Endwall Heat Transfer for a Turbine Blade With an Upstream Cavity and Rim Seal Leakage

Abstract

Aerodynamic loss and endwall heat transfer for a turbine blade are influenced by complex vortical flows that are generated at the airfoil-endwall junction. In an engine, those flows interact with clearance gaps between stationary and rotating components, as well as with leakage flow that is designed to exhaust through the gaps. This paper describes experimental measurements of endwall heat transfer for a highpressure turbine blade with an endwall overlap geometry, as well as an upstream leakage feature that supplied swirled or unswirled leakage relative to the blade. For unswirled leakage, increasing its mass flow increased the magnitude and pitchwise uniformity of the heat transfer coefficient upstream of the blades although heat transfer further into the passage was unchanged. Leakage flow with swirl shifted the horseshoe vortex in the direction of swirl and increased heat transfer on the upstream blade endwall, as compared to unswirled leakage. For a nominal leakage mass flow ratio of 0.75%, swirled leakage did not increase area-averaged heat transfer relative to unswirled leakage. At a mass flow ratio of 1.0%, however, swirled leakage increased overall heat transfer by 4% due to an increase in the strength of the vortical flows.

Heat Transfer and Film Cooling on a Contoured Blade Endwall With Platform Gap Leakage

“…Although the effect of the nonaxisymmetric contour on the endwall heat transfer or film cooling was not directly tested, previous work by the same authors [23,22] suggests that the presence of the rim cavity and platform gap play a dominant role in the endwall flow pattern. The contour studied here may not significantly affect the endwall heat transfer or film cooling, compared to the effect of the leakage features.…”

“…The design and construction of the linear cascade is described in Lynch et al [22] and Lynch et al [23], and only a short description will be given here. The cascade contained six blades based on a high-pressure turbine airfoil geometry.…”

“…The leakage feature induced swirl to the flow, such as would occur in an engine when there is a mismatch between the rotor hub speed and the tangential velocity of the leakage flow. At a net rim seal mass flow ratio of 0.75% MFR, small turning vanes in the rim seal feature imparted a tangential velocity component to the leakage flow relative to the blade (in the þY direction) that was 10% of the estimated rotor hub speed, as obtained by assuming a stage degree of reaction of 0.5 [23]. In the stationary reference frame of an engine, this would be 90% of the hub speed.…”

Computational and Experimental Studies of Midpassage Gap Leakage and Misalignment for a Non-Axisymmetric Contoured Turbine Blade Endwall

“…This value of freestream turbulence falls within the range expected for first stage turbine blades produced by the combustor section, as reported by numerous previous studies, such as those by Bunker [28], Arts et al [29], and Giel et al [30], in which turbine blade relevant freestream turbulence ranges from 1% to 12%. The endwall overlap between the stationary vane and rotating blade rows was simulated as shown in Figure 2 and described by Lynch et al [16,19,27]. The blade endwall extended upstream of the blade leading edge and below the nominal endwall height, resulting in a cavity referred to as a rim cavity in this study.…”

“…The blade cascade contained six blades based on a highpressure turbine airfoil geometry also studied by MacIsaac et al [26] and Lynch et al [16,19,27]. Table 1 lists the geometric details of the cascade.…”