Inflow-rotor interaction in Tesla disc turbines: Effects of discrete inflows, finite disc thickness, and radial clearance on the fluid dynamics and performance of the turbine

Abstract

The article establishes the physics of the complex interaction of discrete multiple inflows with the stationary shroud and the rotating channel of a Tesla disc turbine. Using a large number (150) of separate, fully three-dimensional computational fluid dynamic simulations, we demonstrate the (sometimes dramatic) role of four important input parameters, namely the number of nozzles (N nozzle ), rotational speed of the discs (), radial clearance between the rotor and the shroud (Á rc ), and disc thickness (d t ), in the fluid dynamics and performance of a Tesla turbine. An increase in N nozzle or Á rc assists in the attainment of axisymmetric condition at rotor inlet. influences significantly the distribution of radial velocity including the fundamental shape of its z-profile (parabolic, flat or W-shaped). The paper demonstrates the existence of an optimum Á rc for which the efficiency of the rotor () is maximized. Present computational fluid dynamics simulations for many combinations of N nozzle and establish that the versus curves, for each fixed value of N nozzle , are of the shape of an inverted bucket. With increasing N nozzle , the operable range of decreases, the buckets become more peaky and the maximum possible increases substantially (by a factor of 2 in the example calculation shown). The present systematic work thus demonstrates quantitatively, for the first time, that an axisymmetric rotor inflow condition represents the best possible design for the rotor. It is further shown that, as the disc thickness is increased, the efficiency may decrease substantially (even dramatically) and its maxima occur at lower rotational speeds. Chamfering of the disc edge or partial admission decreases the turbine efficiency. Thus, small disc thickness, flat disc edge, full nozzle opening, optimum radial clearance, and inlet condition as close to axisymmetry as is possible are recommended for the design of an efficient Tesla disc turbine.

Influence of Disc Tip Geometry on the Aerodynamic Performance and Flow Characteristics of Multichannel Tesla Turbines

“…The effects of nozzle and outlet geometries, disc spacing distance and disc thickness on the aerodynamic performance and flow mechanism were investigated by our research group, and the results indicate that the flow field in each channel has a large difference [22,23]. In the research of Sengupta and Guha, the model of one disc channel and nozzle-rotor (N-R) chamber was adopted to reduce the calculation domain of multichannel Tesla turbine using symmetry boundary conditions, however the influence of the disc channels close to the rotor casing was not considered [24].…”

“…The schematic diagram of the one-to-many turbine with sharp disc tips is shown in Figure 3. Sengupta et al calculated numerically a similar model with sharp disc tips, however, the influence of the nozzle channel and the disc channel close to the rotor casing was not included [24]. In addition, the relative height and tip profile of sharp tips must affect the aerodynamic performance of Tesla turbines, which was also not considered in their research.…”

CFD Analysis of a Turbo Expander Stator for Non-Conventional Fluids

“…Its effect on the performance of a Tesla turbine has been investigated by (Sengupta & Guha, 2018). They varied the tip clearance in a simplified 8-nozzle configuration by changing the outer diameter of the casing while keeping the mass-flow and the rotational speed of the rotor fixed.…”

Disc Thickness and Spacing Distance Impacts on Flow Characteristics of Multichannel Tesla Turbines

“…The flow fields in the disc channel of one channel Tesla turbine (no stator) with different inlet conditions, including flow coefficient and inlet geometries, were simulated numerically; the efficiency decreases dramatically with increasing flow coefficient, and the inlet non-uniformity is also a factor that makes turbine efficiency decrease [30]. Sengupta et al studied the influence of four parameters, namely the nozzle number, disc thickness, rotational speed and nozzle-rotor radial clearance, on the performance of a Tesla turbine, and the results show that in the turbine design, thin discs with flat disc tip edge, more nuzzles and an optimal radial clearance are suggested [31].…”

“…The effect of disc thickness is studied in Ref. [31], but only the flow in the nozzle-rotor chamber and the rotor are included in numerical calculations. In addition, it has been analyzed experimentally for the one-to-many turbine, while, for the one-to-one turbine, its influence and the fluid mechanism have not been investigated [32].…”