CFD investigation of erosion in particulate flows · PDF fileCFD investigation of erosion in particulate flows ... Particulate flow such as in Francis turbine ... Comparison of d max

http://www.mv.uni-kl.de/tvt/

CFD investigation of erosion in particulate flows

Mehdi Azimian & Hans-Jörg Bart

University of Kaiserslautern, Chair of Separation Science and

Technology, 67653 Kaiserslautern, Germany

E-Mail: mehdi.azimian@mv.uni-kl.de

Aims:

• Investigation of particulate (solid-liquid) flows

• Comparison of different numerical methods

• Validation of simulation results with exp. data

• Erosion mechanisms of various materials

DEM: Ductile behavior of material under erosion modeled

FEM: Chip separation and material pile-up due to particle impact

CFD: Particulate flow such as in Francis turbine

Exp.: Tester setup and erosion studies of different materials

Details: Azimian et al., Open Chem. Eng. J. 8 (2014).

* Ref.: M. Takaffoli, M. Papini, Wear 267 (2009).

Acknowledgement: The authors would like to thank “Stiftung Rheinland-Pfalz für Innovation” for financial support.

Poster to go

Outlook:

• FEM: Particle abrasion modeling

• CFD: Coupling techniques for surface deformation modeling

CFX simulation

Euler-Lagrange approach

Integration of force balance on particles

Momentum transfer from fluid to discrete phase

ProcessNet-Jahrestagung und 31. DECHEMA-Jahrestagung der Biotechnologen 2014, 30. Sep. - 2. Okt. 2014, Eurogress Aachen

Introduction

DEM simulation

Conclusions

DEM modeling of Erosion

Cohesion force models implemented in EDEM:

• Linear bonding model

No damping component & no bond breakage under compression

• Johnson-Kendall-Roberts (JKR) model

Applicable only for small cohesion forces like high porous mediums

Fig. 2: Random distribution of tensile strength

30°30 m/s

30 m/s30°

Fig. 3: Impact effects of different particle forms

Definition of a material model as unit cell bonds

Bond reconnecting number: Brittle material: 0 Ductile material> 5

Time step

Based on particle size & contact forces: 5×10-12 - 2×10-11 s

Bond status

0: New contact 1, 2: Intact contact 3: Destructed contact

Fig. 1: Applied numerical techniques from DEM to CFD

Simulation tool: ANSYS-AutoDyn

Element erosion approach:

Chip separation and material pile-up modeling

Equation of state (EOS):

Shock equation of state (for solid metallic

material)

Critical plastic strain: 1.5

Dynamic friction coefficient: 0.1

(neglected mostly in previous studies)

Particle material model: Rigid body

Target material model: Johnson-Cook viscoplastic strength model

Boundary conditions: Zero displacement at bottom & sides

FEM simulation Table 2: Material properties of particle & surface

Material properties Symbol Steel OFHC copper

Density ρ 7800 kg/m3 8960 kg/m3

Young's modulus E 200 Gpa 123.28 Gpa

Shear modulus G 76.923 Gpa 46 Gpa

Bulk modulus K 166.7 Gpa 128.42 Gpa

Poisson's ratio ν 0.3 0.34

Hardness HB 752 26

Table 1: DEM simulation outputs

CaseImpact

velocity & angle

Rebound velocity

Destructed bonds

Roundparticle

30 m/s, 30° 29.5 m/s 10145

Unround particle

30 m/s, 30° 18.1 m/s 18090

Incident direction

Rebound direction

Target sample

Fig. 4: Experimental tester and a particle during impact

hlip

dmax

Fig. 5: Particle and crater parameters definition

Fig. 7: Chip separation & material pile-up in case 2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1 2 3 4 5 6 7 8

dm

ax

(mm

)

Simulation case 1-8

Comparison of dmax in experiment and simulation

Experiment*

Autodyn (3-D)

LS-DYNA* (2-D)

CaseVi

(m/s)αi (°) θi (°)

1 80 80 20

2 81 60 20

3 46 60 20

4 81 60 40

5 50 60 40

6 85 50 50

7 51 50 50

8 80 40 40

Fig. 6: Comparison of dmax in experiment & simulation for eight cases

Fig. 12: From left to right: Geometry generation, meshing & grid study, boundary conditions definition and final CFD simulation

Fig. 8: Schema of experimental setup Fig. 9: Centrifugal accelerator disc Fig. 10: Sample holder adjustment

0

0.5

1

1.5

2

2.5

3

3.5

4

1.5 2 2.5 3 3.5

Mate

rial lo

ss in 4

h (

mg)

Sand concentration (%)

Aluminium alloy (WNR 3.1645)

Stainless steel (WNR 1.4305)

Cast iron HBN 480 (WNR 0.9650)

Cast iron HBN 450 (WNR 0.9635)

Hawiflex

Fig. 11: Erosion of five different materials

Experiments

Tester setup by application of a slurry centrifugal pump

Sample weight measurement with balance with 0.1 mg sensitivity

stationary roughness tester Hommel T8000 for surface analysis

Francis turbine parameters

• Runner diameter: 4 m

• Blade thickness: 5 cm

• Rotational speed: 300 rpm

• Hub diameter: 1 m

• Number of blades: 13

• Efficiency: 92%

Pros of DEM & FEM in comparison with CFD:

• Fundamental mechanisms of material removal

• Material properties & process parameters effects

• Rebound kinematics of particles

DEM: No. of destructed bonds in micro scale

FEM: Single particle impacts & rebound kinematics

CFD: Investigation of real particulate flows

Exp. & CFD simulation of particulate flows

Single particle exp.*

• Compressed nitrogen gas gus

• Rectangular cross-section barrel

• Constant particle orientation angle during inject

• High speed camera for impact parameters capturing

• Optical profilometer for deformation analysis