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Flow-Field and Performance Study of Coaxial Supersonic Nozzles Operating in Hypersonic Environment

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The integration of multiple propulsion systems in a coaxial configuration is one of the challenges to realize hypersonic passenger transportation. This study is an attempt to understand the performance of two co-axial jets exiting from the base of slender body, operating in single and dual operation mode in freestream hypersonic flow environment. In addition, the effects on performance by adding a different length common channel to both co-axial jets are studied. In the first part of this study, the experiments have been performed for small slender body kept in hypersonic Mach 7 flow, which consists of two inner high-pressure chambers and two co-axial nozzles at the base: central nozzle (Mach 4) and surrounding nozzle (Mach 2.8) along with extended common region, termed as common channel. Schlieren images have been captured for single and dual operation modes. Axisymmetric numerical simulations have been performed for further understanding of the flow interactions and have been qualitatively validated with experimental images. In the second part, the parametric study has been performed using numerical simulations for resized model with various exit Mach numbers for central and surrounding jets along with effect of no common channel and with common channel for various operation modes. One of the findings of the study is that dual jets should operate and exit at same plane (no common channel) with the same exit area (each nozzle with half of total available exit area) in order to have higher total thrust from both jets than the sum of individual jets operating in single operation mode. For higher central jet Mach numbers, the corresponding surrounding jet Mach number will be lower, and in dual operation mode (without common channel), the total thrust will be the same or lower than the sum of the individual jet operations. Regarding the effect of common channel, it has been found out that the introduction of the extended short or long common channel in dual mode operation does not have significant effect on thrust, while the jet flow field is strongly affected by the common channel presence. In single operation mode, for Mach 2 central-jet, the thrust performance decreases 12.2-14.6 % in presence of short and long (29.5 mm and 59 mm) common channel, while for Mach 2 surrounding jet, the thrust performance increases by 15-17.4 % in presence of common channel.
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Hypersonic Flow; Supersonic Jets; CFD; Wind Tunnel Experiment; Co-Axial Nozzles

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