本文来自2022年IYPT的赛题，主要探究蜡烛周围流场性质并用数学方法研究纸螺旋转动时的扭矩. 蜡烛周围流场性质通过查阅文献得出并由数据验证. 流场用COMSOL Multiphysics仿真模拟并用纹影法可视化. 又用两种方法推导纸螺旋扭矩的影响因素. 积分得到纸螺旋转动惯量的表达式. 用实验数据拟合纸螺旋转动的运动曲线并求出角加速度. 最终计算扭矩，然后分析其与纸张密度、悬挂高度、纸螺旋层数的定性关系. 本文用实验数据还验证了上述方法的合理性.

This article comes from 2022 IYPT’s problem. Main researches are properties of flow field around a candle and the paper spiral’s torque. This article consults literature and uses data to verify the properties of flow field around a candle. The pictures of flow field are simulated by COMSOL Multiphysics and flow visualization is realized striation technique. Then two different methods are used to derive influencing factors of paper spiral’s torque. An expression for paper spiral’s rotational inertia comes from integration method. Experimental data are used to fit the curve of paper spiral’s rotation. Angular acceleration can be obtained from the curve. Finally calculate paper spiral’s torque and analyze relationship between paper density, suspension height, layers of spiral and the torque. Data also prove the theory and calculation method are rational and feasible.