# Optimization of Airflow Organization in Bidirectional Air Supply Data Centers in China
## 3 Results
### Air Supply Characteristics  
The airflow characteristics in the plenum chamber of the bidirectional air supply system are illustrated in Figure 5. As shown in Figure 5a, uneven velocity distribution is observed within the plenum chamber. The airflow streamlines exhibit turbulent patterns under this supply configuration. The CRAC supply air enters the plenum through air ducts at relatively high initial velocities that gradually decay, while non-supply zones maintain lower flow speeds. The airflow from CRAC6 (left side) diverges after colliding with opposing flows from CRAC1 and CRAC2 (right side), generating strong wall-adjacent vortices with their cores proximate to the left-side CRAC units exhibiting lower supply rates. Another air stream intertwines with terminal flows from CRAC2, CRAC3, and CRAC7. The collision between CRAC7 and CRAC3 flows, combined with entrained terminal flow from CRAC4, directs a consolidated stream toward the lower-left zone, simultaneously deflecting CRAC5 airflow toward the wall and forming mid-plenum vortices.  
Figure 6b presents the pressure distribution within the plenum, revealing marked spatial heterogeneity. Under the current supply mode, the plenum develops both unidirectional and bidirectional supply zones. Unidirectional zones exhibit higher static pressure at distal regions (5-10 Pa) versus proximal areas near CRAC units. Bidirectional zones demonstrate pressure inversion due to flow collisions, with peak static pressures (6-14 Pa) at collision interfaces flanked by lower-pressure zones, creating steep pressure gradients.  
Figure 7 presents the airflow distribution of perforated tiles in each row. Figure 7a shows the airflow distribution trends differ among cold aisles, while the two rows within the same cold aisle exhibit nearly identical variation patterns, indicating non-uniform airflow supply. Cold aisle AB demonstrates higher airflow rates at both ends and lower values in the middle, whereas cold aisles CD, EF, and GH display the opposite trend with higher central airflow and lower values at the ends.  
Figure 7b reveals that despite supplemental airflow from other air conditioning units, the average airflow rates of rows AA, AB, AC, and AD in the unidirectional supply zone remain approximately 0.20 m\({}^{3}\)/s, lower than the 0.25 m\({}^{3}\)/s average in the bidirectional supply zone. Among these, row AD, closest to the bidirectional supply zone, exhibits the highest average airflow rate. Furthermore, the minimum airflow rates in rows AE and AF of the bidirectional supply zone drop to 0.14 m\({}^{3}\)/s, significantly below the zonal average, reflecting poor supply air uniformity.  
A comparison between Figures 6 and 7 demonstrates a positive correlation between perforated tile airflow rates and underfloor static pressure distribution. Higher static pressure corresponds to increased airflow supply, while abrupt airflow reductions coincide with low-pressure zones induced by vortices.  
Figure 6: Airflow distribution of plenum. (**a**) Streamline distribution; (**b**) pressure distribution.  
Figure 7: Airflow distribution of perforated tiles. (**a**) Line plot of airflow velocity distribution; (**b**) box plot of airflow velocity distributions.