1 1 ISABE-2011-1733 Numerical and Experimental Investigations of Boundary Layer Separation Control by Means of Synthetic Jets in Low Pressure Turbine Adverse Pressure Gradient Conditions Chiara Bernardini * , Mauro Carnevale * , Daniele Simoni † * Università degli Studi di Firenze Dipartimento di Energetica “Sergio Stecco” Firenze – 50131 Italy † Università degli Studi di Genova Dipartimento di Macchine Sistemi Energetici e Trasporti Genova – 16143 Italy Abstract Due to the low Reynolds number flow regime of aero engine Low Pressure Turbines (LPT) associated with cruise conditions, suction side blade boundary layer may be subject to laminar separation and consequently to performance decrease. This kind of phenomenon is more and more accentuated due to the current design trend of blade loading increasing, bringing to more severe adverse pressure gradients. The beneficial effects of inducing transition in boundary layer which prevents the occurrence of laminar separation, have been largely proven in literature. In this paper the authors focus on the exploitation of a synthetic jet device (zero net mass flow rate pulsating jet) to control separation. Particularly, the unsteady behavior of the boundary layer subject to active control is here in depth surveyed. Experimental and numerical investigations have been carried out on a flat plate boundary layer under a pressure distribution typical of a high lift LPT at low Reynolds number conditions. Nomenclature C f skin friction coefficient in tin tin p p p p p C - - = pressure coefficient C μ jet momentum coefficient f act actuator frequency k l laminar kinetic energy k t turbulent kinetic energy L flat plate length L sep streamwise separation length p static pressure p t total pressure in act U U r = jet to main flow velocity ratio Re isentropic inlet Reynolds number =U in L/ν in act U L f St = jet Strouhal number T jet period Tu turbulence intensity u streamwise velocity U in inlet streamwise velocity magnitude U M,act maximum outstroke velocity x streamwise coordinate x sep streamwise separation onset coordinate y normal to the wall coordinate Introduction Nowadays, aero-engine design mainly focuses on environmental issues, these concerns being addressed with efforts for higher efficiency, lower noise and higher payload. Particular attention is paid to the improvement of the system components, whose performance may degrade both at take-off and cruise conditions, especially in modern high by-pass ratio turbofans. The low-pressure turbine is one of the components struggling with remarkable changes in flow characteristics associated with altitude. Due to the low