舒适惬意的火车旅行

作者:Thomas Plinninger, 德国慕尼黑西门子交通部门系统工程师;Alexander Hildebrandt, 德国克雷费尔德西门子交通部门团队负责人

法律法规和客户需求迫使铁路设计人员交付拥有舒适气候的铁路客车。在过去,西门子工程师大约耗费四个月时间在气候风洞中测试铁路客车,以验证供暖、通风和冷却(HVAC)系统的设计。现在,他们可在建造第一节车厢之前利用ANSYS Fluent计算流体动力学(CFD)软件对设计进行验证,从而将测试时间与成本减少高达50%。

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Siemens ICE 4 train

“西门子工程师的设计一次性成功,有望将风洞测试的工作量减少50%,相当于缩短两个月的时间。”

在世界上的许多国家,火车旅行是一种流行的交通方式。例如在欧洲,2014年火车旅客的出行里程数超过了4,750亿公里,而在亚洲和中东,这个值更是高达五倍之多。[1] 由于政府法规日益完善,客户需求不断提高,铁路客车的气候控制也变得越来越重要。例如欧洲标准13129 (EN13129)在控制乘客车厢内的空气温度、相对湿度和空气速度方面制定了严格的要求。过去,为设计出满足这一标准的最新客车车厢的HVAC系统,我们需要在气候风洞中花费四个月的时间对HVAC系统设计进行测试和修改,仅租赁费每天就要花费数千欧元。此外,由于列车交付期限紧迫,仿真时间十分受限。

在过去几年里,西门子工程师成功利用 ANSYS Fluent CFD 软件对完整的铁路客车进行了准确的仿真,得到的详细结果与物理测量结果极为吻合。而获得仿真结果所用的时间仅为测试所用时间的几分之一。与以往相比,工程师能够评估更多的设计迭代,并且总会得到出色的HVAC性能。虽然铁路客车仍须进行测试,以验证是否符合该标准的要求,但是最新产品的测试时间已经缩短了50%,既节省了大笔的风洞租赁费用,又额外节约了相当可观的人员和设备成本。

“西门子工程师成功利用ANSYS Fluent CFD软件对完整的铁路客车进行了准确的仿真,得到的详细结果与物理测量结果极为吻合。”

HVAC 设计挑战

欧洲标准在城际铁路客车的气候控制方面规定了广泛而且颇具挑战性的要求。内部平均温度只能在设定温度的+/-1摄氏度之间变化。距离地板1.1米高的车内水平温度分布值的变化范围不超过2摄氏度。垂直温度分布值的变化范围不超过3摄氏度。此外,该标准还对墙壁、车顶、窗户、窗框和地板的表面温度,以及走廊、厕所、附属设施和列车其他部分的内部温度规定了相关要求。最后,该标准还定义了相对湿度和新鲜气流的要求。

exploded view train model

仿真模型分解图
testing train comfort

载客测试可用于检查满载列车的功能。其中用红色发热垫来仿真乘客的体温,用加湿器仿真他们的汗液蒸发,这样就能测试在实际操作条件下满载列车的所有系统是否能正常工作。一名坐着的乘客大约会辐射120瓦的热量。在设计和调整ICE 4列车的空调系统时,西门子工程师会将这些因素全部纳入考量范围。

在第一个产品建造完成之前我们无法获得HVAC系统性能的相关反馈,而此时客户通常着急提货。车厢必须安装500到800个传感器,大约花费两周时间。然后需要进行大约14周的测试,以在多种不同的气候条件下评估单节车厢设计是否符合该标准。然后进行典型的冷却测试,让车内的每一个座位都处于40摄氏度的环境温度下,并将行驶速度设置为15 km/h,内部温度设置为27摄氏度。

