Premixed Turbulent Combustion Modeling PhD student: Ehsan Yasari - PowerPoint PPT Presentation

Applied Mechanics Premixed Turbulent Combustion Modeling PhD student: Ehsan Yasari yasari@chalmers.se Department of Applied Mechanics Chalmers University of Technology Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 1 of 17

Applied Mechanics Outline • Project Description • Tools and Solver • Problems and Difficulties • Possible Solutions Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 2 of 17

Applied Mechanics Project Description • Premixed Turbulent Combustion Modeling • Supervisor: Andrei Lipatnikov • PhD student: Ehsan Yasari • Project start date: 2010-01-01 Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 3 of 17

Applied Mechanics Project Goals • Implementing new combustion models. • Simulation different premixed turbulent flames. • Link this project to internal combustion engine simulation. Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 4 of 17

Applied Mechanics Tools and Solver • OpenFOAM • XiFoam solver: compressible premixed/partially- premixed combustion with turbulence modeling • Combustion model: based on Weller model |-- ftEqn.H |-- UEqn.H |-- hEqn.H |-- XiFoam.C |-- huEqn.H |-- bEqn.H |-- pEqn.H |-- createFields.H `-- readCombustionProperties.H Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 5 of 17

Applied Mechanics Implementing the Chalmers Model  ~          c ~ ~ ~   ~         c u c D U c         k t , u t ,   t x x x k k k ~ 2 C k   D  ~   t , c 1 4 1 4 1 4        2 L LS           1 4 t L U 0 . 5 u ' Da 0 . 5 u ' 0 . 5 u ' 0 . 5 u '           t ,       u ' u ' c c u    1        u t 2 L L u t             1 exp  D D U U  1 exp   t t ,        t t ,   L   u t u t L Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 6 of 17

Applied Mechanics Problems and Difficulties fvScalarMatrix bEqn ( fvm::ddt(rho, b) + mvConvection->fvmDiv(phi, b) + fvm::div(phiSt, b, "div(phiSt,b)") - fvm::Sp(fvc::div(phiSt), b) - fvm::laplacian(turbulence->alphaEff(), b) ); Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 7 of 17

Applied Mechanics Problems and Difficulties • Negative value of b • Temperature Calculation in OpenFoam Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 8 of 17

Applied Mechanics Possible solution for negative b problem • Finer Mesh- Smaller time-step • Schemes for strictly bounded scalar fields: • limitedLinear • vanLeer • Gamma • Different fvSolution • Limit the b when solve the bEqn.H ?!  b b 1     old old if b 0 : b , if b 1 : b 2 2 Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 9 of 17

Applied Mechanics Temperature Calculation Method ~ ~ ~    T T b T ( 1 b ) u b ~ • Transport equation for regress variable . b ~ • Transport equation for enthalpy . h ~ h W a a a a       2 3 4 5 3 5 r 2 r r 4 r r a T T T T T a 1 r u u u u u 6 r R 2 3 4 5 ~ h W a a a a       2 3 4 5 p 2 p 3 p 4 p 5 p a T T T T T a 1 p b b b b b 6 p R 2 3 4 5  T P        u b , 1 ~ ~    T 1 ( 1 b ) R T u Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 10 of 17

Applied Mechanics ~ Problem in Computation T • Mean density and Favre averaged temperature yielded by OpenFOAM library differs significantly from well-known equations:  ~ ~ ~ T         u b T T b T ( 1 b ) , , 1 ~ u b    T 1 ( 1 b ) u Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 11 of 17

Applied Mechanics Multi Component Mixture OpenFOAM Approach b u N H Y    l h ( H ) l W W  l 1 • Multi Component Mixture • OpenFoam Approach l   a N 5 Y     l , k k    l  R ( T a ) a 5 ~ R ~  l , 6     m , k   k W k h  T a    hhuMixtureThermo.C l 1 k 1 l m , 6   W k janafThermoI.H  k 1 m   a 5 R      m , k k ~ ~ h  T a     Y b , Y ( 1 b ) m , 6   W k  1 2 k 1 m   ~ ~ 1 1 1 N 1 Y      b 1 b l homogeneousMixture.C specieI.H W W W W W  m u b l 1 m l   a a a ~ ~ a N    Y m , k u , k b , k  1 b b  m , k l homogeneousMixture.C a W W W l , k janafThermoI.H W W  u b l 1 m l Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 12 of 17

Applied Mechanics What is the problem in this Approach? • Mean state of burning mixture should not considered as super-mixture(multi-component mixture). • Non-linearity problem Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 13 of 17

Applied Mechanics Super-mixture Problem : • Mean state of burning mixture should not considered as super-mixture(multi-component mixture). T  I. Two totally different phenomena T r p  N    II. Mean density    u ~    l 1 ( 1 b )  l 1           u b u b   0 Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 14 of 17

Applied Mechanics Correct Temperature Calculation Method ~ ~ ~    T T b T ( 1 b ) u b ~ • Transport equation for regress variable in bEqn.H b ~ • Transport equation for enthalpy in hEqn.H h ~ h W a a a a       p 2 p 2 3 p 3 4 p 4 5 p 5 a T T T T T a T 1 6 p b b b b b p b R 2 3 4 5 ~ h W a a a a       2 3 4 5 T r 2 r 3 r 4 r 5 r a T T T T T a u 1 r u u u u u 6 r R 2 3 4 5  T P        u b , 1 ~ ~    T 1 ( 1 b ) R T u Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 15 of 17

Applied Mechanics ~ Results: Modification the T • Mean density and Favre averaged temperature yielded by OpenFOAM library differs significantly from well-known equations:  ~ ~ ~ T         u b T T b T ( 1 b ) , , 1 ~ u b    T 1 ( 1 b ) u Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 16 of 17

Applied Mechanics Thank you for your attention Ehsan Yasari - Gothenburg region OpenFOAM user group meeting 17 of 17