Application Of Particle Image Velocimetry Research Articles

Estimation of an Airfoil Drag at High Angles of Attack from PIV Data

Abstract The paper presents application of Particle Image Velocimetry for determination of an airfoil’s drag coefficient in wind tunnel tests. The purpose of the study was to investigate the feasibility of using PIV as an alternative to pressure rake measurements, especially at high angles of attack. The integral momentum concept was applied for determination of fluid drag from experimental low speed wind tunnel data. The drag coefficient was calculated from velocity and pressure rake data for intermediate angles of attack from 5° to 10°. Additionally, the experimental results were compared to panel method results. After validating the procedures at low angles of attack, the drag coefficient was calculated at close to critical angles of attack. The presented study proved that PIV technique can be considered as an attractive alternative for drag coefficient determination of an airfoil.

Missing data recovery using data fusion of incomplete complementary data sets: A particle image velocimetry application

A data-fusion approach is reported to reconstruct missing data and is applied to particle image velocimetry (PIV) measurements. This approach departs from the existing ones in that the datasets involved in its operation are incomplete. Two sets of incomplete but complementary data with fault regions, obtained using different measurement setups, are combined to yield a complete dataset by reconstructing the missing data. In this report, the capability of the current approach is first demonstrated by using three fabricated scalar patterns with different frequency spectra. Second, this method is applied to PIV measurements pertaining to the natural wake of a circular cylinder with a Reynolds number ReD = 1.8 × 103. The performance of this approach is also examined under different configurations, size, location, and direction, of the fault regions. For the real-world data with turbulence and fluctuations, this approach encounters an overfitting problem. To employ this approach in real-world applications without ground-truth data, a method is also proposed to avoid the overfitting problem and estimate reconstruction accuracy. Then, the method is applied on a spectrally richer flow, i.e., wake flow of two side-by-side cylinders with different diameters, and a wake flow of a blunt plate at a relatively higher Reynolds number ReD = 1.6 × 104. The errors are observed to be below 6% for the velocity and fluctuating components.

Relationship between bubble characteristics and hydrodynamic parameters for single bubbles in presence of surface active agents

Rising single air bubbles were investigated in aqueous solutions of hexadecylamine (HDA) and methyl isobutyl carbinol (MIBC) as surface active agents at varying concentrations at a constant gas flow rate. Shadowgraphy was applied to determine main bubble characteristics, such as equivalent diameter, morphology, and rising velocity. From these characteristics, critical parameters like the concentration at the minimum bubble velocity were derived. Simultaneous application of Particle Image Velocimetry (PIV) provided information about hydrodynamic parameters, e.g. the induced liquid velocities and vortex shedding.From surface tension measurements, the concentration of adsorbed species on the interface and packing densities of HDA and MIBC on the bubble surface could be calculated. HDA exhibited a better adsorption and a higher packing density on the bubble surface compared to MIBC due to the ionic character and the straight hydrocarbon chain. The bubble characteristics were therefore more strongly affected by HDA than by MIBC.Combining the Shadowgraphy and PIV results it was found that the mean liquid velocity as well as the amount of induced turbulent kinetic energy increased with increasing concentration of surfactants in the solutions, while the investigated bubble characteristics such as equivalent diameter and rising velocity decreased. The increase in mean liquid velocity and induced turbulent kinetic energy could be correlated with the oscillating frequency of the bubble trajectory, which also increased with increasing surfactant concentration. The vortex shedding process could be visualised using Proper Orthogonal Decomposition (POD) revealing the micro-process of energy cascading.

The effects of unsteady change in wind direction on the airflow over the helicopter platform of a polar icebreaker

The effects of the unsteady change of the wind direction on the airwake over the helicopter platform of a Canadian Coast Guard polar icebreaker were studied experimentally. By application of particle image velocimetry on a scaled model of the icebreaker, quantitative flow field data were obtained for several rates of change in the wind direction. This study was conducted in a water channel that featured a simulated atmospheric boundary layer as inflow condition. The rate of change in the incidence angle, α˙, varied in the range −0.25 ≤ α˙L/U ≤ 0.25, where L and U are the characteristic length and velocity, respectively. In addition to the time-averaged velocity fields, the turbulence intensity was evaluated to investigate the unsteadiness of the flow. Increasing the rate of change of the incidence angle of the incoming flow resulted in an increase of the turbulent intensity for all considered nominal incidence angles of the inflow. A notable exception to this trend was observed at α = 60°, where the direction of the inflow change had a pronounced effect on the structure of the flow over the helicopter deck. Thus, negative values of α˙L/U resulted in the wake of the superstructure not affecting the flow over the helicopter platform.

