Computation of the Matching Performance of Diesel Engine with Variable Geometry Turbocharger

To compute the matching performance of diesel engine with variable geometry turboeharger（VGT）, the formerly used program is improved through adjustment of turbine mass flow rate and efficiency characteristics. The calculation result is applied to forecast the performance of J6110Z diesel engine with rotary-vaned VGT70, and to guide the improvement of engine fuel supply. The computed engine performance curve coincides with the experiment result well： the low-speed torque, fuel economy, exhaust temperature and boost pressure of the VGT engine are all improved.

Dynamics and control of variable geometry truss manipulator

Variable geometry truss manipulator （VGTM） has potential to work in the future space applications, of which a dynamic model is important to dynamic analysis and control of the system. In this paper, an approach is presented to model the dynamic equations of a VGTM by independent variables, which consists of two double-octahedral truss units and a 3-revolute-prismatic-spherical （3-RPS） parallel manipulator. In this ap- proach, the kinematic recursive relations of two adjacent bodies and geometric constrains are used to deduce the kinematic equations of the VGTM, and Jourdain＇s velocity varia- tion principle is adopted to establish the dynamic equations of the system. The validity of the proposed dynamic model is verified by comparison of numerical simulations with the software ADAMS. Besides, an active controller for trajectory tracking of the system is designed by the computed torque method. The effectiveness of the controller is numer- ically proved.

Data-driven based variable geometry design

Conventionally,the method to make up for the missing data of middle-shallow layer in the obstacle area is by variable geometry,for example,deviating physical points and adding sources and receivers.And the missing data of middle-shallow layer is evaluated according to the effective coverage of the target layer.Since the traditional method doesn't consider the actual seismic data,it is impossible to actually predict the gap of section and the imaging effect.The paper proposes the evaluation method of data-driven based variable geometry:Firstly,the obstacle avoidance design is realized according to the coordinate range and safe distance of the obstacle area;Secondly,the local similarity of each common image gather(CIG)is calculated,and the contribution of the sources and receivers to the target area is also calculated;Thirdly,according to the variable geometry design,choose the required trace to perform sorting and stacking according to the contribution of the sources and receivers in the CIG,the stack data volume of the whole work area is generated;finally,evaluate the missing data in the obstacle area by the extracted seismic stacked sections in different direction and guide the designer in the infilling plan.Meanwhile,for area with very low signal to noise ratio(SNR),the new method can be used to evaluate the imaging potential and guide the survey design.The new method has achieved very good effect in the production,and the analysis result is very consistent with the processed result of the actual seismic data.

Flow and Leakage Characteristics in Sealing Chamber of a Variable Geometry Hypersonic Inlet

When the variable geometry hypersonic inlet is sealed with ceramic wafers,the cavity flows inside the sealing chamber can be affected by the boundary layer near the side wall.To study the influence of the boundary layer thickness near the side wall on the flow and leakage characteristics in sealing chamber,the numerical calculation of the cavity flow in the sealing chamber under different inflow boundary layer thicknesses is carried out.The results show that three-dimensional cavity flow structures are close to being asymmetric,and the entrance pressure of the leakage path can also be affected by asymmetry;with the increase of the thickness of the boundary layer,the pressure at the cavity floor and the seal entrance decreases.Finally,the existing leakage prediction model is modified according to the distribution rule of the cavity floor and the flow properties in the leakage path.

Design and study on variable nozzle mixed-flow turbocharger

A spatial motion mechanism was designed which could make all the nozzle vanes rotate a- round the center of ball with the same radius synchronously to realize control of the variable nozzle mixed-flow turbocharger （VN-MT）. The back and abdomen of the nozzle vane was designed as arc- shaped. A variable nozzle ring perfectly combined with the mixed-flow turbine was made available. The turbine geometric model of VN-MT was established through the computational fluid dynamics （CFD）. Compared with nozzleless mixed-flow turbine, the flow range of variable nozzle mixed-flow turbine was broadened tremendously while the peak turbine efficiency point was lower slightly. Flow field analysis in turbine stage showed that the energy was larger and the blade load of rotor was lower than loss of the VN-MT under designed condition the nozzleless mixed-flow turbocharger.

VARIABLE STRUCTURE CONTROL OF AIRCRAFTFOR ATMOSPHERIC DISTURBANCE

Variable structure control (VSC) applied to atmospheric disturbance sup-pression is presented. The conditions are stipulated: the sliding mode existenee condi-tion, and invanance condition of atmospheric disturbanee in the variable structuresystem (VSS). A method of eigenstructure assignment technique for switching surfaeedesign is proposed. Based on different atmospheric disturbanee characteristics, such asrandom turbulence, discrete gust and wind shear, two kinds of control laws are derived that possess strong robustness. An example shows that this control approach isfeasible and effective.

