Slip flow in Tesla disk turbines

Purpose This study aims to provide a theoretical analysis of the influence of radial and tangential slip effects on the flow and pressure fields within a Tesla disc turbine. Design/methodology/approach This study closely follows the recently proposed theory in Sengupta and Guha (2012), which builds upon the verified experimental results of Lemma et al. (2008). This study modifies the parabolic nature of the velocity field by introducing radial and azimuthal slip factors. The mathematical formulation establishes that the effective radial velocity depends solely on radial slip, while the effective tangential velocity and pressure become functions of both radial and azimuthal slip. Findings Closed-form solutions reveal the impact of these slips on the performance of velocity and pressure gradient profiles from the inlet rotor to the central outlet rotor of the turbine. The analysis reveals that slip action reduces the Tesla disc turbine’s flow field, prioritizing the conservation of angular momentum over drag forces. However, as particles move away from the inlet rotor, slips also enhance the pressure gradient. Interestingly, this study identifies a threshold for the combination of slip parameters: below this threshold, drag torque increases, but it sharply decreases above it. Originality/value This study showcases that the rotational speed of the Tesla disc for zero torque initially increases with small slips but decreases for larger ones.