【机械类毕业论文中英文对照文献翻译】轿车气动制动装置
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附录A轿车气动制动装置罗伯托卡帕塔(Roberto Capata)，塞拉利昂罗马大学机械和航天工程系，罗马，意大利罗马2015年8月21日收到；2015年10月23日接受；2015年10月26日公布【摘要】在过去的几年里，在方程式赛车锦标赛中，空气动力作为一个性能参数达到了越来越重要的地位。在过去的四个赛季里， ER设计了他们的一级方程式赛车，具体的目的是产生最优的下压力，相对于汽车的瞬时设置。然而，这种对更高下压力的极端研究带来了一些 当一辆车跟在另一辆车后面时，会产生负面影响；事实上，众所周知，在这种情况下，空气动力受到干扰，很难超过领先的汽车。到 部分地解决了这个问题，公式1规定了2011的减阻系统（DRS），它是位于后翼上的可调节襟翼；如果是扁平的，可以减少T。 他向下用力，大大提高了速度，因此，有机会超过领先的汽车。反之亦然，当皮瓣关闭时，它可以确保更高的抓地力，这是非常有用的，特别是 中低速旋转。把重心放在后翼上，但是通过转移注意力从增加的最高速度来增加中间速度和慢速曲线的抓地力，我们决定学习。 一种类似于DRS的装置，但效果相反。目的是设计一种与后翼结合的气动制动器。特别是，项目构思是在上表面雕刻。 机翼(压力侧)的一系列“C”形型腔，也不是由适当的滑动板覆盖。这些空腔，当它们被发现时，在制动阶段的开始，产生一个 湍流和额外的下压力增加，减轻了制动系统的负荷，并允许驾驶员大幅减少滑行和延迟制动。因为看起来 国际汽联一级方程式锦标赛通过的是不允许这样的装置，它已经决定将这一概念应用在一辆4方程式赛车上。本文介绍了该设计，并对其影响进行了分析。 f使用商用CFD软件，在标准翼腔上提供这些细节。关键词：气动制动器；空腔；动力效应；流体动力学模拟【问题定式化】本文介绍了一种公式轿车后翼气动制动器的实现方法。第一步是选择合适的空气动力学附录。我 特别是，它决定研究意大利4方程式赛车1，这是一个类别在发展的第一阶段。而且，这场锦标赛的规则很容易找到，而且赛车也很容易找到。 以力学和翼型的均匀性为特征的。因此，考虑到国际汽联网站上的技术规定，决定对上翼型进行研究。 绘制(图1)。它是一个铝合金机翼，有237.9毫米的弦线和54.2mm的高度。方程式第四届锦标赛将提供使用4T热机(奥托/博德罗卡斯循环)：它可以是纳吸入或涡轮增压，最大功率在120千瓦(160马力)左右。考虑 考虑到赛车的重量和锦标赛的赛道，预计最高时速为230公里/小时(64米/秒)。在操作条件方面，假设空气温度为300 K大气压力。【翼型行式简述】考虑到翼型，有几个元素有一个特定的命名：平均弧度线：与平均腔线垂直测量的上、下表面中间点的轨迹；前缘：平均弧度线的最前方点；后缘：平均弧度线的后一点；和弦：连接前缘与后缘的直线；上表面：剖面的上边界；下表面：剖面的下边界；厚度：下表面与上表面之间的距离。不同翼型的标志是一个逻辑编号系统，这是由美国馈送机构NACA。这个系统由四个数字组成，它们有明确的含义：第一个数字表示最大弯曲度，以百分之一的和弦表示；第二位代表从弦的前缘沿和弦最大弯曲度的位置，以和弦的十分之一为单位；第三和第四是最大的厚度，以百分之一的和弦。当翼型相对于空气运动时，它产生气动力，在一个与相对运动方向成一个角度的后向方向上。 分为两个部分：提升和拖动。升力是垂直于相对运动方向的力分量，而阻力是与相对运动方向平行的力分量。这些 在不同的攻角下研究了力，即翼型切割流体的角度。实验数据表明，CL随攻角的变化而变化：更准确地说，是在低角度下。形成一个“死气沉沉”的区域后面的轮廓。本文通过对上述物理现象的流场分析，提出了一种新的解决方案。 更好地了解在后一种情况下正在发生的情况。从图2中可以清楚地看出，随着压力的大幅度降低，尾翼的速度趋于增大，而 在停滞点，速度趋向于零，普瑞斯-当然会急剧上升。它会产生一个不利的压力梯度，从而使流体颗粒从后缘移动到停滞点， 然后，它有一个快速分离的边界层下面。停滞点在这些条件下没有稳定的位置，因为没有压力恢复。图1.F4后翼的尺寸图(毫米)Figure 1. Dimensions of F4 rear wing这个方程组是一个描述斯托克流体行为的偏微分方程组：流体可以被认为是连续的。有一个关于 在简化的情况下，用简化的数值分析方法可以得到其他情况下的解。湍流f的最直接数值模拟方法 LOW是直接数值模拟DNS，它将Navier-Stokes方程分解为离散的数值模拟.它解决了整个范围的湍流长度尺度，因此对流动的描述是如此的详细， e仿真的有效性与实验相似。计算量与Re3成正比，因此有必要用不同的方法来研究高雷诺数BEC下的湍流流动。 因为DNS所需的计算资源将超过当前可用的最强大的COM-计算机的容量。在实际应用中，平均数量的知识是 足够解决湍流问题的技术Rans(雷诺平均Navier-Stokes方程)的基本思想是只从Nav中求出平均参数(在时间上是中介的)。 IER-Stokes方程，减少了DNS所需的巨大计算费用.在实践中，湍流运动由平均运动和随时间变化的波动组成。利用Reynol的分解 days after sight ：除了应力张量的发散外：由Navier-Stokes方程导出的系统是封闭的，而t则是封闭的。 由于雷诺张量引入了6个额外的未知数，因此RANS模拟的系统是不开放的。上述问题被称为解决的湍流闭合问题。 通过引入TUR-Bulent波动模型，再现波动项对平均运动的作用。k-模型是最常见的湍流模型之一，即使在强烈的不利压力梯度的情况下也是不合适的。它是一个具有两个方程的模型：它包括两个加法 描述湍流特性的Al输运方程，以及湍流能量的对流和扩散等效应。第一个变量是湍流动能k。第二个变量是湍流耗散；第二个变量决定湍流的尺度，而第一个变量K决定湍流中的能量。有 K-模型的两个公式：标准k-epsilon模型和RNGk-epsilon模型。在标准的k-epsilon模型中，涡粘性是由单长尺度湍流决定的，因此涡旋扩散只能通过一定的尺度来计算，而在实际中则是全部尺度。 S的运动将有助于湍流扩散。【项目描述】本课题的目的是为了提高赛车性能，缩短拉断距离，提高弯曲速度。因此，我们决定干预机翼产生的阻力。 E断裂，也有下压力提供的抓地力，速度的作用。为了解释升力，然后是下压力，可以参考飞机的机翼，观察它的剖面。大 后者是不对称的，顶部有一个比底部更长的轮廓：当机翼移动时，它将相对流动分离成两个部分，因此空气层在顶部滚动得更快。出水 英航经历了一个助推，然后是空气动力制动的公式汽车加速向尾部的速度高于机翼下的空气，这是一个较短的路径。所以两个洋流 e在同一时间间隔后在尾部重新团聚，没有造成不平衡。这不仅是事实，而且作为第一个近似，我们可以参考这个模型。关于伯努利特林 由于在较低流速下的压力低于上部，所以机翼下的压力必须大于机翼上方的压力。因此，两个压力基因之间的差异 将结果向上，即将飞机置于空中的升力。详细地说，可以表示为：式中：为中等密度；V是空气速度；A是参照面；C是一个升力无量纲系数；是翼攻角。在赛车，机翼是倒装和垂直推力向地面(下压力)：这是相关的轮胎抓地力系数。运行阻力取决于它的前部。 它的前向速度、介质密度和阻力系数。阻力系数(Cd)取决于物体的形状和尺寸、介质密度和粘度、表面。 粗糙度和物体速度。气动力阻力(在一般流体力学中)或阻力，首先，用摩擦阻力、尾迹阻力和诱导阻力之和，给出流体介质对物体前进运动的总阻力。 起重机。在颗粒中，对于锥形物体，流动阻力是通过摩擦(层流和/或湍流)来实现的，即表面对介质的摩擦。为此，我们引进了 边界层的概念：它的动态范围，层流或湍流，在其中内的电流速度受强梯度(连续变化)，由于流体的粘度。 它可以被认为是经历无序的区域，在层表面上速度为零。边界层的厚度很小，比物体的整体尺寸低一个数量级，从而产生粘胶扰动。然后，在边界内 Ry层，切向剪切应力为“致密”。因此，在层施加强烈的耗散制动作用时，在热搅动中转换部分运动。耗散A 限制物体与周围流体的相对速度。在湍流边界层中，由于横向的交换，粘性应力也会增加应力。 rse动量；这些作用随着流体密度的增加而增加。湍流运动的混沌意味着较高的热耗散，因此，在湍流条件下，制动力是相反的， 大于层流制度。以这种方式产生的阻力受到表面粗糙度的影响：而且，粗糙的表面点燃较早，更容易湍流。 在流动中的条件，然后，确定较高的电阻。因此，决定设计一些管道，在机翼的压力侧，最初用特殊的滑板盖住，以便增加。 唱气动阻力和下压力。设计的第一阶段是用CAD软件绘制机翼的轮廓。这样，就有可能进行cfd模拟，评估机翼的气动性能。 在失速现象发生前，对下向力和阻力进行了估计，并估计了有效攻角3。在流体力学中，失速是由于Ang的增加而产生的升力系数的缩回。 在空气动力剖面上，如翼型、螺旋桨叶片或叶轮机械转子上，由于入射速度的下降。对象的攻角的最小值。 失速的发生称为临界攻角。这个值对应于最大升力系数，根据特定的剖面或考虑的雷诺数而有很大的变化。 编号4。同样地，还报告了活动腔的轮廓，并进行了适当的模拟。通过这种方式，可以估计出achiev的大小和配置。 e项目目标。在收集到的数据的基础上，对这些腔体在机翼上的应用进行了研究，并对不同可能布置的空穴的性能进行了评价。在这里 S时刻只有二维模拟已经形成，3D系列被认为是未来的改进项目。模型，不同的配置和所有的结果上述案例将在以下段落中详细显示。【几何模型】关于有源腔，几何如图2所示。