Computational investigation of partial admission effects on the flow field of a tesla turbine for ORC applications

Over recent years, the Tesla turbine gained a renewed interest from the scientific community, as its simple structure guarantees low cost and reliability. These are key aspects of the success of an expander suitable for small-distributed energy systems. The reference case for the computational analysis was selected from the available data of an experimental campaign conducted with R1233zd(E) as the working fluid. The analysed turbine has an efficiency of 29% and a power output of 0.57 kW. The fluid dynamics inside the stator, the stator-rotor gap and the rotor was assessed by means of a 3-D computational model. The comprehensive evaluation of the three regions is of paramount importance to determine the machine flow field and the related performance, as they are significantly affected by the interactions amongst the internal components. The effects of the discrete admission to the rotor are relevant in terms of flow field distortion, while the effects on the performance parameters (power and efficiency) are of minor importance. The performance results of the 3-D computational fluid dynamics are in line with those of the analytical 2-D code, which assumes the uniform admission to the rotor. Finally, after that the detailed analysis of the selected test case was conducted, several simulations with different thermodynamic conditions were carried out and compared to the results of the 2-D analytical code and the experiments.