Particle Image Velocimetry Study Research Articles

On the fluid dynamics of a laboratory scale single-use stirred bioreactor

The commercial success of mammalian cell-derived recombinant proteins has fostered an increase in demand for novel single-use bioreactor (SUB) systems that facilitate greater productivity, increased flexibility and reduced costs (Zhang et al., 2010). These systems exhibit fluid flow regimes unlike those encountered in traditional glass/stainless steel bioreactors because of the way in which they are designed. With such disparate hydrodynamic environments between SUBs currently on the market, traditional scale-up approaches applied to stirred tanks should be revised. One such SUB is the Mobius® 3L CellReady, which consists of an upward-pumping marine scoping impeller. This work represents the first experimental study of the flow within the CellReady using a Particle Image Velocimetry (PIV) approach, combined with a biological study into the impact of these fluid dynamic characteristics on cell culture performance. The PIV study was conducted within the actual vessel, rather than using a purpose-built mimic. PIV measurements conveyed a degree of fluid compartmentalisation resulting from the up-pumping impeller. Both impeller tip speed and fluid working volume had an impact upon the fluid velocities and spatial distribution of turbulence within the vessel. Cell cultures were conducted using the GS-CHO cell-line (Lonza) producing an IgG4 antibody. Disparity in cellular growth and viability throughout the range of operating conditions used (80–350rpm and 1–2.4L working volume) was not substantial, although a significant reduction in recombinant protein productivity was found at 350rpm and 1L working volume (corresponding to the highest Reynolds number tested in this work). The study shows promise in the use of PIV to improve understanding of the hydrodynamic environment within individual SUBs and allows identification of the critical hydrodynamic parameters under the different flow regimes for compatibility and scalability across the range of bioreactor platforms.

A particle image velocimetry study of the flow physics generated by a thin lamina oscillating in a viscous fluid

In this paper, we study the flow physics produced by a thin rigid lamina oscillating in an otherwise quiescent viscous fluid. Particle image velocimetry (PIV) is used to extract the flow kinematics, which is, in turn, utilized to reconstruct the pressure distribution around the lamina through the integration of Navier-Stokes equations. The hydrodynamic loading experienced by the lamina is ultimately estimated from PIV data to investigate added mass and fluid damping phenomena. Experiments are conducted for varying Reynolds and Keulegan-Carpenter numbers to elucidate the relative weight of inertial, convective, and viscous phenomena on the resulting flow physics. In agreement with prior numerical studies, experimental results demonstrate that increasing the Reynolds and the Keulegan-Carpenter numbers results into the formation of coherent structures that are shed at the edges of the lamina and advected by the flow. This phenomenon is associated with nonlinearities in the hydrodynamic loading, whereby fluid damping is found to increase nonlinearly with the oscillation of the lamina.

A Particle Image Velocimetry Study of Hydroelastic Slamming

Abstract In this work, a non-intrusive pressure reconstruction method based on particle image velocimetry (PIV) is utilized to investigate hydroelastic phenomena associated with the water entry of flexible structures. Experiments are conducted on flexible cantilevered wedges entering the water in free fall. PIV is leveraged to evaluate the effect of the mutual interaction between the fluid flow and structural deformation on the distributed hydrodynamic loading. The wedge compliance is found to strongly influence the hydrodynamic loading, resulting into marked oscillations in the distribution and evolution of the pressure on the wetted surface of the impacting body.

Engineering characterisation of single-use bioreactor technology for mammalian cell culture applications

