DNS of the turbulence modulation by dispersed particles in compressible spatially developing two-phase jets

Particleladenturbulentjetsareusuallyfoundinmanyengineeringapplications,suchasjetpropulsion,spraycombustion,andpulverizedcoalcombustion.Inmanyoftheseapplications,thedispersionoftheparticlesbecomesacontrollingfactorintheefficiencyandstabilityoftheprocess.Hence,theabilitytopredictandcontroltheparticledispersioninjetsisofsignificancetoimprovedesigningleveloftheindustrialequipmentandobtainefficientapplications.Thesinglephaseturbulentjetshavebeenwidelystudiedbymanyexperimentaltechnologiesandnumerica…     

轴对称等离子体射流的实验研究

等离子体射流具有广泛的应用前景。建立了轴对称等离子体射流的模型,得出层流状态下等离子体射流的长度与流量成正比。采用Ne、He、Ar在大气压下用介质阻挡放电的手段得到了等离子体射流,发现层流状态下等离子体射流长度与模型结论一致,但是随着激励电压的升高和气体流量的增大,等离子体射流会发生从辉光放电到丝状放电、从层流到湍流的转捩,射流长度会先增大后减小;工作气体的不同对等离子体射流的性质也有重要影响。     

蒸发粘性液体射流不稳定性理论分析

通过线性不稳定性理论,对蒸发粘性液体射流稳定性理论问题进行了研究,分析了小扰动随时间的发展情况,讨论了可解性条件,求出了解的特征方程式。     

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在不同泵压和淹没压力每件下,针对不同类型的空化喷嘴对高压空化水射流破碎岩石效果进行了一系列实验研究,其主要目的是探讨高压空化水射流的冲蚀能力与水力参数的相互关系,提高破岩效率。结果表明：射流的驱动泵压与冲蚀深度成正比;围压增加将使冲蚀深度降低;水射流存在一个最佳靶距;冲蚀时间具有区域性,冲蚀深度最终将趋于稳定,增加不明显;收敛型喷嘴的冲蚀深度远小于缩放型喷嘴的冲蚀深度．     

波流环境下双孔浮射流运动特性

利用粒子图像测速技术(PIV)对波流环境下双孔浮射流的速度场进行测量,对不同组次的相位平均速度场、时均速度场进行定性描述;通过引入考虑横流、波浪、浮力影响的综合特征长度l_(mb),给出了轴线垂向速度衰减过程分区的定量结果。研究表明,波流作用下会产生污染物云团现象,加快双孔射流速度衰减;波浪的作用能够减弱孔间相互影响;浮力的作用能够减小射流体偏转角度和侧向展宽;无量纲的轴线垂向速度变化可以分为近区(z/l_(mb)3)、过渡区(3z/l_(mb)6)、远区(z/l_(mb)6)3个区段。     

实验室研究HH天体喷流进展介绍

实验室天体物理是一门利用实验室环境来模拟、研究天体物理现象的新兴学科.天体物理中的喷流现象, 尤其是Herbig-Haro天体, 一直是实验室天体物理的研究热点. 通过不同的实验方法, 如激波挤压、Z箍缩装置和激光驱动等方式制造喷流, 研究者对于实验室天体物理中的喷流现象的认识在不断深入.本文对这些研究进行简要介绍, 并对未来的研究进行一些展望.      

高压水射流切割装置和切割试验研究

高压水射流切割是一项正在发展中的新技术,由于它具有许多其它切割技术所不能比拟的优点,因此日益受到人们的注意和重视。本文介绍了高压水射流切割的装置和对非金属板材切割试验的情况,得到了射流压力、喷嘴口径、靶距、进给速度与切割深度之间的关系,探讨了高分子聚合物对射流性能的影响。此外,还介绍了对板材进行复杂形状的切割等。     

DNS of the turbulence modulation by dispersed particles in compressible spatially developing two-phase jets

A new two-way coupled direct numerical simulation (DNS) method is developed to study the turbulence modulation in the compressible and spatial developing particle-laden turbulent jets with higher Reynolds number. The high-resolution solver is performed for the gas phase flow-field and the Lagrangian method is used to trace particles. It is found that the particles with Stokes number of 0.01and 50 advance the evolution of the coherent structures in the flow-field, but the particles with Stokes number of 1 delay it. All particles increase the turbulent kinetic energy and decrease the vorticity thickness, in which the particles with the Stokes number of 1 exhibit the maximum modulation. The jet velocity half-width and the decay of the streamwise mean velocity along the centerline are reduced by particles with Stokes number of 0.01 and 1. The momentum thickness is increased by particles and the larger the Stokes number is, the larger the momentum thickness is.     

Direct numerical simulation of a particle-laden weak-shearing plane jet

Direct numerical simulation (DNS) has been utilized to solve numerically a two-dimensional compressible weak-shearing plane jet, in which the jet exit velocity and the co-flow velocity are in the same magnitude (2∶1 in this paper). We also use the one-way coupling method to simulate the dispersion behaviors of solid particles in various representative sizes, i.e. St=0.01, 1, 10, 100, where St is the Stokes number. We get a vorticity field with fully varicose (symmetrical) modes and the entire precise processes of the rolling-up of one spanwise vortex, the pairing of two vortexes and the mixing of three vortexes. The mean longitudinal velocity (U) profile compares well against the experimental results. The Reynolds stress profile looks special due to the symmetrical vorticity field. The particles whose St=0.01 reproduce the vortex structures in detail, and the ones of St=1 exhibit interesting self-organized behaviors and possess the most non-uniform concentration field. They disperse uniformly around the single and pairing vortex kernels, while a few of them are arranged almost in a straight line in the center region of the paring vortexes, which is caused by the contribution of the border of two vortexes in the pairing process. St=10 and 100 can be treated as large particles, on which the flow field has few impacts.     

淬火新工艺中的平行射流

本文介绍平行射流组在喷射气雾完成淬火时的流场速度分布和浓度分布的计算方法.在孤立平面紊流射流理论基础上,研究并提出了在工业上应用平行平面紊流湮没射流的设计计算方法.给出了实测结果,与理论计算及前人实验结果对照吻合很好.经生产实践检验,采用该方法后取得了显著的经济、环境效益.