1. Lorentz Centre, 19 Sep. 2006 Particle transport and flow modification in planar temporally evolving mixing layers Djamel Lakehal, Chidambaram Narayanan (G. Yadigaroglu, ETH Zurich) Adjunct Lecturer at ETH & Manager of ASCOMP GmbH (www.ascomp.ch)

2. Outline Motivations: environmental concerns Mixing layer basic flow features Transport under 1-way coupling Transport under 2-way coupling Summary

3. Transport & dispersion of sand Volcanic ash dispersion CO2 H20H20 Environmental flows with particles and droplets

4. Simulation: Eulerian-Lagrangian formulation FLUIDFLUID PARTICLEPARTICLE

5. Details Re=400, 64 X 129 Fourier Chebyshev collocation; L x =4  /K m Tangent-hyperbolic U velocity field Amplitude of Fund. & Sub. modes E f = 10 -2 ; E s = 10 -4 Re p < 1; N p = 2-4.10 5 particles; St= 0.3 - 5; M = 0.1-0.5 2 nd order Runge-Kutta for Particle Equation 4 th order Lagrangian ploynomial velocity interpolation

6. DNS of Particle dispersion in a mixing layer; St = 1.0

7. 2D particle-laden mixing layer under 1- and 2-way Coupling: What is new ? The analysis is Eulerian-Eulerian based The controlling mechanisms The mean vertical particle-phase velocity induced by KH The correlation between particle-phase and fluid-phase modal (KH induced) stress The effect of particle-phase modal velocity on the growth of the particle-phase mixing layer

8. Basic Flow Features:  flow evolution  Kinetic energy balances Particle Transport under One-way  centrifuging effect  statistics  momentum balance I- Outline: Particle Transport under 1-way Coupling

9. Saturation of fund. mode at t=48 initiation of pairing at t=72 end of pairing at t=96 single vortex at t=120

11. u= +u’

13. t=72 t=96

14. t=72 t=96

15. St=0.3St=0.6St=1 t=72

16. St=0.3St=0.6St=1 t=96

17. Analysis: Continuum formulation CONTINUMFIELDCONTINUMFIELD FLUIDWFLUIDW

18. t=48 t=96

19. t=48 t=96 t=72

20. Only the sub-harmonic is “really” nutating: effective St have diminished; L has increased

21. t=96, St=0.6t=96, St=1 momentum depletion region accumulation region

22. II- Outline: Particle Transport under 2-way Coupling Computational parameters Particle accumulation patterns Fundamental mode saturation & pairing Particle Statistics  Generation of small scales  Evolution of average modal stress  Mean kinetic energy balance

24. St=1 St=0.3 St=0.6 M=0.2 t=72 St=0.3 M=0

25. M=0.5M=0.2 St=1 t=96

26. St=2 M=0.2 No new instability forms for low M and uniformly distributed particles: rather drag effect t=72 t=96

27. St=1, time=72 M=0 M=0.2M=0.5 M=0.1

28. M=0 M=0.5M=0.2 M=0.1 St=1, time=96

30. t=48 t=96 Centrifuging effect of KH is lower in 2-way coupling

31. t=48 t=96

33. St=0.3 St=1

36. Summary  Particle transport in turbulent mixing layers was analyzed using DNS + Lagrangian particle tracking.  Particles modify the flow evolution dramatically even at mass loadings of 0.5; generation of small scales.  Intricate undulating patterns are formed.  Effect of preferential concentration on particle statistics was emphasized.

37. Related publications

38.  Narayanan C., Lakehal, D.: DNS of particle-laden mixing-layers. Part I: One-way coupled flow and dispersed-phase features. Phys. Fluids, 18(9), pp. 15, 2006.  Narayanan C., Lakehal, D.: DNS of particle-laden mixing-layers. Part II: Two-way coupled induced generation of small-scale vorticity, Phys. Fluids, 18(9), 2006.  Botto L., Narayanan C., Fulgosi M., Lakehal D.: Effect of near-wall turbulence enhancement on the mechanism of particle deposition, Int. J. Multiphase Flow, 31(8), 2005.  Lakehal D., Narayanan C.: Numerical Analysis of the continuum formulation for the Initial Evolution of Mixing Layers with Particles, Int. J. Multiphase Flow, 29(6), 2003.  Narayanan C., Lakehal D., Botto L., Soldati A.: Mechanisms of particle deposition in a fully-developed turbulent open channel flow, Phys. of Fluids, 15(3), pp. 763, (2003).  Narayanan C., Lakehal D.: Temporal instabilities of a mixing-layer with uniform and non- uniform particle loadings, Physics of Fluids, 14(11), pp. 3775, (2002).  Narayanan C., Lakehal D.: Linear Stabilities Analysis of Particle-Laden Mixing Layers using Lagrangian Particle Tracking, Powder Technology, 125, pp. 122, (2002).