Effect of variable polarity frequency on 2A14-T6 aluminum alloy welds using HPVP-GTAW process

Hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding （HPVP-GTAW） for 2A14-T6 high strength aluminum alloy was carried out and the effects of variable polarity frequency with constant pulse current frequency 40 kHz on weld bead geometry, microstrueture and microhardness were analyzed. Experimental results indicate that, compared to that of the conventional VP-GTAW process, the weld depth and ratio of weld depth to width are improved significantly by the variable polarity frequency in the HPVP-GTAW process, which the ratio of weld depth to width is improved by 36% at equal variable polarity frequency of 100 Hz, and improved by 55% with that of 200 Hz. Weld microstructure and microhardness distribution are changed obviously with the increase of variable polarity frequency. In the conventional VP-GTA W process, the grains in weld central zone are coarser, and the microhardness in weld central zone and fusion zone is about 95 HV and the lowest 82 HV, respectively. The microhardness is enhanced to a certain extent both in the weld central zone and fusion zone with the variation of variable polarity frequency in the HPVP-GTAW process due to the refinement and uniformity of weld microstructure. With the variable polarity frequency of 600 Hz, the microhardness in weld central zone and fusion zone reaches nearly 110 HV and 97 HV, respectively.

Vacuum Solutions of Classical Gravity on Cyclic Groups from Noncommutative Geometry

Based on the observation that the moduli of a link variable on a cyclic group modify Connes' distance on this group, we construct several action functionals for this link variable within the framework of noncommutative geometry. After solving the equations of motion, we find that one type of action gives nontrivial vacuum solution for gravity on this cyclic group in a broad range of coupling constants and that such a solution can be expressed with Chebyshev's polynomials.

宽速域可调进气道密封腔流动特性研究

为了满足高超声速飞行器的宽速域进气需求,一般考虑使用可调进气道,此时进气道内部需要安装动密封结构。陶瓷栅片密封凭借其优异的耐磨损性和抗高温氧化能力是最理想的选择。使用陶瓷栅片作为密封件后,密封室内会形成受侧板边界层影响的三维空腔流动。以密封腔模型为基础,提出对密封腔流动和泄漏通道流动解耦化处理,并分别对进气道密封模型和泄漏模型进行了建模。利用数值模拟方法,改变来流边界层厚度以及来流速度研究不同来流条件对长密封腔结构类型流动特性及泄漏规律的影响。分析发现,长密封腔在Ma4.5高超声速来流下表现为开式空腔流动,对边界层厚度以及来流马赫数的变化相较于短密封腔更为敏感;来流马赫数的改变使得密封腔内流动结构变化较大,相应泄漏通道的入口压力分布也存在很大区别。

向后微分公式在六角形几何物理-热工耦合上的应用

针对六角形几何物理-热工耦合求解问题,提出了一种二阶变步长向后微分公式,物理和热工采用相同的步长和时间离散格式,并利用变步长技巧,提高计算效率。物理-热工采用模块化方式耦合,物理模块采用基于六角形几何的节块法,热工采用子通道程序,2个模块之间的数据传递通过共享内存的方式实现,开发了基于向后微分公式的HEXCOB-BDF程序。利用两个VVER堆芯弹棒事故验证该方法在物理-热工耦合上的准确性和计算效率。计算结果表明,HEXCOB-BDF程序与KIKO3D,DYN3D,PARCS计算结果相符,同时计算时间约为隐式Euler法计算时间的1/4。表明本文算法具有较好的准确性和较高的计算效率,可为六角形几何物理-热工耦合求解提供参考。

基于可变高增压方式的航空活塞发动机变海拔工作特性仿真研究

以一台直列四冲程压燃式航空活塞发动机为研究机型,通过GT-Power构建一维热力学模型,首先对比研究了不同海拔下固定截面增压(fixed geometry turbocharger,FGT)、可变几何截面增压(variable geometry turbocharger,VGT)和两级可变几何截面增压(twinvariable geometry turbocharger,TVGT)对发动机性能的影响;然后基于搭建的TVGT增压系统,探究了高、低压级VGT叶片开度对发动机变海拔条件下工作特性的影响。结果表明:在不同海拔和转速工况下,发动机匹配TVGT增压系统后,其海拔适应性更佳。针对TVGT系统,在不同海拔下,当高压级VGT叶片开度位于0.2~0.4范围内,低压级VGT叶片开度位于0.6~0.8范围内时可以获得较高的动力性及经济性。通过对高、低压级VGT叶片开度的优化,在巡航工况转速3397 r/min时可在6000 m海拔下实现106.8%的功率恢复目标,可满足发动机对高海拔工作运行的功率恢复要求。

