Optimization of Wall Paramaters Using CFD

Computational Fluid Dynamics (CFD) is commonly used to calculate the pressure drop in systems with internal flow. To get accurate results the physics of the flow must be well defined together with the right material parameters of the considered geometry. The material parameter considered in this report is the wall roughness, or sand-grain roughness, and during the thesis work it has been investigated how different wall roughnesses affects the pressure drop. It has also been investigated how to set up a CFD simulation to accurately calculate the pressure drop. When setting up a simulation, a good mesh is essential to get accurate results, while using a turbulence model and wall function that is correct for the geometry and physics involved. Pressure drop measurements and the corresponding CAD geometries were available at the start of the thesis work. The simulations were adapted to these to find the sand-grain roughness for the different materials. The main conclusions is that the pressure drop can be accurately calculated when the sand-grain roughness is known and the CFD simulation is well defined. It was found from the mesh sensitivity study that it is essential that the first cell size is at least twice the size of the sand-grain roughness and that at least two cell layers are used to resolve the turbulent boundary layer.