Detail investigations on the primary breakup of high-viscosity liquids using external-mixing twin-fluid nozzles at increased system pressure are scarce. Therefore, the research work of the present study is focused on the investigation of pressure influence (1 - 11 bar (abs)) on the primary breakup by numerical simulation based on a previously studied nozzle [Müller et al., ASME Turbo Expo 2016, GT2016-56371]. The pressure influence was investigated for two liquids applying a wide range of viscosities (100 mPa s; 400 mPa s) and two atomizing air velocities (58 m/s; 74 m/s). To describe the disintegration process of the fluids, characteristic features like liquid jet morphology, breakup length and breakup frequency were evaluated.

The primary breakup was investigated using the open source CFD software OpenFOAM. To gather the morphology of the primary breakup and the flow field characteristics compressible large eddy simulations (LES) were performed and the movement of the gas-liquid interface was captured by means of the Volume of Fluid-Method (VOF).

The conducted simulations showed good agreement with experimental results with respect to the characteristic features (e.g. morphology and breakup length) and revealed a decrease of the breakup length with increasing ambient pressure for a constant liquid mass flow and atomizing air velocity. Moreover, those findings will contribute to a better understanding of the physics of the breakup of high-viscosity liquid jets and as well to create an experimentally validated CFD based tool for future burner development and optimization.

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