基于遗传算法的压气机叶片的多目标三维优化

为了提高轴流压气机的效率,需要研究一种新的高性能的转子叶片.采用人工神经网络与遗传算法寻优相结合的方法对某单级轴流压气机亚音速叶片进行三维叶片型线优化设计.优化目标是尽可能的提高转子叶片的总压比、流量和等熵效率.优化仿真结果显示,流动分离区明显后移,损失显著降低,等熵效率提高了0.48%,同时总压比和流量也都得到了提高,优化叶片的气动性能较原型叶片明显提高.结果表明,优化方法能很好的完成亚音速叶片的优化设计,是获得低损失高效率性能的叶片的有效途径.     

压气机叶片扭曲规律的多目标三维气动优化

为了提高轴流压气机的等熵效率和总压比,采用基于人工神经网络及遗传算法的叶轮机械叶片三维优化设计方法,开发了一种高性能的动叶片。优化目标是在流量不减小的情况下,尽可能的提高转子叶片的总压比和等熵效率。优化仿真结果显示,优化后所获得的扭曲叶片可以有效地改善叶根处的流动分离,流动分离区明显后移,损失显著降低,在整个工作范围,等熵效率提高了1.27%-7.08%,流量和总压比也都得到了大幅度的提高。结果表明,对亚音叶片进行扭曲规律优化效果很明显,优化方法是获得高性能转子叶片的有效途径。     

基于NSGA-Ⅲ的跨声速转子弯掠组合MOO设计北大核心

为提高跨声速压气机转子的气动性能,建立快速有效的轴流压气机优化方案。研究应用贝塞尔曲线(Bezier curve)控制叶片积叠线,利用ANSYS CFX软件建立样本库。基于BP神经网络建立样本库中设计变量(积叠线控制参数)和目标变量(压气机性能参数)之间关系的近似模型。以压气机峰值效率点的绝热效率、压比、流量为优化目标,通过NSGA-Ⅲ多目标遗传算法寻找近似模型的Pareto前沿最优解,最终得到最优的设计变量组合。利用上述方法对跨音速转子Rotor67进行弯掠组合优化设计,研究结果表明:BP神经网络的拟合效果良好,经过优化后的转子的峰值效率点绝热效率、压比、流量分别提高了0.646%、0.873%、0.513%;其堵塞点流量提高了1.0065%,全工况范围内的气动性能均有提升,其稳定工作范围也得到一定程度拓宽,转子内部流动明显改善。     

跨音级轴流压气机转子轮毂非轴对称造型研究

关于优化提高压气机效能问题,由于压气机通道的二次流流动会造成流动损失,引起效率下降.为了解决上述问题,通过改变轮毂端壁结构,可以控制二次流流动,以提高压气机效率.采用人工神经网络及遗传算法的叶轮机械三维优化建模方法,使在最高效率工况下可以保持流量不变,压比不低于优化前.对压气机转子轮毂结构进行了优化,得到新型非轴对称端壁结构,并进行仿真.结果表明,降低了转子通道内的相对总压损失,抑制了下游静叶角区分离,可使压气机提高效率,并能有效控制端壁附近的流动损失,提高压气机效率.     

基于最小熵产的飞机环境控制系统优化分析

针对飞机环境控制系统的优化分析问题,提出采用以热力学第二定律为基础的熵产分析方法。选取起飞、加速爬升和高空超音速巡航为设计点,以系统熵产最小为目标函数,将热交换器效率、压气机和涡轮压力比、引气质量流量作为设计变量,建立优化模型。在优化计算结果的基础上分析设计变量对系统熵产的影响,该分析结果对飞机环境控制系统的优化设计具有一定指导作用。     

跨音速轴流压气机叶片造型及数值仿真

针对跨音速轴流压气机的多圆弧叶片.提出了一种基于锥面展开面的叶片造型方法.设计了某型压气机第一级转子,通过三维粘性流计算软件NUMECA对此孤立转子进行了性能仿真,仿真结果与实验结果符合较好;分析了叶型厚度分布对转子性能的影响:采用标准厚度分布对叶片重新生成,并与多圆弧叶片进行了对比,结果表明用标准厚度生成的叶片更薄一些,性能也更佳;同时当叶型最大厚度的位置后移时,转子的稳定工作范围变宽,效率略有降低.     

