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《工程热物理学报》2021,42(7):1752-1759
压气机缩尺模化中,由于粗糙度与雷诺数无法严格满足相似准则,导致由模型机性能换算全尺寸机性能时存在偏差,需要对其影响进行修正。本文选择某燃机压气机前1.5级作为原型机,由缩尺模化生成一组模型机,采用数值模拟方法研究缩尺模化过程中雷诺数和粗糙度对性能换算的影响规律。结果表明,随着表面粗糙度增加,压气机的多变效率下降;缩尺模化中,压气机雷诺数减小,多变效率下降。通过缩尺模化性能换算研究,本文提出在Casey的多变效率修正方法中引入流量系数作为自变量,由此获得该方法中经验参数B_(ref)的新型高精度公式。它是雷诺数、粗糙度和流量系数的函数。将改进后的修正方法应用于全尺寸原型机多变效率换算,在稳定工况范围内,多变效率偏差小于0.1%。 相似文献
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在中等雷诺数(3000~7000)下的广泛温度范围内(300~700℃)水测量了水蒸汽和干空气的混合介质(rH2O= 0.25~ 0.45)横流单管和管排的对流换热系数,并与经典的Zhukauskas方法计算结果进行了比较,实验结果表明,高水分烟气横流圆管对流换热系数伴随烟气水分浓度的增大和温度的升高而加强,这种加强的趋势比使用Zhukauskas关联式计算得到的结果更为显著,本文使用烟气水分含量作为修正因子,通过修正的Zhukauskas关联式,给出了高水分烟气横流圆管对流换热计算关联式。 相似文献
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基于平板边界层理论和对流换热的雷诺比拟关系,通过粗糙度和雷诺数对表面摩擦因子f的影响规律,建立了透平叶栅模化实验的叶型损失系数ω和表面平均换热系数h-与f之间的修正关联式。对比模化叶型与实验叶型的数值分析结果,在选定参数范围内,ω和h-与f之间呈现良好的相关性,采用近似线性关系修正实验模型的叶型损失和平均表面换热系数,与模化叶型实际性能之间的误差均可控制在10%以内。 相似文献
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核磁共振T2谱换算孔隙半径分布方法研究 总被引:4,自引:0,他引:4
岩芯核磁共振T2谱和压汞分析数据均在一定程度上反映了岩石的孔隙结构特征,理论分析和二者频率分布图对比表明,这两组数据有较好的相关性,核磁共振T2谱能够换算为反映岩石孔隙结构特征的孔隙半径分布图. 本文应用最大相关性原理、最小二乘法及插值算法等数学方法,给出了一个改进的将T2谱换算为孔隙半径分布图的实用有效新方法,求得了T2弛豫时间与岩芯孔隙半径r之间的换算系数C,计算过程中着重对比了T2谱与压汞数据的主要分布区间,并考虑了压汞进汞饱和度小于100%对换算结果的影响. 天然砂岩岩芯核磁共振T2谱换算为孔隙半径分布图的实际应用效果表明,着重对比T2谱与压汞数据的主要分布区间,同时考虑压汞进汞饱和度小于100%对换算结果的影响是必要的,换算结果更加真实可信. 相似文献
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传统LBM方法在用来分析大雷诺数非牛顿流体时,体现出较低的稳定性和精度,当逐步增大雷诺数到一定数值时,此种现象更为突出。文中针对这个问题,提出一种修正LBM可以有效提高大雷诺数的Herschel-Bulkley流体流动分析时的稳定性和精度,将Herschel-Bulkley流体的非牛顿性看作一项特殊的外力项,并将上述提出的方法应用于顶盖驱动流的数值模拟分析中,讨论了在剪切变稀和剪切增稠两种情况下,逐步增大雷诺数时流线图以及主涡中心位置的变化,结果证明提出的方法可以有效应用于大雷诺数Herschel-Bulkley流体流动的分析中。为了验证此方法的可行性,利用泊肃叶流的理论解与上述方法的数值解进行对比,并分析了初始屈服应力,幂律指数以及格子大小对LBM数值模拟结果的影响。 相似文献
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分析了斯托克斯定律及其修正项的适用范围,讨论了落球法测液体粘滞系数实验中液体粘滞系数和落球直径对雷诺数的影响,从理论上给出了实验中落球进入液体后匀速运动的判据. 相似文献
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The Kutta Joukowski(KJ) theorem, relating the lift of an airfoil to circulation, was widely accepted for predicting the lift of viscous high Reynolds number flow without separation. However, this theorem was only proved for inviscid flow and it is thus of academic importance to see whether there is a viscous equivalent of this theorem. For lower Reynolds number flow around objects of small size, it is difficult to measure the lift force directly and it is thus convenient to measure the velocity flow field solely and then, if possible, relate the lift to the circulation in a similar way as for the inviscid KJ theorem. The purpose of this paper is to discuss the relevant conditions under which a viscous equivalent of the KJ theorem exists that reduces to the inviscid KJ theorem for high Reynolds number viscous flow and remains correct for low Reynolds number steady flow. It has been shown that if the lift is expressed as a linear function of the circulation as in the classical KJ theorem, then the freestream velocity must be corrected by a component called mean deficit velocity resulting from the wake. This correction is small only when the Reynolds number is relatively large. Moreover, the circulation, defined along a loop containing the boundary layer and a part of the wake, is generally smaller than that based on inviscid flow assumption. For unsteady viscous flow, there is an inevitable additional correction due to unsteadiness. 相似文献
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以工程上常用的66%的乙二醇水溶液作为工质,对几何特性相似而高宽比不同的4种纯铝矩形微通道内的流动特性进行了实验研究,得到了微通道冷板基础性的设计数据。实验测量了Reynolds数在50~500之间的流动阻力系数。实验结果表明:通道高度H与宽度W之比对微通道流阻特性有显著的影响;当Re数小于100时,在实验误差内,流动阻力系数的值近似等于经典理论计算值;随着Re数的增大和高宽比的变化,f的值远大于理论值,这可能是由微通道内部壁面粗糙度效应所导致的。 相似文献
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Bendiks Jan Boersma 《Journal of computational physics》2011,230(12):4940-4954
In a previous paper we have developed a staggered compact finite difference method for the compressible Navier–Stokes equations. In this paper we will extend this method to the case of incompressible Navier–Stokes equations. In an incompressible flow conservation of mass is ensured by the well known pressure correction method and . The advection and diffusion terms are discretized with 6th order spatial accuracy. The discrete Poisson equation, which has to be solved in the pressure correction step, has the same spatial accuracy as the advection and diffusion operators. The equations are integrated in time with a third order Adams–Bashforth method. Results are presented for a 1D advection–diffusion equation, a 2D lid driven cavity at a Reynolds number of 1000 and 10,000 and finally a 3D fully developed turbulent duct flow at a bulk Reynolds number of 5400. In all cases the methods show excellent agreement with analytical and other numerical and experimental work. 相似文献
