MEASUREMENT AND VISUALIZATION OF FLOW FIELD IN AXIAL FLOW FAN

An experimental investigation associated with the basic fluid mechanics in an axial flow fan is described in this paper. The flow field in the tip region has been studied by laser Doppler anemometer (LDA) and flow visualization technique. Some experimental data and images are interpreted to understand the complex interactions between the annulus wall boundary layer and the leakage flow. It shows that the vortex inside the blade passage is produced by the separation of annulus wall boundary layer rather than the rolling up of leakage flow.

VISUALIZATION OF FLOW THROUGH A ROTATING U-BEND DUCT

The flow through a rotating U bend duct is investigated by means of visualization. The U bend duct has a cross section of 50 mm×50 mm and a ratio of bend mean radius R c to hydraulic diameter of the duct D of 0.65. The rotation axis is parallel with the bend axis. Three cases with rotation number of Ro=-0.2, 0 and 0.2, respectively, are studied at a Reynolds number of 100 000. The results show that the combined effect of rotation and bend curvature strongly influences the flow field, especially in the downstream region of the bend. The evident difference among the flow patterns with different rotation number shows that the secondary flow induced by Coriolis force takes an important role in determining the flow structure.

Study on Internal Supersonic Flows with Pseudo-shock Wave Using Liquid Crystal Flow Visualization Method

The flow visualization technique using shear-sensitive liquid crystal is applied to the investigation of a Mach 2 internal supersonic flow with pseudo-shock wave （PSW） in a pressure-vacuum supersonic wind tunnel. It provides qualitative information mainly concerning the overall flow structure, such as the turbulent boundary layer separation, reattachment locations and the dimensionalities of the flow. Besides, it can also give understanding of the surface streamlines, vortices in separation region and the corner effect of duct flow. Two kinds of crystals with different viscosities are used in experiments to analyze the viscosity effect. Results are compared with schlieren picture, confirming the effectiveness of liquid crystal in flow-visualization.

Experimental Study on Local Mass Transfer of Structured Packing with the Method of Flow Visualization

A chromochemical reactive mass transfer technique has been employed to study local mass transfer characteristics of structured packing. This technology adopted by experiment is an Ammonia Adsorption Method （AAM） that yields the surface distribution of transferred mass by analyzing the color distribution on a filter paper with the results of the color chemical reaction. A digital image processing technology is applied for data visualiza-tion. The three-dimensional plot of the local mass transfer coefficients shows that there exist three peak values on different positions of a unit cell of structured packing. In order to improve mass transfer efficiency of the structured packing, one piece of baffle is added between packing sheets. As a result, the average mass transfer coefficient increases by （10 20）% and the pressure drop decreases by （15-55）%.

SURFACE OIL FLOW TECHNIQUE AND LIQUID CRYSTAL THERMOGRAPHY FOR FLOW VISUALIZATION IN IMPULSE WIND TUNNELS

This paper describes flow visualization techniques employing surface oil flow and liquid crystal thermography suitable for use in impulse wind tunnels.High spatial resolution photographs of oil flow patterns and liquid crystal thermograms have been obtained within test times ranging from 7 to 500 ms and have been shown to be very useful for revealing the detailed features of 3-D separated flow.The results from oil flow patterns,liquid crystal thermograms,schlieren photographs and heat flux measurements are shown to be in good agreement.

VISUALIZATION OF FLOW STRUCTURES IN A TURBULENT BOUNDARY LAYER USING A NEW TECHNIQUE

In this paper, an experimental investigation on the flow structures in a turbulent bounda- ry layer employing a special laser light sheet-Hydrogen bubble flow visualization technique is described. It is observed that the high/low speed streaks are directly related to the hairpin or horseshoe-like vortices. This observation can give a better understanding of the physical mechanism in the turbulent boundary layer.