空气动力和空腔的几何周围的空间是用专用软件av进行离散的。 可用的ANSYS软件包。此外，为了观察边界层的进展情况，从相邻的高度剖面出发，在5层参考网格上建立了生长因子1.1的参考网格。 t 0.18毫米(图5)。为了达到这一姿势，通过足够精确的数值模拟，创建了一组相当大的数据，以求出初始值。在三维模块上进行了仿真。 使用商用CFD模拟代码ANSYS/FLUENT对运动相似度进行分析。湍流模型是可实现的k-，具有二阶精度。每个模型都网格化以确保y+max5 网格的质量对数值模拟的准确性和稳定性有着重要的影响。图2. 边界层Figure 2. Boundary layer商业软件允许将细胞层“抹灰”到控制体积的临界边界，在这种情况下，这显然是轮毂、外壳和叶片的壁面。在这 e区通常的做法是创建一个完全结构化的边界层，尽可能指定第一行细胞的高度和“生长比率”，即： 确定连续单元格的高度。在这个过程中，第一行细胞的高度通常是通过一个经验公式来确定的，这个公式给出了基于壁面的局部雷诺值。 以y(y=u*y/v)表示，其中u*=(墙/)1/2，壁为壁面剪应力)。对于机翼分析控制体积被分割成几个较小的子体积，以达到更多的c。 持续的一组面孔，并更好地利用创建一个局部更精细的网格的可能性。边界条件的选择如下：它是启发式地执行，开始。 根据初步的测量数据，通过第一次模拟对其进行标定，通过迭代地重置近尾迹径向区域的出口静压来调整数值。 后缘。通过随后的数值模拟，确定了进口总压力和温度值，以保证质量流的守恒。速率(采用所谓的“质量流入口条件”).【仿真结果】在这一段中，对机翼的性能进行了分析。使用CFD模拟得到的结果(见图6-8)被用作后续试验的参考模型5。既然， 下图显示了0迎角的结果。特别是对于假设的单一延伸翼(1米)，它得到：图3.0迎角的压力、速度和紊流图Fig3.0 angle of attack pressure velocity and turbulence diagram图4.CD和CDW随攻角变化的图解Fig4. Diagram of CD and CDW varying with angle of attack图5.(A)两个空腔，(B)两个空腔，(C)见(B)(D)三个空腔Fig. 5. A) two cavities and two cavities.最后，为了使失速角个性化，在不同的攻角下进行了额外的模拟，精确地说是2，4，6，8和10，报告了表1中的数值。它可以 注意，攻角大于8时的失速。【有源腔性能分析】经初步试验，洞口尺寸为3.5mm，洞室深度为3mm。后来，建立了一个控制管道，附加仿真以寻找最佳。 配置已经完成。特别是所使用的配置是：位于8.22mm距离的两个腔体，11.5毫米，19.72毫米，最后是三个洞，两个相等，一个较大半径，插入到12.2毫米和其余两枚为22.74毫米(图8)。分析表明，准最优结构是位于中间距离：infa的两个等腔的结构。 CT，最后一个配置对应于距离限制，超过该距离极限，由前面的空腔产生的气泡压力重新吸收（在图9中以红色圈）。基于这些 考虑因素，它可以继续使机翼的机身得到最理想的气动效果的配置。图9.空腔产生的压力气泡Figure 9. Pressure bubble produced by cavity表1.CD和CDW作为攻角函数的变化Table 1.Variations of CD and CDW as angle of attack functionAngle of attack Drag coefficient CdDownforce coefficient Cdw00.0480.25820.0530.27840.0610.31360.0710.33680.0840.361100.0960.343它被认为在机翼的前半部有许多管道，因为该部分的压力低于剩余的空气动力部分。在此之后，对CAD几何进行了修改。 导入选定的构型比例，然后进行CFD模拟（图11中的结果）。获得的值证实了先前的考虑。【实验结果分析】计算流体力学模拟证实了理论的预期：特别是上述三种构型的深入分析。详细地说，它可以注意到带有活动腔的机翼在扩展。 到整个表面和一个只有管道的尾部，大致显示相同的拖曳值(分别为65.88N和61.04N)：然而，在第一种情况下，它会产生更大的下垂。 Orce(365 N对N 341)。从这一观察，可以推断，尾翼与18导管，以最有效的方式，一个更好的性能，在制动期间。而同一条翅膀， 但是在转弯时可以使用仅位于靠背中的具有稍微低的阻力的腔：事实上，参考车辆的性能，目标是具有高的抓握力来处理 这些转弯越快越好。因此，选择最有效的集合(在上述配置之间)取决于曲线的类型(或多或少的速度)以及两者之间的平衡。 因此，配备8-9对和13-14对机翼，其特性是比平滑的空气动力剖面产生更大的下压力和更低的阻力，可用于 馅饼。事实上，在这种情况下，要有好的冲刺，最好是低空气动力阻力，防止后轮打滑：这种现象可以通过开发利用来实现。 机翼在这种结构中产生的下压力。结果会是更好的抓地力。最终，你应该有一个能够令人满意地回答这两种情况的翅膀。配置必须 能够提供良好的抓地力和较低的阻力启动，并获得更好的行为曲线。这可以通过装备打开或关闭凹穴的滑动板的翼面来实现。【结论和可能的改进】计算流体力学模拟结果表明，在配方车后翼上进行活动腔的效果是有序的。实现空气动力制动。具体来说，我们可以断言，在向下力和阻力之间保持最佳平衡的结构是在ae的整个上表面上延伸的管道。 轮动力(Fl=365.172 N，FD=65.88N)。最后，正如前面所解释的那样，通过利用滑动板的选择性，可以实现不同的机翼配置，这取决于r的需ACE和灵敏度。至于对制动器性能测试的任何改进(本文研究的对象)，可以在终端部分使用垂直舱壁进行更多的cfd模拟。 以及三维模拟。这样，就有可能观察到应该微型化的升力阻力的影响。那么下一步就是实现这个设备的物理功能。 ，将其安装在配方车上，并将实验数据与CFD模拟结果进行比较。这项研究是由意大利政府资助的，部分是关于方程式赛车/方程式4项目的框架。【作者贡献】罗伯托卡帕塔(Roberto Capata)和里昂马特尔卢奇(MartelLucci)的贡献涉及测试和比较，而Enrico Sciubba则负责与CFD模拟有关的所有方面。12辽宁工程技术大学毕业设计13附录BProblem FormulationIn this paper, the realization of an aerodynamic brake integrated in a rear wing of a formula car has been consi- dered. The first step consists in the choice of an appropriate aerodynamic appendix. In particular, it was decided to study an Italian Formula 4 race car 1, being a category in the first stages of development. Also, the regula- tion of this championship is easy to find and the car is characterized by uniformity of the mechanics and the air- foils. Therefore, taken note of the technical regulation on FIA website, it was decided to study the upper airfoil, of which was shown a dimensioned drawing (Figure 1). It is an aluminum alloy wing, with a chord line of 237.9 mm and a height of 54.2 mm.Formula 4 championship will provide the use of a 4T heat engine (Otto/Beau de Rochas cycle): it can be na- turally aspirated or turbocharged, with maximum power in the order of 120 kW (160 HP). Considering the weight of the car and the race tracks of the championship, it is predicted a maximum speed of 230 km/h (64 m/s). Regarding the operating conditions, an air temperature of 300K was assumed at atmospheric pressure.Briefing Description of Airfoil BehaviorConsidering an airfoil, there are several elements that have a specific nomenclature:Mean camber line: locus of points halfway between the upper and lower surface as measured