PIV Methods Research Articles

Laboratory modeling of hydrodynamic instability and sound generation processes in the ship NPS

This work is devoted to investigations of the self-oscillation regimes in the model of emergency stop valve chamber in the ductline of the systems of heat exchange in the ship nuclear power setup (NPS). Experiments were carried out on special aeroacoustical setup with simultaneous use of PIV methods for measuring velocity fields and measurements of sound generation characteristics. Dependency of parameters of self-oscillation regimes on the parameter of the length of the gap between the inlet and outlet ducts in the chamber was investigated. An explanation of the observed regimes was proposed.

Influence of jet exit conditions on mixing and statistics of flow fine structures

Mixing in a coaxial jet mixer was investigated at variable initial conditions simultaneously using PIV and PLIF methods. Velocity and concentration fields were measured at two spatial resolutions: across the mixer and in a small area at its axis resolving Kolmogorov's scale. Jet exit conditions were modeled by varying flow rate (3⋅103 ≤ Red ≤ 1.78⋅104) and by applying vortex generators (tabs) at the jet exit. The study was executed within a transition flow region. Nevertheless, it is possible to claim that in the self-similarity flow region mean flow parameters do not depend on the initial conditions but turbulence does. The influence of the initial conditions is manifested in turbulent characteristics measured at a high spatial resolution and in the size of fine structures of the studied flows.

Measurements of Turbulence in a Gas-Liquid Two-Phase Flow by Using an Electro-Magnetic Probe and PIV Methods

Measurements of Turbulence in a Gas-Liquid Two-Phase Flow by Using an Electro-Magnetic Probe and PIV Methods

Studies by PIV-methods of self oscillating hydrodynamic processes in the elements of pipeline

Investigation of the self-oscillation regimes in the flow chamber modelling elements of stop valves in the pipeline in the systems of heat exchange in the power plants were performed by using PIV methods. Dependency of parameters of self-oscillation regimes on the parameter of the gap between the inlet and outlet pipe line in the chamber was investigated. Simultaneous measurements of the hydrodynamic and acoustic fluctuations allows us to offer explanation of the observed regimes.

Исследование свободной конвекции в кубической полости методами PIV и POD

Исследование свободной конвекции в кубической полости методами PIV и POD

Prototype of an Echo-PIV Method for Use in Underwater Nuclear Decommissioning Inspections

The ongoing decommissioning of the Fukushima Daiichi (1F) nuclear power plant requires the inspection of the inside of containment vessels that have been submerged in water. These inspections must locate leaks and map the distribution of fuel debris in water with very low visibility. This paper reports the design and testing of an echo-PIV system that uses a single divergent signal wave and delay-and-sum processing to efficiently map the interior and fluid flow within a submerged vessel. The diverging wave and delay-and-sum processing improve upon the performance of conventional ultrasound PIV methods specifically to meet the demands of containment vessel inspections. The imaging method uses an ultrasonic linear sensor array that emits a diverging wave that covers a wide angle with a single transmission. The delay-and-sum algorithm combines echo signals recorded by each element of the sensor array. We optimized the design of an echo-PIV system in laboratory-scale tests, and then tested the prototype with a mockup of a containment vessel in a water tank. The small-scale prototype successfully located a mock leak and mapped the surface of a piece of mock debris. This prototype can be scaled up readily for inspections at the Fukushima Daiichi plant.

The analysis of plasma acitretin and etretinate levels in patients treated with acitretin

A guide vane cascade is developed for the study of flow in the distributor of a low specific speed Francis turbine. Velocity and pressure measurements are done with Reynold's number 1.15 E+07, at 80% of BEP flow as in a reference prototype turbine. This work illustrates the development of test setup and focuses on investigation of PIV methods applied for the velocity measurements. Techniques developed for ‘in-situ’ calibration of PIV setup and methods applied for image processing are discussed in details. Approach to estimate total uncertainty in PIV measurements and minimum no of image pairs required for statistical convergence of velocity field is presented. Reference measurements are done along the plane of chord, from guide vane wall to its mid-span. Flow velocity exceeding 35 m/s, at the runner inlet of Francis turbine, is reported for the first time from such experimental studies. Flow phenomenon inside Francis turbine distributor are characterized and comparison are done with the cases for prototype turbines. The cascade setup is found to reproduce the flow conditions inside a Francis turbine distributor, except the rotor-stator-interaction. PIV methods are generalized for the cases of similar measurements and the results will be applicable to validate numerical studies.

Comparison of intracranial aneurysm flow quantification techniques: standard PIV vs stereoscopic PIV vs tomographic PIV vs phase-contrast MRI vs CFD

Image-based hemodynamic simulations to assess the rupture risk or improve the treatment planning of intracranial aneurysms have become popular recently. However, due to strong modeling assumptions and limitations, the acceptance...