Experimental investigations on co-rotating vortex pair merger in convergent/divergent channel flow with single-side-wall deflection

The co-rotating vortex pair merger in the convergent and divergent channel flow was investigated in both equal and unequal cases. The crossflow flow phenomenon of vortex pair merger was acquired by applying particle image velocimetry in a series of streamwise locations. The main finding is that the resultant single-side-wall deflection convergent and divergent channel flow can vary the merging rate and merging trajectories of the equal vortex pair. In the unequal vortex merger, distortion and absorption of the weaker vortex by the stronger vortex were observed, which is different from the mutual induction phenomenon in the equal strength vortex pair case. Furthermore, it was found that the flow converging and diverging have common effects on the merging process in both equal and unequal vortex merger. In the convergent channel flow, vortex pair separation experienced early reduction at upper stream locations, and the merger was accelerated. As the vortex pair developed further downstream, the difference in the merger progress among different channel flow environments becomes less significant, which is believed to be due to the combined effect of pressure gradient and developing time variations.

Measuring the velocity fields of granular flows – Employment of a multi-pass two-dimensional particle image velocimetry (2D-PIV) approach

Measuring velocity fields plays a crucial role in investigating the dynamics of granular flows, which can improve the modeling of hazardous geophysical flows (e.g. avalanches and debris flows) and the control of powder flows in industrial applications. Non-invasive optical methods are invaluable tools for estimating this physical quantity at the laboratory scale. Despite the recent improvements of particle image velocimetry (PIV) algorithms, the employment of PIV to granular flows is still a non-trivial application, where there are several specific aspects to be carefully addressed. Here, we address the main challenges of granular PIV applications and systematically test the open-source window deformation multi-pass code, PIVlab [Thielicke and Stamhuis, J. Open Res. Soft., 2014], for dry granular flows in rotating drum and chute flow experiments. Three granular media (glass spheres, Ottawa sand and acetalic resin beads) with different optical properties are used as a broad test bench for validating the PIV approach. As well, comparisons between the estimations by PIVlab and those obtained by the commercial code, IDT ProVision-XS, are reported, where the advantages of the multi-pass approach are highlighted. This extensive experimental investigation allowed the evaluation of the accuracy of PIVlab in granular flow applications and also helped to assess the reliability of measurements of second-order statistics, such as the granular temperature. Finally, a guideline for setting a reliable PIV arrangement is suggested.

THE USE OF PARTICLE IMAGE VELOCIMETRY FOR DISPLACEMENT MEASUREMENTS IN STEEL COLUMNS SUBJECTED TO BUCKLING

Displacements in structural columns have many challenges regarding to monitoring since it is a complex phenomenon. The monitoring of steel column subjected to buckling is one challenge in order to identify its structural behavior based on displacement measurements. In some cases, this effect is studied under steel rectangular column subjected to axial compressive loads. It is necessary in order to quantify the horizontal column deformation by using optical techniques based on displacements from images to evaluate its structural behavior. This paper is aimed to apply the Particle Image Velocimetry (PIV) technique as a robust and cheap optical method on buckling study of columns as a contactless measurement technique compared to Finite Element Method (FEM). Experiments using rectangular bar samples were used to evaluate the behavior of columns under axial compressive load causing the buckling effect. In order to quantify displacements, PIV technique was applied based on pre-defined positions of the points in the images and the column displacements were measured and compared to FEM. Results indicated displacements difference around 1.08% between PIV and FEM, providing that PIV technique can be used to quantify column displacements in a plane when compared to FEM results. This allows PIV applications for any structures monitoring such as building, bridges and silos.

