Recent advances in vibroacoustics
Numerous vibroacoustics advances and problems in the aerospace industry have occurred over the last 15 years. This article addresses some of these that developed from engineering programmatic task-work at the NASA Glenn Research Center at Lewis Field.
NOISE AND VIBRATION OF SPACECRAFT STRUCTURES RUIDO Y VIBRACIÓN DE ESTRUCTURAS DE VEHÍCULOS ESPACIALES
The launch of space craft generates extreme conditions, such as vibrations and acoustics that can affect the launch pad, space craft, and their payloads. The noise at launch and during the two-minute liftoff and transonic climb phase causes intense acoustic loads. These acoustic loads are the result of an intense acoustic environment generated by the interaction of the rocket-engine exhaust stream mixing with the atmosphere. Pyroshocks, that occur when spacecraft vehicle stages separate, cause additional vibration problems. In this article, an overview of the main aspects related to noise and vibration problems experienced by spacecraft structures is presented. Most of the information is based on the Space Shuttle experiences at the NASA’s John F. Kennedy Space Center (KSC). In addition, a review of the vibroacoustic research being conducted at KSC is presented. These research programs are aimed at designing future space launch facilities, where cost and rocket exhaust launch noise are significantly reduced.
Effect of superficial gas velocity on the particle temperature distribution in a fluidized bed with heat production
The heat transfer behavior of particles and gas in an olefin polymerization fluidized bed was numerically analyzed using an in-house developed 3-D computational fluid dynamics discrete element model (CFD-DEM). First the implementation of the model was verified by comparing simulation results with analytical results. A constant volumetric heat production rate was implemented in the particle energy equation to mimic the heat production due to the polymerization reaction. It was found that the probability density function (PDF) of the particle temperature becomes more homogeneous with increasing superficial gas velocity. Furthermore, instantaneous snapshots of the thermal driving force (the difference between the single particle temperature and bed-average gas temperature, Tp− ) for different heat production rates provide detailed insight in the particle temperature distribution inside the fluidized bed. The time- and bed-averaged particle convective heat transfer coefficient, which was calculated by Gunn׳s correlation, was found to be independent of the superficial gas velocity. This is explained by the fact that the relative velocity of gas and particles in the emulsion phase, where most of the particles and gas interact, is hardly influenced when increasing the gas superficial velocity. From the spatial distribution of Nusselt number, it becomes apparent that the high heat transfer regions are found in the wake of rising bubbles, whereas low heat transfer rates are found in the clouds of the bubbles.