EAEC 2011 Presentation - Ruben Jacob D

7/31/2019 EAEC 2011 Presentation - Ruben Jacob D

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Establishment methodologies for CFDanalysis using NX, and proposals forredesign the carbody for competitionShell Eco-marathon

13th EAEC European Automotive Congress

Industrial Designer, University of Valp

Master in Design, Management andProducts

Master CAD CAM CIM

PhD Candidate in Design, Manufactu

of Industrials ProjectsPolytechnic University of Valencia, Spa


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1. Theoretical Framework

2. Goals and research structure.

3. Stablishment of procedures for CFD analysis.

4. Redesign proposals and outcomes achieved

5. Final considerations


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Introduction and theoretical framework


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Aerodynamics is the branch of fluid mechanicsthat studies the actions that appear on solidbodies when exist a relative motion betweenthem and the gaseous fluid that surroundsthem.

Aim: to improve the capacity of the vehicles topenetrate the air with the smaller possibleeffort...

Through the modification of the forms and

surfaces.


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The method of the finite elements consists oftaking a body and dividing it in smallelements that together correspond with theoriginal body in their geometry.(discretization)

For a smallest element, bettermatch with the real geometry and moreaccurate results


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the forces between them areregistered and operating in the contact point.

surface following, around

the solid, maintaining close contact between

all "points"

The forces in this system must be considered in

all points of the solid surface, actually almost

infinite, determined by the size of molecules of

the fluid.


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Due of complexity of effects of air over vehiclethis relations between forces it are made

depend of only one variable (coefficient)

Cx coefficient it is obtained from a specific

formula with a unique unknown value: "force in

X (Fx), obtained through CFD analysis or wind

tunnel experiments


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research approach and empirical work.


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1. Perform a proper documentation of theproceedings.

2. Establish a clear and strong method for theproper conduct of this type of analysis in NX

4. Define the scope and actual capacity toperform CFD analysis of NX platform regardingits accuracy and usability, and compared tootherssoftware applications.


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method followed for the conduct of CFD analysis


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needed to perform the necessary iterationsand the calculation of equations for thesolution according to the conditions imposed.

once the calculation of the solution isover, you get the graphical presentation ofresults, can be seen the flow using

streamlines, colored fields and scales, andnumerical data


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Proposals of modifications and results.


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Velocity of Fluid/vehicle: 30 km/h

Turbulence model: k- (Kepsilon)

Mesh of vehicle: type subdivision, element size 25mm over STEP model, 2D mesh with element typeTRI3 Thin Shell.

Solution: Flow/stationary state.

Solution units: Meter/Newton. Flow Mesh: 0,06-0,03-0,01

Tunnel model dimension 6000 mm lenght, 2000high y 3000 width.

Accuracy on previous test analysis: 0,01 (sphere)


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x-comp y-comp z-comp |R|

------------------------------------------------------------------

GLOBAL FLOW SURFACE

CG location (m): 1.371E+00 2.511E-05 2.856E-02

CP location (m): 1.160E+00 3.358E-03 4.762E-01

Total Force (N): 4.365E+00 1 .159E-01 2 .053E+0 0 4.825E+ 00

Total Torque (N-m): -2.070E-04 2.388E+00 -1.787E-02 2.388E+00

Shear Force (N): 1.046E+00 6 .276E-04 6 .139E-0 3 1.046E +00

Shear Torque (N-m): 2.373E-05 3.214E-02 -6.243E-04 3.214E-02

Press ure Force (N): 3.319E+00 1.152E-01 2.047E+00 3.902E+00

Pressure Torque (N-m): -2.307E-04 2.355E+00 -1.725E-02 2.355E+00

Extract of file *.log from NX analysis of finalvehicle 3D model

Fx= 3,319 Newtons


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Air density= 1,204 kg/m3

Velocity=30 k 50 km/h= 9 14 m/s

Projected frontal area: 0,304 m2

Projected lateral area: 1,284 m2


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1 0.316 m2 3.991 N

2 0.305 m2 4.151 N

3 0.303 m2 3.968 N

4 0.307 m2 3.497 N

5 0.306 m2 3.463 N

6 0.304 m2 3.319 N


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conclusions of research and empirical work

25


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6.00 12.01 2,988 5,479

6.00 12,11 3,200 5,073

6.00 19.56 3,194 5,042

6.00 20.14 3,268 4,960

6.00 20.08 3,381 5,067

6.00 20.37 3,413 5,111

6.00 21.42 3,378 5,085

6.00 21.45 3,354 5,041

6.00 21.00 3,377 5,086

6.00 22.15 3,382 5,102

Fixed conditions: Type of Fluid meshing element is relative, values 0.06 for the fluidand 0.03 for the limits, 0.015 for the fluid in contact with the vehicle. Analysis at 30

km/h Turbulence Mod. k-

0

5

10

15

20

25

10 60 110

Valorestiempos-Fx-Fuerzatotal

Tamao de elemento mallado vehculo

According to the fidthe mesh representationthe original form (mesh been considered the va20 mm as the acceptabsizeof either element medivision or cobble (affect the result)


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0.30 1.00 5,077 6,457

1.00 2.54 4,385 6,071

2.00 6.42 3,867 5,637

4.00 8.09 3,584 5,234

6.00 21.45 3,354 5,041

10.00 26.49 3,298 4,927

The optimal calculationsize-accuracy relation ivalue 0.12 (0.04 tolimits and the area inthe vehicle).


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0.30 1.09 4.635 6.047

1.00 2.07 4.336 5.732

3.00 3.05 4.310 5,721

2.30 8.48 3.794 5,294

4.00 16.11 3,480 5,074

5.00 19.22 3,224 4,801

For type of e"absolute" values 1chosen as the opt imal relat ionshipprecision and calculatio65-35 as optimal val

want more accuraexpense of increased co


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NX are suitable and adequate for thedevelopment of these tests.

The software provides accurate and reliableresults, consistent with one another whenexternal conditions change.

The way to show numerical data canbe improved to be more understandable.

CFD simulations carried out have proveduseful in the development process andoptimize aerodynamics of the vehicle.
http://www.adventuresofgreg.com/images/02.jpg


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There is no informationabout the implementation of "Rolling-road" by NX.

Confirm the trends discovered and generatespecific documentation for NX, no longer

exists.

The type of mesh element must be studied ina similar way to define its impact ontheaccuracy and computational time.

The boundary layer should be integrated into

the analysis.
http://www.adventuresofgreg.com/images/02.jpg


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Establishment methodologies for CFD analysis usingNX, and proposals for redesign the carbody for

competition Shell Eco-marathon

Rubn Jacob D. - Vicente Colomer R.

Documents

EAEC 2011 Presentation - Ruben Jacob D