Particle Image Velocimetery Research Articles

Predicting erosion in a non-Newtonian shear-thinning jet flow with validated CFD models from PIV and PTV measurements

In oil and gas industry, an increase in production is often achieved by injecting fracturing fluids with particles/proppants into rocks and reservoirs. There are various fracking fluids that oil and gas companies use, and some of these fracturing fluids demonstrate non-Newtonian flow behavior. In this paper, sand erosion behavior in shear-thinning carboxymethyl cellulose (CMC) solution is investigated with a jet impingement facility. Particularly, near wall flow speeds and particle impinging speeds are investigated in shear-thinning CMC fluids by Particle Image Velocimetery (PIV) and Particle Tracing Velocimetery (PTV) techniques. Computational Fluid Dynamics (CFD) are also used to predict the near wall particle impact information. The results indicate that different turbulence models resolve different near wall flow and particle impact characteristics. User Defined Functions (UDF) are developed and used to implement erosion ratio equations and simulate solid particle erosion behavior in the non-Newtonian fluid. The predictions are compared with experimental results. The results of this study can help improving erosion prediction in the hydraulic fracturing process utilizing CFD.

Scattering of Low-Mode Internal Tides at a Continental Shelf

AbstractA series of laboratory experiments are performed to investigate the scattering of low-mode internal tides at a continental shelf by varying the criticality parameter and normalized topographic height independently. A wide-range synchronized particle image velocimetery (PIV) measures the velocity fields of the internal tides. Beams radiate from both the shelf break and the bottom of the slope, indicating that energy transfers from low modes to higher modes, which is verified by the modal decomposition. Energy is also transferred to higher harmonics, whose amplitude is less than a quarter of that of the first harmonic. The fraction of energy transmitted onshore and dissipated on the topography is determined by both the criticality parameter and the normalized topographic height, while the fraction of energy reflected offshore is dependent only on the criticality parameter. Mean flow with a shear structure induced by internal tides is observed along the continental slope, with horizontal velocity generally half of the amplitude of the incident waves. A net onshore transport along the slope is caused by the onshore current with larger thickness. The strength of the mean flow is dependent on both the criticality parameter and the normalized topographic height, and a linear relationship between the energy of the mean flow and the vertical shear of internal tides is revealed.

3D dynamics of debris flows quantified at sub-second intervals from laser profiles

We use pairs of parallel mounted laser profile scanners to measure main debris-flow variables in two debris-flow channels in central and southern Switzerland. The scanners measure the instantaneous cross-sectional geometry of debris flows at rates of 25–100 Hz, and we apply large-scale particle image velocimetery to estimate velocity. The scanners also provide direct measurements of flow depth. From these data, we were able to estimate debris-flow depth, velocity and discharge for 16 out of 17 events. These results are consistent with discharge estimated from a system of geophones and a radar gauge for two available datasets. We also investigated debris-flow geometry to quantify rheology-controlled cross-flow convexity and found that four events manifest strong surface convexity at their surge fronts where we expect the largest boulders and low pore-fluid pressures. The scanners provide a completely new view of debris-flow dynamics and channel morphology and present novel opportunities to measure discharge and investigate debris-flow geometries.

An experimental study of the flow through and over two dimensional rectangular roughness elements: Deductions for urban boundary layer parameterizations and exchange processes

This paper investigates the flow through and over two-dimensional rectangular roughness elements, arranged in a building-street canyon geometry through a series of experiments. Geometries of different packing densities of the roughness elements (λp) were examined and the packing density values ranged from λp = 0.30 to 0.67. The purpose of the work is: (i) to investigate the flow physics observed both at the boundary layer scale as well as at the scale within the roughness elements for a range of packing densities, (ii) to deduce parameterizations of the adjusted rough boundary layer and their variation with a change in the packing density, and (iii) given a particular interest in and application to the urban atmosphere, a final aim at the roughness-element scale is to deduce the variation of the breathability with the packing density variation. Particle image velocimetery measurements of the velocity flow field as well as the turbulent kinetic energy and the Reynolds Stress (within and up to well-above the street canyons) were conducted. The results reveal qualitative flow features as well as features of the adjusted boundary layer structure—in particular the roughness and inertial sublayers, which can be associated with the surface roughness length, zero-plane displacement thickness, and the friction velocity. The lowest friction velocities are exhibited in the geometries with the highest- and lowest packing densities while the maximum friction velocities are observed in the medium-packed geometries. The exchange processes and breathability at the level of the roughness elements top were characterized and quantified by a mean exchange velocity. The results show that unlike friction velocity, the normalized exchange velocity (over the mean bulk velocity) for the most dense and sparse geometries differ by more than 80%, with the denser-packed geometries exhibiting lower exchange velocities; this is shown to be related with the thickness of the developed roughness sublayer.

