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SIMULATION OF DUST DEVILS. Zhaolin GU, PhD, Professor Xi’an Jiaotong University October , 2006, CCFD Forum , Tokyo University. Background. Atmospheric dust has important impacts on global and regional climates.

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Simulation of dust devils

SIMULATION OF DUST DEVILS

Zhaolin GU, PhD, Professor

Xi’an Jiaotong University

October , 2006, CCFD Forum , Tokyo University


Background
Background

  • Atmospheric dust has important impacts on global and regional climates.

  • Some specific convective wind systems in the convective boundary layer (CBL), such as, dust storms, dust devils etc., can carry dust into the atmosphere.


Simulation of dust devils

Dust transportation in Northwestern arid area of China

Dust storm

Meso-scale meteorological process

Dust devil

Micro-scale meteorological process


About dust storms some pictures
About dust storms – Some pictures

The vision of Lanzhou Train Station at 16:00, April 10, 2004

The vision of Dunhuang Grottoes at 16:00, April 10, 2004

The vision of Xi’an City Wall, April 9, 2006

The destroyed window by the dust storm, April 9, 2006


About dust storms meteorological aspects
About dust storms – Meteorological aspects

  • A Mesoscale meteorological process, composed of strong convection cells

    • Height of dust front 300-400 m

    • Length of dust front around 100 km

    • second dust front 10-20 km

    • Horizontal velocity more than 20 ms-1

    • Vertical velocity more than 15 ms-1

    • Temperature increment (DT ) 4–8 K

    • Pressure depression (Dp) 2.0–3.5 hPa

      ΔT and Δp are departures from ambient values of temperature and pressure.


About dust devils meteorological aspects
About dust devils – Meteorological aspects

  • A special case of convective vortex occurring in the atmosphere boundary layer.

  • The most common, small-scale dust transmitting system.

  • Maybe the primary atmospheric dust-loading mechanism in non-storm seasons

  • Mixing grains in dust devils becoming tribo-electrified.


Typical observed dust devil physical characteristics
Typical Observed Dust Devil Physical Characteristics

  • Diameter Tens to 141 m

  • Height 300–660 m

  • Horizontal velocity 5-20 ms-1

  • Vertical velocity 3–15 ms-1

  • Rotation sense Random

  • Temperature increment (ΔT ) 2–8 K

  • Pressure depression (Δp) 2.5–4.5 hPa

    ΔT and Δp are departures from ambient values of temperature and pressure.


Inducement of dust devils background vorticity
Inducement of dust devils—Background vorticity

The Benard’s Convection in atmospheric boundary layer



Inducement of dust devils surface roughness
Inducement of dust devils— Surface roughness

At h=5.2m and h=9.4m (V7and V31 in the figure), the value of tangential velocities at r=50m is different, where is far from the dust devil center and maybe the boundary of the dust devil. (P. C. Sinclair, 1973)


Inducement of dust devils buoyancy
Inducement of dust devils— Buoyancy

  • Heat radiation from the sun causing the rise of surface temperature

  • The temperature difference between the ground surface and the near-surface air parcels is over 20-30K at sunny mid-day in deserts (Li J. F. , Desert Climate, Meteorological Press, Beijing, 2002)

  • The temperature difference is related to the heat flux on the surface.


Tool and methods for dust devil study
Tool and methods for dust devil study

  • Field observation and test

  • Laboratory experiment, e.g. dry ice simulator in Arizona University

  • Numerical simulation

    gas-solid two-phase flow


Numerical simulation
Numerical simulation

C. B.Leovy, Nature, 424 ,2003

  • Promise to be an important tool for interpreting laboratory and field observations of dust devils

    (C. B.Leovy, Nature, 424 ,2003)

  • Getting insights into the dynamics of boundary-layer vortices

    Two scale methods: convective boundary layer (CBL) scale simulation, and dust devil-scale simulation


Dust devil scale simulation method les lagrangian discrete phase model ldpm model
Dust devil-scale simulation method LES- Lagrangian discrete phase model (LDPM) model

  • LES for the turbulent flow

  • LDPM for the grain movement—one way coupling

  • Lifting of dust not actually appearing to be of major dynamical importance for the development of these vertical vortices ( P. C. Sinclair,J. Appl. Meteorol. 8,1969)


Les equations
LES Equations

Continuity equation

Momentum equation

Energy equation


Dynamic subgrid scheme
Dynamic subgrid scheme

Least-squares approach, Lilly (1992)



Involution of dust devils
Involution of dust devils

a) Weak vortex phase; b) Single cell phase;

c) Transition phase of single cell to double cell; d) Double cell phase .


