Application of Deterministic Correlations in the Analysis of Rotor-Stator Interactions in Axial Flow Fans

Abstract

Deterministic stresses account for the time-averaged contribution of the periodic unsteadiness in single-stage turbomachinery. An accurate modelling of these stresses allows for the development of steady simulations with full contribution of deterministic unsteady sources. Moreover, introducing both relative and absolute reference frames, the deterministic tensor can be split into a set of correlations which addresses the influence of the stator and rotor non-uniformities separately. As a consequence, a pure unsteady term showing rotor-stator interaction is rediscovered and can be established as an essential indicator of the strength of viscous, non-linear effects in multistage turbomachinery environments. This work provides a comprehensive description of these correlations in the interrow region of a single stage axial flow fan. Two configurations are analyzed here: the upstream stator acting as a non-uniform inflow for the rotor and the complementary stator placed downstream of the rotor for pressure recovery at the exit. To illustrate the driven mechanisms in the tensor, a three-dimensional numerical simulation at the midspan section of a low-speed axial fan is employed in the present investigation. A deep analysis of the interaction between the rows using the deterministic framework is shown as a useful tool to devise deterministic models for steady computations. The commercial code FLUENT is used to resolve the full unsteady 3-D Navier-Stokes equations using LES schemes. Nominal and off-design flow conditions have been considered to observe the relevance of the different deterministic correlations in the establishment of the unsteady sources. The final objective pursues a deep understanding of the correlations behavior under variable flow conditions and different stage configurations. Thus, physical insight will be gained and more efficient and reliable deterministic models could be proposed, available for researchers and experts in the field.