virtual temperature cycle test (tct) for validation of...

MAHLE Behr GmbH & Co. KG © MAHLE MAHLE Behr © MAHLE

G. Apostolopoulos, R. Stauch, C. Marola, F. Schmidt, J. Schlottke, W. KühnelMAHLE Behr GmbH & Co. KG, Stuttgart, Germany

Virtual Temperature Cycle Test (TCT) for validation ofindirect Charge Air Coolers and Exhaust Gas Recirculation Coolers

STAR Global Conference 2014Vienna, March 17-19

MAHLE Behr, TDR4, Georgios Apostolopoulos, 18.03.20142 © MAHLE

Introduction

MAHLE Behr – System Partner for Thermal Management

BUSINESS UNITS

Thermal Management

= MAHLE Behr

Engine Systems andComponents

Filtration and Engine Peripherals

AftermarketIndustry

Sales andApplication Engineering

Advanced Engineering

Air Conditioning Engine Cooling

As a leading global development partner for the automotive and engine industry, MAHLE is working on innovative products for new generations of vehicles and mobility concepts.

As of October 2013, the Behr Group - one of the leading OEMs worldwide in vehicle air conditioning and engine cooling - is integrated into the MAHLE Group as the Thermal Management business unit.


CFD simulation @ MAHLE Behr

Engine cooling applications

ComponentsOptimization of pressure loss & massflow distribution

Cooling ModulesInteraction of heat exchangers, fan & blockage

Underhood SimulationPrediction of available cooling air, flow and temperature distribution for components

Fins, TubesTrade Off for heat transfer & pressure loss


Simulation workflow

What is an iCAC/EGR?

Charge air inlet

Charge air outlet Charge air cooling enables to increase the amount of air available to the engine for combustion. Lower fuel consumption, reducing emissions, increasing power

Indirect charge air cooling (iCAC) offers benefits in terms of package size and dynamic response and will play an increasingly important role in the future.

The combustion temperature in the engine can be lowered by the cooling of recirculating exhaust gas

The lower combustion temperature reduces the formation of nitrogen oxides (NOx)

In gasoline engines, cooled EGR will be implemented in the coming years to reduce fuel consumption

Coolant inlets

Coolant outlets


Simulation workflow

TCT: Common standard testing procedure for heat exchangers in the automotive industry for durability performance under thermal stress load

High temperature gradients induce high thermal stress loads

Heat exchanger is exposed to a cyclic variation of gas temperature and gas mass flow

Defined profiles for temperature and mass flow

A predefined number of cycles needs to be reached before the component fails

MAHLE Behr is performing TCT simulations for over 10 years

0 90 180 270 360t [s]

Tem

pera

ture

s/C

oolin

g A

ir M

ass

Flow

Virtual Temperature Cycle Test (TCT)


Simulation workflow

Workflow of numerical simulation of TCT

Mapping of temperature data

Thermal stress data

Lifetime predicition andmost damaged position

CFD simulation

FEA simulation

Fatigue simulation

Turbulent flow for both fluids Conjugate heat transfer

to and from all solids Heat conduction in solids Dual-cell HX method to model fins

and turbulator inlays Boiling of coolant can be predicted


CFD simulation process

Standardized workflow

GeometrypreparationGeometry

preparation

Imprinting

MeshingMeshing

SurfaceRemeshing

Volume structured(MEDINA)

Volume unstructured

(STAR-CCM+)

PhysicalmodelingPhysicalmodeling

Fin & Tubes

Boiling

Radiation

Simulation run

Simulation run

Post-processing

Post-processing

Automatedstandard

report

Predefinedscenes

Plots

Mapping (NASTRAN)

Mapping (NASTRAN)

FEA (PERMAS ®)

FEA (PERMAS ®)


Geometry preparation

iCAC – Difficult imprinting

Not suitable within geometry preparation process

Standard imprinting fails

Succesful imprinting requires fine surface mesh


Meshing

iCAC - Advances in meshing

MEDINA structured mesh combined with STAR-CCM+ mesh

Massively reduced number of cells compared to a pureSTAR-CCM+ mesh:

STAR-CCM+ mesh → approx. 32 million cells

MEDINA - STAR-CCM+ mesh → approx. 4 million cells

“Directed Meshing” fails


Meshing

EGR - Advances in meshing

Desired mesh for CHT simulations Symmetry of geometry is taken into account Repeating, hexahedral, structured mesh pattern

“Directed Meshing” fails

Extension of „Directed Meshing“ features ?


