Monitoring shear deformation of sliding zone via fiber Bragg grating and particle image velocimetry

Monitoring shear deformation of sliding zones is of great significance for understanding the landslide evolution mechanism,in which fiber optic strain sensing has shown great potential.However,the cor-relation between strain measurements of quasi-distributed fiber Bragg grating(FBG)sensing arrays and shear displacements of surrounding soil remains elusive.In this study,a direct shear model test was conducted to simulate the shear deformation of sliding zones,in which the soil internal deformation was captured using FBG strain sensors and the soil surface deformation was measured by particle image velocimetry(PIV).The test results show that there were two main slip surfaces and two secondary ones,developing a spindle-shaped shear band in the soil.The formation of the shear band was successfully captured by FBG sensors.A sinusoidal model was proposed to describe the fiber optic cable deformation behavior.On this basis,the shear displacements and shear band widths were calculated by using strain measurements.This work provides important insight into the deduction of soil shear deformation using soil-embedded FBG strain sensors.

Particle image velocimetry (PIV) measurements of tip vortex wake structure of wind turbine

Large-view flow field measurements using the particle image velocimetry （PIV） technique with high resolution CCD cameras on a rotating 1/8 scale blade model of the NREL UAE phase VI wind turbine are conducted in the engineering-oriented q53.2 m wind tunnel. The motivation is to establish the database of the initiation and development of the tip vortex to study the flow structure and mechanism of the wind turbine. The results show that the tip vortex first moves inward for a very short period and then moves outward with the wake expansion, while its vorticity decreases with time after being trailed from the trailing edge of the blade tip, and then increases continuously with the rapid rolling-up to form a strong tip vortex. The measurements also indicate that the downstream movement of the tip vortex is nearly linear in the very near wake under the test condition.

TWO-DIMENSIONAL PARTICLE IMAGE VELOCIMETRY(PIV) MEASUREMENTS IN A TRANSPARENT CENTRIFUGAL PUMP

A special transparent centrifugal pump is designed. Detailed opticalmeasurements of the flow inside the rotating passages of a five-bladed shroud centrifugal pumpimpeller have been performed by using two-dimensional particle image velocimetry (PIV). The flow issurveyed at three load conditions q_V/q_(Vd) = 0.4, q_V/q_(Vd) = 1.0, q_V/q_(Vd) = 1.5,respectively. As a result, phase averaged PIV velocity vector maps on three planes between hub andshroud of the impeller are presented. At design load, the mean field of relative velocity ispredominantly vane congruent, showing well-behaved flow without separation. The distributions of therelative velocity on different plane along the pump shaft are very different and there is always alow velocity zone near the pressure-side of the blade at both low and design flow rate, but thelow-velocity-zone at the low flow rate is much larger than that at the design one. The studydemonstrates that the PIV technique is efficient in providing reliable and detailed velocity dataover a full impeller passage.

Measurement on soil deformation caused by expanded-base pile in transparent soil using particle image velocimetry (PIV)

A new small-scale geotechnical physical model in 1-g and unconfined condition, combining the transparent soil, close-range photogrammetry and particle image velocimetry(PIV), was employed, which provides a non-intrusively internal deformation measurement approach to monitor the internal deformation of soil caused by expanded-base pile jacking with casing. The transparent soil was made of fused quartz and its refractive index matched blended oil, adding reflective particles(glass beads). Closerange photogrammetry was employed to record the images of the process of casing jacking and extraction in transparent soil, allowing the use of Matlab-based Geo-PIV to figure out the displacement field converted from image space to object space. Analysis of test results indicates that the maximum displacement caused by casing jacking for expandedconical-base pile is decreased by 29% compared with that for expanded-flat-base pile. The main movement happens at the early stage of casing extraction. The maximum displacement caused by casing extraction for the conical base is about 43% of that for the flatbase, while the affected zone caused by casing extraction for the conical base accounts for about 1/3 of that for the flat base. The contraction for horizontal displacements tends to decrease with the depth increasing. By contrast, the contraction under pile base decreases with the increasing of displacement. The displacements generated by jacking a conventional pile having a diameter equal to the casing diameter of the expanded-base pile were comparable to the net displacement taking place due to expanded-base pile installation for the conical base pile.

Study of Diesel Spray Particle Velocity Field Using a Particle Image Velocimetry Setup

Aim To investigate the spray particle velocity and its distribution characteristics. Methods\ A set of PIV (particle image velocimetry) system was developed and used to observe and analyze the spray particle velocity field. Results and Conclusion\ Double exposure image of the spray particle within the region of 10-50 mm from the nozzle tip was recorded and analyzed by the IBAS2000 analysis system. Some characteristics of the spray particle velocity and its distribution were obtained.

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 2.123×104and 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.