perpendicular to the mean chamber line itself;Leading edge: the most forward point of the mean camber line;Trailing edge: the rearmost point of the mean camber line;Chord: the straight line joining the leading edge with the trailing edge;Upper surface: the upper boundary of the profile;Lower surface: the lower boundary of the profile;Thickness: the distance between the lower surface and the upper surface.The different airfoil shapes are marked by a logical numbering system which was introduced by the U.S. fed- eral agency NACA. This system consists of four digits which have a definite meaning:the first digit indicates the maximum camber in hundredths of chord;the second digit represents the location of maximum camber along the chord from leading edge in tenths of chord;the third and fourth give the maximum thickness in hundredths of chord.When an airfoil is moving relative to the air, it generates an aerodynamic force, in a rearward direction at an angle with the direction of relative motion. This aerodynamic force is commonly resolved into two components: lift and drag. Lift is the force component perpendicular to the direction of relative motion while Drag is the force component parallel to the direction of relative motion. These forces are studied at different angles of attack which is the angle at whices smoothly over the airfoil and is attached to the back of the wing. As soon as increases, the flow tends to separate from the surface of the airfoil, creating a region of “dead air” behind the profile. A briefing flow analysis of the physical phenomenon in question in order to understand better what is happening in the latter case is reported. It is clear from Figure 2 that the speed at the trailing edge tends to in- crease, with a strong reduction of the pressure, while in the stagnation point the speed tends to be zero and pres- sure rises sharply. It creates an adverse pressure gradient, thus particles of fluid move from the trailing edge to the stagnation point, and then it has a rapid separation of the boundary layer below. Stagnation point does not have a stable position in these conditions because there is not pressure recovery. The recirculation generated .Figure 1. Dimensioned Drawing of a F4 rear wing (in mm).the detachment of the boundary layer creates first vortex that causes a wake vortex. It is necessary to study the turbulent behavior of the fluid that meets the wing, through the Navier-Stokes equations in order to consider the stall of the wing:where u(x, t) is the instantaneous velocity, the medium density, the viscosity and f the applied force.This system of equations is a system of partial differential equations that describe the behavior of a Stokesian fluid: the fluid can be considered to be continuous. There is an analytical solution only in simplified cases, while solutions in the other cases can be obtained using simplified methods of numerical analysis. The most straight- forward method for the numerical simulation of turbulent flows is direct numerical simulation DNS which dis- cretizes the Navier-Stokes equations. It resolves the entire range of turbulent length scales thus the description of the flow is so detailed that the validity of the simulation is similar to an experiment. The computational cost is proportional to Re3, thus it is necessary to use a different solution studying turbulent flows at high Reynolds, because the computational resources required by a DNS would exceed the capacity of the most powerful com- puter currently available. In practical applications, the knowledge of the average quantities is enough to solve the problem of a turbulent flow; the basic idea of the technique RANS (Reynolds Averaged Navier-Stokes Equ- ations) is to derive only the average parameters (mediated in time) from Navier-Stokes equations, reducing the enormous computational cost required by DNS. In practice, the turbulent motion consists of a mean motion and fluctuation over time. Using the decomposition of Reynolds:The K- model is one of the