Meshing

EGR - Advances in meshing

Possible improvements ofmeshing process in STAR-CCM+?

D1477 - Conformal interface from directed mesh to surrounding poly mesh

D1478 - Ability to automatic patch creation for directed meshing

D1523 - periodic meshing of specific parts when using the directed mesher


Physical modeling

Boiling modeling

Consideration of enthalpy of vaporization (“latent heat”) of the coolant by modification of the temperature enthalpy correlation

Boiling temperature ≠ dew temperature for mixtures Enthalpy of vaporization, boiling and dew temperatures are dependent on operating point and

coolant Enhancement of heat transfer due to (nucleate) boiling by an enhancement factor Film boiling effects are not taken into account

The modeling of the boiling coolant volumes has a significant influence on heat transfer between exhaust gas or charge air and coolant.

The coolant is usually a mixture of water and glycol.


Physical modeling

Boiling modeling

Using Segregated Fluid Enthalpy modeling:simulation is diverging due to non converging temperature of enthalpy

Which numerical procedure is conservative for integral energy:Segregated Fluid Temperature orSegregated Fluid Enthalpy ?

Why has default changed fromEnthalpy to Temperature?

D1491 - Improvement of convergence of Enthalpy Temperature Relation(like coteet.f)


Mapping

Mapping process

Mapping of transient temperature fields from STAR-CCM+ to NASTRAN imported mesh

• Current version used

• BUG A• BUG B

• BUG A• BUG B

• BUG A

BUG A:Double vertices appear in the mapped results file, if the NASTRAN file that was imported has different “properties”

BUG B:Only time step number, but not physical time can be included in the name of the exported ccm files


Automated workflow guided by iCAC Wizard

Fully automated workflow integrated in a “iCAC Wizard” plugin for STAR-CCM+

Applicable to all types of iCACs (parallel flow, cross flow, stacked plates, tube-bundle, i²CAC etc)

CFD results are automatically exported and mapped to the FEA mesh for a complete Thermo-cycle thermal stress prediction

CFD simulation process


Post processing

Results - Plots

Maximum temperatures plot for different parts of an EGR (test design)

Charge air

Coolant


Post processing

Results - Animations

Solid temperature distribution during thermocycles


Post processing

Results - Animations

Charge air temperature distribution during thermocycles


Validation

TCT correlation of simulation and thermography


Life time prediction

Reliable evaluation of design variants

EGR Design variant 1





Significant deviations of number of load cycles of design variants compared to numerical/experimental deviations Reliable evaluation of design variants by numerical simulations


Simulation Workflow

Summary and Outlook

Summary

Outlook

Feasible simulation workflow for virtual testing of indirect Charge Air Coolers (iCACs) and Exhaust Gas Recirculation Coolers (EGRs)

High level of standardization is necessary for reproducible simulation results and has been achieved with this workflow

Definition of “STAR-CCM+ version to use” is very important for the reliability of the workflow

Improvement of stability, robustness, convergence and reliability of TCT simulations for providing virtual testing facility

Some steps of workflow could be improved (imprinting, (directed) meshing, …) or could become more user-friendly

Speed up of simulation/turnaround time (simulation time of several days at the moment)

MAHLE Behr GmbH & Co. KG © MAHLE MAHLE Behr © MAHLE

G. Apostolopoulos, R. Stauch, C. Marola, F. Schmidt, J. Schlottke, W. KühnelMAHLE Behr GmbH & Co. KG, Stuttgart, Germany

Thank you for your attention!

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