potential of the virtual blade model in the analysis of wind turbine wakes using wind tunnel blind tests

Abstract The present research frontier on wind turbine wake analysis is leading to a massive use of large-eddy simulations to completely solve the flow field surrounding the rotors; on the other hand, there is still room for lower-fidelity models with a more affordable computational cost to be used in extended optimization analyses, e.g. for a park layout definition. In this study, a customized version of the Virtual Blade Model (VBM) for ANSYS ® FLUENT ® is presented. The model allows a hybrid solution of the flow, in which the surrounding environment is simulated through a conventional RANS approach, while blades are replaced by a body force, calculated by a simplified version of the Blade Element Theory. The potential of the newly-customized VBM was evaluated by applying it to the famous NOWITECH-NORCOWE blind tests for horizontal axis wind turbines. Several test cases were analyzed and discussed including: 1) a single turbine; 2) an array of two turbines with one rotor working in the wake of the other one; 3) an array of two staggered rotors; 4) several configurations of rotors working in yawed-flow. The study proves that the VBM model can represent a valuable tool for the analysis of wind turbines wakes and of their interaction with near rotors

Comparative analysis of different numerical techniques to analyze the wake of a wind turbine

The analysis of wind turbine wakes' structure and interaction with other machines installed in the same array or park has become a key element in the current wind energy research due to the notable impact that wakes can have on the actual energy production of the turbines themselves. The present frontier of the research in this field is leading to the massive use of large-eddy simulations to completely solve the flow field surrounding the rotors. By doing so, however, enormous calculation resources are needed, which are often not available in an industrial context and also generally not compatible with extended optimization analyses (e.g. for a park layout definition). In this latter case, several cases need to be solved in a reasonable amount of time and therefore more computationally efficient methods are still needed. Within this context, the present study reports a comparative analysis between three different techniques to analyse the wind turbine wakes' structure and their mutual interaction. In particular, a state-of-the-art 3D RANS calculation of the famous NREL Phase VI rotor was used as a benchmark for comparison with two other methods. The first one is based on the Virtual Blade Model (VBM) of the commercial solver ANSYS® FLUENT®, in which a 3D RANS calculation of the flow field is carried out for the outer domain, while the effect of the rotating blades on the fluid is simulated through a body force, which acts inside a disk of fluid with an area equal to the swept area of the turbine. The value of the body force is timeaveraged over a cycle from the forces calculated by a simplified Blade Element Method. In the present study, a stall delay model was also implemented within the VBM module. The second one is instead based on the even more simple approach with an Actuator Disk Model (ADM), in which the turbine presence is actually modelled as a sink of momentum in the main flow. Cross-comparisons between the techniques are shown, both in terms of single wake description and of waketurbine interaction, leading to the conclusion that the VBM model may represent a valuable and computationally affordable tool in many wind energy applications

Fire behavior of polyamide 12 nanocomposites containing POSS and CNT

Nanocomposites of polyamide 12 with multiwall carbon nanotubes (CNT) and octaisobutyl polyhedral oligomeric silsesquioxanes (POSS) were studied to assess their flame retardancy properties. The fire behavior was investigated with a cone calorimeter using 50 kW/m2 heat fluxes, by means of the oxygen index and the UL 94 H classification. The fire residue was characterized using FT-IR and SEM. The best overall performance was observed for the composites containing 3.3 wt% of POSS and 4 wt% of CNT. This composite achieved HB in UL 94, an oxygen index of 27 and a 74% reduction in the peak heat release rate. A synergistic effect was evidenced using POSS and CNT together whereas FT-IR and SEM analysis of the residue from fire experiments confirms the formation of SiO2 shield on the surface of the burning sample

Mitochondrial DNA Copy-Number Variation and Pancreatic Cancer Risk in the Prospective EPIC Cohort.

BACKGROUND: Mitochondrial DNA (mtDNA) copy number in peripheral blood has been found to be associated with risk of developing several cancers. However, data on pancreatic ductal adenocarcinoma (PDAC) are very limited. METHODS: To further our knowledge on this topic, we measured relative mtDNA copy number by a quantitative real-time PCR assay in peripheral leukocyte samples of 476 PDAC cases and 357 controls nested within the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. RESULTS: We observed lower mtDNA copy number with advancing age (P = 6.54 × 10-5) and with a high body mass index (BMI) level (P = 0.004) and no association with sex, smoking behavior, and alcohol consumption. We found an association between increased mtDNA copy number and decreased risk of developing PDAC with an odds ratios (OR) of 0.35 [95% confidence interval (CI), 0.16-0.79; P = 0.01] when comparing the fifth quintile with the first using an unconditional logistic regression and an OR of 0.19 (95% CI, 0.07-0.52; P = 0.001) with a conditional analysis. Analyses stratified by BMI showed an association between high mtDNA copy number and decreased risk in the stratum of normal weight, consistent with the main analyses. CONCLUSIONS: Our results suggest a protective effect of a higher number of mitochondria, measured in peripheral blood leukocytes, on PDAC risk. IMPACT: Our findings highlight the importance of understanding the mitochondrial biology in pancreatic cancer