07 aerodynamics gfr fsg workshop beg abstatt 20111029

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  Aero Design Process

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Name: Michael Wax

Task: Technical Director 

Major: 3rd year Mechanical Engineering Student

 About me

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 Agenda

1. Introduction 

2.  Approach

3.  Aerodynamics design process

Lap time Simulation

CFD Simulation

Testing

4. Results

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Customer requirements

Modular Design

Low Mass

High Downforce

Low Drag

Balanced center of pressure

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Designprocess Aerodynamic

Laptime Simulation

CFD Simulation

Manufacturing

Physical Testing

29.10.2011Management 8

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Laptime Simulation

Definition of raw concept

Do we want an aerodynamic package ?

Evaluate the most sensitive parameters

Calculation of qualitative results

Performance improvement in percent

Analysis of best vehicle concept for FSAE competitions

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What is a lapsim

= ∗a = ∗ −   =²

  = ∗  

• comprehensive computer simulation

• allows chassis designers and race engineers toinvestigate the effects of car, driver, tire and

environmental variables on performance on a

race course.

You basically add the times you need to pass a defined part of a racetrack in a certain race condition

(Engine RPM, downforce, tire coefficient…) 

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Laptime simulation

= ∗a = ∗ −   =²

  = ∗  

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Laptime Simulation

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The tire model

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The aerodynamic model

• Aerodynamics drag increases quadratically with speed

  =

∗ ∗ ∗ ∗ ² 

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Sensitivity results

Downforce is the most sensitive vehicle

parameter

Vehicle weight as second most sensitive factor is less

important by a factor of 5

Drag on an aero-car the 3rd most sensitive

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Performance factors

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Concept comparison 4 cylinder car

Most common

Powerful

Relatively simple

4 cylinder car with wings

Powerful

Outright fastest

Most complex

Poor fuel economy

Single cylinder car

Most simple

Most fuel efficient

Lacking in outright

speed

Single cylinder car with

wings 

Mix of speed and simplicity

Untested and unique concept

More complex than singleconcept

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Benchmark

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CFD Simulation

Evaluation of fine concept

Calculation of drag / lift coefficient

Iterate for the center of pressure

Calculate a rough number for downforce and drag

Ensure sufficient cooling under bad airflow conditions

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CFD Simulation

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CFD Simulation

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CFD Simulations – Boundary Conditions

3-6 Mio. cells (symmetry-plane)

k- turbulence model

Reynolds Averaged Navier Stokes

Rolling road / rolling tires

CFD Parameter 

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Fine concept

2 part front wing 

Best downforce by feasible manufacturing complexity

Sufficient supply of radiators 

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Fine concept

2 part front wing 

Best downforce by feasible manufacturing complexity

Sufficient supply of radiators 

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Fine concept

2 part rear wing

Simulation complexity feasible

Manufacturing still reasonable

Satisfying downforce results

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Underbody Diffuser

2 Venturi Tunnels 

Side Gurney Flaps, Tunnel fences, Rear Gurney Flaps

Fine concept

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Rigid Mounting and solid structure

Easy and fast to replicate

High quality surface

Easy to be implemented to the car 

Sustain high ability to maintain the car 

Manufacturing Concept

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Manufacturing

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Testing

Yarn Tuft testing to visualize stalling

Coast Down Tests:

Car will be slowed down from 100km/h only be essential resistance

forces (rolling resistance and drag)

Drag and downforce can be measured in pull and pushrods

Back to back Tests:

Standardized test track for laptime comparison

Evaluation of load distribution, package refinement… 

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Coast down testing data

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CFD vs. Testing results

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Conclusion - Outlook

Improvement on performance could be clearly seen in the dynamicevents

A ~ 15% higher fuel consumption didn‘t hurt us in fuel efficiency.

Further development is focused on validation and weigt

decreasement

eCar with an aero package would not cause a decrease in

acceleration performance by a limited power output

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Thank you for your attention

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Laptime Simulation

Corner speeds are converged

Acceleration and Braking are transisioning

Both longitudinal accelerations are added

29.10.2011Management 36

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