THE COUPLE MOTION BETWEEN VESSEL WALL AN DBLOOD IN THE ENTRANCE REGION OF A TAPERED VESSEL

ＴＨＥＣＯＵＰＬＥＭＯＴＩＯＮＢＥＴＷＥＥＮＶＥＳＳＥＬＷＡＬＬＡＮＤＢＬＯＯＤＩＮＴＨＥＥＮＴＲＡＮＣＥＲＥＧＩＯＮＯＦＡＴＡＰＥＲＥＤＶＥＳＳＥＬＣｅｎＲｅｎ－ｊｉｎｇ（岑人经）ＱｉｎＣｈａｎ（秦婵）ＴａｎＺｈｅ－ｄｏｎｇ（谭哲东）（ＳｏｕｔｈＣ...     

The stress analysis of vessel wall in the entrance region of a tapered vessel

ＴＨＥＳＴＲＥＳＳＡＮＡＬＹＳＩＳＯＦＶＥＳＳＥＬＷＡＬＬＩＮＴＨＥＥＮＴＲＡＮＣＥＲＥＧＩＯＮＯＦＡＴＡＰＥＲＥＤＶＥＳＳＥＬＣｅｎＲｅｎ－Ｊｉｎｇ（岑人经）ＴａｎＺｈｅ－ｄｏｎｇ（谭哲东）ＣｈｅｎＺｈｅｎｇ－ｚｏｎｇ（陈正宗）（ＳｏｕｔｈＣｈｉｎ...     

Early stages of an impulsively started unsteady laminar flow past tapered trapezoidal cylinders

Characteristics of the developing recirculation region behind a tapered trapezoidal cylinder and its interaction with the separating shear layer from the leading edges were studied numerically for an impulsively started laminar flow. An unsteady stream function–vorticity formulation was used. The Reynolds numbers considered range from 25 to 1000. Pressure contours, surface pressure coefficient, wake length and drag coefficient were studied through the streamline flow field. Main flow and subflow regimes were identified by an analysis of the evolution of the flow characteristics. It was found that typically, for a given trapezoidal cylinder, flow starts with no separation. As time advances, the symmetrical standing zone of recirculation develops aft of the trapezoidal cylinder. The rate of growth in width, length and structure of the aft end eddies depends on the Reynolds number. In time, separated flow from the leading edges of the trapezoidal cylinder also develops and forms growing separation bubbles on the upper and lower inclined surfaces of the trapezoidal cylinder. As time advances, the separation bubbles on the upper and lower inclined surfaces of the cylinder grow towards the downstream regions and eventually merge with the swelling symmetrical eddies aft of the cylinder. This merging of the flows creates a complex flow regime with a disturbed tertiary flow zone near the merging junction. Eventually, depending on the Reynolds number and the tapered angle of the trapezoidal cylinder, the flow develops into a specific category of symmetrical standing recirculatory flow with its own distinct characteristics. Comparisons with the available results of other investigators showed very good agreement. © 1998 John Wiley & Sons, Ltd.     

Thermal and dynamic characteristics of the separated flow behind a flat rib with different angles of alignment toward the flow

Results of an experimental study of a turbulent flow past a flat rib with different angles of alignment toward the flow and with different rib heights are presented. The angle of rib alignment toward the flow is varied within ϕ = 50–90°. Vortex formation is visualized, and the coordinates of the reattachment line are determined. It is demonstrated that a decrease in the angle ϕ forms a reattachment region and makes the flow behind the rib more three-dimensional. Pressure coefficients are measured in different longitudinal sections of the channel behind the rib with a varied angle of rib alignment ϕ. Temperature fields on the surface behind the rib are measured by means of an infrared imager and by thermocouples, and the corresponding heat-transfer coefficients are calculated. The effect of the angle of rib alignment toward the flow and the rib height on dynamic and thermal characteristics of the separated flow is analyzed. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 1, pp. 103–109, January–February, 2007.     

