Turbulent mixing for a jet in crossflow and plans for turbulent combustion simulations James Glimm

The Team/Collaborators  Stony Brook University James Glimm James Glimm Xiaolin Li Xiaolin Li Xiangmin Jiao Xiangmin Jiao Yan Yu Yan Yu Ryan Kaufman Ryan Kaufman Ying Xu Ying Xu Vinay Mahadeo Vinay Mahadeo Hao Zhang Hao Zhang Hyunkyung Lim Hyunkyung Lim  Drew University Srabasti Dutta Srabasti Dutta  Los Alamos National Laboratory David H. Sharp John Grove Bradley Plohr Wurigen Bo Baolian Cheng

Outline of Presentation  Problem specification and dimensional analysis Experimental configuration Experimental configuration HyShot II configuration HyShot II configuration  Plans for combustion simulations Fine scale simulations for V&V purposes Fine scale simulations for V&V purposes HyShot II simulation plans HyShot II simulation plans  Preliminary simulation results for mixing  Comments on the nature of LES convergence

Main Objective   Compare to the Stanford code development effort. Chemistry to be computed without a model (beyond dynamic turbulence model). Hereby we can offer a UQ assessment of the accuracy of the Stanford code.   If the comparison is satisfactory and the two codes agree, the UQ analysis of the Stanford code (in this aspect) will be complete.   If the comparison is unsatisfactory, we will attempt to determine which of the differing results are to be believed.

Problem Specification and Dimensional Analysis  Experimental configuration Problem dimensions = 8.6 x 2 x 2 cm Problem dimensions = 8.6 x 2 x 2 cm Parameters for crossflow (air) Parameters for crossflow (air) Crossflow Ma = 2.4; flow velocity = 1800 m/sCrossflow Ma = 2.4; flow velocity = 1800 m/s Crossflow pressure = 0.4 BarCrossflow pressure = 0.4 Bar Crossflow Temperature = 1548KCrossflow Temperature = 1548K L (air) = distance of nozzle downstream = mL (air) = distance of nozzle downstream = m Viscosity (air) = 5.36e-4 m 2 /sViscosity (air) = 5.36e-4 m 2 /s Re (air) = 2.25e5Re (air) = 2.25e5 Kolmogorov scale (air) = L Re -3/4 = 6.5 micronsKolmogorov scale (air) = L Re -3/4 = 6.5 microns Parameters for H 2 Parameters for H 2 H 2 flow M = 1; H 2 velocity = 1205 m/sH 2 flow M = 1; H 2 velocity = 1205 m/s H 2 pressure = 20.2 BarH 2 pressure = 20.2 Bar H 2 Temperature = 300 KH 2 Temperature = 300 K Viscosity of H 2 = 0.16e-4 m 2 /sViscosity of H 2 = 0.16e-4 m 2 /s L (H 2 ) = nozzle diameter = 2 mmL (H 2 ) = nozzle diameter = 2 mm Re (H 2 ) = 1.5e5Re (H 2 ) = 1.5e5 Kolmogorov scale (H 2 ) = LRe -3/4 = 11 micronsKolmogorov scale (H 2 ) = LRe -3/4 = 11 microns Flame width (OH, from experiment) = 200 microns Flame width (OH, from experiment) = 200 microns Momentum flux ratio J = jet/crossflow = 5 Momentum flux ratio J = jet/crossflow = 5

Problem Specification and Dimensional Analysis  HyShot II Scramjet configuration * Combustion chamber dimensions = 29.5 x 0.98 x 7.5 cm Combustion chamber dimensions = 29.5 x 0.98 x 7.5 cm Reduced by symmetry to 29.5 x 0.98 x cmReduced by symmetry to 29.5 x 0.98 x cm Volume is 0.79 as a fraction of the experimental combustion chamber (after symmetry reduction)Volume is 0.79 as a fraction of the experimental combustion chamber (after symmetry reduction) Crossflow (air) parameters Crossflow (air) parameters Crossflow Ma = 2.4; flow velocity = 1720 m/sCrossflow Ma = 2.4; flow velocity = 1720 m/s Crossflow pressure = 130 KPaCrossflow pressure = 130 KPa Crossflow Temperature = 1300 KCrossflow Temperature = 1300 K Viscosity of air = m/sViscosity of air = m/s L (air) = 5 cm (from inflow plane to injector)L (air) = 5 cm (from inflow plane to injector) Re (air) = 4.7e5Re (air) = 4.7e5 Kolmogorov scale (air) = LRe -3/4 = 2.8 micronsKolmogorov scale (air) = LRe -3/4 = 2.8 microns H 2 parameters (at injector exit) H 2 parameters (at injector exit) H 2 flow M = 1; velocity = 1200 m/sH 2 flow M = 1; velocity = 1200 m/s H 2 pressure = 4.6 barH 2 pressure = 4.6 bar H 2 Temperature = 300 KH 2 Temperature = 300 K Viscosity of H 2 = 2.22e-5 m 2 /sViscosity of H 2 = 2.22e-5 m 2 /s L (H 2 ) = nozzle diameter = 2 mmL (H 2 ) = nozzle diameter = 2 mm Re (H 2 ) = 1.1 e5Re (H 2 ) = 1.1 e5 Kolmogorov scale (H 2 ) = LRe -3/4 = 35 micronsKolmogorov scale (H 2 ) = LRe -3/4 = 35 microns Flame width (OH, from experiment) = 200 microns Flame width (OH, from experiment) = 200 microns J = ratio of momentum flux jet/crossflow = 0.55 J = ratio of momentum flux jet/crossflow = 0.55 *Sebastian Karl, Klaus Hannemann, Andreas Mack, Johan Steelant, “CFD Analysis of the HyShot II Scramjet Experiments in the HEG Shock Tunnel”, 15 th AIAA International Space Planes and Hypersonic Systems and Technologies Conference

