数值模拟不等距叶片对贯流风机的影响

贯流风机的通过频率(BPF)是其重要的噪声频率.降低BPF噪声可以降低基频处的声压级,其中一种方法是采用不等距叶片.本文采用3种叶片距分布形式,采用realizable k-ε两方程和大涡模拟(LES)湍流模型模拟了风机的内流场,计算线性欧拉方程(LEE)中声源项得到声源位置及强度,采用基于Lighthill声类比的FW-H积分方程获得了叶轮和蜗舌处偶极子型的离散噪声频谱.比较了不同叶片距对风机性能,噪声特别是BPF噪声的影响.计算结果表明在对性能影响较小的情况下,不等距叶轮可降低BPF噪声和总A声级噪声.     

使用多孔蜗舌的贯流风机

将贯流风机的蜗舌替代为多孔板与容腔组合的结构,定性地研究其控制气动噪声的可行性。通过对气动特性和辐射声信号的实验测量,结合内部流场的非稳态雷诺平均数值模拟,分析了这种蜗舌改造对贯流风机的整体特性和内部流动特征的影响,结果表明多孔蜗舌对贯流风机的压力-流量曲线作用并不明显,但对风机的噪声有着重要的影响,改变蜗舌迎风面的穿孔率可以有效地控制贯流风机的噪声。     

交叉流聚丙烯中空纤维膜式氧合器的传质研究Ⅰ结构因子α、β的测定和氧合器传质效果评价

在膜式氧合器水气传递实验装置上分别对二种不同的交叉流微孔聚丙烯中空纤维膜式氧合器进行了水气传递实验，测得了氧合器的结构因子α、β，并用Ｍｏｃｋｒｏｓ和Ｌｅｏｎａｒｄ对Ｏ２传递建立的半经验数学模型拟合了血气传递实验中氧气在血中的传递速率。结果表明，理论计算与实验数据十分吻合，偏差小于１０％。讨论了α、β与膜式氧合器的传递效果的关系。     

Fluid-Damping Controlled Instability in Tube Bundles Subjected to Air Cross-Flow

There are different excitation mechanisms that cause fatal damages due to undesirable vibrations in heat exchanger tube bundles subjected to cross-flow. One of them is the fluid-damping-controlled instability (galloping) that is characterised by a sudden appearance of large amplitudes of the tubes exclusively in cross-flow direction. This paper reports on investigations using an experimental set-up in a wind tunnel where the galloping mechanism in a tube bundle can be observed as an isolated phenomenon. The apparatus allows to realise several tube bundle configurations and geometry's of real heat exchangers. The position of a flexible test tube with a linear iso-viscoelastic mounting inside the tube array is variable. The test tube is equipped with dynamical pressure sensors which are placed directly under pressure holes inside the tube. For the investigation of the acting fluid forces the non-stationary pressure distribution is measured simultaneously at 30 points on the circumference in mid plane and at 15 points in line along the tube together with the tube motion. The acting fluid forces are determined by integration of the whole pressure field process. The study gives insights into the effect of the fluid-damping-controlled instability that is still not fully understood. Moreover, a flow visualization gives an impression of the mechanism at relevant Reynolds-numbers. The results show that in case of instability due to galloping the correlation length of the forces acting along the tube axis increases suddenly to large values. The fluid forces are correlated well for the whole tube when galloping is dominant. The exciting fluid forces show harmonic character and lead to a classical resonance behaviour. Instead of a simple free vibration test in vacuum or still air, which is done mostly for fluid excited structures, the damping coefficient of the oscillating system is determined under operating conditions on the basis of the measured fluid forces. A comparison of the results with those of a free vibration test in still air is shown. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dynamics of turbulent air-flow in droplet driven sprays

This paper presents a study of the fundamental mechanics of droplet and gas motion in sprays. Only vertical sprays are considered and our theoretical analysis identifies two main flow zones, corresponding to where the droplet velocity is much greater than or of the same order as the induced air velocity. Analytical asymptotic results for the induced air velocity for small and large downstream distances confirmed a full numerical calculation and also agreed with experimental results. The second half of the paper deals with some of the most important aspects of spray jets in a cross flow. We find that the ratio of the cross-wind speed to the induced air jet speedU ₀/V _j is a crucial factor for specifying the dynamical behaviour. We present results for an axi-symmetric spray in uniform cross flow for bothweak andstrong cross-winds.     