The micropolar fluid model for blood flow through a tapered artery with a stenosis

A micropolar model for axisymmetric blood flow through an axially nonsymmetreic but radially symmetric mild stenosis tapered artery is presented. To estimate the effect of the stenosis shape, a suitable geometry has been considered such that the axial shape of the stenosis can be changed easily just by varying a parameter （referred to as the shape parameter）. The model is also used to study the effect of the taper angle Ф. Flow parameters such as the velocity, the resistance to flow （the resistance impedance）, the wall shear stress distribution in the stenotic region and its magnitude at the maximum height of the stenosis （stenosis throat） have been computed for different values of the shape parameter n, the taper angle Ф, the coupling number N and the micropolar parameter m. It is shown that the resistance to flow decreases with increasing the shape parameter n and the micropolar parameter m while it increases with increasing the coupling number N. So, the magnitude of the resistance impedance is higher for a micropolar fluid than that for a Newtonian fluid model. Finally, the velocity profile, the wall shear stress distribution in the stenotic region and its magnitude at the maximum height of the stenosis are discussed for different values of the parameters involved on the problem.     

带涡襟翼翼型流场的数值模拟

以数值计算为手段,分析了带涡襟翼的翼型的流场特性,分别对迎角及扰流板偏角对翼型气动性能的影响做了分析。结果表明,在小迎角来流情况下,保持迎角不变,涡襟翼偏转角度越大,升力越小,阻力越大,呈现较好的线性关系。在大迎角情况下,绕翼型的流动发生分离,通过适当控制涡襟翼的偏转角度,能够有效的改善翼型的失速特性,从而达到流动控制的目的,迎角越大,涡襟翼所需偏转的角度越大。     

计算动脉血管发展流动的新差分格式

在引用守恒型N—S方程和SIMPLE方法的基础上，对血管发展流动的控制方程提出了新的差分格式。算例结果表明：本差分格式对血管发展流动的数值研究是可行的。     

Pressure development in a non-Newtonian flow through a tapered tube

Summary The flow of viscous fluids through a tapered tube is very interesting from the standpoint of blood flow in blood vessels. The taper of the tube is an important factor in the pressure development. In the first place, we have given a brief summary of our theory of the steady convergent flow of non-Newtonian fluids characterized by an arbitrary time-independent flow curve through a slightly tapered tube. Based on our general formula for the flow per unit time, explicit formulae of the pressure gradient are obtained in several cases of non-Newtonian fluids specified by particular flow curves: power law fluid,Bingham body, and the fluid obeyingCassons equation. In all these cases it is shown that the pressure gradient is not constant along the axis but increases with decrease in the radius of the tapered tube. If we neglect quantities of order ² (: angle of taper), then the pressure gradient increases linearly with the distance along the axis of the tube.With 2 figures     

The flow of closely fitting particles in tapered tubes

The flow of rigid spheres, truncated cones and elastic incompressible spheres in tapered tubes is investigated assuming that the Reynolds equation is valid in the fluid and the linear theory of elasticity is applicable in the solid. It is shown that leading terms in the asymptotic expansion of pressure drop in terms of minimum fluid film thickness for neutrally buoyant rigid spheres and truncated cones are of higher order of magnitude compared to the corresponding terms for the flow of these particles in circular cylindrical tubes. The effect of taper angle on pressure drop is reduced in the case of soft elastic particles because of particle deformations and significant velocities at the particle surface.     

65°三角翼亚音速复杂流场计算和数据可视化

提出一种基于非结构混合网格和有限体积法的有效计算策略,对第二期国际涡流试验项目(second international vortex flow experiment,VFE-2)的尖前缘65°三角翼在马赫数0.4,迎角20.3°,雷诺数2×10~6条件下的亚音速复杂流场结构进行数值模拟,重点探讨了基于计算数据进行该类型复杂涡系干扰表面和空间流场关键特征提取和数据可视化问题.通过与相关试验类比,建立了与先进试验流动显示技术相比拟的定性和定量分析方法,为三角翼这类复杂流场结构的精细分析奠定了技术基础.采用上述方法,细致分析了亚音速三角翼的大迎角复杂旋涡流场结构,得到了与试验一致的结论.研究证实:在大迎角条件下,三角翼流动物理复杂,黏性效应耦合严重,只有通过N-S方程计算才能准确地捕捉主涡和二次涡的发展.     

