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13-12-2023 | Posted by Joaquín Martí
Train aerodynamics has a significant impact on energy efficiency and fuel consumption. Computational fluid dynamics (CFD) simulation allows engineers to analyse aerodynamics and minimise air resistance long before wind tunnel testing.
The railway industry realised early the importance of aerodynamics. Already in the 1930s, iconic streamliner locomotives in Europe and America reached notable speeds thanks in part to their sleek designs. Later, the Japanese Shinkansen and the French TGV made the “bullet train” nose famous. The importance of drag on high-speed passenger trains is obvious because it scales with the speed squared and dominates other sources of resistance, but it also affects the efficiency of lower-speed, even freight, trains.
CFD models the flow of fluids around and inside bodies, including turbulence, boundary layers, wakes, and jets, which need to be resolved accurately. The techniques used to simulate this complex behaviour are Reynolds Averaged Navier Stokes (RANS) and Lattice Boltzmann Method (LBM).
CFD simulation allows analysing and optimising the drag on locomotives and rail cars during design, well before prototypes and wind tunnel testing. Improving energy efficiency helps to reduce operating costs and meet emissions targets. CFD simulation also affects many other areas of rail design, from wind noise to air conditioning.
The earlier a problem is identified, the easier it is to fix. By the time a prototype has been built and track testing starts, significant resources have been sunk. Simulation allows reducing the risk of late-stage design changes and cost overruns. It can also reveal causes that are otherwise difficult to identify. SIMULIA PowerFLOW offers clear, high-resolution, 3D visualization that makes air flow, heat distribution and noise propagation visible, allowing engineers to understand the root causes of problems and to develop effective mitigation methods. Automated design of experiments and optimisation can explore numerous different scenarios quickly.
There are many potential sources of drag on a train, not just the front, but also the rear, the gaps between carriages, the underbody, the pantographs, and cargo on freight trains. Manufacturers can use simulation to optimise the streamlining of the locomotive and wagons, and freight operators to organise the containers and their spacing, or to choose aerodynamic add-ons to reduce drag.
The pressure transients generated by high-speed trains passing through tunnels are of concern to both passengers and nearby residents. Principia has used CFD simulation to analyse that problem in high-speed railway tunnels.
Aerodynamic noise can be generated wherever turbulent airflow arises. Simulation identifies the sources and helps designers to mitigate them through aerodynamic improvements or insulation. A SIMULIA PowerFLOW user can calculate noise levels at any point and even listen to the simulated noise.
Engines, motors, transformers, and brakes generate heat and need to be cooled efficiently. Simulation can be used to design fans and cooling systems, for example modelling the air flow and heat distribution within the engine. Even the noise from cooling system fans can be simulated and mitigated.
A related issue is the heating, ventilation, and air conditioning (HVAC) systems inside the cab and passenger vehicles. Design requirements include an even distribution of treated air and limit the noise perceived by the passengers.
In brief, aerodynamics problems are key in the development of rail vehicles. CFD simulation allows engineers to analyse aerodynamics and minimise air resistance long before wind tunnel testing. It can also be used to study and minimise noise from trains for passengers and neighbouring communities. And coupled CFD-thermal simulation can also be used to design the cooling systems for the locomotive and to ensure that HVAC systems provide a safe, comfortable environment for passengers.
If you want to read more on this topic, this post is mostly taken from a recent one by Dassault Systèmes.