Characterization of base bleed effects on subsonic trailing edge flows

Abstract

Trailing edge injection enables control of the detached and unsteady flow within the base region. The interaction of the jet with the base region alters the flow topology causing pressure bifurcations at the trailing edge that affect the aerodynamic performance of the system and modify the vortex patterns downstream the body. The purpose of this work is to fully characterize the physical effects related to the use of base bleed on the trailing edge of an airfoil at subsonic conditions. Defining a non-dimensional base bleed rate Cb=m˙/ρ∞U∞h, a wide range from Cb=0 to Cb=1 is applied to a simplified model of a turbine blade. The influence of the trailing edge geometry shape is also evaluated, showing that rounded geometries have the potential to minimize the undesirable effects of the injection. Vortex shedding is neutralized when the (non-dimensional) ejected mass flow exceeds the value of Cb=0.8 and Cb=0.55 for straight and rounded geometries, respectively. Additionally, neutralization of the shedding also occurs for relatively low base bleed rates, often accompanied by the onset of a non-symmetrical configuration at the trailing edge. This work has particular relevance in aerothermal gas turbine design, where coolant flow may be ejected at the trailing edge to ensure adequate thermal protection of the airfoils.