Research on advanced PIV algorithms and their aplication in measuring complex flow fields.pdf

1、This repot focuses on the development and validation of a bootstrap filter based particle image tracking algorithm, an intelligent PIV image processing platform and highefficient TR-PIV algorithms.A detailed analysis of

2、the mainstream particle imageinterrogation algorithms are firstly carried out by summarising their principles, procedures and pointing out their advantages and disadvantages.One of the commonproblems of these methods is

3、the deployment of the constant velocity assumption forparticle motion between two image frames, which will result in serious errors whenapplied in high velocity gradient flows.Therefore, a simple nonlinear dynamic modelw

4、hich takes particle acceleration into account is proposed and a sequential Monte Carlomethod-bootstrap filter is employed to strengthen the particle image tracking performance.This new method is validated by using numeri

5、cally generated and real PIVimages.It is proved that the Bootstrap Filter Tracking method is very reliable and robust for processing high velocity gradient, low particle density flows, and it can yieldup to 0.8 times mor

6、e valid particle image pairs than the Super-PIV and Kalman FilterTracking methods.
　　 The second work of the report is the development of a software package which encapsulates six widely used interrogation algorithms

7、.The influence of particle imagedensity on the measurement accuracy of the pattern match schemes are evaluated withartificial particle images.The measurement accuracy of the six algorithms are thenstudied by using partic

8、le images generated from synthetic Rankine vortex flow as wellas real vortex and turbulent jet flows.Finally, an automated particle image processingprocedure is proposed and verified by the artificial and real particle i

9、mages.
　　 Aiming to reduce the computational cost of time-series TR-PIV measurements, thethird part of this report presents improvements made for two widely used PIV algorithms, namely the multi-grid and iterative im

10、age deformation cross correlation.Thehistorical displacement field and its variation were employed to determine the windowoffset and image deformation calculation in the above-mentioned algorithms, respectively.Performan

11、ce of the improved algorithms was extensively evaluated by usingsynthetic images of artificial Rankine vortex flow and wake flow behind square cylinderdetermined by CFD as well as real time-series TR-PIV measurements.The

12、 comparison between improved TR-PIV methods and traditional ones show that the improvedalgorithms can save up to 50％ computational time while keep measurement accuracysame as the traditional iterative PIV algorithms.By t

13、aking displacement variation intoaccount, the improved methods can successfully handle unsteady flows where localdisplacements vary more than 20％ between the image frames.
　　 The last section of this report applies a

14、dvanced PIV algorithms to measure fluid flowaround a bio-inspired airfoil with corrugated surfaces and its smooth counterpart atchord Reynolds number Re =2000.The global characteristics of the fluid flow aroundtwo airfoi

15、ls were analyzed by ensemble-averaged velocity field, distribution of reverseflow intermittency, and time-series flow visualizations.Through PIV experimentalstudies, it was found that at AOA =0~, no significant variation

16、 of the global flow patterns was recognized for both configurations.The statistical results of reverse flowintermittency results demonstrated that the protruding peaks of the corrugated airfoildelay flow separation atAOA

17、 =40.At large AOAs (80 and 120), however, the flow wasmassively separated in both configurations; the combination of large separation bubbleabove the corrugated airfoil and small recirculation zones in the upstream upper