英文翻译外文文献翻译474流动类型及其压缩性
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英文翻译外文文献翻译474流动类型及其压缩性,机械毕业设计英文翻译
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安徽工业大学 毕业设计说明书 共 页 第 1 页 装 订 线 流动类型及其压缩性 COSMOSFloWorks 模仿不可压缩液体的流动状态（包括非牛顿状态下的液体），可压缩液体（液体密度由压力决定）或可压缩气体（目前 COSMOSFloWorks不能解答双阶段的流动）。在开始一个 COSMOSFloWorks项目之前，检查该项目所用物质已存在于工程数据库中以及这些材料物理特性的准确性。 如果某些特殊物质未被工程数据库包括，就将这一特殊物质及其相关特性添加到工程数据库中。 在 COSMOSFloWorks项目中，可以指定流动类型（液体或气体）和物质，这些将会在Wizard或 General Settings对话框中被分析。若你的项目是关于一个高 Mach number 的气体流动，且 Mach number的最大值在稳定状态下超过 3及在瞬时分析中为 1，则无论在 Wizard或在 General Setting中的物理特性选框中都选择高 Mach number 流动。如果你的初始值（外部问题的环境状态）或边界状态表明流动速度较大时，COSMOSFloWorks将报出一个警告信息。 在计算过程中， COSMOSFloWorks也会告知此流动是高 Mach number气体流动还是低Mach number气体流动 （参考 Monitoring Calculation， Information）。 注意如果你将High Mach number flow当作低速度气体流动（最大值 M1.5） , 那么答案的准确性就会降低。 重力作用 对于自然对流问题， 在 Wizard或 General Settings 中通过选择相应的复选框可以将重力作用包括在内。同时应该在 Gravitational Settings中设定相应的 X， Y和 Z来确定重力的加速度矢量。 COSMOSFloWorks 介绍 3 6 对于液体，确定它们在 工程数据库 中指定的密度是由其流动温度决定的， 而对于气体，只有在 High Mach number flow复选框未被选中时， 重力作用 才会起作用。 若考虑重力作用的影响，缺省情况下， Pressure potential复选框是处于被选中状态。此时，假定指定的静态压力是压力（或潜在压力）；通过参考密度，重力加速度矢量和位移矢量，就可以计算出绝对压力（ Pabs） (gi 是 重力加速度矢量的组件， x,y,z对应于整体坐标系中的坐标 )。当 Pressure potential复选框未被选中时，指定的静态压力就被当作绝对 压力，且相应的压力可以分别被计算出来。若你有一个局部，你就可以在这个局部建立一个集合从而可以简易地改变整体坐标系原点的位置。显示整体坐标系，只需在 COSMOSFloWorks 设计树 中打开 数据输出 文件夹，右击 整体坐标系统项并选择 Show。 湍流 COSMOSFloWorks解决了缺省情况下的 湍流问题，你也可以在 Wizard或 General Settings中选择 Laminar Only流动来停止 湍流。 一般情况下，湍流出现在大面积的流动区域内及壁旁的边界层中。 如果你未指定 Laminar Only或 Turbulent Only流动，则流动将是 薄片状或 湍流或从一nts 安徽工业大学 毕业设计说明书 共 页 第 2 页 装 订 线 种状态到另一状态的转变（取决于流动特性）。 缺省的湍流参数 由 COSMOSFloWorks定义的。 湍流参数可能是手动设定湍流强度和湍流长度，或湍流能量和湍流消散。 对于大部分流动来说： specified piezo abs x y z P P P gx gy gz 因为很难正确的预计湍流，因此建议使用缺省湍流参数。湍流参数是在内部条件，进口临界条件或在外部问题的外部条件下已确定的。此外，进口模拟墙的临界层参数在缺省情况下都由 COSMOSFloWorks确定。 缺省临界层类型由 （ 是开放交叉区域， 是开放区域的周长）。层厚度是由 雷诺数 数值决定的有效墙的长度决定。在 边界条件 对话框中，你可以通过在 设置 页中单击Show advanced parameters复选框来指定临界层系数。你也可以指定一个薄片状或湍流（若你没有指定薄片式流动的情况下）的临界层及其厚度。 若要了解初始，周围和临界条件下的更多信息，请参考 Overview of Conditions。 多孔媒介物 如果 SolidWorks 是集合物（或聚集物），在液体流过 SolidWorks 时， COSMOSFloWorks 将 SolidWorks 的某些部分当作多孔媒介物。液体流通过多孔媒介由多孔媒介的性质以及外部流动的条件决定。为了简化你的工作， COSMOSFloWorks为你指定多孔媒介性质提供了多种选择。首先在工程数据库中定义多孔媒介的有效多孔性，多孔媒介定义为与整个媒介容量相关的相连的孔的容量。然后从下列几种类型中选择多孔媒介的渗透类型。 等方性 媒介的渗透性与媒介内方向无关 单向性 媒介只是在某个方向可以渗透 轴对称性 媒介的渗透性由与指定方向相关的轴截面和横 截面决定 支架结构型 当媒介的渗透性随方向改变，且完全由 3个基本方向决定的 3个组件决定时，大多是此种情形。 然后以媒介对液体流动的阻力（阻力计算公式）来确定媒介的渗透性（它的成分，如果它是轴对称或支架结构型）。阻力计算公式， K grad(P)/(V)，其中 P, , V分别是液体压力，密度，及流动速率。你可以用下列四个公式中的一个来计算矢量 k的值： k = PS/(mL) (为压强下降 ,流量 ,尺寸 ), P 为并列多孔物质两边的压力差 ; m 是通过物体的大量流动率 ;相应的， S 和 L 为截（断）面 面积和长度。所有的都在被选择的方向，你可以指定 -P 为 m 的函数， S 和 L 为常数。指定卷积流动率 v 来代替大量流动率，在这种情况下 COMOSFloWorks 计算式为 m = v。另外，在指定压降 -P 或者压量流动率 m 通常正比于液体动力的情况下，多孔媒介阻力系数 K 决定于另一种液体，这种液体不是当前液体而是被我们称为校准液体，通过指定校准液体的非零动力粘度（也叫着校准动力粘度），你可以纠正 K， k = PSm /(mL cal),因此，在这里叫做液体的动力粘度。所有插入到 SolidWorks 的模型的值没有 具体说明，但是说明了多孔媒介的属性 k = (AV+B)/（由速度决定的）， V 为流体速度， A 和 B 为常数，指定 A 为 kg/m4,Bnts 安徽工业大学 毕业设计说明书 共 页 第 3 页 装 订 线 为 kg/(sm3). k= /(D2)（是由参考气孔尺寸 D 所决定的），在这个式子中和是流体动力粘度以及密度， D 是根据实验所确定的参数气孔的尺寸 ，只需确定 D 就可以（ 和 是通过计算得到的）。 k= /(D2)f(Re)（是由参数气孔尺寸 D 和雷诺数决定的）用 f(Re)因子来区别以前式子，可以得到一个更为普遍的式子，除了 D 以外，还要将 f(Re)为式子的决定 因素来确定。 介绍 COSMOSFloWorks 注释：可容电阻说明了下列极限的存在，必须比和小，而和分别代表多空装置内部流动速度以及最大孔径。否则，结果将可能出错，若大于这个极限，必须通过改善多空装置内部的网孔，尤其是在分界面上的来减小。 在 多孔条件 对话框中，明确剩余的依据来确定把多孔装置插入下列模式中： 工程数据库 中的多孔装置 把多孔装置应用到模式组成中 如果一个装置的渗透性图形是单向的或者是轴对称的，那么就必须按照选择的坐标系统的轴线或按照选择的曲线来确定方向（对于一个周轴对称多孔装置来说是轴方向），它 们的方向是正切方向。 