Fluid Flow Visualization Research Articles

Numerical study of flow characteristics on wing airfoil eppler 562 with whitcomb winglet variations

Winglet is a tool used to improve the efficiency of aircraft and UAV performance by preventing fluid flow jump from lower surface to upper surface at wingtip. The addition of this winglet resulted in improved lift and reduction of drag force from the aircraft wing or UAV. From Whitcomb's research, it was found that the use of winglet on a full size airplane can increase fuel efficiency by 7%. The research led to the idea of conducting research on fluid flow characteristics on the UAV wing with the Eppler 562 airfoil combined with the whitcomb winglet. This numerical study was conducted using the Computational Fluid Dynamics (CFD) method based on the advantages of using this simulation that can review the fluid flow in macroscopic way. This study is provide accurate fluid flow visualization results and can improve the performance of the wings when compared with wings without winglet (plain wing). Wing with the Eppler 562 airfoil combined with the whitcomb winglet results reduction in rotating motion that makes velocity components as opposed to lift.

Computational Fluid Dynamics along the Energy Value Chain: From Natural Gas processing to Industrial End-Use

Systems involving fluid flows are commonly found along the energy value chain and are most of the time complex. Having good understanding and control are essential to warrant the system performance. Computational fluid dynamics (CFD) is a unique tool which predicts fluid flow phenomena using numerical algorithms. It gives access to non-measureable variables and allows the visualization of fluid flow patterns.With the rapid advancement in computer sciences, it is now possible to handle most industrial processes involving fluid flows with CFD. The scope of application is large and issues that can be addressed are numerous, from process design validation and optimization to management of operational conditions changes to troubleshooting.The application of CFD in troubleshooting will be highlighted through a few example of studies conducted by ENGIE Lab, on upstream natural gas treatment systems to downstream industrial end-use for combined heat and power plant and petrochemical furnace.

Visualization of Wormlike Micelle Fluid Flow in a Mixing Tank

In this study, particle image velocimetry was applied to investigate flow fields of wormlike micelle (WLM) fluids in a mixing tank equipped with a four-blade, down-pumping, pitched blade turbine. First, the rheology of WLM fluids was investigated, and the Carreau model was utilized to describe their apparent viscosity. Then, the effects of the rotation speeds and rheological properties on the flow fields were studied using different WLM fluids at different rotation speeds. The results revealed that with increasing Reynolds number, the discharge angle decreases and the carven size increases. Furthermore, elastic effects of WLM fluids lead to a more curved flow and a smaller carven.

Fluid-flow pressure measurements and thermo-fluid characterization of a single loop two-phase passive heat transfer device

A Novel Single Loop Pulsating Heat Pipe (SLPHP), with an inner diameter of 2 mm, filled up with two working fluids (Ethanol and FC-72, Filling Ratio of 60%), is tested in Bottom Heated mode varying the heating power and the orientation. The static confinement diameter for Ethanol and FC-72, respectively 3.4 mm and 1.7mm, is above and slightly under the inner diameter of the tube. This is important for a better understanding of the working principle of the device very close to the limit between the Loop Thermosyphon and Pulsating Heat Pipe working modes. With respect to previous SLPHP experiments found in the literature, such device is designed with two transparent inserts mounted between the evaporator and the condenser allowing direct fluid flow visualization. Two highly accurate pressure transducers permit local pressure measurements just at the edges of one of the transparent inserts. Additionally, three heating elements are controlled independently, so as to vary the heating distribution at the evaporator. It is found that peculiar heating distributions promote the slug/plug flow motion in a preferential direction, increasing the device overall performance. Pressure measurements point out that the pressure drop between the evaporator and the condenser are related to the flow pattern. Furthermore, at high heat inputs, the flow regimes recorded for the two fluids are very similar, stressing that, when the dynamic effects start to play a major role in the system, the device classification between Loop Thermosyphon and Pulsating Heat Pipe is not that sharp anymore.

Flow visualization and numerical simulation of a two-dimensional fluid flow over a foil

This paper deals with a simple, fast and economical visualization method to validate two-dimensional large eddy simulations (LES) of the flow over a foil. This technique exploits the optical properties of soap film and relies on the wake patterns and the frequency at which these are shed at the trailing edge of the foil.

Hybrid Pulsating Heat Pipe for space applications with non-uniform heating patterns: Ground and microgravity experiments

A hybrid Closed Loop Thermosyphon/Pulsating Heat Pipe with an inner diameter bigger than the capillary threshold is tested both on ground and in hyper/microgravity conditions. The device, partially filled up with FC-72, consists of an aluminum tube (inner diameter: 3mm) bent into a planar serpentine with five curves at the evaporator. A transparent section closes the loop in the condenser zone, allowing fluid flow visualization. Five heaters are mounted alternatively on the branches, just above the turns and controlled independently, in order to investigate the effect of non-uniform heating configurations. On ground, where the device works as a thermosyphon, the non-uniform heating configurations promote the fluid net circulation in a preferential direction, increasing the thermal performance with respect to the homogeneous heating. Parabolic flights point out that during the 20s of microgravity, the sudden absence of the buoyancy force activates an oscillating slug/plug flow regime, typical of the Pulsating Heat Pipes, allowing the device to work also without the assistance of gravity. Furthermore, peculiar heating configurations can shorten the stop-over periods and stabilize the pulsating two-phase flow motion.