3D visualization of the material flow in friction stir welding process

The material flow in friction stir welded 2014 Al alloy has been investigated using a marker insert technique （MIT）. Results of the flow visualization show that the material flow is asymmetrical during the friction stir welding （FSW） process and there are also significant differences in the flow patterns observed on advancing side and retreating side. On advancing side, some material transport forward and some move backward, but on retreating side, material only transport backward. At the top surface of the weld, significant material transport forward due to the action of the rotating tool shoulder. Combining the data from all the markers, a three-dituensional flow visualization, similar to the 3D image reconstruction technique, was obtained. The three-dimensional plot gives the tendency chart of material flow in friction stir welding process and from the plot it can be seen that there is a vertical, circular motion around the longitudinal axis of the weld. On the advancing side of the weld, the material is pushed downward but on the retreating side, the material is pushed toward the crown of the weld. The net result of the two relative motions in both side of the advancing and the retreating is that a circular motion comes into being. Comparatively, the material flow around the longitudinal axis is a secondary motion.

Effect of shear-induced contact area and aperture variations on nonlinear flow behaviors in fractal rock fractures

This study experimentally analyzes the nonlinear flow characteristics and channelization of fluid through rough-walled fractures during the shear process using a shear-flow-visualization apparatus.A series of fluid flow and visualization tests is performed on four transparent fracture specimens with various shear displacements of 1 mm,3 mm,5 mm,7 mm and 10 mm under a normal stress of 0.5 MPa.Four granite fractures with different roughnesses are selected and quantified using variogram fractal dimensions.The obtained results show that the critical Reynolds number tends to increase with increasing shear displacement but decrease with increasing roughness of fracture surface.The flow paths are more tortuous at the beginning of shear because of the wide distribution of small contact spots.As the shear displacement continues to increase,preferential flow paths are more distinctly observed due to the decrease in the number of contact spots caused by shear dilation;yet the area of single contacts in-creases.Based on the experimental results,an empirical mathematical equation is proposed to quantify the critical Reynolds number using the contact area ratio and fractal dimension.

Groundwater flow through fractured rocks and seepage control in geotechnical engineering: Theories and practices

Groundwater flow through fractured rocks has been recognized as an important issue in many geotechnical engineering practices.Several key aspects of fundamental mechanisms,numerical modeling and engineering applications of flow in fractured rocks are discussed.First,the microscopic mechanisms of fluid flow in fractured rocks,especially under the complex conditions of non-Darcian flow,multiphase flow,rock dissolution,and particle transport,have been revealed through a com-bined effort of visualized experiments and theoretical analysis.Then,laboratory and field methods of characterizing hydraulic properties(e.g.intrinsic permeability,inertial permeability,and unsaturated flow parameters)of fractured rocks in different flow regimes have been proposed.Subsequently,high-performance numerical simulation approaches for large-scale modeling of groundwater flow in frac-tured rocks and aquifers have been developed.Numerical procedures for optimization design of seepage control systems in various settings have also been proposed.Mechanisms of coupled hydro-mechanical processes and control of flow-induced deformation have been discussed.Finally,three case studies are presented to illustrate the applications of the improved theoretical understanding,characterization methods,modeling approaches,and seepage and deformation control strategies to geotechnical engi-neering projects.

Streamline pair selection for comparative flow field visualization

Fluid dynamics simulation is often repeated under varying conditions.This leads to a generation of large amounts of results,which are difficult to compare.To compare results under different conditions,it is effective to overlap the streamlines generated from each condition in a single three-dimensional space.Streamline is a curved line,which represents a wind flow.This paper presents a technique to automatically select and visualize important streamlines that are suitable for the comparison of the simulation results.Additionally,we present an implementation to observe the flow fields in virtual reality spaces.

Flow Visualization of Multi-Hole Film-Cooling Flow under Varying Freestream Turbulence Levels