轴流压气机转子叶顶间隙流动结构及机理研究

研究某轴流压气机叶顶复杂流动问题,为深入了解压气机叶顶泄漏流流动机制和引发失速的机理,对一亚音速轴流压气机进行全工况数值仿真与试验测量。提出通过对比试验数据和分析泄漏流的流动特性,随着压气机负荷的提高,泄漏流方向的改变引起叶顶堵塞区增大,并诱发压气机失速。采用不同工况下叶顶流场进行仿真对比分析。仿真结果表明,泄漏流与主流相互作用形成泄漏涡,距前缘40%弦长范围内泄漏流影响泄漏涡形态变化,其余部分泄漏流主要通过周向输运低能流体进一步堵塞通道;叶顶压力分布是决定泄漏流方向的主要因素。     

高压压气机动叶叶尖间隙流动数值仿真研究

运用NUMECA CFD对某高压压气机12级动叶尖部间隙流场进行数值仿真,并与无间隙条件下的流动情况进行对比、分析,详细揭示了动叶叶尖间隙区域的流动特征.结果表明无叶尖间隙时压气机并不能获得最优的性能参数;叶尖间隙的存在使得在动叶尖部形成表现为多种复杂涡结构的泄漏流;叶尖问隙在较小范围变化时,压气机的性能参数变化显著,在最佳间隙0.135mm时压气机获得较高增压比和等熵效率,但当叶尖间隙超过临界值继续增大,压气机性能急剧下降.     

带有弯曲静子的压气机数值仿真

针对某两级低速轴流压气机第一级静子通道小流量范围内存在轮毂-角区失速现象,为了提高压气机的效率,采用计算流体力学方法,对第一级静子进行了不同的弯曲变化数值仿真,分析研究了静子弯曲对压气机性能和轮毂-角区失速的影响。结果表明,弯曲叶片能够通过改变静子轮毂表面静压分布,减缓低能流体的横向流动,从而有效地抑制小流量范围内的轮毂-角区失速,压气机的压比和效率得到较大的提升。     

基于人工神经网络的轴流压气机可调导叶系统辨识

本文针对低速轴流压气机,采用神经网络方法辨识不同导叶角度时流量与压气机效率之间的关系,给出了详细的辨识过程,采用神经网络BP算法辨识出流量和效率的关系,结果表明,辨识效果良好,能够很好的获得相同转速下不同流量时最大效率所对应的最优导叶角度,而且不同导叶角度时,流量的范围也不同,为实现在线闭环控制提供解决思路。     

On-chip whole blood plasma separator based on microfiltration,sedimentation and wetting contrast

Miniaturized on-chip blood separators have a great value for point-of-care diagnosis. In our work, a combined design strategy—microfiltration, sedimentation in a retarded flow, and wetting contrast—was taken to overcome the known limitations of on-chip blood separators. Our microfluidic chip consists of a polydimethylsiloxane micropillar array and an etched glass with microchannel branches. The red blood cells are significantly slowed and gradually settled down due to micropillars and enlarged dimension of a chamber. An etched glass microchannel allows the extraction of blood plasma exclusively due to the capillary effect. The fabricated microfluidic device can separate blood plasma from a whole blood sample without any external driving force or dilution. The measured plasma separation efficiency was close to 100 % from human whole blood. Autonomous on-chip separation and collection of blood plasma was demonstrated.     

Enhancement of separation efficiency on continuous magnetophoresis by utilizing L/T-shaped microchannels

In this article a novel design of on-chip continuous magnetophoretic separator was proposed by utilizing the magnetic field and L-turning/T-junction effect of the flow field for high throughput applications. The motion of the magnetic bead was simulated based on Lagrangian tracking method and the separation efficiency was calculated according to the trajectories. Impact parameters including geometrical configuration, fluid velocity, magnetic flux density, magnetic bead size, and temperature on separation efficiency were discussed. The results show that both the L- and T-microchannel separators have higher separation efficiency as compared with the conventional straight-microchannel separator because of the L-turning/T-junction effect of the flow field. The separation efficiencies for L- and T-microchannel separators are 63.4 and 100%, respectively, while it is only 43.7% for straight-microchannel separator at the same conditions. Above a critical flow rate the separation efficiency drops drastically from nearly 100% to zero while this decrease is much slower for T-shaped configurations. The separation efficiency increases initially with the increase of the external magnetic flux density and keeps nearly constant at high magnetic flux density owing to saturated magnetization of the beads. It is also found that both the magnetic bead diameter and fluid temperature have great effect on the separation efficiency. The L/T-microchannel separators presented in this article are simple and efficient for magnetophoretic separation at high flow rates and thus useful for the high-efficiency on-chip enrichment of analytes with very low concentrations.     

