Abstract: This study aims to advance ventilation efficiency and thermal regulation in the large-scale swine housing in summer. The critical deficiencies were found in the tunnel-ventilated gestation facilities—specifically, inadequate localized airflow and heat stress risks within sow activity zones. The integrated methods were employed in the high-fidelity computational fluid dynamics (CFD) modeling on Ansys Fluent 19.0. The physical model was incorporated to geometrically simplify 3D representations of a full-scale gestation house (98 m × 47 m × 4 m), including the interior components, such as free-access stall arrangements and underground ventilation duct networks. These numerical models were calibrated and then validated against the extensive empirical measurements. The characteristic peaks were collected in summer (outdoor ambient temperature range: 33.4-34.2 ℃, and relative humidity range: 72.0%-75.1%). Advanced monitoring instrumentation was strategically deployed in the facility. Particularly, much attention was paid to the animal-occupied zones, where the thermal stress developed typically. Validation datasets were acquired from 24 monitoring points at 0.5 m height (sow breathing zone). The exceptional model accuracy was achieved after the simulation of the temperature fields. The temperature and air velocity were predicted with the mean relative error of 0.97% and 4.15%, respectively, compared with the measured values. There were the strong statistical determination coefficients (R² = 0.92 for temperature comparisons, R²= 0.90 for velocity comparisons) after validation. The reliability of the improved model was found suitable for the building environment in modern agriculture. Systematic computational analysis revealed that the critical microclimate deficiencies were characterized by the symmetrical airflow dispersion from underground outlet configurations that generated persistent recirculation vortices above animal-occupied zones, when the conventional architecture of the tunnel ventilation maintained acceptable macro-environmental uniformity (temperature non-uniformity coefficient: 0.11; velocity non-uniformity coefficient: 0.14). Aerodynamic microenvironments were featured by the critically insufficient air movement (average velocity: 0.3 m/s) and elevated temperature conditions (average: 28 ℃), precisely where the sows experienced the greatest thermal stress. Furthermore, this ventilation was particularly pronounced in the areas furthest from air intake points. The momentum dissipation was identified by the inadequate air mixing and heat removal. The effective environmental temperature calculation at 90% relative humidity reached 28.2 ℃—significantly exceeding the 27 ℃ threshold for the porcine heat stress initiation, according to the national standards of animal welfare. An airflow optimization strategy was proposed to fabricate the targeted fabric duct supplementation in order to resolve these fundamental deficiencies. Specifically, precision air distribution components and momentum-based delivery were determined to identify the vortex formation. Practical implementation demonstrated the transformative efficacy after airflow optimization, the substantial velocity enhancement in critical sow zones (achieving ≥1.0 m/s), temperature reduction to 27.0 ℃, and the effective environmental temperature decrease to 19.0 ℃—within the optimal porcine thermoneutral zone (15-27 ℃) for the excellent environmental uniformity. The optimal system also demonstrated that the improved temperature distribution was consistent with the reduced spatial variation over the animal-occupied zones, particularly in the areas previously experienced ones. Additional analysis confirmed that the modified system was maintained in the varying external climate. The seminal contributions were as follows: 1) CFD-based identification of vortex-induced microclimate failures in the tunnel ventilation; 2) "Tunnel-duct synergy" for the precision air delivery without structural modification; and 3) Validated integrated measurement-simulation protocols for agricultural environmental optimization. The finding can provide both practical solutions and theoretical foundations for the efficient and precise upgrades of tunnel ventilation. The significant engineering value can also offer to improve animal welfare in intensive livestock operations.