Inlet Gap Influence on Low-Frequency Flow Unsteadiness in a Centrifugal Fan

Abstract

In this study, unsteady low-frequency characteristics in a voluteless low-speed centrifugal fan operating at a high mass flow rate are studied with improved delayed detached eddy simulation (IDDES). This study is motivated by a recent finding that the non-uniformly distributed pressure inside this type of fan could be alleviated by improving the gap geometry. The present simulation results show that the velocity magnitudes of the gap have distinct low and high regions. Intensive turbulent structures are developed in the low-velocity regions and are swept downstream along the intersection between the blade and shroud, on the pressure side of the blade. Eventually, the turbulence gives rise to a high-pressure region near the blade’s trailing edge. This unsteady flow behavior revolves around the fan rotation axis. Additionally, its period is 5% of the fan rotation speed, based on the analysis of the time history of the gap velocity magnitudes and the evolution of the high-pressure region. The same frequency of high pressure was also found in previous experimental measurements. To the authors’ knowledge, this is the first time that the trigger of the gap turbulence, i.e., the unsteady local low velocity, has been determined.

Special Issue “Aeroacoustics and Noise Mitigation”

“…By adjusting the ejector geometry, experiments and numerical simulations showed that the thrust was increased, but the specific fuel consumption and noise emissions were reduced. In addition to the above works, Ottersten et al [9] found a new mechanism that triggers turbulence in a voluteless fan, which is a benchmark configuration for HVAC air units. A region of relatively small flow velocity rotates within the fan clearance passage, and turbulence commences downstream of this region.…”