A simple control law for reducing the effective characteristic acceleration of a solar sail

The direction and magnitude of a solar sail acceleration are strongly related. For this reason, once the characteristic acceleration has been fixed, it is not possible to modulate the acceleration in a particular direction. In this work, a semi-analytical switching control law is derived, enabling a solar sail to emulate a smaller effective characteristic acceleration (without changes in geometry or optical properties); by periodically changing the pitch (cone) angle of the sail, in average over time, the acceleration produced by the sail matches exactly (in both direction and magnitude) that of a “smaller” sail. The range in which this is possible is determined, and the limitations on this range due to the size difference is computed. The method is validated on optimal Earth-Mars trajectories.     

On the station keeping of a solar sail in the elliptic Sun–Earth system

In this work we focus on the dynamics of a solar sail in the Sun–Earth Elliptic Restricted Three-Body Problem with solar radiation pressure. The considered situation is the motion of a sail close to the L₁ point, but displacing the equilibrium point with the sail so that it is possible to have continuous communication with the Earth. In previous works we derived a station keeping strategy for this situation but using the Circular RTBP as a model.     

Results of solar observations by the CORONAS-F payload

The CORONAS-F mission experiments and results have been reviewed. The observations with the DIFOS multi-channel photometer in a broad spectral range from 350 to 1500 nm have revealed the dependence of the relative amplitudes of p-modes of the global solar oscillations on the wavelength that agrees perfectly well with the earlier data obtained in a narrower spectral ranges. The SPIRIT EUV observations have enabled the study of various manifestations of solar activity and high-temperature events on the Sun. The data from the X-ray spectrometer RESIK, gamma spectrometer HELICON, flare spectrometer IRIS, amplitude–temporal spectrometer AVS-F, and X-ray spectrometer RPS-1 have been used to analyze the X- and gamma-ray emission from solar flares and for diagnostics of the flaring plasma. The absolute and relative content of various elements (such as potassium, argon, and sulfur) of solar plasma in flares has been determined for the first time with the X-ray spectrometer RESIK. The Solar Cosmic Ray Complex monitored the solar flare effects in the Earth’s environment. The UV emission variations recorded during solar flares in the vicinity of the 120-nm wavelength have been analyzed and the amplitude of relative variations has been determined.     

Effects on winter circulation of short and long term solar wind changes

Indices of the North Atlantic Oscillation and the Arctic Oscillation show correlations on the day-to-day timescale with the solar wind speed (SWS). Minima in the indices were found on days of SWS minima during years of high stratospheric aerosol loading. The spatial distribution of surface pressure changes during 1963–2011 with day-to-day changes in SWS shows a pattern resembling the NAO. Such a pattern was noted for year-to-year variations by Boberg and Lundstedt (2002), who compared NAO variations with the geo-effective solar wind electric field (the monthly average SWS multiplied by the average southward component, i.e., negative Bz component, of the interplanetary magnetic field). The spatial distribution of the correlations of geopotential height changes in the troposphere and stratosphere with the SWS; the geo-effective electric field (SWS∗Bz); and the solar 10.7 cm flux suggests that solar wind inputs connected to the troposphere via the global electric circuit, together with solar ultraviolet irradiance acting on the stratosphere, affect regional atmospheric dynamics.     

Sunspot cycle 23 descent to an unusual minimum and forecasts for cycle 24 activity

The decay phase of the sunspot cycle 23 exhibited two unusual features. First, it lasted too long. Second, the interplanetary magnetic field intensity at earth orbit reached the lowest value since in situ measurements in space began in October 1963. These physical anomalies significantly altered the early forecasts for the sunspot activity parameters for cycle 24, made by several colleagues. We note that there was a significant change in the solar behavior during cycle 22. We discuss the observed trends and their effect on our empirical solar activity forecast technique, leading to our prediction for cycle 24 parameters; cycle 24 will be only half as active as cycle 23, reaching its peak in May 2013. We speculate on the possible implications of this outcome on future earth climate change and the ensuing socio-economic consequences.     

蜂窝式轴心通风器油气分离性能计算

为对航空发动机蜂窝式轴心通风器油气分离效率进行研究,建立考虑油气双向耦合的流场计算方法及油滴/壁面相互作用模型,在验证通风阻力及油气分离效率可靠性的基础上,对不同转速、通风流量和环境温度下蜂窝式轴心通风器的油气分离效果进行计算和分析.结果表明:转速的增加会使油气分离效率得到提升,而通风流量和环境温度的增加则导致油气分离效率的降低.蜂窝孔结构的加入对通风阻力影响不大,却对通风器的滑油分离过程起主要作用,计算表明其对滑油分离贡献率在80%以上.      

