Abstract
Rotating stalls are generally the first instability met in turbomachinery, before surges. This 3D phenomenon is characterized by one or more stalled flow cells which rotate at a fraction of the impeller speed. The goal of the present work is to shed some light on the entropy generation in a centrifugal fan under rotating stall conditions. A numerical simulation of entropy generation is carried out with the ANSYS Fluent software which solves the Navier-Stokes equations and user defined function (UDF). The entropy generation characteristics in the centrifugal fan for five typical conditions are presented and discussed, involving the design condition, conditions on occurrence and development of stall inception, the rotating stall conditions with two throttle coefficients. The results show that the entropy generation increases after the occurrence of stall inception. The high entropy generation areas move along the circumferential and axial directions, and finally merge into one stall cell. The entropy generation rate during circumferential propagation of the stall cell is also discussed, showing that the entropy generation history is similar to sine curves in impeller and volute, and the volute tongue has a great influence on entropy generation in the centrifugal fan.
Highlights
Nowadays, fans are used extensively in the chemical industry, thermal power plants and so on.Rotating stalls which occur for small flow rates are a common instability phenomenon
This paper numerically studies the entropy generation in a centrifugal fan under stall conditions
There are two high entropy generation areas and one of them is near the volute tongue
Summary
Rotating stalls which occur for small flow rates are a common instability phenomenon. This instability is responsible for the reduction of performance and large vibrations. Analysis of the entropy generation characteristics could help engineers to find out the zones for which energy is lost. This would contribute to the energy savings and optimization of the fan. It helps understanding the mechanism of stalls from the energy point of view. Bejan [2,3] studied the decrease of available energy and the increase of entropy generation in the heat transfer process. Researchers have mainly focused on the mechanism and active control of stalls
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