assignment a2: airfoil aerodynamics · assignment a2: airfoil aerodynamics version 1 18 september...

AJNM_JFTA005: CFD in Vehicle Engineering Széchenyi University Instructor: D. Feszty Audi Hungaria Dept. of Whole Vehicle Development

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Assignment A2:

Airfoil Aerodynamics

Version 1 18 September 2018

1. Introduction

The purpose of this assignment is to make students to practice running Computational Fluid

Dynamics simulation for a simple yet practical case in race car engineering.

The basic idea is to examine whether it is worth to employ wings on a Formula SAE racecar

(Fig. 1). These cars are designed, built and raced by university students every year around the

globe. The cars have an empty weight around 160 – 220 kg and are equipped with either a 50

HP internal combustion engine or an electric motor. Although their top speed is usually in

excess of 150 km/h, for safety reasons the tracks are assembled in a way so that their top

speed in a straight does not exceed about 80-90 km/h. The typical corner speeds are around

40-60 km/h.

Fig. 1. The Arrabona Racing Team’s ART02 race car from 2015. This is the race car designed and built by students

at the Audi Department of Vehicle Engineering at Szechenyi University in Győr, Hungary.

Your task is to calculate the lift (in our case: the downforce) of an airfoil at the typical corner

speeds, i.e. 50 km/h. The task is to simulate an airfoil in isolation and in classical aerodynamic

configuration, i.e. with lift pointing upwards and in pure freestream (far away from the ground or

any other objects).


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2. Objectives

Goals: - Generate the curves of aerodynamic characteristics for the FX 63-137 airfoil

via CFD and compare them to experiment

- The aerodynamic curves consist of:

o lift curve (i.e. cl – curve)

o drag polar (i.e. cl – cd curve)

o pitching moment curve (i.e. cm – curve)

- for generating the above curves, use a 2 degrees increment for the Angle of

Attack, i.e. run eight (8) steady-state CFD simulations at 0, 2, 4, 6, 8, 10, 12,

14 degrees and extract the above plots from these results.

Fig. 2. Test case for TASK 1. Note: dynamic viscosity of air at sea-level conditions is

1.81×10−5

kg/(m·s).

Specific step-by-step tasks:

- understand the test case (see Fig. 2 below)

- determine Re and Mach numbers and decide about the nature of flow

(laminar/turbulent or compressible/incompressible)


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- enter the airfoil coordinates from App. A into an electronic format suitable to

be read in into ANSYS-Fluent for the geometry generation (see the airfoil

Tutorial link below on what format is suitable)

- Based on the Re number, select the appropriate experimental airfoil data,

and enter them (from the provided tables) into a suitable electronic format for

future evaluation.

- Perform CFD simulation by:

o generate computational domain

o setup the boundary conditions

o generate mesh

o setup initial conditions

o make notes for yourself about the numerical method (i.e. key features

of the CFD code used and the specific numerical parameters)

o perform verification (grid dependence tests, with at a medium AOA,

for example 4 degrees)

o run the CFD simulations at 2, 4, 6, 8, 10, 12, 14 degrees AOA

Note: beyond stall (about 10-12 deg) the flow might become

unsteady

Solving an unsteady flow with a steady solver might exhibit

itself in a lack convergence

o post-process the results, i.e. extract:

velocity magnitude contour plots at all eight AOA’s

velocity vector plots at all eight AOA’s

pressure contour plots at all eight AOA’s

cP plots at all eight AOA’s (these are equivalent to the v/v∞

plots shown on p. 7 in App. A)

total lift force (in N), drag force (in N) and pitching moment (in

Nm) at all eight AOA’s

lift coefficient (cl), drag coefficient (cd) and pitching moment

coefficient (cm) at all eight AOA’s

o validate the CFD results (i.e. compare them to experimental results)

plot the CFD results as dots over the experimental curves

discuss how good or bad the comparison is to experiment

- submit a Technical Report describing all the above according to the format

shown in Sec. 3.

Note: Elements of this task will be fully explained in the Tutorial Sessions.

Theoretical background on airfoils as well as detailed instructions and help on

how to setup, run and analyze the CFD simulation of an airfoil at one specific

AOA is provided in the following online tutorial:

https://www.youtube.com/watch?v=tZ1ippYSTOI&feature=youtu.be

Students should be able to complete Assignment A2 with ease if they attend the

Tutorial Sessions.

https://www.youtube.com/watch?v=tZ1ippYSTOI&feature=youtu.be


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3. Deliverables:

The deliverable is a Technical Report written according to the international engineering

and scientific standards. The structure and format of Technical Reports in the Western

world is rather rigid and therefore easy to learn (once learned, it can be reused for the

rest of the students career). In general, a Technical Report should have sufficient

information so that the reader can repeat the work we have done. It is important to

describe the reasons of the choices we have made, i.e. not just WHAT have we

done, but also WHY? (For example, why did we choose the concrete boundary

conditions we applied, etc.)

