加热条件下粘性液膜射流破碎机理的研究

利用线性不稳定性理论，对具有温度梯度的粘性液膜射流模型所对应的色散方程进行了数值求解。利用计算结果，研究了加热条件下反对称模式和对称模式粘性液膜射流大、小尺度破碎模式的破碎机理，探讨了韦伯数(We)、密度比(Q)、Marangoni数(Mα)和Ohnesorge数(x)对液膜射流表面波的最大扰动增长率及占优波数的影响。     

射流参数对加热条件下液膜射流破碎不稳定性的影响(1)--射流参数对液膜反对称模式破碎的影响

基于线性不稳定性理论，利用对具有温度梯度的粘性液膜射流模型进行的数值计算结果，研究了射流速度，气体密度，液体粘性，液膜厚度，温度梯度，液体种类等实际射流参数对反对称模式扰动作用下液膜射流大、大尺度破碎模式的最大扰动增长率及占优波数等破碎特征的影响规律。     

射流参数对加热条件下液膜射流破碎不稳定性的影响(2)--射流参数对液膜对称模式破碎的影响

利用对具有温度梯度的粘性液膜射流模型进行的不稳定性计算结果，研究了实际射流参数（射流速度）气体密度，液体粘性，液膜厚度，温度梯度，液体种类等）对对称模式扰动作用下液膜射流大，小尺度破碎模式破碎特征的影响规律，并探讨了决定液膜射流破碎尺度的实际因素。     

加热条件下液膜射流破碎尺度影响因素的研究

利用线性不稳定性理论对加热条件下粘性液膜射流模型所对应的色散方程进行了数值求解。利用得到的计算结果研究了加热条件下无量纲数对液膜射流破碎尺度的影响。结果表明:在反对称模式下,当We·Q<1时,液膜破碎处于大尺度模式,反之则处于小尺度模式;在对称模式下,当We·Q<1且Ma相似文献   

实际射流参数对加热条件下液体燃料射流不稳定性的影响

利用线性热不稳定性理论,对黏性液体射入高温气体介质所对应的色散方程进行了数值求解．利用所得到的计算结果,研究了加热条件下射流速度、气液密度比、液体黏度、温度梯度及液体种类等实际射流参数对射流最大扰动增长率及占优波数的影响规律．研究结果表明：对于加热条件下Reyleigh模式的液体射流,气液密度比、温度梯度是射流破碎的失稳因素,而射流速度、液体黏度则是液体射流破碎的促稳因素;对于Taylor模式的液体射流,射流速度、温度梯度、气液密度比是射流破碎的失稳因素,而液体黏度是液体射流破碎的促稳因素．研究结果同时证明了液体种类的改变对射流不稳定性的影响是多种因素共同作用的结果．     

液体燃料射流破碎机理研究中的时间模式与空间模式

利用线性不稳定性理论分析了液体燃料射流在分别采用时间模式与空间模式两种方法下液体表面扰动波的波数、频率及最大扰动增长率之间的关系,讨论了两种模式下液体射流结构特征的差别。应用基于粘性液体射流射入气体介质中的物理模型,计算分析了 Ｒｅ 数、 Ｗｅ 数和密度比 Ｑ对时间模式与空间模式差值的影响,结果发现采用时间模式或空间模式并不改变液体射流各阶模式之间的相互关系, Ｗｅ 数和 Ｑ是影响时间模式与空间模式差值的主要因素,而 Ｒｅ 数影响不大。在一定条件下,时间模式与空间模式具有等效性。     

加热条件下液体燃料射流破碎机理的研究

利用线性热不稳定性理论,对黏性液体射入高温气体介质模型所对应的色散方程进行了数值求解。利用所得到的计算结果,研究了加热条件下轴对称模式扰动液体射流破碎机理,探讨了表征各种影响射流破碎作用力的无量纲Weber数（We）、密度比（Q）、Marangoni数（Ma）和Ohnesorge数（Z）对液体射流破碎最大扰动增长率及占优波数的影响。研究结果表明,液体和气体介质之间的温度梯度对液体射流稳定性有着非常显著的影响,表明热毛细力对于液体射流的破碎有促进作用,这种作用对处于Taylor模式下的液体射流尤为显著,并且这种热力作用可使液体射流从一种模式进入另一种模式,并可以大大改变射流的破碎尺序。     

