This paper reports the results of an experimental and analytical study dealing with the effect of loading level and distribution on low-pressure turbine (LPT) blade performance. Only a single blade row is considered here, and the study is conducted in a stationary linear cascade that simulates the aero characteristics of a modern LPT design. The loading level and distribution are systematically varied by changing the number of blades (solidity), the stagger angle, and the unguided turning angle. The exit Mach number for this high-speed test is set at 0.64. The Zweifel number ranges from ∼ 1 (nominal lift) to ∼ 1.27 (high lift). The Reynolds number (based on chord and exit velocity) is varied from ∼70,000 to ∼350,000, a range that is broad enough to cover typical cruise and take-off conditions. While some data is taken near the end-walls, the primary focus of this study is on measurements at the mid-span. In addition to the profile loss, measurements include static pressure distribution on the blade surface (loading) and flow visualization. Data demonstrates increased suction side separation and consequent high losses as the loading level increases, the loading is moved aft, or the Reynolds number decreases. Three-dimensional CFD simulations, in conjunction with a turbulence transition model, corroborate these findings.
Analysis and testing were conducted to optimize an axial diffuser-collector gas turbine exhaust. Two subsonic wind tunnel facilities were designed and built to support this pro gram. A 1112th scale test rig enabled rapid and efficient evaluation of multiple geome tries. This test facility was designed to run continuously at an inlet Mach number of 0.41 and an inlet hydraulic diameter-based Reynolds number of 3.4 x 10s. A H4th geometric scale test rig was designed and built to validate the data in the 1112th scale rig. This blow-down rig facilitated testing at a nominally equivalent inlet Mach number, while the Reynolds number was matched to realistic engine conditions via back pressure. Multihole pneumatic pressure probes, particle image velocimetry (PIV), and surface oil flow visual ization were deployed in conjunction with computational tools to explore physics-based alterations to the exhaust geometry. The design modifications resulted in a substantial increase in the overall pressure recovery coefficient of +0.07 (experimental result) above the baseline geometry. The optimized petformance, first measured at 1112th scale and obtained using computational fluid dynamics (CFD) was validated at the full scale Reynolds number.
A comprehensive experimental investigation was initiated to evaluate the aerodynamic performance of a gas turbine exhaust diffuser/collector for various strut geometries over a range of inlet angle. The test was conducted on a 1/12th scale rig developed for rapid and accurate evaluation of multiple test configurations. The facility was designed to run continuously at an inlet Mach number of 0.40 and an inlet hydraulic diameter-based Reynolds number of 3.4×105. Multi-hole pneumatic pressure probes and surface oil flow visualization were deployed to ascertain the effects of inlet flow angle and strut geometry. Initial baseline diffuser-only tests with struts omitted showed a weakly increasing trend in pressure recovery with increasing swirl, peaking at 14° before rapidly dropping. Tests on profiled struts showed a similar trend with reduced recovery across the range of swirl and increased recovery drop beyond the peak. Subsequent tests for a full diffuser/collector configuration with profiled struts revealed a rising trend at lower swirl when compared to diffuser-only results, albeit with a reduction in recovery. When tested without struts, the addition of the collector to the diffuser not only reduced the pressure recovery at all angles but also resulted in a shift of the overall characteristic to a peak recovery at a lower value of swirl. The increased operation range associated with the implementation of struts in the full configuration is attributed to the de-swirling effects of the profiled struts. In this case the decreased swirl reduces the flow asymmetry responsible for the reduction in pressure recovery attributed to the formation of a localized reverse-flow vortex near the bottom of the collector. This research indicates that strut setting angle and, to a lesser extent, strut shape can be optimized to provide peak engine performance over a wide range of operation.
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