Gravitational Convection of a Liquid Mixture in a Horizontal Cylindrical Gap at Moderate Grashof Numbers

Weak concentration convection which arises in the process of diffusion of impurities into the solvent filling a gap between two coaxial cylinders is studied experimentally. It is found that convective motion in the range of Grashof numbers 10³–5 × 10⁴ has a clear boundary-layer character. Near the inner porous cylinder, which is a source of impurity, a diffusion boundary layer passing into a two-dimensional convective plume is formed. The data on the structure and thickness of this layer are presented depending on the integral flux of impurity. The prospects of making an experiment in order to discover concentration convection onboard an orbital station are discussed.     

高超声速绕平板上直立圆柱流动特性研究

以平板上直立平无限谪圆柱体为研究对象，采用和Ｒｏｅ三阶通量差分分裂格式求解雷诺平均Ｎ－Ｓ方程，数值模拟研究了高超声速且壁面有传热条件下三维流流场的激波边界层干扰特性，物面压力分布计算值与值吻合良好，数值模拟结果可见圆柱上游分离区流场是一个马蹄形五涡结构且存在有二次分离激波，这是一种值得深入研究的流动新现象。     

Turbulent fluctuations of plasma and magnetic field parameters in the magnetosheath and the low-latitude boundary layer formation: Multisatellite observations on March 2, 1996

The results of simultaneous analysis of plasma and magnetic field characteristics measured on the INTERBALL/Tail Probe, WIND and Geotail satellites on March 2, 1996, are presented. During these observations the INTERBALL/Tail Probe crossed the low-latitude boundary layer, and the WIND and Geotail satellites measured the solar wind’s and magnetosheath’s parameters, respectively. The plasma and magnetic field characteristics in these regions have been compared. The data of the Corall, Electron, and MIF instruments on the INTERBALL/Tail Probe satellite are analyzed. Fluctuations of the magnetic field components and plasma velocity in the solar wind and magnetosheath, measured onboard the WIND and Geotail satellites, are compared. The causes resulting in appearance of plasma jet flows in the low-latitude boundary layer are analyzed. The amplitude of magnetic field fluctuations in the magnetosheath for a studied magnetosphere boundary crossing is shown to exceed the magnetic field value below the magnetopause near the cusp. The possibility of local violation of pressure balance on the magnetopause is discussed, as well as penetration of magnetosheath plasma into the magnetosphere, as a result of magnetic field and plasma flux fluctuations in the magnetosheath.     

Estimation of the current density and analysis of the geometry of the current system surrounding the Earth

The results of an investigation of the distribution of plasma pressure, pressure gradients, and magnetic field near the equatorial plane in the plasma ring surrounding the Earth under magneto-quiet conditions are presented. Observational data obtained during the international THEMIS mission are used. The picture of the distribution of transverse-current density near the equatorial plane was obtained under assumption of observing the magnetostatic balance condition at geocentric distances from 6 to 12R _E. In estimating the integral transverse current it was accepted that in daytime sector the magnetic-field minima on magnetic field lines are not localized in the equatorial plane. Estimates of the integral transverse current were obtained, which demonstrate the possibility of closing nighttime transverse currents at geocentric distances of up to ～12R _E inside the magnetosphere, which form a high-latitudinal continuation of the ring current.     

超燃冲压发动机隔离段内附面层/激波串相互干扰研究

隔离段内激波串的产生和发展以及激波/附面层相互干扰现象是极为复杂的,有效地进行激波串的组织是研究隔离段的关键所在,而其性能的好坏直接影响着超燃冲压发动机的性能。采用数值模拟的方法对不同来流附面层厚度工况的二维轴对称隔离段内流场流动特性进行了数值计算,分析了附面层/激波相互作用机理和附面层对隔离段激波串及隔离段性能的影响。结构表明:压缩-膨胀-再压缩-再膨胀……的气流流动挤压过程导致激波串的形成,逆压梯度的存在构成了附面层分离;附面层厚度的增加影响着激波串起始位置和结构;随着附面层厚度的增加,出口总压恢复系数和质量平均马赫数降低,且随着反压增大,变化趋势趋于明显。     

某型号仪器舱组合体联合动强度试验方法

针对某型号导弹仪器舱组合体结构和设备的联合动强度考核需求，开展组合体的动强度试验方法研究:设计专门的气瓶过载弹性加载装置，实现了气瓶过载力的等效模拟；通过整舱振动试验边界模拟和传递特性分析，验证了噪声激励振动传递与机械振动传递的差异性，提出采用大刚度模拟边界代替级间段真实边界与仪器舱组合进行联合动强度试验的方法；针对3个重点结构部段提出各自的试验条件，并通过预试验和归一化输入响应的比较分析确定了舱段不同部位结构和设备的联合考核方法。该试验方法可以有效模拟由发动机脉动和气动噪声引起的声振环境，避免产品过试验，达到对舱段结构及设备的动强度考核和设备支架动特性及放大倍数评估的目的。     