Particle Image Velocimetry Measurement of the Flow Field in the Play of the Drilling Pump Valve

The failure of a drilling pump is always due to the break of the drilling pump valve, which is one of the most important but also the weakest parts of the drilling pump. Over the decades, the degradation of drilling pump valves has been investigated extensively and various failure mechanisms have been proposed. However, no experimental test on the fluid has been successfully performed to support some of these mechanisms. In this paper, tests of the flow within the valve play are carried out to investigate the factors resulting in the failure of the valve. In the tests, particle image velocimetry（PIV） technology is employed to measure the flow field distribution of the valve play in the model. From these tests, the distributions of velocity and vorticity of fluid in ＇various valves with different valve angles and different valve lifts are obtained, from which the features of flow fields are derived and generalized. Subsequently, a general rule of the influence of valve angles and valve lifts on the flow velocity is concluded according to chart analyses of maximal velocities and mean velocities. Finally, an analysis is made on the possibility of valve failure caused by erosion and abrasion in a working valve, with the application of the failure mechanisms of drilling pump valves. PIV measurement improves the study on the failure of the drilling pump valve, and the results show good agreement with previous computational fluid dynamics（CFD） simulations.

3D Particle Image Velocimetry Test of Inner Flow in a Double Blade Pump Impeller

The double blade pump is widely used in sewage treatment industry,however,the research on the internal flow characteristics of the double blade pump with particle image velocimetry（PIV） technology is very little at present.To reveal inner flow characteristics in double blade pump impeller under off-design and design conditions,inner flows in a double blade pump impeller,whose specific speed is 111,are measured under the five off-design conditions and design condition by using 3D PIV test technology.In order to ensure the accuracy of the 3D PIV test,the external trigger synchronization system which makes use of fiber optic and equivalent calibration method are applied.The 3D PIV relative velocity synthesis procedure is compiled by using Visual C＋＋ 2005.Then absolute velocity distribution and relative velocity distribution in the double blade pump impeller are obtained.Test results show that vortex exists in each condition,but the location,size and velocity of vortex core are different.Average absolute velocity value of impeller outlet increases at first,then decreases,and then increases again with increase of flow rate.Again average relative velocity values under 0.4,0.8,and 1.2 design condition are higher than that under 1.0 design condition,while under 0.6 and 1.4 design condition it is lower.Under low flow rate conditions,radial vectors of absolute velocities at impeller outlet and blade inlet near the pump shaft decrease with increase of flow rate,while that of relative velocities at the suction side near the pump shaft decreases.Radial vectors of absolute velocities and relative velocities change slightly under the two large flow rate conditions.The research results can be applied to instruct the hydraulic optimization design of double blade pumps.

Investigation of Unsteady Flow Fields for Flow Control Research by Means of Particle Image Velocimetry

Unsteady three-dimensional flow phenomena must be investigated and well understood to be able to design devices to control such complex flow phenomena in order to achieve the desired behavior of the flow and to assess their performance, even in harsh industrial environments. Experimental investigations for flow control research require measurement techniques capable to resolve the flow field with high spatial and temporal resolution to be able to perceive the relevant phenomena. Particle Image Velocimetry (PIV), providing access to the unsteady flow velocity field, is a measurement technique which is readily available commercially today. This explains why PIV is widely used for flow control research. A number of standard configurations exist, which, with increasing complexity, allow capturing flow velocity data instantaneously in geometrical arrangements extending from planes to volumes and in temporal arrangements extending from snapshots to temporarily well resolved data. With increasing complexity these PIV systems require advancing expertise of the user and growing investment costs. Using typical problems of flow control research, three different standard PIV systems will be characterized briefly. It is possible to upgrade a PIV system from a simple planar to a “high end” tomographic PIV system over a period of time, if sufficient PIV expertise can be built up and budget for additional investments becomes available.

A Review of Particle Image Velocimetry for Fish Migration

Understanding the flow characteristic in fishways is crucial for efficient fish migration. Flow characteristic measurements can generally provide quantitative information of velocity distributions in such passages;Particle Image Velocimetry (PIV) has become one of the most versatile techniques to disclose flow fields in general and in fishways, in particular. This paper firstly gives an overview of fish migration along with fish ladders and then the application of PIV measurements on the fish migration process. The overview shows that the quantitative and detailed turbulent flow information in fish ladders obtained by PIV is critical for analyzing turbulent properties and validating numerical results.

Experimental study on movement of particles in centrifugal impeller

The slurry pump is the key component of a dredger. Solid particles have strong influence on the performance of a slurry pump. The movement of solid particles in a centrifugal impeller was studied using particle image velocimetry(PIV) measurement. The experiments were conducted in a dredging pump model at Hohai University. Some transparent glass spheres with diameter of 0. 2-0. 4 mm were used as solid particles. The concentration and relative velocities of the particles were analyzed to investigate the particle trajectory. The results show that the concentration of the particles on the pressure surfaces of the blades is higher than on the suction surfaces,and the particles tend to move towards the suction surfaces. Moreover,the particles have faster relative velocities than the liquid phase through the flow channels of the impeller.

