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The present study deals with the unsteady flow simulation of trailing edge film cooling on the pressure side cut back of gas turbine airfoils. Before being ejected tangentially on the inclined cut-back surface, the coolant air passes a partly converging passage that is equipped with turbulators such as pin fins and ribs. The film mixing process on the cut back is complicated. In the near slot region, due to the turbulators and the blunt pressure side lip, turbulence is expected to be anisotropic. Furthermore, unsteady flow phenomena like vortex shedding from the pressure side lip might influence the mixing process (i.e., the film cooling effectiveness on the cut-back surface). In the current study, three different internal cooling designs are numerically investigated starting from the steady RaNS solution, and ending with unsteady detached eddy simulations (DES). Blowing ratios M = 0.5; 0.8; 1.1 are considered. To obtain both, film cooling effectiveness as well as heat transfer coefficients on the cut-back surface, the simulations are performed using adiabatic and diabatic wall boundary conditions. The DES simulations give a detailed insight into the unsteady film mixing process on the trailing edge cut back, which is indeed influenced by vortex shedding from the pressure side lip. Furthermore, the time averaged DES results show very good agreement with the experimental data in terms of film cooling effectiveness and heat transfer coefficients. Transactions of the ASME Downloaded From: http://turbomachinery.asmedigitalcollection.asme.org/ on 09/18/2013 Terms of Use: http://asme.org/terms Journal of Turbomachinery APRIL 2006, Vol. 128 / 299 Downloaded From: http://turbomachinery.asmedigitalcollection.asme.org/ on 09/18/2013 Terms of Use: http://asme.org/terms

The present study deals with trailing edge film cooling on the pressure side cutback of gas turbine airfoils. Before being ejected tangentially onto the inclined cut-back surface the coolant air passes a partly converging passage that is equipped with turbulators such as pin fins and ribs. The experiments are conducted in a generic setup and cover a broad variety of internal cooling designs. A subsonic atmospheric open-loop wind tunnel is utilized for the tests. The test conditions are characterized by a constant Reynolds number of Re hg = 250 000, a turbulence intensity of Tu hg =7%, and a hot gas temperature of T hg = 500 K. Due to the ambient temperature of the coolant, engine realistic density ratios between coolant and hot gas can be realized. Blowing ratios cover a range of 0.20 Ͻ M Ͻ 1.25. The experimental data to be presented include discharge coefficients, adiabatic film cooling effectiveness, and heat transfer coefficients in the near slot region ͑x / H Ͻ 15͒. The results clearly demonstrate the strong influence of the internal cooling design and the relatively thick pressure side lip ͑t / H =1͒ on film cooling performance downstream of the ejection slot. Transactions of the ASME Downloaded From: http://turbomachinery.asmedigitalcollection.asme.org/ on 09/18/2013 Terms of Use: http://asme.org/terms Journal of Turbomachinery JANUARY 2006, Vol. 128 / 197 Downloaded From: http://turbomachinery.asmedigitalcollection.asme.org/ on 09/18/2013 Terms of Use: http://asme.org/terms Journal of Turbomachinery JANUARY 2006, Vol. 128 / 199 Downloaded From: http://turbomachinery.asmedigitalcollection.asme.org/ on 09/18/2013 Terms of Use: http://asme.org/terms

The paper presents results from film thickness measurements in a bearing chamber test rig. The measurements were performed at different operating conditions and with two offtake designs. A discussion of the measurement technique using in situ calibrated capacitive sensors shows good accuracy and repeatability. The film thickness results are first compared to measurements with the same chamber in a vented configuration. The analysis of the measurements at various operating conditions shows a strong influence of the shaft speed, the chamber pressure, and the offtake design. In contrast to that, flow rate and scavenge ratio have only minor influence. Furthermore, the momentum flux of the core air flow is proposed as a suitable parameter with which the influence of shaft speed and pressure can be correlated to the film thickness distribution.