Characterising the near-wake of a cross-flow turbine

The performance and detailed near-wake characteristics of a vertical axis, cross-flow turbine (CFT) of aspect ratio 1 were measured in a large cross-section towing tank. The near-wake at one turbine diameter downstream was examined using acoustic Doppler velocimetry, where essential features regarding momentum, energy, and vorticity are highlighted. Dominant scales and their relative importance were investigated and compared at various locations in the measurement plane. Estimates for the terms in the mean streamwise momentum and mean kinetic energy equation were computed, showing that the unique mean vertical velocity field of this wake, characterised by counter-rotating swirling motion, contributes significantly more to recovery than the turbulent transport. This result sheds light on previous CFT studies showing relatively fast downstream wake recovery compared to axial-flow turbines. Finally, predictions from a Reynolds-averaged Navier–Stokes simulation with the commonly used actuator disk model were compared with the experimental results, evaluating its use as an engineering tool for studying flow in CFT arrays. Unsurprisingly, the model was not able to predict the near-wake structure accurately. This comparison highlights the need for improved parameterised engineering models to accurately predict the near-wake physics of CFTs.     

A numerical study of rotation effects on jets effusing from inclined holes into a cross-flow

In this work, the complexity of the flow field arising from the impact of the interaction of coolant jets with a hot cross-flow under rotation conditions was numerically simulated using large eddy simulation with artificial inflow boundary condition. The finite-volume method and the unsteady PISO (Pressure Implicit with Splitting of Operators) algorithm were applied on a non-uniform staggered grid. The simulations were performed for four different values of rotation number (Ro) of 0.0, 0.03021, 0.06042, and 0.12084, a jet Reynolds number of 4700, based on the hole width and the jet exit velocity. The air jet was injected at 30° and 90° in the streamwise direction with a density ratio of 1.04 and a velocity ratio of 0.5. The flow fields of the present study were compared with experimental data in order to validate the reliability of the LES technique. It was shown that the rotation has a strong impact on the jet trajectory behaviour and the film cooling effectiveness. The film trajectory always inclines centrifugally. Under rotating conditions, the film trajectory departs from the centreline to the left boundary. The deflection becomes greater as Ro increases. Furthermore, it was also found that the injection angle has a strong impact on separation and reattachment behaviour as well as the strength of the penetration into the cross-flow. As it increases, the distribution of the film cooling downstream the jet exit is more non-uniform and the film cooling effectiveness level slightly decreases.     

移动床热煤气脱硫气固反应过程模拟——Ⅱ-错流移动床非催化气固反应过程模拟

基于前文错流移动床反应器模型方程,模拟计算并分析了该类反应器中气、固相流动对热煤气脱硫等非催化气固反应过程的影响。研究表明,床层在床深方向按反应速率的快慢可分为粗脱区和精脱区,在颗粒流动方向上气相浓度差异较大,并主要体现在粗脱区内,床层出口处颗粒转化率呈现较大分布,反应器内气固交错流动、气相浓度和颗粒转化率共同作用（ 于气固反应速率） 等因素是造成过程特征的主要因素。因此反应器优化应满足对两相流动的优化,将粗脱区设置成错流移动床而精脱区设置成固定床,并使粗脱区内颗粒流速沿气流方向逐渐减小,以减小出口颗粒转化率的分布并提高颗粒利用率,同时沿颗粒流动方向应逐渐减小过床气流体积分率以利于床内气固反应速率的均一分布。由此指出对该类床型其底部渐缩下料段和过床气流对床内颗粒流动的影响以及床层结构及颗粒流动对过床气流分布的影响研究的必要性。     

Wire-Arc Spray Modeling

A model is presented describing the details of the wire-arc spray process. The model consists of several submodels each treating a different part of the process. A compressible flow model describes the supersonic nozzle flow upstream of the wire tips. The arc is described by a 3-D arc in cross-flow model using different boundary conditions for the cathode and the anode boundary. The resulting temperature and velocity contours serve as upstream boundary for a 2-D turbulent jet model. Particle generation and acceleration is described by treating the initial droplet formation for the anode and the cathode wire separately and then using the resulting particle size and velocity distributions in a secondary break-up model. Comparison with some experimental results show acceptable agreement. This modeling approach may be used for optimization of wire-arc spray equipment.     

High cell density cultures of schizosaccharomyces pombe in a cell-recycle reactor

Cultivation of the fission yeastSchizosaccharomyces pombe in a cellrecycle fermentor with cross-flow filtration using mineral membranes to recycle the biomass is described. Total cell retention resulted in high cell density cultures with high productivities. The dependence of both the growth kinetics and metabolic status on the operating conditions was identified and quantified. Growth was controlled by the inhibitory effect of ethanol so long as glucose was in excess as might be expected for fermentative metabolism. Under oxygen excess conditions, a partly oxidative catabolism of glucose occurred due to growth limitation by the glucose feed flow. The cells displayed a purely oxidative metabolism when ethanol was not present in the broth but a respiro-fermentative metabolism when ethanol was present as was the case when oxygen supply to the culture was limiting.