Control of squealer-tip leakage flow with perforated-rib coolant injection in an axial turbine cascade

A novel perforated-rib configuration is proposed for controlling the tip leakage flow at the rotor tip of an axial turbine. Three perforated-rib layouts are considered, wherein a perforated rib is installed at (A) the Suction-Side squealer (SS-rib), (B) the Pressure-Side squealer (PS-rib), and (C) the additional squealer along the blade Camber Line (CL-rib). A numerical method is used to show how the novel rib layouts affect the aerodynamic performance of the tip leakage flow. Results show that the coolant jets issuing from the perforated-rib injection holes penetrate deeper into the tip clearance than those in the baseline squealer-tip case, and how the perforated-rib coolant injection affects the tip leakage flow depends strongly on the rib layout. The PS-rib and CL-rib layouts appear promising for controlling the tip leakage flow, playing a significant role in reducing the total pressure loss and improving the turbine blade’s isentropic efficiency. In particular, under an injection mass flow ratio of 1% and a tip clearance of 1% blade span, the PS-rib layout reduces the leakage mass flow rate by 27% and increases the isentropic efficiency by 1.25% compared with those in the baseline squealer-tip case. Meanwhile, the advantages of the PS-rib layout in tip leakage control are confirmed under small and large tip clearances.     

基于LMI的过渡态主控回路闭环控制律优化设计

针对涡扇发动机过渡态多变量控制设计难的问题，提出了一种基于抽功法在过渡态加减速线上的准稳态工作点处提取线性模型的方法，并在此基础上提出了一种过渡态主控回路闭环控制律的优化设计方法。通过功率输入和功率提取解决过渡态动态特征提取难题，基于增益调度可作为非线性动态控制策略的基本原理，将稳态多变量控制规律的线性矩阵不等式(LMI)设计方法推广到涡扇发动机过渡态主控回路闭环控制的设计中，并通过最小化矩阵迹优化闭环极点配置。针对2种不同过渡态主控回路闭环控制策略，分别设计了最小化矩阵迹寻优的过渡态主控回路的多变量闭环控制律，并进行从慢车到中间状态的基于涡扇发动机非线性动态模型的双通道过渡态性能仿真验证，结果表明:方案1过渡态控制双通道N₁、N₂的调节时间不大于5.0 s，超调量不大于0.8%；方案2过渡态控制双通道π_T、N₂的调节时间不大于5.6 s，超调量不大于0.8%。      

Feasibility analysis of solar thermal propulsion system with thermal energy storage

Possessing relatively high specific impulse and moderate thrust levels, solar thermal propulsion (STP) is a promising candidate in spacecraft propulsion system. However, the traditional solar thermal propulsion system suffers from thrust failure in the shadow area, which seriously affects its applicability. In this paper, we investigate feasibility of regenerative solar thermal propulsion system (RSTP) incorporating thermal energy storage, which can effectively overcome unmatched synchronous working time and illumination time. A numerical model for RSTP considering the whole energy transfer process from light concentrating, heat storage, to thrust generation is built, which is verified by experiment measurements with relative errors less than 15 %. The result shows that the maximum time to complete heat storage is about 4000 s, which is within the illumination time for low Earth orbit. In the solar eclipse region, the thrust (F_t) and the specific impulse (I_sp) of the system increase with the propellant flow rate, which can reach about 2 N and 690 s, respectively. What’s more, the system can operate for around 100 s continuously at the maximum thrust in the shadow area. This work provides alternative approaches for microsatellite propulsion with high specific impulse, high thrust, and continuous operation despite presence of solar eclipse.     

An FV-EE model to predict lean blowout limits for gas turbine combustors with different structures and sprays

The occurrence of Lean Blowout(LBO) is a disadvantage that endangers a stable operation of gas turbines. A determination of LBO limits is essential in the design of gas turbine combustors. A semiempirical model is one of the most widely used methods to predict LBO limits.Among the existing semiempirical models for predicting LBO limits, Lefebvre’s LBO model and the Flame Volume(FV) model are particularly suitable for gas turbine combustors. On the basis of Lefebvre’s and FV models, the concept o...     

Mechanism of interconnected synchronized switch damping for vibration control of blades

