Thesis Defense - Onur Şen (MSME)

Onur Şen – M.Sc. in Mechanical Engineering

Assoc. Prof. Özgür Ertunç – Advisor

Date: 24.07.2025

Time: 16:00

Location: AB 246

“INVESTIGATION OF DROPLET BREAKUP IN ACTIVE-GRID GENERATED ANISOTROPIC TURBULENT FLOW”

Assoc. Prof. Dr. Özgür Ertunç, Özyeğin University

Asst. Prof. Altuğ Melik Başol, Özyeğin University

Prof. Dr. Metin Muradoğlu, Koç University

Abstract:

Droplet breakup mechanisms play a critical role in various engineering systems, with their behavior strongly dependent on continuous fluid parameters, particularly velocity. While traditional studies define breakup modes across Weber number regimes under uniform flow conditions, the influence of turbulence on droplet breakup remains poorly understood. This study investigates the effect of turbulence on droplet instability to enhance atomization understanding. An experimental setup was designed incorporating a radial fan and an active grid system with ten independent shafts and square winglets, coupled with a specific-ratio nozzle to generate controlled anisotropic turbulence. Through high-speed imaging and hotwire-anemometry measurements, 7,200 droplets were analyzed alongside nearly 1 billion hotwire measurements. Results demonstrated that active grid motion significantly altered droplet breakup mechanisms, particularly in lower Weber number ranges where atomization changes were most pronounced. Image processing quantification of atomization intensity confirmed these effects. These results also display the significant effects of the local turbulent structures and their properties, such as turbulent kinetic energy and dissipation rate, on the instability and breakup regimes of the droplets. These results may be used to update existing models for more accurate prediction of turbulent breakup mechanisms and, at the same time, design effective systems with increased atomization efficiency.

Bio:

Onur Şen received his Bachelor’s degree in Mechanical Engineering from Özyeğin University in 2020. Building upon the knowledge and experience gained during his undergraduate studies, he began his Master’s studies focusing on turbulence and secondary atomization, as part of a TÜBİTAK 1001 research project under the supervision of Assoc. Prof. Özgür Ertunç. Alongside his academic work, he commenced his professional career at Kale Jet Engines, where he currently serves as an Aerodynamics Engineer specializing in gas turbine injection systems and combustion dynamics. He has designed and built an atmospheric test setup to evaluate the performance of various injector configurations. His experimental investigations continue at Kale Jet Engines, contributing to the development and optimization of propulsion system components.