Study on visualization of immiscible multi-phase fluid flows in microfluidic device

Study on visualization of immiscible multi-phase fluid flows in microfluidic device

タンデム羽ばたき翼飛翔体周りの流れ場および流体力特性の検討

タンデム羽ばたき翼飛翔体周りの流れ場および流体力特性の検討

Creation of a dual-porosity and dual-depth micromodel for the study of multiphase flow in complex porous media.

Silicon-based microfluidic devices, so-called micromodels in this application, are particularly useful laboratory tools for the direct visualization of fluid flow revealing pore-scale mechanisms controlling flow and transport phenomena in natural porous media. Current microfluidic devices with uniform etched depths, however, are limited when representing complex geometries such as the multiple-scale pore sizes common in carbonate rocks. In this study, we successfully developed optimized sequential photolithography to etch micropores (1.5 to 21 μm width) less deeply than the depth of wider macropores (>21 μm width) to improve the structural realism of an existing single-depth micromodel with a carbonate-derived pore structure. Surface profilimetry illustrates the configuration of the dual-depth dual-porosity micromodel and is used to estimate the corresponding pore volume change for the dual-depth micromodel compared to the equivalent uniform- or single-depth model. The flow characteristics of the dual-depth dual-porosity micromodel were characterized using micro-particle image velocimetry (μ-PIV), relative permeability measurements, and pore-scale observations during imbibition and drainage processes. The μ-PIV technique provides insights into the fluid dynamics within microfluidic channels and relevant fluid velocities controlled predominantly by changes in etching depth. In addition, the reduction of end-point relative permeability for both oil and water in the new dual-depth dual-porosity micromodel compared to the equivalent single-depth micromodel implies more realistic capillary forces occurring in the new dual-depth micromodel. Throughout the imbibition and drainage experiments, the flow behaviors of single- and dual-depth micromodels are further differentiated using direct visualization of the trapped non-wetting phase and the preferential mobilization of the wetting phase in the dual-depth micromodel. The visual observations agree with the relative permeability results. These findings indicate that dual-porosity and dual-depth micromodels have enhanced physical realism that is pertinent to oil recovery processes in complex porous media.

Visualization of various working fluids flow regimes in gravity heat pipe

Heat pipe is device working with phase changes of working fluid inside hermetically closed pipe at specific pressure. The phase changes of working fluid from fluid to vapour and vice versa help heat pipe to transport high heat flux. Amount of heat flux transferred by heat pipe, of course depends on kind of working fluid. The article deal about visualization of various working fluids flow regimes in glass gravity heat pipe by high speed camera and processes casing inside during heat pipe operation. Experiment working fluid flow visualization is performed with two glass heat pipes with different inner diameter (13 mm and 22 mm) filled with water, ethanol and fluorinert FC 72. The working fluid flow visualization explains the phenomena as a working fluid boiling, nucleation of bubbles, and vapour condensation on the wall, vapour and condensate flow interaction, flow down condensate film thickness on the wall occurred during the heat pipe operation.

Flow visualization of heat and fluid flow

Flow visualization of heat and fluid flow

Evaluation of a Transparent Analog Fluid of Digested Sludge: Xanthan Gum Aqueous Solution

To verify the accuracy and reliability of the computational fluid dynamics simulation of sludge anaerobic digester, fluid flow visualization experiment is a reliable approach. However, it cannot be used for anaerobic digester due to the opaque nature of sludge. Xanthan gum (XG) aqueous solution was selected as the analog fluid of the digested sludge (DS) due to its good optical clarity and good stability. The rheological properties of DS and the XG aqueous solution were measured by applying a rotational viscometer and the measuring results qualitatively and quantitatively compared by graphics and mathematical statistics analysis. The experimental results revealed the rheological behaviour of XG aqueous solution was similar to DS. They were both typical pseudo-plastic non-Newtonian fluid and showed the same trend in the rheological curves with similar curvatures. Carreau model (R2=0.9578) was proposed to describe the rheological behaviour and calculate the rheological parameters of the analog fluid. The limiting viscosity of the XG aqueous solution linearly increased with the increases of the concentration within the concentration range of 0.20g/L∼1.60g/L. According to the linear relationship, 0.50g/L, 1.00g/L and 1.50g/L XG aqueous solution were selected to compare with DS. The result of Welch's t-test demonstrated that there is no significant difference in the rheological parameters of DS and the 1.00g/L XG aqueous solution at the significant level of α=0.05, which indicated the feasibility of choosing the 1.00g/L XG aqueous solution as transparent analog fluid of DS, and build a foundation for visualization experiment in anaerobic digester.