most common models of turbulence, even if it is not appropriate in the case of strong adverse pressure gradients. It is a model with two equations: it includes two additional transport equations to represent properties of the turbulent flow and effects such as convection and diffusion of turbulent energy. The first variable transported is the turbulent kinetic energy, k. The second variable transported is the turbulent dissipation, ; the second variable determines the scale of turbulence, while the first variable k determines the energy in the turbulence. There are two formulations of the K- models: the standard k-epsilon model and the RNG k-epsilon model.In the standard k-epsilon model, eddy viscosity is determined by single length scale turbulence, so the turbu- lent diffusion is calculated only through a specified scale, whereas in reality all scales of motion will contribute to turbulent diffusion.The approach RNG (Re-Normalisation Group), a mathematical technique that can be used to obtain a model similar to the k-epsilon turbulence, presents a modified equation , which attempts to explain the different scales of turbulence through changes at the term of production of turbulence. Project DescriptionThe purpose of this project is to improve the race performance, reducing the breaking distance and increasing the bending speed. So, we decided to intervene on the drag generated by the wing during the breaking, and also on the grip provided by downforce, function of velocity. To explain the lift, and then the downforce, reference may be made to the wing of an airplane, observing its section. The latter is asymmetric, the top has a profile longer than the bottom: when the wing moves, it separates the relative flow in two parts, so the air layers scroll faster in the top. The outflow over the wing undergoes a boost and then is aerodynamic brake for formula cars accelerated towards the tail at a higher velocity than the air under the wing, which follows a shorter path. So the two currents are reunited in the tail after a same time interval, without creating imbalances. This is not just the facts, but as a first approximation, we can refer to this model. In reference to the Bernoulli trinomial law, since in the lower flow velocity is lower than in the upper, the pressure under the wing has to be greater than that above the wing. Therefore, the difference between the two pressures generates a resultant directed upwards, that is the lift, which holds the aircraft in the air. In detail, lift can be expressed as:The overall resistance opposed by a fluid medium to the object forward movement is given, in first approxi- mation, by the sum of the frictional resistance, the wake resistance and the induced resistance of lift. In particu- lar, for a tapered body, the flow resistance is given by friction (laminar and/or turbulent), that is the rubbing of the surface against the medium. For this purpose we introduce the concept of boundary layer: its the dynamic range, laminar or turbulent, in which internal current speed is subject to strong gradients (continuous changes), due to the viscosity of the fluid.The thickness of the boundary layer is very small, and it is of one order of magnitude lower than the overall dimensions of the object, that generates the viscose perturbation. Then, inside the boundary layer, the tangential shear stress is “dense”. For this reason in the layer is exerted an intense dissipative braking action, converting part of the movement in thermal agitation. The dissipative action limits the relative velocity between the object and the fluid, which surrounds it. In a turbulent boundary layer, the viscous stresses are added also the stresses, due to the exchange of transverse momentum; these actions increase with the fluid density. The chaos of the turbulent fluid motions implies higher thermal dissipation, so the braking opposing force, in turbulent flow con- ditions, is greater than that of the laminar regime. The resistance generated, in this way, is affected by