The Effect of Leading Edge Diameter on the Horse Shoe Vortex and Endwall Heat Transfer

Abstract

The endwall of the first stage vane / blade of modern high temperature gas turbine has been exposed to severe heat transfer environments. Due to the formation of a horse shoe vortex (HV), the flow field of a vane and blade leading edge juncture to endwall is especially complicated and it is difficult to estimate the heat transfer coefficients and the film cooling effectiveness levels in this area. This paper describes the results of experimental and numerical studies on the heat transfer and flow dynamics in the leading edge endwall region of a symmetric airfoil. The effects of inlet velocity, boundary layer thickness and leading edge diameter of a symmetric airfoil were investigated on the endwall heat transfer in a low speed wind tunnel facility. The time averaged local heat transfer coefficients were measured by naphthalene sublimation method and the instantaneous velocity field was obtained by Particle Image Velocimetry (PIV). As the leading edge diameter of symmetric airfoil decreases, the heat transfer coefficients on an endwall increases and is proportional to Re0.71 that is base on the leading edge diameter. However, the boundary layer thickness was found to have a marginal effect on the endwall heat transfer.

Experimental Measurements of Turbulent Junction Flow Using High Speed Stereo PIV and IR Thermography

“…The time-mean velocity is typical of other studies, with a large primary vortex that is elliptical-shaped. These results do not indicate strong secondary or tertiary vortices upstream of the primary vortex, as found by some researchers [2,15], although those vortices are also not apparent in the Rood wing results of Devenport and Simpson [4]. The time-mean turbulent kinetic energy is also typical of other studies, with high turbulence in the core of the vortex.…”

“…Unsteady heat flux measurements upstream of the Rood wing by Lewis et al [5] did not exhibit any bimodal behavior in PDF's in the junction flow region, despite the bimodal flow behavior seen by Devenport and Simpson [4]. Hada et al [15] replicated the "double-band" heat transfer phenomenon in their study of a wide range of inlet velocities, boundary layer thicknesses, and body thicknesses. They also reported that as the body thickness decreased, the endwall heat transfer increased proportionally.…”

“…In Table 3, all the datasets except Praisner and Smith as well as Hada et al used the Rood wing [4,7]. In Table 3, JFL dataset came from Fleming et al, 1991 [16]; SCD dataset came from Dickinson, 1986 a,b [17&18]; HMM was obtained McMahon et al, 1987 [19]; JS was from Shin, 1989 [20]; WJD1 was received from Simpson, 1990b andDevenport et al, 1990 [4]; PS is from Praisner and Smith, 2006 [2]; and Haha is from Hada et al, [15]. As seen in Table 3, the current study encompasses a wide range of momentum thickness Reynolds numbers found in other studies, while keeping the ratio of momentum thickness to body relatively constant and in the middle of the range of prior studies.…”

Unsteady Heat Flux Measurements of Junction Flow With Reynolds Number and Freestream Turbulence Effects

“…Praisner and Smith [1] and Hada et al [11] complemented time mean flowfield measurements with time mean heat transfer measurements to help explain the convective heat transfer at the junction. They found a primary high heat transfer band very close to the junction, which follows the leading edge contour, and a further upstream secondary high heat transfer band linked to the secondary vortex upstream of the large primary vortex.…”

“…They found a primary high heat transfer band very close to the junction, which follows the leading edge contour, and a further upstream secondary high heat transfer band linked to the secondary vortex upstream of the large primary vortex. Hada et al [11] also examined the effects of varying boundary layer thickness, body thickness of the bluff body, and incoming Reynolds number on the surface Stanton number and found that the double bands of high wall heat transfer persisted in all those instances. Swisher et al [14] investigated the unsteadiness in heat flux along the stagnation streamline in front of a streamlined cylinder using a high-frequency-response heat flux microsensor (HFM) and found an increase in the RMS of heat flux unsteadiness as much as 30% over the mean heat flux in the vortex core.…”