Aerodynamics Flashcards
the property of fluid to resist shearing stress
viscosity
the sticky or adhesive characteristic of a fluid
viscosity
It can also be described in terms of a fluid’s thickness
viscosity
no drag
frictionless flow
finite drag
Real flow
there is a drag force on the sphere tending to retard the motion of the sphere.
real flow
This is a concept used in physics and engineering to study the behavior of fluids under idealized conditions.
frictionless flow
The flow separates on the rear surface of the sphere, setting up a complicated flow in the wake and causing the pressure on the rear surface to be less than that on the forward surface. Hence, a drag force is exerted on the sphere
real flow
all fluids experience some degree of friction and viscosity, which affects their flow and energy transfer.
frictionless flow
The idea of a ______ is useful as a starting point to understand the basic principles of fluid mechanics, but it is not applicable to real-world situations.
frictionless fluid
Another region of _____ (sometimes called potential flow) outside the boundary layer.
frictionless flow
Fluid that experiences no friction or viscosity, meaning that there is no resistance to the flow of the fluid.
frictionless flow
if the flow is incompressible, V2 can be calculated from ____:
P1 + 1/2 ρV12 = P2 + 1/2 ρV22
Bernoulli’s equation
The region of viscous flow which has been retarded owing to friction at the surface.
boundary layer
Friction is important. It is the layer near the surface.
boundary layer
Thickness grows as the flow moves over the body
More and more of the flow is affected by friction as the distance along the surface increases.
boundary layer
The presence of friction creates a shear stress at the surface “τw”.
This shear stress has dimensions of force/area and acts in a direction tangential to the surface.
boundary layer
Τw gives rise to a drag force called
“skin friction drag”
Where μ is called the ______ (viscosity of the gas). It has dimensions of mass/(length)(time).
absolute viscosity coefficient
For ____, μ decreases as T increases. “Oil gets thin when Temp Increases.
liquids
for __, μ increases as T increases (Air gets “thicker” when temperature is increased).
gases
Flow in which the streamlines are smooth and regular and the fluid element moves smoothly along the streamline.
Smooth motion fluid elements in a ___
laminar flow
TWO BASIC TYPES OF VISCOUS FLOWS
laminar flow
turbulent flow
Flow in which the streamlines break up and a fluid element moves in a random, irregular, and tortuous fashion.
Tortuous, irregular motion of fluid elements in a _______.
turbulent flow
It is a measure of the ratio of inertia forces to viscous forces.
Helps determine whether the flows in a body and its scaled version are aerodynamically similar
Reynold’s number
Can be applied in determining whether all, or portion of boundary layer is laminar or turbulent.
Dimensionless, It varies linearly with X. Sometimes called a local Reynolds number, because it is based on the local coordinate X.
Reynold’s number
The flow always starts out from the leading edge as laminar. Then, becomes unstable and small “bursts” of turbulent flow begin to grow in the flow.
transition
Over a certain region called the ______, the boundary layer becomes completely turbulent.
transition region
FACTORS AFFECTING TRANSITION FROM LAMINAR TO TURBULENT
Increased surface roughness
Increased turbulence in the free stream
Adverse pressure gradients
Heating of the fluid by the surface
Similarity parameters of the flow (Mach Number and Reynold’s Number)
Two Major Consequences of Separated Flow Over an Airfoil
A drastic loss of lift (stalling).
A major increase in drag, caused by pressure drag due to separation.
A drastic loss of lift
stalling
Friction also causes another phenomenon, called ______, which, in turn, creates another source of aerodynamic drag, called pressure drag due to separation (Form Drag).
flow separation
A condition wherein the angle of attack increases beyond a certain point such that the lift begins to decrease.
stall
Typically about 15 degrees, but it may vary significantly depending on the fluid, and Reynolds number.
stall
Occurs when the critical angle of attack of the airfoil is exceeded.
stall
was named after aerodynamicist Theodor Von Karman
KARMAN VORTEX STREET
a repeating pattern of swirling vortices caused by the unsteady separation of a fluid around blunt bodies.
KARMAN VORTEX STREET
is a streamlined body which when set at a suitable angle of attack, produces more lift than drag while also producing a manageable pitching moment
airfoil
An airfoil is said to be _____ if the upper and lower cambers are equal in shape.
SYMMETRICAL
An airfoil is said to be _____if the upper and lower cambers are not equal in shape.
ASYMMETRICAL
The Precise distance from the Leading edge measured along the chord line.
Chord
– A straight line connecting the leading and trailing edges of an airfoil.
Chord Line
– Locus of all points equidistant from the top and bottom of the airfoil.
Mean Camber Line
– The maximum distance between the chord line and the mean camber line.
Camber
– Maximum distance between the top and bottom surfaces of the wing.
Thickness
– The most forward points of the mean camber line.
Leading Edge
– Is the maximum thickness-to-chord ratio.
Thickness Ratio
– The most rearward points of the mean camber line.
Trailing Edge
– The distance from wing tip to wing tip.
Wingspan
– The area of the projection of the actual outline on the plane of the chord.
Wing Area
– The ratio of the span to the chord. If the wing is not rectangular in shape, it is the square of the spane to the area.
Aspect Ratio
– angle between the relative wind and the chord line.
Angle of Attack
– Defined as the component of aerodynamic force perpendicular to the relative wind.
Lift
- Defined as the component of the aerodynamic force parallel to the relative wind.
Drag
– The air far upstream of the airfoil.
Relative Wind
Developed by the National Advisory Committee for Aeronautics
NACA AIRFOIL
These are airfoil shapes for aircraft wings.
NACA AIRFOIL
The shape is described by a series of digits followed by the word___. Can either be 4, 5, or 6 – digits.
NACA
The first digit specifies the maximum camber in percentage of the chord.
The second indicates the position of the maximum camber in tenths of the chord.
The last two numbers provide the maximum thickness of the airfoil in percentage of the chord.
4-Digits Airfoil
The first digit specifies the maximum camber in percentage of the chord.
The second and third digits indicate the position of the camber in tenths divided by 2.
The last two numbers provide the maximum thickness of the airfoil in percentage of the chord.
5- Digit Airfoils
