Performance Assessment of Tesla Expander Using ThreeDimensional Numerical Simulation

Abstract

Bladeless or Tesla turbines consist of several flat parallel disks mounted on a shaft with a narrow gap between them. The analytical solution of Navier–Stokes equations for the flow between disks has been extensively studied in the past. However, there is a significant impact of the stator exitflow conditions on the performance and flow behavior inside the rotor of the Tesla turbine. There is limited research on flow characterization and performance evaluation of stator–rotor interaction of the Tesla expander using threedimensional (3D) numerical simulation. The challenge arises due to a very high aspect ratio of the Tesla rotor (diameter to gap ratio > 1000). 3D numerical modeling with a hexahedral mesh of the nozzle/stator with the commercial software is presented. The simulation is performed for a wide range of inlet pressures and rotational speeds. This work focuses on the stator performance, the stator–rotor interaction, the rotor entry losses due to disk tip, the rotor tip velocity ratio, and the degree of reaction on the performance of the Tesla expander. The peak efficiency of 58% is predicted for 3 bar inlet pressure and a rotational speed of 30,000 rpm for a 3kW machine with air as a working fluid. The 3D numerical analysis provides insights on flow characterization, mainly stator–rotor interaction and flow between disks at different mass flows. Numerical results are also compared with experimented test results performed on a 100W and a 3kW air expander.