This study shows an extensive analysis of dynamic stall on wind turbine airfoils, preparing for the development of a reduced-order model applicable to thick airfoils ($t/c>\mathrm{0.21}$ ) in the future. Utilizing unsteady Reynolds-averaged Navier–Stokes (URANS) simulations of a pitching FFA-W3-211 airfoil with a Reynolds number of 15 × 10⁶, our analysis identifies the distinct phases in the course of the evolution of dynamic stall. While the dynamic stall is conventionally categorized into the primary-instability transitioning to the vortex formation stage, we suggest two sub-categories for the first phase and an intermediate stage featuring a plateau in lift prior to entering the full stall region. This delays the inception of deep stall, approximately 3° for a simulation case. This is not predictable with existing dynamic-stall models, which are optimized for applications with a low Reynolds number. These features are attributed to the enhanced flow attachment near the leading edge, restricting the stall region downstream of the position of maximum thickness. The analysis of the frequency spectra of unsteady pressure confirms the distinct characteristics of the leading-edge vortex street and its interaction with large-scale mid-chord vortices in forming the dynamic-stall vortices (DSVs). Examination of the leading-edge suction parameter (LESP) proposed by Ramesh et al. (2014) for thin airfoils with low Reynolds numbers reveals that the LESP is a valid criterion in predicting the onset of the stall for thick airfoils with high Reynolds numbers. Based on the localized separation behavior during a dynamic-stall cycle, we suggest a mid-chord suction parameter (MCSP) and trailing-edge suction parameter (TESP) as supplementary criteria for the identification of each stage. The MCSP exhibits a breakdown in magnitude at the onset of the dynamic-stall formation stage and full stall, while the TESP supports indicating the emergence of a full stall by detecting the trailing-edge vortex.

The aerodynamic performance of a wind turbine rotor blade depends on the geometry of the airfoils used. The airfoil shape can be affected by elastic deformations of the blade during operation due to structural loads. This paper provides an initial estimation of the extent to which cross-sectional deformations influence the aerodynamic loads on the rotor. The IEA 15 MW reference wind turbine model is used for this study. A constant wind field at rated wind speed is applied as an operational load test case. The resulting loads are calculated by an aero-servo-elastic simulation of the turbine. The loads are applied to a three-dimensional (3D) finite shell element model of the rotor blade, which serves to calculate the cross-sectional deformations. For the individual cross-sections in the deformed configuration, the new lift and drag coefficients are calculated. These are then included in the aero-servo-elastic simulation, and the obtained results are compared with those of the initial simulation that is based on the undeformed cross-sections. The cross-sectional deformations consist of a change in the chord length and the geometry of the trailing edge panels and depend on the azimuth position of the blade. The change in the airfoil geometries results in altered aerodynamic characteristics and therefore a deviation of the blade root bending moments, the maximum change of which is −1.4 % in the in-plane direction and +0.71 % in the out-of-plane direction. These results show that cross-sectional deformations have a minor influence on the internal loads of rotor blades in normal operation.

In recent years, the research on roughness has focused on various roughness features, rather than the roughness height only, in order to improve the understanding of roughness effects on wall bounded flows. A special focus is placed on the skewness of the roughness height profile. The skewness...

This paper presents those flow parameters at which coherent structures appear in the blade tip cavities of shrouded turbine blades. To the authors’ knowledge, this is reported for the first time in the open literature. The unsteady flow in a shroud cavity is analysed based on experimental data...

Measurements of the discharge coefficient of labyrinth seals reveal a strong sensitivity of the cavity flow to even small changes in geometrical parameters. It is shown that accurate measurements of the seal clearance are required to model the flow with a degree of certainty, which permits further conclusions. Based on accurate representations of the geometry in CFD models, it can be demonstrated that RANS flow solvers have substantial deficits in correctly predicting labyrinth seal flow. A novel test rig has been designed and put into operation for studying the labyrinth seal leakage flow in detail using temperature and pressure as well as optical flow velocity measurement methods. The rig uses a rotating disc with a labyrinth seal on its outer perimeter, and an annular flow channel to represent the shroud cavity. Homogeneity of the inlet and outlet boundary conditions is verified by means of circumferentially and radially distributed measurements of the total temperature and pressure. The rig mirrors the geometrical and aerodynamic parameters of the cavities in an axial turbine, which will subsequently be used for further investigations.

Defects in the hot-gas path of aero engines have been shown to leave typical signatures in the density distribution of the exhaust jet. These signatures are superposed when several defects are present. For improved maintenance and monitoring applications, it is important to not only detect that...