Computational Fluid Dynamics (CFD) is widely used to simulate tunnels and partially substitute on-site tests. As technology advances, new application opportunities appear; some examples are the optimal operation of ventilation and emergency systems, risk assessment of tunnels and training of the operators. Even when the computational capacity of computers has grown, CFD is still constrained by the large amount of computational resources needed in long tunnels. This introduces a need for methods able to reduce the amount of time required for simulations. To face this need, a novel 1D–3D multiscale model is presented in this paper. The model incorporates the code Whitesmoke into FDS (Fire Dynamics Simulator) through a direct coupling. Whitesmoke manages the fluid dynamics, temperature and concentration of species in the 1D portion, while FDS calculates these fields in the portion where fire occurs. Using this multiscale model, the computation time for long tunnels is reduced, proportionally to the 1D length in the domain. Also, additional simulation capabilities particularly useful for tunnel analysis are obtained. Some new characteristics are pressure boundary conditions can be easily imposed at the tunnel portals or at the ventilation shafts; the characteristic curves of the fans/jet-fans can be included, also considering the degradation effects due to smoke propagation; the piston effect can be properly considered. Our research verifies most of its capabilities, also clarifying its limitations and the criteria used to set the domain for the analysis. As a final step, the model is tested in a tunnel with a cross section of 4.8 m and 600 m of length with a 2 MW fire, comparing its performance with a full 3D FDS simulation. The difference in temperature and velocity is minimal for most of the domain, making It a good way to optimize resource usage in large simulations. Furthermore, the multiscale manages to reduce the computational time of more than a 50%.

计算流体动力学（CFD）被广泛用于模拟隧道并部分替代现场测试。随着技术的进步，出现了新的应用机会。例如通风和应急系统的最佳运行，隧道的风险评估以及对操作员的培训。即使计算机的计算能力已经增长，CFD仍然受到长隧道中所需的大量计算资源的限制。这就需要一种能够减少仿真所需时间的方法。为了满足这一需求，本文提出了一种新颖的1D–3D多尺度模型。该模型通过直接耦合将代码Whitesmoke合并到FDS（Fire Dynamics模拟器）中。Whitesmoke管理一维部分的流体动力学，温度和物质浓度，而FDS会在发生火灾的部分计算这些字段。使用这种多尺度模型，长隧道的计算时间与域中的一维长度成比例地减少了。此外，还获得了对隧道分析特别有用的附加仿真功能。一些新的特征是，可以很容易地在隧道入口或通风井处施加压力边界条件。可以包括风扇/喷气风扇的特性曲线，同时考虑由于烟的传播而造成的退化影响；可以适当考虑活塞效应。我们的研究验证了其大多数功能，还阐明了其局限性以及用于设置分析领域的标准。最后一步，模型是在横截面为4.8 m，长度为600 m的隧道中以2 MW的火力进行测试的，将其性能与完整的3D FDS仿真进行比较。在大多数情况下，温度和速度的差异很小，这是在大型仿真中优化资源使用的一种好方法。此外，多刻度可以将计算时间减少50％以上。