Pressure-swirl spray in a low-turbulence cross-flow

Abstract

Pressure-swirl atomisers (PSA) produce fine spray and are used in many industrial, chemical and agricultural applications of sprays in flowing environments. The study examines spray from a small low-PSA exposed to low-turbulence cross-flowing air. The PSA spray was investigated experimentally using phase Doppler anemometry (PDA) and high-speed visualisation (HSV). The atomiser sprayed water into cross-flowing air at varying flow velocities. The tests were provided at a newly developed wind tunnel facility in the Spray laboratory at Brno University of Technology. PDA results contain information on the size and velocity of individual droplets in multiple positions of the developed spray (after the liquid break up is completed). A high-speed camera (HSC) documented the complexity of the liquid discharge, the formation and break-up of the liquid film, and the spray morphology. The data is relevant to CFD engineers and scientists involved in modelling as they can highlight the crucial phenomena to be considered in numerical simulations of the disperse two-phase flow case. The case allows us to study 1) Liquid discharge and sheet formation, the primary break-up of the liquid sheet, 2) secondary break-up and spray formation and 3) the Interaction of the sprayed liquid with surrounding air: gas–liquid mixing, droplet collisions, droplet clustering and droplet reposition.

Figure 1a: Spray image form high-speed imaging
Figure 1b: Optical measurement using PDA (taken from [1])

References

[1] CEJPEK and Ondřej, University of Technology, 2020.

Nomenclature

Symbol Description
A cross-section
AT arrival time to the measurement volume
Bo Bond number
c droplet concentration
CD discharge coefficient
D mean droplet diameter
d diameter
D10 arithmetic mean diameter
D20 surface mean diameter
D32 Sauter mean diameter
F force acting on a liquid element
Fr Froude number
G gravitational acceleration
K nozzle dimension constant
L characteristic distance
lb break-up distance
LDA1 velocity in Z-direction
LDA4 velocity in Y-direction
n wave number
Oh Ohnesorge number
p pressure
Q flow rate
q liquid-to-air momentum ratio
r radius
Re Reynolds number
S swirl number
Stk Stokes number
SCA spray cone angle
t time
TT transit time through the measurement volume
Tu turbulence intensity
u velocity
U12 phase shift between photomultipliers 1 and 2
U13 phase shift between photomultipliers 1 and 3
w swirl component of the velocity
We Weber number
X, Y, Z Cartesian coordinates

Greek symbols
v difference between the gas and droplet velocity
ηn nozzle efficiency
µ dynamic viscosity
ρ liquid density
σ surface tension

Indices
a aerodynamic
ac air core
c swirl chamber
cf cross-flow
Cr critical
D droplet
g gas
i index number of a droplet
in atomiser inlet (inlet ports)
l liquid
m inertia
n total number of droplets
o exit orifice
p pressure
r relative
v0.1, v0.5, v0.9 volumetric fractions 0.1, 0.5 and 0.9 of the total droplet volume
µ related to dynamic viscosity
σ related to surface tension
$\tau$ liquid film thickness

Abbreviations
AC air core
fps frames per second
GT gas turbine
HSC high-speed camera
HSV high-speed vizualization
LDA laser Doppler anemometry,
PDA phase Doppler anemometry
PSA pressure-swirl atomiser
RSF relative diameter span factor

Contributed by: Ondrej Cejpek, Milan Maly, Jan Jedelsky — Brno University of Technology

Front Page

Introduction

Review of experimental studies

Description

Experimental Set Up

Measurement Quantities and Techniques

Data Quality and Accuracy

Measurement Data and Results