Surface Roughness Effects on External Heat Transfer of a HP Turbine Vane

Abstract

External heat transfer measurements on a highly loaded turbine vane with varying surface roughness are presented. The investigation comprises nine different roughness configurations and a smooth reference surface. The rough surfaces consist of evenly spaced truncated cones with varying height, diameter, and distance, thus covering the full range of roughness Reynolds numbers in the transitionally and fully rough regimes. Measurements for each type of roughness are conducted at several freestream turbulence levels (Tu1=4% to 8.8%) and Reynolds numbers, hereby quantifying their combined effect on heat transfer and laminar-turbulent transition. In complementary studies a trip wire is used on the suction side in order to fix the transition location close to the stagnation point, thereby allowing a deeper insight into the effect of roughness on the turbulent boundary layer. The results presented show a strong influence of roughness on the onset of transition even for the smallest roughness Reynolds numbers. Heat transfer coefficients in the turbulent boundary layer are increased by up to 50% when compared to the smooth reference surface.

The Influence of Thermal Barrier Coating Surface Roughness on Spark-Ignition Engine Performance and Emissions

“…Similar results were seen by artificially inducing a turbulent inlet flow over a test sample using different turbulenceinducing devices (i.e. steps [67], trip wire [69]). In these studies, it was seen that while the turbulent inlet flow greatly increased heat transfer to relatively smooth samples, increasing roughness height had little effect on overall heat loss since the flow characteristics were the predominant factor in heat loss as opposed to the surface roughness (i.e.…”

“…The desire to quantify and minimize the aerodynamic and heat transfer losses due to surface roughness in gas turbines has led to a great deal of research investigating the effects of both into the samples became independent of Re since the turbulence intensity of the flow over the airfoil became governed by the roughness height rather than flow velocity, thus showing minimal heat flux augmentation with increased flow velocity [69]. Similar results were seen by artificially inducing a turbulent inlet flow over a test sample using different turbulenceinducing devices (i.e.…”

Simplified Approach to Predicting Rough Surface Transition

“…The first determines a correlation for the equivalent sand grain roughness, ks, that is consistent with the experimental data of Stripf et al [24]. The second part determines modifications to transition start and relaminarization criteria to yield heat transfer predictions consistent with the same experimental data.…”

A Bypass Transition Model Based on the Intermittency Function

“…An experimental database is available in Stripf et al (2005) and Stripf (2007). Coordinates for the turbine blade geometry are provided by Stripf (2007).…”