旋转气体介质对环膜液体射流破碎不稳定性影响的研究

利用线性不稳定性理论研究了旋转气体介质对黏性环膜液体射流破碎的影响。研究结果表明，无论是轴对称模式还是非轴对称模式，由液体环膜内部气体介质旋转所产生的离心力是液体射流的失稳因素，有助于液体射流的破碎。另外，由液体环膜外部气体介质旋转所产生的离心力是液体射流的促稳因素，不利于液体射流的破碎。当相同强度的旋转同时存在于内部和外部气体介质中时，对于轴对称模式，内部气体介质的影响显著，而对于非轴对称模式，则外部气体介质的影响更为明显。通常情况下，非轴对称模式的扰动增长率强于轴对称模式的扰动增长率，因此会在环膜液体射流的破碎中占据主导地位。     

幂律流体液膜射流的时间不稳定性分析（英文）

基于时间模式不稳定性理论,研究了无黏静止气体中二维幂律流体液膜射流不稳定过程.在对幂律流体本构方程线性近似的基础上,通过对非对称模式和对称模式的色散方程的推导和求解,研究了广义雷诺数、韦伯数、气/液密度比以及幂律指数对于液膜破碎的影响.结果表明:在两种模式下,不论剪切变稀流体还是剪切变稠流体,液体的黏性和表面张力都会抑制液膜破碎,而气/液相互作用力则促进液膜破碎.而且,幂律指数越小,液膜射流越容易破碎.同时,尽管非对称模式在液膜破碎过程总是占据主导地位,但是当两种模式的最大扰动增长率的量级同阶时,对称模式对于液膜破碎也起着重要作用.     

高速粘性液体射流的不稳定模式

本利用线性不稳定性理论研究了高速粘液性射流的破碎问题，并利用先进的高速分幅全息摄影技术首次比较系统地观察了几种不稳定模式的表明形态，实验观察结果与理论预测基本一致。研究结果表明，在适当的条件下，非轴对称模式也有可能成为最不稳定模式，从而肯定了非轴对称模式在射流破碎中的重要作用。     

Study on transient process of mode transition in a scramjet combustor with pilot hydrogen

Effective control of mode transition is one of the key technologies for dual‐mode scramjet. In this study, a 3‐dimensional unsteady Reynolds‐averaged Navier‐Stokes modeling was used to investigate the effects of equivalence ratio, inflow temperature, and pilot hydrogen on transient process of mode transition in a dual‐mode scramjet combustor. The isolator entrance Mach number was 2.5, and the fuel of vaporized kerosene was used in the combustor with pilot hydrogen. The results showed that during mode transition from ram mode to scram mode induced by reducing the equivalence ratio of kerosene, the disappearance of the high‐pressure zone around the kerosene injector was the sign of approaching the achievement of mode transition. The leading edge of the shock train moved downstream and the strength of shock train was significantly weakened. During this process, the distribution of heat release zone transformed from scattered along the combustor to being concentrated in the cavity. Then, the opposite process was studied when the inflow temperature was reduced from 1750 to 1000 K while the equivalence ratio was kept the same. The thickness of shear layers originated from the fuel injectors significantly increased. Altering the amount of pilot hydrogen can significantly influence the flow field in the combustor. It showed that the increase of pilot hydrogen could shield the kerosene vapor entering into the high‐temperature zone in the cavity and hindered the formation of concentrated heat release. Thus, the overall heat release became more dispersed.     