Detailed heat transfer measurements inside straight and tapered two-pass channels with rib turbulators

Most of the studies on gas turbine blade internal channels have focused on constant cross-sectional areas from entrance to turn. Gas turbine blades are typically tapered from hub to tip to reduce thermal loading. These channels exist inside high-performance turbine blades for providing effective cooling to the blade external surface, which is exposed to high-temperature gas flow. Heat transfer measurements are presented for both the straight and tapered square channels including the turn region with and without rib turbulators. The straight channels will have a uniform square cross-section area of 5.08×5.08 cm². For the tapered channels, the square cross-sectional area reduces from entrance into the first pass (5.08×5.08 cm²) to the 180° turn (2.54×2.54 cm²) and then expands from turn to exit in the second pass (5.08×5.08 cm²). The heat transfer results for tapered channels are compared with results for straight channels. Results show that heat transfer in tapered smooth channels is enhanced significantly due to flow acceleration in the first pass, a combination of taper and turn and flow deceleration in the second pass. Overall, the tapered channels significantly produce higher heat transfer enhancements compared to the Dittus–Boelter correlation for fully developed flow especially in the after-turn region. Based on the results from this study, the heat transfer inside tapered channels in the after-turn region cannot be predicted by calculating local Reynolds numbers and using straight channel heat transfer correlations. However, the first pass Nusselt number enhancement distributions are similar for both straight and tapered channels when normalized using the local Nusselt number based on local Reynolds number. The difference in the after-turn region between the straight and tapered channels is reduced with the addition of rib turbulators.     

明渠交汇口分离区三维几何特性的大涡模拟研究

为更准确地把握交汇角对分离区三维几何特性的影响,建立了不同角度的交汇水槽模型并进行数值模拟.采用大涡模拟(LES)方法求解交汇区的湍流流场,并基于平衡层模型的Werner壁面函数法处理近壁区流场.模拟所得垂向流速分布及分离区尺寸等结果与实测资料吻合程度较高.以90°交汇水槽为例较详尽地分析了分离区的三维几何特性,并从流...     

Non-orthogonal stagnation point flow towards a stretching sheet

The steady flow of a viscous and incompressible fluid impinging at some angle of incidence on a stretching sheet is studied. It is shown that the stream function splits into a Hiemenz and a tangential component. Numerical solutions of the relevant functions as well as the structure of the flow field are presented and discussed. It is found that the free stream obliqueness is the shift of the stagnation point toward the incoming flow and it depends on the inclination angle.     

张量方程在三维粘性绕流计算中的应用

本文采用张量形式的粘性激波层方程,用空间推进的数值方法计算了球锥、椭球锥有攻角高超音速绕流问题,并计算了组合椭球锥的粘性绕流,从而说明了本文的方法可推广应用于一般外型飞行器的小攻角绕流计算问题。文中考虑了在高超音速流动条件下空气的非平衡化学反应,认为化学反应的速率是有限的     

Studies on two-phase co-current air/non-Newtonian shear-thinning fluid flows in inclined smooth pipes

In this work, co-current flow characteristics of air/non-Newtonian liquid systems in inclined smooth pipes are studied experimentally and theoretically using transparent tubes of 20, 40 and 60 mm in diameter. Each tube includes two 10 m long pipe branches connected by a U-bend that is capable of being inclined to any angle, from a completely horizontal to a fully vertical position. The flow rate of each phase is varied over a wide range. The studied flow phenomena are bubbly flow, stratified flow, plug flow, slug flow, churn flow and annular flow. These are observed and recorded by a high-speed camera over a wide range of operating conditions. The effects of the liquid phase properties, the inclination angle and the pipe diameter on two-phase flow characteristics are systematically studied. The Heywood–Charles model for horizontal flow was modified to accommodate stratified flow in inclined pipes, taking into account the average void fraction and pressure drop of the mixture flow of a gas/non-Newtonian liquid. The pressure drop gradient model of Taitel and Barnea for a gas/Newtonian liquid slug flow was extended to include liquids possessing shear-thinning flow behaviour in inclined pipes. The comparison of the predicted values with the experimental data shows that the models presented here provide a reasonable estimate of the average void fraction and the corresponding pressure drop for the mixture flow of a gas/non-Newtonian liquid.     

