The prediction of internal flows within industrial centrifugal fans

[摘要] During the last twenty years there has been a gradual growth in the field of Computational Fluid Mechanics (CFD). Many of these techniques have been applied to a variety of fluid and thermodynamic problems. Unfortunately, many of the computer codes were written with particular applications in mind, restricting the flow physics and, occasionally, the possible problem geometry. Consequently, there are a multitude of computer codes available to a prospective user, differing not only in the equations solved but also in the user friendliness and generality of their pre-and postprocessors. A small number of these CFD codes are commercially available today and claim to be suitable for solving a wide range of flow situations. It is understandable that these are treated with some suspicion by potential users, such as industrial fan manufacturers, due to the inherent difficulty traditionally found in solving such problems. This present work has been carried out to alleviate some of the fears of this particular group through a series of CFD investigations using proprietary codes. The aim of this present investigation is to test the suitability of such codes to model the flow within centrifugal fans. The internal flow field within a centrifugal fan is described and the salient flow features that affect the gross flow are highlighted. Also included is a review of methods used for predicting flows in centrifugal and radial machines, from which it is apparent that the centrifugal fan has been relatively neglected compared with its higher pressure counterpart, the radial compressor. Use is made of these proven techniques which are adapted here for use on lower pressure centrifugal fan machines. In all, three impeller geometries are examined covering a range of specific speeds. CFD techniques were applied to each of these geometries, incorporating configuration adaptations and changes in operational conditions. In this way known techniques for radial compressors were initially utilised and latterly enhanced for application to centrifugal fans. This step-wise approach proved successful and it is shown that such codes can be used to predict the gross flow features within centrifugal fans. Also included in this work is an experimental investigation into the effect of the fan discharge configuration on flow stability. It is shown that the discharge has little influence over the flow at duties near stall for low pressure centrifugal fans. This present work addresses many of the problems associated with the simulation of centrifugal fan internal flow and will allow potential investigators to quickly implement codes. This will reduce the number of confidence checks necessary prior to application. Suitable boundary conditions and modelling generalisations are discussed.

[发布机构] University:University of Glasgow

[关键词] Mechanical engineering