实现 HVAC 设计的仿真

很长一段时间以来,西门子使用CFD评估铁路客车气候控制,但是仿真并未对设计流程产生重大影响,这个情况直到近期才发生变化。内存和处理功能的限制使我们无法将整个车厢作为求解域。这意味着结果的可靠性取决于为问题指定边界的准确性。令人遗憾的是,大多数边界所位于的区域,无论是通过测量还是理论计算都无法进行准确确定。例如,许多列车都有为回流留有开口的内门。唯一能准确预测流经这些开口的气流的方式是,将门另一侧的空间也包含在求解域内。

simulation model ICE 4 train

ICE 4 列车的仿真模型

久而久之, 西门子气候控制工程师有能力向他们的管理人员展示仿真的价值,并利用所需的计算资源,以扩大模型的范围,直至它们把整个车厢包含在内。计算域的边界从提取的流体内部的浸湿表面移动到车辆的外墙。通过使用共轭热传递,外墙可被当作固体包含在模型内。外墙通常是一个由塑料、隔热材料和铝材等构成的多层结构,每一层都必须进行建模。根据标准要求来定义环境条件。此外,还需根据标准中所规定的,将乘客热源添加到模型中。

每节铁路客车由15万个组件组成。HVAC仿真所需的部件数量大于结构仿真的部件数量,但仍然远远小于总体仿真的部件数量。从产品数据管理系统手动传输所需的部件极为耗时。只要设计有显著变化,就需要重复该流程。因此西门子工程师研发了一个例行程序,该例行程序能够将PDM系统中选定的本地或中性格式的数据自动导出,并将数据转换为ANSYS SpaceClaim格式。然后,工程师使用SpaceClaim 半自动工具清理螺栓和螺栓孔等小部件以及复杂的供应商部件。所有几何相关的细节均进行显式建模。工程师还创建了用于流体分析的反向几何模型。

“这些成本节约还意味着能够加速产品交付,并增加收入。”

climatic wind tunnel
气候风洞中的 ICE 4 列车

simulation model train coach interior

车厢内部仿真模型的详细视图

西门子工程师使用 ANSYS Meshing 自动化例行程序来划分表面网格和体积网格。他们创建了大约200个不同的子域,这样就能针对模型的不同区域优化网格。对于有复杂几何模型的区域,四面体网格是最佳选择。针对尤其需要较高的边界层精度以准确计算固体表面热传递的边界层,可配合使用六面体单元以及混合的四面体-六面体网格。共轭热传递仿真可用于预测乘客可能会接触的墙壁的表面温度,以及与列车内部交换热量的通道的表面温度。结果是一个通常有5亿到6亿个单元的仿真模型,该模型可使用 ANSYS Fluent 在高性能计算(HPC)集群上进行求解。

可协助工程师检查体积流率和能量分布,以及包括车厢内所有座椅位置在内的400多个测量点的仿真结果。西门子工程师详细地评估仿真结果,将它们与EN13129标准以及客户的额外要求进行比较。仿真结果帮助工程师全面了解车厢内的温度和气流分布,并提示能够对设计进行改进的地方。工程师经常手动开展参数研究,以确定HVAC系统运行的最佳方式。

“西门子工程师的设计一次性成功,有望将风洞测试的工作量减少50%,相当于缩短两个月时间。”

仿真结果的验证

仿真验证是CFD流程中一项严格的要求。工程师首先为仿真的参考项目开展验证,然后在气候风洞中进行测试。试验研究的结果与CFD仿真的结果良好吻合,但也显示了该流程仍需要改进的地方。

借助仿真准确预测HVAC系统的性能,让西门子工程师在建造和测试第一个产品之前就能以高精确度验证车厢内的各种条件。在大多数情况下,他们能让设计一次性成功,有望将风洞测试的工作量减少50%,相当于缩短两个月时间。这样可节省风洞租赁费、人力和设备成本。如此一来,西门子工程师能够更轻松地评估备选设计方案,将乘客的舒适度提升到标准要求之上,同时无需测试多个产品变型。一旦HVAC系统成为项目的关键路径(虽然这种情况不常见),这些成本节约还意味着能够加速产品交付,并增加收入。

PrevNext
air velocity simulation vs. testing
 
空气速率的仿真结果与物理测试的比较。仿真与测量间的差异大约在20%,鉴于这是对流湍流中空气速率的局
部点值,已属于良好吻合的情况。
PrevNext
temperature simulation
Air velocity simulation

参考资料

[1] International Union of Railways, Railway Statistics 2014, 
http://www.uic.org/IMG/pdf/synopsis_2014.pdf

By Thomas Plinninger, Systems Engineer, Siemens Mobility, Munich, Germany, and Alexander Hildebrandt, Group Leader, Siemens Mobility, Krefeld, Germany

Regulations and customer demands put pressure on rail designers to deliver passenger coaches with comfortable climates. In the past, Siemens engineers spent about four months testing passenger coaches in a climate wind tunnel to validate the design of the heating, ventilation and cooling (HVAC) system. Now they use ANSYS Fluent computational fluid dynamics (CFD) software to validate the design before building the first coach to reduce the testing time and cost by up to 50 percent.