A flat plate film cooling flow from a multi-exit hole configuration has been numerically simulated using both steady and unsteady Reynolds Averaged Navier Stokes (RANS and URANS) Computational Fluid Dynamics (CFD) formulations. This multi-exit hole concept, the Anti-Vortex Hole (AVH), has been developed and studied by previous research groups and shown to mitigate or counter the vorticity generated by conventional holes resulting in a more attached film cooling layer and higher film cooling effectiveness. The film cooling jets interaction with the free stream flow is a long studied area in gas turbine heat transfer. The present study numerically simulates the jet interaction with the multi-exit hole concept at a high blowing ratio (M = 2.0) and density ratio (DR = 2.0) in order to provide a more detailed, graphical explanation of the improvement in film cooling effectiveness. This paper presents a numerical study of the flow visualization of the interaction of film cooling jets with a subsonic crossflow. The contour plots of adiabatic cooling effectiveness were used to compare the multi-exit hole and conventional single hole configurations. The vortex structures in the flow were analyzed by URANS formulations and the effect of these vortices on the cooling effectiveness was investigated together with the coolant jet lift-off predictions. Quasi-Instantaneous Temperature Isosurface plots are used in the investigations of the effect of turbulence intensity on the cooling effectiveness and coolant jet coverage. The effect of varying turbulence intensity was investigated when analyzing the jets’ interaction with the cross flow and the corresponding temperatures at the wall. The results show that as the turbulence intensity is increased, the cooling flow will stay more attached to the wall and have more pronounced lateral spreading far downstream of the cooling holes.

Boundary Layer Development on a Concave Surface： Flow Visualization and Hot Wire Velocity Measurements

Gortler vortices are key issues in the design of gas turbine blades. The present study deals with flow visualization over concave surface for gas turbine applications. The aim is to comprehend qualitatively the flow trends, particularly the Gortler vortices formation and development. Gortler vortices have the shape of mushroom-like vortices regularly spaced at 25 mm. These vortices grow and increase in strength more rapidly along the surface in the case of the same grid of turbulence applied to the measuring section. The curvature radius of the studied blade is 0.5 m and the stream turbulence intensity level is 2.6%. The velocity field is measured by hot wire anemometer in the streamwise direction. The velocity profile is found to be highly distorted by the momentum transfer associated with Gortler vortices. The results are compared to Blasius flow and to literature data for a blade with curvature radius equal to 2 m.

基于Visual Modflow的某化工园区地下水污染运移研究

通过对某化工园区开展物探测量、钻探、水文地质试验、测井、水质分析等工作得到相关水文地质参数,应用Visual Modflow软件建立相应的数学模型,并通过MT3DMS溶质运移模块对特征污染物在连续源强、瞬态源强下及储罐火灾爆炸风险工况下化工原料渗漏及污水泄露进行污染物运移规律的模拟和预测。结果表明,在连续源强、瞬态源强下,起初一年间污染物浓度会因污染源渗漏或泄露而增加,但随时间的增加浓度会随地下水的流动扩散,且逐渐被稀释,这为地下水环境影响预测提供了可靠依据。

Multiphase fluid dynamics and transport processes of low capillary number cavitating flows

To better understand the multiphase fluid dynamics and associated transport processes of cavitating flows at the capillary number of 0.74 and 0.54, and to validate the numerical results, a combined computational and experimental investigation of flows around a hydrofoil is studied based on flow visualizations and time-resolved interface movement. The computational model is based on a modified RNG k-ε model as turbulence closure, along with a vapor-liquid mass transfer model for treating the cavitation process. Overall, favorable agreement between the numerical and experimental results is observed. It is shown that the cavi- tation structure depends on the interaction of the water-vapor mixture and the vapor among the whole cavitation stage, the interface between the vapor and the two-phase mixture exhibits substantial unsteadiness. And, the adverse motion of the interface relates to pressure and velocity fluctuations inside the cavity. In particular, the velocity in the vapor region is lower than that in the two-phase region.

Study of Turbulent Flow of Film Cooling Holes with Lateral Expanded Exits

Hot wire measurements and flow visualization are presented for studying the turbulent flow field over a flat gas turbine film cooling blade with lateral expanded holes. Three mass flux ratios of jet to free stream, M = 0.5, 0.89, 1.5, are tested. The streamwise velocity, the turbulent intensities and the Reynolds shear stress are measured. The effect of the lateral expanded holes on the improvement of the turbulent flow field for film cooling of gas turbines can be analyzed from the measured spatial di...

