【求翻译】 Small but Mighty Powerful
When talking about jet engines in aerospace visions of the enormous assemblies that propel passenger aircrafts that carry business and vacation travelers inevitably spring to mind. However just as notable and impressive are the much smaller micro-turbines which propel radio controlled model aircrafts and Unmanned Aerial Vehicles (UAVs). Used primarily for military purposes, also increasingly in civil applications such as firefighting and surveillance, UAVs or Drones are controlled either by computers in the craft or by remote control. In more recent years, jet engine development has been focused on fuel efficiency, reducing emissions and quieter engines. These goals go hand in hand with the latest component designs, fuel types or utilization of flow behavior. The biggest influence on the aforementioned parameters was achieved by a high-bypass ratio, developed in the mid-1960s as seen today in every passenger aircraft. Reaching up to 115,000 pound (514 kN) of thrust at a bypass ratio (BPR) of 10:1 with a mass flow rate of up to 1,300 kg/s, is enough to impress any engineer. Now of course so called smaller micro-turbine jet engines cannot compete with such numbers but it doesn’t make them less impressive or complex. Whilst designers of micro-turbines must also achieve efficiency and power goals, they have an added challenge of doing so to a much smaller scale which poses more problems for materials and components. The best way to efficiently design such high performance engines is by using virtual prototyping such as computational fluid dynamics (CFD) and structural analysis. This article explores how FloEFD is used to simulate the fluid flow, heat condition and combustion of a micro-turbine and how these simulation results apply to a structural analysis model.Micro-turbine engines are developed for specific flight applications. They are used in UAVs which are designed for short flight duration. Today, lots of different UAVs are operating worldwide for all kinds of mission types. In general UAV missions range from reconnaissance, surveillance, target acquisition, signals intelligence (SIGINT) to scientific research, to name just a few. Another common use for small gas turbines is for auxiliary power units (APU), supplementing aircraft engines which provide additional power for non-propulsion functions when required. Due to their small size, micro-turbine engines have small air mass flow rates and low pressure ratios, but very high rotational speeds of turbine and compressor stage.For the purposes of this study a KJ 66 (Figure. 1) was chosen, as it is one of the more robust small engines with accessible design data.
Figure 1 The model (left) and real prototype (right) of KJ 66 micro-turbine engine.
Turbojet engines have complex geometries and physical processes. Understanding these processes is very important for designing such a high-performance product. The complex geometry and small size of this kind of engine limits the access of typical instruments used for the measurement of flow parameters as is required for a better understanding of the complex flow structure. As well as this, creating the optimal design for individual parts of an engine during testing can be an expensive procedure, making CFD analysis a very useful tool.
This article presents the CFD analysis of the KJ 66 micro-turbine engine, which is calculated as one unit without any transferred, symmetrical and periodical conditions between its parts. It takes into account the rotation of air in the compressor and turbine, conjugate heat transfer and air/kerosene combustion all within the multiCAD-embedded full-featured general purpose CFD tool FloEFD. Thermal and structural analysis were conducted using PTC’s CreoSimulate together with thermal and pressure load results obtained from FloEFD.
Five cases of varying rotational speeds of 40000, 60000, 80000, 100000 (the normal mode) and 120000 rpm were considered for the compressor and turbine by specifying local rotational zones. The solid parts are specified as aluminum, steel and inconel for the consideration of conjugate heat transfer.
The air mass flow at the inlet of the engine at various rotational speeds of the compressor can be seen in Figure 2. The FloEFD results are compared with the experimental data of Kamps Tii, and show the values of mass flow match the experimental data very well with almost no dependence on the number of mesh cells.
The calculation results Figure 3 show flow trajectories colored by velocity magnitude and pressure distribution with Line Integral Convolution (LIC) on the surfaces of the compressor and diffuser at the normal mode. The pressure on the compressor’s blades can be lower than 65000 Pa and can reach 180000 Pa on the diffuser’s blades.
