The accidental ignition of combustible atmospheres by hot surfaces is of great concern for chemical and process plant safety. In this paper, we present our research regarding the evolution of thermal plumes originating from hot hemispheres and discs. In particular, we focus on the effect of the orientation of the surface on the ignition process. The auto-ignition temperatures and ignition locations were studied experimentally. To get further insight, we conducted detailed numerical simulations and validated them with measurements. Three-dimensional simulations were performed on hot hemispheres and hot discs for different orientations ranging from 0° to 180°. The solver employs a transient, implicit scheme which is based on the coupled heat transfer and flow equations. The mesh in the vicinity of the hot surfaces is refined to resolve the steep temperature gradients and to capture the boundary layer separation. The influence of the orientation on critical hot spots in the gas mixture is analysed by examining the flow structures and the temperature evolution of the buoyancy-driven flow. Using the obtained results, we discuss the change of the onset and location of the ignition.

热表面意外点燃可燃环境是化学和加工厂安全的重大问题。在本文中，我们介绍了我们对源自热半球和圆盘的热羽流演化的研究。我们特别关注表面取向对点火过程的影响。实验研究了自燃温度和点火位置。为了获得更深入的了解，我们进行了详细的数值模拟并通过测量对其进行了验证。对从 0° 到 180° 的不同方向的热半球和热盘进行了三维模拟。求解器采用基于耦合传热和流动方程的瞬态隐式方案。热表面附近的网格被细化以解决陡峭的温度梯度并捕获边界层分离。通过检查浮力驱动流的流动结构和温度演变，分析了取向对气体混合物中临界热点的影响。使用获得的结果，我们讨论了点火开始和位置的变化。