Gas Phase Velocity Measurements in a Swirled Air/Kerosene Burning Spray downstream from an Actual Turbojet Injection System

Abstract

The validation of spray combustion models requires experimental data which are still lacking in configurations representative of actual air-breathing combustors. This paper presents successful measurements of the velocity field of the gaseous phase in an air/kerosene burning spray downstream from an actual injection system of a gas turbine, Fig. 1. The injection system was fitted in a square section combustion chamber with windows, Fig. 2 . The experiments were performed at atmospheric pressure. The gas phase was seeded with Zirconia particles of a few micrometer size. Stokes number evaluation and cold flow LDV measurements demonstrated that Zirconia particles tagged well the gaseous flow. The measurements were performed with a Phase Doppler device measuring simultaneously the velocity and the size of the Zirconia particles and of the kerosene droplets. To obtain the average velocity values and the RMS values of the velocity fluctuations of the gas phase, the samples of particles were sorted according to the size to keep only the particles smaller than five micrometers, Fig. 16. Then, the reduced samples were first decomposed, with the MIXMOD software, in several Gaussian distributions or populations, one of them corresponding to the Zirconia particles tagging the gas phase, the others to populations of small kerosene droplets. Figures 18 and 19 present the velocity distributions of the two main populations extracted from the sample of fig. 16, with the MIXMOD software. Then the discrimination between the Zirconia particles and the small kerosene droplets was performed according to the size, the size/velocity distribution, Fig. 19, and the velocity distribution shape of the smaller particles or droplets. For the quasi bimodal velocity distribution shown Fig. 16, it was easy to discriminate on the corresponding size-velocity plot, Fig. 19, the small kerosene droplets population with an average velocity of about 35 m/s, which is contiguous to the velocities of the larger kerosene droplets, from the Zirconia particles population with an average velocity of about 70 m/s, which the size distribution does not extend further than 10 μm. The exact average and RMS velocity values of each population were given by the MIXMOD software. The measurements were carried out along several radii, for the three velocity components (axial, tangential and radial). Then, for every measurement point, the data were processed: size filtering, extraction of Gaussian populations, reading of average and RMS velocity values for each population, identification of the Zirconia particle population tagging the gas phase. An example of the result of such a process is given Fig. 20 and 21 for the section 10 mm downstream from the injector. Such results have been obtained up to the end of the combustion zone, to provide CFD modelers with as much accurate and as many data as possible for the validation of spray combustion models.