de Siqueira, Joao V. M. B.Rosa, Mauricio A. P.Ribeiro, Guilherme B.
11页
查看更多>>摘要：Scramjet (supersonic combustion ramjet) engines are often seen as a promising alternative to place payloads in the Earth's orbit. Such air-breathing engines have a simple structure and few moving parts. On the other hand, high heat fluxes and pressure loads on the walls, shock-wave-boundary-layer interactions, and the risk of choked flow inside the isolator channel are a few examples of obstacles that need to be addressed during scramjet design. Therefore, this study aims to evaluate of different air freestream conditions on the flow field in a scramjet inlet (compression ramps and isolator) through detailed three-dimensional computational fluid dynamics (CFD) simulations. The Mach number, flight altitude, and angle of attack were the evaluated conditions. Moreover, this study also focuses on the behavior of the boundary layer separation located at the compression ramp corners, isolator entrance, and scramjet sidewalls. Regarding the Mach number variation, the results showed that high Mach numbers yielded high-pressure levels throughout the engine. Furthermore, a higher altitude promoted a lower total pressure field. Considering the angle of attack changes, it is evident that a higher angle of attack results in a decrease in airflow pressure, while an increase in the total pressure along the walls is observed. By investigating these freestream parameters, this work can contribute to the early phase of engine design, avoiding critical failures in the scramjet structure due to aerodynamic load and thermal stress.
查看更多>>摘要：The use of phase change materials (PCMs) is an efficient passive technique for thermal energy management. However, its low thermal conductivity presents significant technological challenges. Several methods have thus been employed to improve the thermal performance of a latent heat thermal energy storage (LHTES) unit. Here, the melting and heat transfer characteristics for the multi-walled carbon nanotube (MWCNT) enhanced PCM (noctadecane) inside a square duct with a vertical undulated wall has been examined. Extensive results on streamlines, temperature contours, rate of melting and energy storage, and the Nusselt number have been presented to delineate the influence of various pertinent parameters as: amplitude of undulations (0 <=& nbsp;alpha <=& nbsp;0.002 m), wavelength of undulations (0.0025 <=& nbsp;lambda <= 0.02 m) and volume fraction of MWCNT particles (0 <=& nbsp;phi <<= 0.06). In addition, the results from two different heat flux conditions, namely, uniform and sinusoidal heat flux have also been compared. Overall, the complete melting time reduces drastically with an increase in the value of the amplitude to wavelength ratio (alpha/lambda). This functional dependence has been presented in form of a simple predictive correlation. Also, an increase in the volume fraction of MWCNT particles in the PCM enhances the rate of melting. However, this enhancement is more significant for high values of alpha/lambda.
NSTL
Elsevier