Background The commercial success of mammalian cell-derived recombinant proteins has fostered an increase in demand for novel single-use bioreactor (SUB) systems, that facilitate greater productivity, increased flexibility and reduced costs. Whilst maintaining auspicious mixing parameters, these systems exhibit fluid flow regimes unlike those encountered in traditional glass/stainless steel bioreactors. With such disparate mixing environments between SUBs currently on the market, the traditional scale-up procedures applied to stirred tank reactors (STRs) are not adequate. The aim of this work is to conduct a fundamental investigation into the hydrodynamics of single-use bioreactors at laboratory scale to understand its impact upon the growth, metabolic activity and protein productivity of an antibody-producing mammalian cell culture. Materials and methods This work presents a study characterising the macromixing, fluid flow pattern, turbulent kinetic energy (TKE), energy dissipation rates (EDRs), and shear stresses within these bioreactor systems carried out using 2dimensional Particle Image Velocimetry (PIV). PIV enables acquisition of whole-field flow characteristics through instantaneous velocity measurements. The SUBs employed in the PIV measurements include the 3L CellReady (Merck Millipore), PBS Biotech’ sP BS 3 bioreactor and the Sartorius 2L BIOSTAT Cultibag RM. The CellReady is a stirred tank bioreactor (3 litre volume), housing a 3-bladed upward-pumping marine scoping impeller. The PIV study was conducted using the actual vessel which has an internal diameter (DT )o f 137mm and height (HT) of 249mm. The marine scoping impeller (DI) is 76.2mm in diameter and is located near the bottom with a clearance of 30mm from the base. Measurements were obtained at varying impeller rates from 80 to 350rpm (corresponding to Re =8 699 to 38057). The PBS 3 is a pneumatically driven bioreactor (3 litre volume) whose mixing is induced through the buoyancy of bubbles. PIV measurements were again obtained utilising the actual PBS 3 vessel in the central vertical plane of the bioreactor at wheel speeds of 20, 27, 33 and 38rpm. The Sartorius Cultibag RM is a rocked bag bioreactor with a 2 litre total volume. A custom-made Sartorius Cultibag mimic and rocking platform was manufactured to enable the required optical access for PIV investigations. Measurements were taken at a rocking speed of 25rpm, in the vertical plane 8.5cm from the outer edge of the bioreactor. Fluid working volume (wv) was varied at 30, 40, 50 and 60% wv. A biological study into the impact of these fluid dynamic characteristics on mammalian cell culture performance and behaviour is presented. CellReady and Cultibag cell cultures were conducted using the GSCHO cell-line (Lonza) producing an IgG4 (B72.3) antibody. The impeller speed and working volume are used to vary the hydrodynamic environment within the CellReady, whilst the rocker speed is the varied parameter in the Cultibag RM. Results and discussion The upward-pumping 3-bladed impeller within the CellReady engenders compartmentalisation of the fluid flow. This in turn contributes to the wide range of turbulence levels conveyed between the lower quarter and upper three quarters of the fluid. The maximum fluid velocity of 0.25Utip is achieved in the impeller discharge stream

Fish and robots swimming together in a water tunnel: robot color and tail-beat frequency influence fish behavior.

The possibility of integrating bioinspired robots in groups of live social animals may constitute a valuable tool to study the basis of social behavior and uncover the fundamental determinants of animal functions and dysfunctions. In this study, we investigate the interactions between individual golden shiners (Notemigonus crysoleucas) and robotic fish swimming together in a water tunnel at constant flow velocity. The robotic fish is designed to mimic its live counterpart in the aspect ratio, body shape, dimension, and locomotory pattern. Fish positional preference with respect to the robot is experimentally analyzed as the robot's color pattern and tail-beat frequency are varied. Behavioral observations are corroborated by particle image velocimetry studies aimed at investigating the flow structure behind the robotic fish. Experimental results show that the time spent by golden shiners in the vicinity of the bioinspired robotic fish is the highest when the robot mimics their natural color pattern and beats its tail at the same frequency. In these conditions, fish tend to swim at the same depth of the robotic fish, where the wake from the robotic fish is stronger and hydrodynamic return is most likely to be effective.

Experimental investigation and CFD simulation of heave damping effects due to circular plates attached to spar hull

ABSTRACTDamping elements are used in ships and offshore structures as response reduction devices for maintaining the motion response within acceptable limits. The design of these elements relies on a combination of empirical approach and past experience. In this paper, an investigation of the wave excitation and hydrodynamic reaction forces acting on floating structures with and without damping elements is presented taking spar platform as the candidate structure. Understanding the flow pattern and vortex structure around these circular heave damping plates helps correlate the energy dissipation and damping. In the present study, measurement of hydrodynamic damping and inertia forces and response were carried out to establish the relationship between wave frequency and damping ratio. Flow pattern around the damping elements has been simulated using computational fluid dynamics (CFD) approach. Furthermore, flow visualisation and velocity measurement using particle image velocimetry (PIV) technique has been carried out in a wave flume for comparison and evaluation of the CFD approach. It was observed that the damping varies with wave period in a nonlinear fashion and it varies linearly with wave height. It was also observed that increase in added mass combined with viscous damping is a key factor for the effectiveness of heave plates in reducing motion response of spar platforms. Of the various configurations tested, the one with spar with double heave plate at the keel has higher damping and superior motion response compared to other configurations. The velocity pattern and vortex formation around the circular plates obtained through PIV study and CFD simulation showed good agreement.

