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Improvements in numerical airflow modeling around multiple buildings.

机译：围绕多个建筑物的数值气流建模的改进。

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摘要

The main objective of the thesis was to provide faster, yet reliable and simple modeling tool for simulation of outdoor airflow around multiple buildings. The intent was to improve the existing zero-equation turbulence models mainly developed and used for modeling of airflows in indoor environments. The zero-equation turbulence model adopts the local mean velocity and distance to the nearest wall surface as the characteristic velocity and length scale to estimate the turbulent viscosity. However, the coefficients in the model equation require assessment for each particular application. For that reason, the wind tunnel modeling of complex airflow around four scaled student dorm buildings at the Penn State University campus has been carried out in the closed loop, low speed wind tunnel at the Department of Aerospace Engineering at the Pennsylvania State University using triple hot wire anemometry to collect the velocity time series. The obtained results on 1:250 scale modeled buildings provided the base for calibration of the coefficients in the zero-equation turbulent model. The derived expression for calibration coefficient implements both the bulk and turbulent Reynolds number as relevant characteristics of approaching wind flow. The calibrated zero-equation turbulence model has been incorporated in commercial CFD software PHOENICS and tested against the wind tunnel results. The simulation results show satisfactory agreement with measured data for longitudinal velocity components. The prediction of vertical velocity component was less accurate and inferior performance of the model was observed for lateral velocity component prediction. Limitations in measurement equipment and negligence of all mean strain rate tensor components including lateral and vertical velocity gradients are two most likely sources of discrepancy between the numerical and wind tunnel experimental results. Further estimate of exponents in the derived expression for calibration coefficient is recommended for different buildings layouts.;Experimental study with regular array of cubes placed in the boundary layer wind tunnel provided the data for additional validation of the developed model. The experimental results comprised of streamwise and vertical velocity profiles along the centerline of the modeled building cube array. The developed model for calibration coefficients in the expression for turbulent eddy viscosity in the zero-equation turbulence model demonstrated good agreement in streamwise velocity prediction with experimentally acquired results. Implemented turbulence model showed comparative competitiveness with more advanced one-point turbulence closure models, such as two equation "k-epsilon" and modified "Kato-Launder" version of the "k-epsilon " model, although, the full adjustment of the calibration coefficients in the model was not feasible due to lack of input information that was not measured in the wind tunnel experiment.;Part of the thesis effort focused on possible improvements in the description of inlet boundary conditions of incoming wind. For that purpose, an extensive literature review on the atmospheric surface layer flows, their characterization and parameterization has been performed. In addition, the systematic overview of various strategies for synthetic turbulent wind speeds generation has been discussed in detail. As an outcome, the most suitable techniques for implementation in CFD models are described with sufficient level of detail for easy coding. The described techniques should provide substantial foundation for the future implementation of unsteady Reynolds averaged Navier-Stokes equations (URANS) turbulence modeling approach for simulation of outdoor airflow in complex urban settings.;The developed methodology for calibration coefficients in the zero-equation turbulence models represents the major contribution of this study. Further improvements of the model are possible with provision of experimental data with high spatial resolution using advanced non-invasive measurement techniques such as Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA). More comprehensive set of experimental data would enable further refinement of the proposed model in terms of adjustment of the exponents in the proposed equation for calibration coefficients. Instead of using single constant value, the exponents should be defined as a function of plan area density, frontal area density and other morphological parameters already established to describe various buildings layouts and boundary layer flows in urban environments. (Abstract shortened by UMI.)
机译：本文的主要目的是提供一种更快，更可靠，更简单的建模工具，用于模拟多个建筑物周围的室外气流。目的是改进现有的零等值湍流模型，该模型主要开发并用于室内环境中的气流建模。零方程湍流模型采用局部平均速度和到最近壁面的距离作为特征速度和长度尺度来估计湍流粘度。但是，模型方程中的系数需要针对每个特定应用进行评估。因此，宾夕法尼亚州立大学航空航天工程系的闭环低速风洞采用三重热法，在宾夕法尼亚州立大学校园的四座按比例缩放的学生宿舍楼周围的复杂气流的风洞模型中进行了建模。线风速仪收集速度时间序列。在1：250比例的建模建筑物上获得的结果为零方程湍流模型中的系数校准提供了基础。导出的校准系数表达式将体积和湍流雷诺数实现为接近风的相关特征。校准的零方程湍流模型已被纳入商业CFD软件PHOENICS中，并针对风洞结果进行了测试。仿真结果表明与纵向速度分量的测量数据具有令人满意的一致性。垂直速度分量的预测准确性较差，而横向速度分量的预测模型的性能较差。测量设备的局限性以及所有平均应变率张量分量（包括横向和垂直速度梯度）的疏忽是数值和风洞实验结果之间最可能出现差异的两个来源。建议针对不同的建筑布局进一步估计导出的校准系数表达式中的指数。;在边界层风洞中放置规则立方体的实验研究为进一步验证开发的模型提供了数据。实验结果包括沿建模的建筑立方体阵列的中心线的水流速度和垂直速度剖面。开发的零方程湍流模型中湍流涡流粘度表达式中的校准系数模型在流速度预测中与实验获得的结果显示出良好的一致性。已实施的湍流模型显示了与更先进的单点湍流闭合模型（例如两个方程式“k-ε”和改进的“ k-epsilon”模型的“ Kato-Launder”版本）相比的竞争能力，尽管对校准进行了全面调整由于缺少风洞实验中未测量到的输入信息，因此该模型中的系数不可行。；论文的一部分工作重点在于对传入风的入口边界条件的描述可能进行的改进。为此，已经对大气表层流动，其表征和参数化进行了广泛的文献综述。另外，已经详细讨论了用于合成湍流风速产生的各种策略的系统概述。结果，对CFD模型中实现的最合适的技术进行了详细描述，以便于编码。所描述的技术应为未来的非稳态雷诺平均Navier-Stokes方程（URANS）湍流建模方法的仿真提供基础，以模拟复杂城市环境中的室外气流。;零方程湍流模型中校准系数的已开发方法代表这项研究的主要贡献。使用先进的非侵入式测量技术（例如粒子图像测速技术（PIV）和激光多普勒风速术（LDA）），通过提供具有高空间分辨率的实验数据，可以对模型进行进一步的改进。更全面的实验数据集将能够根据所提出的校准系数方程式中的指数调整来进一步完善所提出的模型。代替使用单个常数，应该将指数定义为平面面积密度，额叶面积密度和其他已经建立的描述城市环境中各种建筑物布局和边界层流量的形态参数。 （摘要由UMI缩短。）

著录项

  • 作者

    Davidovic, Danko.;

  • 作者单位

    The Pennsylvania State University.;

  • 授予单位 The Pennsylvania State University.;
  • 学科 Engineering Architectural.;Engineering Civil.;Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 416 p.
  • 总页数 416
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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