Experimental investigation on flow characteristics in circular tube inserted with rotor-assembled strand using PIV

Rotor-assembled strand works as a typical tube insert to achieve heat transfer augmentation and scale inhibition in a heat exchanger.In this work, the PIV experiment regarding the flow fields in a circular tube inserted with rotor-assembled strand was conducted and the flow characteristics on transverse section and longitudinal section were analyzed.The results showed that swirling flow was produced in the tube inserted with rotors and it was particularly strong within the swing diameter of the rotor on the section that contains the rotor;the average turbulence intensity and the radial velocity were improved notably; the velocity vectors on the longitudinal section remained along the direction of a straight line; both the swirling flow and average turbulence intensity were higher for the rotor with three blades than for the rotor with two blades except that the radial velocity was approximate, but they were all reduced by enlarging the lead of the rotor.Characterization of the flow patterns in a circular tube contributes to understanding the heat transfer efficiency and scale inhibition performance of the rotor-assembled strand and provides guidance for its application.

Experimental investigation on the effect of surface characterization of electrodes on the gas bubble dynamics in electrolyte flow and performance of FLA batteries by using PIV

In the flooded lead_acid batteries(FLAB),gas bubbles are initially formed on the surface of the electrodes,which are produced by electrochemical reactions,and then released into the electrolyte.In the present investigation,the effect of surface characterization of electrodes of FLAB on the gas bubble dynamic parameters in the electrolyte flow at different charging/discharging rates(C-rates)are studied utilizing particle image velocimetry(PIV)method.The results show that the capacity of FLAB have a linear behavior due to changes in each of the two parameters of the surface characterization of electrodes and the Crate.At all State of charges(SOCs)of FLAB cells in different tests,increasing average roughness(Ra)and average wavelength of the roughness(λa)in the electrode surfaces,results in an increase in average bubble diameter and bubble rising velocity.Nevertheless,a sharp decrease in the void fraction of bubbles within the electrolyte was observed due to the increment inλa and Ra.Also,the effect of the rising movement of gas bubbles within the electrolyte on the average electrolyte velocity pattern in the gap between the electrodes by changing the surface characterization of electrodes are investigated in detail.

水流作用下的群桩流场特性PIV试验研究

基于粒子图像测速技术(PIV)开展物理模型试验,对雷诺数Re分别为2400、6000、12000条件下,流向桩心距比为5、横向桩心距比为4时,3×3矩形排列圆桩群桩的局部流场特性开展研究。结果表明,中下游桩间与上中游桩间的流场特性存在显著差异,雷诺数对桩间流场变化影响明显。当Re为2400和6000时,上游中间桩后的尾流涡漩生成长度及回流区长度明显大于两侧边桩,Re为6000时现象更明显,而当Re增大至12000时此现象消失。受上游桩遮蔽作用,中游桩桩后的尾涡强度明显弱于前排桩,回流区面积随之减小。随着雷诺数增大,上游桩桩后尾涡生成长度、回流区尺度逐渐减小。此外,还分析了紊动强度与雷诺切应力在群桩内部平面上的分布变化。本研究以高桩码头桩基础为原型,分析群桩内部流场特性变化,研究结论有助于推进高桩码头泥沙冲淤变化机理的研究,提高高桩码头的安全评估能力。

Experimental evaluation of mechanically stabilized earth walls with recycled crumb rubbers

Traditional techniques for treatment of waste rubber, such as burning, generate some highly non- degradable synthetic materials that cause unrepairable environmental damages by releasing heavy metals, such as arsenic, chromium, lead, manganese and nickel. For this, scrap tires are used as light- weight alternative materials in many engineering applications, such as retaining wall backfilling. In the present study, 90 laboratory models were prepared to evaluate the stability of mechanically stabilized earth （MSE） walls with plate anchors. Then, the bearing capacity and horizontal displacements of the retaining walls were monitored by exerting a static loading to investigate the effects of adding different contents （5 wt%, 10 wt%, 15 wt% and 20 wt%） of recycled crumb rubber （RCR） to the fill of a mechanically stabilized retaining wall with plate anchors. To visualize the critical slip surface of the wall, the particle image velocimetry （PIV） technique was employed. Results showed that the circular anchor plates almost continually provided a higher bearing capacity and wall stability than the square plates. Moreover, the backfill with 15 wt% RCR provided the maximum bearing capacity of the wall. Increasing the weight percentage of RCR to 20 wt% resulted in a significant reduction in horizontal displacement of the wall, which occurred due to the decrease in lateral earth pressure against the whole walls. An increase in RCR content resulted in the decrease in the formation of failure wedge and the expansion of the wall slip surface, and the failure wedge did not form in the sand mixtures with 15 wt% and 20 wt% RCRs.

