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A computational model has been developed to study the mechanisms responsible for hot gas ingestion into the wheel-space cavity of a stationary high pressure turbine (HPT) cascade rig. Simulations were undertaken for the stationary rig described by Bunker et al. (2009, "An Investigation of Turbine Wheelspace Cooling Flow Interactions With a Transonic Hot Gas Path-Part I: Experimental Measurements," ASME Paper No. GT2009-59237) in a companion paper. The rig consists of five vanes, a wheel-space cavity, and five cylinders that represent the blockage due to the leading edge of the rotor airfoils. The experimental program investigated two cylinder diameters and three clocking positions for a nominal coolant flow rate. Comparisons are made between the computed and measured flow-fields for the smaller of the two cylinders. It is demonstrated that the circumferential variation of pressure established by the vane wake and leading edge bow wave results in an unstable shear layer over the rim seal axial gap (trench) that causes hot gases to ingest for a nominal coolant flow. Steady-state computational fluid dynamics (CFD) simulations did not capture this effect and it was determined that an unsteady analysis was required in order to match the experimental data. Favorable agreement is noted between the time-averaged computed and measured pressure distributions in the circumferential direction both upstream and downstream of the trench, as well as within the trench itself. Furthermore, it is noted that time-averaged buffer cavity effectiveness agrees to within 5% of the experimental data for the cases studied. The validated CFD model is then used to simulate the effect of rotation by rotating the cylinders and disk at rotational rate that scales with a typical engine. A sliding mesh interface is utilized to communicate data between the stator and rotor domains. The stationary cases tend to ingest past the first angel-wing for a nominal coolant flow condition, whereas the effect of rotation helps pressurize the cavity and is responsible for preventing hot gas from entering the buffer cavity. [ABSTRACT FROM AUTHOR]

The desire for higher power output combined with lower fuel consumption has focused recent design and research attention on the interaction of required secondary systems cooling flows with the turbine hot gas path. The flow physics associated with the rotor-stator wheelspaces, and in particular the trench and buffer cavity areas just inboard of the hot gas path, demand an increased level of design sophistication to account for the unsteady fluid and thermal effects associated with periodic vane wakes, circumferential pressure gradients, purge flows, and blade lead edge blockages. Part 1 of this study utilizes a wheelspace sector cascade rig for the purpose of gathering fundamental data on flow and thermal effects in a nonrotating environment. This experimental rig is a simplified screening tool for the investigation of basic geometry and flow effects that maintains the bulk of the correct flow physics in the absence of rotation. The test rig is also a validation data generation device for the unsteady CFD modeling efforts described in Part 2. The present cascade is composed of a five-passage annular sector of a transonic turbine inlet guide vane, a complete sector of the upper wheelspace, buffer and trench cavities, and equivalent flow blockages for a blade row represented as leading edge cylinders. The geometry is three-dimensional including all sealing features of the wheelspace. The vane and blade rows can be clocked to any relative position. Secondary cooling flows are adjustable for the wheelspace purge flow and the leakage flow across the vane support. Detailed measurements in the form of static pressures throughout the interaction region, surface temperature distributions, and buffer cavity air temperatures are presented for various clocked positions. The circumferential pressure distribution peak-to-peak variations just aft of the vane are here as much as 18%. These variations are key to the resulting forcing of hot gas inboard of the rim seal. The blade leading edge bow wave is found to have an equal or even greater influence in generating this peak-to-peak variation than the vane trailing edge wake. Buffer cavity cooling effectiveness levels vary with the clocked positions and decrease as cylinder size is increased. Significantly, the effect of the leading edge blockage can reduce buffer cavity cooling effectiveness by a factor of 0.1. [ABSTRACT FROM AUTHOR]