From 14df730ae4f7b18897169e87a3ecaae6ba1059ed Mon Sep 17 00:00:00 2001 From: EleHa Date: Thu, 25 Feb 2021 06:35:50 +0800 Subject: [PATCH 1/2] complete 32.4 --- 32.Turbulence_Models.md | 332 +++++++++++++++++----------------------- 1 file changed, 142 insertions(+), 190 deletions(-) diff --git a/32.Turbulence_Models.md b/32.Turbulence_Models.md index 061447d..309c9db 100644 --- a/32.Turbulence_Models.md +++ b/32.Turbulence_Models.md @@ -4,104 +4,77 @@ 作者在使用OpenFOAM的这段时间内79，湍流模型源代码的组织方式发生了改变。 OpenFOAM-2.3.080的发布推出了一种新的、（甚至）更通用的代码组织方式。 -旧方式实质上依靠命名空间（namespace）和继承来实现通用性和抽象性，新方式则基于模板（template）、继承和从模板的继承。本节将对这两种代码组织方式进行讨论。尤其，新方式疯狂使用模板，以致于初看时可能会难以理解其代码。因此，作者希望能够阐明对于新方式的疑惑。 +旧方式实质上依靠命名空间和继承来实现通用性和抽象性，新方式则基于模板、继承和从模板的继承。本节将对这两种代码组织方式进行讨论。尤其，新方式中模板被疯狂使用，以致于初看时可能会有代码理解的困难。因此，作者希望能够解开新方式实现功能的谜团。 随着OpenFOAM-3.0的发布，向新湍流模型框架的过渡正式完成81。源文件中不再有`$FOAM_SRC/turbulenceModels`的文件夹。因此，对旧方式的讨论仅出于历史意义。然而，作者希望，在这个不断扩展的资料集中，即使其过时的部分也可以为读者提供一些领悟。 -##### 32.1.1 旧方式 +##### 32.1.1 旧组织方式 -尽管本节的目的并不是要批评新事物，但旧组织方式更易于理解。您可以在`$FOAM_SRC/turbulenceModels`中对其进行查看。旧湍流模型框架基于命名空间来区分可压缩模型和不可压缩模型。 +虽说，本节的目的并不是要批评新事物，但旧组织方式更易于理解。您可以在`$FOAM_SRC/turbulenceModels`中对其进行查看。旧湍流模型框架基于命名空间来区分可压缩模型和不可压缩模型。 在该旧框架内，多相求解器要么使用混合物的湍流模型（*multiphaseEulerFoam*或*interFoam*），要么仅在连续相中应用湍流模型（*twoPhaseEulerFoam*）。在旧框架内，仅有一种湍流模型被应用于多相流模拟。 图像76显示了旧湍流模型框架的组织方式。类层次结构在某种程度上是重复的，命名空间`Foam::compressible`和`Foam::incompressible`中的类大致相同或等效。对比命名空间`Foam::compressible`和`Foam::incompressible`中的文件`RASModel.H`和`RASModel.C`发现，代码相同的行数多于不同的行数。 -在新湍流模型框架的发布说明中，甚至用更迫切的方式来阐述了这个问题： +在新湍流模型框架的发布说明书中，甚至用更迫切的方式来阐述了这个问题： >多年来，我们一直通过使用两个不同的湍流模型框架来解决可压缩性问题，一个用于恒定密度流，另一个用于可变密度流。然而，这两个框架均不适用于多相系统。因为，在守恒形式中，相分数必须包含在湍流方程的所有输运项和源项中。这两个框架中的代码大部分是重复的，这与OpenFOAM代码开发策略不一致。OpenFOAM代码开发策略是最大程度地减少代码重复量，从而提高代码的可维护性和可持续性。如果要把当前的代码架构扩展到多相流动，层次结构的数量将会从两个增加到四个，每个层次结构均是相分数和密度表达形式的两两组合。 -![图象76](images/fig76.PNG) -图象76：旧湍流模型框架基础的类层次结构。命名空间`Foam::incompressible`和`Foam::compressible`分别由红色和蓝色表示。 +![图像76](images/fig76.PNG)\ +图像76：旧湍流模型框架的基础类层次结构。命名空间`Foam::incompressible`和`Foam::compressible`分别由红色和蓝色表示。 -##### 32.1.2 新方式 +##### 32.1.2 新组织方式 -The new framework for all turbulence models is located at $FOAM_SRC/TurbulenceModels, notice the capital T82. The use of templates is necessary, since this framework is meant to be used by all solvers of OpenFOAM at some point of time. All solvers means compressible and incompressible, as well as single- and multiphase. This makes sense, since the concept of turbulence is general, and not related to the specific sitation in question. The advantages of this approach is best said by the release note itself: +包含所有湍流模型的新框架位于`$FOAM_SRC/TurbulenceModels`，注意T字母大写82。模板的使用是必要的，因为计划在未来该框架将被所有OpenFOAM求解器使用。所有求解器意味着可压缩流和不可压缩流求解器，以及单相流和多相流求解器。这一点很有意义，因为湍流是个通用的概念，它与问题中的特定情况无关。发布说明书很好地解释了这种方式的优点： -所有湍流模型的新框架位于`$FOAM_SRC/TurbulenceModels`，注意大写字母T82。模板的使用是必要的，因为该框架打算在某个时间点被所有OpenFOAM求解器使用。所有求解器都意味着可压缩和不可压缩以及单相和多相。这是有道理的，因为湍流是笼统的概念，与所讨论的特定位点无关。发布说明本身可以最好地说明这种方法的优点： +>该新框架十分强大，它支持目前为止所有的湍流模型需求。在未来的OpenFOAM版本中，新框架将进一步增强和扩展，以包含多种模型和子模型，并期望能取代现行的湍流模型双重层次结构，从而提高代码的可维护性和可持续性。 ->This new framework is very powerful and supports all of the turbulence modelling requirements needed so far. It will be enhanced and extended in future OpenFOAM releases to include a wide range of models and sub-models, with the expectation to replace the current dual hierarchies of turbulence models, to aid code maintainability and sustainability.这个新框架非常强大，并支持到目前为止所需的所有湍流建模要求。 它会在将来的OpenFOAM版本中进行增强和扩展，以包括各种模型和子模型，以期取代现有的湍流模型的双重层次结构，以帮助代码保持可维护性和可持续性。 +新湍流模型框架最初是随着多相求解器的更新而被引入的。在OpenFOAM-2.3.0版本中，仅*twoPhaseEulerFoam*和*DPMFoam*使用该新框架。随时间推移，越来越多的求解器更新后使用新框架取代了旧框架。在撰写本段落时（2015年10月），OpenFOAM-dev存储库中已有数十个求解器完成了移植。 -Initially the new turbulence modelling framework was introduced with an update of the multiphase solvers. In the OpenFOAM-2.3.0 release only twoPhaseEulerFoam and DPMFoam. As time progresses more and more solvers are updated to use the new framework instead of the old. By the time of writing this paragraph (October 2015) dozens of solvers in the OpenFOAM-dev repository were already ported.最初，随着多相求解器的更新，引入了新的湍流建模框架。 在OpenFOAM-2.3.0版本中，仅两个PhaseEulerFoam和DPMFoam。 随着时间的流逝，越来越多的求解器被更新为使用新框架而不是旧框架。 在撰写本段时（2015年10月），已经移植了OpenFOAM-dev存储库中的数十个求解器。 +###### 一统天下 -**One to rule them all** +每当某个概念化为多种形式出现时83，OpenFOAM的开发人员都会牢记住《指环王》中的这句话。单一的湍流模型类就这样被建立起来了，它适用于OpenFOAM所实现的任意物理过程。为此，这个最基本的湍流模型仅包含能被充分抽象化以应用于一切情况的内容。湍流模型的纯粹存在84，即是（不依赖于可压缩性或相数这一特征）最简单的例子。 -Whenever, a certain concept manifests itself in a variety of incarnations83, the developers of OpenFOAM take this rough quote from Lord of the Rings by heart. A single turbulence model class was created to be applied to whatever physics OpenFOAM implements. For this to work, this most basic turbulence model contains only the things which can be abstracted enough to apply everything. The most trivial example of this (a feature independent of compressibiltiy or the number of phases involved), is the sheer existence of a turbulence model84. +图像77显示了新湍流模型框架的基础类层次结构。除了这种基础的、非模板化的类层次结构以外，还存在实现类的模板化层次结构。基本类所表现的正是抽象化。继承树的顶部是`IOdictionary`类，该类提供输入输出功能。在OpenFOAM的使用中，我们得知有一个控制湍流模型的字典。从`IOdictionary`派生出的湍流模型类就是湍流模型的字典。 -Figure 77 shows the basic class hierarchy of the new turbulence framework. Besides this basic, non-templated class hierarchy, there is the templated hierarchy of the implementing classes. The basic classes represent the very abstraction. On top of the familiy tree is the class IOdictionary, which provides the IO facilities. From using OpenFOAM, we know, that there is a dictionary controlling the turbulence modelling. By deriving the turbulence model class from IOdictionary, the turbulence model is its dictionary. +`turbulenceModel`类从`IOdictionary`派生而来。注意首字母小写。`turbulenceModel`类不是湍流模型唯一的基类，我们还将遇到首字母大写的类。如前所述，OpenFOAM极度依赖文件系统的大小写敏感性。因此，我们需要对字母大小写多加注意（`turbulenceModel`≠`TurbulenceModel`）。`turbulenceModel`类声明了大量纯虚函数，其后的派生类则不可避免地要给出这些纯虚函数的实现。该类是存在湍流模型这一事实在源代码层面上的体现。到目前为止，除了这是湍流模型外，没有更多关于湍流模型的已知信息。因此，该类的资料匮乏。该类的最重要的数据成员是对运行时对象和对网格的引用。更多信息可以在`$FOAM_SRC/TurbulenceModels/turbulenceModels/turbulenceModel.H`文件中获取。 -From IOdictionary the class turbulenceModel is derived. Note the lower case letter at the beginning. This is not the only base class for turbulence models, we will also encounter a capital letter class. As already mentioned, OpenFOAM makes heavy use of the file system’s case sensitivity. Thus, we need to pay attention to the letter (turbulenceModel 6= TurbulenceModel). The class turbulenceModel declares a large number of pure virtual functions which the derived classes down the family tree inevitably need to implement. This class is the source-code-wise incarnation of the fact that there is a turbulence model. No further information is as of this point known to the turbulence model, except that it is a turbulence model. The data of this class is consequently sparse. The most important data members of this class are references to the run-time object and the mesh. More information can be found in the file $FOAM_SRC/TurbulenceModels/turbulenceModels/turbulenceModel.H. From the class turbulenceModel two classes are derived: incompressibleTurbulenceModel and compressibleTurbulenceModel. These two classes represent the fact, that flow can be considered incompressible or compressible. The consequence of this difference can be seen in the treatment of the density by these two classes. In Figure 77 we see, that the incompressible turbulence model has a geometricOneField as density data member, in contrast to the compressible model, which has a reference to the actual density field. +从`turbulenceModel`类派生出两个子类：`incompressibleTurbulenceModel`和`compressibleTurbulenceModel`。这两个子类的存在体现了以下事实：流动可以是不可压缩的或是可压缩的。这种差别的重要性可以在这两个子类对于密度的处理中看出。在图像77中可见，不可压湍流模型具有密度数据成员`geometryOneField`，相反，可压缩模型则引用了实际的密度场。 -![图象77: The class hierarchy of the basis of the new turbulence model framework.](images/fig77.PNG) +![图像77](images/fig77.PNG)\ +图像77：新湍流模型框架的基础类层次结构 -A little note on ancestry: in the class hierarchy of the ye olden ways, see Figure 76, we saw that the base -classes for the turbulence models, were derived from regIObject. Thus, allowing access to the turbulence model -via OpenFOAM’s registry. +关于祖先类的一点说明：在旧方法的类层次结构中，见图像76，湍流模型的基类是从`regIObject`派生的。因此，允许通过OpenFOAM的注册表访问湍流模型。 -In the class hierarchy of the fancy new order, see Figure 77, we see that the base class for all turbulence -models is derived from the class IOdictionary. In Figure 133, all the way down in Section 57.7, we see that the -class IOdictionary is derived from regIOobject85. Thus, the turbulence model base class is derived indirectly -derived from regIOobject. Thus, allowing access to the turbulence model via OpenFOAM’s registry. +而在这个复杂的新组织方式的类层次结构中，见图像77，所有湍流模型的基类均从`IOdictionary`类派生而来。在57.7节图像133中，可见`IOdictionary`类是从`regIOobject`85派生的。从而，湍流模型的基类是间接从`regIOobject`派生的。因此，允许通过OpenFOAM的注册表访问湍流模型。 -A mere comparison of Figures 76 and 77 might have suggested otherwise, however, as the list of ancestors -got longer for the new modelling framework, this fact (the derivation from regIOobject) has travelled up the -family tree. +随着新模型框架祖先列表的增长，这一事实（派生自`regIOobject`）即可从继承树中得出，而仅仅比较图像76和图像77则可能会得出相反的结论。 -**Many to rule the many** +###### 各自为政 -The distinction between incompressible and compressible, as well as, single-phase and multi-phase, turbulence -modelling is made by passing appropriate template parameters to the base class TurbulenceModel. Note that -TurbulenceModel is derived from the template parameter BasicTurbulenceModel. In Figure 78 we see the -(templated) class hierarchy of the new turbulence modelling framework. This class hierarchy is related to the -classes depicted in Figure 77 by the use of the template parameter BasicTurbulenceModel, which is either -incompressibleTurbulenceModel or compressibleTurbulenceModel, note the lower case first letter. +将合适的模板参数传递给基类`TurbulenceModel`，可以区分不可压缩和可压缩湍流模型，以及单相和多相湍流模型。注意`TurbulenceModel`是从模板参数`BasicTurbulenceModel`派生的。在图像78中可见新湍流模型框架的（模板化）类层次结构。该类层次结构通过模板参数`BasicTurbulenceModel`与图像77所示的类相关联，该模板参数可为`incompressibleTurbulenceModel`或`compressibleTurbulenceModel`，注意首字母小写。 -The distinction between incompressible and compressible modelling is made by the template parameters -Rho and BasicTurbulenceModel. In the case of incompressible models a geometricOneField86 is passed for -the parameter Rho. The distinction between single-phase and multi-phase modelling is made by the template -parameter Alpha. In the case of single-phase modelling a geometricOneField is passed. +通过模板参数`Rho`和`BasicTurbulenceModel`,可以区分不可压缩模型和可压缩模型。在不可压缩模型中，对参数`Rho`传递`geometricOneField`86。通过模板参数`Alpha`，可以区分单相模型和多相模型。在单相模型中，对参数`Alpha`传递`geometricOneField`。 -The approach, that TurbulenceModel is derived from its template parameter BasicTurbulenceModel, which -is either an incompressibleTurbulenceModel or compressibleTurbulenceModel, which in turn are derived -from a common base class, demonstrates the great flexibility a high-level programming language, such as C++. -However, the presence of templates and their heavy, sophisticated use – as demonstrated in OpenFOAM – raises -the bar when it comes to reading the source code and finding out what is happening. +`TurbulenceModel`从其模板参数`BasicTurbulenceModel`派生而来，该模板参数可为`incompressibleTurbulenceModel`或`compressibleTurbulenceModel`，而它们又是从公共基类派生的。该方法体现了高级编程语言（如C++）巨大的灵活性。但是，如同在OpenFOAM中所见，模板的存在及其大量而复杂的使用，提高了阅读源代码和理解原理的门槛。 -![图象78: The base class TurbulenceModel has four template parameters and it is derived from one of its template parameters. Note, that the four derived classes – the four incarnations of the turbulence model – differ in the template parameters.](images/78.PNG) +![图像78](images/fig78.PNG)\ +图像78：基类`TurbulenceModel`具有四个模板参数，并从它的其中一个模板参数派生而来。注意，四个派生类——湍流模型的四个形式，具有不同的模板参数。 -**Branching the family tree** +###### 继承树的分支 -In turbulence modelling, we can identify three elementary choices: we can treat a fluid flow as laminar, or -apply a RAS or LES turbulence model. This basic choice is reflected in the three classes derived from the -template parameter in Figure 79. Since RAS and LES turbulence models are turbulence models87, those -two base classes are derived from the common template parameter BasicTurbulenceModel. The nature of -BasicTurbulenceModel has been discussed above. +对于湍流模型，我们有三个基本选择：将流动视为层流、应用RAS湍流模型或应用LES湍流模型。见图像79，该基本选择反映在从模板参数派生的三个类中。由于RAS和LES湍流模型属于湍流模型87，所以这两个基本类是从通用模板参数`BasicTurbulenceModel`派生的。上文已经对`BasicTurbulenceModel`的本质进行了讨论。 -By treating the laminar case as a turbulence model, the OpenFOAM developers got rid of the special case -laminar flow. In Figure 79, the behaviour of the laminar turbulence model is indicated by the methods R() -and nut(). The laminar turbulence returns zero (with the appropriate dimension) for all turbulent quantities. -Thus, the method R(), which computes the Reynolds stress tensor, returns a volumetric88 field of symmetric -tensors will all-zero components89. This behaviour is indicated in Figure 79 with the (= 0) appended to the -method’s names. +通过将层流视为一种湍流模型，OpenFOAM的开发人员避免了层流这种特殊情况。在图像79中，`laminar`湍流模型的行为由方法`R()`和`nut()`指示。`laminar`模型对所有湍流特征量返回零值（具有相应的维数）。因此，计算雷诺应力张量的方法`R()`返回一个对称张量的体积场88，其分量全为零89。图像79在方法名称后附加了（= 0）以表示该行为。 -The class eddyViscosity is a class which implements the ideas behind the Boussinesq hypothesis, which is -discussed below. +`eddyViscosity`类实现了Boussinesq假设的构想，将在下文进行讨论。 -![图象79](images/fig79.PNG) -图象79: 新湍流模型框架中的基本湍流模型类层次结构。注意缩写BTM表示BasicTurbulenceModel类。 +![图像79](images/fig79.PNG)\ +图像79：新湍流模型框架中基本湍流模型的类层次结构。注意缩写BTM表示`BasicTurbulenceModel`类。 -**Further down the family tree** +###### 继承树的延伸 -A great number of turbulence models are based on the so-called Boussinesq hypothesis which computes the Reynolds stresses from an eddy viscosity μt and the mean strain-rate tensor, and was proposed by Boussinesq [11] [64]. +大量湍流模型基于所谓的*Boussinesq假设*建立。该假设通过*涡粘系数*$\mu_t$计算雷诺应力和平均应变率张量，由Boussinesq[11][64]提出。 $$ \mathbf{R} = \mu_t ({\nabla \overline{\mathbf{u}}} + {\nabla \overline{\mathbf{u}}}^T) - \frac{2}{3} \rho \mathbf{I} k @@ -110,95 +83,67 @@ $$ k = \frac{1}{2} \sum_{i} \overline{u^\prime_i u^\prime_i} = \frac{1}{2} \sum_i \overline{\mathbf{u^\prime} \cdot \mathbf{u^\prime}} $$ -The quantity k is the specific kinetic energy of the turbulent fluctuations. A great part of literature refers -to k as turbulent kinetic energy [53, 35, 7, 8], most probably for reasons of keeping the vocabulary short. The -unit tensor I is often denoted with the Kronecker delta ij in literature. +物理量$k$为湍流波动的比动能。一大部分文献将$k$称为*湍流动能*[53, 35, 7, 8]，很可能是为了保持词汇简短。单位张量$\mathbf{I}$在文献中常用克罗内克delta函数$\delta_{ij}$表示。 -The Boussinesq hypothesis is common to both RAS and LES turbulence models. This can be translated into -a class relationship. In Figure 80 we see how the kEpsilon and the Smagorinsky turbulence models are derived. -Those two models are discussed since these are widely used. The class eddyViscosityModel implements the -general idea of the Boussinesq hypothesis, thus, it is the common base for both turbulence models. In the case -of LES models, an intermediate class (lesEddyViscosityModel) is in between the class eddyViscosityModel -and the actual turbulence model. This class serves to hold data and define methods specific to LES models -using the Boussinesq hypothesis. +Boussinesq假设为RAS和LES湍流模型所共有。这可以转换成类关系。图80显示了`kEpsilon`和`Smagorinsky`湍流模型的派生过程。由于这两种模型被广泛使用，我们将对其进行讨论。`eddyViscosityModel`类实现了Boussinesq假设的一般思想，因此，它是这两种湍流模型的共同基类。对于LES模型，中间类（`lesEddyViscosityModel`）存在于`eddyViscosityModel`类和实际的湍流模型之间。该中间类用于保存数据，以及使用Boussinesq假设来定义LES模型的特有方法。 -The distinction between RAS models and LES models is made by the template parameter inserted in -eddyViscosityModel. In the case of RAS models, the template parameter of eddyViscosityModel from which -e.g. the kEpsilon model is derived is RASModel. Since RASModel is derived from -BasicTurbulenceModel, the class RASModel is a BasicTurbulenceModel. Thus, this operation is perfectly -valid. In the case of LES models, LESModel is inserted as the template parameter of -eddyViscosityModel. +通过在`eddyViscosityModel`中插入模板参数，可区分RAS模型和LES模型。在RAS模型中，`eddyViscosityModel`模板参数是`RASModel`，如`kEpsilon`模型便派生自该模板参数。由于`RASModel`是从`BasicTurbulenceModel`派生的，所以`RASModel`类属于`BasicTurbulenceModel`。因此，该操作是完全可行的。在LES模型中，插入`LESModel`作为`eddyViscosityModel`的模板参数。 -Sounds complicated, which it probably also is. Nevertheless, we admire the versatility of generality of the -new turbulence modelling framework and stomach the mental pain caused by all the template and inheritance -wizardry. +听起来很复杂，可能也的确如此。尽管这样，我们还是要称赞新湍流模型框架的通用性，并忍受所有模板和继承的魔法所引起的精神痛苦。 -![图象80: The class hierarchy of a selection of turbulence models of the new turbulence model framework.Note the shorthand notation BTM for the class BasicTurbulenceModel, and EVM for eddyViscosityModel.](images/fig80.PNG) +![图像80](images/fig80.PNG)\ +图像80：新湍流模型框架中一些湍流模型的类层次结构。注意缩写BTM表示`BasicTurbulenceModel`类，EVM表示`eddyViscosityModel`类。 -The method signature in italics of the class eddyViscosityModel indicates a pure virtual function. This -method has to be implemented by the classes derived from eddyViscosityModel. In the case of the kEpsilon -class it is the class derived directly from eddyViscosityModel which implements k(). In the case of the -Smagorinsky class, the pure virtual function was inherited via lesEddyViscosityModel. A class containing a -pure virtual function can not be instantiated, thus, there can be no usable turbulence model lesEddyViscosityModel. -This class can only serve as an intermediary. +`eddyViscosityModel`类中的斜体方法名称表示这是个纯虚函数。该方法必须由`eddyViscosityModel`的派生类实现。`kEpsilon`类直接派生自`eddyViscosityModel`，该类给出了`k()`的实现。`Smagorinsky`类则通过`lesEddyViscosityModel`继承了该纯虚函数。包含纯虚函数的类不可被实例化，因此，`lesEddyViscosityModel`不是可用的湍流模型，而只能作为中介。 -#### 32.2 Reynolds averaged models (RAS)雷诺平均模型（RAS） -##### 32.2.1 kEpsilon and low-Reynolds flows kEpsilon模型和低雷诺数流动 +#### 32.2 雷诺平均模型（RAS） -The standard wall functions require the yPlus value to fall into a certain range. If the yPlus value is outside -of that range, the simulation’s results can become quite wrong. Thus, the use of the kEpsilon model creates an -effective upper limit on the mesh resolution at the walls [19]. This becomes a problem, when we want to finely -resolve the flow at and near the wall, e.g. when solving heat-transfer problems. +##### 32.2.1 kEpsilon模型和低雷诺数流动 -For cases, when the yPlus value is too small, i.e. it is smaller than the lower bound of the standard -wall-function’s validity range, there are the so-called low Reynolds formulations. +标准壁面函数要求`yPlus`值处于某个范围内。如果`yPlus`值超出该范围，模拟结果可能会有误。