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Consistent Improvement of the Charging Technology of Audi TFSI Engines by CFD

K. Vehreschild, Audi AG Ingolstadt

4th European Automotive Simulation Conference - EASC 2009

► Introduction - Charging technology and CFD at Audi

► CFD modelling approach - Supercharger 3.0 TFSI

► Results - Transient flow phenomena

► Summary

Contents

EASC 20094th European Automotive Simulation Conference

Munich, Germany6-7 July 2009

1

Cooling

►Water jacket►Components (Thermostat)►Thermal management

Introduction

CFD areas in engine development

Oil►Oil circuit

►Crank caseventilation

Gas exchange► Intake / exhaust

manifold design►Gas dynamics►Valve lift curves►Boundary conditions

for 3D CFD / FEA

Engine-thermodynamics►Intake manifold►Exhaust manifold►Intake / exhaust ports►Charge motion flap

Car components►Air intake ducts, air filter

►Charge air ducts, intercooler

►Exhaust system

►Water / spray in inlet duct

►Deep wading►Cooling system

Exhaust gas after-treatment► Catalyst► O2 sensor► Secondary air injection

Combustion TFSI,TDI►Charge motion►Injection►Combustion►Oil dilution

Charging technology TFSI, TDI►Turbine, compressor►Supercharger

Introduction

V6 supercharged engine

► In August 2008 the 3.0 TFSI, a

supercharged V6 engine was

introduced

► For the new Audi S4 e.g., this high

power V6 replaces the naturally

aspirated 4.2 FSI (V8), reducing

weight and fuel consumption

EASC 20094th European Automotive Simulation Conference

Munich, Germany6-7 July 2009

2

Introduction

CFD covered topics of the supercharger device

Flow through supercharger

Introduction

Motivation for complex supercharger flow investigation

► Focus on basic flow phenomena rather than on detail optimization

► Airflow into and out of the supercharger

► Flow phenomena inside the supercharger

► Closer look at the compression

► If possible, acoustic excitation mechanisms

EASC 20094th European Automotive Simulation Conference

Munich, Germany6-7 July 2009

3

► Introduction - Charging technology and CFD at Audi

► CFD modelling approach - Supercharger 3.0 TFSI

► Results - Transient flow phenomena

► Summary

Contents

CFD modelling approach

Domains

► Modelling was done in collaboration

with Ansys

► Moving mesh domain inside the rotor

drillings, everything else is a static

tetrahedral mesh

► Housing can be exchanged easily

► Intercoolers modelled as porous media

Yellow: Moving mesh domainGrey: Stationary domainRed / Blue lines: Interface bordersBoxes: Intercoolers

EASC 20094th European Automotive Simulation Conference

Munich, Germany6-7 July 2009

4

RotorsRotors

CFD modelling approach

Moving mesh domain

► Rotors are more or less cogwheel-

shaped and longitudinally extruded

with a screw angle of 160°

► Meshing is basically 2D , made out of

several parameter based key meshes

► In between the key mesh positions

mesh morphing is used to interpolate

► 3d mesh is just a sequence of 2D

meshes in different angular rotor

positions

► A 1-1 interface is set in between the

rotors to connect both sides to control

the deformation

► No user subroutines, only CCL

CFD modelling approach

Moving mesh domain

Dividing surface with 1:1 connection

EASC 20094th European Automotive Simulation Conference

Munich, Germany6-7 July 2009

5

CFD modelling approach

Moving mesh domain

CFD modelling approach

CFD model setup

► Stationary boundary conditions at inlet and outlet

► Investigated operating points:

► 10000 rpm / full load (bypass throttle closed)

► 5625 rpm / full load (bypass throttle closed)

► 5625 rpm / part load (bypass throttle open)

► 4 revolutions of the rotors were calculated

► Rotation per time step: 0.6°

► Calculation time: approx. 4 days on 12 processors

EASC 20094th European Automotive Simulation Conference

Munich, Germany6-7 July 2009

6

► Introduction - Charging technology and CFD at Audi

► CFD modelling approach - Supercharger 3.0 TFSI

► Results - Transient flow phenomena

► Air inlet

► Pressure build up

► Outlet flow

► Summary

Contents

Results

Air Inlet

56%

44%49% 51%

InletOutlet

50% 50%50% 50%

InletOutlet

EASC 20094th European Automotive Simulation Conference

Munich, Germany6-7 July 2009

7

Results

Air inlet

Blow holes connect all chambers in the suction part

► Introduction - Charging technology and CFD at Audi

► CFD modelling approach - Supercharger 3.0 TFSI

► Results - Transient flow phenomena

► Air inlet

► Pressure build up

► Outlet flow

► Summary

Contents

EASC 20094th European Automotive Simulation Conference

Munich, Germany6-7 July 2009

8

Results

Pressure build up (full load)

0 90 180 270 360 450

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

0 90 180 270 360 450

0

10

20

30

40

50

60

70

80

90

100

Chamber Pressurech

am

be

r p

ress

ure

[b

ar]

rotor angle [°]

Inlet Area Chamber Volume Outlet Area Blow hole

re

lati

ve v

olu

me

/ a

rea

[%

]

rotor angle [°]

Upper blow holes connect chambers –continuous pressure rise

Results

Pressure build up (full load)S

tati

cp

ress

ure

EASC 20094th European Automotive Simulation Conference

Munich, Germany6-7 July 2009

9

► Introduction - Charging technology and CFD at Audi

► CFD modelling approach - Supercharger 3.0 TFSI

► Results - Transient flow phenomena

► Air inlet

► Pressure build up

► Outlet flow

► Summary

Contents

Results

Outlet flow

Part load: medium mass flow

► Strong axial flow direction

► forced upwards by left wall

► Zigzag flow

EASC 20094th European Automotive Simulation Conference

Munich, Germany6-7 July 2009

10

Results

Outlet flow

Full load: High mass flow

► Vortices at triangle top

caused by outlet pocket

► High mass flow forces air to

go upwards instead of axial

► No apparent zigzag flow, but

left-right direction change

► Introduction - Charging technology and CFD at Audi

► CFD modelling approach - Supercharger 3.0 TFSI

► Results - Transient flow phenomena

► Air inlet

► pressure build up

► Outlet flow

► Summary

Contents

EASC 20094th European Automotive Simulation Conference

Munich, Germany6-7 July 2009

11

Summary

► The transient simulation of the 3.0 TFSI supercharger module is one sophisticated

example for CFD applications in the development of charging technology at Audi.

► Besides this complex moving mesh simulation many other "standard" CFD topics

were applied during the development of the module.

► The key aspects of this consistent CFD improvement of charging technology in

general are:

► "tailored CFD process“: optimum definition of CFD topics for each separate

development project, with respects to development targets, time-scales, etc.

► Development of new methods "on-the-fly" : continuous improvement of CFD

efficiency, accuracy and portfolio directly in the process chain - according to the

necessities of the technology development

► Development expertise of CFD experts : despite the fact that CFD experts have

to be CFD experts, nowadays they also have to be experienced developers

EASC 20094th European Automotive Simulation Conference

Munich, Germany6-7 July 2009

12