Effect of flow confinement on the hydrodynamics of circular impinging jets: implications for erosion assessment

The fluid dynamics of a water jet impinging on a flat surface in confined conditions were studied using particle image velocimetery. The experiments were meant to replicate conditions expected in a jet erosion test (JET) designed to assess cohesive sediment erosion parameters in field applications. High-resolution two-dimensional velocity vectors were measured in a plane passing the jet centerline including free jet, impingement, and wall jet regions within a fixed-wall box. The general flow behavior in the free jet and wall jet regions is in good agreement with the behavior of impinging jets in an unconfined environment. Results show that the entrainment coefficient, however, is lower than values in unconfined conditions, lowering lateral spreading rates. The rate of momentum transfer also increases along the axial direction since the confinement causes secondary flow and recirculation in the box. Wall shear stress is calculated based on extrapolation of Reynolds shear stress and turbulent kinetic energy, where the latter procedure provides more consistent results with expected scour hole shape under an impinging jet. This wall shear stress distribution shows higher values near jet impingement in comparison to previously reported distributions, especially as formulated for the JET under unconfined conditions. The maximum value of wall shear stress is found to be about 2.4 times greater than the commonly accepted value in the literature, and also occurs at a position closer to the impingement point. The shear stress at the impingement point is also close to its maximum value, which is consistent with the expected scour hole shape beneath an impinging jet. These findings have important implications for the use of jet impingement theory to assess sediment erosion, especially in the application of the JET.

Design considerations for large field particle image velocimetery (LF-PIV)

We discuss the challenges and limitations associated with the development of a large field of view particle image velocimetry (LF-PIV) diagnostic, capable of resolving large-scale motions (>1 m per camera) in gas phase laboratory and field experiments. While this diagnostic is developed for the measurement of wakes and local inflow conditions around research wind turbines, the design considerations provided here are also relevant for the application of LF-PIV to atmospheric boundary layer, rotorcraft dynamics and large-scale wind tunnel flows. Measurements over an area of 0.75 m × 1.0 m on a confined vortex were obtained using a standard 2MP camera, with the potential for increasing this area significantly using 11MP cameras. The cameras in this case were oriented orthogonal to the measurement plane receiving only the side-scattered component of light from the particles. Scaling laws associated with LF-PIV systems are also presented along with the performance analysis of low-density, large diameter Expancel particles, that appear to be promising candidates for LF-PIV seeding.

Effect of differential spoiler settings (DSS) on the wake vortices of a wing at high-lift-configuration (HLC)

An experimental investigation has been carried out to evaluate the capabilities of differential spoiler setting (DSS) in modifying the wingspan loading. The particle image velocimetery (PIV) technique was used in a low speed wind tunnel facility to measure wake velocities at four locations downstream of the half model in the near wake field. The model was investigated at a high lift configuration (called base-line configuration) and at two different DSSs believed to modify the base-line wingspan loading. Those settings were obtained by deflecting spoiler number 1 at 10° (outboard loading case 1) and spoiler numbers 2, 3, 4, 5 and 6 at 5° (outboard loading case 2). Results reveal that, introducing a highly turbulent oscillatory wake due to a spoiler in the flow field increases the flap tip vortex meandering amplitude by up to 2.17 times the flap tip vortex core radius value. This result emphasizes the importance of using spatially corrected data in extracting mean vortex parameters values. Moreover meandering can lead to accelerated vortex breakdown especially when the vortex motion intensifies further downstream, contributing favorably to wake vortex alleviation. Integration of the streamwise vorticity shows a mild outboard wing loading shift for outboard loading case 1, while the outboard loading case 2 leads to a reduction in the span-wise circulation with no change in the spanwise load distribution. Evaluation of the effects of outboard loading case 1 on the flap tip vortex structure shows a reduction in the peak vorticity value to 0.46 of the base-line configuration value. This result indicates the effect of diffusion experienced by the vortex due to the increased level of turbulence in the wake. Result of the outboard loading case 2 shows a limited effect in terms of the wing tip vortex structure. This can be due to the relatively large separation distance between the wing tip and the deployed spoilers, preventing the spoiler wake/wing tip vortex interaction in the near field.