PIV Study of Ventilation Quality in Certain Occupied Regions of a Two-Dimensional Room Model with Rapidly Varying Flow Rates

The use of supply jet flows is the most common type of air distribution for general ventilation. Usually the supply flow rate is constant or slowly varying (VAV-systems) to cope with a varying load. A novel air distribution method, with the potential to reduce stagnation and to increase the ventilation efficiency, is to introduce rapid flow variations (pulsations). This paper reports on a fundamental study of this type of air distribution. The purpose of the study was to explore the effect of flow variations on stagnant zones and the levels of the turbulent kinetic energy and the relative turbulence intensity. A small scale room model is used that consists of an enclosure with a ventilation supply at the bottom and an extract at the top of the opposite wall. Water was used as an operating fluid and the model had a design which mainly generated a two-dimensional flow. The size of the model made it possible to investigate the two-dimensional velocity vector field using the Particle Image Velocimetry (PIV) method in regions corresponding to occupied regions. Further post processing was conducted from the resulting vector fields. The comparison between cases of constant inflow and pulsated inflow (flow variations with frequency of 0.5 Hz) was conducted for three domains: two belonging to the far-field occupied zone and one belonging to the near-field, downstream of the supply wall jet.

Particle image velocimetry and numerical simulations of the hydrodynamic characteristics of an artificial reef

This article reports a particle image velocimetry study and the comparative results of a numerical simulation into the hydrodynamic characteristics around an artificial reef. We reveal the process of flow separation and vortex evolution, and compare the force terms generated by our artificial reef model. The numerical simulation agrees well with experimental results, showing the applicability of computational fluid dynamics to the hydrodynamics of an artificial reef. Furthermore, we numerically simulate the hydrodynamics of the reef model for seven velocities. The results show that the drag coefficient is approximately 1.21 in a self-modeling region for Reynolds numbers between 2.123×104 and 9×104. Therefore, the upwelling height and current width of the flow field do not change significantly when the inflow velocity increases. Our study indicates that computational fluid dynamics can be applied to study the hydrodynamics of an artificial reef and offer clues to its construction.

Fluorescent eco-particles for surface flow physics analysis

In this letter, we describe a novel methodology for fabricating inexpensive environmentally-friendly fluorescent microparticles for quantitative surface flow visualization. Particles are synthesized from natural white beeswax and a highly diluted solution of a nontoxic fluorescent red dye. Bead fluorescence exhibits a long lifetime in adverse conditions, such as exposure to weathering agents, and is enhanced by Ultra Violet radiation. The fluorescent eco-particles are integrated in a particle image velocimetry study of circular hydraulic jump to demonstrate their feasibility in tracing complex surface flows.

Head on collisions of compressible vortex rings on a smooth solid surface

An experimental study has been conducted on the effects of distance variation on the impingement process of compressible vortex rings on a stationary solid wall. An experimental incident Mach number of 1.61 was used. Qualitative and quantitative studies compared the impingement and interaction flow characteristics of a compressible vortex ring with a stationary, solid, smooth surface at three distances: 1.66, 3.33, and 5.00 inner diameters. The three distances corresponded to an under-developed vortex ring (1.66 inner diameters), a vortex ring at its development threshold (3.33 inner diameters), and a fully developed one (5.00 inner diameters). Qualitative schlieren results showed that the surface distance affected the shock/vortex interaction process along with the impingement process of the vortex ring and the flow structure of its trailing jet. Quantitative data were extrapolated to evaluate the propagation velocity of the vortex ring prior to impingement. The boundary layer thickness was also estimated. Particle image velocimetry studies showed the main and secondary vortices to have opposite vorticity, with the magnitude of the vorticity of the secondary vortices being approximately half of that of the main vortex. Surface pressure results reveal the symmetrical properties of the impinging flow, along with a direct correlation between the maximum pressure measured at the instant the vortex ring impingement and an increase in surface distance.

