Dust acoustic dressed solitons in a four component dusty plasma with nonthermal electron

Nonlinear dust acoustic dressed soliton are studied in a four component dusty plasma. Nonthermal distributions for electrons are considered. The Korteweg–de Vries (KdV) equation is derived by using reductive perturbation technique. A higher order inhomogeneous differential equation is obtained for the higher order correction. The expression for dressed soliton is obtained by the renormalization method. The expressions for higher order correction are determined using a series solution technique.     

超燃燃烧室等离子体点火和火焰稳定性能

为了研究热等离子点火器在超燃冲压发动机中的应用,在来流马赫数2.0工况下,针对乙烯和氢气两种燃料,进行了超燃环境中等离子体点火的试验和仿真研究.在来流总温1 500~1 950 K,燃料当量比0.1~0.55范围内对等离子点火器的点火和改善燃烧性能的性质进行了详细分析.结果显示:对于氢气和乙烯燃料,等离子体点火器使两种燃料的点火性能均得到明显改善,点火延迟时间大大缩短,燃料着火范围扩大、贫燃极限当量比降低.但未观察到其在加速掺混以及改善燃烧性能方面的明显作用.进行了与乙烯燃烧试验对应的数值仿真工作,选用了两种乙烯化学反应模型进行对比研究.仿真结果显示:8步9组分反应模型与试验结果符合较好,而3步6组分反应模型过高的估计了反应剧烈程度,燃烧室压力值偏高,压力起始上升位置偏向上游.所用的8步模型比3步模型更适合于超燃燃烧室中乙烯反应的模拟.     

端壁等离子体气动激励抑制高负荷压气机叶栅角区流动分离实验

为揭示端壁等离子体气动激励抑制高负荷压气机叶栅角区流动分离的影响规律和流场特征,在不同流场参数和激励条件下分别开展了微秒脉冲和纳秒脉冲等离子体气动激励抑制叶栅流动分离的实验研究.结果表明:端壁等离子体气动激励可以有效抑制叶栅角区的流动分离,其作用效果在攻角为3°时最佳,随攻角的增大逐渐下降;微秒脉冲激励的流动控制效果随来流速度的增大而降低,随激励电压和占空比的增大而提高,最佳非定常脉冲频率为500Hz;在较高来流速度下,微秒脉冲激励的作用效果十分微弱,但纳秒脉冲激励能够有效抑制角区流动分离;纳秒脉冲激励的流动控制效果随激励电压增大而提高,激励频率对控制效果至关重要,作用效果随激励频率的增大而不断增强,但当激励频率为5kHz时,作用效果有所下降.      

用于各向异性媒质的TLM算法

对一种用于各向异性媒质的全新时域数值方法（TLM算法）进行了研究。将Z变换引入TLM算法,用于处理各向异性媒质的电磁问题,推导递推计算公式。计算各向异性磁化等离子体层对电磁渡的反射系数和透射系数。计算结果与解析解吻合较好,表明该法用于各向异性媒质时有高效性和高精度性。     

等离子体气动激励抑制机翼失速分离的实验

进行了等离子体气动激励抑制机翼失速分离的风洞实验,研究了等离子体气动激励频率、电压、占空比和激励位置等对流动控制效果的影响.研究表明:在来流速度35m/s时,等离子体气动激励可以有效地抑制机翼大攻角下吸力面的流动分离,将机翼临界失速迎角由17°提高到19°;施加激励后,机翼最大升力系数提高了9.45%,阻力系数减小20.9%;激励频率在200Hz时,控制效果最好,对应的量纲一激励频率为1;迎角越大,流动分离越严重,需要更大的激励电压才能够有效抑制流动分离;最佳激励位置在流动分离起始点的前缘;在流动控制效果相当时,减小占空比可以降低能耗.      

纳秒脉冲等离子体气动激励数值仿真

从纳秒脉冲等离子体气动激励对流场的作用机理出发,将其对流场的作用等效为热源对流场的快速加热,建立了纳秒脉冲等离子体气动激励的空气动力学模型.应用模型计算了单次纳秒脉冲等离子体气动激励下静止流场的响应,计算结果表明:纳秒脉冲等离子体气动激励可在静止流场中形成一个高温升压升区(716K,225.95kPa)和一个低温升压升区(380K,131.7kPa),分别可诱导一强一弱两道压缩波,压缩波后各有一道稀疏波.压缩波与稀疏波同速向外传播,传播速度开始较大(大于400m/s),随着逐渐向外传播,其传播速度逐渐减小(357m/s).压缩波经过的区域可诱导局部速度,初期诱导的局部速度较大,在激励器切向和法向可诱导60m/s以上的局部速度,随着压缩波的衰减,诱导局部速度的能力减弱,最大可诱导10m/s左右的局部速度.      

