Study of the Aerodynamic Characteristics of Chevron Nozzles on the Basis of a Numerical Calculation of the Flowfield

The flow in a convergent nozzle equipped with chevrons and the flow around the chevrons are numerically simulated and studied on the basis of the numerical integration of the system of Reynolds equations closed by a differential model for the turbulent viscosity. From the calculated results, the flow pattern, the action of the chevrons on the flow, the circulation generated, and the values of the parameters characterizing the streamwise vorticity are determined. The results of calculations of the thrust and flow-rate characteristics of nozzles equipped with chevrons are presented. The data for chevron and conical nozzles are compared.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 76–88.Original Russian Text Copyright © 2005 by Brailko and Krasheninnikov.     

低功率电弧加热发动机喷管扩张段内壁面温度测量

采用滤光成像,摒弃电弧及羽流干扰,实验获得了采用纯氮、纯氢以及氢-氮混合气为推进剂时,低功率电弧加热发动机喷管内壁面的热辐射强度分布。通过辐射强度-温度标定以及图像分析,导出了相应的温度分布。实验结果表明,喷管扩张段内壁面温度最高处位于喉道出口附近。采用不同推进剂时,喷管内壁面温度分布情况有显著区别。     

时间分辨原子发射光谱诊断脉冲放电气体束等离子体

建成了一套脉冲放电气体束和原子发射光谱等离子体诊断实验装置,利用这套实验装置测量了不同放电条件下等离子体的时间分辨发射光谱,并采用玻尔兹曼作图法和Hα谱线斯塔克展宽法研究了等离子体的原子温度、离子温度和自由电子密度等参数的演化。实验结果表明,脉冲放电的总电量对等离子体参数的演化有较大影响;脉冲放电气体束等离子体中的离子温度远高于原子温度,自由电子密度相对较低,等离子体处于非局域热平衡状态。A special designed pulsed discharge nozzle (PDN) ion source and a plasma diagnostics system based on the atomic emission spectroscopy were constructed. The time-resolved emission spectra of Argon atoms and ions in the region of 300-800 nm were observed and analyzed. The plasma temperatures, including atomic and ionic temperatures, were simulated by Boltzmann plot method, and the free electron density was simulated through the Stark broadening of Hα line. The evolution of these plasma parameters were investigated by high-resolution time-resolved emission spectra. The results show that the total energy struck on the pulsed gas beam is the most important factor which determines the plasma properties and its evolution. The plasma in PDN is concluded into non-local thermodynamic equilibrium (non-LTE) during the evaluation because of the low electron density and the big difference between the temperatures of Argon atoms and ions in all discharge conditions.     

IR signature study of aircraft engine for variation in nozzle exit area

In general, jet engines operate with choked nozzle during take-off, climb and cruise, whereas unchoking occurs while landing and taxiing (when engine is not running at full power). Appropriate thrust in an aircraft in all stages of the flight, i.e., take-off, climb, cruise, descent and landing is achieved through variation in the nozzle exit area. This paper describes the effect on thrust and IR radiance of a turbojet engine due to variation in the exit area of a just choked converging nozzle (M_e = 1). The variations in the nozzle exit area result in either choking or unchoking of a just choked converging nozzle. Results for the change in nozzle exit area are analyzed in terms of thrust, mass flow rate and specific fuel consumption. The solid angle subtended (Ω) by the exhaust system is estimated analytically, for the variation in nozzle exit area (A_ne), as it affects the visibility of the hot engine parts from the rear aspect. For constant design point thrust, IR radiance is studied from the boresight (ϕ = 0°, directly from the rear side) for various percentage changes in nozzle exit area (%ΔA_ne), in the 1.9–2.9 μm and 3–5 μm bands.     

高马赫数高压力的氧碘化学激光器阵列喷管的数值模拟

 采用计算流体力学方法,研究了以氮气为载气的新型高总压氧碘化学激光器(COIL)阵列喷管。模拟结果表明:采用高马赫数的氮气流引射低马赫数的氧气流,可以提高光腔出口的驻点压力;高超声速的氮气与声速的氧气混合较慢,在喷管出口安装翼片有利于增强气流混合;喷管出口安装大翼片,翼片诱导的横向涡可以到达氮喷管的中心,光腔内混合比较充分。通过采用10组分21反应的化学反应模型,模拟了阵列喷管内多组分气体的混合和化学反应过程。模拟结果表明：光腔内生成了激发态碘原子和基态碘原子,光腔中获得了正增益,而且光腔出口的总压也由2.6 kPa提升至28.9 kPa。     

气体凝聚团簇源中团簇形成的DSMC研究

利用直接模拟蒙特卡洛方法(DSMC) ,模拟了气体凝聚团簇源的引出口尺寸和中心位置不同的条件下,Cu团簇的尺寸分布以及模拟了随着时间的增长,腔内团簇数目的变化.模拟结果表明:引出口的直径越大,产生大团簇的比例越小;在引出口的直径相同的情况下,引出口的中心位置偏离坐标原点比在原点产生的大团簇的比例要大;随着时间的增长,腔内团簇数目先变多后变少.     