Particle tracking velocimetry and particle image velocimetry study of the slow motion of rough and smooth solid spheres in a yield-stress fluid

We report experimental evidence of an effect opposite to the "solidification" of small bubbles in liquid where the surface can become immobile. Namely, it is demonstrated that smooth solid spheres falling in a yield-stress fluid under the action of gravity can behave similar to drops. Particle tracking velocimetry was used to determine the shape of the yielded region around solid spherical particles undergoing slow stationary motion in 0.07% w/w Carbopol gel due to gravity under creeping flow conditions. The flow field inside the yielded region was determined by particle image velocimetry. It was found that the shape of the yielded region and the flow field around slow-moving rough particles is similar to the published results of numerical simulations, whereas those around smooth spheres resemble the experimental results obtained for viscous drops. The effect was explained by a slip of the gel on the smooth surface. Most likely, the slip originated from seepage of clean water from the gel, forming a thin lubricating layer near the solid surface.

Particle image velocimetry studies on the swirling flow structure in the vortex gripper

In this article, particle image velocimetry was used to measure the two-dimensional flow field for vortex gripper. The vortex gripper was divided into two parts for respective research, including vortex cup and the gas film gap. In the part of vortex cup, the tangential velocity increases gradually, and the velocity decreases intensely in the vicinity of the vortex cup’s wall after it reaches maximum. In addition, the velocity decreases gradually with the increase of the gas film gap. In the part of gas film gap, the tangential velocity increases to maximum along the radial direction first; after the air flows into the gas film gap due to the viscous impedance, it decreases gradually. When the gas film gap’s thickness is smaller, the velocity almost decreases to zero at the external edge of the skirt. However, when the gas film gap increases to a certain thickness, the velocity does not decrease to zero, and the flow air still keeps a certain speed out of it. The velocity decreases gradually with the increase of the gas film gap. The radial velocity in the vortex cup and the gas film gap is of very small order of magnitude comparing with the average velocity and tangential velocity. The analysis of the Reynolds number shows that the flow in the vortex cup is the turbulent flow, and at the part of the gas film gap, the Reynolds number increases with the increase of the gas film gap, and the flow changes from the laminar flow to the turbulent flow. Through the particle image velocimetry experiment, the vortex gripper’s internal flow structure is studied. It is the theory support of the computational fluid dynamics simulation study for vortex gripper and the structure optimization in the future work.

PTV and PIV study of the motion of viscous drops in yield stress material

We report a study of the slow viscous sedimentation of viscous Newtonian drops in a viscoplastic domain comprised of low concentration Carbopol aqueous solution. The study applies visualization methods. Direct photography is used to track the drop settling speed. In steady sedimentation PTV (Particle Tracking Velocimetry) is applied to determine the boundary of the yield stress region around the drop, while PIV (Particle Image Velocimetry) techniques are employed for the quantitative description of the flow field within this region. In infinite domains, the study addresses undisturbed sedimentation of slow and fast moving single drops and a tracking of the coalescence process of a train of two drops. Maps of the flow structure and intensity within the yielded regions around the drops in these cases are provided. When the sedimentation occurs in the vicinity of an adjacent vertical glass wall the drop settling speed may be either enhanced or retarded depending on the proximity to the wall. It is shown that the motion is retarded when the yielded region boundary remain intact but is deformed toward the drop on the wall side. Whenever the yielded region achieves complete contact with the wall the drop speed is augmented and an apparent slip is evident at the wall.

Particle image velocimetry (PIV) study of rotating cylindrical filters for animal cell perfusion processes

In the present work, the main fluid flow features inside a rotating cylindrical filtration (RCF) system used as external cell retention device for animal cell perfusion processes were investigated using particle image velocimetry (PIV). The motivation behind this work was to provide experimental fluid dynamic data for such turbulent flow using a high-permeability filter, given the lack of information about this system in the literature. The results shown herein gave evidence that, at the boundary between the filter mesh and the fluid, a slip velocity condition in the tangential direction does exist, which had not been reported in the literature so far. In the RCF system tested, this accounted for a fluid velocity 10% lower than that of the filter tip, which could be important for the cake formation kinetics during filtration. Evidence confirming the existence of Taylor vortices under conditions of turbulent flow and high permeability, typical of animal cell perfusion RCF systems, was obtained. Second-order turbulence statistics were successfully calculated. The radial behavior of the second-order turbulent moments revealed that turbulence in this system is highly anisotropic, which is relevant for performing numerical simulations of this system.

