共查询到20条相似文献,搜索用时 187 毫秒
1.
2.
提出了适用于高速流场气动光学数值模拟的RANS/DSMC混合算法.通过RANS对全局时均流场进行数值模拟,再对其中局部流场的脉动量采用DSMC进行数值模拟,以Maxwellian速度分布实现RANS宏观量信息向DSMC微观量信息的传递.采用超声速环境下尖劈模型对该混合算法进行校验,对比试验结果论证了算法的正确性.在计算... 相似文献
3.
在雷诺数Re=200的情况,利用Maxwell方程直接数值计算表面包覆电极与磁极圆柱体产生的电磁力分布,将其加入到动量方程中,在各种电磁力作用参数和电磁极宽度的组合下,对表面覆盖电磁极圆柱体在弱电解质中的绕流场结构及其升阻力特性进行了数值模拟与分析.结果表明,当电磁极宽度较小时,圆柱体绕流场的分离点越容易接近后驻点,而电磁力对总阻力的影响并不明显,但对压差和摩擦阻力均有明显影响.当电磁极宽度较大时,圆柱体尾部区域越容易产生射流现象,而且总阻力随电磁力作用参数和电磁极宽度增大而减小.在电磁力尚不足以完全抑制周期性涡脱落的情况下,升力幅值随电磁力作用参数增大而减小,但随电磁极宽度则先减小后略有增加,升力脉动频率则均随电磁力作用参数和电磁极宽度增大而增加.研究表明,电磁力可以有效地改善圆柱体绕流场结构,达到减小圆柱体阻力并抑制其脉动升力之目的,因此是圆柱型结构的一种有效流动控制手段. 相似文献
4.
首次在普通抽油烟机前部加装旋转的屏蔽射流装置,使抽油烟机抽吸流场与旋转射流流场相耦合以得到人造龙卷风流动流场,并利用该人造龙卷风实现对油烟的控制抽吸。建立了加装旋转射流装置的抽油烟机数值计算模型,依据计算流体动力学理论对所建立的模型进行了数值计算分析,得到了稳定的人造龙卷抽吸流场;同时,通过与实验得到的稳定的龙卷抽吸流场进行对比,进一步证实了人造龙卷风控制抽吸应用于抽油烟机的可行性。另外,研究了旋转屏蔽射流流量对龙卷抽吸流场的影响,数值计算分析结果表明:当射流流量从0m3/s增加到0.068m3/s时,龙卷中心负压值增加,距抽吸口0.6m的位置负压值从-0.0025Pa增至-2.0356Pa;轴向速度衰减速度变缓,距抽吸口0.6m位置的轴向速度值从0.1m/s增至0.28m/s;切向旋转速度增大。可见,射流流量的增加对龙卷抽吸流场的形成是有利的。 相似文献
5.
固体火箭燃气射流驱动液柱过程的CFD分析 总被引:1,自引:0,他引:1
固体火箭燃气射流驱动液柱过程会产生一个复杂的非稳态多相流场,为了研究液柱对固体火箭发动机工作过程中射流流场的降温效果,并揭示燃气冲击液柱的流动演化和气水之间的相互作用,利用FLUENT软件中耦合了液态水汽化方程的VOF多相流计算模型对燃气与液柱之间的耦合流动及相变过程进行了数值模拟,并与无液柱情况下射流流场的计算结果进行了对比分析。计算结果表明,当有液柱平衡体时射流流场中的压力、温度、速度波动幅度均减小,减弱了射流流场中的湍流脉动强度;液柱与燃气之间的汽化以及液柱的阻碍作用减小了射流流场的轴向发展位移,尾管后的完全发展射流流场核心区域内的压力峰值降低了0.9 MPa,温度峰值降低了503 K,速度峰值降低了291 m/s,验证了实验中液柱对燃气射流流场的降温效果。 相似文献
6.
为了研究旋转爆震燃烧室与涡轮的匹配特性,利用二维欧拉方程数值研究了基于当量H2/Air燃烧的旋转爆震燃烧室出口流场特性,对比分析了不同燃烧室轴向长度和周向长度出口总压脉动、总压畸变以及出口温度分布规律。结果表明:旋转爆震燃烧室在稳定工作状态下,其出口总压的脉动值会呈现周期性振荡;燃烧室尺度对发动机出口流场的不均匀性有很大影响,随着燃烧室轴向长度的增大或周向尺寸的减小,其出口总压脉动均值、畸变指数和出口温度分布系数均会减小,其出口流场均匀性提高。此外,爆震波高度随着周向尺寸的增大而增大;轴向尺寸对爆震波高度几乎不产生影响。 相似文献
7.