非牛顿状态的液体 COSMOSFloWorks 具有技术非弹性非牛顿状态液体的层流量能力。所有可用的模式都是基于以下假设的：流量少，剪应力是流量剪切程度的函数，或者将液体的动粘滞度近似引入非牛顿状态下的液体，下面了解非弹性非牛顿状态粘性液体是可用的： 模式，其中 K代表液体的粘度系数； n代表的密定律指数（无维），代表液体的屈服应力 (Pa)，这种模式包括以下几种特殊形式： x V 100 f o n K n s Pa n=1, o=0 表示牛顿状态液体，在这种情况下 K 代表液体的粘度； n=1, o=0 表示牛顿状态液体的宾厄姆模型，特点是非容域压力（ o），在非容域压力下的液体的状态为固体。为了能够使之变为流动的液体，必须提高这个临界剪切力（这个临界值由 K 自动地模式化生成，在这种情况下被称着塑性粘度，在 o 时达到实际最大值）； nts 安徽工业大学 毕业设计说明书 共 页 第 4 页 装 订 线 0 n 1, o=0 表示薄剪切非牛顿状态液体的幂定律模型 n 1, o=0 表示厚剪切非牛顿状态液体的幂定律模型 幂定律模型：与上面 提到的赫歇耳模型的特殊例子不同的是，在幂定律模型中这个值|受到具体的限定： |min | max 因此这个最大动粘度和最小动粘度应具体说明除了一致性系数 K()和幂定律指数 n（无尺寸的） Carreau 模型，在这个模型中代表液体在无限剪切力下的绝对粘度，例如，最小动粘度 (Pas)，是在容剪切力下液体的动粘度，最大动粘度 (Pas)，是时间常数（ s），是幂定律指数（无尺寸的），这个模型是上面提到的限定的幂定律模型的平滑方案。 可压缩液体 可压缩液体的密度在工程数据库中被具体说明，要么是一常数，要么是在液体状态下取决于温度的某一值，另外在非牛顿压缩液体下你可以说明液体的密度也受压力影响。例如：液体的可压缩性可由下面方程式的形式来描述： n K 1 n K n s Pa 2 / 1 2 1 1 n o K 在这里 0 是在参考大气压 P0 下液体的密度， C 和 B 是系 数， ( 0, C, B,和 P0 有使用者具体说明，作为一个常数或者是取决于温度的某一值例如 P0， P 是计算出来的压力，这里是动力指数由使用者具体说明，是一个常数或者是取决于温度的某一值； 面与面之间的辐射 如果你解决一个固体间的热交换，在这里必须是一个固体的温度很高而且或者气体是稀薄的，由于热交换是通过传导方式进行的，因此通过辐射进行的固体间的热交换是明显的。（例如固体间的热辐射在这个问题里起了一个明显的作用，明显地影响了这个固体的温度）你可以选择使它产生放射性，并且说明固体表面的放射性，另外，如果问题需要的 话，你可以通过临界的放射率和温度极值从非计算领域边界（模型的开口）进入到计算领域（模型）去具体描述热辐射，结果，辐射热作用在模型的表面并加热它们。下面的标准的（定义的）面在工程数据库中是可用的。 无辐射面，这个工作面既不发射也不吸收热辐射，不能参加辐射热交换。 吸收面：这个工作面充分地吸收所有落到它上面的辐射，例如一个黑体，但是和黑体相反的是，它不能发射出任何热（例如：没有射线从中放出） 黑体面：工作面的发射率为（黑体），工作面能充分吸收所有落到它上面的辐射，而且它的发射根据 Stefan-Boltzman定 律， 0 0 nts 安徽工业大学 毕业设计说明书 共 页 第 5 页 装 订 线 / 1 ln B P C B P 1/ 0 0 n P B P B 白体面：工作面的发射率为 0（白体），例如：工作面充分地反射所有的辐射（遵循朗伯定律）并且自身不发射出任何热，因此工作面的温度不受热辐射影响。 对称： 如果你在一个工作面中使用了理想面条件去说明问题的对称表面的话，那么这个对称辐射面的类型应该在这个面上具体说明出来，如果问题考虑到了热辐射。 对于非计算领域边界或者模型的开口，下面的标 准（ FW-定义的）工作面发射率性能是可用的 无辐射面：根据上面，使用不同的要素，这个要素不是固体面，而且一个非计算领域的边界或模型的开口。 黑体外部边界：表面发射率为（黑体），因此表面辐射作为一个黑体进入到计算领域，它的温度不能被计算出来，但是你自己可以说明。（对于在指南或者垂直背景对话盒里的非计算领域应使用环境温度辐射盒；对于在辐射面对话盒里的模型的开口应使用辐射盒，如果黑体外部边界辐射表面类型在这些对话盒中被选择，这些将会出现在对话盒里） 太阳能开口：一个面（一个模型的开口或者非计算领域边界）辐射热（定 向辐射）进入到计算领域（或模型）随着方向和在辐射面对话盒里具体说明的强度 一个通常的辐射向由发射率系数和下面工作面的发射性能的其中一个来定义的 工作面：一个由你在发射率系数盒里具体说明的发射率（范围从 0 到 1，灰度具体说明）的面辐射出热。 外部边界：一个面（一个模型的开口或者非计算领域边界能够发射出热进入到计算领域模型）发射率由你在发射率系数盒里具体说明的（范围从 0 到 1），表面的温度不能计算，但可由你自己具体说明（对于在指南或者普通背景对话盒里的非计算领域边界使用环境温度辐射盒，对于在辐射面对话盒里的nts 安徽工业大学 毕业设计说明书 共 页 第 6 页 装 订 线 模型的开 口应使用辐射温度盒，如果外部边界类型被选择了，这些将会出现） 周围面：一个由你在发射率系数盒里具体说明的发射率（范围从 0 到 1）的面能够辐射热，但是这热不能到达模型的工作面，而且出现在空间周围（结果，从这个面出来的辐射不能被计算出来） 说明：在所有例子中，工程流体既不发射也不吸收热辐射（对于热辐射它们能透过），因此，热辐射仅和固体相关联。 辐射固体面既不是黑体也不是白体，被假设为理想的灰体，例如，和黑体有相似的连续发射光谱。因此，单色发射率取决于发射波长，这些辐射由波长决定，对于某一特定表面条件的某一材料（ 从工程数据库辐射表面中的一些是可应用的）这个灰体发射率仅取决于工作面温度。 在这些所有情况下，固体表面的热辐射被认为是发散的，遵守朗伯定律，根据每单位面积和每单位固体角度的辐射强度在各个方向上是相同的。 模型辐射面间的净辐射热交换可以根据固体间传热和热传递来计算。 当观察计算结果，你可以看见下面的辐射特点： 面（当选择流体作为媒体）的局部特点：净辐射流动（在这个面上的一点离开和到这辐射流动的不同，如果离开的流动比达到的流动大的话，那么这个就是有意义的）和出口辐射流动（离开了面的辐射流动） 在整个面参 数中的整体特点：净辐射率（集成在选择面上的），开口辐射率（集成在选择面上的）可压缩流动 如果流体的密度取决于压力那么这流动被看着是可压缩的，因此密度变化的影响是不可忽略的。在中气体总是可压缩的，液体是不可压缩的，如果你的任务是处理高速气体流动的话，你应该把气体流动看作流动，在这里最大值，对于稳态分析增加了对于系统分析增加，为了考虑高气体流动，应选择在或者普通背景里的高气体流动检查盒。如果任务是超声波被局限在相对小的流体量和大的压声速流动，那应选择小气体流动，如果流量在这里流动变成计算域大小的一半成或大一点， 那么你应该把这个流动看作气体流动。 不可压缩流动 如果流体密度仅仅取决于温度和粘度，那么这个流动是不可压缩的，因此密度变化的影响可以忽略 基啮合 当整个计算域在啮合过程的开始，基啮合就会被构建，它由计算域被分开成平行相同的面板形式，这些面板垂直于整体坐标系，计算领域的边界面就在这些当中 介绍 基啮合被放置在对称整体坐标系方向，它们之间的距离由这些方向具体说明的单元决定。如果需要，你可以抽一些额外的啮合面极限具体说明它们之间的位置，通过加一个控制面来完成。 