Motion of tracer particles in a centrifugal pump and its tracking characteristics

The Basset-Boussinesq-Oseen (BBO) equation can be used for most flows to trace the motion of a particle, but in a centrifugal pump, among the forces that act on the particles, one should also include those due to the impeller rotation, as additional effects. This paper firstly reviews various approximations of the BBO equation for the motion of dispersion particles in a viscous fluid. Then based on the motion equation for particles in low Reynolds number centrifugal pumps, a formula for calculating the tracking characteristics of tracer particles is deduced through the Fourier integral transformation. After that the deviations of the particle motion from the fluid motion, as predicted by the various approximations, are discussed and compared. At last, with an emphasis on the Particle Image Velocimetry (PIV) results, the tracking characteristics of particles are estimated. Also, advantages and disadvantages of different tracer particles are discussed and suitable tracer particles for application in PIV studies for flow fields in centrifugal pumps are suggested.

Particle image velocimetry study of fractal-generated turbulence

AbstractAn experimental investigation involving space-filling fractal square grids is presented. The flow is documented using particle image velocimetry (PIV) in a water tunnel as opposed to previous experiments which mostly used hot-wire anemometry in wind tunnels. The experimental facility has non-negligible incoming free-stream turbulence (with 2.8 % and 4.4 % in the streamwise (${u}^{\ensuremath{\prime} } / U$) and spanwise (${v}^{\ensuremath{\prime} } / U$) directions, respectively) which presents a challenge in terms of comparison with previous wind tunnel results. An attempt to characterize the effects of the incoming free stream turbulence on the grid-generated turbulent flow is made and an improved wake-interaction length scale is proposed which enables the comparison of the present results with previous ones for both fractal square and regular grids. This length scale also proves to be a good estimator of the turbulence intensity peak location. Furthermore, a new turbulence intensity normalization capable of collapsing${u}^{\ensuremath{\prime} } / U$for various grids in various facilities is proposed. Comparison with previous experiments indicates good agreement in turbulence intensities, Taylor microscale, as well as various other quantities, if the improved wake-interaction length scale is used. Global and local isotropy of fractal-generated turbulence is assessed using the velocity gradients of the two-component (2C) two-dimensional (2D) PIV and compared with regular grid results. Finally, the PIV data appear to confirm the new dissipation behaviour previously observed in hot-wire measurements.

High-speed micro particle image velocimetry studies of boundary-layer flows in a direct-injection engine

Mass and energy exchange processes near the in-cylinder walls have become increasingly important for internal combustion engine research and development. Heat-transfer and fuel-deposition processes are not well enough understood to fully predict their magnitude and temporal and spatial variation. To a large extent, improvements in modeling are limited because of a lack of experimental guidance on the dynamics of boundary-layer flows in engines. High-speed particle image velocimetry and micro particle image velocimetry were used to study the boundary-layer flow field at the cylinder head of a motored internal combustion engine for three different engine speeds (400, 800 and 1100 r/min). Velocity measurements were taken throughout the compression stroke and the beginning of the expansion stroke, and comparisons to the frequently used law-of-the-wall were made. The low-resolution particle image velocimetry images showed that the average bulk flow maintained a tumble flow throughout the compression and expansion strokes and velocities scaled with engine speed. Adequate spatial resolution of the boundary-layer flow required the use of high-resolution (micro particle image velocimetry) measurements which showed that the log-law does not accurately describe the experimental boundary-layer structure in the outer layer ([Formula: see text]). Using the log-law, the velocity for earlier crank angles (180–260 crank angle degrees) was over predicted while the velocity for later crank angles (300–330 crank angle degrees) was under predicted, as engine speed increased. However, the experimental velocity profiles near the wall ([Formula: see text]) matched the description of the viscous sublayer ([Formula: see text]). Furthermore, it was observed that the thickness of the viscous sublayer decreased as the engine speed increased. The viscous sublayer could not be adequately resolved at 1100 r/min because of the limitations in adequate seeding density near the surface and the resulting loss of data points closest to the wall. The capability of high-speed particle image velocimetry measurements is demonstrated by the ability to identify and track vortical structures that move through the outer and buffer layers. Future work must address the evolution of such flow structures, along with measurements of temperature, to enable development and validation of boundary-layer models that are not restricted by the assumptions necessary for the law-of-the-wall such as steady bulk flow conditions and properties.

