Author: Zhenbo Lu Publisher: ISBN: Category : Fluid dynamics Languages : en Pages : 424
Book Description
4) Closed-loop tests were proposed for a semi-circular leading edge test model, along with a down-sampling control algorithm. It was observed that the closed-loop control could achieve a better control performance than that of the open-loop control. At the optimum control voltage and control phase delay, a noise reduction of 17.5 dB in the duct and 22.6 dB inside the cavity was obtained. In particular, the phase delay of control actuation could be optimally tuned so that the strength of vortex shedding energy could be minimized effectively, leading to a satisfactory noise reduction in the duct and cavity. This process was evident from the spectral phase shift results, where the vortex traveling time has been delayed at downstream of the test model. 5) For the square leading edge test model, the developed surface perturbation technique was also effective. However, the control mechanism was found to be different from that of the semi-circular leading edge test model. The path of the leading edge vortex shedding started from the leading edge and then propagated downstream. The vertical velocity generated by the perturbation played the key role in the vortex strength reduction. More significant reductions can be achieved when the velocity disturbance was near the propagation path of the vortex shedding. 6) The control strategies for two primary leading edge geometries have been investigated. The optimal control strategy for the semi-circular leading edge test model consists in arranging the perturbation at the position where the pressure pulse was the smallest. This way, the targeted noise reduction can be achieved by using perturbation within a relatively small area at a low control voltage. While for the square leading edge test model, the optimal control strategy requires applying the perturbation near the propagation path of the LEVS for achieving sufficient vortex strength abasement. 7) The energy distribution at vortex shedding frequency along the up surface of test model measured by the hot wire was used to identify the existence of the pressure pulse for the semi-circular leading edge test model. It was found that the pressure pulse had strong directivity characteristics; therefore, a small disturbance generated by the surface perturbation can change the direction of the pressure pulse and then influence the generation the vortex shedding.
Author: Publisher: ScholarlyEditions ISBN: 1490108394 Category : Technology & Engineering Languages : en Pages : 607
Book Description
Issues in Aerospace and Defense Research and Application: 2013 Edition is a ScholarlyEditions™ book that delivers timely, authoritative, and comprehensive information about Aerospace Research. The editors have built Issues in Aerospace and Defense Research and Application: 2013 Edition on the vast information databases of ScholarlyNews.™ You can expect the information about Aerospace Research in this book to be deeper than what you can access anywhere else, as well as consistently reliable, authoritative, informed, and relevant. The content of Issues in Aerospace and Defense Research and Application: 2013 Edition has been produced by the world’s leading scientists, engineers, analysts, research institutions, and companies. All of the content is from peer-reviewed sources, and all of it is written, assembled, and edited by the editors at ScholarlyEditions™ and available exclusively from us. You now have a source you can cite with authority, confidence, and credibility. More information is available at http://www.ScholarlyEditions.com/.
Author: M. C. Welsh Publisher: ISBN: Category : Fluid dynamics Languages : en Pages :
Book Description
The active control and attenuation of an acoustic resonance excited by the flow around a plate in a duct is described. The acoustic mode is an evanescent first-cross mode of the duct upstream and downstream of the plate and is known as a Parker-beta mode. It is shown that the minimum gain setting on the power amplifier which generates maximum attenuation is obtained when the sound pressure is fed back into the duct 180 deg. out of phase with the flow-excited sound pressure field. It is also shown that the resonant sound is attenuated at four distinctly different rates as the gain on the power amplifier increases. Initially there is a low rate, followed by a high rate and then a low rate again before the system becomes unstable and rapidly amplifies the sound. It is hypothesised that the higher rate of attenuation is due to the vortex shedding becoming uncorrelated along the trailing edge of the plate. The feedback system initially reduces the amplitude of the acoustic field approximately linearly with gain setting on the power amplifier. When the acoustic particle velocity is less than the threshold necessary to ensure that the vortices are shed in phase from the trailing edge of the plate, the vortex street no longer acts as a strong acoustic source and the resonant sound is rapidly attenuated. This feature of active control systems influencing the source of the sound is distinctly different from the active noise attenuators investigated during the past decade. Using a simple non-adaptive active feedback control system, the resonant acoustic field at the fundamental frequency is attenuated 24 dB, while the first and second harmonics are attenuated by 38 and 12 dB respectively.
Author: Haym Benaroya Publisher: Springer Science & Business Media ISBN: 9400709951 Category : Technology & Engineering Languages : en Pages : 516
Book Description
This plenary paper and the accompanying presentation have highlighted field problems involving fluid-structure interaction over a wide span of Navy operations. Considering the vast size and versatility of the Navy's inventory, the cases presented represent examples of a much larger problem. But even this limited set provides sufficient evidence that fluid-structure interaction does hinder the Navy's ability to accomplish its missions. This survey has also established that there are no accurate and generally applicable design tools for addressing these problems. In the majority of cases the state-of-practice is to either make ad-hoc adjustments and estimates based on historical evidence, or conduct expensive focused tests directed at each specific problem and/or candidate solution. Unfortunately, these approaches do not provide insight into the fundamental problem, and neither can be considered reliable regarding their likelihood of success. So the opportunities for applying computational fluid-structure interaction modeling to Navy problems appear limitless. Scenarios range from the "simple" resonant strumming of underwater and in-air cables, to the "self-contained" flow field and vibration of aircraft/ordnance bodies at various Mach numbers, to violent underwater transient detonations and local hull structural collapse. Generally applicable and computationally tractable design-oriented models for these phenomena are of course still far in the future. But the Navy has taken the first steps in that direction by sponsoring specialized numerical models, validation experiments tailored for specific applications, and conferences such as this one.
Author: Zhenbo Lu
Author: 
Author: L. Mongeau
Author: Louis Cattafesta
Author: M. C. Welsh
Author: Paul Zoccola (Jr., J.)
Author: Haym Benaroya
Author: Jinjun Wang
Author: M. P. Paidoussis
Author: