CFD - Finals

Flaps

are movable high-lift devices located on the trailing edge of an aircraft wing

Flaps

their primary function is to increase lift at low speeds, especially during takeoff and landing phases

1. Increasing the camber of the airfoil

2. Increassing the effective angle of attack

3. Sometimes increasing the wing area

4. Delaying or controlling flow

(4) From a CFD Standpoint, flaps work by

Wright Brothers

who achieved ethe first successful powered flight

1903

when was the first successful powered flight

Kitty Hawk

where was the first successful powered flight

Wright Brothers in 1903 at Kitty Hawk

marked the beginning of controlled aerodynamics in aviation

a decade later (after the first successful powered flight)

early aircraft had limited control at low speeds, when did engineers began developing high-lift devices, including early forms of wing flaps

1. Camber increases

2. Effective AOA increases

3. Boundary Layer effects

3 things that happen whenflaps are deployed

Camber increases

• wing curvature increases

• lift coefficient increases

Effective Angle of Attack Increase

• airfoil behaves as if it is more “tilted” into the flow

Boundary Layer Effects

• higher risk of separation if not controlled

• slotted designs help re-energize airflow

Plain Flap

a simple hinged flap that deflects downward from the trailing edge

Plain Flap

Plain Flap

Aerodynamic Effect:

• Increases chamber

• Moderate lift increase

• High drag at larger deflections

CFD Behavior:

• Early flow separation at high angles

• Strong wake turbulence

• Simple pressure distribution

Split flap

only the lower surface deflectts downward

Split Flap

Splif Flap

Aerodynamic Effect:

• High drag generation

• Moderate lift increase

CFD Behavior:

• Strong pressure discontinuity

• Large separated flow regioon behind flap

• High Turbulent wake

Slotted Flap

includes a slot between wing and flap

Slotted Flap

Slotted Flap

Aerodynamic Effect:

• Delays flow separation

• Increases lift significantly

CFD Behavior:

• High-energy air from lower surface reattaches upper surface

• Reduced separation zones

• Improved lift-to-drag ratio compared to plain flaps

Fowler Flap

extends rearward and downward

Fowler Flap

Fowler Flap

Aerodynamic Effect:

• Increases wing area AND camber

• Very high lift increase

• Moderate drag increase
  

CFD Behavior:

• Larger effective lifting surface

• Increased suction peak over extended chord

• More complex wake but stable attached flow at moderate angles

Slotted Fowler Flap

Slotted Fowler Flap

Aerodynamic Effect:

• Extremely high lift augmentation

• Efficient takeoff/landing performance
  

CFD Behavior:

• Multi-element flow interaction

• Strong but controlled vortical structures

• Delayed stall significantly

Gouge Flap

adjustable flap system with variable positioning

Gouge Flap

Gouge Flap

Aerodynamic Effect:

• Flexible lift/drag control depending on setting
  

CFD Behavior:

• Multiple stable operating points

• Flow adapts based on flap configuration

• Useful for optimization studies

Junkers Flap

mounted below trailing edge, separated from wing

Junkers Flap

Junkers Flap

Aerodynamic Effect:

• Effective at high angles

• Strong control authority
  

CFD Behavior:

• Fully exposed flap generates independent airflow field

• Strong vortex shedding

• Reduced wing interference effects

Zap Flaps

complex multi-link mechanism increasing chord length

Zap Flaps

Zap Flaps

Aerodynamic Effect:

• Very high lift coefficient

• High drag when fully deployed
  

CFD Behavior:

• Strong camber + chord extension effect

• Highly nonlinear flow response

• Large lift increase but complex wake

Krueger Flaps

deploys from the leading edge downward/forward

Krueger Flaps

Krueger Flaps

Aerodynamic Effect:

• Improves stall characteristics

• Enhances low-speed lift
  

CFD Behavior:

• Re-energizes leading-edge flow

• Delays leading-edge separation bubble

• Improves overall pressure recovery

Gurney Flaps

small vertical tab at trailing edge

Gurney Flaps

Gurney Flaps

Aerodynamic Effect:

• Increases lift with minimal mechanical complexity

• Slight drag penalty
  

CFD Behavior:

• Generates strong trailing-edge vortex

• Increases pressure difference between upper and lower surfaces

• Improves circulation around airfoil

Drag

is the aerodynamic force that opposes an object’s motion as it moves through air, and it is a critical factor in aircraft performance because it directly affects fuel efficinecy, speed, and overall aerodynamic efficiency

Drag measurements

in aerodynamics, are typically obtained using wind tunnel testing or computational fluid dynamics (CFD), where the drag force is analyzed using coefficients such as the drag coefficient to compate the aerodynamic effciency of diffrent shapes and designs

1. Skin Friction Drag

2. Form Drag

3. Profile Drag

4. Interference Drag

5. Parasite Drag

6. Induced Drag

7. Zero-lift Drag

8. Wave Drag

8 Types of Drag

Induced drag

when an airfoil is flown at a positive AOA, a pressure differential exists between the upper and lower surfaces of the airfoil.

• the pressure above the wing is less than atmospheric pressure and the pressure below the wing is equal of greater than atmospheric pressure

Vortex

air flows from high to low presure and tends to move outward tward the airfoil tips, causing spanwise flow from the fuselage to the tips. This results in air spilling over the tips and forming a swirling motion known as a ________

1. Size of lift

2. Aircraft speed

3. Aspect Ratio

3 Factors Affecting Induced Draf

Induced drag

is a component of the lift force;

• the greater the lift, the greater it will be

weight

L=W in flight so, induced drag will depend on the _______ of the aircraft

Load Factor

relationship of lift to weight ratio is known as

Induced drag

decreases with increasing speed

Induced drag

decreases because as speed increases, the downwash caused by the tip vortices becomes less significant, the rearward inclination of the lift is less, and therefore induced drag is less