Save PDF 

Siemens ICE 4 train

"Siemens engineers get the design right the first time, which makes it possible to reduce the amount of wind tunnel testing by 50 percent — a two-month reduction."

In many countries around the world, train travel is pervasive. For example, in Europe, passengers traveled over 475 billion kilometers by train in 2014, and in Asia and the Middle East the number was more than five times greater. [1] Climate control of rail passenger coaches is increasingly important due to growing government regulations and mounting customer demands. For example, European Standard 13129 (EN13129) sets out strict requirements for controlling the air temperature, relative humidity and air speed within passenger compartments. Designing the HVAC system of a new passenger coach to meet this standard used to require four months of testing and modifying the HVAC system design in a climate wind tunnel that costs thousands of euros per day for rental fees alone. In addition, simulation time was limited due to tight deadlines for coach delivery.

Over the last few years, Siemens engineers have succeeded in accurately simulating the complete passenger coach using ANSYS Fluent CFD software and producing detailed results that closely match physical measurements. Simulation results can be generated in a fraction of the time required for testing. Engineers can evaluate more design iterations than was possible in the past, often resulting in superior HVAC performance. The passenger coach still must be tested to validate conformance with the standard, but testing time has been reduced by 50 percent on the latest products, saving significantly in wind tunnel rental expenses, as well as considerable additional savings in personnel and equipment costs.

"Siemens engineers succeeded in accurately simulating the complete passenger coach using ANSYS Fluent CFD software and producing detailed results that closely match physical measurement."

HVAC Design Challenges

The European standard prescribes wide-ranging and challenging requirements for climate control in intercity passenger coaches. The mean interior temperature can vary by no more than +/- 1 C from the temperature setting. The horizontal temperature distribution in the car measured at 1.1 meters from the floor can vary by no more than 2 C. The vertical temperature distribution can vary by no more than 3 C. The standard also specifies requirements for the surface temperatures of walls, ceilings, windows, window frames and floors, as well as interior temperatures in corridors, bathrooms, annexes and other parts of the train. Finally, the standard defines requirements for relative humidity and fresh air flow.

exploded view train model

Exploded view of simulation model
testing train comfort
Occupancy tests check the functionality of a fully occupied train. With red heating pads simulating the body warmth of passengers and humidifiers simulating their transpiration, the proper functioning of all systems can be tested for a fully occupied train under realistic operating conditions. A seated passenger radiates around 120 watts of heat. The Siemens engineers take this and other factors into account when designing and adjusting the ICE 4's air conditioning system.

In Siemens passenger coaches, warm air is delivered by a complex channel system over the side walls to the floor. Cold air is delivered by a central channel in the ceiling with approximately 30,000 4-mm-diameter air inlet holes. In the past, Siemens relied upon experience and very expensive experiments to validate the HVAC system's ability to meet the requirements of the standard. Due to the high costs of building a complete passenger coach, building a prototype is out of the question. This means that feedback cannot be obtained on the performance of the HVAC system until the first product has been built, at which point the customer is usually anxious to take delivery. The coach must be instrumented with 500 to 800 sensors, which takes about two weeks. Then about 14 weeks of testing are required to fully evaluate the compliance of a single coach design with the standard under many different climatic conditions. A typical cooling test would be run, with every seat in the car occupied at 40 C ambient temperature, at 15 km/h driving speed and at an interior temperature set point of 27 C.

