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978-3-8439-1619-6, Reihe Ingenieurwissenschaften
Direct numerical simulation of the primary breakup of aircraft engine related two-phase flows
167 Seiten, Dissertation Technische Universität Darmstadt (2014), Softcover, A5
Numerical experiments represent an alternative for the investigation of the primary breakup of prefilming airblast atomizers under aircraft engine operating conditions. Direct Numerical Simulations (DNS) resolving the phase interface are computationally demanding as the grid needs to be fine enough to resolve the turbulence and the smallest structures resulting from the breakup. In addition, the prefilming geometry requires a significant domain size to facilitate the breakup. The spatial domain extension and the temporal development of the liquid sheet disintegration complicates the numerical simulation.
The overall goal of this work was a validation of the applicability of the embedded DNS approach. The embedded DNS methodology consisted of three major steps: First, the complex annular airblast atomizer geometry was simplified to the generic planar configuration. Second, the embedded domain required turbulent inflow boundary conditions for the co-flowing air streams. These transient data were gained from highly-resolved Large Eddy Simulations of the turbulent channel flow. Third, only the primary breakup region was computed using interface resolving two-phase flow DNS. Different operating points were simulated ranging from low Reynolds and Weber numbers to conditions approaching the operating range of aircraft engines.
In a first step, the turbulent channel flow set-up was utilized to gain turbulent inflow conditions for the embedded domain. A zonal grid approach was applied to assure high result quality while mitigating the computational demand. The approach showed good agreement to DNS results even at high Reynolds numbers. In a second step, the embedded DNS of the breakup region was computed. A qualitative and quantitative investgation proved the agreement with experimental studies within the low Reynolds and Weber number range. Atomization mechanisms determined in these experiments were identified for the computations. This confirmed the applicability of the eDNS methodology. The method then offered the possibility to simulate the primary breakup of an airbasted sheet for aircraft engine operating conditions. For the first time, these conditions were investigated either numerically or by use of an experiment. In addition, the influence of turbulence on the characteristics of the liquid sheet disintegration was shown.