Particle Image Velocimetry Results Research Articles

ESP performance for various dust densities

In this paper, results of particle image velocimetry (PIV) measurements of the electrohydrodynamic (EHD) flow velocity fields in an electrostatic precipitator (ESP) are presented. The measurements were carried out for various densities of submicron dust. The ESP was an acrylic parallelepiped with a wire discharge electrode, placed perpendicularly to the main flow, and two plate collecting electrodes. The positive DC voltage was applied to the wire electrode. The PIV measurements were carried out in an observation plane set perpendicularly to the wire electrode at its half-length. The obtained results show that the general shape of the flow patterns at different dust densities is similar in the bulk of the flow. However, the flow velocity and the level of its turbulence strongly depend on the dust density, in particular in the region around the wire electrode.

Numerical and Experimental Study of a Continuous Electrostatic Smoking Process

The smoking process is a batch one with long duration processing (some hours). Deposition of smoke particles can be enhanced by electrostatic precipitation. However, a better knowledge of the fundamental physics is needed to optimize the process. We carried out experimental and numerical studies to obtain essential information on the smoke flow. First, experiments physically characterized the wood smoke. These measures lead us to study the turbulent two-phase flow using an algebraic slip model. The main coupling with electrical forces is taken into account through the slip velocity. Various assumptions were tested concerning the coupled phenomena in order to build an algorithm that is able to simulate these phenomena. Numerical resolutions are compared with data from the literature on a simple electrostatic precipitator (three wires between two plates). Simultaneously, experiments were performed on a simplified scaled-down model of the smoking process (wires and one plate). The results of particle image velocimetry show clearly that the electrostatic precipitation phenomenon is effective above a threshold voltage and is significantly influenced by geometry of electrodes. Experiments and numerical resolutions underwent a validation phase. A small-size industrial demonstrator, of which the promising results will not be discussed in this paper, was conceived by exploiting the presented works.

Flow-adaptive data validation scheme in PIV

A post-interrogation data validation technique is used to remove the spurious vectors in particle image velocimetry (PIV) results. The local-median method with constant user-adjustable thresholds usually works well when an appropriate threshold is set for a specified flow field. However, the selection of the appropriate threshold is not always easy since no guidance, such as the under-detected and over-detected percentages, is available to follow. In addition, a single constant threshold is generally not applicable in complicated flows such as inhomogeneous gradient flows or vortical flows. A flow-adaptive data validation (FADV) scheme is proposed in this study to avoid the selection of the appropriate thresholds for specified flow fields. Simulated non-uniform gradient flows and vortical flows with a noise distribution are added with simulated single or clusters of error vectors to evaluate the performance of the FADV scheme. Its performance is compared with the local-median method. The results show that the performance of the FADV scheme is superior to the local-median method, although the performance of the latter is optimized with the optimal threshold in each set of simulated conditions. The FADV scheme is also applied in a real measured turbulent swirling flow in gas cyclones.

Pneumatic Transport of Granular Materials in an Inclined Conveying Pipe: Comparison of Computational Fluid Dynamics−Discrete Element Method (CFD−DEM), Electrical Capacitance Tomography (ECT), and Particle Image Velocimetry (PIV) Results

This paper presents three flow patternsdispersed flow, reverse flow, and half-ring flowin the post-bend region of a 45° inclined pneumatic conveying pipe. Solid concentration and velocity distribution were measured using electrical capacitance tomography (ECT), particle image velocimetry (PIV), and a high-speed camera. The axial velocity of particles and solid transverse motion in the pipe cross section were obtained using a modified cross-correlation method from the ECT data for the three flow patterns. The axial velocity profile over the pipe cross section was compared with data obtained from the PIV system. In particular, emphasis has been placed on the characterization of the reverse-flow pattern, where negative values of solid velocities were observed. By analyzing the images captured with the high-speed camera, three distinct regions in the solid phase of the reverse-flow regime may be discerned. A dense region with high solid concentration formed next to the bottom wall of the inclined conveying pipe, while a dilute region with a relatively low solid concentration formed near the center of the pipe. Reverse flow was observed to occur predominantly in the dense region and a transition region between the two. Finally, the dynamic forces acting on single particles were analyzed for the three flow patterns. This analysis showed that the phenomena of reverse-flow and half-ring flow structure formation may be attributed to the effects of electrostatics. This finding has also been validated with results of numerical simulations performed in the present study.

