Three-dimensional imaging of swirled spray injection in a generic aero engine burner under realistic operating conditions

• Published in: Experiments in fluids Vol. 63; no. 1
• Main Authors: Klinner, Joachim, Willert, Christian E.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 2022; Springer Nature B.V
• Subjects: Aerospace engines; Air temperature; Atomizing; Burners; Cameras; Cross correlation; Cross flow; Depth of field; Diameters; Droplets; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Error analysis; Fluid- and Aerodynamics; Focal plane; Fuel injection; Heat and Mass Transfer; Injectors; Point spread functions; Pulse duration; Random errors; Research Article; Velocity gradient; Weber number
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-021-03343-z

Tomographic shadowgraph imaging is applied to reconstruct the instantaneous three-dimensional spray field immediately downstream of a generic aero engine fuel injector. Within the swirl passage of the injector model, a single kerosene jet undergoes air-blast atomization in a cross-flow configuration at Weber numbers of We = 360 - 770 , air pressures of p a = 4 - 7 bar and air temperatures of T a = 440 - 570 K . High-speed, high magnification shadowgraphy is used to visualize the initial fuel atomization stages within the fuel injector before the spray enters the spray chamber. The 4-camera tomographic measurement setup is described in detail and includes a depth-of-field analysis with respect to droplet size based on Mie simulations and calibration data of the point-spread function. For a volume size of 16 × 13 × 10 mm 3 , the smallest resolvable droplet diameter is estimated to be d = 10 μ m within the focal plane and increases to d ≈ 20 μ m toward the edges of the volume. Droplet velocities above the resolution limit were retrieved by 3-d cross-correlation of two volumetric reconstructions recorded at two consecutive time-steps. This is accompanied by an error analysis on the random error dependency on the camera viewing geometry. The results indicate increasing motion and fluctuations of the spray tail with increasing temperature and Weber number. Validation against PDA data further downstream of the burner plate revealed consistency for size classes d = 10 μ m and d = 15 μ m . Deviations from PDA occur in regions with strong velocity gradients due to different spatial resolutions, the presence of reconstruction ambiguities (ghost particles), uncertainties inherent to the two-frame cross-correlation of spray volumes and the finite LED pulse duration. Graphical Abstract