[Objective] Natural draft wet cooling towe rs (NDWCTs) are key cold -end components in 1000 MW power units, owing to their buoyancy -driven ventilation, low auxiliary power consumption, low maintenance demand, and high operational reliability. However, ambient crosswinds can significantly deteriorate their thermal performance by disturbing the originally axisymmetric airflow field, inducing local flow separation and recirculation, and weakening air-water heat and mass transfer within the tower. Conventional optimization strategies for fill arrangement mainly rely on globally symmetric non -uniform configurations, which are unable to fully accommodate the inherently asymmetric aerodynamic structure formed under crosswind conditions. To overcome this limitation, this study proposes a windward -sector fill arrangement optimization method based on three -zone non-uniform fill heights, aiming to actively reconstruct the asymmetric flow field and improve the c rosswind resistance of super -large NDWCTs. 

[Methods] A super -large NDWCT with a water -spraying area of 13 000 m² 2 serving a 1 000 MW power unit was investigated. A three-dimensional numerical model was established by solving the conservation equations of ma ss, momentum, energy, and species transport, with the standard k –ε model used for turbulence closure. The model reliability was verified by grid independence analysis and field measurements. A mesh with 2.86 million cells yielded an outlet water temperatur e deviation of 0.04%, and validation under four typical operating conditions showed relative errors of 2.42%~3.78%. Based on the original three-zone fill heights of 1.5 m, 1.75 m, and 2.0 m for the inner, middle, and outer zones, respectively, the fill sheet spacing in the windward sector was reduced from 30 mm to 26 mm. The effects of windward-sector angle θ from 0° to 180° and inner radius Rs from 0 to 59 m were then examined using the control variable method. 

[Results] Under the dominant crosswind speed of 3 m/s, the air flow rate G, water temperature drop Δt, and Merkel number N first increased and then decreased with increasing θ or decreasing R s. The optimal configuration was obtained at θ = 150° and R s = 19 m, where Δt, N, and G increased by 0.218°C, 0.14, and 75.01 kg/s, respectively, compared with the original design. Within crosswind speeds of 1 ~7 m/s, the optimized scheme consistently improved thermal performance, with Δt increasing by 0.233、0.221、0.218、0.215、0.213、0.192 and 0.163° C at the correspo nding wind speeds. The improvement gradually weakened as crossflow momentum became dominant. 

[Conclusion] The proposed windward-sector fill optimization method effectively mitigates crosswind -induced thermal performance degradation by targeting the asymmetric flow characteristics of NDWCTs. It provides a practical and cost-effective strategy for crosswind-resistant design and retrofit of super-large NDWCTs.