Abstract
ABSTRACT
This paper shows a numerical simulation in capturing the dynamic and static pressure effects inside a centrifugal fan due to the impeller-volute interaction.The fan used in this study is a single-stage machine with an unshrouded impeller and external volute.Three volute tongue designs were investigated. Volute C had a full tongue and did not allow any flow recirculation. Volute B had a reduced tongue length thereby opening the recirculation port. Finally the tongue of volute A had a rounded leading edge to make it less sensitive to off-design flow conditions. For the numerical simulation, the viscous Navier-Stokes equations are handled with unstructured grid and the relative reference frames technique is applied to take into account the impeller-volute interaction. The data obtained allow the analysis of the main phenomena existent in these fans, such as: pressure changes in the volute for different flow rates and the secondary flow generated in the volute due to the width change between the impeller and the volute. Numerical results are compared with the experimental pressure data measured in the volute and agreement is found show that at low flow rates ,the volute decelerates the airflow leading to an increase in pressure throw the volute. At these low flow rates separation or flow unsteadiness can occur from the underside of the tongue and the strength of the instability increased when the mass flow rate was reduced further. The pressure fluctuation for various mass flow rates is a non-periodical nature and it is manifest as the broad band components in higher level of random frequency (up to nearly 500 Hz).This investigation concentrates on the measurement of the flow characteristic in the volute casing and the volute tongue configuration.
KEYWORDS Flow in volute, Centrifugal fan, volute tongue
