Introduction• What Is Computational Aerodynamics ?

• The Role of Computational Aerodynamics

• Current status

• Guiding principles in using Computational Aerodynamics

• Typical steps to using Computational Aerodynamics

• Aerodynamics design and analysis

• A brief history of Computational Aerodynamics

• Typical method/code development cycle

• Typical elements in a CFD software system

• Overview of the following chapters

• What are you expected ?

What Is Computational Aerodynamics?• Theoretical Aerodynamics

– Analytical formulas provide insight on the role of key parameters

• airfoil theory (Kutta and Joukowsky )• Boundary layer (Prandtl )• Lifting line theories• Vortex street (Von Karman )• Linearized supersonic theory• Transonic area rule (Whitcomb)

• Experimental Aerodynamics

• Computational Aerodynamics– Numerical methods of governing

equations One of most important branch in the development advanced vehicles

One of most important branch in the development advanced vehicles

Comparison of Different Methods

• Truncation errors• Boundary condition problems• Computer costs

• No restriction to linearity• Complicated physics can be treated• Time evolution of flow can be obtained

Numerical

• Restricted to simple geometry and physics• Usually restricted to linear problems

• Clear, general information which is usually in formula form

Theoretical

• Equipment required• Scaling problems• Tunnel correction• Measurement difficulties• Operation costs

• Capable of being most realisticExperimental

DisadvantageAdvantageMethod

The Role of Computational Aerodynamics

• Vehicle Design– Development of optimum airfoils and wings for external

performance, and inlets, diffusers, and nozzles for internal performance and aero-propulsion integration

– Multidisciplinary Design Optimization (MDO)

The Role of Computational Aerodynamics

• Performance estimation– Estimation of the drag, lift, and moment of the vehicle

The Role of Computational Aerodynamics

• Definition of Loads for Structural Design

The Role of Computational Aerodynamics

• Definition of Aerodynamic Characteristics– Evaluation of stability, control, and handling characteristics (i.e.,

provide the math model for flight simulation)

The Role of Computational Aerodynamics

• Aeroelastic Analysis– flutter and divergence (requiring coupling with structural

analysis and control system design analysis methodology)

Current Status: A Review

PoorPoorPoorPoorFair Special Purpose Aircraft

PoorFairFairPoorFair FighterAircraft

PoorFairFairFair GoodTransportAircraft

PoorFairFairFair GoodResearchWing/Body

PoorPoorPoorFairGood2-D

MixedVortex

Separated

MixedVortex

Attached

VortexFlow

SeparatedFlow

AttachedFlow

Current Status: Case studies

• Inability to solve some problems– Subtle aspects of attached flow airfoil and wing aerodynamics

– Ability to compute deep stall characteristics of T-tail aircraft

– Use of nacelle strakes to improve high lift

– Fuselage strakes to improve high alpha directional stability

Current Status: Case studies

• YF-23– Euler analysis was

used quite successfully

Current Status: Challenges

• Using CFD at conceptual design level– Still time consuming !

– CFD is essentially an analysis tool !

• Drag prediction– Absolute values of drag are still difficult to

compute

Guiding Principles in Using CA

• Is the answer right ?

• Assuming the answer is correct, what is computational aerodynamics revealing about the physics of the flow field ?

Typical Steps to Using CA

• Start with the real flow around the aircraft• Create a physical model of the flowfield• Create the simplified mathematical model(s) to be solved.• Carry out the numerical solution.• Examine the results.• Interpret the sequence of physical model, mathematical model, and numerical

solution, together with the computed results to provide the final aerodynamic solution.

Design and Analysis• Classical Method

– repetitive analysis to design

• Inverse Methods

• Optimization-based Method

Optimal Airfoil Optimal Wing

DL/D= +70%Shock disappeared

Final design

Initial referenceShock at trailing edge

A Brief History of Computational Aerodynamics

A Brief History of Computational Aerodynamics

• 60’s:– Vortex lattice method (Sweden, Boeing, Grumman)– Panel method (Douglas)

• 70’s:– Solutions for linearized inviscid 3-D incompressible

flow problems – Two dimensional boundary layer methods – Development of solutions for 2-D transonic flow.– 3-D transonic small disturbance theory solutions

• 80’s:– Solutions for the full Euler equations– Grid generation became a discipline in its own right

Pressure contours for the Boeing 747-200Density contours for the MD-11

• 90’s:– Solutions for the Reynolds averaged Navier-

Stokes (RANS) equations

CFD calculation of Hermes Spacecraft, Mach 8 and 30 degrees angle of attack, black is free-stream, yellow-red the Mach number range from 3-6, and green-white the range from Mach number range from 3 to 0

CFD calculation of Hermes Spacecraft,

Comparison of Mach number distribution for in-

viscid (A) and viscous (B) flow

• 90’s:– Aerodynamic Shape Optimization

Density contours for a business jet

at M =2, angle of attack 2°Pressure distribution at 66 % wing span

Before Optimization

After Optimization

Pressure distribution at 66 % wing span

Density contours for a business jet

at M=0.8, angle of attack 2.3

Typical Method/Code Development Cycle

Typical Elements in a CFD Software

Overview of the following chapters

• The Governing Equations• Pre-CFD

– Panel method & Vortex lattice method– Aerodynamics analysis for airfoils and wings – Drag calculation methods

• CFD– The basics of CFD – Grid generation– Viscous effects– Transonic and high speed flows in aerodynamics.– Software

Overview of the following chapters

• The theory is described

• The fundamental assumptions is identified

• A numerical implementation is presented

• Examples illustrating the use of the method to understand aerodynamic design and analysis are given

In each case:

What are you expected ?

• You should be able to- formulate the problem

- select a method

- obtain a solution using software

• You should be able to use engineering judgment to decide if you have a valid engineering answer.

Homework 1• Pick an airfoil. Select any airfoil of your choice for which you can find

geometry, and the experimental pressure distributions, and force & moment data.– Plot the airfoil.– Plot the pressure distribution at one angle of attack.– Plot the force and moment data over a range of angles of attack.

Make sure to include the drag polar.– Describe airfoil and data source.

• Caution– You will use these data to compare with results from a computer

program, and this data set will play a role in several assignments, so pick an airfoil you can use all semester.

– Homework must be written in English.

An Example for Homework

• Example– the airfoil contour

Homework• Example

– Plot the force and moment data over a range of angles of attack at a specific Reynolds number