing skin? A) It decreases to zero B) It increases C) It remains exactly fixed

B) It increases

What is a streamline? A) A random eddy B) A pressure gauge C) A smooth regular path followed by fluid flow

C) A smooth regular path followed by fluid flow

How are streamlines arranged in steady smooth flow? A) Parallel and non-crossing B) Crossing at every point C) Randomly intersecting

A) Parallel and non-crossing

What is laminar flow? A) Chaotic eddying flow B) Layered flow in which particles follow regular trajectories C) Flow with no velocity

B) Layered flow in which particles follow regular trajectories

What happens when streamlines meet irregularities? A) The fluid becomes solid B) Pressure becomes zero C) The flow can become turbulent

C) The flow can become turbulent

What characterises turbulence? A) Irregular chaotic motion with eddies and vortices B) Parallel layers only C) No mixing

A) Irregular chaotic motion with eddies and vortices

What can cause turbulent flow around an object? A) A perfectly smooth path B) Fluid inertia and insufficient force to follow the surface C) No pressure difference

B) Fluid inertia and insufficient force to follow the surface

What does the Coanda effect describe? A) A fluid becoming incompressible B) A fluid stopping at a wall C) A fluid tending to follow the surface over which it flows

C) A fluid tending to follow the surface over which it flows

Why does turbulent flow create high drag? A) It absorbs energy while the fluid direction changes B) It removes all mass C) It eliminates acceleration

A) It absorbs energy while the fluid direction changes

What is a venturi tube? A) A tube with constant area only B) A tube narrowing smoothly then widening C) A solid rod

B) A tube narrowing smoothly then widening

What happens to streamline spacing at the constriction? A) They disappear B) They become wider than at the entrance C) Streamlines crowd together

C) Streamlines crowd together

What happens to fluid velocity at the constriction? A) It increases B) It decreases to zero C) It is unchanged regardless of area

A) It increases

What happens to static pressure at the constriction? A) It rises B) It falls C) It becomes equal to dynamic pressure only

B) It falls

What pressure is associated with fluid motion? A) Static pressure only B) Atmospheric datum pressure C) Dynamic pressure

C) Dynamic pressure

Which is an application of the venturi principle named in the notes? A) A carburettor B) A padded gyro case C) A hydrometer stem

A) A carburettor

What unit is commonly used for fluid flow rate? A) kg/m³ B) m³/s C) N/m²

B) m³/s

Which equation gives volume flow rate? A) Q = A/v B) Q = v/A C) Q = Av

C) Q = Av

What determines flow rate through a pipe? A) Cross-sectional area and fluid velocity B) Temperature only C) Mass and time period only

A) Cross-sectional area and fluid velocity

What is constant in steady incompressible flow through a tapering tube? A) Cross-sectional area B) Rate of flow C) Velocity at every point

B) Rate of flow

Which continuity equation is correct? A) Q = A1/v1 = A2/v2 B) Q = A1A2v1v2 C) Q = A1v1 = A2v2

C) Q = A1v1 = A2v2

If pipe area is halved what happens to velocity for constant flow rate? A) Velocity doubles B) Velocity halves C) Velocity is unchanged

A) Velocity doubles

Why does a fire hose nozzle produce higher water velocity? A) It increases fluid mass B) Its smaller area increases velocity at constant flow rate C) It removes pressure

B) Its smaller area increases velocity at constant flow rate

What remains constant in Bernoulli principle for streamlined flow? A) Static pressure alone B) Velocity alone C) Total mechanical energy

C) Total mechanical energy

What happens to pressure when fluid speed increases? A) Pressure or potential energy decreases B) Pressure always increases C) Pressure is unchanged

A) Pressure or potential energy decreases

Which energy forms are considered in the tapered tube? A) Heat sound and chemical energy only B) Pressure kinetic and potential energy C) Mass force and time

B) Pressure kinetic and potential energy

What is kinetic energy of a fluid mass? A) mgh B) PV C) 1/2 mv²

C) 1/2 mv²

What is potential energy in the tube? A) mgh B) 1/2 mv² C) ma

A) mgh

What is static pressure? A) Pressure due only to movement B) Pressure energy of a stationary fluid C) Pressure due only to height

B) Pressure energy of a stationary fluid

What is dynamic pressure? A) Pressure in a stationary fluid B) Pressure due to datum height only C) Pressure energy due to fluid movement

C) Pressure energy due to fluid movement

Which equation gives dynamic pressure? A) 1/2 ρv² B) ρgh C) ρ/v²

A) 1/2 ρv²

For a horizontal tube what happens to the height term? A) It doubles B) It is constant and can be cancelled C) It becomes the dynamic pressure

B) It is constant and can be cancelled

Which expression gives total pressure in a horizontal flow? A) P − 1/2ρv² = zero B) Pρv² = constant C) P + 1/2ρv² = constant

C) P + 1/2ρv² = constant

If dynamic pressure increases along a streamline what happens to static pressure? A) It decreases B) It increases by the same amount C) It becomes zero in every case

A) It decreases

If fluid is not flowing what is total pressure equal to? A) Dynamic pressure only B) Static pressure C) Zero pressure

B) Static pressure

For which fluids is Bernoulli equation presented as applicable? A) Only solids B) Only highly compressible gases C) Incompressible fluids

C) Incompressible fluids

Why is pressure lower above the wing in the notes? A) Air moves faster over the larger top surface B) Air is denser above the wing C) The bottom surface is longer

A) Air moves faster over the larger top surface

What pressure difference provides lift? A) Higher pressure above and lower below B) Lower pressure above and higher pressure below C) Equal pressure on both surfaces

B) Lower pressure above and higher pressure below

What defines a convergent duct? A) Exit area is larger than entrance area B) Areas are always equal C) Exit area is smaller than entrance area

C) Exit area is smaller than entrance area

What happens to velocity in a convergent duct at low speed? A) It increases B) It decreases C) It becomes zero

A) It increases

What happens to dynamic pressure in a convergent duct? A) It decreases B) It increases C) It is independent of velocity

B) It increases

What happens to static pressure in a convergent duct? A) It increases B) It is unchanged C) It decreases

C) It decreases

What defines a divergent duct? A) Area increases in the direction of flow B) Area decreases in the direction of flow C) It has no cross-section

A) Area increases in the direction of flow

What happens to velocity in a divergent duct? A) It increases B) It decreases C) It is always zero

B) It decreases

What happens to dynamic pressure in a divergent duct? A) It increases B) It becomes total pressure C) It decreases

C) It decreases

What happens to static pressure in a divergent duct? A) It increases B) It decreases C) It is unchanged

A) It increases

Why does incompressible theory work well for liquids? A) Liquids have no density B) Liquids compress very little C) Liquids always flow faster than sound

B) Liquids compress very little

At approximately what air speed is incompressible theory still sufficiently valid in the notes? A) Above 3400 m/s only B) Only at zero speed C) Below about 130–150 m/s

C) Below about 130–150 m/s

What speed of sound is stated for sea level standard ISA conditions? A) About 340 m/s B) About 34 m/s C) About 3400 m/s

A) About 340 m/s

When must air compressibility effects be considered? A) Only for stationary liquids B) In high-speed flight near or above sound speed C) Only in a sealed hydrometer

B) In high-speed flight near or above sound speed

Which aircraft instruments can be affected by compressibility inaccuracies? A) Hydrometer graduations B) Gyro gimbals only C) Pitot-static instruments

C) Pitot-static instruments

At high speed how do venturi effects compare with low-speed flow in the notes? A) They are reversed B) They are always identical C) They disappear completely

A) They are reversed