The simulation of coherent structures in a laminar boundary layer

Coherent structures in turbulent shear flows were studied extensively by several techniques, including the VITA technique which selects rapidly accelerating or decelerating regions in the flow. The evolution of a localized disturbance in a laminar boundary layer shows strong similarity to the evolution of coherent structures in a turbulent-wall bounded flow. Starting from a liftup-sweep motion, a strong shear layer develops which shares many of the features seen in conditionally-sampled turbulent velocity fields. The structure of the shear layer, Reynolds stress distribution, and wall pressure footprint are qualitatively the same, indicating that the dynamics responsible for the structure's evolution are simple mechanisms dependent only on the presence of a high mean shear and a wall and independent of the effects of local random fluctuations and outer flow effects. As the disturbance progressed, the development of streak-like-high- and low-speed regions associated with the three-dimensionality

Biomechanics of smart wings in a bat robot: morphing wings using SMA actuators

This paper presents the design of a bat-like micro aerial vehicle with actuated morphing wings. NiTi shape memory alloys (SMAs) acting as artificial biceps and triceps muscles are used for mimicking the morphing wing mechanism of the bat flight apparatus. Our objective is twofold. Firstly, we have implemented a control architecture that allows an accurate and fast SMA actuation. This control makes use of the electrical resistance measurements of SMAs to adjust morphing wing motions. Secondly, the feasibility of using SMA actuation technology is evaluated for the application at hand. To this purpose, experiments are conducted to analyze the control performance in terms of nominal and overloaded operation modes of the SMAs. This analysis includes: (i) inertial forces regarding the stretchable wing membrane and aerodynamic loads, and (ii) uncertainties due to impact of airflow conditions over the resistance–motion relationship of SMAs. With the proposed control, morphing actuation speed can be increased up to 2.5 Hz, being sufficient to generate lift forces at a cruising speed of 5ms−1

Genomic investigations of unexplained acute hepatitis in children

Since its first identification in Scotland, over 1,000 cases of unexplained paediatric hepatitis in children have been reported worldwide, including 278 cases in the UK1. Here we report an investigation of 38 cases, 66 age-matched immunocompetent controls and 21 immunocompromised comparator participants, using a combination of genomic, transcriptomic, proteomic and immunohistochemical methods. We detected high levels of adeno-associated virus 2 (AAV2) DNA in the liver, blood, plasma or stool from 27 of 28 cases. We found low levels of adenovirus (HAdV) and human herpesvirus 6B (HHV-6B) in 23 of 31 and 16 of 23, respectively, of the cases tested. By contrast, AAV2 was infrequently detected and at low titre in the blood or the liver from control children with HAdV, even when profoundly immunosuppressed. AAV2, HAdV and HHV-6 phylogeny excluded the emergence of novel strains in cases. Histological analyses of explanted livers showed enrichment for T cells and B lineage cells. Proteomic comparison of liver tissue from cases and healthy controls identified increased expression of HLA class 2, immunoglobulin variable regions and complement proteins. HAdV and AAV2 proteins were not detected in the livers. Instead, we identified AAV2 DNA complexes reflecting both HAdV-mediated and HHV-6B-mediated replication. We hypothesize that high levels of abnormal AAV2 replication products aided by HAdV and, in severe cases, HHV-6B may have triggered immune-mediated hepatic disease in genetically and immunologically predisposed children

Enhanced Aerodynamic Performance of a Wind Turbine Airfoil Section using Plasma Actuation

The aerodynamic effects of a dual plasma actuator arrangement on a GOE 735, 23% thickness airfoil, modeled after a Renewegy VP-20 wind turbine blade cross section, were studied. Experiments demonstrating actuator thrust capabilities are compared to previous reports to better understand the relationship between actuator geometry and performance. Characterizations of the effects of plasma actuators for aerodynamic flow control on the resultant coefficient of lift and drag curves are discussed at Re = 1.50 x 10^5. Additionally, the dual plasma actuator arrangement was tested at various applied voltage amplitudes, ranging from 1-9kV_(rms) and frequencies ranging from 2-6kHz at Re = 1.50 x 10^4 to study the aerodynamic effects and the electrical costs of this type of flow control. The voltage and current waveforms were sampled during 10s measurements so that the power dissipated by the actuators could be calculated. Relationships between the thrust produced by the actuators, the voltage amplitude and frequency, the coefficient of lift just before stall, and the dissipated power are discussed. In addition the effects of multiple actuators, the coefficient of drag just before stall, and the phase offsets of the voltage and current signals are discussed

Enhanced Aerodynamic Performance of a Wind Turbine Airfoil Section using Plasma Actuation

The aerodynamic effects of a dual plasma actuator arrangement on a GOE 735, 23% thickness airfoil, modeled after a Renewegy VP-20 wind turbine blade cross section, were studied. Experiments demonstrating actuator thrust capabilities are compared to previous reports to better understand the relationship between actuator geometry and performance. Characterizations of the effects of plasma actuators for aerodynamic flow control on the resultant coefficient of lift and drag curves are discussed at Re = 1.50 x 10^5. Additionally, the dual plasma actuator arrangement was tested at various applied voltage amplitudes, ranging from 1-9kV_(rms) and frequencies ranging from 2-6kHz at Re = 1.50 x 10^4 to study the aerodynamic effects and the electrical costs of this type of flow control. The voltage and current waveforms were sampled during 10s measurements so that the power dissipated by the actuators could be calculated. Relationships between the thrust produced by the actuators, the voltage amplitude and frequency, the coefficient of lift just before stall, and the dissipated power are discussed. In addition the effects of multiple actuators, the coefficient of drag just before stall, and the phase offsets of the voltage and current signals are discussed