Large-scale Turbine Blade Research Articles

Structural integrity analysis and damage assessment of a long composite wind turbine blade under extreme loading

The high demand of low cost wind energy needs to design large scale turbine blades with reduced weight which poses great challenges to their structural integrity while prone to extreme wind gusts. The loading can cause large-deflection bending and damage leading to significant drop in the load-bearing ability of long composite wind turbine (WT) blades. In this study, a comprehensive finite element (FE) modelling procedure is developed to simulate structural integrity and damage in composite blade using ANSYS software. The three-dimensional blade model is analyzed by carrying out geometrically nonlinear FE analysis to investigate the blade deformation and highly stressed regions leading to possible failure modes. The results show that the blade suction side is subjected to high compressive stress causing local skin buckling, which is further investigated using linear buckling analysis. Such local buckling drives interfacial debonding between skin and spar joined with a weak adhesive. Subsequently, the interfacial damage in the identified critical region is modelled by developing a damage submodel employing cohesive zone model (CZM) approach at the skin-spar interface. The analysis results indicate that buckling driven skin-spar debonding at adhesive interface is initial damage mode which can lead to progressive failure of the blade structure. Consequently, the ultimate load bearing capacity of WT blade is governed by a coupled buckling and debonding phenomenon even at load level below the ultimate design load. The simulation methodology adopted in this study can be employed to develop reliable and cost-effective computational tools for analyzing structural integrity and assessing damage in blade structure than expensive experimental testing.

Modeling and Measurements of Heat/Mass Transfer in a Linear Turbine Cascade

Measurements of the mass/heat transfer coefficients on the blade and end wall surfaces of a linear turbine cascade are compared to numerical predictions using the standard shear stress transport (SST) closure and the SST model in combination with the Reθ–γ transition model (SST-TRANS). Experiments were carried out in a wind tunnel test section composed of five large-scale turbine blades, using the naphthalene sublimation technique. Two cases were tested, with exit Reynolds number of 600,000 and inlet turbulence values of 0.2% and 4%, respectively. The main secondary flow features, consisting of the horseshoe vortex system, the passage vortex, and the corner vortices, are identified and their influence on heat/mass transfer is analyzed. Numerical simulations were carried out to match the conditions of the experiments. Results show that large improvements are obtained with the introduction of the Reθ–γ transition model. In particular, excellent agreement with the experiments is found, for the whole spanwise extension of the blade, on the pressure surface. On the suction surface, performance is very good in the highly three-dimensional region close to the end wall, but some weaknesses appear in predicting the location of transition in the two-dimensional region. On the end wall surface, the SST model in combination with the transition model produces satisfactory results, greatly improved compared to the standard SST model.

Experimental investigation of film cooling flow induced by shaped holes on a turbine blade.

The present study is the second half of a piece of work carried out in collaboration with SNECMA. It investigates shaped hole film cooling, numerically and experimentally. The aim of this paper is the experimental analysis of shaped hole film cooling on a large scale turbine blade (1.4 m chord). The test section is a large scale turbine inlet guide vane cascade. The test airfoil is equipped with a row of nine 50 degrees sloped shaped holes. They are located on the suction side at 20% of the curvilinear length of the blade from the stagnation point. The inlet film cooling hole diameter is 12 mm. The jet flow is heated to 55 degrees C above the crossflow temperature. Velocity and temperature field measurements have been done to obtain mean and fluctuating values. The results are compared to those obtained by Béral on the same experimental apparatus and in the same test conditions, for a row of cylindrical holes.

Closure to “Discussion of ‘An Experimental Study of Endwall and Airfoil Surface Heat Transfer in a Large Scale Turbine Blade Cascade’” (1981, ASME J. Eng. Power, 103, p. 602)

Closure to “Discussion of ‘An Experimental Study of Endwall and Airfoil Surface Heat Transfer in a Large Scale Turbine Blade Cascade’” (1981, ASME J. Eng. Power, 103, p. 602)

An Experimental Study of Endwall and Airfoil Surface Heat Transfer in a Large Scale Turbine Blade Cascade

Local rates of heat transfer on the endwall, suction, and pressure surfaces of a large scale turbine blade cascade were measured for two inlet boundary layer thicknesses and for a Reynolds number typical of gas turbine engine operation. The accuracy and spatial resolution of the measurements were sufficient to reveal local variations of heat transfer associated with distinct flow regimes and with regions of strong three-dimensional flow. Pertinent results of surface flow visualization and pressure measurements are included. The dominant role of the passage vortex, which develops from the singular separation of the inlet boundary layer, in determining heat transfer at the endwall and at certain regions of the airfoil surface is illustrated. Heat transfer on the passage surfaces is discussed and measurements at airfoil midspan are compared with current finite difference prediction methods.