| Planar laser-induced fluorescence is a kind of laser spectral measurement technology which can realize the concentration distribution measurement of planar flow field,due to its excellent tracer particle followability and the multi-component synchronous measurement capablity,this technology can be applied to flow field structure visualization of aircraft external environment and equivalence ratio measurement of flow field in engine.However,the current PLIF technology is difficult to realize the structural stability analysis of the flow field.The dual-tracer PLIF technology lacks the quantitative research on the interaction rule of the tracers,which results in a large local measurement uncertainty.In view of the limitations of these PLIF technologies,this paper studies the flow field structure stability analysis method based on the high-frequency acetone PLIF technology and the acetone/toluene dual tracer PLIF technology for simultaneous measurement of two components concentration.Acetone PLIF system was designed to realize the visualization of airfoil boundary layer flow field structure in wind tunnel.In this study,dynamic modal decomposition was used for the first time to calculate continuous time series PLIF images of flow field structure,the frequency spectrum and oscillatory region distribution of the main modes in the flow field can be obtained by computational decomposition.Based on this,the dynamic change process and structural stability of the local area of the flow field can be analyzed.Using acetone and toluene as dual tracers,the acetone/toluene PLIF technology for the concentration measurement of two components was studied.In order to improve the concentration measurement accuracy of acetone/toluene PLIF technology,the absorption,quenching and enhancement effects of tracer on fluorescence signal were studied to for the first time,which uesd for establishing the quantitative relationship between these effects and tracer concentration.The experimental results show that acetone has obvious absorption effect on the fluorescence signal of toluene,the effective absorption cross section is(5.77±0.41)×10-20 cm-2,while toluene has no obvious absorption effect on the acetone's fluorescence signal.Acetone molecule has obvious quenching effect on toluene fluorescence signal,the quenching law is in accordance with Stern-Volmer equation,and the quenching constant is(0.50±0.03)k Pa-1.Toluene has enhanced effect on the acetone's fluorescence signal,and the enhancement coefficient decreases with the increase of acetone concentration,showing an exponential relationship.Based on the above experimental results,the photophysical process of fluorescent radiation signals of tracer was summarized,providing a theoretical basis for the implementation of acetone/toluene PLIF technology.The research method of tracer interaction in this paper can also be applied to the research process of other dual-tracer PLIF technologies in the future.Based on the quantitative relations and the photophysical process in the interaction between acetone and toluene,the relationship equations between the fluorescence intensity of acetone/toluene and the two tracers'concentrations were established.Using two detectors to capture the fluorescence intensity of acetone and toluene corresponding to space and time respectively,the concentration of acetone and toluene can be obtained by solving the equations,and the two components concentration can be measured.The first acetone/toluene PLIF system was designed to achieve the synchronous quantitative concentration distribution measurement of two gas components,and the correctness of the measurement results was verified by the simulation results of Fluent.Compared with the traditional dual tracer PLIF technology with a maximum relative measurement uncertainty of 20%,the acetone/toluene PLIF technology in this paper reduces the maximum relative measurement uncertainty of concentration to 10.4%due to the consideration of the tracers'interaction,thus achieving the improvement of measurement accuracy.Finally,the equivalent ratio distribution of the cold flow field was calculated based on the concentration measurements of the two components obtained by acetone/toluene PLIF technology.The experimental results show that although acetone/toluene PLIF technology cannot be directly applied to the equivalent ratio measurement of combustion field,when the measured object is laminar flame,the variation trend of equivalent ratio distribution in cold flow field under the same working condition obtained by acetone/toluene PLIF technology is consistent with that of combustion field.This fully demonstrates that the measurement data of acetone/toluene PLIF technology can be used to analyze and predict the variation trend of equivalent ratio distribution in laminar flame combustion field. |
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