Chaos and multifractals in the solar wind

By using the false-nearest-neighbours method, we have argued that the deterministic component of solar wind plasma dynamics should be low-dimensional. In fact, the results we have obtained using the method of topological embedding indicate that the behaviour of the solar wind can be approximately described by a low-dimensional chaotic attractor in the inertial manifold, which is a subspace of system phase space. We have also shown that the multifractal spectrum of the solar wind attractor is consistent with that for the multifractal measure of the self-similar generalized weighted Cantor set with two different scaling parameters and one probability measure parameter responsible for nonuniform compression in phase space and multifractality. The values of the parameters fitted also demonstrate that the complex solar wind system could only be weakly non-conservative (small dissipation) and quantify nonlinear dynamics; some parts of the attractor in phase space are visited much more frequently than other parts. In addition, to quantify the multifractality of space plasma intermittent turbulence, we consider that generalized Cantor set also in the context of scaling properties of solar wind turbulence. We investigate the resulting multifractal spectrum of a one-dimensional phenomenological model of turbulence cascade depending on its parameters, especially for asymmetric scaling. In particular, we have shown that intermittent pulses are stronger for the cascade model with two different scaling parameters. Even thought solar wind turbulence appears to be rather space filling, a better agreement with the data is obtained, especially for the negative index of generalized dimensions. Therefore we argue that there is a need to use a two-scale asymmetric cascade model. We hope that this generalized multifractal model will be a useful tool for analysis of intermittent turbulence in space plasmas. We thus believe that fractal analysis of chaotic systems could lead us to a deeper understanding of their nature, and maybe even to predict their seemingly unpredictable behaviour.     

基于唯象模型的等离子激励诱导流场数值模拟

通过在Navier-Stokes方程组中添加体积力源项的方法,模拟了二维不可压流中等离子体激励器对周围流场的诱导作用.计算结果表明等离子体激励器在其下游会产生一股贴近物面的壁面射流,该射流各截面的速度型、最大速度衰减、射流宽度增长等均与典型的层流射流(壁面射流或二维狭缝射流)一致,表明等离子体激励对周围中性流体的诱导是一种势流影响.最后通过积分得到了等离子体诱导壁面射流的吹气系数,通过与传统吹气流动控制技术比较,指出目前等离子体激励产生的壁面射流吹气系数较小,仅适用于低速条件下的流动控制.     

活性粒子对H_2/Air混合物燃烧的影响

建立H2/Air混合物燃烧的化学动力学模型,计算与分析了在非平衡等离子体条件下,气体放电产生的活性粒子(O,H)和活性基(OH)在不同当量比下对参与燃烧的组分以及温度和压力的影响,为航空发动机燃烧室等离子体助燃(PAC)实验研究和实际应用提供理论依据.计算结果表明等离子体助燃可以提高反应效率、燃烧温度和火焰传播速率,减少燃烧上升时间,强烈影响H2/Air混合物燃烧.     

Experimental Investigation into Characteristics of Plasma Aerodynamic Actuation Generated by Dielectric Barrier Discharge

This article carries out synthetic measurements and analysis of the characteristics of the asymmetric surface dielectric barrier discharge plasma aerodynamic actuation.The rotational and vibrational temperatures of an N2 (C3Пu) molecule are measured in terms of the optical emission spectra from the N2 second positive system.A simplified collision-radiation model for N2(C) and N2+(B) is established on the basis of the ratio of emission intensity at 391.4 nm to that at 380.5 nm and the ratio of emission intensity at 371.1 nm to that at 380.5 nm for calculating temporal and spatial averaged electron temperatures and densities.Under one atmosphere pressure,the electron temperature and density are on the order of 1.6 eV and 1011cm-3 respectively.The body force induced by the plasma aerodynamic actuation is on the order of tens of mN while the induced flow velocity is around 1.3m/s.Starting vortex is firstly induced by the actuation;then it develops into a near-wall jet,about 70 mm downstream of the actuator.Unsteady plasma aerodynamic actuation might stimulate more vortexes in the flow field.The induced flow direction by nanosecond discharge plasma aerodynamic actuation is not parallel,but vertical to the dielectric layer surface.