Evaluating a Turbocharger Design with Rotordynamics Analysis

July 11, 2018

“涡轮增压”一词通常被通话用来描述提高的速度,例如“涡轮增压”咖啡,它比常规的乔更快地为您充满活力。实际的涡轮增压器也会提高速度,但在燃烧发动机而不是您的早晨杯子中。涡轮增压器通过涡轮驱动的强制诱导操作,并且通常依靠流体动力轴承进行支撑。但是,这些轴承自然包括跨性力,会导致负面阻尼和系统故障。使用旋转动力学建模,您可以分析这些力如何影响涡轮增压器设计。

什么是涡轮增压器?

Turbochargers increase efficiency and power generation in combustion engines by forcing extra air into the engine’s combustion chamber. These devices are commonly used in our basic modes of transportation, such as cars (both gas-powered and diesel) and motorcycles, and are also found in more large-scale applications, such as trains, ships, aircraft, and spacecraft.

照片显示了涡轮增压器的剖视图。
用于航空推进的涡轮增压器的切割景观。昆汀·施温(Quentin Schwinn)(NASA)和美国公共领域的图像通过Wikimedia Commons

用于支撑发动机系统中涡轮增压器的流体动力轴承通常包括交叉耦合力,这些力在转子中引起负面阻尼。这增加了轴承故障的风险,实际上是整个系统的失败。当车辆发动机中的涡轮增压器发生故障时,可能会导致汽车着火。

为了设计成功运行的涡轮增压器,您可以使用该动力学分析旋转动力学模块,是结构力学模块188金宝搏优惠COMSOL Multiphysics® software

2 Studies of a Turbocharger Design in the 188金宝搏优惠COMSOL® Software

The simple turbocharger model used for this example includes a turbine, compressor, and two hydrodynamic bearings:

Schematic of a typical turbocharger.

The Rotordynamics Module includes specialized features for this modeling scenario, which makes it easy for you to set up the model geometry as well as the physics and study settings.

Overlay of two images showing two different rotordynamics studies in the 188金宝搏优惠COMSOL® software.
涡轮增压器模型的两项旋转动力学研究。

教程模型包括两项研究:

  1. Eigenfrequency analysis
  2. Frequency response analysis

The results from these studies give you insight into a turbocharger’s design and operating conditions, such as the angular speed and damping.

Results of the Eigenfrequency Study

The first study computes the eigenfrequency for the turbocharger at different angular speeds. A notable result here is thelogarithmic decrement, a value used to determine the stability of the rotor system. If the logarithmic decrement is positive, then the system is considered stable. A negative value means the system is unstable, while a value of zero means that there is no damping in the mode.

A plot showing logarithmic decrement in a turbocharger.

图形绘制对数减小的涡轮增压器的刚度。

Plots of the logarithmic decrement for the turbocharger model without (left) and with (right) cross-coupled stiffness.

The logarithmic decrement of the turbocharger has mostly negative values after including the cross-coupled stiffness terms for the bearing. This means that stable vibration modes in the presence of cross-coupled stiffness become unstable — and that it is dangerous to operate the turbocharger at the tested speeds.

对数减小,因此可以通过对涡轮增压器设计进行某些添加来改善系统稳定性,例如:

  • 倾斜垫轴承
  • Floating ring bearings
  • Material damping in the rotor
  • 挤压胶片阻尼器

频率响应模拟结果

对于频率响应研究的结果,您可以生成瀑布plots that show how the frequency spectrum of the rotor varies with the different angular speeds. Again, the responses of the turbocharger with and without the cross-coupling forces are compared.

Plot showing the frequency response of a turbocharger in 188金宝搏优惠COMSOL Multiphysics.

具有交叉耦合刚度的涡轮增压器的瀑布图。

瀑布无(左)和(右)交叉耦合刚度的涡轮增压器模型的图。

如上图所示,由于涡轮增压器中涡轮机和压缩机的偏心率没有交叉耦合的刚度,因此许多模式被激发了,如上图所示。但是,对于涡轮增压器刚度,并非所有模式都很兴奋。该结果意味着,由于涡轮机和压缩机的偏心率,在缺乏交叉耦合刚度的情况下,某些模式不再在刚度存在下激发。因此,在存在交叉耦合刚度的情况下,可能需要不同的负载组合才能激发这些模式。

下一步

尝试分析交叉耦合的轴承力如何影响涡轮增压器的操作:单击下面的按钮进入应用程序库,您可以在其中下载分步教程和随附的MPH文件。

Read more about applying simulation to turbocharger design:


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