the sur- face roughness: moreover, the rougher surfaces ignite earlier and more easily the turbulent condition in the flow, and then, determine higher resistances. Wing DesignThe first phase of the design is to draw the profile of the wing with a CAD software. In this way, it is possible to make a CFD simulation, to evaluate the aerodynamic performance of the wing, in terms of downforce and drag, and estimate the useful angles of attack before stall phenomenon occurs 3. In fluid dynamics the stall is a re- duction of the lift coefficient due to an increase of the angle of attack or due to the incident velocity decrease on an aerodynamic profile, such as an airfoil, a propeller blade or a turbomachinery rotor. The minimum value of the angle of attack for which the stall occurs is called critical angle of attack. This value which corresponds to the maximum lift coefficient, changes significantly, depending on the particular profile or on the considered Reynolds number 4. Similarly, the profile of the active cavities has been reported, and appropriate simulations were performed. In this way it was possible to estimate the sizes and configurations to achieve the project target. Based on the data collected, the application of these cavities on the wing is studied, evaluating the performance on the different possible arrangements of these cavities. At this moment only 2D simulations have been per- formed, and a 3D series is considered as future improvement of the project. The models, the different configura- tions and the results obtained from all the cases mentioned above, will be shown in detail in the following para- graphs.Geometry ModelingTo this pur- pose, a sizeable set of data was created by means of sufficiently accurate numerical simulations, to derive initial values. The simulations were performed on 3-D models in kinematic similarity using a commercial CFD simula- tion code, ANSYS/Fluent. The turbulence model was the k- realizable, with second order accuracy. Each model was meshed to ensure a y+max 5, a necessary condition for adopting the enhanced wall treatment, since the quality of the grid has a relevant importance on the accuracy and stability of the numerical simulation.Figure 2. Boundary layer.Regarding to the active cavity, the geometry is illustrated in Figure 4(b). The space surrounding the geometry of the aerodynamic and the cavities was discretized using a special dedicated software available as ANSYS package. Furthermore, to observe the progress of the boundary layer, it was built on a reference mesh of 5 layers, with growth factor 1.1, starting from the adjacent profiles of height 0.18 mm (Figure 5). To this pur- pose, a sizeable set of data was created by means of sufficiently accurate numerical simulations, to derive initial values. The simulations were performed on 3-D models in kinematic similarity using a commercial CFD simula- tion code, ANSYS/Fluent. The turbulence model was the k- realizable, with second order accuracy. Each model was meshed to ensure a y+max 5, a necessary condition for adopting the enhanced wall treatment, since the quality of the grid has a relevant importance on the accuracy and stability of the numerical simulation.Commercial software allows the “plastering” of cell layers to the critical boundaries of the control volume, which are obviously, in this case, the wall surfaces of the hub, casing and blades. In these zones the usual practice is that of creating a completely structured boundary layer, specifying whenever possible both the height of the first row of cells and the “growth ratio”, i.e. the rate that determines the height of the successive cells. In this process, the height of the first row of cells is usually determined via an empirical formula that gives the value of a wall-based local Reynolds number, denoted by y+ (y+ = u*y/v where u* = (wall/)1/2, with wall being the wall shear stress). For the wing analysis control volume was split in several smaller sub-volumes, to achieve a more con- sistent set of faces