Optimise the Aero-Acoustic Performance of a Backward Curved Impeller

Optimise the Aero-Acoustic Performance of a Backward Curved Impeller

The backward curved impeller is a unique type of centrifugal fan that has blades that are curved away from the rotation direction.backward curved impeller This creates a smoother airflow inside the fan and increases its static efficiency meaning that it uses less energy and produces less noise than other types of fans. They are ideal for industrial applications such as cooling towers and process ventilation systems where they can provide high levels of air pressure with low power consumption.

A backward curved impeller is a great choice for dusty environments as the curvature of the blades helps to minimise the amount of debris that can build up on them. This helps to keep the performance of the fan stable and prevents a reduction in airflow and increase in noise due to contamination. They are also well suited for use in particulate filtration as the curved blades help to reduce the amount of debris that can be caught by the filter allowing it to remain clean and efficient over longer periods of time.

Unlike other fan types, a backward curved impeller does not have a stall point on its characteristic which makes it easy to use in systems that require higher airflow or lower operating pressures. However, it is important to select the correct impeller for the application as operating outside the optimum range will result in significant turbulence induced noise and loss of aerodynamic efficiency.

In order to optimise the aero-acoustic performance of a backward curved centrifugal fan, an experimental study has been conducted. The first part of the experiment was dedicated to modifying the geometry of the impeller shroud plate using open-cell metal foam (OCMF). The second part was focused on analysing the effect of this modification on the flow pattern at a plane mid-span cut at different operation points.

Results show that the geometric modification of the impeller shroud plate significantly decreases the strength of rotating structures located at a distance of the blade trailing edge from the inlet. The frequency of the interaction between the rotational velocity of these flow structures and the impeller rotational speed was correlated with the volume flow rate QV and showed a clear dependency on this variable.

A comparison between the flow pictures on the mid-span cut at the three operation points was performed and shows that the modified geometry leads to a more deterministic and organised flow pattern. This is reflected in the fact that at decreasing QV, there are significantly less significative rotating structures present downstream of the blade trailing edge and this is also confirmed by modal analysis.

This is a very promising result as it will help to further improve the aero-acoustic performance of this type of fan and minimize the tonal noise emitted by this system. Further optimization on the geometric parameters is required to further improve the performance and efficiency of this type of fan. It is also worth mentioning that large-eddy simulation confirms the effectiveness of this modification in terms of improving the flow picture of the impeller and volute under the designed conditions and reducing the pressure fluctuations.

Tags:axial fan impeller | backward curved centrifugal fan | backward curved centrifugal fans