Flow measurements around guide vanes of Francis turbine: A PIV approach

A guide vane cascade is developed for the study of flow in the distributor of a low specific speed Francis turbine. Velocity and pressure measurements are done with Reynold's number 1.15 E+07, at 80% of BEP flow as in a reference prototype turbine. This work illustrates the development of test setup and focuses on investigation of PIV methods applied for the velocity measurements. Techniques developed for ‘in-situ’ calibration of PIV setup and methods applied for image processing are discussed in details. Approach to estimate total uncertainty in PIV measurements and minimum no of image pairs required for statistical convergence of velocity field is presented. Reference measurements are done along the plane of chord, from guide vane wall to its mid-span. Flow velocity exceeding 35 m/s, at the runner inlet of Francis turbine, is reported for the first time from such experimental studies. Flow phenomenon inside Francis turbine distributor are characterized and comparison are done with the cases for prototype turbines. The cascade setup is found to reproduce the flow conditions inside a Francis turbine distributor, except the rotor-stator-interaction. PIV methods are generalized for the cases of similar measurements and the results will be applicable to validate numerical studies.

PIV-DCNN: cascaded deep convolutional neural networks for particle image velocimetry

Velocity estimation (extracting the displacement vector information) from the particle image pairs is of critical importance for particle image velocimetry. This problem is mostly transformed into finding the sub-pixel peak in a correlation map. To address the original displacement extraction problem, we propose a different evaluation scheme (PIV-DCNN) with four-level regression deep convolutional neural networks. At each level, the networks are trained to predict a vector from two input image patches. The low-level network is skilled at large displacement estimation and the high- level networks are devoted to improving the accuracy. Outlier replacement and symmetric window offset operation glue the well- functioning networks in a cascaded manner. Through comparison with the standard PIV methods (one-pass cross-correlation method, three-pass window deformation), the practicability of the proposed PIV-DCNN is verified by the application to a diversity of synthetic and experimental PIV images.

The particular use of PIV methods for the modelling of heat and hydrophysical processes in the nuclear power plants

In this paper we describe PIV-system specially designed for the study of the hydrophysical processes in large-scale benchmark setup of promising fast reactor. The system allows the PIV-measurements for the conditions of complicated configuration of the reactor benchmark, reflections and distortions section of the laser sheet, blackout, in the closed volume. The use of filtering techniques and method of masks images enabled us to reduce the number of incorrect measurement of flow velocity vectors by an order. The method of conversion of image coordinates and velocity field in the reference model of the reactor using a virtual 3D simulation targets, without loss of accuracy in comparison with a method of using physical objects in filming area was released. The results of measurements of velocity fields in various modes, both stationary (workers), as well as in non-stationary (emergency).

A laser sheet self-calibration method for scanning PIV

Knowledge of laser sheet position, orientation, and thickness is a fundamental requirement of scanning PIV and other laser-scanning methods. This paper describes the development and evaluation of a new laser sheet self-calibration method for stereoscopic scanning PIV, which allows the measurement of these properties from particle images themselves. The approach is to fit a laser sheet model by treating particles as randomly distributed probes of the laser sheet profile, whose position is obtained via a triangulation procedure enhanced by matching particle images according to their variation in brightness over a scan. Numerical simulations and tests with experimental data were used to quantify the sensitivity of the method to typical experimental error sources and validate its performance in practice. The numerical simulations demonstrate the accurate recovery of the laser sheet parameters over range of different seeding densities and sheet thicknesses. Furthermore, they show that the method is robust to significant image noise and camera misalignment. Tests with experimental data confirm that the laser sheet model can be accurately reconstructed with no impairment to PIV measurement accuracy. The new method is more efficient and robust in comparison with the standard (self-) calibration approach, which requires an involved, separate calibration step that is sensitive to experimental misalignments. The method significantly improves the practicality of making accurate scanning PIV measurements and broadens its potential applicability to scanning systems with significant vibrations.

Study of the effect of external periodic flow perturbations on heat transfer intensity in the impact jet

The aim of this work is to experimentally study unsteady heat transfer in an impact jet flowing onto a heated surface with the presence of large-scale structures and separated flows, as well as to search for possible mechanisms for controlling heat transfer by introducing external disturbances into the flow. In the work, a series of experiments was carried out to study an axisymmetric jet flowing normally onto a heated surface. The jet was both under natural conditions with different flow regimes and under external excitation at various frequencies and amplitudes. The instantaneous and average velocity and temperature fields in the near-wall part of the jet are measured using the PIV and PLIF methods. The correlations of velocity fluctuations and temperature fluctuations, which characterize the intensity of turbulent heat transfer, are calculated. It is shown that at different frequencies of external excitation of the jet, the intensity of turbulent transfer in the region of jet impingement on the wall changes. In the region of jet impingement on the wall, flow separation was recorded. It is shown that the interaction of the coherent structure with the wall leads to a local increase in the outflow of heat from the heated surface. The distributions of the heat transfer coefficient along the heated surface were also measured using a thermal imaging camera for various flow regimes, distances from the nozzle exit to the barrier, frequencies and amplitudes of the external flow disturbance. It is shown that when the jet is excited at different frequencies of the jet excitation, the heat transfer increases or decreases.