Figure 2 Air mass flow at the inlet of KJ 66 engine.
Figure 3 Flow trajectories colored by velocity magnitude (left) and pressure distribution with LIC on surfaces of the compressor and the diffuser (right) at normal mode.
The combustion chamber of the KJ 66 engine features direct fuel injection through 6 vaporizing sticks to ensure complete combustion inside the chamber. Figure 4 presents the fluid temperature and velocity distributions at two longitudinal sections of the combustion chamber with flow vectors at the normal mode. The temperature in the combustion chamber reaches approximately 2400 K. An increase of the velocity in the region of the openings of the combustion chamber can be clearly seen especially on the rear wall of the chamber.
Figure 4 Fluid temperature (left) and velocity (right) distributions at two longitudinal sections of the combustion chamber with flow vectors at the normal mode.
Further evaluation of the results shows a direct comparison of the temperature distribution in the combustion chamber at 120000 rpm obtained with FloEFD (left) and a traditional CFD tool (right) presented by C.A. Gonzales, K.C. Wong and S. Armfield . Both models have been simplified by not examining all parts of the engine, but all features of the combustion chamber have been taken into account. The symmetry conditions are not used in the FloEFD model as they were in that of the traditional CFD model, resulting in some differences in the parameter’s distribution which can be seen in Figure 5. Considering these factors, both FloEFD and the traditional CFD tool, show reasonable accordance in their results. It is clearly visible in Figure 5 that the primary combustion zone is located in the central part of the chamber.
Figure 5 Temperature distribution in the combustion chamber at 120000 rpm obtained in FloEFD (left) and traditional CFD software (right).
Besides thermal simulation, FloEFD also allows some parameters to be exported as loads for structural and thermal analyses with Creo Simulation. In this case the surface temperature was exported from the CFD calculation to run the thermal calculation with Creo Simulation. Then the structural analysis was conducted using the temperature of the previous calculation and the pressure exported from FloEFD. The results in Figure 6 show the displacement distribution of the structural analysis. It can be clearly seen that the combustion chamber is deformed under the loads with the displacement reaching a maximum of 0.001 m.
Figure 6 Displacement distribution on the surface of the combustion chamber in Creo Simulate (scaling 20%).
A pressure and velocity distribution near the surfaces of the engine is presented in Figure 7 and the increase and decrease of the pressure at the compressor and turbine stage is shown respectively.
Figure 7 Pressure (left) and velocity (right) distributions.
The overall performance of the engine is usually measured by thrust and Figure 8 shows the comparisons of measured and predicted values of thrust of the KJ 66 engine at different modes. Experimental and predicted values are similar up to 80000 rpm with some divergence at 100000 rpm.
Figure 8 Thrust of KJ 66 engine.
Comparisons of measured and predicted values of the main integral parameters such as air mass flow at the inlet of the engine, thrust and temperatures at the outlet of the diffuser and combustion chamber are almost identical.
Thereby demonstrating that FloEFD can provide a series of “what-if” CFD analyses and export data values for structural and thermal analyses. With its CAD embedded approach it is very efficient should there be a need to experiment different designs of any component in the model. By simply changing the CAD parameter of a parametric model, such as the opening diameter of the combustion chamber, multiple simulations can be created in little to no time, whilst at the same time changing any boundary conditions. The simulation project is always up-to-date with the CAD data.
FloEFD provides high accuracy in high-end applications such as demonstrated in this aerospace example. With its CAD embedded approach, FloEFD allows the user to set up and run simulations and design iterations quickly in order to determine the appropriate design modifications, saving time and money.
References
Gonzalez, C.A., Wong, K.C., Armfield S. Computational study of a micro-turbine engine combustor using large eddy simulation and Reynolds average turbulence models, Austral Mathematical Soc, Australia, 2008.
Kamps, T. Model jet engines, UK, 2005.
