Tomographic shadowgraphy of swirled non-reactive spray injection in a generic aero engine burner under realistic operating conditions

This contribution describes the application of tomographic shadowgraphy to measure instantaneous velocities of droplets undergoing airblast-atomization in the non-reactive flow of a generic aero engine burner model at Weber numbers of We_aero=360-770, air pressures of pa=4-7bar and air temperatures of Ta=440-570K. The burner employs air-blast atomization of a single jet in cross-flow in the main stage. The measurement setup is described in detail and the depth-of-field with respect to droplet size is estimated. The latter was calculated on the basis of Mie simulations and calibration data of the point-spread function. At a given volume size of 16x13x10mm3 it turned out that the minimum resolvable droplet diameter reduces down to d = 10 µm within the focus and increases up to d = 10 -20 µm towards the volume edges. Velocities of droplets above the resolution limit were retrieved by 3D correlation of two volumetric reconstructions recorded at consecutive time-steps. Extracted slices of the instantaneous axial velocity indicate strong motion and fluctuations of the spray tail with increasing temperature and Weber number. Validation against PDA data revealed good agreement at size classes d = 10 µm; 15 µm. Slight deviations occur in regions with strong velocity gradients probably due to the presence of reconstruction ambiguities (ghost particles)