In Vitro Evaluation of Flow Divertors in an Elastase-Induced Saccular Aneurysm Model in Rabbit

Endovascular coiling is an acceptable treatment of intracranial aneurysms, yet long term follow-ups suggest that endovascular coiling fails to achieve complete aneurysm occlusions particularly in wide-neck and giant aneurysms. Placing of a stentlike device across the aneurysm neck may be sufficient to occlude the aneurysm by promoting intra-aneurysmal thrombosis; however, conclusive evidence of its efficacy is still lacking. In this study, we investigate in vitro the efficacy of custom designed flow divertors that will be subsequently implanted in a large cohort of animals. The aim of this study is to provide a detailed database against which in vivo results can be analyzed. Six custom designed flow divertors were fabricated and tested in vitro. The design matrix included three different porosities (75%, 70%, and 65%). For each porosity, there were two divertors with one having a nominal pore density double than that of the other. To quantify efficacy, the divertors were implanted in a compliant elastomeric model of an elastase-induced aneurysm model in rabbit and intra-aneurysmal flow changes were evaluated by particle image velocimetry (PIV). PIV results indicate a marked reduction in intra-aneurysmal flow activity after divertor implantation in the innominate artery across the aneurysm neck. The mean hydrodynamic circulation after divertor implantation was reduced to 14% or less of the mean circulation in the control and the mean intra-aneurysmal kinetic energy was reduced to 29% or less of its value in the control. The intra-aneurysmal wall shear rate in this model is low and implantation of the flow divertor did not change the wall shear rate magnitude appreciably. This in vitro experiment evaluates the characteristics of local flow phenomena such as hydrodynamic circulation, kinetic energy, wall shear rate, perforator flow, and changes of these parameters as a result of implantation of stentlike flow divertors in an elastomeric replica of elastase-induced saccular aneurysm model in rabbit. These initial findings offer a database for evaluation of in vivo implantations of such devices in the animal model and help in further development of cerebral aneurysm bypass devices.

Aspect-Ratio and Reynolds-Number Effects on Short-Span Cross-Flow Impellers without Casings

The purpose of this experimental research is to clarify both the aspect-ratio effect and the Reynolds-number effect, especially for the flow of cross-flow impellers with shorter axes. Particle-image-velocimetry (PIV) technique and a hot-wire anemometer are used for measurements of flow velocity. The impeller rotates without any casings. The authors study two kinds of the impellers, that is, one with forward-cambered blades and the other with radial-flat blades. As a result, observing eccentric-vortex revolution by using hot-wire measurements and flow visualisations, the flow can be classified into three modes. According to this classification, the authors show flow-regime maps for both impellers. Using PIV results, the authors define outflow rate Q from the impeller. Outflow-rate coefficient CQ is independent of the Reynolds number for both impellers. For the radial-flat-blade impeller, CQ is not affected by aspect ratio L/D2. But, for the forward-cambered-blade impeller, CQ increases with L/D2.

B107 タービンシュラウドの傾斜インピンジメント冷却に関する実験的研究

Very effective cooling methods have been required for high-temperature gas turbines. Reduction of cooling air also contributes to the improvement of jet engine performance, because the cooling air is bled from compressor of jet engine. Therefore, from this point of view, Multiple inclined impingement cooling for turbine shroud cooling has been invented by IHI, JAXA and authors' group. This cooling structure realizes 50% reduction of cooling air compared with conventional one maintaining same cooling efficiency. However detailed internal cooling behavior has not been clarified. This study is one of the researches in collaboration with IET, JAXA and us. The main purpose is to clarify the cooling behavior by Particle Image Velocimetry (PIV) and heat transfer measurement on the impingement wall by IR camera. In this paper, we describe the results of PIV for 4 types of acrylic test pieces (impingement angle=90°, 45°, 35°, 25°). The characteristics of time-averaged velocity, turbulence intensity and pressure drop were considered.

