Simulating the aerodynamic performance and wake dynamics of a vertical-axis wind turbine

The accurate prediction of the aerodynamics and performance of vertical-axis wind turbines is essential if their design is to be improved but poses a signifi cant challenge to numerical simulation tools. The cyclic motion of the blades induces large variations in the angle of attack of the blades that can manifest as dynamic stall. In addition, predicting the interaction between the blades and the wake developed by the rotor requires a high-fi delity representation of the vortical structures within the fl ow fi eld in which the turbine operates. The aerodynamic performance and wake dynamics of a Darrieus-type vertical-axis wind turbine consisting of two straight blades is simulated using Brown’s Vorticity Transport Model. The predicted variation with azimuth of the normal and tangential force on the turbine blades compares well with experimental measurements. The interaction between the blades and the vortices that are shed and trailed in previous revolutions of the turbine is shown to have a signifi cant effect on the distribution of aerodynamic loading on the blades. Furthermore, it is suggested that the disagreement between experimental and numerical data that has been presented in previous studies arises because the blade–vortex interactions on the rotor were not modelled with sufficient fidelity

Predicting wind turbine blade loads using vorticity transport and RANS methodologies

Two computational methods, one based on the solution of the vorticity transport equation, and a second based on the solution of the Reynolds-Averaged Navier-Stokes equations, have been used to simulate the aerodynamic performance of a horizontal axis wind turbine. Comparisons have been made against data obtained during Phase VI of the NREL Unsteady Aerodynamics Experimental and against existing numerical data for a range of wind conditions. The Reynolds-Averaged Navier-Stokes method demonstrates the potential to predict accurately the flow around the blades and the distribution of aerodynamic loads developed on them. The Vorticity Transport Model possesses a considerable advantage in those situtations where the accurate, but computationally efficient, modelling of the structure of the wake and the associated induced velocity is critical, but where the prediction of blade loads can be achieved with sufficient accuracy using a lifting-line model augmented by incorporating a semi-empirical stall delay model. The largest benefits can be extracted when the two methods are used to complement each other in order to understand better the physical mechanisms governing the aerodynamic performance of wind turbines

Fungicide resistance among Cladobotryum spp. – causal agents of cobweb disease of the edible mushroom Agaricus bisporus

A survey of fungicide resistance among isolates of the mushroom pathogens Cladobotryum mycophilum and C. dendroides Types I and II was undertaken, with respect to the active ingredients thiabendazole, carbendazim (benzimidazoles) and prochloraz manganese following an epidemic in Britain and Ireland in 1994/95. The majority of isolates (41/57) were strongly resistant to thiabendazole (ED50 > 200 ppm) and were exclusively C. dendroides Type II. All C. mycophilum and C. dendroides Type I isolates, and four C. dendroides Type II isolates, were weakly resistant to thiabendazole (ED50 1–10 ppm). Thiabendazole-resistant C. dendroides Type II isolates were only weakly resistant to carbendazim (ED50 2–10 ppm) and isolates which were weakly resistant to thiabendazole were carbendazim-sensitive (ED50 < 1 ppm), demonstrating a lack of complete cross resistance between these two benzimidazole fungicides. The ED50 values for all isolates with respect to prochloraz manganese ranged from 0.14 to 7.8 ppm. Benzimidazole resistance was considered to have been an important factor influencing the severity of the 1994/95 cobweb epidemic but 25% of isolates collected were benzimidazole sensitive

Polyimide processing additives

A process for preparing polyimides having enhanced melt flow properties is described. The process consists of heating a mixture of a high molecular weight poly-(amic acid) or polyimide with a low molecular weight amic acid or imide additive in the range of 0.05 to 15 percent by weight of additive. The polyimide powders so obtained show improved processability, as evidenced by lower melt viscosity by capillary rheometry. Likewise, films prepared from mixtures of polymers with additives show improved processability with earlier onset of stretching by TMA

Digital demodulator-correlator

An apparatus for demodulation and correlation of a code modulated 10 MHz signal is presented. The apparatus is comprised of a sample and hold analog-to-digital converter synchronized by a frequency coherent 40 MHz pulse to obtain four evenly spaced samples of each of the signal. Each sample is added or subtracted to or from one of four accumulators to or from the separate sums. The correlation functions are then computed. As a further feature of the invention, multipliers are each multiplied by a squarewave chopper signal having a period that is long relative to the period of the received signal to foreclose contamination of the received signal by leakage from either of the other two terms of the multipliers