V型Transformer的遥感影像障碍物提取方法

遥感影像中的障碍物是地震采集观测系统变观的重要依据之一。传统的人工提取障碍物方法效率低,且易受人为因素影响,难以保证结果的一致性,不适用于复杂地表环境及数量庞大的障碍物。当前通用的卷积神经网络自动提取障碍物方法,由于卷积核的尺寸受限,无法直接进行远距离的语义交互,也不能准确提取具有较大跨度且部分被遮蔽的障碍物(乡间道路、河流等)。为此,提出了基于V型全自注意力网络(MTNet)提取遥感影像障碍物的方法。首先,MTNet采用端到端的V型编码器—解码器结构,通过跳跃连接实现信息交互;其次,用具有远距离建模能力的Mix-Transformer模块取代传统卷积层,提取和重建更准确的障碍物多尺度特征;最后,用轻量的块扩展层取代转置卷积,实现上采样和图像分割,重建障碍物信息。实验结果表明,该网络分割障碍物的精度和速度显著优于现有方法,尤其在道路识别方面,优势更明显。

变几何进气道不起动流场非定常特性数值研究

为研究变几何进气道在不起动状态下的非定常流动现象,利用二维非定常数值计算方法对唇罩可前移的进气道流场进行模拟,探究唇罩位置变化对高超声速进气道不起动流场非定常特性的影响。对比了唇罩位于高马赫数位置及低马赫数位置时的进气道流动振荡情况,并对其流动振荡特性进行研究。结果表明,在唇罩位于高马赫数位置时,流动振荡幅度随来流马赫数升高明显增大,流量振荡幅值由Ma=4.0工况的0.8 kg/s增大至Ma=4.6工况的2.7 kg/s。而在唇罩位于低马赫数位置时,流动振荡幅度随来流马赫数升高反而逐渐减小。进气道中的小分离区与激波串会导致壁面压力的急剧上升,引发压力的非线性变化。在Ma=4.6工况下,壁面无量纲压强峰值在短时间内从20急剧上升至50以上,而在流场变化较为缓和的Ma=3.3工况,压力峰值仅在12.4~15.74小范围波动。在Ma=4.6工况,进气道流动振荡规律与各壁面监测点基本一致,而Ma=3.3工况下的流动振荡规律则与唇口及喉道处监测点之间出现较大差异。这是因为唇罩前移后进气道内的气流流速增大至声速以上,阻碍了上下壁面间的扰动传播及振荡耦合,因此减弱了进气道内的流动振荡现象。

变几何涡轮燃气轮机总体性能研究

为深入了解变几何涡轮对燃气轮机的总体性能影响机理,通过部件法对燃气轮机进行建模,然后分别改变高压涡轮、中压涡轮和动力涡轮的第一级导向器喉道面积,在不考虑导叶两端调节机构和导叶间隙等对涡轮效率影响情况下,对燃气轮机总体性能的变化情况进行了系统地分析,并得出各截面的总温与总压变化情况。结果表明:在采用保持高压涡轮入口总温恒定的控制规律时,增大燃气轮机的高压涡轮流通能力,燃气轮机输出轴功率与耗油率均不断增加,高压涡轮流通能力增加10%,输出轴功率与耗油率分别上升2.83%与1.13%;增大燃气轮机的中压涡轮流通能力,导致燃气轮机输出轴功率降低,耗油率上升,中压涡轮流通能力增加10%,输出轴功率降低9.96%,耗油率上升3.63%;动力涡轮流通能力增加,燃气轮机输出轴功率先上升,后有小幅下降,耗油率增大,动力涡轮流通能力变化量从0增加到10%,输出轴功率降低0.05%,耗油率增加2.01%。

Experiment of drag characteristics of a novel variable geometry flame-holder

A novel variable geometry flame-holder(VGF) based on V-gutter was presented.The structural characteristics of the flame holder were introduced.Experimental study on drag characteristics of the VGF on un-burning and burning states was conducted in a rectangular combustion test rig.The influence of the change of gutter trailing edge width w on pressure recovery in different operating conditions was analyzed emphatically.Furthermore,drag characteristics in different trailing edge width variation modes were discussed.Results show that:(1) Narrowing w can observably raise the total pressure recovery σ but the highest σ is not obtained at minimum w.(2) The relationship of drag coefficient ψ and w in the un-burning conditions can be well expressed in a form of exponential equation(w/d>0.4).(3) Drag characteristics are not sensitive to the variation modes and speeds of w.(4) In the burning condition,σ decreases with the increasing of w basically and the course can be divided into three stages.The results and experimental data presented in this paper would enhance the phenomenological understanding of this type of VGF,and would contribute to the next experimental study and numerical calculus of this novel VGF.

