Ardeshir Riahi

Gas turbine combustor heat shield impingement cooling baffle

A heat shield for a combustor dome includes U-shaped baffles on the outer diameter area of the upstream surface of the heat shield. The baffles are clocked with respect to the impingement openings in the combustor dome. The baffles increase cooling of the heat shield by segregating the cooling air flow from the impingement openings and by reducing cross-flow at the outer diameter of the heat shield. The baffles also function as heat shield stiffeners. Slots extend radially inward from the outer rim of the heat shield. Keyholes are at the inner ends of the slots. The slots and keyholes reduce the hoop stresses of the heat shield.

Unsteady 360 Computational Fluid Dynamics Validation of a Turbine Stage Mainstream/Disk Cavity Interaction

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% (Cw = 1540) to 1.74% (Cw = 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.

Influence of Shock Wave on Turbine Vane Suction Side Film Cooling With Compound-Angle Shaped Holes

This paper studies the effect of shock wave on turbine vane suction side film cooling using a conduction-free Pressure Sensitive Paint (PSP) technique. Tests were performed in a five-vane annular cascade with a blow-down flow loop facility. The exit Mach numbers are controlled to be 0.7, 1.1, and 1.3, from subsonic to transonic flow conditions. Two foreign gases N2 and CO2 are selected to study the effects of two coolant-to-mainstream density ratios, 1.0 and 1.5, on film cooling. Four averaged coolant blowing ratios in the range, 0.4 to 1.6 are investigated. The test vane features 3 rows of radial-angle cylindrical holes around the leading edge, and 2 rows of compound-angle shaped holes on the suction side. Results suggest that the PSP is an accurate technique capable of producing clear and detailed film cooling effectiveness contours at transonic flow conditions. At lower blowing ratio, film cooling effectiveness decreases with increasing exit Mach number. On the other hand, an opposite trend is observed at high blowing ratio. In transonic flow, the rapid rise in pressure caused by shock benefits film-cooling by deflecting the coolant jet toward the vane surface at higher blowing ratio. Results show that denser coolant performs better, typically at higher blowing ratio in transonic flow. Results also show that the optimum momentum flux ratio decreases with density ratio at subsonic condition. In transonic flow, however, the trend is reversed and the peak effectiveness values plateau over a long range of momentum flux ratio.Copyright

Unsteady 360 CFD Validation of a Turbine Stage Mainstream/Disc Cavity Interaction

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 disc 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 disc cavity were performed at Arizona State University. 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% (Cw = 1540) to 1.74% (Cw = 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 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 RANS, 360-degree 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 non-periodic/time-dependent unstable flow patterns which at the present are not accurately modeled by a 360 degree 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 disc cavity such as assessing the observed unsteadiness in the frequency domain in order to identify any critical frequencies driving the system.Copyright

High Pressure Turbine Low Radius Radial TOBI Discharge Coefficient Validation Process

A TOBI (tangential on board injection) or preswirl system is a critical component of a high pressure turbine cooling delivery system. Its efficient performance and characterization are critical because the blade and disk life depend on the accuracy of delivering the required flow at the correct temperature and pressure. This paper presents a TOBI flow discharge coefficient validation process applied to a low radius radial configuration starting from a 1D network flow analysis to a 3D frozen rotor CFD analysis of the rotor cooling air delivery system. The analysis domain commences in the combustor plenum stationary reference frame, includes the TOBI, transitions to the rotating reference frame as the flow travels through the rotating cover plate orifice, continues up the turbine disk into the slot bottom blade feed cavity, and terminates in the turbine blade. The present effort includes matching a 1D network model with 3D CFD results using simultaneous goal-matching of pressure predictions throughout the circuit, defining test rig pressure measurements at critical “non-disturbing” locations for quanification of pressure ratio across the TOBI, and finally comparing the TOBI flow coefficient resulting from stationary cold flow tests with what was obtained from the 3D CFD results. Analysis of the results indicates that the discharge coefficient varies with pressure ratio and that the traditional method of using a constant discharge coefficient extracted from a cold flow test run under choked conditions leads to over-predicting turbine cooling flows. TOBI flow coefficient prediction for the present study compares well with the stationary data published by author researchers for the configuration under investigation, and the process described in this paper is general for any TOBI configuration.Copyright