Effects of pressure waves on the cooling-fan performance and indoor flow of air-conditioning units on the roof of a high-speed maglev train

Abstract

Air-conditioning units (ACUs) are important components of trains, and their performance directly affects the thermal environment of train cabins. Their operational performance is affected by the ventilation capacity of its core component, the cooling fan. The compressible unsteady Reynolds-averaged Navier-Stockes (URANS) and the shear-stress transport (SST) k-ω turbulence model were used to simulate the flow field and pressure waves of high-speed maglev trains, both in open air and tunnels with different lengths, at 600 km/h. We validated the numerical method and settings using a scaled model test. The effects of pressure waves on the fan flow of the ACUs and the flow field around them on the roof of the train were analyzed. The results demonstrated reduced cooling-fan flow due to the high-speed flow generated by the train operation, with the flow of the downstream fan affected by the indoor flow from the upstream fan in the same ACU. The pressure waves from trains passing each other in the open air can cause significant fluctuations in the cooling-fan flow and are positively correlated with the pressure wave amplitude. Moreover, the cooling-fan flow of the ACUs was significantly affected by the tunnel pressure wave, particularly that coming from two trains passing each other in the tunnel. The impact of airflow caused by trains exiting the tunnel on the cooling-fan flow was significantly greater than that entering the tunnel, and the amplitude of the sudden change in the cooling-fan flow was closely related to the gradient of the tunnel pressure wave. Some Findings would help improve the cooling-fan performance and the internal construction design of ACUs.