CO 2 in 2050. [5] Due to the second law of thermodynamics, cooling is generally more challenging than heating. Conventional vapor-compression cooling not only results in excessive energy consumption, accelerating the depletion of fossil fuels, but also degrades the atmospheric ozone, leading to notorious environmental issues. Therefore, developing novel and pollutionfree cooling technology has become an urgent demand in the following decades.Radiative sky cooling (RSC) can harvest the coldness of the universe via the 8-13 µm atmospheric window without any pollution and energy consumption, which has witnessed great progress in the last few years. [6][7][8] Since the first demonstration of daytime radiative cooling via multilayer photonic structure by Fan and co-workers in 2014, this facile cooling technology has drawn worldwide attention. [9,10] With the joint efforts, RSC technology has achieved striking advances in building cooling, [4,11] photovoltaic cooling, [12][13][14] cryogenic cooling, [15,16] RSC driving thermoelectricity, [17][18][19] atmospheric water harvesting, [20,21] personal thermal management [3,22,23] and wearable devices. [24][25][26] For building cooling, the pioneering reports by Goldstein et al. and Zhao et al. have demonstrated that building-integrated RSC modules can provide continuous day-and-night cooling and can potentially save 32%-45% of the electricity consumption for cooling in summer. [4,11] For photovoltaic cooling, selective photonic cooler can lower the temperature of solar panels by over 5.7 K and afford the greater cooling

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The cave is of great importance for the storage of equipment and to avoid having workers in the tunnel, but it changes the tunnel section, leads to a change of slipstream and affects the safety of trains and workers. The Re-normalization group (RNG) k-ε turbulence method is used to investigate the slipstream induced by a single train passing through a double-track tunnel at 350 km/h. The slipstream in a tunnel with and without a cave is compared. The slipstream components in three directions are reported comprehensively. The results show that the existence of a cave changes the slipstream at the tail of the train. At measurement points before and after the train passes the cave, the intensity of the slipstream at the tail is mitigated; as the train passes the cave, the tail slipstream is enhanced to a certain extent. With increasing lateral distance, the peak value of the slipstream with a cave decreases faster than that without a cave. These findings suggest that the presence of a cave mitigates the slipstream intensity, but special attention should be paid to the design of ancillary facilities, especially their relative location.