experimental study on the effect of reynolds number in a

EXPERIMENTAL STUDY ON THE EFFECT OF REYNOLDS
NUMBER IN A FULLY-DEVELOPED TURBULENT JET
GIORGIA SINIBALDI (DIPARTIMENTO DI INGEGNERIA MECCANICA E AEROSPAZIALE. UNIVERSITÀ DI ROMA "LA SAPIENZA" );
LUCA MARINO (DIPARTIMENTO DI INGEGNERIA MECCANICA E AEROSPAZIALE. UNIVERSITÀ DI ROMA "LA SAPIENZA" );
GIOVANNI PAOLO ROMANO (DIPARTIMENTO DI INGEGNERIA MECCANICA E AEROSPAZIALE. UNIVERSITÀ DI ROMA "LA
SAPIENZA" )
Turbulent jets have been widely considered in fluid dynamic research due to their relatively simple
geometry coupled with the huge variety of large- and small-scale phenomena involved. Moreover, this
kind of flows are relevant for several engineering applications, such as e.g. mixing, combustion,
propulsion and biomedical applications (Grizzi & Camussi, J Fluid Mech 2012). The main goal of the
present work is to investigate the effect of Reynolds number on a fully developed turbulent air jet,
analyzed by means of Particle Image Velocimetry. The analysis is focused on the near and intermediate
fields of the jet, which often dominate practical applications for which upstream conditions can
significantly influence heat, mass, and momentum transfer (Ball et al, Prog Aero Sci 2012). The set-up
consists of a cylindrical stagnation chamber, connected to a high pressure circuit and a seeding system
for PIV, and a cylindrical test chamber, provided with two windows for optical access. The two chambers
are connected by means of a pipe. The pipe geometry, diameter D = 0.6 cm and length L = 70 cm , i.e.
L = 116D, allows to obtain a fully developed turbulent jet at the outlet, in agreement with what reported in
the available literature (Zagarola & Smits, J Fluid Mech 1998). The PIV system consists of a doublepulse Nd:YAG Quantel laser and a PCO Pixelfly Usb camera, used to acquire pairs of images. The flow
is seeded in the stagnation chamber with olive oil droplets of diameter 1 - 2 µm by means of a Laskin
Nozzle. An accurate analysis of the mean and fluctuating velocity fields are performed, together with
turbulence statistics. A jet length of around 20 diameters is reached by overlapping three different
measurement regions for the Mach number which spans between 0.1≤ M ≤ 0.6. In Figure jet snapshots
at Re=16000 are shown. The picture of the olive oil droplets is reported at the top and an instantaneous
velocity field obtained by PIV is reported at the bottom of the figure.
Snapshots, olive oil droplets (top) and axial velocity (bottom).
Re = 16000.