Transport phenomena associated with the heating of a stationary fluid near saturation by an inclined, partially submerged copper plate were studied analytically. Under steady-state evaporation, the meniscus profile was derived using an appropriate liquid film velocity and temperature distribution in an integral approach similar to boundary layer analysis. Derivation of the meniscus profile led to predicting heat transfer and performance as a function of angle of inclination of the plate.

The amount of cooling air assigned to seal high pressure turbine (HPT) rim cavities is critical for performance as well as component life. Insufficient air leads to excessive hot annulus gas ingestion and its penetration deep into the cavity compromising disk or cover plate life. Excessive purge air, on the other hand, adversely affects performance. Experiments on a rotating turbine stage rig which included a rotor-stator forward disk cavity were performed at Arizona State University (ASU). The turbine rig has 22 vanes and 28 blades, while the cavity is composed of a single-tooth lab seal and a rim platform overlap seal. Time-averaged static pressures were measured in the gas path and the cavity, while mainstream gas ingestion into the cavity was determined by measuring the concentration distribution of tracer gas (carbon dioxide) under a range of purge flows from 0.435% (C w ¼ 1540) to 1.74% (C w ¼ 6161). Additionally, particle image velocimetry (PIV) was used to measure fluid velocity inside the cavity between the lab seal and the rim seal. The data from the experiments were compared to time-dependent computational fluid dynamics (CFD) simulations using FLUENT CFD software. The CFD simulations brought to light the unsteadiness present in the flow during the experiment which the slower response data did not fully capture. An unsteady Reynolds averaged Navier-Stokes (RANS), 360-deg CFD model of the complete turbine stage was employed in order to increase the understanding of the swirl physics which dominate cavity flows and better predict rim seal ingestion. Although the rotor-stator cavity is geometrically axisymmetric, it was found that the interaction between swirling flows in the cavity and swirling flows in the gas path create nonperiodic/time-dependent unstable flow patterns which at the present are not accurately modeled by a 360 deg full stage unsteady analysis. At low purge flow conditions, the vortices that form inside the cavities are greatly influenced by mainstream ingestion. Conversely at high purge flow conditions the vortices are influenced by the purge flow, therefore ingestion is minimized. The paper also discusses details of meshing, convergence of time-dependent CFD simulations, and recommendations for future simulations in a rotor-stator disk cavity such as assessing the observed unsteadiness in the frequency domain in order to identify any critical frequencies driving the system.

Flow and heat transfer in the row-1 upstream rotor-stator disk cavity of a large 3600-rpm industrial gas turbine was investigated using an integrated approach. A two dimensional axisymmetric transient thermal analysis using aeroengine-based correlations was performed to predict the steady-state metal temperatures and hot running seal clearances at ISO rated power condition. The cooling mass flow and the flow pattern assumption for the thermal model were obtained from the steady-state two dimensional axisymmetric CFD study. The CFD model with wall heat transfer was validated using cavity steady-state air temperatures and static pressures measured at inlet to the labyrinth seal and four cavity radial positions in an engine test which included the mean annulus static pressure at hub radius. The predicted wall temperature distribution from the matched thermal model was used in the CFD model by incorporating wall temperature curve-fit polynomial functions. Results indicate that although the high rim seal effectiveness prevents ingestion from entering the cavity, the disk pumping flow draws air from within the cavity to satisfy entrainment leading to an inflow along the stator. The supplied cooling flow exceeds the minimum sealing flow predicted from both the rotational Reynolds-number-based correlation and the annulus Reynolds number correlation. However, the minimum disk pumping flow was found to be based on a modified entrainment expression with a turbulent flow parameter of 0.08. The predicted coefficient of discharge (Cd) of the industrial labyrinth seal from CFD was confirmed by modifying the carryover effect of a correlation reported recently in the literature. Moreover, the relative effects of seal windage and heat transfer were obtained and it was found that contrary to what was expected, the universal windage correlation was more applicable than the aeroengine-based labyrinth seal windage correlation. The CFD predicted disk heat flux profile showed reasonably good agreement with the free disk calculated heat flux. The irregular cavity shape and high rotational Reynolds number (in the order of 7×107) leads to entrance effects that produce a thicker turbulent boundary layer profile compared to that predicted by the 1/7 power velocity profile assumption.

