Analys av turbulensmodeller för CFD
This thesis has been a part of Forsmarks Kraftgrupp AB's evaluation of a turbulencemodel used in simulation of turbulent flow called PRNS (Partially Resolved NumericalSimulation). This model has promising properties and may be of use in savingcomputational resources. The purpose of this thesis was to analyze this model andcompare it with industrially applied models such as k-omega SST and LES (Large EddySimulations).PRNS works as a hybrid of the k-omega SST and DNS (Direct Numerical Simulation)where a constant, RCP (Resolution Control Parameter) with a value between 0 and 1are selected. This constant is then used in the calculations and determines thebehavior of the simulation. When RCP is set to zero the equation are the same as fora DNS simulation and when RCP is set to one the equations for k-omega SST issolved. In this report four different PRNS models have been used, three where RCPwas given a constant value (0.1, 0.4 and 0.6). In the fourth model RCP is calculatedfrom the flow field variablesThe models have been compared to an experiment from 2008 and simulations havebeen made to resemble the experiment. In the experiment a Particle ImageVelocimeter (PIV) was used as method of measurement. From the experimentalreport data such as velocity (U), turbulent kinetic energy (k) and standard deviation(URMS) have been obtained and have formed the basis for comparison. The modelshave been simulated in two different software programs: OpenFOAM and Fluent. Thedata have thereafter been post processed in the software programs MatLab andParaView, to be compared with experimental data.The results of the simulations have shown that PRNS models generally show a goodaccordance with experimental data. In particular, PRNS models with constant RCPhave shown good results, however, there are some discrepancies. The PRNS modelwith varying RCP has in most cases showed the largest deviation from experimentaldata but also a deviation from the other models, including the reference models.Due to the design of the mesh (coarse) further evaluation of the PRNS models will beneeded. First, simulate with a finer mesh, but also more complex geometries shouldbe simulated in order to sort out PRNS strengths and weaknesses and thus determineif the model can be used in the daily work at Forsmarks Kraftgrupp AB.