Velocity measurements of a bench scale buoyant plume applying particle image velocimetry

This paper presents the experimental investigation of the buoyant plume above an electrically heated block of copper. The velocity field in a vertical plane along the plume axis is investigated via particle image velocimetry. Experiments with electrical power from 30 W to 96 W are carried out, which lead to heat source temperatures of 149–307 °C. The resulting flow is laminar for the lowest power setting and undergoes a transition to turbulent flow for higher heat inputs. With increasing heat input the point of transition from laminar to turbulent flow occurs at lower heights.Time-averaged velocity fields are presented together with the according measurement uncertainty that results from the evaluation with particle image velocimetry. Based on these velocity fields a number of characteristic values for the plume is derived in different heights, e.g.maximum velocities, plume widths and flow integrals. In order to further evaluate the transition from laminar to turbulent flow the vertical velocity and the standard deviation of the horizontal velocity along the plume axis and as a function of the Grashof number are investigated. The transition occurs at Grashof numbers in the range 4×108<Gr<2×109, which is in accordance with previous findings. In addition to the velocity measurements, the temperature stratification inside the enclosure is measured to quantify the ambient conditions.

Quantitative Visualisation of Compressible Flows

Abstract The paper demonstrates the feasibility of quantitative flow visualisation methods for investigation of transonic and supersonic flows. Two methods and their application for retrieving compressible flow field properties has been described: Background Oriented Schlieren (BOS) and Particle Image Velocimetry (PIV). Recently introduced BOS technique extends the capabilities of classical Schlieren technique by use of digital image processing and allow to measure density gradients field. In the presented paper a review of applications of BOS technique has been presented. The PIV is well established technique for whole field velocity measurements. This paper presents application of PIV for determination of the shock wave position above airfoil in transonic flow regime. The study showed that application of quantitative flow visualisation techniques allows to gain new insights on the complex phenomenon of supersonic and transonic flow over airfoils like shock-boundary layer interaction and shock induced flow separation.

Application of Particle Image Velocimetry (PIV) for Measuring Water Velocity in Laboratory Sedimentation Tank

Over the past three decades, Particle Image Velocimetry (PIV), fundamentally based on pattern matching principles, has seen a rapid growth in its usage as a flow measurement technique. PIV is a ‘digital’ tracking process to measure the time taken for water to move from one point to the other. The particle displacements can be ascertained by measuring the movement of the fluid of interest from the images captured by a camera. In this study, PIV is employed to measure surface flow velocity. The flow velocity was obtained by analyzing the series of captured images using MatPIV codes. The experiment was carried out at Swinburne Sarawak Fluid Lab. Digital SLR camera model used is Nikon D40X which is capable of taking 5 frames per second. Various tracer particles were used for the experiments include food dye, beads and ping pong balls. The experiments were conducted in a SOLTEQ Sedimentation Tank. Through the implementation of a standardized correction factor, the corrected PIV velocity has an error margin less than 5% which is deemed to be fairly accurate. The PIV velocity (V&lt;sub&gt;piv&lt;/sub&gt;) results showed to be in good agreement with the actual velocity (V&lt;sub&gt;actual&lt;/sub&gt;).

Digital image processing techniques for the analysis of fuel sprays global pattern

We studied the fuel atomization process of two fuel injectors to be fitted in a new small rotary engine design. The aim was to improve the efficiency of the engine by optimizing the fuel injection system. Fuel sprays were visualised by an optical diagnostic system. Images of fuel sprays were produced under various testing conditions, by changing the line pressure, nozzle size, injection frequency, etc. The atomisers were a high-frequency microfluidic dispensing system and a standard low flow-rate fuel injector. A series of image processing procedures were developed in order to acquire information from the laser-scattering images. This paper presents the macroscopic characterisation of Jet fuel (JP8) sprays. We observed the droplet density distribution, tip velocity, and spray-cone angle against line-pressure and nozzle-size. The analysis was performed for low line-pressure (up to 10 bar) and short injection period (1-2 ms). Local velocity components were measured by applying particle image velocimetry (PIV) on double-exposure images. The discharge velocity was lower in the micro dispensing nozzle sprays and the tip penetration slowed down at higher rates compared to the gasoline injector. The PIV test confirmed that the gasoline injector produced sprays with higher velocity elements at the centre and the tip regions.

Impact of mismatched and misaligned laser light sheet profiles on PIV performance

The effect of mismatched or misaligned laser light sheet profiles on the quality of particle image velocimetry (PIV) results is considered in this study. Light sheet profiles with differing widths, shapes, or alignment can reduce the correlation between PIV images and increase experimental errors. Systematic PIV simulations isolate these behaviours to assess the sensitivity and implications of light sheet mismatch on measurements. The simulations in this work use flow fields from a turbulent boundary layer; however, the behaviours and impacts of laser profile mismatch are highly relevant to any fluid flow or PIV application. Experimental measurements from a turbulent boundary layer facility are incorporated, as well as additional simulations matched to experimental image characteristics, to validate the synthetic image analysis. Experimental laser profiles are captured using a modular laser profiling camera, designed to quantify the distribution of laser light sheet intensities and inform any corrective adjustments to an experimental configuration. Results suggest that an offset of just 1.35 standard deviations in the Gaussian light sheet intensity distributions can cause a 40% reduction in the average correlation coefficient and a 45% increase in spurious vectors. Errors in measured flow statistics are also amplified when two successive laser profiles are no longer well matched in alignment or intensity distribution. Consequently, an awareness of how laser light sheet overlap influences PIV results can guide faster setup of an experiment, as well as achieve superior experimental measurements.