nts 安徽工业大学 毕业设计说明书 共 页 第 7 页 装 订 线 nts 1 solution (by specifying a smaller time step then the automatically selected one, e.g. for resolving periodic solutions of too small period) or to calculate a heat transfer in solids faster (by specifying a larger time step then the automatically selected one, e.g. if the fluid flow does not changed), it is expedient to specify the time step manually. If you solve a time-dependent problem with heat transfer in solids only, i.e., without calculating a fluid flow (the Heat transfer in solids only option is enabled) a manual specification of the time step is preferable. You can set the Total analysis time and the Output time moments in the Time Settings dialog box in the Wizard. Alternatively, after passing the Wizard, you can set the Maximum physical time for finishing the calculation (see Finishing the Calculation), Introducing COSMOSFloWorks 3-5 as well as strategy and moments of saving results during calculation (see Saving Results) in the Calculation Control Options dialog box. To specify time-dependent boundary conditions, use the Design dialog box. See also Initial Conditions Basic Information. Fluid Type and Compressibility COSMOSFloWorks simulates flows of incompressible liquids (including non- Newtonian liquids), compressible liquids (liquid density is dependent on pressure) or compressible gases (two-phase flows cannot currently be solved by COSMOSFloWorks). Before starting a COSMOSFloWorks project, check that the substances for the project are present in the Engineering Database and that their physical properties are correct. If particular substances are not present, just add the substances and associated properties to the Engineering Database. In the COSMOSFloWorks project, you specify the Fluid type (liquid or gas) and the substances to be analyzed in either the Wizard or the General Settings dialog boxes. If your project deals with a high Mach number gas flow, where the Mach number maximum value exceeds about 3 for steady-state or 1 for transient analyses, select High Mach number flow in the Physical features box in either the Wizard or the General Settings. COSMOSFloWorks will give you a warning message if your initial (or ambient conditions for External problems) or boundary conditions indicate high velocity flow. During the calculation COSMOSFloWorks will also inform you whether the flow can be considered as a high Mach number gas flow or as a low Mach number gas flow (see Monitoring Calculation, Information). Be aware that if you consider High Mach number flow for low-velocity gas flow (maximum M 0 describes the Bingham model of non-Newtonian liquids, featured by a non-zero yield stress ( o), below of which the liquid behaves as a solid, so to achieve a flow this threshold shear stress must be exceeded (this threshold is modeled by automatically equating K, named plastic viscosity in this case, to a substantially high value at o); 0 1, o = 0 describes the power-law model of shear-thickening non- Newtonian liquids. The power-law model. , i.e., , in contrast to the abovementioned Herschel-Bulkley model special case, the values are restricted: min max, so these minimum and maximum dynamic viscosities (Pas) are specified in addition to consistency coefficient K ( ) and power-law index n (dimensionless); The Carreau model. , , where is the liquids dynamic viscosity at an infinite shear rate, i.e., the minimum dynamic viscosity (Pas), o is the liquids dynamic viscosity at zero shear rate, i.e., the maximum dynamic viscosity (Pas), K1 is the time constant (s), n