CFD validation of cyclone separator using star ccm+

Cyclone Separator

STAR-CCM+ v6.02

Introduction

Cyclones are employed for removal of particulate

contaminants from polluted air streams in a wide variety of

engineering applications

Nature of flow-particle dynamics in the cyclone lends itself

as an excellent example for demonstrating the Lagrangian

Particle Transport (LPT) approach

In this tutorial, we have outlined the methodology to set-up

a simulation to characterize the performance of a cyclone;

Incidentally, results of the current effort also serve to

validate the applicability of STAR-CCM+ for similar

applications (strong swirling flows)

Further, additional information elucidating the fluid and

particle behaviour inside the cyclone are presented

Simulation of Cyclone Separators with STAR-CCM+


Geometry and Operating Conditions

a/D b/D De/D S/D h/D H/D B/D

.5 .25 .5 .625 2. 4. .25

D = 0.2 m

H

h

S

a

b

D

De PRESSURE

OUTLET (1 bar)

VELOCITY INLET

Air + Solid particles

Air

velocity, m/s 20

density, kg/m3 1.205

Solid Particles

velocity, m/s 20

density, kg/m3 3320

volume fraction 3%

size, mm 5x10-3

Reference: Numerical Study of Gas-Solid

Flow in a Cyclone Seperator, Wang et al.,

Third International Conference on CFD in

the Mineral and Process Industries,

CSIRO, Australia, PP 371-376, 2003

Models & Reference Conditions

The following models were involved in the problem setup:

Three-dimensional, Gravity

Constant Density Gas (Air)

Implicit Unsteady

Turbulent, Reynolds-Averaged Navier-Stokes

Reynolds Stress Turbulence

Two-layer All Y+ Wall Treatment

Linear Pressure Strain Two-layer

Segregated Flow

Segregated Fluid Isothermal

Reference Conditions

Pressure: Atmospheric

Temperature: 300 K

Turbulent Intensity and Viscosity Ratio: 1 % & 10

Modeling Information

CAD model of the geometry was created in star-design

based on data provided in the reference

Geometry imported into STAR-CCM+

Surface and Volume meshing performed using the Surface

Remesher and Polyhedral Volume Mesher

Prism layer option was activated at the volume meshing

stage to generate prism layers on all wall boundaries

Final computational mesh comprised polyhedral cells and

two prismatic cells (of total thickness 5 mm) at all wall

boundaries

Mesh count (trimmer + 2 prism layers on the walls)

35732


Polyhedral Mesh

Number of cells:

35732

2 prism layers

Boundary Conditions

Velocity inlet (with base case value of 20 m/s)

Pressure outlet (with atmospheric pressure)

Rest all boundaries treated as no-slip walls

Simulations performed in the implicit unsteady fashion

with a time step 0.01 sec

Continued till the residuals attained a steady value @

which time a four-order reduction in the residuals was

observed

Further, a plot of mass-flow averaged inlet pressure value

was also monitored to judge convergence

For validation purposes, simulations were repeated at six

more inlet velocity values (ranging from 5 to 35 m/s) to

generate the pressure drop curve as a function of velocity


Velocity and Static Pressure Contours(@ 20 m/s)


Velocity Vectors and Streamlines


Axial and Tangential Velocity @ Line Probe


Location

Comparison @ Different Inlet Velocities

(35, 20 and 5 m/s)



Validation (Expt & FLUENT data from reference)

Performance Characterization

Performance of a Cyclone is normally characterized by

its ability to classify particles of different sizes

For a particular geometrical configuration, a unique

curve expressing the classification (particle collection

efficiency in the outflow stream) as a function of particle

size is obtained for a particular flow rate

The detailed procedure to generate the classification

curve for the base case (20 m/s) is outlined in the next

few slides

Further salient features with respect to particle tracking

are illustrated using

Particle Tracking

One-way coupling (from gas to particle) was assumed

between the gas and particle phases

Particle tracking performed under the steady flow mode

Spherical particles (parcels) with client supplied density

were tracked on the converged flow field

Drag (Schiller-Neumann), Virtual Mass and turbulence

dispersion forces were considered to act on the particles

Particles (parcels) impacting on the wall surfaces were

assumed to be rebounding except the bottom one where

they were assumed to escape

Particles were released on the presentation grid and

tracked till they exited either the bottom wall (or) the top

outlet


Injection Definition

Particle injection into the domain can be achieved by different mechanisms

In the present case, a presentation grid (as shown in the illustration below) was defined and located just downstream of the inlet patch

Injection points were uniformally distributed in a grid 8 x 16 = 128 total points

Methodology

Specified number of mono-disperse particles (parcels) of

different sizes (ranging from a minimum to a maximum

value) are seeded at the inlet boundary and tracked in

succession through the frozen flow field

A no-slip condition is assumed for the parcels seeded at the

inlet boundary

Efficiency of separation for each particle (parcel) size is

estimated by calculating the fraction of the total number of

parcels seeded at the inlet boundary that reach the either

boundary (top/bottom outlet)

In the present case, we have estimated the separation

efficiency based on the fraction collected at both the bottom

as well as the top outlet

Classification Characteristics [@ 20 m/s]


Observations

Results of the LPT indicate that the cut point diameter

(particle size corresponding to 50% separation) is of the

order of 1.2 mm

Separation performance for particle sizes 1.5 mm and

above is ~ 95% and above, whereas, that for 0.75 mm

and below is ~ 5 % and below

Classification curve seen to be pretty steep with a

sharpness of cut (D95%/D5%) of ~2

Simulation of Cyclone Separators with STAR-CCM+, CD-adapco Torino Office


Tracks for 1 mm, 1.25 mm, 1.5 mm Particles


Velocity/Residence Time for 0.5 mm & 2.0 mm


Animation Depicting 25 Tracks (1.25 mm)

(individual tracks)


Animation Depicting Transport of 25 Tracks (1.25 mm)

(gradual progress as a group)

Detailed step-wide procedure involved in setting up a

LPT routine to simulate fluid-particle flow in a cyclone

separator was demonstrated

Predicted pressure drop curve @ various flow rates

generated from simulation results seen to be in very

good comparison to experimental results

Methodology to generate the particle classification curve

for the cyclone was elucidated

Classification curve generated for the base flow rate

value seen to be pretty steep (value ~2) ; cut point

diameter seems to be ~ 1.2 mm


Summary

Documents

CFD validation of cyclone separator using star ccm+