Experimental Analysis of a Wind-Turbine Rotor Blade Airfoil by means of Temperature-Sensitive Paint

Abstract

Knowledge on the boundary-layer transition location at large chordReynolds numbers is essential to evaluate the performance of airfoils designed for modern wind-turbine rotor blades. In the present work, a temperature-sensitive paint was used to systematically study boundary-layer transition on the suction side of a DU 91-W2-250 airfoil. The experiments were performed in the High-Pressure Wind Tunnel Göttingen at chord Reynolds numbers up to 12 million and angles-of-attack from -14° to 20°. The coefficients of airfoil lift, drag, and pitching moment were also obtained after integration of the pressure distributions measured on the surface and in the wake of the wind-tunnel model. The global information obtained via temperature-sensitive paint not only enabled the analysis of the change in the transition location with varying angle-of-attack and chord Reynolds number, but also provided an explanation for the evolution of the aerodynamic coefficients measured at stall and post-stall conditions. The stability of the laminar boundary layers investigated in the experiments was analyzed according to linear stability theory. The results of the stability

A thick aerodynamic profile with regions of negative lift slope and possible implications on profiles for wind turbine blades

“…This results in a distribution that is fanned up by an angle of 15° in a span‐wise direction. Wind‐turbine profiles were measured several times at HDG before, see other studies 33,38,39 …”

Skin-Friction-Based Identification of the Critical Lines in a Transonic, High Reynolds Number Flow via Temperature-Sensitive Paint

“…The luminophores can be excited by the absorption of light in an appropriate (luminophore-specific) wavelength range, and one of the mechanisms for their return to the electronic ground state is the emission of light, which occurs at a higher wavelength than that of the excitation light (Stokes shift). The intensity of the emitted light decreases at higher temperatures, and this property is used to measure the surface temperature distribution via TSP [ 63 , 64 , 65 ].…”

“…Since the forced-convection heat transfer coefficient is generally a function of the skin friction, the imposed flow-surface temperature difference is transferred at different rates depending on the local skin friction, thus leading to augmented surface temperature variations that can be measured by means of TSP. The surface heat flux can be imposed through a variety of methods reported in previous work [ 25 , 60 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 ].…”

“…In this work, the surface heat flux was imposed via two different types of electrical heating systems integrated beneath the TSP: a layer of Carbon NanoTubes (CNT) [ 65 , 70 , 71 , 72 ] and a current-carrying carbon fiber layer [ 64 , 73 , 74 ]. The integration of these electrical heating layers in the TSP layer composition was specifically designed for the examined test conditions in a transonic wind tunnel, as described in Section 3.2 .…”

“…The composition of the TSP layers in the port pocket was designed to integrate a layer of CNT, in a manner analogous to that presented in [ 65 , 70 , 72 ], but with the layer thicknesses adjusted for the considered transonic flow conditions at a high Reynolds number. In order to guarantee the adhesion of the paint to the metallic surface, the model was first coated with a primer layer; a white screening layer for thermal and electrical insulation was then applied on the primer layer, and the layer of CNT was applied on this first screening layer; a second screening layer, with the same properties as the first one, was applied on the CNT layer (also functioning as a diffusive light-scattering background); finally, the active layer, in which the luminophores were embedded, was applied on the screening layer.…”