Unsteady laminar separation over impulsively moved cylinders

A numerical method is employed to integrate the unsteady laminar boundary layers about circular and elliptic cylinders started impulsively from rest. An upwind differencing scheme permits the integration through thin layers of reversed flow that are embedded in the boundary layer. The results are in agreement with numerical solutions of the full Navier-Stokes equations and with small time inner-outer expansion solutions. At later times, a singularity of the Goldstein type appears; Sears and Telionis defined this singularity as unsteady boundary-layer separation. For the circular cylinder, this singularity travels upstream and for large times, arrives asymptotically at the point of steady-state separation.     

Drag reduction research in supersonic flow with opposing jet

A CFD study on drag reduction in supersonic flow with opposing jet has been conducted. Flowfield parameters, reattachment point position and surface pressure distributions are obtained and validated with experiments. From the analysis on the physical mechanism of drag reduction, it shows the phenomenon that, when the opposing jet blows, the high pressure region is located between the bow shock wave and the Mach disk, which makes the nose region much lower pressure. As the pressure ratio increases, the high pressure region is gradually pushed away from the surface. Larger the total pressure ratio is, the lower of the drag coefficient is. To study the effect of the intensity of opposing jet more reasonably, a new parameter R_PA has been introduced by combining the flux and the total pressure ratio. The study shows that the same shock wave position and drag coefficient can be obtained with the same R_PA with different fluxes and the total pressures, which means the new parameter could stand for the intensity of opposing jet and could be used to analyze the influence of opposing jet on flow field and aerodynamic force.     

“人字形小肋”对激波/边界层干扰的影响研究

在曼彻斯特大学跨声速风洞开展激波/边界层干扰及“人字形小肋”对其影响的实验研究。在马赫数1.85流场条件下，应用高速纹影、油流、皮托压力测量和基于压敏漆的壁面压力测量技术，研究“人字形小肋”流动控制方法对激波/边界层干扰的流动分离结构与尺寸、压力分布特性与波系特征等影响。结果显示激波/边界层干扰诱发流动分离，分离区呈现三维特征，在“人字形小肋”的作用下，分离线呈现“波浪”形且整体向上游移动，干扰区流向尺寸增大，分离区高度减小且长度略增大，再附区的压力极值降低，这些特征与叶片、尖楔等微涡发生器的影响趋势相反。下一步工作中，拟针对“人字形小肋”开展参数优化研究，“人字形小肋”可能成为降低激波/边界层干扰诱发的高热流载荷的有效方法。     

纺丝工艺对炭纤维缠绕复合材料强度转化率的影响

通过不同纺丝工艺的聚丙烯腈基炭纤维表面状态、NOL环及Φ150 mm容器的实验研究,分析了不同纺丝工艺对湿法缠绕复合材料聚丙烯腈基炭纤维强度转化率的影响。结果表明,干喷湿纺炭纤维比湿法纺丝Φ150 mm容器环向纤维强度转化率要高出11.9%~15.4%,湿法纺丝的炭纤维复合材料NOL环层间剪切强度要比干喷湿纺炭纤维复合材料高7.4~34.1 MPa。因此,干喷湿纺的炭纤维可应用于固体火箭发动机缠绕壳体、压力容器等主要承受拉伸应力的领域,可充分发挥其纤维强度;而湿法纺丝工艺制成的炭纤维与树脂基体结合紧密,利于载荷的传递,可应用于承受压缩剪切等复杂载荷的领域,从而发挥这两种纤维各自不同优势。     

Mapping orbits with low station keeping costs for constellations of satellites based on the integral over the time of the perturbing forces

The present paper is concerned with the search for orbits that have potential to require low fuel consumption for station-keeping maneuvers for constellations of satellites. The method used to study this problem is based on the integral over the time of the undesired perturbing forces. This integral measures the change of velocity caused by the perturbation forces acting on the satellite, so mapping orbits that are less perturbed, which generates good candidates for orbits that requires low fuel consumption for station-keeping maneuvers. The integral over the time depends only on the orbit of the spacecraft and the dynamical system considered. The type of engine and the control technique applied to the spacecraft are not considered to search for those orbits. It can be a good strategy to be applied for a first mapping of orbits. For this search, it is analyzed the integral of orbits with different values of the Keplerian elements in order to find the best ones with respect to this criterion. The perturbations considered are the ones caused by the third body, which includes the Sun and the Moon, and the J₂ term of the geopotential. The results presented here show numerical simulations to obtain the integral of those perturbing forces for different orbits. The GPS and the Molniya constellations are used as examples for those calculations.     

