Comparison of 3D transitional CFD simulations for rotating wind turbine wings with measurements:Paper

Since the investigation of van Ingen et al., attempts were undertaken to search for laminar parts within the boundary layer of wind turbines operating in the lower atmosphere with much higher turbulence levels than seen in wind tunnels or at higher altitudes where airplanes usually fly. Based on the results of the DAN-Aero experiment and the Aerodynamic Glove project, a special work package Boundary Layer Transition was embedded in IAEwind Task 29 MexNext 3rd phase (MN3). Here, we report on the results of the application of various CFD tools to predict transition on the MEXICO blade. In addition, recent results from a comparison of thermographic pictures (aimed at detecting transition) with 3D transitional CFD are included as well. The MEXICO (2006) and NEW MEXICO (2014) wind tunnel experiments on a turbine equipped with three 2.5 m blades have been described extensively in the literature. In addition, during MN3, high-frequency Kulite data from experiments were used to detect traces of transitional effects. Complementary, the following set of codes were applied to cases 1.1 and 1.2 (axial inflow with 10 m/s and 15 m/s respectively) – elsA, CFX, OpenFOAM (with 2 different turbulence/transitional models), Ellipsys, (with 2 different turbulence models and eN transition prediction tool), FLOWer and TAU – to search for detection of laminar parts by means of simulation. Obviously, the flow around a rotating blade is much more complicated than around a simple 2D section. Therefore, results for even integrated quantities like thrust and torque are varying strongly. Nevertheless, visible differences between fully turbulent and transitional set-ups are present. We discuss our findings, especially with respect to turbulence and transition models used

Numerical analyses and optimizations on the flow in the nacelle region of a wind turbine

The present study investigates flow dynamics in the hub region of a wind turbine focusing on the influence of nacelle geometry on the root aerodynamics by means of Reynolds averaged Navier–Stokes simulations with the code FLOWer. The turbine considered is a generic version of the Enercon E44 converter incorporating blades with flat-back-profiled root sections. First, a comparison is drawn between an isolated rotor assumption and a setup including the baseline nacelle geometry in order to elaborate the basic flow features of the blade root. It was found that the nacelle reduces the trailed circulation of the root vortices and improves aerodynamic efficiency for the inner portion of the rotor; on the other hand, it induces a complex vortex system at the juncture to the blade that causes flow separation. The origin of these effects is analyzed in detail. In a second step, the effects of basic geometric parameters describing the nacelle have been analyzed with the purpose of increasing the aerodynamic efficiency in the root region. Therefore, three modification categories have been addressed: the first alters the nacelle diameter, the second varies the blade position relative to the nacelle and the third comprises modifications in the vicinity of the blade–nacelle junction. The impact of the geometrical modifications on the local flow physics are discussed and assessed with respect to aerodynamic performance in the blade root region. It was found that increasing the nacelle diameter deteriorates the root aerodynamics, since the flow separation becomes more pronounced. Possible solutions identified to reduce the flow separation are a shift of the blade in the direction of the rotation or the installation of a fairing fillet in the junction between the blade and the nacelle.</p

Structural and Functional Evaluation of C. elegans Filamins FLN-1 and FLN-2

Filamins are long, flexible, multi-domain proteins composed of an N-terminal actin-binding domain (ABD) followed by multiple immunoglobulin-like repeats (IgFLN). They function to organize and maintain the actin cytoskeleton, to provide scaffolds for signaling components, and to act as mechanical force sensors. In this study, we used transcript sequencing and homology modeling to characterize the gene and protein structures of the C. elegans filamin orthologs fln-1 and fln-2. Our results reveal that C. elegans FLN-1 is well conserved at the sequence level to vertebrate filamins, particularly in the ABD and several key IgFLN repeats. Both FLN-1 and the more divergent FLN-2 colocalize with actin in vivo. FLN-2 is poorly conserved, with at least 23 IgFLN repeats interrupted by large regions that appear to be nematode-specific. Our results indicate that many of the key features of vertebrate filamins are preserved in C. elegans FLN-1 and FLN-2, and suggest the nematode may be a very useful model system for further study of filamin function

Heat transfer enhancement in a ribbed channel: Development of turbulence closures

The ability to accurately predict turbulent heat transfer in massively separated flows is of immense practical importance especially in the field of heat transfer enhancement in compact heat exchangers. This paper describes new developments in the modeling of the flow and the turbulent heat fluxes in a representative benchmark flow namely that in a heated channel with periodic surface ribs. This flow, which is well-documented by experiments, poses severe challenges to conventional closures due to the significant non-equilibrium effects that are present. Several closure strategies were therefore considered ranging from the eddy-viscosity closures that are routinely used in practice, to the more sophisticated full differential transport closures that can better capture rapidly-evolving flow and thermal fields. As the heat transfer rates are largely determined by the flow conditions in the near-wall region, low Reynolds number versions of these closures were also considered. As for the turbulent heat fluxes, two alternative models were considered: the conventional Fourier's law, and a more complete, algebraic model which is explicit in these fluxes and which correctly allows for their dependence on the turbulent stresses and on the gradients of mean velocity. The models were implemented in the open source software OpenFOAM and the computations were performed with cyclic boundary conditions that are appropriate for this periodic flow. Details of models implementation are reported. Comparisons with experimental measurement indicate significant improvements over existing approaches. © 2014 Elsevier Ltd. All rights reserved

Heat transfer enhancement in a ribbed channel: Development of turbulence closures

The ability to accurately predict turbulent heat transfer in massively separated flows is of immense practical importance especially in the field of heat transfer enhancement in compact heat exchangers. This paper describes new developments in the modeling of the flow and the turbulent heat fluxes in a representative benchmark flow namely that in a heated channel with periodic surface ribs. This flow, which is well-documented by experiments, poses severe challenges to conventional closures due to the significant non-equilibrium effects that are present. Several closure strategies were therefore considered ranging from the eddy-viscosity closures that are routinely used in practice, to the more sophisticated full differential transport closures that can better capture rapidly-evolving flow and thermal fields. As the heat transfer rates are largely determined by the flow conditions in the near-wall region, low Reynolds number versions of these closures were also considered. As for the turbulent heat fluxes, two alternative models were considered: the conventional Fourier's law, and a more complete, algebraic model which is explicit in these fluxes and which correctly allows for their dependence on the turbulent stresses and on the gradients of mean velocity. The models were implemented in the open source software OpenFOAM and the computations were performed with cyclic boundary conditions that are appropriate for this periodic flow. Details of models implementation are reported. Comparisons with experimental measurement indicate significant improvements over existing approaches. © 2014 Elsevier Ltd. All rights reserved