Measurement of condenser airflow rate under train-induced shear flow using particle image velocimetry

During train operation, high-speed roof slipstreams exert strong shear on the airflow through the air-conditioning unit (ACU) condenser, reducing the condenser airflow rate. This decrease can trigger ACU overheating alarms or shutdowns, compromising both operational safety and passenger comfort. Conventional experimental techniques, however, struggle to accurately measure condenser airflow rate under such complex shear flow conditions. To overcome this limitation, we performed wind tunnel tests on a full-scale train ACU and developed a novel measurement strategy integrating particle image velocimetry, multiple field-of-view stitching, and airflow flux integral surface extraction. This approach enables, for the first time, reconstruction of the flow field in the ACU air-inlet region and yields high-precision measurement of condenser airflow rate under shear flow. The experiments show that increasing the incoming airflow speed from 15 to 20 m/s intensifies the shear effect, enhancing turbulent dissipation and pressure loss at the air inlets and reducing condenser airflow rate by 3.2%. Analysis further reveals that under the combined effects of shear flow and fan rotation, the windward side retains uniform flow, whereas the leeward side develops vortices and localized backflow. These effects produce a characteristic strip-like, asymmetric distribution of vertical velocity across the air inlets. This study provides valuable data on complex intake flow behavior under shear conditions and technical support for investigating airflow interactions in train ACUs and other ventilation systems.