and to better exploit the possibility of creating a locally more refined grid. The choice of the boundary conditions was made as follows: it was performed heuristically, starting from the preliminary sizing data, calibrating them by means of a first simulation, adjusting the values by iteratively resetting the outlet static pressure on the near-wake radial area downstream of the trailing edge. Through subsequent simulations the values of the inlet total pressure and temperature were refined as well in order to ensure conservation.Simulation ResultsWing PerformanceIn this paragraph, the performance of the wing has been analyzed. The results obtained by using CFD simulation (see Figures 6-8), were used as the reference model for the subsequent tests 5. Since, the following figure shows the results for a 0 angle of attack. In particular, for a hypothetical unitary extension wing (1 m), it is obtained:The thickness of the boundary layer is very small, and it is of one order of magnitude lower than the overall dimensions of the object, that generates the viscose perturbation. Then, inside the boundary layer, the tangential shear stress is “dense”. For this reason in the layer is exerted an intense dissipative braking action, converting part of the movement in thermal agitation. The dissipative action limits the relative velocity between the object and the fluid, which surrounds it. In a turbulent boundary layer, the viscous stresses are added also the stresses, due to the exchange of transverse momentum; these actions increase with the fluid density. The chaos of the turbulent fluid motions implies higher thermal dissipation, so the braking opposing force, in turbulent flow con- ditions, is greater than that of the laminar regime. The resistance generated, in this way, is affected by the sur- face roughness: moreover, the rougher surfaces ignite earlier and more easily the turbulentThe thickness of the boundary layer is very small, and it is of one order of magnitude lower than the overall dimensions of the object, that generates the viscose perturbation. Then, inside the boundary layer, the tangential shear stress is “dense”. For this reason in the layer is exerted an intense dissipative braking action, converting part of the movement in thermal agitation. The dissipative action limits the relative velocity between the object and the fluid, which surrounds it. In a turbulent boundary layer, the viscous stresses are added also the stresses, due to the exchange of transverse momentum; these actions increase with the fluid density. The chaos of the turbulent fluid motions implies higher thermal dissipation, so the braking opposing force, in turbulent flow con- ditions, is greater than that of the laminar regime. The resistance generated, in this way, is affected by the sur- face roughness: moreover, the rougher surfaces ignite earlier and more easily the turbulentThe thickness of the boundary layer is very small, and it is of one order of magnitude lower than the overall dimensions of the object, that generates the viscose perturbation. Then, inside the boundary layer, the tangential shear stress is “dense”. For this reason in the layer is exerted an intense dissipative braking action, converting part of the movement in thermal agitation. The dissipative action limits the relative velocity between the object and the fluid, which surrounds it. In a turbulent boundary layer, the viscous stresses are added also the stresses, due to the exchange of transverse momentum; these actions increase with the fluid density. The chaos of the turbulent fluid motions implies higher thermal dissipation, so the braking opposing force, in turbulent flow con- ditions, is greater than that of the laminar regime. The resistance generated, in this way, is affected by the sur- face roughness: moreover, the rougher surfaces ignite earlier and more easily the turbulentThe thickness of the boundary layer is very small, and it is of one order of magnitude lower than the overall dimensions of the object, that