Impact of vane clocking on the TEC loss in Rig

Abstract

The 30% span profile section of the H-TEC highly loaded Turbine Exit Casing was transformed into a plain cascade configuration with identical pressure distribution and loading level. At increasing levels of complexity the incompressible flow in cascade is studied first at different inlet turbulence levels at the Technische Universität Braunschweig. Unsteady inlet conditions were then generated using rotating bars at the cascade wind tunnel of the Armed Forces University Munich at compressible flow speeds and varying Reynolds numbers. Finally the TEC configuration is investigated in the TU Graz STTF 1.5 stage turbine rig using a conventional 5-hole-probe, a miniature Pitot-probe and a hot wire anemometer. A special test-and evaluation concept allows for highly accurate data. The results show a strong vane-TEC clocking, which for the TEC total pressure inlet profile may be approximated by a sine-function. Downstream the TEC, between the wakes, still a sinus shaped total pressure variation is found. Two loss coefficients are evaluated (i) by a classical control volume approach between TEC inlet and exit plane and (ii) by a so-called viscous wake approach. This method compares the viscous flow in the wake region with a hypothetical potential flow deduced from the flow in the same exit plane between the TEC wakes. The viscous wake method compared at 30% span quite nicely to the cascade data. However, the control volume approach yields more than twice the cascade loss, which indicates further loss sources to exist, e.g. unsteady losses to rise from a vane wake-rotor-TEC interaction or turbulence to impact the probe reading. KEYWORDS LPT exit guide vane, TEC, vane clocking, unsteady losses NOMENCLATURE Indices and Abbreviations AR aspect ratio AR=H/c, H passage height Ma 1 inlet Mach number av mass averaged quantity PHI/g normalized circumferential coordinate c, cax chord, axial chord Pit Pitot probe cp 1c pressure coefficient, see eq. (1) Pot quasi potential flow cv control volume loss evaluation Pt, p total pressure, static pressure EIZ+40 wake generator (moving bars) q dynamic head q = Pt-p EIZ_st steady case (without bars) Re 1 Reynolds number g pitch sin all sinus approx. quasi pot. flow all pitch