旋转射流冷却数值模拟研究

使用 ANSYS FLUENT 软件和 RNG k-ε 湍流模型分别研究了十字形、内十字形和花形结构的螺旋喷 嘴内部流动特性和耦合面换热特性。模拟结果研究表明,螺旋角 θ 越小喷嘴出口速度越高,喷出的水流更集中, 水流运动轨迹越清晰且规律越明显。同一工况下,θ=30°的花形喷嘴的换热效率和换热均匀性均优于其余两种喷嘴的值;耦合面努塞尔数 Nu 最大值会随着雷诺数 Re 不断增加而逐渐远离射流中心处(r/d_j=0,d_j 为喷嘴当量直径); 随着靶距 H 逐渐增大,Nu 逐渐减小,旋流效果逐渐减弱。当 H=2d_j、4d_j 时,Nu 最大值位于 r/d_j=1 处;当 H=6d_j 时,Nu 最大值位于射流中心处。     

Electrospinning Instabilities in the Drop Formation and Multi-Jet Ejection Part II: Various Nozzle Diameters for PVA (Polyvinyl Alcohol) Polymer Solution

Electrospinning is recognized as a simple and easy method to produce fibers with nanoscale diameters. However, the methods for controlling the shape, structure, and uniformity of electrospun fibers have not yet been fully investigated. In this research, the electrospinning jet behavior, corresponding nanofiber deposition, and average fiber diameter are examined for various nozzle diameters. Fluctuations in the sequence of drop growing, electrospinning, and/or termination of electrospinning are analyzed. We propose two different fluctuations according to nozzle diameter. The multi-jet ejections, that are closely related to the amount of nanoweb deposition and the deposition pattern, are explored.     

展向喷嘴湍流横向射流大涡模拟及其统计分析

采用大涡模拟方法数值模拟了展向椭圆喷嘴的湍流横向射流,对其大尺度结构的时空演化和湍流脉动速度场的时间序列分析、频谱分析、PDF分析以及时、空截面上的统计平均特性进行分析.结果表明,在射流出口附近的下游核心区中速度脉动剧烈,显现出明显的湍流特征.除了三维涡环脱落、扭曲、变形、摆动所对应频率之外,还存在很宽的湍流基频,它与在喷嘴出口附近产生的三维涡环的时空演化过程密切相关.由于展向椭圆喷嘴的湍流横向射流中的三维涡环快速脱落和强相互作用导致射流尾迹中的强湍流脉动,展向椭圆喷嘴湍流横向射流的PDF空间演化特征结构复杂.在射流核心区的湍流偏应力变化平缓,其统计平均值分布接近左右对称.展向椭圆喷嘴的湍流横向射流脉动速度场具有极为复杂的统计行为,与流向椭圆喷嘴相比具有更好的掺混能力.     

Effects of the gas phase molecular weight and bubble size on effervescent atomization

The effervescent atomization from an industrial Coker feed nozzle is compared for two different gas densities (air and mixed gas of 81.4 vol.% helium/18.6 vol.% nitrogen) at equivalent operating temperatures. The application is to observe the similarity of lab tests using air at 20 °C to the industrial process using steam at 300-400 °C. The effects of operating conditions, such as gas to liquid mass ratio, mixing pressure and void fraction on the flow regime, bubble size, and droplet size distribution were also examined in this study. The experiments were performed using mixtures of water with air or mixed gas, which resulted in gas to liquid mass ratios ranging from 1% to 4%.Stroboscopic back scattered imagery (SBSI) indicates that the average bubble size inside the nozzle conduit is similar when air and water are used as the process fluids, when compared to the case when mixed gas and water are used as the process fluids. Under similar conditions, the Phase Doppler Particle Anemometer (PDPA) data indicate that the droplet size in the spray is similar when using either mixed gas or air as the atomization gas.Experimental results obtained by high-speed video shadowgraphy (HSVS) indicate that the flow pattern inside the nozzle feeding conduit was slug flow with a tendency to attain annular flow with increased air to liquid mass ratios. Thus, from the experimental results it is evident that the smaller molecular weight of the mixed gas versus air (8.4 versus 29) does not significantly reduce the bubble (<±10% difference) and droplet size (<±1.5% difference), indicating a weak dependence of the gas phase density on two-phase atomization. This confirms that laboratory experiments on effervescent nozzles using air have reliable similarity to systems that use high temperature steam for the gas phase.