The Synchronized Switch Damping (SSD) is regarded as a promising alternative to mitigate the vibration of thin-walled structures in aero-engines, especially for blades or bladed disks. The common manner is to shunt the switch circuit independently to a single piezoelectric structure. This paper is aimed at exploring a novel way of using the SSD, i.e., the SSD is interconnected between two piezoelectric structures or substructures. The damping mechanism, performance, and effective range of the interconnected SSD are studied numerically and experimentally. First, based on a dual cantilever beam finite element model, the time domain and frequency domain modeling and solving methods of the interconnected SSD are deduced and validated. Then, the influence of the amplitude and phase relationship on the damping effect of the interconnected SSD is numerically studied and compared with the shunted SSD. A self-sensing SSD control board is developed, and experimental studies are carried out. The results show that the interconnected SSD establishes an additional energy channel between the corresponding piezoelectric structures. When the amplitudes of the two cantilever beams are different, the interconnected SSD balances the vibration level of each beam. When the amplitudes of the two cantilever beams are the same, if the appropriate interconnection manner is selected according to the phase, the resonance peak can be reduced by more than 30%. When the vibration is in-phase/out-of-phase, the damping generated by the interconnected SSD in a cross/parallel manner is even more significant than the shunted SSD. Furthermore, this novel connection scheme reduces the number of SSD circuits in half. Finally, for engineering applications, we implement the proposed damping technology to the finite element model of a typical dummy bladed disk. A piezoelectric damping ratio of 13.7% is achieved when the amount of piezo material is only 10% of blade mass. Compared with traditional friction dampers, the major advancements of the interconnected SSD are: (A) it can reduce the vibration level of blades without friction interface; (B) the space constraint is overcome, i.e., the vibration energy is not necessarily dissipated independently in one sector or through physically adjacent blades, and instead, the dissipation and transfer of vibrational energy can be realized between any blade pair. If a specific gating circuit is adopted to adjust the interconnection manner of the SSD, vibration mitigation under variable working conditions with different engine orders will be expected; (C) designers do not need to worry about the annoying nonlinearities related to working conditions anymore.     

基于有限时间引导律的欠驱智能船舶循迹控制

针对欠驱智能船舶在执行循迹任务时，受路径曲率和环境力干扰影响导致横向偏差增大的问题，对欠驱智能船舶的引导策略进行了研究。提出了一种有限时间收敛的自适应引导律，并基于该引导律实现了欠驱智能船舶循迹控制，使循迹过程中的横向偏差在有限时间内收敛至零。相比于传统积分引导律，所提方法的控制参数可以根据横向偏差的变化进行自适应调整，更快地引导欠驱智能船舶进行直线和曲线循迹。通过仿真对比验证了所提方法的有效性和先进性。      

含铝固体燃料冲压发动机工作性能分析

为探究含铝固体燃料冲压发动机的燃烧特性和工作性能，基于纳米铝颗粒和端羟基聚丁二烯（HTPB）的混合固体燃料，采用雷诺转捩模型、颗粒表面反应模型和涡概念耗散模型，建立了二维两相湍流燃烧模型；数值计算分析了含铝固体燃料冲压发动机内流场，以及不同含铝质量分数和粒径下的燃面退移速率、推力与比冲。结果表明：发动机的进气条件对颗粒相的燃烧与运动起主导作用；与纯HTPB推进剂相比，添加质量分数为5%的铝颗粒能够提高补燃室压强和温度，增大燃烧室内高温区面积，可使推进剂平均燃面退移速率提高18.53%，发动机推力提高21.37%，密度比冲提高2.38%，适当增加铝颗粒含量或减小粒径，对提高推进剂燃面退移速率、发动机推力和密度比冲具有积极作用。     

减涡器破裂转速预测方法及试验验证

采用数值分析同试验相结合的方法研究了减涡器破裂转速问题。根据减涡器支撑环孔边的应力状态，设计了支撑环结构的模拟试验件，开展了单调拉伸载荷下的破坏试验，得到了体现结构应力特征的破坏参数。进而基于有限元方法，将模拟试验件的破坏参数引入减涡器支撑环破裂转速预测中，并对比了不同破裂准则对破裂转速预测结果的影响。分析表明:所设计的模拟试验件与减涡器支撑环的应力梯度吻合较好，可准确描述结构应力特征；局部塑性法和基于材料强度的方法预测破裂转速时结果更为保守，分别比平均应力法的预测值低15%和23%，对此类结构的破裂分析具有工程参考价值。      

Method for utilizing PIV to investigate high curvature and acceleration boundary layer flows around the compressor blade leading edge

Particle Image Velocimetry (PIV) is a well-developed and contactless technique in experimental fluid mechanics, but the strong velocity gradient and streamline curvature near the wall substantially limits its accuracy improvement. This paper presents a data processing procedure combining conventional PIV and newly developed Mirror Interchange (MI) based Interface-PIV for the measurement of the boundary layer parameter development in the blade leading edge region. The synthetic particle images are used to analyze the measurement errors in the entire procedure. Overall, three types of errors, namely the errors caused by the Window Deformation Iterative Multigrid (WIDIM) algorithm, the discrete data interpolation and integration, and the wall offset uncertainty, comprise the main measurement error. Specifically, the errors due to the discrete data interpolation and integration and the WIDIM algorithm comprise the mean bias, which can be corrected through the error analysis method proposed in the present work. Meanwhile, the errors due to the WIDIM algorithm and the wall offset uncertainty contribute to the measurement uncertainty. Computational fluid dynamics-based synthetic particle flows were generated to verify the newly developed PIV data processing procedure and the corresponding error analysis method. Results showed that the data processing method could improve the accuracy of PIV measurements for boundary layer flows with high curvature and acceleration and even with significant flow separation bubbles. Finally, the data processing method is also applied in a PIV experiment to investigate the boundary layer flows around a compressor blade leading edge, and several credible boundary flow parameters were obtained.