Laboratory Experiments on an Internal Solitary Wave over a Triangular Barrier

Laboratory experiments were conducted to investigate the evolution of interfacial internal solitary waves(ISWs)incident on a triangular barrier.ISWs with different amplitudes were generated by gravitational collapse.The ISW energy dissipation and turbulence processes were calculated as waves passed over the triangular barrier.Experimental results showed that ISWs were reflecting back off the triangular barrier,and shoaling ISWs led to wave breaking and mixing when waves propagated over the obstacle.Wave instability created the dissipation of energy as it was transmitted from waves to turbulence.The rate of ISW energy dissipation,the maximum turbulent dissipation,and the buoyancy diffusivity linearly increased with the increase in the incident wave energy.

Experimental investigation of turbulent flows around high-rise structure foundations and implications on scour

Many studies have been undertaken to predict local scour around offshore high-rise structure foundations(HRSFs),which have been used in constructing the Donghai Wind Farm in China.However,there have been few works on the turbulent flow that drives the scour process.In this study,the characteristics of the turbulent flow fields around an HRSF were investigated using the particle image velocimetry technique.The mean flow,vorticity,and turbulence intensity were analyzed in detail.The relationship between the flow feature and scour development around an HRSF was elaborated.The results showed that the flow velocity increased to its maximum value near the third row of the pile group.The shear layer and wake vortices could not be fully developed downstream of the last row of the piles at small Reynolds numbers.The strong flow and turbulent fluctuation near the third piles explained the existence of a longtail scour pattern starting from the HRSF shoulders and a trapezoidal deposition region directly downstream of HRSF.This laboratory experiment gains insight into the mechanism of the turbulent flow around HRSFs and provides a rare dataset for numerical model verifications.

EXPERIMENTAL INVESTIGATION OF TIP CLEARANCE FLOW FOR AN AXIAL FLOW FAN ROTOR

The flow field in the tip region of an axial ventilation fan is investigated with a particle image velocimeter （PIV） system at the design condition. Flow fields with three different tip clearances are surveyed on three different circumferential planes, respectively. The phase-locked average method is used to investigate the generation and the development of a tip leakage vortex. The result from PIV system is compared with that from a particle dynamics anemometer（PDA） system. Both data are in good agreement and the structure of the tip leakage vortex for the rotor is illustrated. The characteristic of a leakage vortex is described in both velocity vectors and vortical contours. The unsteadiness of the leakage vortex and the position of the vortex are surveyed in detail, which interprets the discrepancy between the numerical simulation and PDA experimental results to a certain extent. The center loci of tip leakage vortex at different times and the mean center loci of the leakage vortex are displayed particularly. Finally, the trajectories of the tip leakage vortex by the experimental measurement are compared with predictions from the existing models for high speed and high-pressure compressors and turbines when appropriately interpreted. A good agreement is obtained.

Liquid Flow Field on Evaporator of Wiped Short Path Distillation——Experimental Results and Computer Simulation

Short path distillation (SPD) is a kind of high vacuum distillation method, which is suitable for the separation of high boiling, heat sensitivity and viscidity products.In this paper,through measuring the phase-averaged velocity distributions with a conditional sampling method of the particle imaging velocimetry (PIV), the liquid flow field that affects the heat and mass transfer of evaporating thin-film in an SPD evaporator is investigated.Measured results show that the flow velocities decrease rapidly apart from the wiper at different wiper velocities, the maximum velocity appears before wipers, and the quicker the wiping, the larger the flow velocity. Meanwhile, the evaluation of numerical calculations is carried out.The measured velocity distributions indicate clearly the effect of the wiper both on the flow field along its moving direction and on the vortices behind the wiper.Simulation data show that the performance of liquid flow field on the heating surface not only agrees with the experimental results well,but also can give further more information, such as the distribution of turbulent kinetic energy.In this study,turbulent kinetic energy mainly distributes before wipers and laminar flow appears far away from the wipers.

NUMERICAL SIMULATION BY COMPUTATIONAL FLUID DYNAMICS AND EXPERIMENTAL STUDY ON STIRRED BIOREACTOR WITH PUNCHED IMPELLER

Instantaneous flow field and temperature field of the two-phase fluid are measured by particle image velocimetry （PIV） and steady state method during the state of onflow. A turbulent two-phase fluid model of stirred bioreactor with punched impeller is established by the computational fluid dynamics （CFD）, using a rotating coordinate system and sliding mesh to describe the relative motion between impeller and baffles. The simulation and experiment results of flow and temperature field prove their warps are less than 10% and the mathematic model can well simulate the fields, which will also provide the study on optimized-design and scale-up of bioreactors with reference value.