Computational grid,subgrid, and pixels

Free-surface flows in rivers, estuaries, and coastal areas are strongly dominated by the geometrical details of the study area. Nowadays, accurate bathymetric data are easily available on raster-based digital elevation models with an impressive spatial resolution. These data are often accessible as large two-dimensional arrays containing several millions of pixel values. Recent numerical methods are very efficient and rather accurate but far from being able to solve the governing differential equations on a computational grid with such a fine spatial resolution. In the present investigation, the unaltered pixel values from a digital elevation model are clustered to form subgrids of a coarser computational grid. Artificial cross-flow between disconnected areas is inhibited by introducing cell clones and edge clones. Each clone consists of directly connected pixels. It is shown how the resulting computational grid is able to resolve geometrical details of complex study areas to pixel resolution and for any grid size. As an example, the performance of the proposed algorithm is tested to simulate a typical tidal flow in the San Francisco Bay and the Sacramento-San Joaquin Delta area by using an extreme subgrid resolution given by a digital elevation model containing 196 000 000 pixels with 10 m pixel size.     

Downstream processing of inulinase

Candida kefyr DSM 70106 was cultivated in a medium containing inulin as a carbon source. About 92% of the inulinase was recovered directly from the medium. Different concentration (C_f) and enrichment (E_f) factors were obtained, using the following methods: Cross-flow filtration (microfiltration and cell diafiltration were carried out using a rotary filter; enzyme ultrafiltration and diafiltration were performed using a cassette module): C_f = 7.5 and E_f = 2.2; liquid-liquid extraction ofN-Benzyl-N-Dodecyl-N-bis[2-hydroxyethyl] ammonium chloride (BDBAC) reversed micelles: C_f = 2.5 and E_f = 2.7; and expanded-bed adsorption: C_f = 2.8 and E_f = 4.3.     

高速三维边界层的横流不稳定性

用两点四阶差分格式研究旋转圆锥超音速三维边界层的横流不稳定性和壁面冷却对稳定性的影响数值结果表明，与二维边界层相比横流使三维边界层第一模式增长率增大，对第二模式影响很小；Ｍｅ＜４３第一模式最不稳定，Ｍｅ＞４３第二模式最不稳定；三维边界层最不稳定第二模式是三维波，二维边界层则为二维波；壁面冷却对第一模式起稳定作用，对第二模式起不稳定作用     

具有弱夹层的封闭油藏中的瞬态渗流

多层油藏分为层间无窜流的油藏和层间有窜流的油藏。本文研究了层间有弱渗透夹层的两层油藏中两种情形的瞬态渗流,包括单层打开的瞬态渗流和一层注入、一层采出的两层油藏的瞬态渗流。用面积平均方法求出了弱渗透夹层封闭油藏中瞬态渗流的平均压降。分析表明:在渗流前期,层间窜流量逐渐增大,在后期层间窜流量趋于稳定;在单层开采的情况下:初期两层压降不同,非打开层的压降有滞后现象,并且隔层渗透率越小,油井工作强度越弱,滞后时间越长;后期两层压降趋于一致,可以作为一层油藏处理。在一注一采的油藏中,当注采量相同时,两层压降在后期趋于不同的稳定值;当注采量不同时,两层压降在后期趋于一致,但不能达到稳定。     

Modeling of the permeate flux decline during MF and UF cross-flow filtration of soy sauce lees