PIV study on a shock-induced separation in a transonic flow

A transonic interaction between a steady shock wave and a turbulent boundary layer in a Mach 1.4 channel flow is experimentally investigated by means of particle image velocimetry (PIV). In the test section, the lower wall is equipped with a contour profile shaped as a bump allowing flow separation. The transonic interaction, characterized by the existence in the outer flow of a lambda shock pattern, causes the separation of the boundary layer, and a low-speed recirculating bubble is observed downstream of the shock foot. Two-component PIV velocity measurements have been performed using an iterative gradient-based cross-correlation algorithm, providing high-speed and flexible calculations, instead of the classic multi-pass processing with FFT-based cross-correlation. The experiments are performed discussing all the hypotheses linked to the experimental set-up and the technique of investigation such as the two-dimensionality assumption of the flow, the particle response assessment, the seeding system, and the PIV correlation uncertainty. Mean velocity fields are presented for the whole interaction with particular attention for the recirculating bubble downstream of the detachment, especially in the mixing layer zone where the effects of the shear stress are most relevant. Turbulence is discussed in details, the results are compared to previous study, and new results are given for the turbulent production term and the return to isotropy mechanism. Finally, using different camera lens, a zoom in the vicinity of the wall presents mean and turbulent velocity fields for the incoming boundary layer.

Twin screw granulation using conveying screws: Effects of viscosity of granulation liquids and flow of powders

The effects of increasing viscosity of granulation liquid (amount of binder) at varying powder feed rates on properties of granules and surface velocity of powder in Twin Screw Granulator (TSG) with conveying screws only were studied. The surface velocities of the dry and wet formulation powders were obtained using Particle Image Velocimetry (PIV) and Discrete Element Modelling (DEM) simulation. Granulation at both high viscosity of granulation liquid and powder feed rate led to decrease in granule size, voids reduction, increase in strength and compressibility index of granules. The reverse was observed with lowering both viscosity of granulation liquid and powder feed rate. In the PIV study, the dry formulation powder possessed a higher velocity compared to the wet granules. The surface velocity increased with increasing viscosity of granulation liquid and decreased with increasing powder feed rates. The results helped to qualitatively understand the twin screw granulation process.

PIV Study of Flow in an Aerated Tank with a Hollow Blade Turbine

Liquid phase hydrodynamics in an aerated tank (ID = 0.19 m) stirred by a half elliptical blade disk turbine (HEDT) have been investigated using particle image velocimetry (PIV) under both aerated and unaerated conditions. The effect of the gas flow rate on the aerated mean velocity of the liquid phase, turbulent kinetic energy and turbulent kinetic energy dissipation are discussed, and their comparisons with those under unaerated conditions are also carried out. Under aerated conditions, the presence of gas does not remarkably change the velocity pattern of the liquid phase. When the direction of the liquid flow is the same as the buoyancy, the liquid is accelerated up to 10.4% by bubbles at position of z/T=0.8 and r/T=0.45; while the liquid flow reversely, the liquid is decelerated about 37.5% under the gas flow rate of 0.2 vvm at the position of z/T=0.25 and r/T=0.45. The turbulent kinetic energy in the bulk flow increases after introducing gas phase, and the average turbulent kinetic energy of the upper, middle and lower regions at 0.2 vvm are increased by 37.3%, 37.8% and 142.7%, respectively. Large-eddy PIV approach is carried out to estimate the distribution of the turbulence kinetic energy dissipation. The result shows that the distribution of the turbulent kinetic energy dissipation is similar as those of turbulent kinetic energy.