Evaluation of CFD Accuracy for the Ventilation Study of a Naturally Ventilated Broiler House

Using the CFD model, a new ventilation system design will be found later taking into consideration the ventilation efficiency such as uniformity, stability, and suitability of environmental factors in a naturally ventilated broiler house. Because conducting a field experiment for the ventilation study presented so many difficulties, a reliable 3-dimentional computational fluid dynamics (CFD) model had to be developed to investigate the natural ventilation. Before investigating its accuracy, a wind tunnel and particle image velocimetry (PIV) test was initially conducted to find their best experimental conditions and improve the PIV accuracy13,15. A 1/20 scale model of a naturally ventilated broiler house was used to get qualitative and quantitative airflow distribution in the broiler house using the PIV and CFD. To improve the CFD accuracy, the PIV and CFD computed airflows in the broiler house were compared, particularly on the distribution, local air velocity, and turbulent intensity in the house. The quality of the mesh density and the design of the boundary condition, especially the wind velocity and turbulence profiles, were found to be very important for getting accurate results. Assuming the PIV results were accurate, the most accurate CFD results were obtained when using a RNG k-ε turbulence numerical model. The average error of the CFD computed air velocity when using the RNG k-ε models was -6.2%.

Intensity Capping: a simple method to improve cross-correlation PIV results

A common source of error in particle image velocimetry (PIV) is the presence of bright spots within the images. These bright spots are characterized by grayscale intensities much greater than the mean intensity of the image and are typically generated by intense scattering from seed particles. The displace- ment of bright spots can dominate the cross-correlation calculation within an interrogation window, and may thereby bias the resulting velocity vector. An efficient and easy-to-implement image-enhancement procedure is described to improve PIV results when bright spots are present. The procedure, called Intensity Capping, imposes a user-specified upper limit to the grayscale intensity of the images. The displacement calculation then better represents the displacement of all particles in an interrogation window and the bias due to bright spots is reduced. Four PIV codes and a large set of experimental and simulated images were used to evaluate the performance of Intensity Capping. The results indicate that Intensity Capping can significantly increase the number of valid vectors from experimen- tal image pairs and reduce displacement error in the analysis of simulated images. A comparison with other PIV image-enhancement techniques shows that Inten- sity Capping offers competitive performance, low computational cost, ease of implementation, and min- imal modification to the images.

Phase-Locked Particle Image Velocimetry Measurements of a Flapping Wing

The unsteady aerodynamics of a biomimetic inspired flapping-wing mechanism has been analyzed by performing detailed phase-locked diagnostics of its flow field. Flow visualization and particle image velocimetry results have shown the presence of a shed dynamic stall vortex that spans across most of the wing span. The shedding of this type of leading-edge vortex was accompanied by the formation of another leading-edge vortex before the first vortex reached the midchord, resulting in multiple shedding leading-edge vortices on the top surface of the wing during each wing stroke. A strong starting vortex was also formed at the trailing edge of the wing during the early part of its translational stroke. This vortex continuously gained strength from shed vorticity as the wing accelerated into its stroke. The starting vortex remained close to the trailing edge until the wing reached midstroke. A pair of vortices that continuously trailed from the root and tip of the wing were identified, both of which induced a significant downwash velocity over the wing surface. These trailed vortices were found to exhibit a contracting wake structure as they convected into the wake below the wing, consistent with an increase in slipstream velocity. The evolution of the tip and root vortex pair showed rapid diffusive characteristics with an increase in time (wake age).

Aspect-Ratio and Reynolds-Number Effects on Short-Span Cross-Flow Impellers without Casings

The purpose of this experimental research is to clarify both the aspect-ratio effect and the Reynolds-number effect, especially for the flow of cross-flow impellers with shorter axes. Particle-image-velocimetry (PIV) technique and a hot-wire anemometer are used for measurements of flow velocity. The impeller rotates without any casings. The authors study two kinds of the impellers, that is, one with forward-cambered blades and the other with radial-flat blades. As a result, observing eccentric-vortex revolution by using hot-wire measurements and flow visualisations, the flow can be classified into three modes. According to this classification, the authors show flow-regime maps for both impellers. Using PIV results, the authors define outflow rate Q from the impeller. Outflow-rate coefficient CQ is independent of the Reynolds number for both impellers. For the radial-flat-blade impeller, CQ is not affected by aspect ratio L/D2. But, for the forward-cambered-blade impeller, CQ increases with L/D2.

