流体中速度场检测方案(粒子图像测速)

13" Int. Symp on Appl. Laser Techniques to Fluid Mechanics， Lisbon， Portugal， June 26 - 29， 200613.6 Flare Removal in Gas Phase PIV： Optimization of Fluorescent Tracers Mourad Chennaoui'， Ewan J. McGhee’， Catherine E. Towers’， Anita C. Jones， David P. Towers 1： School of Chemistry， The University of Edinburgh， UK， m.chennaoui@sms.ed.ac.uk 2： School of Engineering and Physical Science， Heriot-Watt University， UK， e.j.mcghee@hw.ac.uk 3： School of Mechanical Engineering， The University of Leeds， UK， c.e.towers@leeds.ac.uk 4： School of Chemistry， The University of Edinburgh， UK， a.c.jones@ed.ac.uk 5： School of Mechanical Engineering， The University of Leeds， UK， d.p.towers@leeds.ac.uk Keywords： Fluorescent PIV， Flare Removal， Gas phase flows， Multi-constituent flows 1. Background and Motivation Fluorescent tracer particles have found a number ofuses inPIV. A light sheet produces flare when it impinges upon anobject within the field of view， preventing particle imagesfrom being obtained and hence ppreventing velocitymeasurements in that locality.An example is shown infigure 1 where 532nm light is used for excitation and imaging.Whilst in some situations flare may be minimized by carefulexperiment setup， in some applications flare is difficult toavoid and prevents information from being obtained， e.g. inboundary layer measurements. A further application hasbeen explored where fluorescent tracers are used to opticallylabel one phase or constituent of a flow and thereby enablesimultaneous multi-constituent PIV [1-3]. Fig. 1 Example of image flare with Mie scattering The general application of fluorescent tracers to gas phaseflow seeding requires sufficient fluorescence emission frommicron sized tracers when imaged over 10’s of mm field ofview. For multi-constituent and multi-phase flows sufficientchromatic separation is also) requiredbetween theilluminationand the fluorescenceandbetween thefluorescence and any wavelengths used for Mie scattering. 2. Fluorescent Tracer Selection The use of UV excitation， e.g. tripled Nd：YAG， at 355nm，with ‘blue’fluorescence emission， at ~450nm， has beenselected to remove the excitation and emission wavelengthsfrom the spectral regions conventionally used with PIV.Furthermore， emission at 450nm lies near the centre of the‘blue’imnaagse layer of color CCD cameras.：A series ofsuitable dyes were evaluated for fluorescence yield andlinearity (absence of quenching) at high concentrations.. Thestudy showed that Bis-MSB provides the best performancewhen dissolved in either olive oil， or for higher yield inparaffin oil. The dye was further evaluated using an oil inwater emulsion to simulate the effect of small tracer particles before experimenting with atomized droplets. 3.Experiments and Results The dye was evaluated using a twin cavity pulsed Nd：YAGlaser (Continuum Surelite II-10) with a common externalfrequency tripler. Images were recorded onto a La VisionImager Intense camera. Droplets of paraffin oil wereatomized and the drop size measured as 0.6-1.6um using aninterferometric technique.It was found that satisfactoryimages could be obtained with ~30mJ of 355nm excitationusing a lens F# of 2. An example image is shown in figure2and the vector map from a double pulse image pair is shownin figure 3. Fig.22fluorescence emission at~450 nm from UV(355 nm) excitation Fig.3 vector map obtained from a double pulse image pairof fluorescence images. 1. D P Towers. C E Towers et al. Measurement ScienceTechnology，10 (1999)824-830 2. T Boedec，S Simoens，3Int. Workshop on PIV (1999)139-144 3. G Rottenkolber et al， 3Int. Workshop on PIV (1999)209-216