is the powerlaw index (dimensionless). This model is a smooth version of the power-law model with the above-mentioned restrictions. Compressible Liquids A liquid density is specified in the Engineering Database as either a constant or a tabular dependence on temperature under the Liquids item. Additionally, under the Non-Newtonian/Compressible liquids item you can specify a dependence of the liquid density on pressure (P), i.e., the liquids compressibility, through one of the following forms of the Tait equation of state: n K 1 n K n s Pa 2 / 1 2 1 1 nts 7 n o K Introducing COSMOSFloWorks 3-11 , where 0 is the liquids density under the reference pressure P0, C and B are coefficients, ( 0, C, B, and P0 are specified by the user as constants or, except for P0, as tabular dependences on temperature), P is the calculated pressure; , where, n is a power index specified by the user as a constant or a tabular dependence on temperature. Surface-to-surface Radiation If you solve a problem including heat transfer in solids, in which a solids temperature is too high and/or the gas is too rarefied, so that heat transfer by radiation from and/or between solids is noticeable with respect to heat transfer by convection (i.e. heat radiation from the solid surfaces and/or to them plays a noticeable role in the problem, noticeably influencing the solids temperature) you have the option to activate the Radiation physical featura and specify the solid surfaces emissivity. In addition, if require by the problems statement, you can specify heat radiation from the computational domains far-field boundaries (or the models openings) into the computational domain (ilto the model) through the boundaries emissivity and temperature values. As a result, this radiative heat acts upon the models wal,s and can heat them. The following standard (FW-Defined) qurfaces are available in the Engineering Database8 Non-raditing surface denotes that this wall qurface does not partibipate in the radiathon heat transfer, i.e. neither emits nor absorbs heat radiation, Absorbent wall denotes that the wall surface fully absorbs all the incident radiation falling upon it, i.e. as a blackbody, but in contrast to it, does not radiate any heat (i.e., no rays start from it), Blackbody wall denotes that the wall surfaces emissivity is equal to 1 (the blackbodx one), h.e., the vall surface fully absorbs all the incident radiation falling upon it and emits the heat in accordance with the Stefan-Boltzman law, 0 0 / 1 ln B P C B P 1/ nts 8 0 0 n P B P B Introducing COSMOSFloWorks 3-12 Whitebody wall denotes that the wall surfaces emissivity is equal to 0 (the whitebody one), i.e., the wall surface fully reflects all the incident radiation (in accordance with the Lambert law) and does not emit any heat by itself, so the surface temperature does not affect the heat radiation, Symmetry. If you use the Ideal Wall condition at a wall to specify the problems symmetry plane, the Symmetry radiative surface type should be specified at this wall if the problem is considered to radiate heat. For the computational domains far-field boundaries or the models openings, the following standard (FW-Defined) surface emissivity properties are available: Non-radiating surface, see above, with the difference being that it is not a solid surface, but either a computational domains far-field boundaries or a models