湍流边界层等动量区演化机理的实验研究 总被引:1,自引:0,他引:1
等动量区是瞬时流场中流体动量接近的局部区域,其生成和分布与相干结构密切相关. 对等动量区的研究有助于更深入认识湍流边界层相干结构,但目前对其演化过程还缺乏实验支持和机理分析. 设计并使用移动式高时间分辨率粒子图像测速技术(TRPIV)系统对光滑平板湍流边界层进行了跟踪测量,用滤波方式对数据进行降噪,结合对直接数值模拟数据的插值结果,获得脉动速度信号. 使用改进方法去掉非湍流的影响,检测边界层内的等动量区,得到其数量的时间序列,结合流向速度概率密度函数分布的变化,分析得出了等动量区的数量在大的时间尺度下从一个稳态到另一个稳态的阶梯状变化特点. 分解不同尺度的脉动速度,对大尺度和小尺度脉动信号进行条件平均,发现大尺度脉动对等动量区数量变化起主要作用,表现为不同速度流体通过发生不同猝发事件改变流向速度概率密度函数分布. 分析流向大尺度脉动空间分布的变化,发现等动量区内常含有多个大尺度脉动区域,不同区域的扩张、收缩、分裂、合并影响流向速度的集中程度,进而导致等动量区数量的变化. 相似文献
8.
油液在运行过程中不可避免地会产生颗粒物,影响油液的正常使用,甚至出现设备故障,因而分析含悬浮颗粒油液的动态特征,掌握在不同压力变化条件下油液及颗粒物的变化规律具有重要意义。利用两相流体理论建立了含悬浮颗粒油液的悬浮流动力学模型,通过特征线法进行了数值求解,将数值结果与实验数据比较,具有较好的一致性;根据所建模型,分析了不同系统压力条件下悬浮流中各相的脉动规律。结果表明,流场中各相参数的脉动幅值随着系统压力的增加而增大;管路始端和终端各相参数的脉动时刻分别位于1/4脉动周期(T)的奇数倍和偶数倍处,管路中段各相参数的脉动时刻则位于T/8的奇数倍处;悬浮颗粒速度会受到油液速度拖曳力作用,其变化趋势与油液速度基本一致,颗粒浓度分布与油液压力的变化趋势完全相反。 相似文献
9.
本文在雷诺数2×104下,同步测量了12个不同间距下串列双圆柱的表面压力分布,积分得到脉动升、阻力的时间历程,并对前、后柱之间的脉动升、阻力以及脉动升阻力和圆柱表面的脉动压力进行了相关分析.在本实验中,串列双圆柱流态切换的临界间距比在3.5~4.0之间,在临界间距前后,相关曲线的形态差别很明显.当串列双圆柱之间的距离小于临界间距时,前后柱之间的影响显著,造成脉动升/阻力和脉动压力之间的相关程度下降.串列双圆柱之间的距离大于临界距离时,前、后柱的脉动升力之间的相位差随间距线性增加.分离点的脉动压力和脉动升力之间以及背压和脉动阻力之间都有较好的相关性,可以用分离点的脉动压力和背压来分别表征脉动升力和脉动阻力. 相似文献
10.
11.
12.
Pulsatile flows in the vicinity of mechanical ring-type constrictions in pipes were studied for transitional turbulent flow with a Reynolds number (Re) of the order of 104. The Womersley number (Nw) is in the range 30–50, with a corresponding Strouhal number (St) range of 0·0143–0·0398. The pulsatile flows considered are a pure sinusoidal flow, a physiological flow and an experimental pulsatile flow profile for mechanical aortic valve flow simulations. Transitional laminar and turbulent flow characteristics in an alternating manner within the pulsatile flow fields were studied numerically. It was observed that fluid accelerations tend to suppress the development of flow disturbances. All the instantaneous maximum values of turbulent kinetic energy, turbulent viscosity and turbulent shear stress are smaller during the acceleration phase than during the deceleration period. Various parametric equations have been formulated through numerical experimentation to better describe the relationships between the instantaneous flow rate (Q), the pressure loss (ΔP), the maximum velocity (Vmax), the maximum vorticity (ζmax), the maximum wall vorticity (ζw,max), the maximum shear stress (τmax) and the maximum wall shear stress (τw,max) for turbulent pulsatile flow in the vicinity of constrictions in the vascular tube. An elliptic relationship has been found to exist between the instantaneous flow rate and the instantaneous pressure gradient. Other linear and quadratic relations between various flow parameters were also obtained. 相似文献
13.
Computer Simulation of Non-Newtonian Flow and Mass Transport Through Coronary Arterial Stenosis 总被引:1,自引:1,他引:0
IntroductionThemostobviouscharacterofatherosclerosisisthelocalintimalaccumulationoflow_densitylipoprotein(LDL) ,theincreaseofthefiberaltissueandthestenosis.Ononehand ,itisfoundthatthediseaseoftenoccursatthecomplexgeometryregion ,suchasbifurcationzone,cure… 相似文献
14.
