Koizumi, TakumaKogawa, TakumaArmfield, StevenTorres, Juan F.Komiya, Atsuki2026-07-032026-07-030735-1933ORCID:/0000-0002-3054-8638/work/219172793https://hdl.handle.net/1885/733812585This study investigates mixed convection formed by vertical natural convection and a low-Reynolds-number jet impinging on an upstream thermal boundary layer. The objective is to clarify the contribution of jet Reynolds number (Re) and nozzle geometry—impingement location (yimp), impingement distance (d), and nozzle height (h)—to the development of oscillations in the jet impingement region and their impact on heat transfer. Two-dimensional numerical simulations were conducted, first to examine the effect of Re under a fixed nozzle configuration and subsequently to assess the sensitivity of oscillatory behavior to systematic variations in nozzle geometry. Oscillations exhibit a non-monotonic dependence on Re: periodic amplification emerges near Re ≈ 95, broadband fluctuations develop at higher Re. Analysis of the turbulent kinetic energy indicates that production-buoyancy balance differs between periodic and chaotic states, and that downstream oscillation intensity is not dictated solely by the dynamics in the impingement region. Geometric effects further modulate oscillation-induced heat transfer: while the impingement location plays a minor role, both the impingement distance and the nozzle height govern a trade-off between peak enhancement and Re range over which significant heat transfer enhancement is maintained. These insights provide a mechanistic foundation for optimizing buoyancy-driven convective heat transfer modulated by a weak impinging jet in thermal management applications.enPublisher Copyright: © 2026 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license. http://creativecommons.org/licenses/by-nc-nd/4.0/Heat transfer enhancementImpinging jetNatural convectionNozzle geometryNumerical simulationOscillatory flow202610.1016/j.icheatmasstransfer.2026.111000105035639568