opening, Blackbody opening/outer boundary denotes that the surfaces emissivity is equal to 1 (the blackbody one), so this surface radiates heat into the computational domain (into the model) as a blackbody, and that its temperature is not calculated, but specified by you (in the Environment radiative temperature box for the computational domains far-field boundaries in the Wizard or in the General Settings dialog box, or in the Radiative temperature box for the models openings in the Radiative surface dialog box, which appear in these dialog boxes if the Blackbody opening/outer boundary type of radiative surface is selected in these dialog boxes). Solar opening denotes a surface (a models opening or the computational domains far-field boundaries) which radiates heat (as directional radiation) into the computational domain (or into a model) along the Direction and with the Intensity specified in the Radiative surface dialog box. A custom radiative surface is defined thought the Emissivity coefficient and one of the following wall surface emissivity properties: Wall. Denotes a surface which radiates heat with emissivity specified by you in the Emissivity coefficient box (in the range from 0 to 1, i.e., a gray-body emissivity can be specified). Opening/outer boundary. Denotes a surface (a models opening or the computational domains far-field boundaries) which radiates heat into the computational domain (or into a model) with emissivity specified by you in the Emissivity coefficient box (in the range from 0 to 1). At that, the surfaces nts 9 Introducing COSMOSFloWorks 3-13 temperature is not calculated, but specified by you (in the Environment radiative temperature box for the computational domains far-field boundaries in the Wizard or in the General Settings dialng box, or in the Radhativd temperature box in the Radiative surface dialog box, which appear if the Opening-outer boundary type is selected). Wall to ambient. Denotes a surface which radiates heat with emissivity specified by you in the Emissivity coefficient box (in the range from 0 to 1), but this heat does not arrive at the models walls, i.e., disappears il the surroundhng space (as a result, the radiation rays from this surface are not calculated). NOTE: In all cases, the project fluids neither emit nor absorb heat radiation (i.e., they are transparent to heat radiation), so the considered heat radiation concerns solid surfaces only. The radiative solid surfaces which are neither blackbody nor whitebody are assumed ideal gray-body, i.e. having a continuous emissive power spectrum similar to the blackbody one, so their monochromatic emissivity is independent of the emission wavelength. The total radiation integrated over all wavelengths is considered only. For certain materials with certain surface conditions (some of them are available from the Radiative Surface tab of the Engineering Database), the gray-body emissivity can depend on the surface temperature only. In all the cases, the heat radiation from the solid surfaces is assumed diffuse, i.e. obeying the Lambert law, according to which the radiation intensity per unit area and per unit solid angle is the same in all directions. The net radiation heat exchange between the models radiative surfaces is calculated along with the convective heat transfer and the heat transfer in solids. When viewing the calculation results, you