Variations of the magnetopause position versus the level of geomagnetic activity (according to data of the INTERBALL-1 Satellite for 1995–1997)

The variations in the deviation of the observed position of the magnetosphere boundary from its mean position predicted by the Shue at al., 1997 (Sh97) model [7] are studied as a function of the substorm activity level (the AE-index value) and magnetic storm intensity (the value of the corrected D _st ^* index). The results obtained make it possible to state that the amplitude of motion of the magnetospheric boundary on the dayside and in the low-latitude tail is small. It is likely that the position of the boundary is either independent of the AE and D _st ^* indices or this dependence is weak. At the same time, the boundary of the high-latitude tail shifts inward on the average by 1.5R _E with an increase of the AE-index in the case of absence of magnetic storms (contraction of the magnetospheric tail). On the contrary, in the presence of magnetic storms, this boundary shifts outward by up to 3R _E with an increase of the AE-index (inflation of the magnetospheric tail). It is also shown that the boundary of the high-latitude tail moves outward with an increase of the D _st ^* index, both at low substorm activity and in periods of high substorm activity. The amplitude of the outward motion of the high-latitude tail of the magnetosphere is by a factor of two higher for moderate magnetic storms with strong substorms than for moderate magnetic storms with weak substorms.     

Empirical model of the high-latitude boundary of the Earth’s outer radiation belt at altitudes of up to 1000 km

An empirical model of the high-latitude boundary of the outer Earth’s radiation belt (ERB) has been presented, which is based on the measurement data of electron fluxes on the polar low-orbit CORONAS-Photon, Meteor-M1, and Meteor-M2 satellites. The boundary was determined by a sharp decrease to the background level of the flux of trapped electrons with energies of 100 or 200 keV in the polar part of the profile of the outer radiation belt. A numerical algorithm has been implemented to determine the time moment, when the fastest flux changes are recorded. The primary search was carried out, first, on 30 s averaged data, then repeated on data with a higher resolution. A functional dependence was obtained in order to approximate the obtained set of intersections of the boundary by elliptical curve. The empirical model constructed using the CORONAS-Photon measurement data in the epoch of anomalously low geomagnetic activity reflects the longitude structure of the high-latitude boundary of the outer radiation belt associated with the internal Earth’s magnetic field (MF), as well as its dependence on the universal time. Based on the data of intersections of the high-latitude boundary of the outer ERB (OERB) in the epoch of 2014–2016, the latitudinal shift of the boundary to the equator dependent on geomagnetic activity has been determined, as well as the nightside shift of the boundary due to the diurnal rotation of the Earth.     

Logiciel de restitution de trajectoire de satellite-application au cas de satellites d'observation

This paper presents an orbit determination program based on two algorithms: Kalman filtering and Rauch smoothing. Novel adaptation of these algorithms lets obtain a posteriori statistical estimations of evolution and measurement noises and of their standard deviation. Analysis of results about these noise estimations lets regulate optimally the a priori levels of noise standard deviations and detect eventually model errors. Such use is presented for Earth observation satellites, at first with simulated data, then with real data (TIROS N satellite).     

半开式离心泵叶顶间隙对泵性能稳定性的影响

为提高火箭发动机涡轮泵性能稳定性,应用边界层理论进行了半开式离心泵叶顶间隙流动特性研究,利用边界层动量积分方程对叶顶间隙内边界层厚度进行求解,并开展了不同叶顶间隙泵性能试验及流场数值模拟研究.结果表明,当叶顶间隙值等于间隙内边界层厚度值时,间隙泄漏涡不再增强,可获得稳定的泵性能;当叶顶间隙过大,会使泵容积效率降低,导致泵性能急剧下降.该理论方法可作为设计过程确定半开式离心泵叶顶间隙的重要参考.     

Numerical investigation on cavity structure of solid-fuel scramjet combustor

The influences of miscellaneous combustor structures for solid fuel scramjet combustion on the performance are investigated, including a detailed interaction analysis between shocks/waves and combustion. Hydroxyl-terminated polybutadiene is chosen as the solid fuel with the non-premixed equilibrium probability density function combustion model. The results show combustion enhancement when structure of combustor is modified. The radical emphasis is to examine the sensitivity of the properties due to variations on the length-to-depth ratio of cavity, aft wall angle, and offset ratio. It is noted that there is an appropriate structure of cavity (L/D=4, θ=45°, and D_d/D_u=1.25–1.5) regarding the combustion efficiency, total pressure loss and specific impulse. The observation of function for combustor components provides instructional insight into the design considerations for a combustor of a solid-fuel scramjet.     

