Aerodynamics

Question 1

Fluids: What are fluids?

Answer 1

Substance that flows and/or deforms when submitted to tangential forces

Question 2

Fluids: What are the two types of flow and what are the differences?

Answer 2

Laminar flow - uniform layers

Turbulent flow - randomized layers

Question 3

What is the theorem related to fluids? What does it suggest? Give an example.

Answer 3

Reynolds Theorem.
Re = (flow speed x length x fluid density)/fluid viscosity.
Suggests higher Re = more turbulence.
Growing up > taller height and greater velocity > greater turbulence

Question 4

What are the 4 factors involved in Fluid Mechanics

Answer 4

WLTD: Weight, Lift, Thrust, Drag

Question 5

What is the formula related to Weight?

Answer 5

W = m x g

Weight of object = mass of object x gravitational acceleration

Question 6

Lift: What is the theorem related? What does it theorize?

Answer 6

Bernoulli’s theorem
For an inviscid flow, an increase in speed of fluid occurs simultaneously with a decrease in pressure or decrease in fluid’s potential energy

Question 7

Lift: Aerofoil, Can you look at diagram of aerofoil and name the parts? Brief description of each.

Answer 7

Can you look at diagram of aerofoil and name the parts?
Leading edge: foremost edge of airfoil section
Chord Line: imaginary straight line joining leading and trailing edge
Trailing edge: rear edge
Angle of incidence: angle between chord line and reference axis
Line parallel to Longitudinal Axis

Question 8

Lift: Aerofoil, can you use Bernoulli’s Equation to explain a typical aerofoil diagram in terms of distance and velocity for convex and concave sides?

Answer 8

d1 > d2, greater distance to travel = higher speed as both particles are required to reach at same time. Hence v1 > v2.
Bernoulli’s Equatin suggests P + Ekinetic = constant

Question 9

Lift: Aerofoil. In what direction does lift occur? Can you draw the diagram?

Answer 9

It occurs perpendicular to motion from high to lower pressure field.

Question 10

Lift: Downforce Aerofoil. Can you draw diagram of F1 car and the % of downforce eac part generates?

Answer 10

Underbody with diffuser = 45%
Rear and front wing = 25%
Rest of bodywork = 5%

Question 11

Can you explain the magnus effect in an aerofoil? Draw a diagram depicting the effect of wind, windspeed, spin, forces

Answer 11

Force is perpendicular to velocity vector of object.
Direction of spin dictates orientation of Magnus force on object
Orientation of force can change but always perpendicular to direction of fluid.
http://ffden-2.phys.uaf.edu/webproj/211_fall_2014/Max_Hesser-Knoll/max_hesserknoll/Slide3.htm

Question 12

Drag: What is Viscosity? What is the difference between Perfect (theoretical) fluid and real fluid?

Answer 12

The quantification of fluid’s resistance to gradual deformation, by shear or tensile stress.
Perfect fluid has no viscosity hence no drag force

Question 13

Drag: What are the components of drag force?

Answer 13

Friction/surface
Pressure/form
Wave

Question 14

Drag: Explain the Friction component of Drag force. In which direction does it act?

Answer 14

A smooth surface has small friction while rough surface has large friction. Acts tangential to the body, opposite to the motion.

Question 15

Drag: Explain the Pressure component of Drag force, in which direction does it act? Can you draw diagram?

Answer 15

Pressure occurs perpendicular to separation fields from high to low pressure. Equation is similar to lift but in opposite direction.

Question 16

Drag: Can you explain the concept of separation point with regards to pressure drag? Can you draw diagram?

Answer 16

Separate point determines pressure drag, earlier separation means higher drag and vice versa. Separation point depends on complete pressure restablization (later separation) or uncomplete pressure restabilization.

Question 17

Can you apply the concept of pressure drag to a golf ball and smooth ball? How about different object shapes?

Answer 17

Golf ball indentations affect separation point, which reduces pressure drag due to later separation point. Same for sphere with housing compared to flat plate.

Question 18

What are two positions in sports that are taken to minimize pressure drag? How do they work?

Answer 18

Aerodynamic position & Hydrodynamic position.

Question 19

Drag: Pressure, What is drafting and explain the concept. What is the key concept?

Answer 19

Two separate bodies moving while aligned in close group, reduces overall drag effect.
Slipstream: region behind body which is moving at velocities comparable to moving body

Question 20

Drag: Wave, when does it occur? Does it occur in water or air?

Answer 20

When solid object compresses water particles, notably on surface.
Wave drag disregarded in air because supersonic speed must be present to have effect.

Question 21

Drag: Wave, what is the Froude number and hull velocity?

Answer 21

Froude number: wave making resistance index (dimensionless) “Froude number represents the ratio of inertial to gravitational forces experienced by a body moving at or close to a fluid/fluid interface”
Hull velocity: E.g. the speed at a Froude number equal to 0.42 > body trapped in hull moving along with the wave system > efficient

Question 22

Fluid Dyanmics: Thrust. What is a vortex? Can you give an example?

Answer 22

Region within fluid where flow is mostly oriented around an axis.
Swimming when changing direction or accelerating limbs.

Question 23

What happens when one exceeds or remains at hull velocity?

Answer 23

Actual displacement same as hull velocity > saves energy

Exceed hull velocity > hydroplaning and ride the waves, may increase effectiveness.