An investigation of classifying the flow over rough surfaces into k- and d- type in turbulent channel flow

• Main Author: Alhinai, Almajd
• Other Authors: Nowakoski, Andrzej
• Published: University of Sheffield 2015
• Subjects: 621
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.675077

This thesis is concerned with the classification of roughness into k- and d- type in turbulent channel flow. Despite the practical importance of this type of flow, the literature review suggest that advancements in the field have been slow due to the difficulty of making accurate measurements close to the wall when using experimental methods. In recent years, numerical modelling has provided a good alternative to studying this type of flow. In this work, an Implicit Large Eddy Simulation (ILES) approach was developed to carry out numerical simulations for turbulent channel flow over rough surfaces. The application was developed based on the Finite Element Method and implemented using the Multi-Physics platform COMSOL. Verification and validation of the numerical model was carried out to asses the predictive capabilities of the model, including sensitivity analysis to quantify the uncertainty and comparison with results from literature to validate the model. In our analysis, we considered rough surfaces with square and triangular roughness elements with a constant roughness height and varying distributions of the roughness elements. The results demonstrated that the model is capable of resolving the coherent large eddy structures associated with the k- and d- type behaviours. The classification reported here is based on the coherent structures associated with the k- and d- type behaviours. Furthermore, we investigated the effects of roughness geometry on the k- and d- type behaviours. To this end, flow visualizations were used to study the interaction between the inner and outer layer of the flow. The results demonstrated that the geometry of the roughness elements has little effect on the coherent structures associated with the k- and d-type behaviours, these effects of the roughness geometry are confined to the inner region. However, the results show that the roughness geometry has a strong influence on the interaction between the inner and outer flow regions.