Water atomization in spray nozzles

Division of Fluid Mechanics

Contents

Introduction

Techniques used in

STAR-CCM+

Case definition

Nozzle description

Results

Conclusions

General facts about

Epsilon

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Introduction

Why study primary atomization?

• In STAR-CCM+ the pressure

swirl injector present the only

choice for primary break up

analysis. What about other

types of spray nozzles with

non conical shape.

When modeling sprays you need

to have knowledge about droplet

and velocity distribution for the

specific nozzle in order to set

injector properties.

Spray nozzle

The water nozzle 1/4MEG1506

Spray data (droplet size)

Minimum droplet size: 80 µm

Maximum droplet size: 500 µm

Mean droplet size: 123 µm

Spray nozzle volume

Techniques used in STAR-CCM+

Geometry handling through

imported parts for improvìng

productivity

Trimmed mesh

Refinement boxes for resolving

the water fluid

Imported parts for definition of non

regular shapes for reducing the

cell count

Techniques used in STAR-CCM+

VOF – model for capturing the

interface between the air and

water

Surface tension modeling

Turbulence modeling

A number of field functions for

spray analysis

Thresholds for detailed analysis

Histogram plots for analyzing

velocity and droplet size

distributions

The image to the left shows the

VOF-interface together with

velocity vectors

The velocity vectors are posted

on the threshold for the water

The vectors indicate the

velocity distribution and the

direction of the velocity

Typical results Velocity

The histogram to the left shows

the calculated velocity

distribution obtained from the

VOF-simulation.

The data from the histogram

will be used for implementing

the velocity distribution in the

injector of the Lagrangian

phase.

Typical results Velocity

The images to the left shows

the calculated droplet size in a

the VOF threshold after the

secondary break up.

The droplet size is estimated

by using force balances on

the VOF-interface.

The final droplet diameter is in

the range of 90 – 110

microns.

Typical results Droplet size

The histogram to the left

shows the droplet size

distribution for the threshold

shown on the previous slide.

The mean droplet size

corresponds well to the

experimental value of 123

microns.

The resulting distribution is in

the injector definition of the

Lagrangian phase.

Typical results Droplet size

Conclusions

STAR-CCM+ provides an easy to

use frame work for analyzing the

atomization process.

The usage of thresholds,

histograms and field function

renders the whole process to be

carried out within STAR-CCM+.

The results are in good agreement

with experimental data and show

that this method may be used

when experimental data is not

available.

Room for improvement

Under specific conditions or

demands on resolution of the

VOF-interface an explicit

numerical scheme would be

desired.

Enhance the capability of adding

user coding in STAR-CCM+ to the

level of STAR-CD. This would

improve the capability of adding

custom models into STAR-CCM+

without the need of using JAVA.