Induced rolling moment for NACA4412 plain and flapped wing

PurposeThe paper aims to compute rolling moments on a follower aircraft wing due to vortices generated by a plain and flapped NACA4412 wing using experimental particle image velocimetery (PIV) data.Design/methodology/approachThis paper describes the detailed variation of the induced rolling moment on a follower aircraft wing derived from a PIV velocity field measurement. A rectangular wing of a subsonic wall interference model is used as a vortex generator in two different configurations: plain wing of NACA4412 cross‐section profile; and flapped wing with trailing edge flap of NACA0012 cross‐section profile extended at 20°.FindingsResults obtained showed that the maximum induced rolling moment coefficient depends on the strength of the vortex produced by the generating aircraft wing and increases linearly with the increment of the angle of attack.Originality/valueThis paper provides an insight on the effects of different angles of attacks for plain and flapped wings on the induced rolling moment coefficient and therefore, the hazard imposed on the following aircraft can be estimated.

Investigation of Unsteady Flow Field in a Vaned Diffuser of a Transonic Centrifugal Compressor

Transonic centrifugal compressors are used with high-load turbochargers and turboshaft engines. These compressors usually have a vaned diffuser to increase the efficiency and the pressure ratio. To improve the performance of such a centrifugal compressor, it is required to optimize not only the impeller but also the diffuser. However the flow field of the diffuser is quite complex and unsteady because of the impeller located upstream. Although some research on vaned diffusers has been published, the diffuser flow is strongly dependent on the particular impeller exit flow, and some of the flow physics remain to be elucidated. In the research reported here, detailed flow measurements within a vaned diffuser were conducted using a particle image velocimetery (PIV). The vaned diffuser was designed with high subsonic inlet conditions marked by an inlet Mach number of 0.95 for the transonic compressor. As a result, a complex three-dimensional flow with distortion between the shroud and the hub was observed. Also, unsteady flow accompanying the inflow of the impeller wake was confirmed. Steady computational flow analysis was performed and compared with the experimental results.

Quantification of flow during suction feeding in bluegill sunfish

Nearly all aquatic-feeding vertebrates use some amount of suction to capture prey items. Suction prey capture occurs by accelerating a volume of water into the mouth and taking a prey item along with it. Yet, until recently, we lacked the necessary techniques and analytical tools to quantify the flow regime generated by feeding fish. We used a new approach; Digital Particle Image Velocimetery (DPIV) to measure several attributes of the flow generated by feeding bluegill sunfish. We found that the temporal pattern of flow was notably compressed during prey capture. Flow velocity increased rapidly to its peak within 20 ms of the onset of the strike, and this peak corresponded to the time that the prey entered the mouth during capture. The rapid acceleration and deceleration of water suggests that timing is critical for the predator in positioning itself relative to the prey so that it can be drawn into the mouth along with the water. We also found that the volume of water affected by suction was spatially limited. Only rarely did we measure significant flow beyond 1.75 cm of the mouth aperture (in 20 cm fish), further emphasizing the importance of mechanisms, like locomotion, that place the fish mouth in close proximity to the prey. We found that the highest flows towards the mouth along the fish midline were generated not immediately in front of the open mouth, but approximately 0.5 cm anterior to the mouth opening. Away from the midline the peak in flow was closer to the mouth. We propose that this pattern indicates the presence of a bow wave created by the locomotor efforts of the fish. In this scheme, the bow wave acts antagonistically to the flow of water generated by suction, the net effect being to push the region of peak flow away from the open mouth. The peak was located farther from the mouth opening in strikes accompanied by faster locomotion, suggesting faster fish created larger bow waves.