be nyah i a subgrid drag models

7/30/2019 Be Nyah i a Subgrid Drag Models

1/20

continuum and discrete simulations?

Sofiane Ben ahiaUS DOE, National Energy Technology Laboratory

May 4-6, 2010


2/20

Collaborations

Research was conducted in collaboration with two groups:

Filtered drag models: Y. Igci and S. Sundaresan1 (Princeton University)

EMMS drag model: W. Wang and J . Li2 (Institute of ProcessEn ineerin , Chinese Academ of Sciences)

1 Igci, Y.; Andrews, A.T.; Sundaresan, S.; Pannala, S.; OBrien, T.AIChE J. 2008; 54; 1431-1448.

2K-2571

u, .; ang, .; , . em. ng. c . ; ; - .

2


3/20

Goals, Objectives, and Challenges

Conduct fast and accurate gas-solids f low simulations

us ng coarse gr s.

Implement EMMS and filtered drag models in MFIX

Conduct comparative study of these drag models with

experimental data3

Challenges:

Subgrid models are still being developed

Consideration of other effects (e.g. polydispersity,particle-wall interaction)

2K-2571

3

3 Benyahia, S. On the effect of subgrid drag closures. Ind. Eng. Chem. Res. DOI: 10.1021/ie900658k


4/20

Simulation Conditions2

Twogassolids

outlets

0.35m

0.14m

Process temperature 297 K

Process pressure 1.01 x 105 Pa

Air density ~1.2 kg/m3

Air viscosity 1.8 x 10-5 Pas

Gas-phase turbulence length-scale 0.01 m

Solids density 930 kg/m3

.

60cells

10.5m

450cells

Particle diameter 54micron

Single-particle terminal velocity 0.074 m/s

Particle-particle restitution coefficient 0.9

2.78m

artc e-wa resttuton coe c ent 0.7

Specularity coefficient 0.0001

Particle-particle angle of internalpi/6

Two

solids

side

inlets

0.35m

0.14meps_mf =0.4

eps =0.3, Vs:computedParticle-wall angle of friction pi/16

Void fraction at maximum packing 0.4

Void fraction at minimum fluidization 0.6

2K-2571

4

as n e

Vg=1.5m/s2 Lu, B.; Wang, W.; Li, J . Chem. Eng. Sci. 2009; 64; 3437-3447.


5/20

Instantaneous values of friction coefficient

1.6

1.2

filtered

EMMS

WenYu

0.8Hd

0

.

0.5 0.6 0.7 0.8 0.9 1

Voidage

2K-2571

5


6/20

Void fraction contour profiles

Wen-Yu drag Filtered drag EMMS drag Wen-Yu dra Filtereddra EMMS dra

2K-2571

6

Instantaneous Time-averaged


7/20

Solids mass flux through outlets40050

Solids massflux (kg/m2s)

Solids massflux (kg/m2s)

EMMS

300

30

40Wen-Yu

10010

20

00

0 10 20 30 40Time (sec)

Drag model Wen-Yu Filtered EMMS Experimental

Solids mass flux(kg/m2s)

205 12.3 16.9 14.3

2K-2571

7

Standard deviation(kg/m2s)

25.2 5.64 5.59 -


8/20

Vertical void fraction profiles10 10

6

8

m)

EMMS

FilteredWenYu

experiment6

8

)

EMMS

Filtered

WenYu

experiment

4

Height(

4

Height(

2 2

0

0.7 0.8 0.9 1Voidfraction

0


2K-2571

8

Numerical data based oncomputed pressure gradient

Numerical data based oncomputed void fraction


9/20

Horizontal profiles at 7 m above inlet

Solidsmassflux2

0.2

EMMS

Filtered

WenYu 0

400

0.1s

400

EMMS

Filtered

WenYu

0

0 0.03 0.06 0.09Width(m)800

0 0.03 0.06 0.09Width(m)

2K-2571

9


10/20

Future work

Why is the pressure gradient under-8

10

HiFriction(phi=0.01)

pre c e a e o om sec on o

riser? 6

eight(m)

LoFriction(phi=0.0001)

experiment

Increase particle-wall friction inJ ohnson-J ackson BC

2

4

Effect of polydispersity is currentlyinvestigated by considering threeparticle sizes of 30, 60, and 120

0


microns

2K-2571

10


11/20

Are subgrid models needed for discretepart c e s mu at ons

There is no reason why not if fluid flow is not properly

resolved (coarse grids)

The same approach3 used for continuum models can be

applied for discrete models, i.e. does the slip velocity

increase from that of homogeneous state as Euleriangrid is refined?

2K-2571

11

3 Agrawal et al. The role of meso-scale structures in rapid gas-solids flows. J. Fluid Mech. 445 (2001) 151.


12/20

-

0 ggggg V

gVxVPVVtV

gg

N

pppg

c

p

pgggggg

ggg T

1

Continuum gas-phase

conservation equations

gVVPPVVt

Vsssgpssgsssss

sss

Continuum solids-phasemomentum equation

sp

sppg

p

p

p

gp PVxV

Pg

td

Vd

Newtons law of motion fordiscrete particles

65.23

g

ppggg

Dp

VxVC

max

max

max

old

ss

ss

s

s

PP

2K-2571

12

pt s


13/20

Simulation conditions

Fully periodic domain

Air density 1.3 kg/m3

Air viscosity 1.8 x 10-5 Pas

0.4 m

So s ens ty 1500 g/m

Particle diameter 75 micron

Void fraction at maximum packing 0.4

Eulerian grid density 8x32, 16x64, 32x128, 64x256

2K-2571

13

0.1 m


14/20

Snapshots of particle position-velocity (8x32)

2K-2571

14

1.0 sec 1.5 sec 2.0 sec 10 sec 20 sec


15/20

Snapshots of particle posit ion-velocity (16x64)

2K-2571

15



16/20


2K-2571

16



17/20


2K-2571

17



18/20

Transient Favre-averaged slip velocity

2K-2571

18


19/20

Slip-velocity for continuum & MP-PIC models

Grid size 8x32 16x64 32x128 64x256

Continuum slipvelocity & St. Dev.

(cm/s)

18.70.16

22.63.9

49.610.8

52.08.7

MP-PIC slipvelocity & St. Dev.

(cm/s)

18.50.005

18.50.005

50.715.1

55.413.8

2K-2571

19


20/20

Summary

Sub-grid corrections are demonstrated to be

both needed and useful for both continuum

and discrete approaches to gas-solids flow

Our limited quantitative analysis indicates thatthe same subgrid corrections developed for

continuum models may be used with DPM

2K-2571

20

be nyah i a subgrid drag models

Documents