Investigation of Orographic Updraft Characteristics and Horizontal Distribution Model

Abstract Bird-inspired autonomous soaring technology enables unmanned aerial vehicles (UAVs) to utilize natural updrafts, akin to avian flight, significantly enhancing core performance metrics such as endurance and range. This technology has been successfully validated across multiple UAV platforms. In nature, thermal updrafts and orographic updrafts represent two prevalent types of ascending airflows, with the latter being more common in mountainous terrain. However, due to the lack of systematic research on the distribution patterns of orographic updrafts, a rational and precise model for such airflow remains underdeveloped. Consequently, real-time and efficient prediction of orographic updrafts remains unattainable, limiting current autonomous soaring technologies to thermal updraft environments and hindering their broader application across UAV industries. In this study, Reynolds-Averaged Navier-Stokes numerical simulations were employed to investigate the vertical and horizontal distribution characteristics of orographic updrafts over isolated hills and continuous mountain terrains. Key findings include: The horizontal distribution pattern of updrafts over isolated hills approximates that of thermal updrafts, allowing existing thermal updraft models to be directly applied. Compared to conventional orographic updraft models, the proposed Orographic Updrafts Horizontal Distribution Model demonstrates significantly improved consistency in describing updraft distribution patterns. Furthermore, it provides a more rational representation of updraft behavior above mountain ridges, enabling real-time and efficient prediction of orographic updrafts for UAV applications. For both isolated hills and continuous mountain terrains, the maximum updraft intensity consistently occurs at two-thirds of the mountain height along the windward slope.