Instantaneous and time-averaged flow structures around a blunt double-cone with or without supersonic film cooling visualized via nano-tracer planar laser scattering

In a Mach 3.8 wind tunnel, both instantaneous and time-averaged flow structures of different scales around a blunt double-cone with or without supersonic film cooling were visualized via nano-tracer planar laser scattering （NPLS）, which has a high spatiotemporal resolution. Three experimental cases with different injection mass flux rates were carried out. Many typical flow structures were clearly shown, such as shock waves, expansion fans, shear layers, mixing layers, and turbulent boundary layers. The analysis of two NPLS images with an interval of 5 us revealed the temporal evolution characteristics of flow structures. With matched pressures, the laminar length of the mixing layer was longer than that in the case with a larger mass flux rate, but the full covered region was shorter. Structures like K-H （Kelvin-Helmholtz） vortices were clearly seen in both flows. Without injection, the flow was similar to the supersonic flow over a backward- facing step, and the structures were relatively simpler, and there was a longer laminar region. Large scale structures such as hairpin vortices were visualized. In addition, the results were compared in part with the schlieren images captured by others under similar conditions.

Smart Grid Wide-Area Transmission System Visualization

The installation of vast quantities of additional new sensing and communication equipment, in conjunction with building the computing infrastructure to store and manage data gathered by this equipment, has been the fi rst step in the creation of what is generically referred to as the "smart grid" for the electric transmission system. With this enormous capital investment in equipment having been made, attention is now focused on developing methods to analyze and visualize this large data set. The most direct use of this large set of new data will be in data visualization. This paper presents a survey of some visualization techniques that have been deployed by the electric power industry for visualizing data over the past several years. These techniques include pie charts, animation, contouring, time-varying graphs, geographic-based displays, image blending, and data aggregation techniques. The paper then emphasizes a newer concept of using word-sized graphics called sparklines as an extremely eff ective method of showing large amounts of timevarying data.

Experimental Investigation on Mixing Enhancement Mechanism of Turbulent Jet Flow with Tabbed Nozzle

Flow visualization and hot-wire measurement techniques were combined to investigate the influence of the size and number of tabs on jet flow field and vortex structure generation mechanism. Streamwise vortices generated by the tabs of different sizes and numbers were observed from the flow visualization images. Combined with flow visualization, hot-wire measurement gave a quantitative insight of the effect of various tabbed jet flows. Instantaneous two-component velocity signals (longitudinal and transverse velocity components) at different cross sections along radius direction and streamwise direction with different tabbed jet nozzles were measured using hot-wire anemometer. Average flow field parameters of tabbed jet flow such as mean velocity, tur-bulence intensity, vorticity were analyzed and the effects of tabs with different sizes and numbers were compared with that of circular no-tab jet flow. It is revealed that the generation of a series of counter-rotating quasi-streamwise vortices, azimuthal vortices and double-row azi-muthal vortex are the reasons for mixing enhancement of tabbed turbulent jet flow.

Experimental Study of Flow around a Circular Cylinder inside a Bubble Plume

This study experimentally explores the flow around a cylinder with circular cross-section placed inside a bubble plume. Small gas bubbles with diameter smaller than 0.06 mm are released from electrodes on the bottom of a water tank by electrolysis of water. The bubbles induce water flow around them as they rise because of buoyancy. Inside the generated bubble plume, a cylinder with diameter D of 30 mm is placed at 6.5D above the electrodes. The bubbles and water flow around the cylinder are visualized, and the bubble velocity distribution is measured. The experiments elucidate the bubble behavior around the cylinder, the separated shear layers originating at the cylinder surface, their roll-up, the bubble entrainment in the resultant large-scale eddies behind the cylinder, and the vortex shedding from the cylinder.

Experimental and Numerical Study of Wall Flow Pattern of Turbine Cascade with Tip Clearance

By means of flow visualization on the wall surface and three dimensional flow field numerical simulation for the turbine cascade with 3.6% relative tip clearance, characteristics of the wall flow of the turbine cascade with large tip clearance is analyzed. The flow pattern on the wall surface near the trailing edge is especially discussed in detail by numerical simulation. Results of the experimental and numerical simulation show that the flow near the cascade trailing edge is very complex, and the wall flow patterns near the upper and down trailing edges are clearly different due to the influence of blade tip clearance.