can visualize the following radiation characteristics: the local characteristics (power per unit area) in Surface Plots (when selecting Fluid as medium): the Net radiant flux (the difference of the radiant flux leaving the surface at this point and the one arriving at it, so it is positive if the leaving flux is greater than the arriving one) and the Leaving radiant flux (the radiant flux leaving the surface); Introducing COSMOSFloWorks 3-14 the integral characteristics (power) among the integral Surface Parameters: the Net radiation rate (the net radiant flux integrated over the selected surface) and the Leaving radiation rate (the leaving radiant flux integrated over the selected surface). Compressible Flows Flows are considered compressible if the fluid density depends on pressure so density change effects are important. In COSMOSFloWorks, gases are always compressible nts 10 and liquids are always incompressible. If your project deals with a high-velocity gas flow, where the Mach number maximum value exceeds about 3 for steady-state analyses or 1 for transient (time-dependent) analyses, you should consider the gas flow as a high Mach number flow. To consider high Mach number gas flow, select the High Mach number flow check box either in the Wizard or General Settings. The low Mach number gas flow is recommended for the tasks where the supersonic flow is localized in relatively small fluid volume and the major flow is subsonic. If the fluid volume in which the flow becomes supersonic is about a half of the computational domain size or greater, it is recommended that you consider the flow as a high Mach number gas flow. Incompressible Flows Flows are considered incompressible if the fluid density depends only on temperature and concentration so density change effects are negligible. Basic Mesh The basic mesh is constructed for the whole computational domain at the beginning of the meshing process. It is formed by dividing the computational domain into slices by parallel planes which are orthogonal to the Global Coordinate Systems axes. The computational domains boundary planes (at X min, Z max) are among these planes. Introducing COSMOSFloWorks 3-15 By default, the basic meshs planes are spaced in the X-, Y-, and Z-directions of the Global Coordinate System nearly uniformly, and the distances between them are determined from the specified numbers of cells in these directions (Nx, Ny, Nz). If necessary, you can insert additional mesh planes and specify another spacing between them (i.e., non-uniform steps) by creating the Control Planes. Travel The term travel, used together with iterations is a unit characterizing the calculation duration. We denote the calculation period (in its turn, it can be measured in iterations or in another unit) required for a flow disturbance to cross the computational domains fluid region. So, value N travels denotes the calculation period required for a flow disturbance to cross the computational domain N times. The travel equivalent in iterations is nts 11 determined just after starting the calculation and can be seen in the Info box while monitoring the calculation. Partial Cells A partial cell is a computational mesh cell lying at the solid/fluid interface, partly in a fluid region and partly in a solid region. Irregular Cells An irregular cell is a computational mesh cell lying at the solid/fluid