A Technical Report on CFD has the following sections:

- Title, Author, Institution and Date

- Abstract (max. 10-15 lines long summary of key contents of paper)

- Nomenclature (list of symbols)

- Introduction

o Normally 4 paragraphs:

Intro into the problem (why are boundary layers important?)

Review of the State-of-the-art

Why do we do this work?

What are the objectives of this paper?

- Test Case:

o Flow conditions (also calculate Reynolds number and Mach number

so that you can decide whether the flow is laminar/turbulent or

compressible/incompressible: comment on these features), test

geometry, provide a figure

- Computational Domain

o How large is it? How many blocks? What layout and why? How far are

the boundaries from the object and why? Show sketch with key

dimensions.

- Boundary and Initial Conditions

o Describe the Boundary and Initial conditions chosen. Show them on

the above sketch or a new one.

- Mesh generation

o What type of mesh is used? (structured, unstructured?) How was the

mesh generated (manually or automatically)? Is the mesh 2D or 3D?

How many cells in each direction? What was the first spacing at the

wall. How many cells and nodes are in the mesh? Show the mesh in a

figure.

- Numerical Method

o Which code (software) is used? What type of equations does it solve?

What type of discretization does it use (Finite Element, Finite Volume,

Finite Difference, Spectral Method?). What is the order of spatial and


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time discretization (1st, 2nd or higher?). What numerical method does it

use to solve the equations (explicit or implicit)? What convergence

levels were set? Did you choose to run inviscid, laminar, turbulent or

transitional simulations? Did we run steady or unsteady simulations?

If turbulent, then what turbulent models are available and which one

did you choose and why? What was the freestream turbulent intensity

and why?

- Verification of results:

o The goal is to verify that the numerical simulations are independent of

the numerical parameter we have chosen, i.e. they are credible

o Perform a grid dependence and/or time step dependence test (the

latter one only if time step was a parameter chosen by us)

o What was the coarse, medium and fine mesh density?

o Show graph of a suitable parameter (for example, shear stress along

wall, or velocity profile – you decide) with the 3 mesh densities

o Make a conclusion that which mesh is suitable for further simulations.

- Validation of results:

o Means comparison with the correct results, i.e. analytical or

experimental results.

o Say that which mesh results (from above) are you going to compare

o Describe briefly that what do you compare to (theory or experiment or

both)

o Show graphs of a suitably chosen parameter to compare them

- Results and Discussions:

o Now that we are confident in the correctness and accuracy of the CFD

simulations, we can start to analyze the results.

o Show the results asked in the specific tasks of the Assignement text.

o Comment on the key physical features of them

- Conclusions:

o Note: this is not a summary! (the Abstract is there for a summary),

but…

o A list of key conclusions, with recommendations for future work

- Acknowledgements:

o Thank here to anyone you wish (usually to sponsoring agencies) or to

a person who is not listed among the authors but helped a lot in

completing this paper

- References:

o List here all literature sources (books, journal papers, conference

papers, weblinks) you took information from BUT..

o You must refer to these reference numbers in the text…

o You can only list references here, which you actually refer to in the

text.

Deadline for submission: Tuesday, 16 October 2018, 16:00


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Form of submission: electronically, as well as a printed report in black and white (this is

the preferred format in scientific literature). As such, it is advised

to save figures from CFD or Excel right away in the format, which

in black and white will be clear to the reader.

Language of submission: English

Location of submission: Department of Whole Vehicle Engineering (Járműfejlesztési

Tanszék), collection boxes inside the doors


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APPENDIX A: AIRFOIL DATA for FX 63-137

(Source: Selig, M.S., McGranahan, B.D., “Wind Tunnel Aerodynamic tests for Six Airfoils for Use on Small Wind

Turbines, Report no. NREL/SR-500-34515, University of Illinois at Urbana Champaign, IL, U.S.A., 2003.)

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Airfoil coordinates


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Airfoil data for FX 63-137 airfoil: Summary of lift and drag data plots for all Reynolds numbers


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Airfoil data for FX 63-137 airfoil:

Lift and moment data plots for Re = 100 000 and 150 000

solid symbols: increasing AOA empty symbols: decreasing AOA


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Lift and moment data plots for Re = 200 000 and 350 000



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Lift and moment data plots for Re = 500 000



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Airfoil data for FX 63-137 airfoil: Tabulated lift and drag data for all Reynolds numbers


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Airfoil data for FX 63-137 airfoil: Tabulated lift and moment data for all Reynolds numbers


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Airfoil data for FX 63-137 airfoil: Tabulated lift and moment data for all Reynolds numbers (contd.)

assignment a2: airfoil aerodynamics · assignment a2: airfoil aerodynamics version 1 18 september...

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