这个很有难度。你能提供全本的资料吗？这个东西很有用。很直观。 谈到航空航天飞机上的喷气式发动机，这架飞机上的巨大组件的愿景是，这架飞机将使旅客的商务和度假旅客的飞机不可避免地要想到。然而，同样值得注意的是，令人印象深刻的是更小的微型涡轮机，推动无线电控制模型飞机和无人机（无人机）。主要用于军事目的，也越来越在民用领域，如消防、监控、无人机和无人机控制无论是在工艺或通过远程控制电脑。在最近几年，喷气发动机的发展一直专注于燃油效率，减少排放和更安静的发动机。这些目标与最新的组件设计，燃料类型和流动行为的利用一起。对上述参数的影响最大的是由一个高旁通比，在上世纪60年代中期发展为每架客机今天看到的。高达115000磅（5 高达115000磅（514千牛）在旁路比推力（BPR）时，有高达1300公斤/秒的流量，就足以打动任何工程师。现在，所谓的小型微型涡轮喷气发动机的发动机不能与这样的数字竞争，但它不会使它们不那么令人印象深刻或复杂。虽然微型涡轮机的设计人员也必须实现效率和功率目标，他们有一个额外的挑战，这样做的一个小规模的材料和组件构成了更多的问题。利用虚拟样机技术，如计算流体力学和结构分析，有效地设计这样的高性能引擎是最好的方法。本文探讨如何FloEFD是用来模拟流体流动，一个微型燃气轮机的热状态和燃烧和如何将这些结果应用于结 引擎开发的特定飞行。它们被用来在无人机设计的短飞行时间。今天，许多不同的无人机在全球范围内经营各种类型的任务类型。在一般的无人机任务范围从侦察、监视、目标捕获、信号情报（SIGINT）科学研究，仅举几例。小型燃气轮机的另一个常见用途是辅助动力装置（APU），补充飞机发动机提供额外动力的非推进功能需要时。由于其体积小，微型涡轮发动机具有小的空气质量流量和低压力比，但非常高的旋转速度的涡轮机和压气机级。本研究的目的有66 kJ（图。1）被选中，因为它是一个更强大的小型引擎，可访问的设计数据。 图1模型（左）和真正的原型（右）KJ 66微型涡轮发动机。涡轮喷气发动机具有复杂的几何形状和物理过程。了解这些过程是非常重要的，设计这样一个高性能的产品。这种发动机的复杂的几何形状和小尺寸限制使用用于测量的流量参数的测量的典型工具，以更好地理解复杂的流动结构。同时，在测试过程中，为单个零件的最佳设计创造了一个非常昂贵的过程，使得计算流体力学分析是一个非常有用的工具。本文介绍了KJ 66微型涡轮发动机的CFD分析计算，这是作为一个单元没有任何转移，各部分之间的对称性和周期性条件。考虑到在压气机和涡轮的空气旋转，共轭传热和空气/煤油燃烧在嵌 共轭传热和空气/煤油燃烧在multicad嵌入式功能齐全的通用CFD工具FloEFD。热结构分析采用PTC的creosimulate连同FloEFD所得的热负载和压力的结果进行。五种情况下，不同的转速为40000，60000，80000，100000（正常模式）和120000转，被认为是通过指定本地的旋转区域的压缩机和涡轮机。固体部分被指定为铝，为考虑共轭传热钢和铬镍铁合金。在发动机的各个转速下，发动机入口的空气质量流量可以看出，在图2。FloEFD的结果与坎普斯TII的实验数据进行了比较，并显示流量值与实验数据在网格细胞的数量几乎无依赖性很好。计算结果 计算结果如图3所示的流动轨迹线积分卷积速度和压力分布的彩色（LIC）在正常模式下的压缩机和扩散器表面。压气机叶片上的压力可以低于65000帕，可在叶片上达到180000帕。 用手机输入真蛋疼
楼上的这是人工翻译的？
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