Fine flow structure in the weak vortex phase
Fine flow structure in the weak vortex phase

The updraft vectors and contours of updraft velocity


Fine flow structure in the single cell phase
Fine flow structure in the single cell phase

The updraft vectors and contours of updraft velocity


Fine structure in transition phase of single cell to double cell
Fine structure in transition phase of single cell to double cell

The updraft vectors and contours of updraft velocity


Fine flow structure in the double cell phase
Fine flow structure in the double cell phase cell

The updraft vectors and contours of updraft velocity




Dust lifting patterns in a dust devil
Dust lifting patterns in a dust devil cell

1-track of fine dust grains;

2-track of medium grains;

3-track of large grains;

4-small vortices induced

by the interaction of

different sized grains;

5-general pattern of

interactions.



Observed near surface patterns of terrestrial dust devils
Observed J. Geophys. Res., 109,2004near-surface patterns of terrestrial dust devils


Modeled dust devils and typical parameters
Modeled dust devils and typical parameters J. Geophys. Res., 109,2004


Simulated near surface patterns of dust devils
Simulated near-surface patterns of dust devils J. Geophys. Res., 109,2004

Near-surface shapes of dust devils simplified by the periphery of the rotating velocity contour of their cores.


Some problems in the numerical simulation
Some problems in the numerical simulation J. Geophys. Res., 109,2004

  • Grain size distribution

  • The influence of electrostatic field on the movement the positive-charged or negative-charged particles

  • The collision of particles resulting in charge neutralization and/or production, and then the particle movement



Particle population balance model
Particle population balance model J. Geophys. Res., 109,2004

  • A method connecting the microcosmic behaviors with the macroscopic token of dispersed phase

  • Description for different microcosmic behaviors in various process, such as crystal, growth, dissolution, breakage, aggregation, erosion, sinter and so on

  • Dealing with some process— formation or transformation of rain, snow and hail, aerosol, sand storm, dust devils


Particle population balance equation ppbe
Particle population balance equation (PPBE) J. Geophys. Res., 109,2004

n (L, us, t, x) particle number density function;

usparticle velocity;

L particle properties;

X dimension ;

Ttime ;

S(L, us, x, t ) source tem, relating to the dispersed phase behaviors;

F forces acting on the dispersed phase.


Particle population balance equation ppbe1

Transformation J. Geophys. Res., 109,2004

Particle population balance equation (PPBE)

Source term with no reaction


Solution of the ppbe
Solution of the PPBE J. Geophys. Res., 109,2004

  • Classification method (CM)—(N+1)-fluid model, one fluid corresponding to the gas phase and N fluids to the different size dispersed phase

  • Quadrature method of moment (QMOM) (McGraw,Aerosol. Sci. Technol., 27, 1997)

  • Direct Quadrature method of moment (DQMOM) (Marchisio et al., Chem. Eng. Sci., 58, 2003)

  • Monte Carlo Methods


Prospect of cfd coupling with ppbe 1
Prospect of CFD coupling with PPBE-1 J. Geophys. Res., 109,2004

  • Extending the physical understanding of the dispersed phase behaviors and process

  • QMOM and DQMOM, based on the fundamental statistical concepts on the microscopic level, are the promise to solve the PPBE

  • Reformulation of the coalescence and breakage, consistent with QMOM and DQMOM

  • Improving the formulation of the turbulence effects, interfacial transfer fluxes

  • Improving the formation of the boundary conditions (inlet and outlet conditions, wall boundary)


Prospect of dust simulation
Prospect of dust simulation J. Geophys. Res., 109,2004

  • The evaluation of dust flux at a level of dust devil on different surface

  • The possibility evaluation of occurring of dust devils in the region

  • The evaluation of regional dust flux from dust devils


Simulation of dust devils

Thanks for your attention! J. Geophys. Res., 109,2004