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1.
The trajectories and decay of the maximum velocity for turbulent jets in a cross flow were simulated by means of the κ — ? two-equation turbulence model in which differential equations were solved for the kinetic energy of turbulence and for the rate of its dissipation. The solution procedure employed an elliptic finite-difference scheme with the three velocity components and the pressure as the main dependent variables. The essential properties of the jet were discussed in the case of different ratios of the rectangular orifice length to the width H/B, ratios of the jet injected velocity to the main stream velocity R; and different injection angles α. The numerical prediction results were presented in the form of equivalent diameter. Lastly, two correlation equations were obtained and the numerical predictions are shown to agree well with the experimental data. 相似文献
2.
射流泵湍流场的数值模拟与实验研究 总被引:12,自引:2,他引:12
采用k-ε湍流模型和非等间距加密网格,对射流泵流场进行了数值模拟和分析,并对相应的流场进行了实验研究.结果表明,流场轴向速度剖面在扩散管段具有较好的自相似性,而在喉管段则不然;这种速度剖面变化的转折点与喉管的长度有关;流场的湍动能分别在喷嘴出口与扩散管入口处产生峰值,并且前者远大于后者,可见射流泵流场中,湍流主要发生在喉管入口处,湍动能的不平衡将导致额外的能量损失.本研究结果对工程应用有指导意义. 相似文献
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In this paper, we present an analytical and experimental study of the mixing region and jet shape in concentric mixers. Based on a simple but effective analytical model, we are able to predict the growth of the mixing region with respect to downstream distance. An experimental study is conducted on the concentric mixing of paper fibre stock and water. By comparing with experimental results, we confirm that the shape of the mixing region is a practical indicator of mixing efficiency with the consideration of jet velocity and geometry including the nozzle wall thickness. 相似文献
4.
采用RNG k-ε湍流模型对实验室级射流循环DTB蒸发结晶器内的单相流流场进行了数值模拟并优化结晶器结构,用欧拉多相流模型对优化的结晶器进行多相流模拟分析。结果表明,导流筒内射流满足线性扩展,其轴向速度分布基本满足高斯分布。刚进入导流筒内的射流段,轴线速度倒数与流程呈良好的线性关系,随射流的发展,轴线速度加速衰减。在入口直径恒定时,循环速率比随导流筒挡板间环隙面积与导流筒横截面积比的增加呈先增大再减小的趋势,存在最优值。优化的实验级DTB结晶器中导流筒内颗粒浓度分布沿径向方向减小,但基本可实现颗粒浓度较为均匀的分布,其循环速率与单相流模拟结果相比较低。 相似文献
5.
穿流式搅拌桨桨叶上的开孔所引起的射流对于提高搅拌效率、降低搅拌能耗起着重要的作用。采用模拟实验方法,研究了全混状态下喷孔出口流速、孔径和孔长对水射流半扩展角β和源点xp/D的影响。研究结果表明:喷孔孔径、孔长以及喷孔前流体的湍动程度对射流发展有很大影响,存在一临界喷孔长径比(H/D)0,1.31 (H/D)0 1.67。当H/D≤(H/D)0时,β随速度(或Re)增加而增大,xp/D随Re增加变化很小;当(H/D)>(H/D)0时,β随速度(或Re)增加而减小,xp/D随Re增加而减小。为了获得较好的混合效果,搅拌桨桨叶上的开孔所引起的射流应有尽量大的扩展效果,因此桨叶上开孔的长径比应小于(H/D)0。 相似文献
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A numerical treatment for determining the particle velocity and the trajectories in a two-phase flow is described herein and this new fluctuation-spectrum-random-trajectory (FSRT) model is proposed to account for the turbulent diffusion of particles. It is predicted for the flow of a turbulent axisymmetric gaseous jet laden with spherical solid particles of nonuniform size. The particle velocity and the concentration field are obtained by the revised volume average method. The predictions are compared with experiment. 相似文献
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利用实验方法探讨旋转圆柱体受狭槽式空气喷流的换热特性,圆柱体的高度与直径为定值,变动参数为(1)喷流Reynolds数(Rej)、(2)旋转Reynolds数(Rer)、(3)圆柱体直径(D)与喷嘴宽度(w)的比例(D/w)、(4)相对喷流冲击距离 (L/w,L为喷嘴距圆柱体的最近距离)等。实验结果显示平均Nusselt数(Nu)随Rej与Rer增大而提升,而D/w增加会使Nu减小,且D/w对Nu的影响将随L/w增大而衰退,且存在一临界L/w值能产生最高的Nu,且临界L/w值将随D/w增大而增大,最后,提出合理而准确的经验公式。 相似文献
9.