Aspect-Ratio and Reynolds-number Effect On Cross-Flow Impellers(Fluid Machinery)

The purpose of this experimental research is to investigate both the aspect-ratio effect and the Reynolds-number effect, especially for the flow of impellers with short axes. Particle-image-velocimetry (PIV) technique and a hot-wire anemometer are used for measurements of flow velocity. The impeller rotates in open space without any casings. The authors have studied two kinds of the impeller, that is with forward-curved blades and with flat-plate blades. As a result, the following were obtained. Observing eccentric vortex revolution using hot-wire measurements and flow visualization, we classified the flow into three modes. And according to this classification, we showed stability diagrams for both impellers. Using PIV results, we defined outflow rate Q from impeller. Outflow rate coefficient C_Q is independent of Re for both impellers. For a flat-blade-impeller, C_Q is not affected by aspect ratio L/D_2. But, for a forward-curved-impeller, C_Q increases with L/D_2.

Observations of flow repeatability and secondary circulation in an oscillating grid-stirred tank

An oscillating grid-stirred tank was studied for flow repeatability and the existence of secondary circulations. For the particular tank studied, results indicate that mean flow values may vary by up to 25% and turbulent fluctuations may vary by up to 15% from one run to another. This result was observed to exhibit a potential grid geometry dependence. More importantly, there is evidence of significant flow field sensitivity to initial conditions. Particle image velocimetry results were used to reveal secondary mean flows in the grid-stirred tank. Because these characteristics are believed to be intrinsic to grid-stirred tanks, studies using such tanks must recognize and consider these effects.

LDA and PIV Analyses of In-Cylinder Steady Flow and Verifications of Numerical Simulation Results with Partial Cells Method

Characteristics of the flow inside an engine cylinder model have been evaluated by a particle image velocimetry (PIV) and a laser Doppler anemometer (LDA). Verifications of the results by Partial Cells in Cartesian coordinate method numerical simulation have been also made by the experiment results. The model engine head that has two intake valves and transparent cylinder are used in the steady state flow condition. The tests are conducted by single- and dual- valve open condition with 8 mm valve lift in-1470 Pa suction gauge pressure. The comparisons between the PIV and the LDA experiments show almost the same tendencies for mean velocities and turbulence intensities in the whole experimental regien qualitatively and also quantitatively. The differences in the valve open condition are clearly observed in the integral length and time scales that are estimated from the PIV and LDA data respectively. It is shown that the PIV results are useful for verification of numerical results, which agree reasonably with those of experiments.

D106 血液ポンプの壁近傍せん断速度の定量化手法の比較

Quantitative flow visualizations using Particle Tracking Velocimetry (PTV) and Particle Image Velocimetry (PIV) were performed to remove the origin of hemolysis to obtain the suitable design criteria. Particular attention was paid to the relationship between the high shear area and hemolysis. As a result, the shear velocities in the high hemolysis pump were higher than those in the low hemolysis pump near the casing wall by the results of both PTV and PIV. However, the shear velocities by PIV were half times as large as those by PTV in a current comparison.

Particle image velocimetry and visualization of natural and forced flow around rectangular cylinders

Particle image velocimetry (PIV) measurements and flow visualization in a water tunnel show that vortex shedding at the leading and trailing edges of rectangular cylinders can be simultaneously phase-locked to transverse velocity perturbations when the applied perturbation Stp is close to an impinging leading-edge vortex/trailing-edge vortex shedding (ILEV/TEVS) frequency. The transverse perturbations, analogous to β-mode duct acoustic resonances, are generated through harmonic oscillations of the sidewalls. When this occurs, the leading-edge vortices are found always to pass the trailing edge at the same phase in the perturbation cycle regardless of the chord-to-thickness (c/t) ratio. Applying perturbations at an Stp not equal to the natural global frequency also results in phase-locked vortex shedding from the leading edge, and a near wake with a frequency equal to the perturbation frequency. This is consistent with previous experimental findings. However, vortex shedding at the trailing edge is either weaker or non-existent. PIV results and flow visualization showed trailing-edge vortex growth was weaker because leading-edge vortices arrive at the trailing edge at a phase in the perturbation cycle where they interfere with trailing-edge shedding. The frequencies at which trailing-edge vortices form for different c/t ratios correspond to the natural ILEV/TEVS frequencies. As in the case of natural shedding, peaks in base suction occur when the leading-edge vortices pass the trailing edge at the phase in the perturbation cycle (and thus in the leading-edge shedding cycle) that allows strong trailing-edge shedding. This is the reason for the similarity in the Stvs.c/t relationship for three seemingly different sets of experiments.