Implementation of Simulation in HVAC Design

Siemens has used CFD for quite some time to evaluate passenger coach climate control; however, until recently, simulation did not have a major impact on the design process. Limitations in memory and processing power made it impractical to use the entire coach as the solution domain. This meant that the reliability of the results was dependent on how accurately the boundaries of the problem could be specified. Unfortunately, most boundaries were in areas where it was impossible to accurately determine them with measurements or theoretical calculations. For example, many trains have internal doors with openings for return flow. The only way to accurately predict the airflow through these openings is to include the room on the other side of the door in the solution domain.

simulation model ICE 4 train

Simulation model of ICE 4 train

Over time, Siemens climate control engineers were able to demonstrate the value of simulation to their management and marshal the computing resources needed to enlarge the scope of their models until they encompassed the entire coach. The boundary of the computational domain was moved from the wetted surface of the extracted fluid interior to the exterior wall of the vehicle. The outside walls were included in the model as solids using conjugate heat transfer. The walls are usually a multilayer structure consisting of materials such as plastic, insulation and aluminum; each layer must be modeled. The ambient conditions are defined by the standard. Occupant heat sources are added to the model as specified by the standard.

Each car has over 150,000 components. The number of parts required for the HVAC simulation is greater than that for a structural simulation, but still much fewer than the total. Manually transferring the needed parts from the product data management system would be very time-consuming. This process would need to be repeated whenever the design changed significantly. So Siemens engineers developed a routine that automatically exports selected data from the PDM system in native or neutral format and converts the data to ANSYS SpaceClaim format. Engineers then use SpaceClaim semi-automatic tools to clean up small parts such as bolts and bolt holes and complex supplier parts. All geometrically relevant details are explicitly modeled. Engineers create the inverse geometry needed for flow analysis.

"These savings also extend to earlier product delivery and increased revenues."

climatic wind tunnel
The ICE 4 in the climatic wind tunnel

simulation model train coach interior

Detailed view of simulation model of coach interior

Siemens engineers use ANSYS Meshing automated routines for both surface and volume meshing. They create approximately 200 different subdomains so that meshing can be optimized for different areas of the model. Tetrahedral meshing is the first choice for areas with complex geometry. Hybrid tetrahedral-hexahedral meshes with hexahedral elements in the boundary layer are used where especially high boundary layer accuracy is needed to precisely calculate heat transfer to a solid surface. Conjugate heat transfer simulation is used to predict surface temperatures of walls that may be touched by passengers and channels that exchange heat with the inside of the car. The result is a simulation model with typically 500 to 600 million cells, which is solved with ANSYS Fluent on a highperformance computing (HPC) cluster.

ANSYS CFD-Post assists engineers in examining simulation results such as volume flow rate and energy distribution, as well as more than 400 measuring points, including all seat positions in the cabin. Siemens engineers evaluate the simulation results in detail and compare them to the EN13129 standard and additional customer requirements. The simulation results provide a good understanding of the temperature and airflow distribution inside the cabin and indicate opportunities for improving the design. Engineers frequently manually perform parametric studies to determine the best way to operate the HVAC system.

"Siemens engineers get the design right the first time, which makes it possible to reduce the amount of wind tunnel testing by 50 percent — a two-month reduction."

Validation of Simulation Results

Validation of the simulation is a crucial requirement in the CFD process. Engineers performed this validation for a reference project that was simulated and also tested in a climate wind tunnel. The results of the experimental investigation and the CFD simulation show good agreement but they also show areas where the process can still be improved.

The ability to accurately predict HVAC system performance with simulation enables Siemens engineers to validate conditions inside the coach with a high level of accuracy prior to building and testing the first product. In most cases, they are able to get the design right the first time, which makes it possible to reduce the amount of wind tunnel testing by 50 percent — a two-month reduction. This saves on wind tunnel rental fees, manpower and equipment. The ability to much more easily evaluate alternative designs often enables Siemens engineers to improve passenger comfort beyond the requirements of the standard and to eliminate the need for testing product variants. When the HVAC system is on the critical path for the program, which is not unusual, these savings also mean earlier product delivery and increased revenues.

