experimental study on the effect of reynolds number in a
Transcript
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.