|
Non-intrusive diagnostics, such as planar laser induced fluorescence (PLIF) provide an excellent means to interrogate flowfields with minimal perturbation to the thermodynamic state of the gas. In the case of PLIF, the diagnostic can provide multidimensional information regarding the spread of a tracer, such as I2, providing an excellent means for quantifying mixing between multiple streams of gases. The images obtained using PLIF can in turn be used to compare directly to images generated by computational fluid dynamic (CFD) simulations for the experiment, providing an excellent mechanism to compare CFD to experiment. An issue that exists with interpreting PLIF images from compressible flows is that the local density and temperature of the I2 varies throughout the field of imaging, leading to variations in the rate of fluorescence and the rate of quenching of the excited state of I2. These variations lead to local changes in the number of photons generated during the course of the laser pulse that excites the I2, beyond the variation due to the varying density of I2. Thus, when comparing PLIF images for compressible flows with CFD simulation data, some effort should be made to ensure that the CFD image reflects the local variations in photon production that occur in compressible flows. A method is presented here where a CFD simulation data for a compressible PLIF experiment is used to predict the local photon production during the course of interrogating laser pulse. The experiment consists of a chemical oxygen-iodine laser mixing nozzle utilizing Mach 3 injection of a He/I2 mixture into a Mach 2.5 crossflow with a mixture of He and O2 and has strong compressibility. The method utilizes numerical solutions for the ordinary differential equations describing the state-to-state processes within the I2 fluorescence process where I2(X) is pumped to the I2(B), fluoresces and is quenched. These equations are solved locally within the flowfield predicted by the CFD simulation to predict the variations within the photon production, and compare directly with PLIF images from the experiment.
|