因此，使用kEpsilon模型时，壁面处网格分辨率具有一个有效上限[19]。当我们要精细地求解壁面及近壁处流动时，例如在求解传热问题时，这将成为一个问题。 +对于`yPlus`值过小的情况（即小于标准壁面函数的有效范围下限），则有所谓的*低雷诺数*公式。 -**Wall functions壁面函数** +###### 壁面函数 -From OpenFOAM-5.0 onwards, there are no special low-Reynolds wall-functions for epsilon, as the standard -and low-Reynolds formulation have been merged into a single wall-function90. -However, other fields, such as k and nut, still require special wall-functions when a low-Reynolds model is -used. +OpenFOAM-5.0之后，不再有`epsilon`的低雷诺数壁面函数，其标准公式和低雷诺数公式已被合并为单个壁面函数89。然而，在使用低雷诺数模型时，其它的物理场，例如`k`和`nut`，仍需要特殊的壁面函数。 -**Disclaimer** +###### 免责声明 -Everthing of Section 32 after this point has been created a while ago. The some of the content of the sub-sections -below might be outdated by the time you read this. +第32节的所有后续内容已写成了一段时间。当您阅读本文时，以下小节中的一些内容可能已经过时。 -#### 32.3 Categories类别 +#### 32.3 类别 -The desired category of turbulence models can be specified in the file turbulenceProperties. There are three -possible entries. +The desired category of turbulence models can be specified in the file `turbulenceProperties`. There are three possible entries. +选择的湍流模型类别可以在文件`turbulenceProperties`中指定。有三个可选条目。 -**laminar** 层流模型The flow is modelled laminar -**RASModel** 雷诺平均模型（RAS模型)A Reynolds averaged turbulence model (RAS-model) is used. -**LESModel** 大涡模型Turbulence is modelled by a large-eddy model. +**laminar** 层流模型 -The file turbulenceProperties contains only one entry. In case of a large eddy simulation, this entry reads: +**RASModel** 雷诺平均模型（RAS模型) + +**LESModel** *大涡*模型 + +文件`turbulenceProperties`仅包含一个条目。在大涡模拟中，该条目为： ``` simulationType LESModel ; ``` -清单187: turbulenceProperties +清单187：*turbulenceProperties* -#### 32.4 RAS-Models RAS模型 +#### 32.4 RAS模型 -The entry in the file turbulenceProperties specifies only the class of turbulence models. The exact turbulence -model is specified in the file RASProperties. This file must contain all necessary parameters. -Listing 272 shows the content of RASProperties. In this case a k- model is used and no further parameters -are necessary. +文件`turbulenceProperties`中的条目仅指定湍流模型的类。确切的湍流模型在文件`RASProperties`中进行指定。该文件须包含所有必要的参数。 +清单272显示了`RASProperty`的内容。该案例使用k-ε模型，并且不需要其他参数。 ``` RASModel kEpsilon ; turbulence on; printCoeffs on; ``` -Listing 188: RASProperties +清单188：*RASProperties* -Depending on the exact model more parameters can be necessary. +根据确切的模型，可能需要更多参数。 -##### 32.4.1 Keywords 关键词 +##### 32.4.1 关键词 -**RASModel** The name of the turbulence model. At this place laminar can also be chosen. The banana test -(see Section 11.2.1) delivers a list of available models. +**RASModel** 湍流模型的名称。该处亦可选择层流。banana测试（见11.2.1节）提供了一系列可选的模型。 ``` --> FOAM FATAL ERROR : Unknown RASModel type banana @@ -224,18 +169,13 @@ qZeta realizableKE ) ``` -Listing 189: Possible RAS-model entries in RASProperties - -**turbulence** This is a switch to activate or deactivate the turbulence modelling. Allowed values are: on/off, -true/false or yes/no. -If this switch is deactivated, then a laminar simulation is conducted. This way of choosing a laminar -model is not recommended, see Section 32.6.1. -**printCoeffs** If this switch is enabled, then the solver will display the coefficients of the selected turbulence -model. -Even if the switch turbulence is disabled, the solver will display the coefficients at the beginning of the -simulation, see Listing 196. The coefficients are not displayed only when RASModel laminar is chosen. -**optional parameters** Some models accept optional parameters to override the default values of the model. -Listing 190 shows how the coefficients of the k- model can be overridden. +清单189：*RASProperties*中可选的RAS模型条目 + +**turbulence** 激活或禁用湍流模型的开关。允许值：*on*/*off*、*true*/*false*或*yes*/*no*。若禁用此开关，则进行层流模拟。不推荐使用这种方法来选择层流模型，参见32.6.1节。 + +**printCoeffs** 若启用此开关，则求解器将显示所选湍流模型的系数。即使禁用了`turbulence`开关，求解器也会在模拟开始时显示系数，见清单196。仅在选择了`RASModel laminar`时不显示系数。 + +**可选参数** Some models accept optional parameters to override the default values of the model. Listing 190 shows how the coefficients of the k- model can be overridden. 一些模型允许用可选参数覆盖模型的默认值。清单190显示了如何覆盖k-ε模型的系数。 ``` kEpsilonCoeffs { @@ -247,19 +187,17 @@ sigmak 1.0; sigmaEps 1.11; // Original value :1.44 } ``` -Listing 190: Definition of model parameters in RASProperties - -##### 32.4.2 Pitfall: meaningless Parameters 陷阱：无意义的参数 -In the above section it was shown how to override default values of the model constants. In this procedure, -there is one source of error hidden. This is not an actual error, but it can lead to a fruitless search for an error. -If nonsensical parameters are added to the kEpsilonCoeffs dictionary, these will be read and also printed. -Listing 191 shows the kEpsilonCoeffs dictionary of the file RASProperties. This dictionary is used to override -default values of the model constants. A fake model constant has been added to this dictionary. -Listing 192 shows parts of the solver output, when this dictionary is used in a simulation. All constants of -the dictionary are read and printed again. It seems as if the constant banana is part of the turbulence model. -Varying this parameter yields no results, which is no error. -The reason for this behaviour is, there is no check whether the defined constants in the dictionary make -sense or not. +清单190：*RASProperties*中的模型参数定义 + +##### 32.4.2 陷阱：无意义的参数 + +上一节展示了如何覆盖模型常量的默认值。该过程中有一个隐藏的错误来源。这并非一个实际的错误，但它可能导致徒劳的错误搜索。 + +如果在`kEpsilonCoeffs`词典中添加无意义的参数，这些参数将被读取和输出。清单191显示了文件`RASProperties`中的`kEpsilonCoeffs`字典。该字典用于覆盖模型常量的默认值。一个无意义的模型常量被添加到了该字典中。 + +清单192显示了在模拟中使用该字典时的一部分求解器输出。字典的所有常量都被读取并输出。看着就像常量`banana`是湍流模型的一部分。更改该参数不会产生任何结果，这没有错。 + +出现这种现象的原因是，程序不会检查字典中定义的常量是否有意义。 ``` kEpsilonCoeffs { @@ -272,7 +210,7 @@ sigmaEps 1.11; // Original value :1.44 banana 0.815; // nonsense parameter } ``` -Listing 191: Definition of model parameters in RASProperties +清单191：*RASProperties*中的模型参数定义 ``` Selecting RAS turbulence model kEpsilon @@ -288,11 +226,15 @@ banana 0.815; } Starting time loop ``` +清单192：求解器输出 + +#### 32.5 LES模型 + +##### 32.5.1 关键词 -#### 32.5 LES-Models LES模型 -##### 32.5.1 Keywords 关键词 The keywords turbulence and printCoeffs have the same meaning with LES models. There is also the possibility – depending on the selected model – of defining optional parameters. + **LESModel** The name of the turbulence model. At this place laminar can also be chosen. The banana test (see Section 11.2.1) delivers a list of available models. Listing 193 shows the result of such a banana test. The model dynamicSmagorinsky was loaded from an external library. See Section 11.3.3 for how to include @@ -320,42 +262,53 @@ oneEqEddy spectEddyVisc ) ``` -Listing 193: Possible LES-model entries in LESProperties +清单193：*LESProperties*中可选的LES模型条目 + +##### 32.5.2 代数子网格模型 -##### 32.5.2 Algebraic sub-grid models Algebraic sub-grid models introduce no further transport equation to the simulation. The turbulent viscosity is calculated from existing quantities. -##### 32.5.3 Dynamic sub-grid models +##### 32.5.3 动态子网格模型 + The dynamic sub-grid models calculate the model constant CS from known quantities instead of prescribing a fixed value. The way how CS is calculated is determined by the sub-grid model. -##### 32.5.4 One equation models +##### 32.5.4 一方程模型 + A further class of LES turbulence models are one equation models. These models add one further equation to the problem. Usually, an additional equation for the sub-grid scale turbulent kinetic energy is solved. -#### 32.6 Pitfalls -##### 32.6.1 Laminar Simulation +#### 32.6 陷阱 + +##### 32.6.1 层流模拟 + As already mentioned – see Section 32.4 – turbulence modelling can be deactivated in a some ways. In the following, different ways to conduct a laminar simulation are listed. This list applys only to solvers that utilize the generic turbulence modelling of OpenFOAM: -1. turbulenceProperties: simulationType laminar +1. **turbulenceProperties**：`simulationType laminar` This is the most general way to turn turbulence modelling off. turbulenceProperties controls the generic turbulence class. The generic turbulence class can take the form of the laminar, RASModel or LESModel class, see Figure 134. This is controlled by the parameter simulationType. +``` Selecting turbulence model type laminar -Listing 194: Solver output for simulationType laminar -2. RASProperties: RASModel laminar -LESProperties: LESModel laminar +``` +Listing 194: `simulationType laminar`的求解器输出 + +2. **RASProperties**：`RASModel laminar` +**LESProperties**:·LESModel laminar· In this case, a certain turbulence modelling strategy is chosen (RASModel or LESModel). However, there is a dummy turbulence model for laminar simulation. This dummy turbulence model is derived from the base class RASModel but it implements a laminar model. See Figure 135. Therefore, RASModel laminar selects the laminar RAS turbulence model. In this point RASModel and LESModel behave similar. +``` Selecting turbulence model type RASModel Selecting RAS turbulence model laminar -Listing 195: Solver output for RASModel laminar -3. RASProperties: turbulence off +``` +清单195: `RASModel laminar`的求解器输出 + +3. **RASProperties**：`turbulence off` The switch turbulence can be used to enable or disable turbulence modelling. When the calculation is started, the turbulence model specified