Experimental study of inert and reactive two-phase flows by optical diagnostics applied in extreme conditions
In aerospace propulsion systems, liquid fuels are used for their compactness, ensuring reasonable tank sizes. Understanding two-phase combustion requires the description of complex multi-physical phenomena (atomization, evaporation, mixing, etc.), over a wide range of spatial and temporal scales. This document deals with experimental work on two-phase flows, inert or reactive, studied at the Multi-Physics for Energetics Department of ONERA. The objective of this work is the understanding of turbulent combustion of liquid fuels by means of coupled optical diagnostics, applied in so-called extreme conditions. By extreme, we define the conditions of application of optical techniques in pressurized combustion chambers, with limited optical access and test durations. This presentation is organized around three two-phase flow injection systems : coaxial assisted, swirl and transverse to a supersonic flow, encountered respectively in rocket engines, aeronautical combustion chambers and ramjets. For each type of injection, the main experimental facilities of ONERA are described to understand the complexity of implementing coupled optical diagnostics.
Figure 1 : Instantaneous image showing the atomization process of assisted coaxial injection in a liquid oxygen/methane combustion on the MASCOTTE test bench of ONERA
The aim of this work is to demonstrate the key role of atomization on flame structure and instabilities in two-phase combustion, in academic and industrial configurations. Backlight imaging and particle sizing systems are used to characterize the dense jet structure and liquid jet atomization, illustrated in Figure 1. Laser Mie scattering and laser particle sizing diagnostics are used to study instabilities in reactive swirling flows. High-speed schlieren and PLIF techniques are implemented to characterize the shock interaction with atomization and the vaporization of a liquid fuel jet injected in a high-temperature Mach 2 supersonic crossflow.
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