Aeroacoustical and Aerodynamical Investigations of Riblets Applied on Low Pressure Turbine Exit Guide Vanes for Two Different Operating Points

Abstract

Abstract One of the main goals for modern aircrafts is to lower the fuel consumption and noise emissions without worsening the aerodynamic performance. One possibility to lower the fuel consumption is to reduce the skin-friction losses of vanes and blades inside the engine. Therefore, this paper is about the aeroacoustical as well as the aerodynamical effects of a riblet foil applied on the suction side surface of turbine exit guide vanes (TEGVs) of a 1½ stage low pressure turbine (LPT). There have been numerous studies concerning riblets but none using them in a LPT. In general, if riblets are applied on the suction side of vanes or blades, they lower the drag and increase the lift. Test runs were performed under two different operating points in a subsonic test turbine facility for aerodynamic, aeroacoustic, and aeroelastic investigations (STTF-AAAI) located at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. One operating point was the design point of the riblets and the second one an off-design point. During the test campaign, two different set-ups have been investigated. One configuration with riblets applied on the suction side of the TEGVs, and one configuration with a smooth foil on the vanes to achieve the same thickness as the first set-up. This smooth configuration serves as a reference case. The tested riblet structure was of trapezoid type with 45 μm tip distance and a height to tip distance ratio of 0.45. The acoustical data has been obtained by using flush mounted condenser microphones, rotated over 360 deg around the flow channel. The aerodynamical data was obtained by using an aerodynamic five-hole-probe as well as a trailing edge probe. Measuring in planes up- and downstream of each TEGV allowed the comparison of a rough pressure loss estimation between the two studied set-ups. The present work gives a closer insight into the change of the acoustical and aerodynamical behaviour by applying riblets to LPT vanes.