An exact similarity solution of the Navier‐Stokes equations is obtained. The solution represents steady axisymmetric stagnation‐point flow towards a stretching surface. It is shown that the flow displays a boundary‐layer structure when the stretching velocity of the surface is less than the free stream velocity. On the other hand, an inverted boundary layer is formed when the surface stretching velocity exceeds the free stream velocity. Temperature distribution in the flow is found when the surface is held at a constant temperature. It turns out that when the surface temperature exceeds the ambient temperature, heat flows from the surface to the fluid near the stagnation point but further away from the stagnation point, heat flows from the fluid to the stretching surface. 相似文献
10.
利用盘管组来加热融化浮顶油罐内含蜡原油是油罐加热融化的主要方式之一。而优化盘管组的布置方式对提高罐内含蜡原油的融化效率、降低生产成本具有重要的意义。基于此,在考虑含蜡原油融化过程中形态和流变性变化的基础上,建立了盘管组加热的浮顶油罐内含蜡原油湍流融化物理数学模型。考虑到罐顶空气层、钢板层、保温层的规则性以及罐内含蜡原油区域的非规则性,利用浸入边界法在结构化网格上处理罐内含蜡原油与盘管组之间的耦合问题。利用文献结果对模型进行验证。以实际1000 m3浮顶油罐为例,对罐内含蜡原油的融化规律进行研究,并对倾角对融化过程的影响进行分析。 相似文献
11.
The effect of flow oscillation to the mass transfer between turbulent fluid and solid wall was investigatedby measuring the mass transfer rate between fluid and pipe wall with imposed oscillating flow usingelectrochemical method.The velocity and concentration field in the viscous sublayer which controls the mass trans-fer in such a process was simulated by a simple wave model of single harmonics.Experimental results confirmthat the flow oscillation has no influene on time averaged mass transfer rate,but the phase difference betweenphase averaged velocity field and concentration field shifts with the frequency of imposed oscillating flow.Numeri-cal analysis reveals that the concentration boundarylayer which is responsible for the mass transfer is muchthinner than the viscous sublayer which greatly weakens the influence of imposed oscillating flow on mass transfer. 相似文献
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文章综述了水处理中絮凝动力学方面的研究进展。在分析絮凝机理基础上,分别回顾了异向絮凝动力学、差速沉降絮凝动力学和同向絮凝动力学的研究历程,从絮凝机理的认识过程到模拟模型的发展,详细介绍了模型的应用情况,并揭示了尚未解决的关键问题。 相似文献
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循环射流混合槽(CJT)作为一种过程强化设备可以提高湍流的混合效率及反应选择性。为进一步提高其工业应用价值,对循环射流混合槽流场的传热能力进行分析并对其射流层数进行结构优化。在恒壁温的条件下,采用SST k-ω模型分析循环射流混合槽流场区域的非稳态流动传热特性。在充分湍流状态下研究了Re=3260~16 303,射流层数M=5~9对循环射流混合槽壁面对流传热特性及流场传热特性的影响。结果表明,M=9时对流换热系数的变异系数Ch随Re增加而减少,壁面传热均匀性提高2.8%~19.3%;流场与温度场协同性随Re增加而增加,Re=16 303时的协同角为75.5o比Re=3260时减小约0.5°。Re=9782时Ch随M增加而降低,壁面传热均匀性提高2.7%~16.3%;速度矢量与温度梯度协同性随M增加而减小,M=9时全局协同性相较于M=5时降低了6.1%。当M=7时中心混合区与射流混合区的场协同角均在73°~74°之间,两区域流场间热量传递能力匹配程度较好;当M<7时中心混合区的协同性优于射流混合区,当M>7时射流混合区协同性优于中心混合区。研究Re及射流层数M对循环射流混合槽热量吸收和传递性能的影响,发现Re的变化对循环射流混合槽吸热量的影响大于射流层数M的变化。 相似文献