Beam stability and warm-up effects of Nd:YAG lasers used in particle image velocimetry

The characteristics and causes of Nd:YAG laser warm-up transients and steady state beam stability effects are investigated in this study. Dynamic laser performance has a particularly noticeable impact on particle image velocimetry (PIV) and other laser-based flow visualisation techniques, where changes in beam pointing can influence the overlap between laser light sheets and thereby degrade the correlation of PIV image pairs. Despite anecdotal knowledge or experience of laser warm-up effects, they have not been formally documented or quantified to date for PIV applications. In this study, the nature of these laser transients are analysed and compared among a selection of typical PIV laser equipment. An investigation into the cause of these transients during the laser warm-up sequence is also presented. Furthermore, the degree of dual cavity transient coupling within a PIV laser system is analysed to determine a practical limit to the laser light sheet overlap that can be expected from PIV experiments. Finally, the results from this study inform a series of recommendations for PIV best practice, which aim to minimise the impact of laser transients on experimental data.

Investigation of boundary-layer separation using ADV and PIV over gravel fixed dunes

This research presents recent advances on morphodynamic modelling over gravel dunes. Boundary-layer separation over gravel fixed dunes is investigated by particle image velocimetry (PIV) and acoustic Doppler velocimetry (ADV). Using the measurements of flow over dunes for different conditions at laboratory scale, advantages of PIV application are investigated for the flow pattern in the lee angle of 38 degree. To compare the experimental results with numerical models over dunes, the 3D numerical model (SSIIM) is applied in this study. The results reveal that the numerical model successfully simulate flow over dune compared with PIV data. Although ADV application near the bed indicates weak performance for high discharge and low water depth, PIV results present more agreement with the numerical model in this region.

Application of Particle Image Velocimetry in Establishing the Field of Zero Extension Lines in Soils

The purpose of this paper is to demonstrate how a recently developed technique of particle image velocimetry can be used in constructing the field of zero extension lines (ZELs) in soils. A brief on the importance and benefits of knowing the pattern of ZELs at any state in a soil mass has first been presented. How the information obtained from the particle image velocimetry technique can be used for obtaining the network of ZELs has been explained afterward. A computer code has been developed in MATLAB environment for this purpose. The validity of the code has been verified using the simple pattern of ZELs. It has then been employed to obtain the network of ZELs in a physical model of a strip footing on the surface of sandy soil mass. The directions along which maximum shear strain develops in the soil mass were found to coincide with the directions of ZELs. It has been concluded that the technique of particle image velocimetry provides a very useful tool for obtaining the field of ZELs. This opens the way for more realistic predictions of the development of deformations and slip surfaces in soil masses.

CFD-DEM simulations and experimental validation of clustering phenomena and riser hydrodynamics

A combined numerical and experimental study of riser hydrodynamics is reported for the fast fluidisation regime. The experimental data sets are used for validation of the CFD-DEM simulations. Special attention is paid to the formation of heterogeneities in the particle distribution, i.e., the formation of clusters. Application of Particle Image Velocimetry (PIV) in combination with Digital Image Analysis (DIA), provides a complete data set for the particle flow in a pseudo-2D riser. A CFD-DEM model is employed to simulate the co-current gas-particle flow. Particle clusters are detected and characterised in our CFD-DEM simulation results and compared to experimental data. Core-annulus flow is well predicted by the model and other hydrodynamic parameters such as cluster frequency, internal solids volume fraction and aspect ratio were also in good agreement with experimental data.

Application of particle image velocimetry to dusty plasma systems

Particle image velocimetry is a fluid measurement technique that has been used for more than 20 years to characterize the particle transport and thermal state of dusty plasma systems. This manuscript provides an overview of this diagnostic technique, highlighting the strengths and limitations that are associated with its use. Additionally, the variations of this technique that have been applied in the study of dusty plasma systems will be discussed, along with a small selection of measurements that can be made with the technique. Potential future directions for this diagnostic tool within the dusty plasma community will also be discussed.

