<p>To elucidate the detailed mechanism of the fan swirling flow on generator internal cooling, a numerical investigation was conducted on a compact fan-generator system designed for small aircraft, characterized by high rotational speeds and elevated power densities. A simplified three-dimensional axial fan-generator integration model was developed, employing coupled fluid-thermal numerical methodology to analyze the internal flow field and heat transfer processes. And the isolated generator with uniform inflow, which usually represents the ram-air cooling in aircraft are also compared with fan-generator integration. The results reveal that the fan swirling flow enhances turbulence generation, effectively modifying flow structures to eliminate stagnant zones and mitigate heat accumulation. It leads to a better cooling performance, especially for the upstream components where the high power-density electric element should be arranged. Additionally, it is revealed that the circumferential and radial components of the velocity play important roles in cooling some hot surfaces of key components of the generator, even at the similar mass flow rate. The augmentation of total fluid velocity induced by the fan swirling further intensifies convective heat transfer. This study provides comprehensive insights into temperature distribution patterns and flow characteristics, offering valuable guidance for optimizing energy-efficient and reliable generator cooling system designs.</p>