Detailed Boundary Layer Measurements on a Turbine Stator Vane at Elevated Freestream Turbulence Levels

Abstract

High freestream turbulence levels have been shown to greatly augment the heat transfer on a gas turbine airfoil. To better understand these effects, this study has examined the effects elevated freestream turbulence levels have on the boundary layer development along a stator vane airfoil. Low freestream turbulence measurements (0.6%) were performed as a baseline for comparison to measurements at combustor simulated turbulence levels (19.5%). A two-component LDV system was used for detailed boundary layer measurements of both the mean and fluctuating velocities on the pressure and suction surfaces. Although the mean velocity profiles appeared to be more consistent with laminar profiles, large velocity fluctuations were measured in the boundary layer along the pressure side at the high freestream turbulence conditions. Along the suction side, transition occurred further upstream due to freestream turbulence.

Direct Numerical Simulations of a High-Pressure Turbine Vane

“…High pressure turbine vanes are likely to experience very high freestream turbulence levels due to the large-scale unsteadiness leaving the combustor. Experimental work at very high turbulence levels (Tu > 10%), generally coupled with large turbulence length scales, show significant increases in surface heat flux and skin friction as compared to low intensity cases (Tu = 2%) [14][15][16]. Interestingly, this work also shows that on the pressure-side the time-average boundary-layer profiles are typically laminar-like even at high turbulence intensities.…”

Aerodynamic Losses in Turbines with and without Film Cooling, as Influenced by Mainstream Turbulence, Surface Roughness, Airfoil Shape, and Mach Number

“…Measurements of blade loading, exit flow angles, and trailing edge base pressures at different Mach numbers show that profile losses at transonic conditions are closely related to base pressure behavior. Radomsky and Thole [33] present measurements of time-averaged velocity components and Reynolds stresses along a turbine stator vane at elevated freestream turbulence levels and present data which show that transition occurs further upstream on the suction side, as the freestream turbulence level increases. Arts [34] describes experimental aerodynamic performance data for a three-dimensional annular transonic nozzle guide vane.…”

MIL SPEC 28 Square Foot Fire Burnback and Extinguishment Testing of FireAde, FlameOut II and Hawk ALLFIRE

“…Note that the stagnation point is theoretically the starting location of the vane surface boundary layer, so the region of valid DPIV data around the stagnation point was in a location of extremely small boundary layer thickness. The expected boundary layer thickness would be less than 0.001C (594 pm), based on boundary layer measurements taken by Radomsky & Thole [2] at locations farther along the pressure and suction surfaces of the airfoil. The magnification of the DPIV system (at 91.6 pm/pixel) would provide approximately six pixels in the boundary layer, but cross-correlation of the PIV image pairs results in a single measurement per 4 or 8 pixels.…”

“…Higher magnification will probably be necessary to resolve the boundary layer near the vane stagnation. However, at a distance s/C = 0.15 from the vane stagnation along the pressure side, Radomsky & Thole [2] measured a boundary layer thickness of 6/C = 0.0034, which would correspond to 22 pixels (4-6 data points) at the same magnification of 91.6 pm/pixel. Figure 3 shows another issue that may be detrimental for near-wall flow field measurements.…”