Effect of height and density of roughness elements on turbulent boundary layers

Abstract

This paper summarises the experimental results of the research undertaken at the School of Aeronautical Engineering at the Queen’s University of Belfast regarding the effects of distributed roughness elements on two-dimensional turbulent boundary layers. All the experiments were conducted on a smooth flat plate model. Data was first collected for the smooth case and analysed to create a database for comparison with the rough cases. Different configurations of distributed roughness were tested by attaching elements to the smooth flat plate model. One set of experiments was conducted when there was a zero pressure gradient along the model, and in the second part of the work a pressure bump was placed above the model to produce favourable and adverse pressure gradients along the model. Data from those experiments was also collected, analysed, and compared with the rest of the findings. The influence of roughness height was observed and it showed that the bigger elements produce more disturbances in the boundary layer. The density of the roughness elements was also found to be an important parameter on the study as its influence was clearly stated when the denser grids produced higher values of skin friction.