Implementation of a Surface Roughness-Based Transition Onset Correction in the γ-Rθt~ Transition Model

This paper presents an extension of the γ-Rθt~ transition model of Menter et al. (2006) that aims to take into account the effect of a specific type of surface roughness on the transition location. This was done by implementing the roughness transition onset correction of Stripf et al. (2009) inside the γ-Rθt~ model. Stripf et al. have developed a correlation that takes into account the height and spacing of distributed roughness elements to correct the transition Reynolds number predicted over a smooth surface. As the transition Reynolds number takes multiple forms in the γ-Rθt~ model, different implementations of the Stripf et al. correction were tested and are discussed here. We find that it is best to correct the value of the critical Reynolds number Rθc. Computation results on a rough, low-pressure turbine vane are presented and compared to experimental results of the Karlsruhe Institute of Technology. We find that there is a good agreement on the transition location between the computations and experiments. In particular, the model displays accurate sensitivity to the roughness height, though the influence of the roughness spacing, which is of second order in these experiments, is not as well captured. We therefore conclude that the roughness transition onset correction of Stripf et al. is well suited for use in the γ-Rθt~ model.

Characterization of a wind turbine wake evolving over an intertidal zone performed with dual-lidar observations

As modern wind power industry quickly develops, it is of high priority to optimize layouts and operations of wind turbines to reduce the influences of wakes induced by upstream wind turbines. The wake behaves complicatedly with land ocean-atmosphere interactions. This complex wake could be observed by two or more synchronously operated Doppler lidars. Accordingly, we characterized a wind turbine wake evolving over an intertidal zone performed with dual-lidar observations. Dynamic process of wakes merging that occurred from approximately 1 D (rotor diameter) downstream was captured and analysed. The phenomenon that wake length increased with rising tide was analysed in details. It suggested that the increase of wake length varied with underlying surface roughness transition from mud to sea water as well as the rising sea level. Finally, wake meandering cases were analyzed in detail. Our research shows that the dual-lidar observation technology is a promising remote sensing tool for characterization of complicated wind turbine wakes.

Simplified Approach to Predicting Rough Surface Transition

Turbine vane heat transfer predictions are given for smooth and rough vanes where the experimental data show transition moving forward on the vane as the surface roughness physical height increases. Consistent with smooth vane heat transfer, the transition moves forward for a fixed roughness height as the Reynolds number increases. Comparisons are presented with published experimental data. Some of the data are for a regular roughness geometry with a range of roughness heights, Reynolds numbers, and inlet turbulence intensities. The approach taken in this analysis is to treat the roughness in a statistical sense, consistent with what would be obtained from blades measured after exposure to actual engine environments. An approach is given to determine the equivalent sand grain roughness from the statistics of the regular geometry. This approach is guided by the experimental data. A roughness transition criterion is developed, and comparisons are made with experimental data over the entire range of experimental test conditions. Additional comparisons are made with experimental heat transfer data, where the roughness geometries are both regular and statistical. Using the developed analysis, heat transfer calculations are presented for the second stage vane of a high pressure turbine at hypothetical engine conditions.