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

Split Flap

Aerodynamic Effect:

• High drag generation

• Moderate lift increase

CFD Behavior:

• Strong pressure discontinuity

• Large separated flow region 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 Drag

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

High Aspect Ratio Wing

in a _________, the tip vortices only affect a smaller portion of the total wingspan

Tip vortices

swirling air at the wing tips

induced drag

the backward tilt of lift is what creates __________

1. Wingtip Shape

2. Winglets

3. Tip Planks

4. Wing End Plates

4 Methods of Reducing Induced Drag

Wingtip Shape

can affect the strength of the tip vortices, and designs such as turned down or turned up wingtips have been used to reduce induced drag

Winglets

small vertical aerofoils which form part of the wing tip

Winglets

shaped and angled to the induced flow, they generate a small forward force

Winglets

partly block the air flowing from the bottom to the top surface of the wing, reducing the strength of the tip vortex

Winglets

the small vortex generated by the ______ interacts with and further reduces the strength of the main wingtip vortices

Tip Planks

fuel tanks placed at the wing tips will have a similar beneficial effect to an end plate

• will reduce the induced drag

• will reduce the wing bending moment

Wing End Plates

a flat plate at the wing tip will restrict the tip vortices and have a similar effect to an increased aspect ratio, but without the extra bending loads

Wing End Plates

will cause parasite drag, and at a higher speeds there may be no overall saving in drag

1. Internal Balances

2. External Balances

2 Location of Balances

Internal Balances

they are placed inside the model, thus no interferences are introduced in the wind flow by the balance components, but a mechanical support for the model is always needed to maintain it in the test chamber and change the model orientation if desired

External Balances

are placed outside the model, either inside or outside the test section, and they can disturb the airflow

External Balances

they make it easy to change test models, providing flexibility

External Balances

their complexity varies depending on the number of measurement channels, typically from 1 to 6

1. Three strut

2. Two Strut

3. Single Strut

4. Sting Mount

4 Mounting Methods

Three Strut Mount

it is a mount that connects to the model near both wing tips and at the aft end

Three Strut Mount

is used most often with external balances

Three Strut Mount

the bottom of the three struts connect to a platform that is instrumented with strain gages

Three Strut Mount

the three movable struts, the AOA, and roll angle can be accurately set and sustained while yaw is provide d by turning the model on the circular section of the platform

Two Strut Mount

supports an aircraft model in a wind tunnel using two struts, typicall attached from below or the sides, resulting in less airflow interference and blockage, which improves flow quality and reduces cost and complexity

Two Strut Model

it is less rigid than a three-strut system, particularly in pitch and roll, making the model more prone to slight movement or vibration that can affect measurement accuracy

Single Strut Model

supports the aircraft model using only one strut, which can be attached either to the top or bottom of the model, resulting in the least expense as well as minimal airflow interference and blockage, allwoing for cleaner flow around the model

Single Strut Model

provides the least rigidity compared to multi-strut systems, making it more susceptible to movement and less stable during testing

Sting Mount Model

has less interference with the model flow field than the one strut mount, but the aft end of the model may be distorted to accept this mount

Single Strut Mount

works very well with internal balances and flow diagnostics

1. One Component

2. Three Component

3. Six Component

3 Types of Balances

Spring Balance (One Component)

is a weighing device that utilizes the relation between the applied load and the deformation of a spring

Linear

the relationship of a spring balance is usually

Linear

if the load is doubled, the deformation is doubled

Strain Gages (Three Component)

measure forces through electrical stretching

Three-Component Balance

detects axial, normal, and bending forces to determint lift, drag, and pitch

1. Side force

2. Roll

3. Yaw

3 things the Three Component Balance cannot measure

1. Lift

2. Drag

3. Side force

4. Pitch

5. Roll

6. Yaw

6 things the Six-Component Balance can Measure

Finite Element Analysis

• Numerical method for solving engineering problems

• Divides domain into small elements

• Used for structural, thermal, and fluid problems

• Based on approximate solutions

Finite Element Analysis

divides a complex fluid domain into small elements to numerically solve the governing equations of fluid flow, calculating variables like velocity, pressure, and temperature under specified boundary conditions

Finite Element Analysis

In aerospace engineering, it is used to analyze aerodynamics, propulsion, and fluid–structure interactions, improving aircraft design while reducing the need for costly experiments

Mesh Generation

Process of dividing a complex domain into small elements and nodes so the governing equations can be solved numerically in FEA and CFD.

Stress Analysis

Process of determining the internal forces and stresses within a material or structure when subjected to external loads, pressure, or temperature changes.

Numerical Solution

Using discretization methods to solve the governing equations and obtain the flow field

Mesh generation

A well-refined mesh improves accuracy while balancing computational cos

Numerical Techniques (Numerical Methods)

CFD problems are solved using _________________ and computations to derive accurate results.

Visualization

Results are visualized to comprehend fluid flow patterns and behavior within the system.

Validation

Comparing simulated results with experimental data to validate the accuracy of the model.

Fluid Flow

Movement of liquids and gases in response to forces

Fluid Flow

Governed by conservation of mass, momentum, and energy