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1 Click to edit Master title style LES LES Applications for for Internal Internal Combustion Engines Engines David Gosman & Richard Johns CD-adapco, June 2011

2 Some Qs and As Why would we use LES calculations in an IC Engine? To be able to model phenomena that are not captured using traditional (U)RANS modeling What are the fundamental differences between RANS and LES? LES is able to compute directly the large-scale fluid motion (modeling is restricted to the smaller, sub-grid scales) and is able to capture turbulent structures that are not seen with RANS What does that deliver to the engine CFD analyst? It potentially provides a more realistic description of the turbulence and all phenomena that depend on that, particularly combustion Any other applications of LES for IC engines? LES can be applied to other processes that are important in engines and where the effects of turbulence are critical, such as the primary breakup of fuel sprays Any disadvantages? It can be computationally expensive for routine use

3 Some Qs and As Why would we use LES calculations in an IC Engine? To be able to model phenomena that are not captured using traditional (U)RANS modeling What are the fundamental differences between RANS and LES? LES is able to compute directly the large-scale fluid motion (modeling is restricted to the smaller, sub-grid scales) and is able to capture turbulent structures that are not seen with RANS What does that deliver to the engine CFD analyst? It potentially provides a more realistic description of the turbulence and all phenomena that depend on that, particularly combustion Any other applications of LES for IC engines? LES can be applied to other processes that are important in engines and where the effects of turbulence are critical, such as the primary breakup of fuel sprays Any disadvantages? It can be computationally expensive for routine use

4 Introduction Engine flows are intrinsically unsteady and turbulence models for ICE simulation must account for a wide range of flow phenomena Unsteady Compressible Tumble Piston motion

5 LES/DES Modelling In STAR-CD: Overview First implemented around 10 years ago Initially Smagorinsky and one-equation k-l subgrid models Later, DES variants (LES hybrid with k-ε and other 2 equation models) Initial validation for canonical flows, e.g.: Decaying homogeneous turbulence Taylor vortex Fully-developed channel flow Many industrial applications, e.g.: Aeroacoustics (automotive, HVAC, wing mirror, turbocharger) Gas turbine combustors Establish best practices: meshing, boundary conditions, data handling. ICE applications during past 5 years Mainly motored, model and real engines University, industrial collaborations Working on establishing best practices Recent extensions to spray, combustion (ECFM-LES)

6 LES VALIDATION: (a) INVISCID TAYLOR VORTEX AND (b) HOMOGENEOUS TURBULENCE DECAY (a)taylor Vortex zero viscosity, so should not decay decay rates for hexahedral and polyhedral meshes similar and low (b)homogeneous Turbulence Decay Smagorinsky model Energy should follow -5/3 law Kinetic Energy Indicators that STAR-CD numerics suitable for LES

7 LES VALIDATION: FULLY-DEVELOPED CHANNEL FLOW Fully-resolved LES simulation very fine near-wall mesh synthetic turbulence inlet conditions comparison with DNS data* Umean Urms

8 LES VALIDATION STUDIES: NON-COMPRESSING MODEL ENGINE (Prof Dan Haworth, Penn State Univ) LES simulations, without/with swirl Smagorinsky, wall functions 1.3M cell mesh, size ~ 1 mm effects of mesh, time step, subgrid model LES better than RANS for same mesh, time step

9 LES VALIDATION STUDIES: NON-COMPRESSING MODEL ENGINE (Prof Dan Haworth, Penn State Univ) Cyclic variations investigated using Proper Orthogonal Decomposition (POD)

10 Application of LES to Primary Breakup of Sprays Understanding and modeling of primary breakup of sprays is increasingly important for advanced fuel injection technology The ATOMIC project was established in 2008 to develop LES/VOF methods to quantify spray breakup drop sizes, velocities, angle etc. The ATOMIC methodology has been successfully applied to both diesel and gasoline injectors In addition to giving an increased understanding of spray breakup, the results can also be used to provide Initial Conditions to Lagrangian spray calculations

11 History of ATOMIC Further investigations at CD-adapco in 2006 examined the primary breakup of a hollow-cone gasoline spray, indicating that a very complex transient 2-phase flow evolution could be computed successfully

12 History of ATOMIC Startup Transient Formation of Hollow Cone Spray Courtesy of Fulldeveloped Spray 12

13 History of ATOMIC

14 Extraction of quantitative data for Lagrangian calculation

15 Summary Although computationally more demanding than RANS calculations, LES/DES have been developed and are starting to be successfully applied to in-cylinder flows and primary breakup of sprays DES In-cylinder flow calculations show good agreement with PIV data and confirm aspects of the origins of cycle-to-cycle variations LES of spray primary breakup has given new insights into the breakup process and is being applied to initialise Lagrangian calculations CD-adapco will continue to invest in both academic research via our university and industrial partners to develop this technology into the spray and combustion areas for application to engine development

16 Click to edit Master title style LES Applications for Internal Combustion Engines THE END THANK YOU