Hot-film measurements of the steady and unsteady boundary layer development on a low-pressure turbine airfoil

The adverse pressure gradients on the suction side of the low pressure (LP) turbine blades increase the possibility of boundary layer separation, particularly under low Reynolds number conditions. Separation bubbles can cause a significant blade loss. Therefore, accurate prediction of boundary layer developments on the blade surface in low Reynolds number conditions is crucial to the improvement of LP turbine design. Recently, the unsteady rotor-stator interaction has received attention. The wakes coming from the previous blade row will impact the boundary layer development on the blade surface.;Boundary layer developments on the suction surface of a linear cascade of LP turbine blades, a set of so-called PAK-B profile blades designed by Pratt & Whitney US, under steady and unsteady conditions at low Reynolds number were investigated by means of surface-mounted hot-films. To achieve a simulation of rotor-stator interactions, a spoked-wheel type wake generator was designed. The Reynolds number based on the cascade inlet velocity and blade axial chord varies from 25000 to 100000 and the free stream turbulence intensity changes between 0.4% and 4.5%. The hot-film data are analyzed in both the time domain and frequency domain. The relationship between the hot-film data and the boundary layer behaviour forms the focus of the present study.;Surface-mounted hot-films can provide information about boundary layer separation, reattachment and transition, even in the case that the hot-film sensors are covered by the separation bubble. Thanks to the fast response of the hot-film sensors, this technique is also suitable for unsteady flow measurement. Under steady flow conditions, boundary layer separation was observed in all examined conditions. At unsteady flow conditions, boundary layer developments are dominated by the incoming wakes.