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首页> 外文学位 >Time-accurate conjugate CFD analysis of a jet-impingement configuration with sudden changes in heating and cooling loads.
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Time-accurate conjugate CFD analysis of a jet-impingement configuration with sudden changes in heating and cooling loads.

机译：在加热和冷却负荷突然变化的情况下，喷射冲击结构的时间精确共轭CFD分析。

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摘要

When the operating condition of a gas-turbine engine changes from one steady state to another, the cooling must ensure that the material temperature and its gradient never exceed the maximum allowable throughout the transient process. The objective of this study is to understand how to cool a material subjected to a sudden increase in heating load by using the minimum cooling flow. The focus is on understanding the unsteady processes associated with the cooling process and the response of the material to sudden changes on its heated and cooled sides. The problem selected to generate the understanding is a flat plate heated on one side by a specified heat flux and cooled on the other side by an array of impinging air jets. The plate is made of either a Ni-based superalloy or a composite-matrix material. The composite matrix consists of a grid made of a material with high thermal conductivity and high thermal diffusivity (denoted as Mat-C) and a material with high heat capacity (denoted as Mat-S), where contact resistance between Mat-C and Mat-S were not considered. For this problem, unsteady conjugate analysis based on RANS with the SST turbulence model for the air and the Fourier Law for the plate was used to study the details of the unsteadiness in the fluid flow and solid and to determine the minimum cooling flow rate.;Results are presented to show the details of the steady states and the transients. At steady state when the plate is made of superalloy, though the Biot number is much less than 0.1, there is considerable temperature variation in the plate because of the large variation in the heat-transfer coefficient on cooled side of the plate. The unsteadiness in the cooling jet involves the reflection and the interaction of finite-amplitude pressure waves, the generation of a starting vortex, and the formation of vortical structures from Helmholtz instability. For the conditions of the present study, the transients in the fluid - though highly complicated - occurs at orders of magnitude faster than the transients in the solid, and the distribution of the heat-transfer coefficient on the cooled side achieved steady state almost instantly when compared to the time scale of conduction in the solid. Though the maximum temperature in the solid at steady state is always just below the maximum allowable for all cases studied, results show that the temperature in a material could exceed the maximum allowable during transients when the heat load is increased despite a corresponding increase in cooling.;Studies were also performed to examine what could be done to the plate to reduce cooling flow for a given heat load with and without pre-cooling. If the plate's material is a composite matrix made of copper (Mat-C) and ceramic (Mat-S) instead of a Ni-based superalloy and subjected to the same heating loads, then the required cooling and period of over temperature were found to reduce greatly. A parametric study on the material properties of Mat-C and Mat-S in the composite matrix was performed to explore the effectiveness of material's thermophysical properties.;To guide designers, a model based on one-dimensional-time-accurate integral solution and volume weighted time constants was developed to estimate the temperature distribution in a flat plate of thickness L that is exposed to a "hot" convective environment on one side and a "cold" convective environment on the other, where the two convective environments can change suddenly. This model provides estimates on the maximum temperature that can occur in a plate during transients when convective environments suddenly change, when that maximum temperature will occur after a sudden change, and how long could the temperature in the material exceed the maximum allowable. (Abstract shortened by UMI.).
机译：当燃气涡轮发动机的运行状态从一种稳态变为另一种稳态时，冷却必须确保物料温度及其梯度在整个过渡过程中都不会超过允许的最大值。这项研究的目的是了解如何通过使用最小冷却流量来冷却承受热负荷突然增加的材料。重点是了解与冷却过程相关的不稳定过程以及材料对加热和冷却侧突然变化的响应。选择来产生理解的问题是平板在一侧被指定的热通量加热，而在另一侧被一系列撞击的空气喷嘴冷却。该板由镍基高温合金或复合基体材料制成。复合基质由网格组成，该网格由具有高导热率和高热扩散率的材料（表示为Mat-C）和具有高热容量的材料（表示为Mat-S）制成，其中Mat-C和Mat之间的接触电阻-S不被考虑。针对这一问题，利用基于RANS的SST空气湍流模型和板的傅立叶定律进行非稳态共轭分析，研究了流体和固体的非稳态细节，并确定了最小冷却流量。给出结果以显示稳态和瞬态的细节。在稳态条件下，当板由高温合金制成时，尽管比奥特数远小于0.1，但由于板的冷却侧传热系数存在较大变化，因此板中存在相当大的温度变化。冷却射流的不稳定性包括有限振幅压力波的反射和相互作用，起始涡旋的产生以及由亥姆霍兹不稳定性形成的涡旋结构。对于本研究的条件，流体中的瞬变尽管非常复杂，但发生的速度要比固体中的瞬变快几个数量级，并且当冷却时，传热系数在冷却侧的分布几乎立即达到稳态。相比于固体中传导的时间尺度。尽管在所有研究情况下，稳态下的固体最高温度始终仅低于最高允许温度，但结果表明，尽管冷却相应增加，但当热负荷增加时，瞬态过程中材料的温度可能会超过最高允许温度。 ；还进行了研究，以检查在有和没有预冷的情况下，对于给定的热负荷，如何减少板的冷却流量。如果板的材料是由铜（Mat-C）和陶瓷（Mat-S）制成的复合基体，而不是镍基高温合金，并且经受相同的加热负荷，则发现所需的冷却和超温周期可以大大减少。对复合基质中Mat-C和Mat-S的材料性质进行了参数研究，以探索材料热物理性质的有效性。；为指导设计人员，建立基于一维时间精确积分解和体积的模型开发了加权时间常数，以估算厚度为L的平板的温度分布，该平板的一侧暴露于“热”对流环境，另一侧暴露于“冷”对流环境，这两种对流环境会突然改变。该模型提供了对流环境突然变化时瞬变期间板中可能出现的最高温度，突然变化后将出现最高温度的估计值，以及材料中温度超过最高允许值的时间。 （摘要由UMI缩短。）。

著录项

  • 作者

    Lee, Chien-Shing.;

  • 作者单位

    Purdue University.;

  • 授予单位 Purdue University.;
  • 学科 Aerospace engineering.;Mechanical engineering.
  • 学位 Ph.D.
  • 年度 2014
  • 页码 113 p.
  • 总页数 113
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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