Problem Specification and Dimensional Analysis  Simulation Parameters: Experimental Configuration Fine grid: approximately 60 micron grid Fine grid: approximately 60 micron grid Mesh = 1500 x 350 x 350 = 183 M cellsMesh = 1500 x 350 x 350 = 183 M cells If necessary, we can simulate only a fraction of the experimental domain If necessary, we can simulate only a fraction of the experimental domain If necessary, a few levels of AMR can be used If necessary, a few levels of AMR can be used Current simulations = 120 microns, about 10 M cells Current simulations = 120 microns, about 10 M cells  HyShot II configuration Resolution problem is similar Resolution problem is similar 3/4 volume after symmetry reduction compared to experiment3/4 volume after symmetry reduction compared to experiment Full (symmetry reduced) domain needed to model unstart Full (symmetry reduced) domain needed to model unstart Resolved chemistry might be feasible Resolved chemistry might be feasible Wall heating an important issue Wall heating an important issue

Flow and Chemistry Regime  Turbulence scale << chemistry scale Broken reaction zone Broken reaction zone  Autoignition flow regime T c << T T c << T Makes flame stable against extinction from turbulent fluctuations within flame structure Makes flame stable against extinction from turbulent fluctuations within flame structure  Unusual regime for turbulent combustion Broken reaction zone autoignition distributed flame regime Broken reaction zone autoignition distributed flame regime Query to Stanford team: literature on this flow regime? Query to Stanford team: literature on this flow regime? Knudsen and Pitsch Comb and Flame 2009Knudsen and Pitsch Comb and Flame 2009 Modification to FlameMaster for this regime?Modification to FlameMaster for this regime? Opportunity to develop validated combustion models for this regime, for use in other applications Opportunity to develop validated combustion models for this regime, for use in other applications Some applications of DOE interestSome applications of DOE interest

Flow, Simulation and Chemistry Scales; Experimental Regime  Turbulence scale << grid scale << chemistry scale Turbulence scale = 10 micronsTurbulence scale = 10 microns << grid scale = 60 microns<< grid scale = 60 microns << chemistry scale 200 microns<< chemistry scale 200 microns  Resolved chemistry, but not resolved turbulence  Need for dynamic SGS models for turbulence  Transport in chemistry simulations must depend on turbulent + laminar fluid transport, not on laminar transport alone

Chemistry Simulation Plans  Resolved Chemistry vs. Flamelets Flamelets Flamelets assumes diffusion flame,assumes diffusion flame, Resolved chemistry Resolved chemistry makes no assumption of flame structuremakes no assumption of flame structure thus resolved chemistry is more suitable for an autoignition flamethus resolved chemistry is more suitable for an autoignition flame FlameMaster has been or will be extended to support autoignition flame structure?FlameMaster has been or will be extended to support autoignition flame structure? Flamelets Flamelets use FlameMaster,use FlameMaster, Resolved chemistry Resolved chemistry uses FlameMaster subroutine for chemical source termsuses FlameMaster subroutine for chemical source terms Flamelets Flamelets assumes a quasi equilibrium solution, thus suppresses certain transients.assumes a quasi equilibrium solution, thus suppresses certain transients. (This can be either/both a strength or a weakness.)(This can be either/both a strength or a weakness.) speed and/or memory advantagesspeed and/or memory advantages Flamelets feasible for coarser gridsFlamelets feasible for coarser grids Resolved chemistry Resolved chemistry allows UQ assessment of flamelet model in Scramjet context.allows UQ assessment of flamelet model in Scramjet context. Has value for Scramjet UQ analysis even if too slow to be feasible for most simulationsHas value for Scramjet UQ analysis even if too slow to be feasible for most simulations May not be feasible for HyShot II configurationMay not be feasible for HyShot II configuration