While it is widely recognized that ingestion of hot gas from the main annulus of axial gas turbine stages into rotor-stator disk cavities depend strongly on the unsteadiness of the prevailing flow field, the large computational effort needed to simulate the flow field renders its use in the design of turbine internal air system and seals difficult. As an alternative, considerable effort has been devoted in recent years to develop simple orifice models of disk cavity rim seals based on time-averaged flow information; these models contain empirical discharge coefficients for ingestion into and egress from the cavities. The present experimental work in a subscale axial turbine stage reports a simple orifice model of an axially-overlapping radial-clearance seal at the disk cavity rim and values of the discharge coefficients over a range of purge flow rate supplied to the cavity. In the experiments, the ingestion process was dominated by the main gas annulus flow. Time-averaged static pressure distribution was measured in the main annulus and in the disk cavity; the driving force for ingestion and egress was taken to be the pressure differential between the main annulus and the rim cavity at prescribed locations. Time-averaged ingestion was measured using the tracer gas technique; the pressure and ingestion data were combined to obtain the ingestion and egress discharge coefficients at several purge flow rates. The location on the vane platform 1mm upstream of its lip represented the main gas annulus pressure in the calculation of discharge coefficients. In the rim cavity, two locations on the stator, one in the ‘seal region’ and the other slightly inward radially, were prescribed to represent the rim cavity pressure as well as the sealing effectiveness. Two corresponding sets of ingestion and egress discharge coefficients are reported for the various purge flow rates. The ingestion discharge coefficient obtained using the seal region location in the rim cavity decreased as the purge flow rate increased; the corresponding egress discharge coefficient increased with purge flow rate. For the rim cavity location slightly inward radially from the seal region, the egress discharge coefficient maintained the same trend; however, the ingestion discharge coefficient decreased only slightly as the purge flow rate increased. It is suggested that the seal region location in the rim cavity is the more appropriate location in calculating the rim seal discharge coefficients. The ratio of ingestion to egress discharge coefficients exhibited considerable variation with purge flow rate.

The amount of cooling air assigned to seal high pressure turbine rim cavities is critical for performance as well as component life. Insufficient air leads to excessive hot annulus gas ingestion and its penetration deep into the cavity compromising disk or cover plate life. Excessive purge air, on the other hand, adversely affects performance. This paper is Part-2 of the authors’ work on ingestion reported last year [1]. Whereas, the main focus of that investigation was to qualitatively describe ingestion driven by annulus circumferential pressure asymmetry under constant annulus conditions and rotational speed, in this paper, the research team investigated the variation of annulus circumferential pressure fluctuation and rotational speed on the double overlap platform rim seal cavity reported in Part-1, and mapped out the resulting non-dimensional minimum sealing flow (minimum value of Cw or Cw,min) as it relates to entrained ingestion in the absence of cavity cooling flow (Cw,ent). As was done in Part-1, the runs were made with 3D CFD in setup/run mode option using Fine/Turbo. At two rotational speeds, annulus conditions were varied by reducing turbine inlet pressure (i.e. mass flow) from the baseline operating condition, and the resulting pressure fluctuation was quantified. In addition, a preliminary investigation to assess the aft-located mixing plane steady state solution for this study was performed. The results yielded the linear decrease in Cw,ent at fixed rotational Reynolds number as annulus Reynolds number was decreased. Moreover, the rate of change in entrained flow sharply increases with increase in rotational Reynolds number. As annulus mass flow is reduced to a critical value defined by annulus-to-rotational Reynolds number ratio, the CFD prediction for Cw,ent converges to the turbulent boundary layer entrainment solution for the rotor, and Cw,min reverts to the rotational Reynolds number dominating region. The results from this study were compared to what has been observed by a previous study for a single overlap platform geometry. The resulting design curve allows insight in relating cavity purge flow requirements versus turbine cycle parameters which could lead to better efficiency.