interface (or solid/ solid interface in case when two or more different solids are within the cell). The irregular cell is partly in one substance and partly in another substance, and characterized by the impossibility of defining the solid/fluid interface position within the cell, given the cells nodes positions relative to solid region and the intersections of the solid/fluid interface with the cell. COSMOSFloWorks has difficulty determining whether the irregular cells nodes belong to the solid or to the fluid region which makes COSMOSFloWorks unable to determine the solid/fluid (or solid/solid) interface position within the cell. Introducing COSMOSFloWorks 3-16 Examples of irregular cells at the solid/fluid interface are shown (colored red). Two ways of possible irregular cell resolution. Note that irregular cells at the solid/fluid interface are always treated as fluid cells. All irregular cells are always split to the maximum level among all the refinement levels specified for the region of irregular cells or until the cells become regular. Thus, if you want to get rid of irregular cells, you should increase the refinement levels, starting with increasing of the Small solid features refinement level, because it will change the existing mesh in other regions to a lesser degree than the other refinement levels. 4-1 Introducing COSMOSFloWorks 4 Conditions and Tools Overview of Conditions nts 12 Any problem solved with COSMOSFloWorks must have initial conditions and boundary conditions. In steady state problems, initial conditions influence the rate of convergence to the steady state, whereas boundary conditions fully govern the flow pattern. In transient (unsteady) problems the time-dependent flow pattern depends both on initial conditions and boundary conditions. You specify flow initial conditions in the Wizard or General Settings using different names: Ambient Conditions for External flows and Initial Conditions for Internal flows. In an assembly (or in a multibody part) you can disable a component and treat it as a fluid (see Component Control). You then specify Initial Conditions inside the fluid component, which are different from the default. If you consider Heat Transfer in Solids, you specify the initial solids temperature in the Wizard or General Settings. In an assembly (or in a multibody part) you can specify a component initial solid temperature that is different from the default (see Initial Condition) solid temperature condition. For internal flows we recommend creating separate Introducing COSMOSFloWorks 4-2 component parts for the lids used to close the openings. Next, specify a material with zero thermal conductivity (insulator) for the lid components. This will prevent heat transfer in the lid components. You can use results of the previous calculation performed either in the current project or other projects, as the initial conditions for the newly prepared calculation. In the Wizard or General Settings you can apply any available results by selecting Transferred initial conditions. See Initial and Ambient Conditions. To apply the current projects results as initial conditions for a new project calculation you can also use the Take previous results option. See Running the Calculation. You can specify flow boundary conditions somewhat differently for External and
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