Measurements and Analyses of Toner Motion in the Development Process

This report presents a study of the measurements and analyses of toner motion in the development process. By employing a laser sheet visualization technique, toner motions around the spaced single-component development system can be measured. In addition, some quantifying analyses of toner motion were conducted using Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV). In addition to these analyses, the analyzing method of “toner trace tracking” is introduced. This method calculates the virtual toner trace from the velocity map obtained from PIV results. The quantified toner traces have allowed us to compare measurements and calculations, and obtain more accurate model calculations.

Direct comparison of 2D PIV and stereoscopic PIV measurements

A stereoscopic particle image velocimetry (PIV) measurement system based onthe translation configuration was developed and applied to the flow behind aforward-swept axial-fan with five blades in a water tank. The 3D calibrationprocedure was employed to compensate the distortion and refraction of particleimages. The perspective error caused by the out-of-plane motion was estimated bydirect comparison of the 2D PIV and stereoscopic PIV (SPIV) results. The SPIVand 2D PIV comparison was carried out for the particle images capturedsimultaneously. The difference of mean velocity data measured by 2D PIV andSPIV techniques is nearly proportional to the mean out-of-plane velocitycomponent. The difference appears to be relatively large in the region nearthe fan blade having higher out-of-plane motion. The perspective errorestimated from the calibration data and mean out-of-plane velocity dataagrees with the mean velocity difference between the 2D PIV and SPIVresults. The turbulence intensity measured by the 2D PIV method isoverestimated in comparison to that of the SPIV method due to the projectedvelocity fluctuations of the out-of-plane velocity component. The turbulentfluctuations caused by the out-of-plane velocity component were estimated bymultiplication of the incident angle obtained in the calibration procedure andout-of-plane velocity fluctuations. The estimated perspective fluctuation ofthe out-of-plane velocity component was compared with the differencemeasured by the two methods. In SPIV measurements of turbulent statistics,therefore, the ratio of out-of-plane to in-plane RMS error determined from thesystem set-up should be considered in order to obtain reliable results.

A study on internal flow field of automotive torque converter—three-dimensional flow analysis around a stator cascade of automotive torque converter by using PIV and CT techniques

The internal flow field around the stator of an automotive torque converter is investigated experimentally in this study by using particle image velocimetry (PIV). The objective of this investigation is to understand the flow field around the stator that plays an important role in enhancing the characteristics of the torque converter performance. Computerized tomography (CT) technique was applied to analyse the three-dimensional flow field using a series of two-dimensional PIV results obtained from two orthogonal directions. The three-dimensional data obtained in this study is utilized to improve the performance of the torque converter through the optimal design of the stator. The experimental results obtained in this way can be used to validate the accuracy of computational fluid dynamics (CFD).

Dual-plane stereoscopic particle image velocimetry: system set-up and its application on a lobed jet mixing flow

The technical basis and system set-up of a dual-plane stereoscopic particle image velocimetry (PIV) system, which can obtain the flow velocity (all three components) fields at two spatially separated planes simultaneously, is summarized. The simultaneous measurements were achieved by using two sets of double-pulsed Nd:Yag lasers with additional optics to illuminate the objective fluid flow with two orthogonally linearly polarized laser sheets at two spatially separated planes, as proposed by Kaehler and Kompenhans in 1999. The light scattered by the tracer particles illuminated by laser sheets with orthogonal linear polarization were separated by using polarizing beam-splitter cubes, then recorded by high-resolution CCD cameras. A three-dimensional in-situ calibration procedure was used to determine the relationships between the 2-D image planes and three-dimensional object fields for both position mapping and velocity three-component reconstruction. Unlike conventional two-component PIV systems or single-plane stereoscopic PIV systems, which can only get one-component of vorticity vectors, the present dual-plane stereoscopic PIV system can provide all the three components of the vorticity vectors and various auto-correlation and cross-correlation coefficients of flow variables instantaneously and simultaneously. The present dual-plane stereoscopic PIV system was applied to measure an air jet mixing flow exhausted from a lobed nozzle. Various vortex structures in the lobed jet mixing flow were revealed quantitatively and instantaneously. In order to evaluate the measurement accuracy of the present dual-plane stereoscopic PIV system, the measurement results were compared with the simultaneous measurement results of a laser Doppler velocimetry (LDV) system. It was found that both the instantaneous data and ensemble-averaged values of the stereoscopic PIV measurement results and the LDV measurement results agree well. For the ensemble-averaged values of the out-of-plane velocity component at comparison points, the differences between the stereoscopic PIV and LDV measurement results were found to be less than 2%.