风电场的主接线、并网和运行方式分析

"十一五"期间,上海南汇地区先后建造了35kV南汇风电场、110kV东海大桥风电场和35kV临港新城风电场。通过对南汇地区3个风电场的建设回顾,比较了风电场的主接线形式和运行方式,分析了风电场的并网操作和低电压穿越等问题,并提出了有待改进的技术措施和相关建议。     

负温度梯度对预混气体反应波传播模态的影响

基于一维数值模拟研究了负温度梯度对氢气/空气混合气反应波传播模态的影响,重点论述燃烧模态的转变机理.研究表明:当反应波沿着负温度梯度传播时,可以观测到超声速爆燃向爆震、爆震向亚声速爆燃的转变;其中,超声速爆燃传播过程由顺序自燃控制;当其传播速度低于当地Chapman-Jouguet爆震速度时,会发生超声速爆燃向爆震的转变.此外,在低温区域也观测到了爆震向亚声速爆燃的转变.Zel’dovich(ZND)结构和RankineHugoniot曲线表明,诱导激波后混合气反应活性对维持爆震传播具有重要作用.     

An experimental study on the high frequency oscillatory combustion in tubular flame burners

In this study, high frequency oscillatory combustion in tubular flame burner was experimentally investigated using large scale 8- and 12-in. diameter tubular flame burners. The conditions for the high frequency oscillatory combustion were determined, and the pressure fluctuations were measured, on which spectral analyses were made. The results showed that a smooth laminar tubular flame could be established, however, high frequency combustion sound was emitted from the 8- and 12-in. burners when the air flow rates exceeded 650 and 1200 m³/h, respectively. Pressure fluctuation measurements and spectral analyses showed that high frequency pressure fluctuations occurred simultaneously during the high frequency oscillation. The flame images were also obtained with a high speed video camera. The flame surface was found to be notably corrugated and the symmetry was broken during the oscillation. By assuming that the tubular flame burner is a simple tube, the natural frequencies of the burners were determined using the fundamental theory of the acoustic resonance in a cylindrical cavity, and the experimental peak frequencies in the spectra were compared with the natural frequencies. As a result, it was found that the high frequency oscillations in both the burners were identified as the tangential/radial mode acoustic resonant oscillations. It was further found that the tangential first mode of oscillation, which had an asymmetric structure, preceded the higher modes of oscillation which indicated that the mode dominated the occurrence of the high frequency oscillation. To verify the occurrence of the tangential first mode oscillation, the pressure fluctuations were measured with two pressure sensors installed at opposed locations. The results showed that the phase of the oscillation was 180° difference, and the asymmetric structure confirmed the occurrence of the tangential first mode of oscillation.     

Performance of 26650 Li-ion cells at elevated temperature under simulated PHEV drive cycles

Cylindrical (type: 26650) Li-ion cells (LiFePO₄ cathodes) currently used in the electric vehicles (EVs), plug-in hybrid electric vehicles etc. were subjected to simulated federal urban driving schedule at 25 and 50 °C for performance evaluation. Drive profiles (current versus time) for charge sustaining and charge depleting modes were derived from the federal urban driving schedule velocity profiles considering acceleration, regenerative braking, rolling resistance, drag force etc. for typical plug-in hybrid electric vehicles. In particular, the batteries were cycled extensively at 50 °C under charge sustaining as well as charge depleting modes to monitor capacity values, followed by analyzing the LiFePO₄ cathode material by X-ray diffraction analysis. The capacity degradation was found to be very significant in both the modes with 13 and 19% under charge sustaining and charge depleting modes after 337 and 1007 cycles, respectively at elevated temperature. High frequency resistance values measured by electrochemical impedance spectroscopy were found to increase significantly under high temperature cycling, leading to power fading. As evident from Rietveld analysis, phase change in LiFePO₄ is observed beyond 1000 cycles at elevated temperature under charge depleting mode, with the observation of FePO₄ from the powder diffraction data of the cathodes from the cycled cells. In addition, there was also significant change in crystallite size of the cathode active materials after charge/discharge cycling under charge depleting mode.     

三相无变压器型光伏并网逆变器共模电压的分析

详细分析了三相无变压器型光伏并网逆变器共模电压的产生机理,构建了共模电压模型,得出了抑制共模电流的一般规律。利用该规律,对三相全桥拓扑结构的共模电流进行了详细分析,提出了新型控制方法,通过仿真试验对该方法进行了验证。