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

Transcription

1 Virtual Temperature Cycle Test (TCT) for validation of indirect Charge Air Coolers and Exhaust Gas Recirculation Coolers STAR Global Conference 2014 Vienna, March G. Apostolopoulos, R. Stauch, C. Marola, F. Schmidt, J. Schlottke, W. Kühnel MAHLE Behr GmbH & Co. KG, Stuttgart, Germany MAHLE Behr GmbH & Co. KG

2 Introduction MAHLE Behr System Partner for Thermal Management BUSINESS UNITS Engine Systems and Components Filtration and Engine Peripherals Thermal Management Industry Aftermarket = MAHLE Behr Sales and Application Engineering Advanced Engineering 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 Air cooling Conditioning - is integrated into the MAHLE Group as the Thermal Engine Management Cooling business unit. 2

3 CFD MAHLE Behr Engine cooling applications Cooling Modules Interaction of heat exchangers, fan & blockage Underhood Simulation Prediction of available cooling air, flow and temperature distribution for components Components Optimization of pressure loss & massflow distribution Fins, Tubes Trade Off for heat transfer & pressure loss 3

4 Simulation workflow What is an icac/egr? Coolant inlets 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 Coolant outlets 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 4

5 Simulation workflow Virtual Temperature Cycle Test (TCT) 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 Temperatures/Cooling Air Mass Flow t [s] 5

6 Simulation workflow Workflow of numerical simulation of TCT CFD simulation Lifetime predicition and most damaged position 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 Fatigue simulation Mapping of temperature data FEA simulation Thermal stress data 6

7 CFD simulation process Standardized workflow Geometry preparation Meshing Physical modeling Simulation run Postprocessing Mapping (NASTRAN) FEA (PERMAS ) Imprinting Surface Remeshing Fin & Tubes Automated standard report Volume structured (MEDINA) Boiling Predefined scenes Volume unstructured (STAR-CCM+) Radiation Plots 7

8 Geometry preparation icac Difficult imprinting Standard imprinting fails Succesful imprinting requires fine surface mesh Not suitable within geometry preparation process 8

9 Meshing icac - Advances in meshing MEDINA structured mesh combined with STAR-CCM+ mesh Massively reduced number of cells compared to a pure STAR-CCM+ mesh: STAR-CCM+ mesh approx. 32 million cells MEDINA - STAR-CCM+ mesh approx. 4 million cells 9 Directed Meshing fails

10 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? 10

11 Meshing EGR - Advances in meshing Possible improvements of meshing process in STAR-CCM+? D Conformal interface from directed mesh to surrounding poly mesh D Ability to automatic patch creation for directed meshing D periodic meshing of specific parts when using the directed mesher 11

12 Physical modeling Boiling modeling 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. 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 12

13 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 or Segregated Fluid Enthalpy? Why has default changed from Enthalpy to Temperature? D Improvement of convergence of Enthalpy Temperature Relation (like coteet.f) 13

14 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: 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 BUG A 14

15 CFD simulation process 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 15

16 Post processing Results - Plots Maximum temperatures plot for different parts of an EGR (test design) Coolant Charge air 16

17 Post processing Results - Animations Solid temperature distribution during thermocycles 17

18 Post processing Results - Animations Charge air temperature distribution during thermocycles 18

19 Validation TCT correlation of simulation and thermography 19

20 Life time prediction Reliable evaluation of design variants Significant deviations of number of load cycles of design variants compared to numerical/experimental deviations Reliable evaluation of design variants by numerical simulations EGR Design variant 1 EGR Design variant 2 EGR Design variant 3 EGR Design variant 4 EGR Design variant 5 20

21 Simulation Workflow Summary and Outlook Summary 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 Outlook 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) 21

22 Thank you for your attention! G. Apostolopoulos, R. Stauch, C. Marola, F. Schmidt, J. Schlottke, W. Kühnel MAHLE Behr GmbH & Co. KG, Stuttgart, Germany MAHLE Behr GmbH & Co. KG