Simulation Plans: Experimental Regime  Mixed fluid physics Accurate multifluid viscosity, diffusion parameters Accurate multifluid viscosity, diffusion parameters Diffusion velocityDiffusion velocity  Numerical issues Finer resolution grids Finer resolution grids No need to track fronts No need to track fronts AMR needed? AMR needed?  Turbulent inflow needed (nozzle/cross flow)?  V&V for pure mixing  Add chemistry  V&V for resolved chemistry  Comparison to flamelet simulations  V&V for flamelets

Simulation Plans: HyShot II Regime  Work with autoignition version of FlameMaster Add this capability if necessary Add this capability if necessary  Compare to laboratory experimental regime and resolved chemistry simulations (V&V)  Simulate in representative flow regimes defined by the large scale MC reduced order model, both for failure conditions (unstart) and for successful conditions.  Provide improved combustion modeling to the MC low order model, for the next iteration of an MC full system search.  Investigate “gates” which serve to couple system components into full system For combustion chamber, primarily fuel nozzle, inlet flow and exit nozzle For combustion chamber, primarily fuel nozzle, inlet flow and exit nozzle Essential step for relating UQ of components to UQ of full system Essential step for relating UQ of components to UQ of full system

Preliminary Simulation Results: Mixing Only 3D simulation. 67% H 2 mass concentration isosurface plot compared to experimental OH-PLIF image (courtesy of Mirko Gamba). The grid is 120 microns, 2 times coarser than the Intended fine grid mesh size.

Preliminary Simulation Results: Mixing Only Black dots are the flame front extracted from the experimental OH-PLIF image.

Preliminary Simulation Results: Mixing Only Velocity divergence plotted at the midline plane. Bow shock, boundary layer separation, barrel shock and Mach disk are visible from the plot.

Preliminary Simulation Results: Mixing Only H 2 H 2 mass fraction contour plotted at the midline plane

Preliminary Simulation Results: Mixing Only Stream-wise velocity Stream-wise velocity contour plotted at the midline plane

Preliminary Simulation Results: Mixing Only H 2 H 2 mass fraction contour plotted at x/d=2.4

Preliminary Simulation Results: Mixing Only Stream-wise velocity Stream-wise velocity contour plotted x/d=2.4

Preliminary Simulation Results: Mixing Only Mixture fraction plot courtesy of Catherine Gorle 0 represents Hydrogen,1 represents Air Mass fraction plot of our simulation 1 represents Hydrogen, 0 represents Air

Preliminary Simulation Results: Mixing Only Comparison between Smagorinsky model (left) and dynamic model (right) Mass fraction plot, using 240 micron grid Mass fraction plot, using 240 micron grid

Preliminary Simulation Results: Mixing Only Comparison between 240 micron grid (left) and 120 micron grid (right) with dynamic model, mass fraction plot with dynamic model, mass fraction plot

The Nature of LES Convergence   A mathematical theorem (G-Q Chen and JG) If one assumes K41 as a property of LES solutions of NS (this is incompressible, but with possible passive scalars) then after to passing to subsequences Velocity field converges in some Lq space Passive scalars (are proved to) converge only as Young measures, ie measure valued distributions

Young Measures and PDFs   Assume this applies to compressible NS as well   Implication is that the LES regime defines a convergent PDF, not a convergent point valued function, even as a weak solution.   If point values are extracted, these are the means of the pdfs   For application to nonlinear processes (chemistry), mean values of pds are not good enough, and fluctuations are needed.   Thus pdf (Young measure) convergence is an important conceptual issue for LES applied to combustion

Young Measure Convergence   How would one define or notice the effects of pdf convergence?   We take a unit size filter (implicit filter). But the values at a point are not meaningful. Rather the ensemble of solution values in an extended neighborhood of the unit filter define an ensemble, which is the pdf for the point or for all points in the extended neighborhood   At the larger filter level size, the limit looks like an ensemble, a pdf, not a point value.

Queries for Stanford  What is the status/need for autoignition in FlameMaster?  In the broken flame regime, with turbulence inside the flame, what is used for the binary diffusion coefficients that drive the effective diffusivity of species k into the mixture? Laminar, from kinetic theory, or turbulent, from an SGS model? what is used for the binary diffusion coefficients that drive the effective diffusivity of species k into the mixture? Laminar, from kinetic theory, or turbulent, from an SGS model? Or are the SGS diffusion terms just a Fickean add on to the multicomponent diffusion? Or are the SGS diffusion terms just a Fickean add on to the multicomponent diffusion? In this case they should be dominant for most grids, and so the multicomponent theory of diffusion might not be needed? In this case they should be dominant for most grids, and so the multicomponent theory of diffusion might not be needed?  References for the broken flame-autoignition regime?