is used. However, in the source code of the solver, there is the test whether turbulence modelling is active or not. See Listing 264. @@ -370,9 +323,9 @@ C2 1.92; sigmaEps 1.3; } ``` -Listing 196: Solver output for turbulence off +清单196：`turbulence off`的求解器输出 -**Solver output** +**求解器输出** The last two prossibilities to conduct a laminar simulation can lead to confusion because the solver output contains word like RASmodel or RAS turbulence model. See Listings 195 and 196. In both cases the simulation @@ -395,7 +348,8 @@ applies to this solver. See Section 32.6.2 for a detailled discussion. ***multiphaseEulerFoam*** This solver only uses LES turbulence models. Items 2 and 3 of the list above apply. -##### 32.6.2 Turbulence models in twoPhaseEulerFoam +##### 32.6.2 *twoPhaseEulerFoam*中的湍流模型 + In the solver twoPhaseEulerFoam, the use of the k- turbulence model is hardcoded. This means that the solver does not use the generic turbulence modelling ususally used by OpenFOAMs solvers. The only choice the user of twoPhaseEulerFoam has is whether to enable or disable the k- turbulence model. @@ -408,7 +362,8 @@ only mandatory keyword in RASproperties is the switch turbulence. This switch is whether to use turbulence modelling or not with twoPhaseEulerFoam. Solvers which use the generic turbulence modelling offer three possible ways to disable turbulence modelling, see Section 32.6.1. -##### 32.6.3 Laminar simulation with twoPhaseEulerFoam +##### 32.6.3 使用*twoPhaseEulerFoam*的层流模拟 + If twoPhaseEulerFoam is used and a laminar simulation is conducted, then the presence of the files like 0/k or 0/epsilon is mandatory. The solver read this files regardless of the fact, that a laminar simulation is conducted. This is due to the fact that the use of the k- model is hardcoded into twoPhaseEulerFoam. @@ -416,20 +371,17 @@ Other solvers read this files based on the condition if and which turbulence mod would be the need for all possible files (0/k, 0/epsilon, 0/omega, etc.) to be present in any case, which would be utter madness. -##### 32.6.4 Initial and boundary conditions +##### 32.6.4 初始条件和边界条件 + All turbulence models can be divided into classes depending on their mathematical properties. -**Algebraic models** These models add an algebraic equation to the problem. The turbulent viscosity is computed -from known quantities using an algebraic equation (e.g. the Baldwin-Lomax model) -**One equation models** These models introduce an additional transport equation to the problem. The eddy -viscosity is computed from this additional quantity (e.g. the Spalart-Allmaras model) -**Two equation models** These models introduce two additional transport equations to the problem. The eddy -viscosity is computed from these additional quantities (z.B. k-, k-!) -Every field quantity of a turbulence model needs its initial and boundary conditions. Consequently, there may -be the need for additional files in the 0 -directory. One way to find out which files are needed is to look at the -tutorials. There, a case may be found which utilises the needed turbulence model. -If a simulation is started and the solver is missing files – i.e. the solver tries to read files which are not -present – then OpenFOAM will issue a corresponding error message. Listing 197 shows an error message of a -case with a missing 0/k file. + +**代数模型** These models add an algebraic equation to the problem. The turbulent viscosity is computed from known quantities using an algebraic equation (e.g. the Baldwin-Lomax model) + +**一方程模型** These models introduce an additional transport equation to the problem. The eddy viscosity is computed from this additional quantity (e.g. the Spalart-Allmaras model) + +**双方程模型** These models introduce two additional transport equations to the problem. The eddy viscosity is computed from these additional quantities (z.B. k-, k-!) +Every field quantity of a turbulence model needs its initial and boundary conditions. Consequently, there may be the need for additional files in the 0 -directory. One way to find out which files are needed is to look at the tutorials. There, a case may be found which utilises the needed turbulence model. +If a simulation is started and the solver is missing files – i.e. the solver tries to read files which are not present – then OpenFOAM will issue a corresponding error message. Listing 197 shows an error message of a case with a missing 0/k file. ``` Selecting turbulence model type RASModel Selecting RAS turbulence model kEpsilon @@ -439,9 +391,9 @@ From function regIOobject :: readStream () in file db/ regIOobject / regIOobjectRead .C at line 