PrevNext
air velocity simulation vs. testing
 
Comparison of air velocity simulation results with physical testing. The difference between simulation and measurement is around 20 percent, which is quite good considering this is a local point value of air velocity in a convective turbulent flow.
PrevNext
temperature simulation
Air velocity simulation

Reference

[1] International Union of Railways, Railway Statistics 2014, 
http://www.uic.org/IMG/pdf/synopsis_2014.pdf

By Thomas Plinninger, Systems Engineer, Siemens Mobility, Munich, Germany, and Alexander Hildebrandt, Group Leader, Siemens Mobility, Krefeld, Germany

Regulations and customer demands put pressure on rail designers to deliver passenger coaches with comfortable climates. In the past, Siemens engineers spent about four months testing passenger coaches in a climate wind tunnel to validate the design of the heating, ventilation and cooling (HVAC) system. Now they use ANSYS Fluent computational fluid dynamics (CFD) software to validate the design before building the first coach to reduce the testing time and cost by up to 50 percent.

Save PDF 

Siemens ICE 4 train

"Siemens engineers get the design right the first time, which makes it possible to reduce the amount of wind tunnel testing by 50 percent — a two-month reduction."

In many countries around the world, train travel is pervasive. For example, in Europe, passengers traveled over 475 billion kilometers by train in 2014, and in Asia and the Middle East the number was more than five times greater. [1] Climate control of rail passenger coaches is increasingly important due to growing government regulations and mounting customer demands. For example, European Standard 13129 (EN13129) sets out strict requirements for controlling the air temperature, relative humidity and air speed within passenger compartments. Designing the HVAC system of a new passenger coach to meet this standard used to require four months of testing and modifying the HVAC system design in a climate wind tunnel that costs thousands of euros per day for rental fees alone. In addition, simulation time was limited due to tight deadlines for coach delivery.

Over the last few years, Siemens engineers have succeeded in accurately simulating the complete passenger coach using ANSYS Fluent CFD software and producing detailed results that closely match physical measurements. Simulation results can be generated in a fraction of the time required for testing. Engineers can evaluate more design iterations than was possible in the past, often resulting in superior HVAC performance. The passenger coach still must be tested to validate conformance with the standard, but testing time has been reduced by 50 percent on the latest products, saving significantly in wind tunnel rental expenses, as well as considerable additional savings in personnel and equipment costs.

"Siemens engineers succeeded in accurately simulating the complete passenger coach using ANSYS Fluent CFD software and producing detailed results that closely match physical measurement."

HVAC Design Challenges

The European standard prescribes wide-ranging and challenging requirements for climate control in intercity passenger coaches. The mean interior temperature can vary by no more than +/- 1 C from the temperature setting. The horizontal temperature distribution in the car measured at 1.1 meters from the floor can vary by no more than 2 C. The vertical temperature distribution can vary by no more than 3 C. The standard also specifies requirements for the surface temperatures of walls, ceilings, windows, window frames and floors, as well as interior temperatures in corridors, bathrooms, annexes and other parts of the train. Finally, the standard defines requirements for relative humidity and fresh air flow.

exploded view train model

Exploded view of simulation model
testing train comfort
Occupancy tests check the functionality of a fully occupied train. With red heating pads simulating the body warmth of passengers and humidifiers simulating their transpiration, the proper functioning of all systems can be tested for a fully occupied train under realistic operating conditions. A seated passenger radiates around 120 watts of heat. The Siemens engineers take this and other factors into account when designing and adjusting the ICE 4's air conditioning system.

In Siemens passenger coaches, warm air is delivered by a complex channel system over the side walls to the floor. Cold air is delivered by a central channel in the ceiling with approximately 30,000 4-mm-diameter air inlet holes. In the past, Siemens relied upon experience and very expensive experiments to validate the HVAC system's ability to meet the requirements of the standard. Due to the high costs of building a complete passenger coach, building a prototype is out of the question. This means that feedback cannot be obtained on the performance of the HVAC system until the first product has been built, at which point the customer is usually anxious to take delivery. The coach must be instrumented with 500 to 800 sensors, which takes about two weeks. Then about 14 weeks of testing are required to fully evaluate the compliance of a single coach design with the standard under many different climatic conditions. A typical cooling test would be run, with every seat in the car occupied at 40 C ambient temperature, at 15 km/h driving speed and at an interior temperature set point of 27 C.