Effect of blade tip winglet on the performance of a highly loaded transonic compressor rotor

The tip leakage flow has an important influence on the performance of transonic com-pressor. Blade tip winglet has been proved to be an effective method to control the tip leakage flow in compressor, while the physical mechanisms of blade tip winglet have been poorly understood. A numerical study for a highly loaded transonic compressor rotor has been conducted to understand the effect of varying the location of blade tip winglet on the performance of the rotor. Two kinds of tip winglet were designed and investigated. The effects of blade tip winglet on the compressor over-all performance, stability and tip flow structure were presented and discussed. It is found that the interaction of the tip winglet with the flow in the tip region is different when the winglet is located at suction-side or pressure-side of the blade tip. Results indicate that the suction-side winglet (SW) is ineffective to improve the performance of compressor rotor. In addition, a significant stall range extension equivalent to 33.74% with a very small penalty in efficiency can be obtained by the pressure-side winglet (PW). An attempt has been made to explain the fundamental mechanisms of blade tip winglet in detail.     

展向振荡对激波/湍流边界层干扰的影响

周期振荡作为一种有效的壁面流动控制手段受到广泛关注,而其对激波/湍流边界层干扰的影响目前鲜有研究。本文采用高精度直接数值模拟（DNS）方法对马赫数2.9、12°激波入射角、强振荡下的激波/湍流边界层干扰进行了系统研究。通过与无振荡工况的定量比较,揭示了展向强振荡对干扰区内复杂流动结构的影响规律及作用机制,如分离泡尺度、物面压力脉动非定常特性、物面剪切的非定常特性及统计特征等。研究发现：在展向强振荡作用下,分离点位置提前,间歇区长度增大;同时由于分离泡内强黏性耗散的影响,展向振荡的穿透高度约为分离泡高度的4%,因而对流动结构不会产生实质影响。但展向强振荡会对壁面附近流动造成显著影响,如强振荡诱导的壁面展向速度远大于流向速度,造成流向剪切与展向剪切之间夹角的概率密度函数峰值从0°偏移到80°~90°之间。物面压力及剪切本征正交分解分析表明,展向振荡会导致模态能量从低阶模态向高阶模态转移,降低低频运动的能量占比,增强再附后Görtler涡等壁面附近旋涡结构的强度。     

流场可压缩性对涡相互作用影响的数值研究

涡相互作用作为冲压发动机喷注装置的典型抽象流动现象,研究其可压缩性影响对于认识包含化学反应的真实燃料喷射场具有一定基础理论价值。基于经过数值验证的可压缩Navier-Stokes算法与压力泊松方程初始条件设置方法研究流场可压缩性对涡相互作用演化过程的影响。结果表明,以较高涡旋马赫数表征的可压缩性在改变涡对形态的同时,具有延缓涡旋相互靠近,迟滞融合进程的作用。关于涡对系统开始融合的临界条件,可压缩相互作用开始的临界展弦比与无量纲时间相比于低速涡对明显提高。为在无量纲时间意义下统一不同马赫数涡对相互作用的进程,从涡心密度随时间变化规律出发在不可压涡对特征时间的基础上,初步构建了考虑可压缩性的时间尺度修正关系。     

超声速膨胀角入射激波/湍流边界层干扰直接数值模拟

为了揭示膨胀效应对激波/湍流边界层干扰区内复杂流动现象的影响规律,采用直接数值模拟方法对来流马赫数2.9、30°激波角的入射激波与10°膨胀角湍流边界层相互作用问题进行了数值研究。系统地探讨了激波入射点分别位于膨胀角上游、膨胀角角点和膨胀角下游3种工况下膨胀角干扰区内若干基本流动现象,如分离泡、物面压力脉动及激波非定常运动、湍流边界层统计特性和相干结构动力学过程等。结果表明,激波入射点流向位置改变对分离区流向和法向尺度的影响显著,尤其是当激波入射点位于角点及其下游区域。研究发现,膨胀角干扰区内物面压力脉动强度急剧减小,分离区内压力波向下游传播速度将降低而在膨胀区内将升高,膨胀效应极大地抑制了分离激波的低频振荡运动。相较于入射激波与平板湍流边界层干扰,入射激波流向位置改变对膨胀角再附区速度剖面对数区及尾迹区影响显著,将导致其内层结构参数升高而外层降低,近壁区内将呈现远离一组元湍流状态的趋势。此外,流向速度脉动场本征正交分解分析指出,主模态空间结构集中在分离激波及剪切层根部附近而高阶模态以边界层内小尺度正负交替脉动结构为主。低阶重构流场结果表明,前者对应为分离泡低频膨胀/收缩过程而后者表征为分离泡高频脉动。