Abstract

A series of experiments were conducted to study the effect of leading-edge roughness on the state of the boundary layer of a wind turbine blade section using multiple hot-film sensors. The experiments involved static and dynamic tests, where airfoil motion was of plunging type oscillation. The application of surface grit roughness simulates surface irregularities that occur on the wind turbine blades. The measurements showed that increasing the angle of attack results in movement of transition locations toward the leading edge. Surface roughness moved the transition point toward the leading edge and caused early trailing edge turbulent separation, which resulted in reducing the effectiveness of the airfoil. Boundary layer instability frequencies were dominated through the transition.

Abstract

Big rollers are used in the paper manufacturing industry, they are composed of layers of different materials (metallic core, polyurethane and composite with epoxy resin between others). The company TECNOCAUCHO is dedicated to the manufacturing of these rollers and towether with AIMPLAS have modified two epoxy resins that are used in two rollers (guide and calendering). In both cases the epoxy resin layer was the weak point of the rollers, consequently the mechanic properties of the resin were improved in order to extend the useful life of each roller and also the conductivity of the guide roller and the roughness and brightness of the calendering roller were improved. Currently, a epoxy resin with the improved properties achieved in this paper is not available on the market.

Guide roller: mechanic properties of the epoxy resin were improved 7,7% compared to original comercial resin through nanofiller addition. Besides, resistivity values below 100 Ωm (company´s target value) were achieved, minimizing the sparks generation.

Calendering roller: mechanic properties were improved to 18,6% (tensile strenght at 130ºC), brightness and roughness (Rz below to 0,2 microns, company´s target value) through nanofillers addition, improving significantly the superficial properties of the paper.

Abstract

Measurements of pressure drop during experiments with fan-induced air flow in the open-cathode proton exchange membrane fuel cells (PEMFCs) show that flow friction in its opencathode side follows logarithmic law similar to Colebrook’s model for flow through pipes. The stable symbolic regression model for both laminar and turbulent flow presented in this article correlates air flow and pressure drop as a function of the variable flow friction factor which further depends on the Reynolds number and the virtual roughness. To follow the measured data, virtual inner roughness related to the mesh of conduits of fuel cell used in the mentioned experiment is 0.03086, whereas for pipes, real physical roughness of their inner pipe surface goes practically from 0 to 0.05. Numerical experiments indicate that the novel approximation of the Wright-ω function reduced the computational time from half of a minute to fragments of a second. The relative error of the estimated friction flow factor is less than 0.5%.