Experimental Investigation of the Mixed Convection of a Gas in a Rectangular Enclosure with a Local Heat Source and Heat Removal at the Outer Boundaries

The mixed convection of a gas in a parallelepiped with heat conducting walls and a local source of energy at its lower side was investigated experimentally. Local temperatures and velocities of the gas flow at different intensities of its convection in this parallelepiped, characterizing the main mechanisms of the mixed convection of a gas in such a close space, were determined. The results of experimental investigations were compared with corresponding calculation data and were in good agreement with them, which allowed the conclusion that the experimental procedure based on the thermocouple measurements and the use of PIV methods is applicable for analysis of the regimes of flow of a heat-conducting viscous gas. Experiments have shown that the approach developed for the experimental investigation of the mixed convection of a gas in a rectangular enclosure with heat-conducting walls and a local source of energy can be used in fairly wide ranges of change in the main parameters of the gas flow and in the conditions of supply of energy to it.

Combination of PIV and PLIF methods to study convective heat transfer in an impinging jet

For simultaneous measurement of instantaneous fields of temperature and velocity in the near-wall areas of the impinging jet combination of PLIF and PIV methods is implemented. The algorithms to reduce the measurement error of PLIF method are proposed. Unsteady heat transfer in axisymmetric jet impinging normally onto the plane heated surface is experimentally investigated. The turbulent heat fluxes in the stagnation point region and self-similar region of the flow have been figured out. The intensity of turbulent heat transfer has been obtained. Up to 25% of heat transfer intensity is provided by a mechanism of turbulence.

Design and development of guide vane cascade for a low speed number Francis turbine

Guide vane cascade of a low speed number Francis turbine is developed for the experimental investigations. The test setup is able to produce similar velocity distributions at the runner inlet as that of a reference prototype turbine. Standard analytical methods are used to design the reference turbine. Periodic walls of flow channel between guide vanes are identified as the starting profile for the boundary of the cascade. Two alternative designs with three guide vanes and two guide vanes, without runner, are studied. A new approach, for the hydraulic design and optimization of the cascade test setup layout, is proposed and investigated in details. CFD based optimization methods are used to define the final layout of the test setup. The optimum design is developed as a test setup and experimental validation is done with PIV methods. The optimized design of cascade with one guide vane between two flow channels is found to produce similar flow conditions to that in the runner inlet of a low speed number Francis turbine.

CFD 해석 및 PIV 실험을 통한 연료유 스크러버의 노즐 위치선정

CFD 해석 및 PIV 실험을 통한 연료유 스크러버의 노즐 위치선정

0301 LIFとPIV法による気泡後流の可視化から気液界面のコンタミが気泡後流に与える影響の考察

0301 LIFとPIV法による気泡後流の可視化から気液界面のコンタミが気泡後流に与える影響の考察

10908 LESとLIF法による正方密閉矩形容器内自然対流の熱流動特性の解明

The present study focuses on the turbulent natural convection heat transfer in a cubical enclosed rectangular container. The container is composed of the heated and the cooled side plates. The working fluid is water to attain larger value of Rayleigh number. The numerical simulation with LES is conducted at the same time in order to elucidate the experimental result with PIV and LIF methods. It is obvious that the heat transfer coefficient using simulation with LES is well correlated with that of the experimental investigation.

Investigation of the turbulent swirl flow in pipe generated by axial fans using PIV and LDA methods

In this paper is presented experimental investigation of the turbulent swirl flow in pipe generated by axial fans. Two various models of industrial axial fans are used. One of these is axial fan W30, model AP 400, Minel, Serbia and has seven blades and outer diameter 0.397m. Second axial fan SP30 is model TGT/2-400-6, S&P, Spain, has six blades and outer diameter 0.386m. This results with greater clearance in the second case. Blades were adjusted for both fans at the angle of 30? at the outer diameter. Test rig length is 27.74-D, where D is average inner diameter app. 0.4 m. Measurements are performed in two measuring sections downstream the axial fans (z/D = 3.35 and z/D = 26.31) with one-component laser Doppler anemometry (LDA) system and stereo particle image velocimetry (SPIV). Obtained Reynolds numbers, calculated on the basis of the average axial velocity (Um) in the first measuring section are for fan SP30 Re = 226757, while for fan W30 Re = 254010. Integral flow parameters are determined such as average circulation and swirl number. Significant downstream axial velocity transformation occurs for both fans, while circumferential velocity is decreased, but non-dimensional velocity profile remains the same. Circumferential velocity distribution for both fans in the central zone corresponds to the solid body, while in r/R > 0.4, where D = 2R, distribution is more uniform. Radial velocity in the case of fan SP30 has almost zero values in the measuring section z/D = 3.35, while its values are significantly increased in the downstream section with the maximum in the vortex core region. On the contrary radial velocity decreases downstream for fan W30 and has also maximum value in the vortex core region for both measuring sections. Level of turbulence, skewness and flatness factors are calculated on the basis of the experimental data. The highest levels of turbulence for circumferential velocity are reached in the vortex core region for both fans. It is shown how statistical moments of the third and fourth order differ from the values for normal Gaussian distribution. In this paper are also analyzed velocity fields by use of SPIV.