Practica 4. Dinmica de Fluidos Computacionales Instituto Politcnico Nacional

Prof. Luis Sergio Mrquez Jaime

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Aerodynamic Aircraft Geometry Design

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The aim of this laboratory work is to generate a new aircraft geometry design by means of

modifying an existing generic aircraft geometry file. Each team will choose a particular

type of aircraft different to the other laboratory teams. The generic aircraft files contain

the dimensions and shapes of the different parts. i.e. fuselage, wings, etc. The

computational tools for this practice are Sumo, Matlab and Wordpad. And the smx files.

The available generic geometries to choose from are shown on figure 1.

Figure 1. Available generic geometries, (a) single engine utralight, (b) a light executive

jet, (c) twin engine utility aircraft, (d) a delta wing interceptor, (e) a sailplane and (f) a

four engine widebody.

Geometry files will be handed out in .smx format. This file contains information about the

airfoils used to create a wing, cross-sections used to create the fuselage, and similar data

that is necessary in order to define the engines, tail geometry, etc. and Typically this is

what a part of an .smx file looks like:

0.577351 -0.866025

1 -0.5

1.1547 -6.12303e-017

1 0.5

0.577351 0.866025

1.41406e-016 1

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0.607419 -0.836536

1 -0.445249

1.12014 0.034712

0.975445 0.499462

0.580461 0.858263

3.28525e-016 1

]]>

0.577351 -0.866025

1 -0.5

1.1547 -6.12323e-017

1 0.5

0.577351 0.866025

1.4141e-016 1

]]>

0.575229 -0.844171

0.967652 -0.4848

1.15052 0.0177901

1 0.532551

0.74537 0.803286

0.426806 1

1.40171e-016 1.02773

]]>

Note that this is only a part of a much larger file. In order to modify the geometrical

characteristics of the aircraft first you will backup the original smx file, this will be useful

later on for comparisons. Now that you have a backup of the original file you can rename

the file as: IPN-5AM1-executive_jet.smx (just to name an example). After this you can

proceed to open the file using wordpad or an equivalent software for other operating

systems. When you start viewing the file you will encounter that it is possible to change

the cross-sections and side sections of the fuselage, or change the dimensions of the

wings, or the airfoils included in the wing. For example for the wing you will see

something like this:

0.982295 0.00274755

0.963393 0.00568075

0.942936 0.00885525

0.920797 0.0122909

0.896836 0.0160091

0.870905 0.0200332

0.842841 0.0243882

0.812469 0.0291018

0.779588 0.0341323

0.743973 0.0393742

0.705385 0.0447285

0.663559 0.0500389

0.61821 0.0550713

0.569024 0.0594233

0.515687 0.0626967

0.457885 0.0644485

0.397464 0.0643604

0.340801 0.0626841

0.291757 0.0600639

0.249322 0.0569096

0.21262 0.0534559

0.180884 0.0498687

0.153452 0.0462589

0.129747 0.0426982

0.109272 0.0392381

0.0915935 0.0359081

0.0763411 0.0327112

0.063193 0.029649

0.0518475 0.026813

0.042046 0.0242523

0.0335971 0.0218812

0.0263481 0.0195948

0.0201674 0.0173263

0.013939 0.0145741

0.00797842 0.0112018

0.00269293 0.00687394

-4.22246e-005 0.000746563

0.00306013 -0.0051263

0.00892471 -0.00862786

0.0153268 -0.0110602

0.0218884 -0.0128602

0.0282779 -0.0142142

0.0357115 -0.0154791

0.0443275 -0.0167222

0.0542888 -0.0180507

0.0657921 -0.0195542

0.0790853 -0.0211796

0.0944564 -0.0228298

0.112223 -0.0245053

0.132752 -0.02621

0.156469 -0.0279266

0.183864 -0.0296245

0.215505 -0.0312646

0.252043 -0.0327856

0.294235 -0.0340952

0.342947 -0.035069

0.399182 -0.0354631

0.459118 -0.0349108

0.516463 -0.0332857

0.569419 -0.0308652

0.61833 -0.0281678

0.663515 -0.0255156

0.705254 -0.0228436

0.74381 -0.0201895

0.779427 -0.0176015

0.81233 -0.0151139

0.842723 -0.0126861

0.870805 -0.0104208

0.896752 -0.00832789

0.920728 -0.00639403

0.942881 -0.00460716

0.963351 -0.0029561

0.982265 -0.00143053

0.99974 -2.09356e-005

A plot of this data can be seen in Figure 2. So what the student has to do now is change

the x,z points in these column vectors.

Figure 2. Points defining an airfoil used to generate the wing volume (for the executive

jet)

In a similar way other properties of the aircraft can be modified. For example for the

fuselage and the fairing definition we have these kind of profiles shown in Figure 3:

Figure 3. Skeletons of the fuselage and the fairing.

And similarly for the rest of the components, i.e. the fin, the left and right nacelle, the

pylon, the stabilizer and other wing airfoils. So the work now is to modify the aircraft

shape, and in the report you will have to:

1. Decide which changes you will make and then justify why you made the changes,

what advantages could the changes give? From an aerodynamic point of view, and

or utility point of view. i.e. changes that reduce drag, or to have more lift and grow

the fuselage for more passenger capacity, etc. Use your imagination, thickness,

lengths, shapes, cross-sections can be modified! In order to render the geometry

use the SUMO tool.

Figure 4. Original 4 engine plane (left) and Modified 4 engine plane similar to the

Airbus A300-600ST Beluga (right).

2. An explanation of how these changes where made, using plots for better

understanding of the original airfoil vs the modified airfoil. Since the last laboratory

works no matlab plots have been made, only ugly plots, here is the matlab code for

this type of plots:

load airfoil_pts.txt scatter(airfoil_pts(:,1),airfoil_pts(:,2),'r*') axis([-0.2 1.2 -0.2 0.2]); xlabel('x'); ylabel('y');

where airfoil_pts.txt is a 2 column data file generated from the smx file.

Figure 5. left. Original airfoil right. Modified airfoil for generating the original and

modified wing.

3. The report should be written in a scientific format for a report, a good example can

be found in: http://fun3d.larc.nasa.gov/papers/MDO7.pdf . In grosso modo, a

good title, a summary, nomenclature,introduction, Shape change, results and

conclusions. A REMINDER: PLOT DATA IN MATLAB!!!!

4. One thing to look for is that the geometry has smooth curves, this is useful if later

if we wish to analize the geometry using numerical methods like potential flow

solvers or CFD for a next laboratory work.

Figure 6. Aircraft discretization for CFD simulations.

Instructions made by: Luis Sergio Marquez Jaime