Wind turbine acoustics

Available information on the physical characteristics of the noise generated by wind turbines is summarized, with example sound pressure time histories, narrow- and broadband frequency spectra, and noise radiation patterns. Reviewed are noise measurement standards, analysis technology, and a method of characterizing wind turbine noise. Prediction methods are given for both low-frequency rotational harmonics and broadband noise components. Also included are atmospheric propagation data showing the effects of distance and refraction by wind shear. Human perception thresholds, based on laboratory and field tests, are given. Building vibration analysis methods are summarized. The bibliography of this report lists technical publications on all aspects of wind turbine acoustics

Investigation of Bio-Inspired Pin Geometries for Enhanced Heat Transfer Applications

Array of circular cylindrical pins or tubes are one of the most widely used type of convection cooling systems, profoundly used in the internal cooling of gas turbine blades. They promote heat transfer due to flow acceleration, secondary flows and wake shedding, at the expense of large pressure loss and unsteadiness in the flow. The need to reduce pressure loss and maintain the heat transfer rates are a much needed requirement for a variety of industries to improve the cooling efficiency. One such prominent line of research is conducted on optimizing the design of the circular cylindrical pins to increase their cooling performance. Bio-mimicked harbor seal whisker have been studied from an aerodynamic standpoint, due to their ability to reduce drag and flow unsteadiness. While applying this mimicked geometry in thermal management research, it was found that they lead to reduction in cooling system pumping power requirements, with the potential to maintain heat transfer performance. The seal whisker geometry consists of streamwise and spanwise undulations which reduce the size of the wake and coherent structures shed from the body; a result of an added component of streamwise vorticity along the pin surface. In addition, the vortex shedding frequency becomes less pronounced, leading to significantly reduced lateral loading on the modified cylinder. These whisker geometries are studied for their aero behavior but not from a thermal performance stand point. Hence the main objective of this study is to understand and utilize different flow physics of these whisker geometries in a wall bounded configuration. Computational studies have shown that the modified wake and vortex shedding structures resulting from the geometry tend to reduce the total pressure loss throughout the system without significantly degrading the cooling levels and experimental results agree with these findings. In comparison to a conventional elliptical pin the bio pins have an increase in thermal performance at constant pressure drop by 9% and by 45% in comparison to a conventional cylindrical pin. These findings are important to the gas turbine community and heat exchangers as reduced penalties associated with cooling flows directly translate to improved thermodynamic and propulsive efficiencies

Princes Charming are not all made equal. The social cognition of mating strategies in four classical fairy tales

In this paper, we apply the so-called Tie-Up Theory to the analysis of the social cognition of mating processes in fairy tales. Our analysis considers the four classical fairy tales that are more relevant to this topic, and proves how their structure systematically reflects the logic of the male–female interaction anticipated by the theory, and in addition allows to formulate an interesting typology of strategic approaches by the male partner. Unlike preexisting interpretations, where fairy tale characters tend to be presented as stereotypes, our analysis shows how, in their most sophisticated and interesting variants, the said fairy tales place an emphasis on the unique individual traits that make the potential partners reciprocally fit to form the couple. This change of perspective is conducive to interesting applications both from the viewpoint of the analysis of fairy tales and in terms of the implications of the related form of social cognition for the study and the understanding of human behavior

High-speed imaging in fluids

High-speed imaging is in popular demand for a broad range of experiments in fluids. It allows for a detailed visualization of the event under study by acquiring a series of image frames captured at high temporal and spatial resolution. This review covers high-speed imaging basics, by defining criteria for high-speed imaging experiments in fluids and to give rule-of-thumbs for a series of cases. It also considers stroboscopic imaging, triggering and illumination, and scaling issues. It provides guidelines for testing and calibration. Ultra high-speed imaging at frame rates exceeding 1 million frames per second is reviewed, and the combination of conventional experiments in fluids techniques with high-speed imaging techniques are discussed. The review is concluded with a high-speed imaging chart, which summarizes criteria for temporal scale and spatial scale and which facilitates the selection of a high-speed imaging system for the applicatio