A tomographic-PIV investigation of vapor-induced flow structures in confined jet impingement boiling

Tomographic particle image velocimetry (PIV) is used to study the effect of confinement gap height on the liquid flow characteristics in jet impingement boiling. This first application of tomographic PIV to flow boiling is significant given the complexity of confined two-phase jet impingement. A jet of subcooled water at a Reynolds number of 5,000 impinges onto a circular heat source undergoing boiling heat transfer at a constant heat input. Confinement gap heights of 8, 4, and 2 jet diameters are investigated. A visual hull method is used to reconstruct the time-varying regions of the vapor in the flow. The vapor motion is found to govern the liquid flow pattern and turbulence generation in the confinement gap. Time-averaged velocities and regions of turbulent kinetic energy in the liquid are highest for a confinement gap height of 8 jet diameters, with lower velocity magnitude and turbulence being observed for the smaller spacings. Coherent vortical structures identified with the λ2-criterion are found to occur most frequently near the moving vapor interface. The most intense regions of turbulent kinetic energy do not coincide with the location of coherent structures within the flow. Irrotational velocity fluctuations in the liquid phase caused by vapor bubble pinch-off are the primary cause of the high turbulent kinetic energy measured in these regions. At a gap height of H/d=2 the vapor plume is constrained as it grows from the heat source, causing bulk flow oscillations in the downstream region of the confinement gap.

Functionalised alginate flow seeding microparticles for use in Particle Image Velocimetry (PIV)

Alginate microparticles as flow seeding fulfil all the requirements that are recommended for the velocity measurements in Particle Image Velocimetry (PIV). These spherical microparticles offer the advantage of being environmentally friendly, having excellent seeding properties and they can be produced via a very simple process. In the present study, the performances of alginate microparticles functionalised with a fluorescent dye, Rhodamine B (RhB), for PIV have been studied. The efficacy of fluorescence is appreciated in a number of PIV applications since it can boost the signal-to-noise ratio. Alginate microparticles functionalised with RhB have high emission efficiency, desirable match with fluid density and controlled size. The study of the particles behaviour in strong acid and basic solutions and ammonia is also included. This type of particles can be used for measurements with PIV and Planar Laser Induced Fluorescence (PLIF) simultaneously, including acid–base reactions.

A framework for synthetic validation of 3D echocardiographic particle image velocimetry

Particle image velocimetry (PIV) has been significantly advanced since its conception in early 1990s. With the advancement of imaging modalities, applications of 2D PIV have far expanded into biology and medicine. One example is echocardiographic particle image velocimetry that is used for in vivo mapping of the flow inside the heart chambers with opaque boundaries. Velocimetry methods can help better understanding the biomechanical problems. The current trend is to develop three-dimensional velocimetry techniques that take advantage of modern medical imaging tools. This study provides a novel framework for validation of velocimetry methods that are inherently three dimensional such as but not limited to those acquired by 3D echocardiography machines. This framework creates 3D synthetic fields based on a known 3D velocity field $${\mathbf{V}}$$ and a given 3D brightness field $${\mathbf{B}}$$ . The method begins with computing the inverse flow $${\mathbf{V}}^{\varvec{*}} $$ based on the velocity field $${\mathbf{V}}$$ . Then the transformation of $${\mathbf{B}}$$ , imposed by $${\mathbf{V}}$$ , is calculated using the computed inverse flow according to $${\mathbf{B}}^{\varvec{*}} \left( {\mathbf{x}} \right) = {\mathbf{B}}\left( {{\mathbf{x}} + {\mathbf{V}}^{\varvec{*}} \left( {\mathbf{x}} \right)} \right)$$ , where x is the coordinates of voxels in $${\mathbf{B}}^{\varvec{*}} $$ , with a 3D weighted average interpolation, which provides high accuracy, low memory requirement, and low computational time. To check the validity of the framework, we generate pairs of 3D brightness fields by employing Hill’s spherical vortex velocity field. $${\mathbf{B}}$$ and the generated $${\mathbf{B}}^{\varvec{*}} $$ are then processed by our in-house 3D particle image velocimetry software to obtain the interrelated velocity field. The results indicates that the computed and imposed velocity fields are in agreement.