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We calculate the correction, due to nonlinear wave-wave interactions, to the Zel'dovich estimate for the turbulent diffusivity of magnetic fields in a model of two-dimensional magnetohydrodynamic turbulence in the presence of stable stratification. Such a model has some relevance to hydromagnetic turbulence in stellar interiors. The significance of this correction is that, unlike the lowest-order Zel'dovich balance, it is independent of the molecular resistivity eta and so will not vanish in the limit of a large magnetic Reynolds number, although the correction is O(sigma;{4}), where sigma is the wave slope, which necessarily is small. Thus, we are led to the counterintuitive result that the presence of stable stratification can actually increase the vertical flux of magnetic fields relative to that in 2D MHD turbulence without stratification. 相似文献
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研究了载气组份、温度、压力以及微球直径和壁厚对液态空心玻璃微球在炉内运动状态的影响。结果表明:在用干凝胶法制备空心玻璃微球工艺的常用载气组份、温度和压力范围内,载气的组份、温度和压力对相同直径和壁厚的液态玻璃微球在炉内运动速度的影响小于8.3%,但载气组份和压力对液态玻璃微球运动雷诺数和韦伯数的影响很显著。玻璃微球的直径和壁厚是液态玻璃微球运动速度、雷诺数和韦伯数的重要影响因素。提高载气中的氦气含量或降低载气压力可以降低载气对液态玻璃微球的非球形化作用,提高载气温度可以降低其球形化的阻力。 相似文献
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Abstract This article investigates the flow and heat transfer characteristics in micro steel tubes with inner diameters of 168 μm, 399 μm and relative roughness of 3.5% and 2.7%, respectively, by measuring the friction factors and the Nusselt number from laminar state to transitional state. Experiments show that the experimental Nusselt numbers are less than those predicted by the classical laminar correlation due to the effect of the variation of the thermophysical properties with temperature when Reynolds number is low. As the Reynolds number is higher than 800, the experimental Nusselt number are 25–50% higher than the predictions of the classical laminar and transitional correlations due to the effects of the roughness and the entrance length. The transition from laminar to turbulent flow occurs at the Reynolds number of 1,100–1,500. 相似文献
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对非牛顿流体在小尺寸方形通道内的低雷诺数受迫对流传热进行了实验研究。实验用介质为1500wppmCarbopol-934中性水溶液。通道顶壁受到等热流加热。结果表明,流体粘弹性与传热的相互作用取决于雷诺数的大小。当表观雷诺数Re>11.5时,非牛顿流体开始强化对流传热。Re数越高,传热强化的程度越大。流体的阻力系数则几乎不受粘弹性的影响。 相似文献
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V. Kumaran L. Srivatsan 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(2):259-266
The stability of the flow of a fluid past a solid membrane of infinitesimal thickness is investigated using a linear stability
analysis. The system consists of two fluids of thicknesses R and H R and bounded by rigid walls moving with velocities and , and separated by a membrane of infinitesimal thickness which is flat in the unperturbed state. The fluids are described
by the Navier-Stokes equations, while the constitutive equation for the membrane incorporates the surface tension, and the
effect of curvature elasticity is also examined for a membrane with no surface tension. The stability of the system depends
on the dimensionless strain rates and in the two fluids, which are defined as and for a membrane with surface tension , and and for a membrane with zero surface tension and curvature elasticity K. In the absence of fluid inertia, the perturbations are always stable. In the limit , the decay rate of the perturbations is O(k
3
) smaller than the frequency of the fluctuations. The effect of fluid inertia in this limit is incorporated using a small
wave number asymptotic analysis, and it is found that there is a correction of smaller than the leading order frequency due to inertial effects. This correction causes long wave fluctuations to be unstable
for certain values of the ratio of strain rates and ratio of thicknesses H. The stability of the system at finite Reynolds number was calculated using numerical techniques for the case where the strain
rate in one of the fluids is zero. The stability depends on the Reynolds number for the fluid with the non-zero strain rate,
and the parameter , where is the surface tension of the membrane. It is found that the Reynolds number for the transition from stable to unstable modes,
, first increases with , undergoes a turning point and a further increase in the results in a decrease in . This indicates that there are unstable perturbations only in a finite domain in the plane, and perturbations are always stable outside this domain.
Received: 29 May 1997 / Revised: 9 October 1997
/ Accepted: 26 November 1997 相似文献