Abstract
The use of blade slots is one of the passive methods of controlling flow in a fan impeller. Numerical CFD analyses indicate a possibility of controlling the point of flow separation in the inter-blade space depending on various configurations of the aperture arrangement. Bench studies confirm the possibility of changing the increase of total pressure and internal efficiency. Additionally, the changes affect the noise level during fan operation.
Highlights
An important aspect taken into account when considering flow control options in rotodynamic machines should be the boundary layer separation phenomenon
In fan designs it can occur in many places, above all in the diffusion areas which are characterised by a positive liquid pressure gradient within the boundary layer
The second requirement indicates a change in the flow direction, which results in the occurrence of flow separation
Summary
An important aspect taken into account when considering flow control options in rotodynamic machines should be the boundary layer separation phenomenon. In fan designs it can occur in many places, above all in the diffusion areas which are characterised by a positive liquid pressure gradient within the boundary layer. The first group comprises technologies employing additional external energy apart from the flow This will include techniques based on partial suction of the boundary layer, generation of micro vortices or surface vibrations, use of acoustic waves or plasma inductors. The passive methods do not require any additional external energy for operation This group comprises the techniques of appropriate cross-section modelling, using slots, perforated surfaces or static micro vortex generators. The selection criteria were the relative change in internal efficiency, the change in total pressure and visualisation of the effect of the slots on flow formation in different cross-sections of the impeller
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