Active control of separation for low-pressure turbine blades

At low Reynolds number conditions the flow over Low-Pressure Turbine (LPT) blades can become susceptible to laminar separation. In general, laminar separation results in high losses of aerodynamic efficiency and has to be avoided. In experiments performed at the Air Force Research Laboratory, separation on the suction side of a LPT blade was successfully controlled by application of pulsed Vortex Generator Jets (VGJs). A transfer of VGJs to real flight vehicles may allow for wider flight envelopes or more aggressive designs. We have carried out numerical simulations in order to shed some light on the physical mechanisms involved in Active Flow Control (AFC) of laminar LPT separation. The flow in the LPT cascade of the experiments was simulated at the design blade spacing and at a 25% larger blade spacing. From 2-D calculations we could demonstrate that the separation could be controlled successfully by pulsed blowing through a slot. The effectiveness of pulsed blowing could be attributed to the generation of strong spanwise coherent structures that increased the wall normal momentum transfer.