Working fluid flow visualization in gravity heat pipe

Heat pipe is device working with phase changes of working fluid inside hermetically closed pipe at specific pressure. The phase changes of working fluid from fluid to vapour and vice versa help heat pipe to transport high heat flux. The article deal about gravity heat pipe construction and processes casing inside during heat pipe operation. Experiment working fluid flow visualization is performed with two glass heat pipes with different inner diameter (13 mm and 22 mm) and filled with water. The working fluid flow visualization explains the phenomena as a working fluid boiling, nucleation of bubbles, and vapour condensation on the wall, vapour and condensate flow interaction, flow down condensate film thickness on the wall occurred during the heat pipe operation.

Visualization and Measurement of Natural Convection from Electrochemically-Generated Density Gradients at Concentric Microdisk and Ring Electrodes in a Microfluidic System

Natural convection actuated by electrochemically-generated density gradients at microelectrodes was investigated under different conditions by simultaneously visualizing fluid flow with the electrochemical response. The studies elucidate deviations of electrochemical behavior from theoretical expectations and parameters that control natural convection, which can be exploited in electroanalysis, microfluidics, and electrodeposition. Experiments involved an enclosed, small volume containing 0.00475-0.095 M each of K3Fe(CN)6 and K4Fe(CN)6 in 0.095 M KCl, over concentric gold disk (radius: 16–156 μm) and ring (inner radius: 200–1600 μm, outer radius: 250–2000 μm) microelectrodes. Fluid velocities were obtained with video microscopy by tracking 10-μm beads added to the solution. Flow radiates near the disk either inwardly or outwardly at the bottom of the cell and reverses direction at the top, producing a vertical circulation. Maximum velocities of ∼10 μm/s were measured for the 156-μm disk in 0.095 M. After application of potential or current, the onset of natural convection occurred at shorter times (6 s) than measurable affects in electrochemical current/voltage responses (tens of seconds). Convection from density gradients occurred without corresponding changes in electrochemical responses for the 78-μm disk at the lowest concentration (0.00475 M) and for the smallest, 16-μm disk at the highest concentration (0.095 M).

Experimental evaluation of a facility for jet induced flow analysis

In this work, the performance of a bench, which was designed for investigating the hydrodynamics of jets and plumes in quiescent environment is evaluated. This bench is mainly composed by a water tank with a nozzle placed at the center of its bottom. Through the nozzle, fluid is injected vertically upward into the tank. The tank, with square cross section, has a device attached to its upper edge for containing overflow. For fluid flow measurement and visualization, the optical technique Stereo Particle Image Velocimetry (SPIV) was employed and the influence parameters for the resulting flow pattern inside the tank were analyzed. The investigations showed that, in order to avoid tank wall effects to the axisymmetric jet profile, the minimum and maximum flow rate of injected liquid allowed in the stagnant environment were 0.05 L/min and 0.20 L/min, respectively. All the measurements were accomplished under the maximum water column in the tank.

Flow visualization of fluid flow through a U-bend channel with periodical high-permeability porous blocks

The issue about the heat transfer enhancement in a 180-deg turned channel has attracted many attentions. The heat transfer capacity is influenced strongly by the behavior of the fluid flow. This work experimentally investigated the fluid flow characteristics in a 180-deg round turned channel with discrete aluminum-foam blocks. The air was used as coolant. Several aluminum-foam blocks (0.90 porosity and 10PPI pore density) were installed discretely in the 180-deg round turned channel with the square cross section. Four kinds of test section were employed to perform the flow visualizations. The results indicate that the arrangement of aluminum-foam blocks impacts on the flow pattern remarkably. The present results can be used to explain the pressure drop characteristics of such aluminum-foam channel, and be benchmarking by other investigators who would like to solve this problem numerically.

Rendering technique of multi-layered domain boundaries and its application to fluid flow in porous media visualizations

Current visualization techniques for computational fluid dynamics applications are sophisticated and work well in simple geometries. For complex geometries such as pore spaces, multiple domain boundaries obstruct the view and make the studying of fluid flow fields difficult. To overcome these deficiencies, we use two-sided materials to render the domain boundaries. Using this technique, it is possible to place the camera inside the domain and have a non-obstructed view of the surrounding flow field without losing spatial reference to the domain boundaries. As a result, a larger part of fluid flow visualization is visible. Two-sided material rendering was successfully applied to display still images with Blender Cycles renderer, in a virtual reality environment, and several implementation techniques were explored for using the Visualization Toolkit.

