| Abstract | Single-sided ventilation (SSV) in multi-storey buildings often suffers from limited flow penetration, strong directional dependence, and floor-to-floor imbalance. This study investigates a façade-integrated Wall Windcatcher (WWC) system designed to overcome these limitations by combining a low-level supply inlet and a high-level exhaust outlet on the same façade, connected by an external vertical duct. A computational fluid dynamics (CFD) framework was first validated against atmospheric boundary layer wind-tunnel measurements using a baseline WWC geometry, which then served as the reference model for a systematic parametric analysis of geometric modifications and contextual factors based on a steady-state RANS (k–ε RNG) approach. Design variants were tested across wind angles from 0° to 180° to capture windward, oblique, perpendicular, and leeward exposures. For the k–ε RNG model, agreement in pressure coefficients (Cp) for WWC cases yielded MAPE = 5.6% (0° wind angle), 4.6% (45°), and 6.8% (90°), respectively, confirming the accuracy of the CFD framework for subsequent analysis. Three design parameters were tested individually and in combination: (i) transitions before each outlet, (ii) enlarged outlet size, and (iii) a thin inlet plane. Transitions reduced junction losses and improved vertical continuity, enlarged outlets strengthened upper-storey extraction but could suppress ground-floor intake at high obliquity, and the inlet plane provided the largest single improvement under oblique winds. The fully integrated design (COC2: inlet plane + transitions + enlarged outlet) achieved the highest and most uniform velocities, with up to 2–3× higher performance than the baseline and measurable improvements even under leeward winds. Increasing building height (to four and five storeys) enhanced mid- and upper-floor ventilation without significantly penalising lower levels. Urban-canyon simulations showed that wider street-to-building ratios improved windward and side-zone performance, while leeward zones remained limited by wake shielding. The results demonstrate that a retrofit-focused WWC can outperform SSV when inlet capture (inlet plane), duct continuity (transitions), and outlet discharge are optimised together. The findings provide practical guidance for passive ventilation design, and the development of modular façade retrofit systems for multi-storey buildings. |
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