15.
The effects of Reynolds number on the physiological‐type of laminar pulsatile flow fields within the vicinity of mechanical ring‐type constriction in small pipes were studied numerically. The parameters considered are: the Reynolds number (Re) in the range of 50–1500; Strouhal number (St) in the range of 0.00156–3.98; Womersley number (Nw) from 0.0 to 50.0. The pulsatile flows considered were physiological‐type of simulated flows. Within a pulsating cycle, detailed flow characteristics were studied through the pulsating contours of streamline (ψ), vorticity (Ω), shear stress (τ) and isobar. The relations between the instantaneous flow rate (Q) and instantaneous pressure gradients (dp/dz) are observed to be elliptic. The relations between the instantaneous flow rate (Q) and pressure loss (Ploss) are quadratic. Linear relations were observed between the instantaneous flow rate (Q) and the maximum velocity, maximum vorticity and maximum shear stress. The Reynolds number of the flow in a pulsating cycle was found to have significant effects on the recirculation length and the pressure gradient within the pulsatile flow regime. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
16.
In this paper, a novel design of a rotary hydraulic flow control valve has been presented for high flow rate fluid power systems. High flow rates in these systems account for substantial flow forces acting on the throttling elements of the valves and cause the application of mechanically sophisticated multi-staged servo valves for flow regulation. The suggested design enables utilisation of single-stage valves in power hydraulics operating at high flow rates regimes. A spool driver and auxiliary mechanisms of the proposed valve design were discussed and selection criteria were suggested. Analytical expressions for metering characteristics as well as steady flow torques have been derived. Computational fluid dynamics (CFD) analysis of steady state flow regimes was conducted to evaluate the hydraulic behaviour of the proposed valve. This study represents a special case of an independent metering concept applied to the design of power hydraulic systems with direct proportional valve control operating at flow rates above 150 litres per minute. The result gained using parametric CFD simulations predicted the induced torque and the pressure drops due to a steady flow. Magnitudes of these values prove that by minimising the number of spool's mobile metering surfaces it is possible to reduce the flow-generated forces in the new generation of hydraulic valves proposed in this study. Calculation of the flow jet angles was analytically verified by measuring the deflection of the velocity vector using flow velocity field distribution, obtained during visualisation of the results of CFD simulations. The derived calculation formulas can predict metering characteristics, values of steady flow torques and jet angles for the specified design and geometry of the suggested valve. The proposed novel structure of the flow control valve promises to attain improved controllability, reliability and efficiency of the hydraulic control units of heavy mobile machinery operating at high flow rates regimes. 相似文献
17.
18.
The effects of pulsatile amplitude on sinusoidal laminar flows through a rigid pipe with sharp-edged ring-type constrictions have been studied numerically. The parameters considered are: mean Reynolds number (Re) of the order of 100; Strouhal number (St) in the range 0·0–3·98; Womersley number (Nw) in the range 0·0–50·0. The pulsatile amplitude (A) varies in the range 0·0–2·0. The flow characteristics were studied through the pulsatile contours of streamline, vorticity, shear stress and isobars. Within a pulsatile cycle the relations between instantaneous flow rate (Q) and instantaneous pressure gradient (dp/dz) are observed to be elliptic. The relations between instantaneous flow rate (Q) and pressure loss (Ploss) are quadratic. Linear relations exist between instantaneous flow rate (Q) and maximum velocity, maximum vorticity and maximum shear stress. © by 1997 John Wiley & Sons, Ltd. 相似文献
19.
An analysis model of pulsatile blood flow in arteries 总被引:3,自引:0,他引:3
IntroductionTheperiodicallypulsatilebloodflowinthearterycausesthecircumferentialandaxialmotionoftheelasticbloodvesselandinturntheoscillationofthevesselaffectsthatofthebloodflow .Womersley[1]resolvedsuccessfullythisfluid_solidcouplingproblembysolvingbothlinearNavier_Stokesequationsandthemotionequationsofthethin_walledelastictubeandgainedtheexpressionsofthebloodflowvelocitiesandthevasculardisplacements.Histheoryhasbeenthebasisforthequantitativeanalysisoftherelationshipofthearterialstructureandi… 相似文献
20.
IntroductionThemeasurementofshearstressinarterialflowhasbeenbestowedbynaturebecauseofthepossiblerelationbetweentheshearstressatthewallandexistenceofatherosclerosis.Theflowphenomenainlargeandmediumsizedarteriesinfluencethedevelopmentofatherosclerosicd… 相似文献