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炭基体结构状态对C/C复合材料抗烧蚀性能的影响 总被引:12,自引:2,他引:12
碳基体在C/C复合材料的组成中占有很大的比重,因此炭基体不同的结构状态往往对C/C复合材料的各项性能有显著的影响。本文利用不同的原料和加工工艺制备出了三种具有不同炭基体的C/C复合材料,这三种碳基体分别是热解炭,沥青炭以及解热炭-树脂炭混合炭基体。对这三种材料多项性能的测试结果表明,炭基体的结构状态如石墨化度,炭片层结构的取向度的不同对C/C复合材料的各项性能均有显著的影响;基本趋势是C/C材料的石墨化度越高,材料的导电性能,导热性能以及抗烧蚀性能越好,压缩强度越低。三种炭基体中沥青炭基体沿纤维轴向的取向度最低,其抗烧蚀性能最差。 相似文献
16.
M. Kataoka 《Drying Technology》1985,3(2):235-254
The optimal nozzle-to-plate spacing is experimentally studied for the case when a free jet of high temperature gas impinges normally on a large flat plate. The stagnation-point heat transfer becomes maximal when the flat plate is placed at the end of the potential core region. A generalized model is proposed which permits prediction of the optimal nozzle-to-plate spacing and stagnation-point heat flux over a wide range of the initial density ratio. 相似文献
17.
射流混合器内气体湍流扩散过程的CFD数值模拟与实验研究 总被引:1,自引:0,他引:1
利用计算流体动力学CFD(Computational Fluid Dynamics)商业软件CFX4.4对二氧化碳与空气的射流混合过程进行数值模拟. 湍流模型采用标准k-e模型和RNG模型,模拟预测不同断面上的CO2浓度分布,并与实验结果进行比较. 结果表明,模拟预测值与实验结果基本吻合,也验证了CFD技术应用于混合扩散过程预测分析的可靠性;靠近空气一侧的CO2浓度普遍高于另一侧,当CO2平均浓度为6%时,距射流出口100 mm剖面上的浓度极差达到6%. 本研究中的气体混合湍流模型影响不明显. 采用标准k-e模型分别对两种进气方式的射流混合器内部速度场、浓度场进行模拟分析,发现T型射流混合器的混合均匀性比单边进气的射流混合器明显提高. 相似文献
18.
An alternative correlation for the flow of purely viscous non-Newtonian fluids in ducts of arbitrary cross-section is proposed. It involves two dimensionless groups which are Unique relationships exist between ? and Re*G for both laminar and turbulent flows which enable direct predictions of pressure drop from flow rate results or vice-versa. Excellent agreement between the new correlations and available experimental data for purely viscous non-Newtonian fluids flowing in circular tubes and square ducts is demonstrated. 相似文献
19.
本文提出了计算流体在水力学光滑管与粗糙管内湍流流动时摩擦系数的两个显式方程,并且将此两式与Colebrook式(4)、Churchill式(13)和其他人提出的式(11)、(12)、(14)、(16)、(15)进行比较,同时都以Murin's的实测数据进行检验,结果表明本文提出的两个公式简便易用,具有足够的准确度。 相似文献
20.
A new method based on the Coanda effect for self oscillation of a circular jet bounded by rectangular enclosure is suggested. The experiments in both air and water reveal regions of stable oscillation wherein relationships are obtained between the Strouhal number and the shape factor of the channel. This oscillation method can also be used to mix different liquids in a vessel. For such applications, an improvement of mixing by oscillation is shown by means of a residual concentration diagram for a salt solution. 相似文献