Aerodynamics Flashcards by RAFA BRENDA DELDIG

the property of fluid to resist shearing stress

viscosity

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the sticky or adhesive characteristic of a fluid

viscosity

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It can also be described in terms of a fluid’s thickness

viscosity

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no drag

frictionless flow

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finite drag

Real flow

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there is a drag force on the sphere tending to retard the motion of the sphere.

real flow

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This is a concept used in physics and engineering to study the behavior of fluids under idealized conditions.

frictionless flow

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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

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all fluids experience some degree of friction and viscosity, which affects their flow and energy transfer.

frictionless flow

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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

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Another region of _____ (sometimes called potential flow) outside the boundary layer.

frictionless flow

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Fluid that experiences no friction or viscosity, meaning that there is no resistance to the flow of the fluid.

frictionless flow

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if the flow is incompressible, V2 can be calculated from ____:

P1 + 1/2 ρV12 = P2 + 1/2 ρV22

Bernoulli’s equation

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The region of viscous flow which has been retarded owing to friction at the surface.

boundary layer

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Friction is important. It is the layer near the surface.

boundary layer

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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

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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

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Τw gives rise to a drag force called

“skin friction drag”

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Where μ is called the ______ (viscosity of the gas). It has dimensions of mass/(length)(time).

absolute viscosity coefficient

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For ____, μ decreases as T increases. “Oil gets thin when Temp Increases.

liquids

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for __, μ increases as T increases (Air gets “thicker” when temperature is increased).

gases

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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

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TWO BASIC TYPES OF VISCOUS FLOWS

laminar flow
turbulent flow

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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

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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