Work

Turbulent natural convection in isothermally heated open-ended building shafts: Numerical analysis of ventilation performance

Year: 2025

Type: article

Abstract: We investigate buoyancy-driven ventilation in open-ended building shafts whose walls are isothermally heated, aiming to quantify passive removal of warm, polluted air from pedestrian-level urban canyons. Three-dimensional RANS CFD imulations (SST k−ω) are carried out for a 36 m building containing a central shaft of height H = 32 m with square cross-sections b = 2, 3, and 4 m and wall–ambient temperature differences ΔT = 10, 20, 30 °C, corresponding to Ra ≈ 2.9 × 10¹³–7.6 × 10¹³ (turbulent regime). The flow remains developing along the shaft and exhibits inlet separation with a delayed reattachment in wider shafts; three zones are identified: recirculation, core-flow, and boundary-dominated. Predicted mass flow rates span 3.76–16.63 kg/s, with ventilation effectiveness (mass flow per unit heat input) 0.179–0.645 kg/kJ; increasing b improves effectiveness, whereas increasing ΔT enhances heat transfer faster than mass flow, reducing effectiveness. Partial validation against Churchill–Chu correlations for an isothermal vertical plate shows average Nusselt numbers within 15% over most of the plate length. Two simplified models (a stack model with losses and a 1-D model) capture trends but underpredict 3-D effects tied to corner dynamics and entry recirculation; accuracy improves when the stack model uses a friction factor inferred from wall shear. From the CFD data, we propose correlations for the average Nusselt number and an effective friction factor as functions of Rayleigh number and aspect ratio b/H, to guide preliminary design of passively ventilated shafts in urban settings.

Source: Case Studies in Thermal Engineering

DOI: 10.1016/j.csite.2025.107553

Authors: Maram Ammar, Charbel Ziade, Aram Yeretzian, Fadl Moukalled, Issam Lakkis

Institution: American University of Beirut

Language: English

Topic: Wind and Air Flow Studies

Subfield: Environmental Engineering

Field: Environmental Science

Domain: Physical Sciences

SDG: Sustainable cities and communities

Open Access status: gold

Estimated APC paid: $1,620