Beyond icosahedral symmetry in packings of proteins in spherical shells

The formation of quasi-spherical cages from protein building blocks is a remarkable self-assembly process in many natural systems, where a small number of elementary building blocks are assembled to build a highly symmetric icosahedral cage. In turn, this has inspired synthetic biologists to design de novo protein cages. We use simple models, on multiple scales, to investigate the self-assembly of a spherical cage, focusing on the regularity of the packing of protein-like objects on the surface. Using building blocks, which are able to pack with icosahedral symmetry, we examine how stable these highly symmetric structures are to perturbations that may arise from the interplay between flexibility of the interacting blocks and entropic effects. We find that, in the presence of those perturbations, icosahedral packing is not the most stable arrangement for a wide range of parameters; rather disordered structures are found to be the most stable. Our results suggest that (i) many designed, or even natural, protein cages may not be regular in the presence of those perturbations, and (ii) that optimizing those flexibilities can be a possible design strategy to obtain regular synthetic cages with full control over their surface properties.Comment: 8 pages, 5 figure

Helicopter tail rotor thrust and main rotor wake coupling in crosswind flight

The tail rotor of a helicopter with a single main rotor configuration can experience a significant reduction in thrust when the aircraft operates in crosswind flight. Brown’s vorticity transport model has been used to simulate a main rotor and tail rotor system translating at a sideslip angle that causes the tail rotor to interact with the main rotor tip vortices as they propagate downstream at the lateral extremities of the wake. The tail rotor is shown to exhibit a distinct directionally dependent mode during which tail rotors that are configured so that the blades travel forward at the top of the disk develop less thrust than tail rotors with the reverse sense of rotation. The range of flight speeds over which this mode exists is shown to vary considerably with the vertical location of the tail rotor. At low flight speeds, the directionally dependent mode occurs because the tail rotor is immersed within not only the downwash from the main rotor but also the rotational flow associated with clusters of largely disorganized vorticity within the main rotor wake. At higher flight speeds, however, the tail rotor is immersed within a coherent supervortex that strongly influences the velocity field surrounding the tail rotor

Prediction of unsteady blade loads of a wind turbine using RANS and vorticity transport methodologies

Numerical simulations of the NREL phase VI wind turbine operating in yawed conditions have been performed using two computational methods; one based on the solution of the Reynolds-averaged Navier-Stokes equations (RANS) using unstructured overset meshes and one known as the Vorticity Transport Model (VTM) that is based on the solution of the vorticity transport equation. The effect of the hub that was present during the NREL experiments was investigated by modeling the hub in the RANS simulations. It was found that the hub influenced the loading significantly at the inboard part of the blade when the blade passed through the wake that was developed by the hub. Both the RANS and VTM codes are able to predict well the unsteady and time-averaged aerodynamic loadings on the wind turbine blades at low wind speeds. At high wind speeds, leading-edge flow separation and strong radial flow are observed on the suction surface of the blades, when the blades are at the retreating side of the rotor. Both the RANS and VTM codes provide less accurate predictions of the blade loads. However, at the advancing side of the rotor, the flow is mostly attached to the surface of the blade, and both the RANS and VTM predictions of the blade loads are in good agreement with the measured data

Gross morphology and microstructure of type locality ossicles of Psephophorus polygonus Meyer, 1847 (Testudines, Dermochelyidae)

Psephophorus polygonus Meyer, 1847, the first fossil leatherback turtle to be named, was described on the basis of shell ossicles from the middle Miocene (MN6-7/8?) of Slovakia. The whereabouts of this material is uncertain but a slab on display at the Naturhistorisches Museum Wien is considered the neotype. We rediscovered further type locality ossicles in four European institutions, re-evaluated their gross morphology and described for the first time their microstructure by comparing them with Dermochelys coriacea, the only living dermochelyid turtle. The gross morphology is congruent with that already described for P. polygonus, but with two significant exceptions: the ridged ossicles of P. polygonus may have a distinctly concave ventral surface as well as a tectiform shape in cross-section. They do not develop the external keel typical of many ossicles of D. coriacea. Both ridged and non-ridged ossicles of P. polygonus are characterized by compact diploe structures with an internal cortex consisting of a coarse fibrous meshwork, whereas the proportionately thinner ossicles of D. coriacea tend to lose the internal cortex, and thus their diploe, during ontogeny. The ossicles of both P. polygonus and D. coriacea differ from those of other lineages of amniotes whose carapace is composed of polygonal ossicles or platelets, in having growth centres situated at the plate centres just interior to the external bone surface and not within the cancellous core or closer to the internal compact layer. The new diagnosis of P. polygonus allows us to preliminarily re-evaluate the taxonomy of some of the Psephophorus-like species. Despite some macro- and micromorphological differences, it seems likely that Psephophorus was as cosmopolitan as extant Dermochelys and had a broadly similar ecology, with a possible difference concerning the dive dept

Effects of Rare-Earth Doping on Femtosecond Laser Waveguide Writing in Zinc Polyphosphate Glass

We have investigated waveguide writing in Er-Yb doped zinc polyphosphate glass using a femtosecond laser with a repetition rate of 1 KHz. We find that fabrication of good waveguides requires a glass composition with an O/P ratio of 3.25. The dependence on laser writing parameters including laser fluence, focusing conditions, and scan speed is reported. Waveguide properties together with absorption and emission data indicate that these glasses can be used for the fabrication of compact, high gain amplifying devices