Turbulent boundary layers over surfaces with temperature and elevation heterogeneities

Secondary motions associated with surface heterogeneities have been a hot research topic for the past decade. The big swirling motions greatly impact the transport in the turbulent boundary layer. Heterogeneity examples include surface elevation (Vanderwel & Ganapathisubramani 2015), roughness (Nugroho et al. 2013), temperature (Bon & Meyers 2022), and heat flux (Salesky et al. 2022). However, in nature, two or more types of heterogeneity coexist. One of the ubiquitous cases is the coincidence of surface elevation and temperature heterogeneity. A better understanding of this case is important for weather forecasting, urban planning, and wind farm planning, among others. To this end, a series of experiments have been performed in the wind tunnel at Portland State University. One line of heterogeneity in the middle of the test section was considered. The different cases covered heterogeneous elevation with homogeneous temperature, homogeneous elevation with heterogeneous temperature, and both heterogeneities in neutral and stable boundary layers. The spanwise vertical plane was captured using stereoscopic PIV. Despite the fact that the secondary motions are not clear in the in-plane velocities, preliminary results show that the extent of the low and high momentum pathways in the streamwise velocity is affected by both types of heterogeneity. Further analysis of the data is under way. The new data set will help understand the tangled phenomenon and provide a benchmark for numerical simulations.