Tamara Worzewski

Thermographic rotor blade inspection from larger distances - a promising tool for the maintenance of wind turbines

The permanently increasing number of wind turbines requires suited inspection and monitoring methods to ensure liability and security. Concerning the inspection of ro-tor blades, only manual inspections are state of the art. Thermographic Testing (TT) has the potential to detect typical failures and damages on rotor blades. The paper presents some results of onsite measurements carried out as “passive thermogra-phy”, i.e. without a defined heating procedure. Due the totally contactless meas-urement principle, TT can be applied to rotating blades as well as to resting blades. Both methods will be compared with respect to their possible realization.A flow around a building has been simulated by employing LES and Smirnov’s inflow generation technique. Accurate inflow data for LES are of paramount importance in order to obtain reliable results for the air velocity and turbulence levels. Otherwise, the flow shows a laminar behavior regardless of the Reynolds number and it requires several characteristic lengths to be recovered. Further, the initialization of the flow is among the top problems in wind engineering. In large Eddy simulations, velocity and turbulence profiles provide detailed information which is necessary for the wind resource assessment of wind turbines or wind farms that are positional at any height throughout the atmospheric boundary layer from any commercial CFD software. One of the biggest problems with LES is that the turbulence throughout the inlet of the computational domain must be fully prescribed. The present work shows the characteristics of the flow around a building by employing Smirnov’s random flow generation technique for the inflow generation data. This study is a part of the European Project New innovative solutions, components and tools for the integration of wind energy in urban and peri-urban areas (acronym SWIP). The building is located in Saragossa in Spain, where a wind turbine will be installed. The energy spectrum is analyzed at different locations in the computational domain and the velocity fluctuations generated initially at the inlet and throughout the entire domain are proven to maintain the turbulence within the entire computational domain. This is also confirmed by the distribution of normal and shear Reynolds stresses throughout the domain. Finally, the present work illustrates the effect of the grid resolution on the results.In the recent years the use of wind energy as an alternative to conventional sources has significantly increased. The growth of installed wind power capacity connected to the transmission and distribution network made an adaptation of the grid code necessary. Indeed, as it is already being experienced in some countries such as Denmark and Germany, this new scenario no longer allows wind farms to simply inject the maximum power they are able to extract from the wind into the grid and to disconnect when a network fault occurs. As a result, a new set of grid connection technical requirements establishes some major constraints and performance that wind farms have to meet to contribute to the proper functioning of the electrical grid. In this work we refer to those involving grid frequency control, power curtailment and other active power injection constraints. Since conventional wind turbine modes of operation are based on maximum power point tracking (MPPT) at low wind speed and power limiting at high wind speed, new advanced control methods need to be employed to let the turbine function in different operating points that would ensure the satisfaction of the grid requirements. In this presentation, we show how, in Matlab/Simulink simulation environment, the proposed control architecture proves to fulfil the aforementioned active power constraints while outperforming classic linear controllers such as the PI one. Simulations for different scenarios of interest are carried out based on CART (Control Advanced Research Turbine) parameters.