generates the viscose perturbation. Then, inside the boundary layer, the tangential shear stress is “dense”. For this reason in the layer is exerted an intense dissipative braking action, converting part of the movement in thermal agitation. The dissipative action limits the relative velocity between the object and the fluid, which surrounds it. In a turbulent boundary layer, the viscous stresses are added also the stresses, due to the exchange of transverse momentum; these actions increase with the fluid density. The chaos of the turbulent fluid motions implies higher thermal dissipation, so the braking opposing force, in turbulent flow con- ditions, is greater than that of the laminar regime. The resistance generated, in this way, is affected by the sur- face roughness: moreover, the rougher surfaces ignite earlier and more easily the turbulent.The thickness of the boundary layer is very small, and it is of one order of magnitude lower than the overall dimensions of the object, that generates the viscose perturbation. Then, inside the boundary layer, the tangential shear stress is “dense”. For this reason in the layer is exerted an intense dissipative braking action, converting part of the movement in thermal agitation. The dissipative action limits the relative velocity between the object and the fluid, which surrounds it. In a turbulent boundary layer, the viscous stresses are added also the stresses, due to the exchange of transverse momentum; these actions increase with the fluid density. The chaos of the turbulent fluid motions implies higher thermal dissipation, so the braking opposing force, in turbulent flow con- ditions, is greater than that of the laminar regime. The resistance generated, in this way, is affected by the sur- face roughness: moreover, the rougher surfaces ignite earlier and more easily the turbulentThe thickness of the boundary layer is very small, and it is of one order of magnitude lower than the overall dimensions of the object, that generates the viscose perturbation. Then, inside the boundary layer, the tangential shear stress is “dense”. For this reason in the layer is exerted an intense dissipative braking action, converting part of the movement in thermal agitation. The dissipative action limits the relative velocity between the object and the fluid, which surrounds it. In a turbulent boundary layer, the viscous stresses are added also the stresses, due to the exchange of transverse momentum; these actions increase with the fluid density. The chaos of the turbulent fluid motions implies higher thermal dissipation, so the braking opposing force, in turbulent flow con- ditions, is greater than that of the laminar regime. The resistance generated, in this way, is affected by the sur- face roughness: moreover, the rougher surfaces ignite earlier and more easily the turbulentThe thickness of the boundary layer is very small, and it is of one order of magnitude lower than the overall dimensions of the object, that generates the viscose perturbation. Then, inside the boundary layer, the tangential shear stress is “dense”. For this reason in the layer is exerted an intense dissipative braking action, converting part of the movement in thermal agitation. The dissipative action limits the relative velocity between the object and the fluid, which surrounds it. In a turbulent boundary layer, the viscous stresses are added also the stresses, due to the exchange of transverse momentum; these actions increase with the fluid density. The chaos of the turbulent fluid motions implies higher thermal dissipation, so the braking opposing force, in turbulent flow con- ditions, is greater than that of the laminar regime. The resistance generated, in this way, is affected by the sur- face roughness: moreover, the rougher surfaces ignite earlier and more easily the turbulentThe thickness of the boundary layer is very small, and it is of one order of magnitude lower than the overall dimensions of the object, that generates the viscose perturbation. Then, inside