북방전복 Haliotis discus hannai (Ino, 1952) 의 폐사규명을 위한 모형 양식시설 주변의 조류 분포 분석

완도에서 주로 사용되는 4열 10행의 가두리 1조를 조합한 형태로 구성된 PE프레임의 내파성 전복가두리를 1/20로 축소하여 모형을 만들고 유체흐름 가시화 실험을 통해 전복가두리 주위의 해수의 흐름을 파악했다. 실험의 결과를 검증하기 위해 노화도 현장의 전복양식 가두리의 내부와 외부의 유속을 측정하였다. 연구의 결과는 아래와 같다. 1. 모형실험에서 전복가두리에 입사하는 해수는 대부분 첫 번째 단위 가두리 (칸) 를 통과하지 못하였다. 2. 모형 전복가두리 중앙 부위에서는 가두리에서 수조바닥으로 향하는 흐름을 관측하였다. 3. 모형 전복가두리의 외측 열을 빠져나가는 유체의 유속이 내측 열을 빠져나가는 유체의 유속보다 빨랐다. 4. 노화도의 현장 양식가두리의 2 m앞의 조류의 유속은 0.11 m/sec였지만 가두리 칸 내부의 유속은 0.0009 m/sec로 거의 움직임이 없었다. 5. 현재의 전복가두리 형태는 해수의 유통이 원활하지 않아 가두리 내부로 새로운 해수를 공급하기 어려울 것으로 판단된다. This study is aimed at figuring out the reasons of the mass mortality of abalone and the increase in its mortality rate in the sea cage. The study suggests that lack seawater circulation in an abalone aquaculture cage is an important culprit for it. We analyzed the current distribution around a 1/20 scaled-down abalone unit cage of 4 rows and 10 columns by fluid flow visualization technique (PIV : Particle Image Velocimetry). The speed of current in the model cage definitely slowed down in the first column of a unit cage. We also observed currents going down to the bottom of a water tank from the unit cages placed in the middle. The speed of wakes behind inside the row in the middle was slower than that outside the row. Water velocity inside and outside a real abalone cage at Nowha Island adjacent to Wan Island was measured to verify results from the tank test. The speed of current in front of the cage by 2 m was 0.11 m/sec while it was only 0.0009 m/sec inside the cage. It had similar findings with those of a tank test.

Investigation of concentrating and nonconcentrating evacuated tube solar water heaters using 2D particle imaging velocimetry

Abstract Under transient climatic conditions, solar water heaters using heat pipes are more effective at capturingincident solar radiation than other equivalent sized solar water heaters. The cost must be reduced toimprove uptake of such systems. To investigate two methods were considered by this study: thermosyphonfluid flow and reflective concentrators. A physical reconfigurable laboratory model of the manifold andassociated condensers of a heat-pipe-evacuated tube system were fabricated; fluid circulation was viathermosyphonic action, particle imaging velocimetry derived velocity maps and the use of concentratorswas simulated. When condenser spacing was doubled, the Nusselt number increased by 43%, the velocityby 55% but the heat transfer efficiency of the model manifold decreased by 9%. Potential annual energysavings of 10207 GWh could be realized if such systems could be successfully fabricated. Keywords: thermosyphon; fluid flow visualization; solarenergy; particle imaging velocimetry;compound parabolicconcentrators; evacuated tube solar water heaters

Criteria for selecting fluorescent dye tracers for soil hydrological applications using Uranine as an example

Abstract Calibrating and verifying 2-D and 3-D vadose zone flow and transport models requires detailed information on water and solute redistribution. Among the different water flow and mass transfer determination methods, staining tracers have the best spatial resolution allowing visualization and quantification of fluid flow including preferential flow paths. Staining techniques have been used successfully for several decades; however, the hydrological community is still searching for an “ideal” vadose zone tracer regarding flow path visualization. To date, most research using staining dyes is carried out with Brilliant Blue FCF. Fluorescent dyes such as Uranine, however, have significant advantages over nonfluorescents which makes them a promising alternative. This paper presents the first analysis of key properties any fluorescent substance must possess to qualify as a staining fluorescent tracer in vadose zone hydrological applications. First, we summarize the main physico-chemical properties of Uranine and evaluate its staining tracer potential with conventional suitability indicators and visibility testing in a soil profile. Based on numerical analysis using the theory of fluorescence, we show that a low molar absorption coefficient is a crucial parameter to quantify concentration accurately. In addition, excitation of a tracer on wavelengths different from the maximum excitation wavelength can extend the linear range of the concentration-fluorescence relationship significantly. Finally, we develop criteria for evaluating the suitability of any potential fluorescent soil staining compound for soil hydrological applications: 1) high quantum yield, 2) low molar absorption coefficient, 3) fluorescence independent of temperature, 4) low photodecomposition rates, and 5) fluorescence stable across a wide range of pH values.