Browsing by Author "Fonseca, Joel Nogueira"
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- Experimental study on the mixing of confined coaxial jetsPublication . Fonseca, Joel Nogueira; Silva, André Resende Rodrigues daThe turbulent mixing of coaxial confined jets is a complex dynamic process that is applied in a large number of devices such as the engineering ejectors, pumps jet, industrial burners, combustion chambers of jet engines, nuclear rockets gas, mixing chambers of turbofans, afterburners, and so on. The study of the aerodynamic performance of coaxial jets in different types of confinement also has a fundamental interest because it involves the interaction of different turbulent flow phenomena, whose details are not yet very well known quantitatively. The parameters that are involved in the process of mixing and are primarily responsible for the complexity of the process are both geometric or operational parameters such as: velocity, temperature or density ratios, compressibility effects, levels of turbulence of jets, pressure gradient, interaction between the walls and the jets or the ratio between the diameters of the mixing duct and the internal jet nozzle. In the literature several studies report the influence of some geometrical parameters and operating in the process of turbulent mixing. Turbulent mixing of two parallel streams is affected by confinement, velocity ratio, and turbulent intensity. The objective of this work is to study the effect of the initial levels of turbulence of each coaxial jet in the process of turbulent mixing for diameter ratios less than 2, which is the case of very low bypass turbofan engines. The use of convenient turbulent intensity ratios between the inner and the outer flow should be a most effective tool to control the turbulent mixing between the inner and outer flow (θ). The aim of the present work is to study the effect of θ on the flow development and to identify the associated regimes, and in particular the production of a flow reversal in the central zone near the jets exit. To isolate the characteristic radial effects of a cylindrical geometry a bi-dimensional configurations was adopted. The present results were obtained for a velocity ratio, λ, of 2, and turbulent intensities of 30% the mean mass flow velocity (Umean) that correspond to a ratio between the outer and inner jets of θ=1.5. Prior to the measurements flow visualization was performed to give a qualitative picture of the flow and to guide the choice of the measurement locations.