Oscillation dynamics in vertical natural convection induced by a weak steady impinging jet: Effects of jet velocity and nozzle geometry

This 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 (y_imp), 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.