Experimental and CFD analysis of stator vanes with trailing edge damage

In this paper we will give an overview on the results of a research project dedicated to the analysis of rotor forcing due to in-service trailing edge damage of high pressure turbine nozzle guide vanes (HPT NGVs). Due to the extremely high temperatures in this region of the engine, which on average exceed the melting temperature of the employed vane material by several hundred degrees during takeoff, any unintended decrease of the vane cooling mass flow can lead to a loss of trailing edge material. The structure of the NGV can withstand a significant amount of trailing edge material loss, but the damage changes the flow through the affected passage, causing a so-called low engine order excitation of the rotor blades downstream. This can lead –in extreme cases– to high cycle fatigue failure of the rotor blade caused by resonances in the operating range. Thus it is very important to be able to quantify the damage-induced rotor forcing in case a trailing edge damage is detected during routine engine inspection. This quantification can be obtained by solving the unsteady fluid flow, typically modeled using the Reynolds-averaged Navier-Stokes equations together with a suitable turbulence model. In order to gain confidence in the CFD analysis results for those configurations, a dedicated measurement campaign with different representative trailing edge damage shapes has been set up at the DLR Göttingen, including both steady, unsteady and pressure-sensitive paint measurements and on both stationary and rotating components. The results of those measurements together with post-test CFD simulations will be presented in this paper