Three-dimensional, three-component wall-PIV

This paper describes a new time-resolved three-dimensional, three-component (3D-3C) measurement technique called wall-PIV. It was developed to assess near wall flow fields and shear rates near non-planar surfaces. The method is based on light absorption according to Beer–Lambert’s law. The fluid containing a molecular dye and seeded with buoyant particles is illuminated by a monochromatic, diffuse light. Due to the dye, the depth of view is limited to the near wall layer. The three-dimensional particle positions can be reconstructed by the intensities of the particle’s projection on an image sensor. The flow estimation is performed by a new algorithm, based on learned particle trajectories. Possible sources of measurement errors related to the wall-PIV technique are analyzed. The accuracy analysis was based on single particle experiments and a three-dimensional artificial data set simulating a rotating sphere.     

Experimental and numerical dye washout flow visualization

Flow visualization in realistic models is very important for the study of pathological vessel enlargements (aneurysms). Furthermore, flow visualization may help in treatment decisions. However, the most interesting parameter, the wall shear stress, is difficult to measure in vivo. This parameter can be provided by computational fluid dynamics. However, the numerical methods don’t visualize the results as does of the dye washout method — a method often used in flow studies. This experimental method simulates the cine angiograms acquired during contrast agent injection used in medicine. In this paper we present the dye washout visualization of CFD results and compare these results with the conventional dye washout experiments in the same aneurysm model under steady flow conditions.     

Injection of granular material

Some civil engineering projects require the injection of granular matter such as sand into the ground. However, granular matter resists pumping through tubes and thus it is difficult to inject such matter into the ground. With the help of several methods forces and movements of grains were visualized. Force chains and arches in a two dimensional granular matter model were visualized with pola rized light and photo-elastic material. The movement of sand grains was visualized on a glass plate in a half-space ground model. With th e p article im age velocimetry (PIV) method the vector field of the movement and the field of the resulting shear rate were assessed. In this way a new method for the injection of granular material, such as, sand into the ground was devised. The method appears to be applicable to lift a building to counter subsidence.     

X-ray-based assessment of the three-dimensional velocity of the liquid phase in a bubble column

Information regarding the local liquid velocity in bubble columns is of great interest for research into its performance. Common optical methods fail in bubble flows that have large void fractions because of the different refraction indices of the liquid and gaseous phases. The new X-ray particle tracking velocimetry (XPTV) described here solves the problem by the use of X-rays instead of light. X-rays penetrate a gas/liquid flow in straight lines. XPTV enables us to measure the three-dimensional velocity of the liquid phase. This method was applied and validated in two bubble columns. The same method is also applicable to opaque liquids. Received: 14 August 2000/Accepted: 12 January 2001     

Visualization of a wall shear flow

In this paper we propose a new method which might be useful to investigate the flow fields close to vaulted walls with spatial and temporal resolution. This kind of flow visualization is important in the field of biofluid mechanics, since a close relationship is assumed between flow and biological phenomena. This new method is non-invasive, and is also applicable for unsteady flows. It has been used to investigate the steady and the unsteady laminar flow in a rectangular duct, as well as the steady, laminar flow in two different U-shaped ducts, both with a backward facing step, one having a rectangular cross-section, the other a nearly elliptical cross-section. The results concurred well with analytical or numerical solutions.     

Wall-PIV as a near wall flow validation tool for CFD: Application in a pathologic vessel enlargement (aneurysm)

Flow visualization of a near wall flow is of great importance in the field of biofluid mechanics in general and for studies of pathologic vessel enlargements (aneurysms) particularly. Wall shear stress (WSS) is one of the important hemodynamic parameters implicated in aneurysm growth and rupture. The WSS distributions in anatomically realistic vessel models are normally investigated by computational fluid dynamics (CFD). However, the results of CFD flow studies should be validated. The recently proposed Wall-PIV method was first applied in an enlarged transparent model of a cerebri anterior artery terminal aneurysm made of silicon rubber. This new method, called Wall-PIV, allows the investigation of a flow adjacent to transparent surfaces with two finite radii of curvature (vaulted walls). Using an optical method which allows the observation of particles up to a predefined depth enables the visualization solely of the boundary layer flow. This is accomplished by adding a specific molecular dye to the fluid which absorbs the monochromatic light used to illuminate the region of observation. The results of the Wall-PIV flow visualization were qualitatively compared with the results of the CFD flow simulation under steady flow conditions. The CFD study was performed using the program FLUENT®. The results of the CFD simulation were visualized using the line integral convolution (LIC) method with a visualization tool from AMIRA®. The comparison found a very good agreement between experimental and numerical results.     

X-ray based measurements of the local solid phase content in a three-phase flow of a bubble column: statistical significance

Information regarding the flow properties in bubble columns with a three-phase flow is of great interest for research into its performance, as well as for the validation of computer models. In an earlier paper, we proposed an X-ray based particle tracking velocimetry (PTV), called XPTV. This method allows not only the measurement of the velocities of both solid and fluid phases in a three-phase flow, but also the assessment of the time-averaged local solid phase content. In this paper, we are concerned with the statistical significance of the obtained measurements.