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321.
Numerical Simulation of Unsteady Flow Around Forward Flight Helicopter with Coaxial Rotors 总被引:4,自引:2,他引:2
XU Heyong YE Zhengyin National Key Laboratory of Science Technology on Aerodynamic Design Research Northwestern Polytechnical University Xi’an China 《中国航空学报》2011,24(1):1-7
Three-dimensional unsteady Euler equations are numerically solved to simulate the unsteady flows around forward flight helicopter with coaxial rotors based on unstructured dynamic overset grids. The performances of the two coaxial rotors both become worse because of the aerodynamic interaction between them, and the influence of the top rotor on the bottom rotor is greater than that of the bottom rotor on the top rotor. The downwash velocity at the bottom rotor plane is much larger than that at the top rotor plane, and the downwash velocity at the top rotor plane is a little larger than that at an individual rotor plane. The downwash velocity and thrust coefficient both become larger when the collective angle of blades is added. When the spacing between the two coaxial rotors increases, the thrust coefficient of the top rotor increases, but the total thrust coefficient reduces a little, because the decrease of the bottom rotor thrust coefficient is larger than the increase of the top rotor thrust coefficient. 相似文献
322.
Energisation of O+ and O+
2 Ions at Mars: An Analysis of a 3-D Quasi-Neutral Hybrid Model Simulation
E. Kallio A. Fedorov S. Barabash P. Janhunen H. Koskinen W. Schmidt R. Lundin H. Gunell M. Holmström Y. Futaana M. Yamauchi A. Grigoriev J. D. Winningham R. Frahm J. R. Sharber 《Space Science Reviews》2006,126(1-4):39-62
We have studied the loss of O+ and O+
2 ions at Mars with a numerical model. In our quasi-neutral hybrid model ions (H+, He++, O+, O+
2) are treated as particles while electrons form a massless charge-neutralising fluid. The employed model version does not
include the Martian magnetic field resulting from the crustal magnetic anomalies. In this study we focus the Martian nightside
where the ASPERA instrument on the Phobos-2 spacecraft and recently the ASPERA-3 instruments on the Mars Express spacecraft
have measured the proprieties of escaping atomic and molecular ions, in particular O+ and O+
2 ions. We study the ion velocity distribution and how the escaping planetary ions are distributed in the tail. We also create
similar types of energy-spectrograms from the simulation as were obtained from ASPERA-3 ion measurements. We found that the
properties of the simulated escaping planetary ions have many qualitative and quantitative similarities with the observations
made by ASPERA instruments. The general agreement with the observations suggest that acceleration of the planetary ions by
the convective electric field associated with the flowing plasma is the key acceleration mechanism for the escaping ions observed
at Mars. 相似文献
323.
本文讨论磁流体中间激波的相互作用规律.主要结论:中间激波汇合的产物为后向快简单波、后向慢简单波或慢激波、接触间断、前向慢激波和前向快激波,其中后向波成份和接触间断很弱.当左(右)激波较强时,中国激波碰撞产物为后(前)向快激波、后(前)向慢简单波或慢激波、负(正)切向间断、前(后)向慢简单波和前(后)向快激波. 相似文献
324.
导弹侧向喷流气动干扰受海拔高度影响显著,主要原因在于雷诺数和压力比会随海拔高度的变化而变化。受大气参数的影响,雷诺数和压力比的变化规律并不一致。为能在现有气动模型基础上既保证插值精度又减少节点数,通过数值模拟方法研究了雷诺数和压力比对轨控喷流气动干扰的影响。结果表明:海拔高度对喷流气动干扰的影响主要由压力比变化造成,雷诺数变化产生的影响相对较小,且喷流干扰与压力比间存在一定的线性关系。因此,提出了一种基于压力比的喷流气动干扰插值方法。相比于传统的基于高度的插值方法,该方法可显著提高插值精度,并减少节点数,适用于全空域轨控喷流气动建模。 相似文献
325.
简述了蜡纸存贮法在高超声速脉冲风洞锥—舵干扰流场显示中的应用,给出了迎风面内舵周围干扰区立体和平面展开两种油流谱图,揭示了其三维干扰流动的特征。 相似文献
326.
D. A. Brain 《Space Science Reviews》2006,126(1-4):77-112
The solar wind at Mars interacts with the extended atmosphere and small-scale crustal magnetic fields. This interaction shares
elements with a variety of solar system bodies, and has direct bearing on studies of the long-term evolution of the Martian
atmosphere, the structure of the upper atmosphere, and fundamental plasma processes. The magnetometer (MAG) and electron reflectometer
(ER) on Mars Global Surveyor (MGS) continue to make many contributions toward understanding the plasma environment, thanks
in large part to a spacecraft orbit that had low periapsis, had good coverage of the interaction region, and has been long-lived
in its mapping orbit. The crustal magnetic fields discovered using MGS data perturb plasma boundaries on timescales associated
with Mars' rotation and enable a complex magnetic field topology near the planet. Every portion of the plasma environment
has been sampled by MGS, confirming previous measurements and making new discoveries in each region. The entire system is
highly variable, and responds to changes in solar EUV flux, upstream pressure, IMF direction, and the orientation of Mars
with respect to the Sun and solar wind flow. New insights from MGS should come from future analysis of new and existing data,
as well as multi-spacecraft observations. 相似文献
327.
We discuss quasi-static and dynamic models of the magnetotail response to perturbations imposed by the solar wind, focusing
particularly on the formation of thin current sheets, their structure and breakup. 相似文献
328.
增强现实系统中,不同标识上虚拟物体交互行为比较单一,且大多根据标识问的距离控制交互,当系统中标识增多时,系统的运行效率将大大降低。本文将虚拟现实中的感知技术引入到系统中,为虚拟物体建立了一种基于空间距离的感知模型,将标识间的距离分级,虚拟物体对处于自己感知域内不同距离级别上的其它虚拟物体采取不同的交互行为。实验结果表明,该方法可以丰富虚拟物体的交互行为,同时满足系统实时性需求。 相似文献
329.
遵循静气弹问题中气动/结构网格之间的数据传递要求,引入了基于径向基函数的流固耦合界面数据传递方法,确定了紧支半径的选取原则,并编制相应的计算程序。以M6机翼为例,将不同径向基函数的插值精度及计算效率进行比较,结果表明体样条(Volume Spline)函数和C2函数具有良好的插值精度和计算效率。这两种流固耦合界面数据传递方法非常适用于工程应用。 相似文献
330.