Cross-flow ultrafiltration and microfiltration have been used to recover refined soy sauce from soy sauce lees for over 25 years. The precise mechanism which dominated the permeate flux during batch cross-flow filtration has not been clarified. In the present study, we proposed a modified analytical method incorporated with the concept of deadend filtration to determine the initial flux of cross-flow filtration and carried out the permeate recycle and batch cross-flow filtration experiments using soy sauce lees. We used UF and MF flat membrane (0.006 m² polysulfone) module under different transmembrane pressures (TMP) and cross-flow velocities. The modified analysis provided an accurate prediction of permeate flux during the filtration of soy sauce lees, because this model can consider the change in J₀ at initial stage of filtration which was caused by the pore constriction and plugging inside membrane, and these changes may not proceed when the cake was formed on the membrane surface. Mean specific resistance of the cake increased with TMP due to the compaction of the cake and decreased with cross-flow velocity due to the change of deposited particle size, but less depended on the membrane in the present study. These results indicate that the value of J₀ determined by modified method was relevant to exclude the effects of the initial membrane fouling by pore constriction due to protein adsorption and plugging with small particles. The modified analytical method for the cake filtration developed in the present study was considered to be capable of selecting an appropriate operating conditions for many cross-flow filtration systems with UF, MF membranes.     

气泡在横流中的生长与脱离特性实验研究

为了系统研究气泡在横流中的运动学特性,利用水循环回路形成横流,采用高速数码摄像技术和图像处理方法对横流中气泡的演化过程进行描述.通过调节横流的平均流速和气体流量,获得了 6种横流中的气泡形态,即单气泡、颈状泡、条带泡、泡囊、离散泡和雾状泡;解释了各类气泡形态的特征,对气泡尺寸及分布进行了统计,对气泡在横流中的发展过程进...     

空调用贯流风机的内流模拟与性能研究

本文针对空调分体室内机采用的贯流风机的特点,对分体室内机采用四折式蒸发器时的贯流风机系统,采用FLUENT(CFD)软件,进行了2D内流模拟分析,指出了内流中易出现回流的三个位置。结果表明,采用多折式蒸发器结构具有较好的内流特性,具有良好的性能和声质量,并得到试验结果的验证,在产品中得到了应用。     

Experimental and Numerical Study of Film Cooling with Internal Coolant Cross-Flow Effects

This study experimentally and numerically analyzes the effect of the coolant cross-flow on film-cooling effectiveness. The three kinds of film holes considered are cylindrical, fan-shaped, and trenched holes. The results show that the internal coolant flow has a large effect on film cooling. The film-cooling effectiveness of the cross-flow coolant model is larger than that of the plenum model for the cylindrical and trenched holes, but it is less for the fan-shaped hole. A comparison of the experimental and numerical results shows that the Reynolds averaged Navier–Stokes model exaggerated the coolant diffusion downstream but underestimates the lateral distribution.     

Three-dimensional computation for flow-induced vibrations of an upstream circular cylinder in two tandem circular cylinders

It is well known from a lot of experimental data that fluid forces acting on two tandem circular cylinders are quite different from those acting on a single circular cylinder. Therefore, we first present numerical results for fluid forces acting on two tandem circular cylinders, which are mounted at various spacings in a smooth flow, and second we present numerical results for flow-induced vibrations of the upstream circular cylinder in the tandem arrangement. The two circular cylinders are arranged at close spacing in a flow field. The upstream circular cylinder is elastically placed by damper-spring systems and moves in both the in-line and cross-flow directions. In such models, each circular cylinder is assumed as a rigid body. On the other hand, we do not introduce a turbulent model such as the Large Eddy Simulation (LES) or Reynolds Averaged Navier-Stokes (RANS) models into the numerical scheme to compute the fluid flow. Our numerical procedure to capture the flow-induced vibration phenomena of the upstream circular cylinder is treated as a fluid-structure interaction problem in which the ideas of weak coupling is taken into consideration.     

气液叉流条件下受热液膜传热特性

在气液叉流条件下,就不同气相雷诺数和液膜雷诺数对液膜传热特性影响进行了实验研究.结果表明：对于确定的被冷却水水温,在液膜雷诺数增加的过程中,液膜厚度逐渐增加,热阻增加,削弱液膜换热,但雷诺数上升使得液膜湍动强度增强,强化了液膜换热;在这两个因素的协同作用下,存在最佳液膜流动雷诺数,使得液膜的换热热阻最小,换热系数最大.层流时,热量传递受温度的影响较大;湍流时,热量传递对液膜进口温度的反应不如层流敏感.