Implementation of Simulation in HVAC Design

Siemens has used CFD for quite some time to evaluate passenger coach climate control; however, until recently, simulation did not have a major impact on the design process. Limitations in memory and processing power made it impractical to use the entire coach as the solution domain. This meant that the reliability of the results was dependent on how accurately the boundaries of the problem could be specified. Unfortunately, most boundaries were in areas where it was impossible to accurately determine them with measurements or theoretical calculations. For example, many trains have internal doors with openings for return flow. The only way to accurately predict the airflow through these openings is to include the room on the other side of the door in the solution domain.

simulation model ICE 4 train

Simulation model of ICE 4 train

Over time, Siemens climate control engineers were able to demonstrate the value of simulation to their management and marshal the computing resources needed to enlarge the scope of their models until they encompassed the entire coach. The boundary of the computational domain was moved from the wetted surface of the extracted fluid interior to the exterior wall of the vehicle. The outside walls were included in the model as solids using conjugate heat transfer. The walls are usually a multilayer structure consisting of materials such as plastic, insulation and aluminum; each layer must be modeled. The ambient conditions are defined by the standard. Occupant heat sources are added to the model as specified by the standard.

Each car has over 150,000 components. The number of parts required for the HVAC simulation is greater than that for a structural simulation, but still much fewer than the total. Manually transferring the needed parts from the product data management system would be very time-consuming. This process would need to be repeated whenever the design changed significantly. So Siemens engineers developed a routine that automatically exports selected data from the PDM system in native or neutral format and converts the data to ANSYS SpaceClaim format. Engineers then use SpaceClaim semi-automatic tools to clean up small parts such as bolts and bolt holes and complex supplier parts. All geometrically relevant details are explicitly modeled. Engineers create the inverse geometry needed for flow analysis.

"These savings also extend to earlier product delivery and increased revenues."

climatic wind tunnel
The ICE 4 in the climatic wind tunnel

simulation model train coach interior

Detailed view of simulation model of coach interior

Siemens engineers use ANSYS Meshing automated routines for both surface and volume meshing. They create approximately 200 different subdomains so that meshing can be optimized for different areas of the model. Tetrahedral meshing is the first choice for areas with complex geometry. Hybrid tetrahedral-hexahedral meshes with hexahedral elements in the boundary layer are used where especially high boundary layer accuracy is needed to precisely calculate heat transfer to a solid surface. Conjugate heat transfer simulation is used to predict surface temperatures of walls that may be touched by passengers and channels that exchange heat with the inside of the car. The result is a simulation model with typically 500 to 600 million cells, which is solved with ANSYS Fluent on a highperformance computing (HPC) cluster.

ANSYS CFD-Post assists engineers in examining simulation results such as volume flow rate and energy distribution, as well as more than 400 measuring points, including all seat positions in the cabin. Siemens engineers evaluate the simulation results in detail and compare them to the EN13129 standard and additional customer requirements. The simulation results provide a good understanding of the temperature and airflow distribution inside the cabin and indicate opportunities for improving the design. Engineers frequently manually perform parametric studies to determine the best way to operate the HVAC system.

"Siemens engineers get the design right the first time, which makes it possible to reduce the amount of wind tunnel testing by 50 percent — a two-month reduction."

Validation of Simulation Results

Validation of the simulation is a crucial requirement in the CFD process. Engineers performed this validation for a reference project that was simulated and also tested in a climate wind tunnel. The results of the experimental investigation and the CFD simulation show good agreement but they also show areas where the process can still be improved.

The ability to accurately predict HVAC system performance with simulation enables Siemens engineers to validate conditions inside the coach with a high level of accuracy prior to building and testing the first product. In most cases, they are able to get the design right the first time, which makes it possible to reduce the amount of wind tunnel testing by 50 percent — a two-month reduction. This saves on wind tunnel rental fees, manpower and equipment. The ability to much more easily evaluate alternative designs often enables Siemens engineers to improve passenger comfort beyond the requirements of the standard and to eliminate the need for testing product variants. When the HVAC system is on the critical path for the program, which is not unusual, these savings also mean earlier product delivery and increased revenues.

PrevNext
air velocity simulation vs. testing
 
Comparison of air velocity simulation results with physical testing. The difference between simulation and measurement is around 20 percent, which is quite good considering this is a local point value of air velocity in a convective turbulent flow.
PrevNext
temperature simulation
Air velocity simulation

Reference

[1] International Union of Railways, Railway Statistics 2014, 
http://www.uic.org/IMG/pdf/synopsis_2014.pdf

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