Optimal Design of Cams

We present a methodology to design cams for motor engine valve trainsusing a constrained optimization algorithm. The imposed constraints arethe maximum valve lift and timings while the objective function is tomaximize the time integral of the valve area opened to gas flow. Apiecewise analytically defined acceleration is imposed, so that the timeinstants controlling the profile of accelerations are used as variablesfor optimization. The strategy takes into account some geometricalconstraints, e.g. to avoid interference between intake and exhaustvalves, and between valves and piston. Also, minimum and maximum levelsof acceleration are limited to avoid excessive forces in the mechanismschain, and to prevent the possibility of separation between cam andfollower. Once an optimal lift profile is determined, the cam shape iscomputed using an inverse kinematics analysis that takes into accountall the geometric nonlinearities introduced by the kinematical chain.Finally, the whole mechanism is verified in a dynamics analysis to checksatisfaction of the criteria for design. Comparisons with standardprofiles of motion were made. Also, the profile was evaluated in anexperimental device, where the actual valve displacement was measured.     

Three-dimensional analysis and enhancement of continuous magnetic separation of particles in microfluidics

In continuous magnetic separation process, particles can be deflected and separated from the direction of laminar flow by means of magnetic force depending on their magnetic susceptibility and size as well as the flow rate. To analyze and control dynamic behavior of these particles flowing in microchannels, a three-dimensional numerical model was proposed and solved for obtaining the particle trajectories under the action of a gradient magnetic field and flow field. The magnetic force distribution and particle trajectories obtained were firstly verified by analytical and experimental results. Then, a detailed analysis for the enhancement of the continuous magnetic separation efficiency by optimizing the flow parameters and microchannel configurations was carried out. The results show that the separation efficiency can be greatly improved by controlling the flow rate ratio of the two fluid streams and introducing a broadened segment in the T-shaped microchannel. And it has been demonstrated to be effective through the sorting of 2-μm and 5-μm non-magnetic particles suspended in a dilute ferrofluid by a permanent magnet. The results reported could be encouraging for the design and optimization of efficient microfluidic separation systems.     

基于接触应力的高参数汽轮机叶片枞树形叶根型线优化

为提高汽轮机叶片叶根型线的设计效率和产品质量,基于接触应力约束下的枞树形叶片叶根型线设计,将传统的基于经验的设计与经典优化理论相结合,推导适合叶根型线的设计方法。采用移动渐近线法（method of moving asymptotes, MMA）进行结构拓扑优化,以某低压末级动叶片设计为例,优化前、后叶根和轮槽的VON Mises应力对比表明,所推导的方法能够快速得到所需的型线设计。该设计使得叶根与轮槽间的接触应力降低,叶片的使用寿命提高。     

Power Density Optimization for an Irreversible Closed Brayton Cycle

In this paper, the power density, defined as the ratio of power output to the maximum specific volume in the cycle, is taken as objective for performance optimization of an irreversible closed Brayton cycle coupled to constant-temperature heat reservoirs in the viewpoint of finite time thermodynamics (FTT) or entropy generation minimization (EGM). The analytical formulas about the relations between power density and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers and the irreversible compression and expansion losses in the compressor and turbine. The maximum power density optimization is performed by searching the optimum heat conductance distribution corresponding to the optimum power density of the hot- and cold- side heat exchangers for the fixed heat exchanger inventory. The influence of some design parameters on the optimum heat conductance distribution, the maximum power density, and the optimum pressure ratio corresponding to the maximum power density are provided. The power plant design with optimization leads to a higher efficiency and smaller size including the compressor, turbine, and the hot- and cold-side heat exchangers.