Heat transfer in a tapered passage

Heat transfer to laminar flow in tapered passages is studied for two types of thermal boundary conditions: prescribed heat flux on both walls, and on one wall with the other wall adiabatic. In the analysis, the flow is assumed to be purely radial. Temperature distributions and Nusselt number are obtained for the heat flux q ∞ r^δ. The Nusselt number depends on Reynolds number and taper angle. The fully developed Nusselt number decreases with increase in δ for converging flow and increases for diverging flow. Constant heat flux boundary conditions, δ = 0, for converging flow yield a reduction in Nusselt number when compared with the case of parallel channel flow.     

Theory of unsteady separation in supersonic flow around a convex corner

A theory of unsteady separation in inviscid supersonic flow around a convex corner is developed. Within the framework of the hypothesis suggested the mechanism of separationless-to-separated flow transition is explained and the forces leading to flow separation are determined as functions of the angle θ and the oncoming flow velocity. The values of the angle θ _k at which the flow is separated from the corner vertex and the stall angle θ _s determining the separated flow direction obtained previously in experiments and by numerical simulation are confirmed.     

A computer model of pulse wave and input impedance in human arteries

To predict the propagation of pressure and flow pulses in arterial system and the variation of vascular input impedance, a branched and tapered tube model is studied through one-dimensional transient flow analysis. Coupling the continuity and momentum equations yields a group of quasilinear hyperbolic partial differential equations which can be solved numerically by using the method of characteristics. Several boundary conditions of the arterial system are also simplified suitably. The propagation of the pulses of the arterial system and the vascular input impedance is calculated on computer by using the dimensions and the physiological data of the arterial system. The results point out that the pressure and flow pulses of the arterial system and the vascular input impedance produced by this theoretical model is consistent quite well with the experimental results published.     

Numerical simulation of free shear flows and far-field sound pressure directivity

An implicit spatial differencing technique with fourth-order accuracy has been developed based on the Pade compact scheme. A dispersion-relation-preserving concept has been incorporated into the numerical scheme. Two-dimensional Euler computation of a spatially developing free shear flow with and without external excitation has been performed to demonstrate the capability of the numerical scheme developed. Results are in good agreement with theory and experimental observation regarding the growth rate of the fluctuating velocity, the convective velocity and the vortex-pairing process. The far-field sound pressure generated by the computed shear flow solution using Lighthill's acoustic analogy shows a strong directivity with a zone of silence at the flow angle.     

Effects of swirl on flow separation and performance of wide angle diffusers

Experimental investigations have been carried out to determine whether the introduction of a circumferential velocity component can produce worthwhile improvements in the performance of, and eliminate flow separation in, wide angle conical diffusers. The swirl generator is a 24 flat-bladed, radial intake type. Systematic experimentation has been carried out for one diffuser configuration fitted with a tailpipe (16.5° and 4.4 area ratio) using varying strengths of inlet swirl and introducing the dissipated mechanical energy as the main criterion of diffuser performance. The best inlet swirl strength produced about 60% reduction of the total diffuser losses in swirl-free flow. The analysis of these results, together with information obtained from flow visualisation experiments, suggests that increasing the swirl beyond an observed threshold completely eliminated flow separation, but it also gave rise to a central zone of recirculating flow and hence additional dissipative losses. We conclude that the optimum improvement achievable in wide angle diffuser performance using swirl does not require the addition of more energy than it saves