基于内收缩比可调的二元TBCC进气道风洞试验及起动特性分析

为拓宽进气道工作马赫数范围,结合型面变几何技术并充分利用迟滞回路效应的优势,基于外压缩面/喉道高度协同调节的二元TBCC进气道模型,采用数值模拟与风洞试验结合的方法,研究了马赫数为4.0的通流状态下进气道内收缩比(即改变喉道高度)增减对起动特性的影响。结果表明:当进气道处于不起动状态时,降低内收缩比使进气道肩部分离包被吞入继而实现再起动;结合纹影和沿程静压分布等分析,进气道入口波系在各内收缩比下与设计值相符,但内流通道的CFD结果与试验结果存在相对误差ε,且起动状态下的εq比不起动状态下的εb约低1.5%(ε_(q)<2.7%,ε_(b)<4.2%),表明采用的数值计算方法对于前体激波的预测较为准确,而对于不起动进气道内流静压预测存在误差;获取此类变几何进气道的迟滞回路特性,当内收缩比≤1.79时,进气道正常起动,当内收缩比≥2.54时,进气道不能正常起动,当1.79<内收缩比<2.54时,进气道的起动特性由初始状态和内收缩比的增减趋势共同决定。

单外涵变循环发动机变几何特性仿真

为了研究单外涵变循环发动机变几何性能收益,建立了一种单外涵变循环发动机总体性能仿真模型,并通过算例验证了仿真模型的计算精度。根据不同飞行状态的发动机控制规律和最优控制目标,模拟生成3种变几何方案最佳变几何参数以及最佳节流特性和高度-速度特性。结果表明:在设定的控制规律下,相对发动机常规变几何方案(方案1),尾喷管、混合器与低压涡轮导向器可调的变几何方案(方案3)使发动机地面节流状态耗油率降低1.7%~3.0%,超声速巡航推力增大14%~29%,亚声速巡航耗油率降低0.9%~3.1%,在3种变几何方案中性能收益最大;尾喷管与混合器可调的变几何方案(方案2)使发动机地面节流状态耗油率降低1.2%~2.2%,超声速巡航推力增大3%~17%,亚声速巡航耗油率降低0.9%~1.2%,在3种变几何方案中性能收益居中。发动机变几何方案的选择应综合考虑结构复杂度、可靠性、质量等方面的代价与基于特定任务需求的总体性能收益的平衡。

不确定性可视化综述

数据从采集到使用的过程不可避免地会引入不确定性.与数据错误和数据矛盾不同的是,不确定性存在于数据处理的各个环节,甚至各个环节会导致新的不确定性.作为数据不可或缺的组成部分,可视化不确定性有助于用户更加准确地分析和理解数据并做出正确的决策.文中简略地介绍了不确定性的基本来源;从不确定性的可视表达形式角度出发,梳理并总结了当前主流的不确定性可视化方法,包括图标法、可视变量编码法、几何体表达法和动画表达法;并探讨了需要进一步探索的研究方向.

可变几何涡轮增压器与发动机稳态匹配模型的研究

首先建立了在稳态工况下可变几何涡轮增压器(VGT)和发动机匹配的数学模型,讨论了建模中的几个关键问题。在此基础上,利用simulink建立了VGT与发动机匹配的模拟模型。通过大量的试验对模型进行了验证,结果表明模型的建立是正确的,应用该模型能较准确地预测各种工况下可调叶片的位置、涡轮流量等。最后,利用该模型模拟了过量空气系数一定时叶片转角随发动机转速、负荷等的变化,以及过量空气系数不同时对叶片转角和增压压力的要求的变化,得出了一些有关可调涡轮增压器匹配和设计的结论。

大型柴油机可变几何涡轮增压器的研制及试验研究

介绍了一种可变几何涡轮增压器的设计过程。对比了这种可变几何涡轮增压器与原涡轮增压器在性能上的差别。对这种可变几何涡轮增压器进行了台架试验和跑车试验。台架试验结果表明:这种可变几何涡轮增压器有效地提高了发动机在最大转矩点的缸内爆发压力和最大转矩点的转矩,改善了发动机的动力性。加速试验结果表明:安装了可变几何涡轮增压器的发动机的加速时间比原发动机的加速时间缩短了5s。