the boundary layer, the tangential shear stress is “dense”. For this reason in the layer is exerted an intense dissipative braking action, converting part of the movement in thermal agitation. The dissipative action limits the relative velocity between the object and the fluid, which surrounds it. In a turbulent boundary layer, the viscous stresses are added also the stresses, due to the exchange of transverse momentum; these actions increase with the fluid density. The chaos of the turbulent fluid motions implies higher thermal dissipation, so the braking opposing force, in turbulent flow con- ditions, is greater than that of the laminar regime. The resistance generated, in this way, is affected by the sur- face roughness: moreover, the rougher surfaces ignite earlier and more easily the turbulentThe thickness of the boundary layer is very small, and it is of one order of magnitude lower than the overall dimensions of the object, that generates the viscose perturbation. Then, inside the boundary layer, the tangential shear stress is “dense”. For this reason in the layer is exerted an intense dissipative braking action, converting part of the movement in thermal agitation. The dissipative action limits the relative velocity between the object and the fluid, which surrounds it. In a turbulent boundary layer, the viscous stresses are added also the stresses, due to the exchange of transverse momentum; these actions increase with the fluid density. The chaos of the turbulent fluid motions implies higher thermal dissipation, so the braking opposing force, in turbulent flow con- ditions, is greater than that of the laminar regime. The resistance generated, in this way, is affected by the sur- face roughness: moreover, the rougher surfaces ignite earlier and more easily the turbulentFigure 3. Cavity boundary layer mesh.Figure 4. Pressure, velocity and turbulence plots for 0 of angle Figure 5. Plot of Cd and Cdw variation as function of the angle of attack.Figure6. Different cavities configurations. Finally, to individuate the stall angle, additional simulations, at different angles of attack, have been per- formed; precisely 2, 4, 6, 8 and 10, reporting the values obtained in Table 1. It can be noticed that stall oc- curs for angles of attack greater than 8. Active Cavity Performance AnalysisAfter some preliminary tests, the dimensions, that characterize the opening and depth of cavities, are 3.5 mm and 3 mm respectively. Later, built a control duct, additional simulation to find the best configuration has been carried out. In particular the configuration used were: two cavities located at 8.22 mm of distance each other,11.5 mm, 19.72 mm and, finally, three cavities, two equal and one larger radius, interposed to 12.2 mm and22.74 mm with respect to the remaining two (Figure 8). The analysis have enlightened that the quasi-optimal configuration is the one with the two equal cavities located at intermediate distance: in fact, the last configura- tion corresponds to the distance limit beyond which the reabsorption of the bubble pressure generated by the cavity in front occurs (circled in red in Figure 9). Based on these considerations, it can proceed to make the cav- ities on the wing to get the configurations that produce the most desired aerodynamic effects. The trend of fluid velocity is reported .Wing with Front CavitiesAccording to the pressures pattern observed in the case of rear wing with zero angle of attack, in the first instance.ticular the configuration used were: two cavities located at 8.22 mm of distance each other,11.5 mm, 19.72 mm and, finally, three cavities, two equal and one larger radius, interposed to 12.2 mm and22.74 mm with respect to the remaining two (Figure 8). The analysis have enlightened that the quasi-optimal configuration is the one witticular the configuration used were: two cavities located at 8.22 mm of distance each other,11.5 mm, 19.72 mm and, finally, three cavities, two equal and one l
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