## 1 Introduction  
With the increasing problems of environmental pollution and energy shortages, electric vehicles have received special attention because of their advantages in energy conservation and emissions reduction. The core to developing electric vehicles is the power battery, and one of the main factors in the lifecycle of a battery is temperature. The power battery pack of an electric or hybrid vehicle is more likely to cause a large amount of heat generation and accumulation under high current charging and discharging conditions. If the heat cannot be released in time, the battery is prone to safety problems such as overheating, burning, and explosions [1, 2, 3]. Moreover, elevated local temperatures cause an increase in the temperature difference within the battery pack. Previous research shows that the optimal operating temperature range of lithium-ion batteries is 25-40 \({}^{\circ}\)C, and the battery pack temperature difference is less than 5 \({}^{\circ}\)C [4]. Hence, a reasonable BTMS can greatly lengthen the cycle life of batteries and accelerate the development of electric automobiles. Depending on whether the air-cooling systems are affected by the external environment, electric vehicles can have either active or passive cooling modes. Passive cooling modes dissipate heat through natural air intake. Due to the influence of the external environment, they can only dissipate heat from the battery pack within a certain range. However, active cooling can reduce the influence of environmental factors and ensure that the battery remains within suitable working temperatures. Active cooling mainly includes forced air cooling [5; 6; 7], liquid cooling [8; 9; 10], and phase change material cooling [11; 12; 13; 14; 15]. Forced air cooling systems are widely used in battery thermal management systems because of their simple structure, low cost, and light weight. According to the arrangement of the batteries, the air-cooling system can be either serial or parallel. [PERSON] et al. [16; 17] showed that serial ventilation with air flowing through the battery from the inlet causes the temperature to gradually rise, so that the battery temperature at the outlet of the battery pack is much higher than the temperature of the battery at the inlet. In parallel ventilation modes, the wedge-shaped inlet and outlet allow the air to be more evenly distributed between the batteries, thereby reducing the temperature difference. Many previous studies have improved the heat dissipation performance by adjusting the structure of the BTMS. [PERSON] et al. [18] evaluated the fans in different positions in air-cooled battery packs, and the results showed that when the fans are installed above the battery pack, a better cooling effect can be obtained. [PERSON] et al. [19] and [PERSON] et al. [20], respectively, studied the effect of battery spacing and battery-to-wall distance on the heat dissipation performance. It was found that when the distance increases, the system power consumption and the temperature difference of the battery pack decrease but the battery temperature increases. In order to improve the cooling effect, some structural optimization approaches were introduced to adjust the structure of the battery pack to improve the heat dissipation performance of the BTMS. [PERSON] et al. [21] used a particle swarm optimization algorithm to adjust the battery spacing and air intake position, reducing the temperature rise of the battery pack by 2 \({}^{\circ}\)C. [PERSON] et al. [22] used a neural network to predict the temperature of the battery and optimized the thermal performance of BTMS by changing the battery spacing. The result showed that the temperature uniformity in the battery pack was improved after optimization. The computational fluid dynamics (CFD) method is widely used in battery thermal management simulation because of its high accuracy. However, when optimizing the battery module, the CFD method usually requires multiple sets of simulations, and each simulation requires several hours of simulation.