The Effect of Hot-Streaks on HP Vane Surface and Endwall Heat Transfer: An Experimental and Numerical Study

Abstract

Pronounced nonuniformities in combustor exit flow temperature (hot-streaks), which arise because of discrete injection of fuel and dilution air jets within the combustor and because of endwall cooling flows, affect both component life and aerodynamics. Because it is very difficult to quantitatively predict the effects of these temperature nonuniformities on the heat transfer rates, designers are forced to budget for hot-streaks in the cooling system design process. Consequently, components are designed for higher working temperatures than the mass-mean gas temperature, and this imposes a significant overall performance penalty. An inadequate cooling budget can lead to reduced component life. An improved understanding of hot-streak migration physics, or robust correlations based on reliable experimental data, would help designers minimize the overhead on cooling flow that is currently a necessity. A number of recent research projects sponsored by a range of industrial gas turbine and aero-engine manufacturers attest to the growing interest in hot-streak physics. This paper presents measurements of surface and endwall heat transfer rate for a high-pressure (HP) nozzle guide vane (NGV) operating as part of a full HP turbine stage in an annular transonic rotating turbine facility. Measurements were conducted with both uniform stage inlet temperature and with two nonuniform temperature profiles. The temperature profiles were nondimensionally similar to profiles measured in an engine. A difference of one-half of an NGV pitch in the circumferential (clocking) position of the hot-streak with respect to the NGV was used to investigate the affect of clocking on the vane surface and endwall heat transfer rate. The vane surface pressure distributions, and the results of a flow-visualization study, which are also given, are used to aid interpretation of the results. The results are compared to two-dimensional predictions conducted using two different boundary layer methods. Experiments were conducted in the Isentropic Light Piston Facility (ILPF) at QinetiQ Farnborough, a short-duration engine-sized turbine facility. Mach number, Reynolds number, and gas-to-wall temperature ratios were correctly modeled. It is believed that the heat transfer measurements presented in this paper are the first of their kind.

Effect of Inlet Temperature Non-Uniformity on High-Pressure Turbine Performance

“…The generated inlet temperature fields studied by Povey et al (2003) and Povey et al (2007) are quite similar to those found by Li et al (2006), in that the hot streaks are clearly subject to mixing and diffusion, while maintaining their general position near the centre of the flow field as they get convected downstream. These artificially-produced profiles seem to be marginally more coherent and uniform than those produced by an actual combustor, which is likely due to the assumed conditions that have a lower turbulence and a more uniform geometry than those in the actual case.…”

“…Gundy-Burlet and Dorney (1997) simulated hot-streak effects using a hyperbolic-tangent temperature distribution, which also corroborates the general shape of the radial profile. The temperature profile generated in the experiments of Povey et al (2003) and Povey et al (2007) follows a similar parabolic-like trend, as does their comparison data taken from an existing engine.…”

“…These artificially-produced profiles seem to be marginally more coherent and uniform than those produced by an actual combustor, which is likely due to the assumed conditions that have a lower turbulence and a more uniform geometry than those in the actual case. A temperature profile measured at the exit of a typical military combustor (Povey et al (2007)) illustrates that, while the hot streaks have diffused together to a much greater extent, the peak temperatures can still be identified and a strong radial gradient persists due to coolant flow. Although it is not clear what type of engine these data represent, they seem to agree with the trend observed in data provided by P&WC, specifically that the temperature peaks are skewed toward the duct casing, rather than being centred between the endwalls as in straight-through combustor flow.…”

The Effect of Hot Streaks on a High Pressure Turbine Vane Cascade with Showerhead Film Cooling

“…Conversely, hot streaks can have a significant impact on high-pressure vane heat transfer. Povey et al [4] and Qureshi et al [5] demonstrated that the heat transfer rate on the suction side of the vane increases, over the uniform inlet temperature results, when hot streaks are aligned with the leading edge. Conversely, the heat transfer rate over the vane pressure side was found to be insensitive to inlet temperature non-uniformities.…”

On the Aerothermal Flow Field in a Transonic HP Turbine Stage with a Multi-Profile LP Stator Vane

“…The unsteady flow interactions between the high-pressure turbine and components downstream (an IP or LP turbine) or upstream (combustor) has only been recently published. Experimental studies were conducted on the effect of flow temperature distortions at the turbine inlet section that simulate the presence of an upstream combustion chamber [22,23], hot-streaks effects on the aerodynamics and heat transfer [24,25], hot-streak clocking [26,27]. As modern engine design philosophy places emphasis on higher blade loading and smaller engine length, the effects of unsteady interactions in a multi-row scenario become of utmost interest for turbine designers.…”