73. FOAM exiting ``` -Listing 197: Solver error message: missing file +清单197：求解器错误信息：文件缺失 -##### 32.6.5 Additional files +##### 32.6.5 附加文件 RAS turbulence models produce additional files. Most RAS models calculate the turbulent viscositiy from certain quantities. These quantities are usually field quantities and depend on the used turbulence model. However, the aim of all RAS turbulence models is to calculate the turbulent viscosity. The turbulent viscosity @@ -453,20 +405,20 @@ After the simulation has finished, the 0 -directory contains more files. The rea is not known. However, the turbulence model created the file nut for storing the turbulent viscosity. The file phi as well as the folder uniform is created by the solver. ``` -user@host :/ OpenFOAM /user -2.1. x/ run / pisoFoam / ras / cavity$ ls +user@host :~/ OpenFOAM /user -2.1. x/ run / pisoFoam / ras / cavity$ ls 0 constant system -user@host :/ OpenFOAM /user -2.1. x/ run / pisoFoam / ras / cavity$ ls 0/ +user@host :~/ OpenFOAM /user -2.1. x/ run / pisoFoam / ras / cavity$ ls 0/ epsilon k p U -user@host :/ OpenFOAM /user -2.1. x/ run / pisoFoam / ras / cavity$ pisoFoam > /dev / null -user@host :/ OpenFOAM /user -2.1. x/ run / pisoFoam / ras / cavity$ ls +user@host :~/ OpenFOAM /user -2.1. x/ run / pisoFoam / ras / cavity$ pisoFoam > /dev / null +user@host :~/ OpenFOAM /user -2.1. x/ run / pisoFoam / ras / cavity$ ls 0 0.5 1 constant system -user@host :/ OpenFOAM /user -2.1. x/ run / pisoFoam / ras / cavity$ ls 0/ +user@host :~/ OpenFOAM /user -2.1. x/ run / pisoFoam / ras / cavity$ ls 0/ epsilon epsilon . old k k. old nut p U -user@host :/ OpenFOAM /user -2.1. x/ run / pisoFoam / ras / cavity$ ls 0.5/ +user@host :~/ OpenFOAM /user -2.1. x/ run / pisoFoam / ras / cavity$ ls 0.5/ epsilon k nut p phi U uniform -user@host :/ OpenFOAM /user -2.1. x/ run / pisoFoam / ras / cavity$ +user@host :~/ OpenFOAM /user -2.1. x/ run / pisoFoam / ras / cavity$ ``` -Listing 198: Folder contents at the begin and the end of a simulation +清单198：模拟开始和结束时的文件夹内容 The 0 -directories of some tutorial cases may already contain such additional files, e.g. nut. In some cases the 0-directory may also contain several of such files due to a change in the naming scheme. Listing 199 shows @@ -476,7 +428,7 @@ case with the k- turbulence model. ``` epsilon k nut nuTilda p U ``` -Listing 199: The content of the 0 -directory of the pitzDaily tutorial case of simpleFoam +清单199：*simpleFoam*教程案例*pitzDaily*的*0*文件夹内容 ##### 32.6.6 Spalart-Allmaras The Spalart-Allmaras is a one-equation turbulence model. Although it introduces only one additional equation @@ -489,4 +441,4 @@ viscosity is not the transported quantity of the Spalart-Allmaras model another ``` nut nuTilda p U ``` -Listing 200: The content of the 0 -directory of the airFoil2D tutorial case of simpleFoam \ No newline at end of file +清单200：*simpleFoam*教程案例*airFoil2D*的*0*文件夹内容 -- Gitee From e4321f3e70f7cc8b927ce2942f5b0f94ffc4b293 Mon Sep 17 00:00:00 2001 From: EleHa Date: Thu, 25 Feb 2021 06:54:08 +0800 Subject: [PATCH 2/2] =?UTF-8?q?=E8=AE=A4=E9=A2=8631=EF=BC=8C34=EF=BC=8C35?= =?UTF-8?q?=E7=AB=A0?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- ...\221\347\253\240\350\212\202\350\256\244\351\242\206.md" | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git "a/\347\277\273\350\257\221\347\253\240\350\212\202\350\256\244\351\242\206.md" "b/\347\277\273\350\257\221\347\253\240\350\212\202\350\256\244\351\242\206.md" index db00a21..88d4aa2 100644 --- "a/\347\277\273\350\257\221\347\253\240\350\212\202\350\256\244\351\242\206.md" +++ "b/\347\277\273\350\257\221\347\253\240\350\212\202\350\256\244\351\242\206.md" @@ -38,11 +38,11 @@ ### 29 **Initialize Fields 129. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 闻久 ### 30 **Case manipulation 135 ## IV Modelling 142 -### 31 **Solution dimensions 142** +### 31 Solution dimensions 142 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . EleHa ### 32 Turbulence-Models 143 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . EleHa ### 33 Thermophysical modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .chuanfeng -### 34 **Radiation modelling 169** -### 35 **Eulerian multiphase modelling 174** +### 34 Radiation modelling 169 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . EleHa +### 35 Eulerian multiphase modelling 174 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . EleHa ### 36 Boundary conditions 186. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 莲花 ### 37 **Mesh interfaces: AMI and ACMI 189** ### 38 The MRF method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . skf0558 -- Gitee