非线性约束的大型旋转火箭瞬态响应模拟

以大长径比、旋转无控火箭为研究对象，探讨弹-架非线性约束系统的发射动力学响应。将火箭模拟为支承、变刚度柔性转子，发射装置则简化具有弹性约束的Euler-Bernoulli，二者通过非线性弹性元件相耦联。数值模拟发射过程中的火箭瞬态响应，分析了系统特性对火箭姿态的影响。     

Recent Advances in the Theoretical and Applied Study on Compressible Turbulent Flow over Aerospace Vehicles

This paper focused on the fundamental and applied research of turbulent flows encountered in the hypersonic flight of aerospace vehicles,which take place in the boundary layer and mixing layer.As to the plate boundary layer,LES approach has been used to simulate the flows over compression corners and incident shock waves,revealing that turbulent flows would significantly inhibit the boundary layer separation caused by shock wave-boundary layer interaction(SWBLI).The boundary layer transition over a circular cone has been analyzed through stability analysis and wind-tunnel test,by which the angle-of-attack effect in case of small angle of attack has been studied.Non-linear evolution process and secondary instability structure in the supersonic mixing layer(Mc=0.5) were initially figured out through the study of mixing layer,and knowledge of the flow control mechanism of the boundary layer and mixing enhancement mechanism of the mixing layer has been obtained through this research.Artificial boundary-layer transition technique based on subharmonic resonance has been proposed and applied to the flow control in a scramjet inlet,inhibiting the flow separation of the boundary layer while improving the inlet performance.To guarantee the mixing of kerosene and supersonic airflow in the scramjet combustor,the mixing enhancement method based on subharmonic resonance has been adopted and a concept of combustor with smooth wall and low internal drag has been proposed for ignition and stable combustion.Finally,future turbulence research and technological development of aerospace vehicles is predicted.     

Modeling the time behavior of the D st index during the main phase of magnetic storms generated by various types of solar wind

Results of modeling the time behavior of the D _st index at the main phase of 93 geomagnetic storms (?250 < D _st ≤ ?50 nT) caused by different types of solar wind (SW) streams: magnetic clouds (MC, 10 storms), corotating interaction regions (CIR, 31 storms), the compression region before interplanetary coronal ejections (Sheath before ICME, 21 storms), and “pistons” (Ejecta, 31 storms) are presented. The “Catalog of Large-Scale Solar Wind Phenomena during 1976–2000” (ftp://ftp.iki.rssi.ru/pub/omni/) created on the basis of the OMNI database was the initial data for the analysis. The main phase of magnetic storms is approximated by a linear dependence on the main parameters of the solar wind: integral electric field sumEy, dynamic pressure P _d , and fluctuation level sB in IMF. For all types of SW, the main phase of magnetic storms is better modeled by individual values of the approximation coefficients: the correlation coefficient is high and the standard deviation between the modeled and measured values of D _st is low. The accuracy of the model in question is higher for storms from MC and is lower by a factor of ～2 for the storms from other types of SW. The version of the model with the approximation coefficients averaged over SW type describes worse variations of the measured D _st index: the correlation coefficient is the lowest for the storms caused by MC and the highest for the Sheath- and CIR-induced storms. The model accuracy is the highest for the storms caused by Ejecta and, for the storms caused by Sheath, is a factor of ～1.42 lower. Addition of corrections for the prehistory of the development of the beginning of the main phase of the magnetic storm improves modeling parameters for all types of interplanetary sources of storms: the correlation coefficient varies within the range from r = 0.81 for the storms caused by Ejecta to r = 0.85 for the storms caused by Sheath. The highest accuracy is for the storms caused by MC. It is, by a factor of ～1.5, lower for the Sheath-induced storms.     

Field-aligned currents and magnetospheric generator in experiments on a laser-produced plasma flowing around a magnetic dipole

A laboratory experiment on modeling the magnetospheric generator of the field-aligned currents and the Earth’s transpolar potential in the absence of IMF is illustrated. The measurements of the total field-aligned current in the generator shorted mode and the transpolar potential in the circuit disconnection mode made it possible to determine the generator internal resistance. A model that explains the saturation current and internal resistance by the feedback between the field-aligned current and plasma flank motions has been proposed. This feedback is described through the effective resistance, which is proportional to the flow rate and the ratio of the boundary layer to the dimension of the magnetosphere. For the experimental conditions, the calculated generator resistance was in good agreement with the measured value. The estimates for the Earth’s magnetosphere indicate that the MHD generator internal resistance in the boundary layer is usually much lower than the reverse integral conductivity of the ionosphere.