the thermal mechanical fatigue (tmf) analysis for … thermal mechanical fatigue (tmf) analysis for...

The Thermal Mechanical Fatigue (TMF) Analysis for an Exhaust Manifold – An Application of File Based Coupling

Shao-Chin FanEngine Design Division

HAITEC / CEC

STAR Global Conference 2015, San Diego March 16-182

CONTENTS

INTRODUCTION

WORK FLOW

BOUNDARY CONDITIONS

• GAS SIDE

• COOLANT SIDE

HEAT TRANSFER

• STEADY STATE

• TRANSIENT

RESULT

CONCLUSIONS


INTRODUCTION

3

With stringent emission and fuel economic regulation, downsizing and

upgraded performance will be the recent trend in IC engine design.

Higher performance will introduce high exhaust temperature in

exhaust system, which was designed to withstand high temperature,

big vibration and stress from leakage-proof seal of tightened-bolt.

A thermal with mechanical coupling analysis was applied in exhaust

system to predict initiated cracks of exhaust manifold.


CFD (STAR-CCM+)Exhaust system

CFD (STAR-CCM+)Water jacket

Temperature & HTC (STAR-CCM+)Mapping

FEM (Abaqus)Thermal Structure Anaylsis

FEM (Abaqus)Transient heat transfer

1D Cycle simulationB.C. for CFD

Preparing Boundary Conditions

Thermal shock pattern

Load

Speed

Coolant

WORK FLOW


Full Load Motored Idle

215 sec 345 sec 495 sec

DESIGN SCENARIO

LoadSpeedCoolant

Thermal shock pattern


Gas side boundary conditions: 1D cycle simulation to calculate full load, motored and idle boundary conditions for CFD model.

The 1D cycle simulation model was verified with test data.

3D CFD simulation to calculate temperature and HTC (heat transfer coefficient) of ports, exhaust

manifold, turbo and catalyst.

Mass Flow

0

0.05

0.1

0.15

0.2

0.25

0.3

Ma

ssF

low

(kg

/s)

0 360 720 1080 1440 1800 2160

CRANKANGLE (deg)

Temperature

500

600

700

800

900

1000

1100

1200

1300

1400

1500

Te

mp

era

ture

(K

)

0 360 720 1080 1440 1800 2160

CRANKANGLE (deg)

Temperature

1090

1100

1110

1120

1130

1140

1150

1160

1170

1180

Te

mp

era

ture

(K

)

0 90 180 270 360 450 540 630 720

CRANKANGLE (deg)

Pressure

148000

149000

150000

151000

152000

153000

154000

155000

Pre

ssu

re (

Pa

)0 90 180 270 360 450 540 630 720

CRANKANGLE (deg)

BOUNDARY CONDITIONS

Wall: constant temperature

Outlet

Inlet


Coolant side boundary conditions: 3D CFD to calculate temperature and HTC of cylinder head.

The boundary conditions are test data.

Mass flow rate

Pressure outlet

Mass flow rate inlet

BOUNDARY CONDITIONS

Wall: constant temperature


Mesh and Physics models

• Polyhedral mesh

• 765,363 cells

• Gradients

• Ideal gas

• Implicit unsteady

• K-Epsilon turbulence

• Multi-Component gas

• Non-reacting

• Realizable K-Epsilon two-layer

• Reynolds-Averaged Navier-Stokes

• Segregated flow

• Segregated fluid temperature

• Segregated species

• Three dimensional

• Turbulent

• Two-Layer all y+ wall treatment

• Polyhedral mesh

• 729,533 cells

• Gradients

• Constant density

• K-Epsilon turbulence

• Liquid

• Realizable K-Epsilon two-layer

• Reynolds-Averaged Navier-Stokes

• Segregated flow

• Segregated fluid temperature

• Steady

• Three dimensional

• Turbulent

• Two-Layer all y+ wall treatment


Temperature distribution on the wall of exhaust manifold

TRANSIENT RESULT


Data Mapping: Import structure model and define the surface map data.

Local Heat Transfer Coefficient and Local Heat Transfer Reference Temperature were mapped to

structure model surfaces.

The gas side CFD calculations are transient, only

averaged 1 engine cycle data will be exported.

1 engine cycle = 720 deg crank angle

BOUNDARY CONDITIONS


BOUNDARY CONDITIONS

Gas side: The averaged Local Heat Transfer Coefficient and Local Heat Transfer Reference Temperature were

mapped to FEM model.

Heat Transfer Coefficient

Temperature


BOUNDARY CONDITIONS

Coolant side: The Local Heat Transfer Coefficient and Local Heat Transfer Reference Temperature were mapped to

FEM model.

Heat Transfer Coefficient

Temperature


HEAT TRANSFER

Steady state heat transfer results – Steady state



Steady state heat transfer results – Steady state vs. transient Full load: due to thermal inertia, areas with higher wall thickness are in the transient analysis cooler in

comparison to the temperatures calculated in steady state analysis.

Motored/Idle: due to thermal inertia opposite effect occur.

HEAT TRANSFER


Steady state Steady state Steady state

Transient 2nd cycle Transient 2nd cycle Transient 2nd cycle


TRANSIENT ANIMATION


STRUCTURE RESULTS

Areas with equivalent plastic strain range ΔPEEQ Locations with highest equivalent plastic strain range are concentrated in the area of the flange

towards the turbocharger.

These locations show very good correlation with hardware test bed results.


Increase the transition

radius as much as

possible.

Reduce this “saddle” shaped

region (make it almost flat) in

order to reduce the stress

concentration.

Increase transition radius from

dividing wall and reshape the ports

in order to achieve bigger radius.

DESIGN OPTIMIZATION


CONCLUSIONS

The work flow coupling with 1D cycle simulation, 3D CFD and FEM

analysis is a reliable method to predict the thermal stress of exhaust

manifolds.

STAR-CCM+® can calculate accurate temperature boundary

conditions for structure FEM model.

Designer can modify the critical locations of the exhaust manifold base

on the simulation results. And verify the new design by simulation

without prototype and test cost.


Thank you !

the thermal mechanical fatigue (tmf) analysis for … thermal mechanical fatigue (tmf) analysis for...

Documents