The interior flowfield analysis of fan has been considered to be one of the most difficult problems in the past. With the advent of computational fluid dynamics (CFD) methods, many flow problems inside the fan can now be solved with a good degree of accuracy. ¡@ A numerical study of the influence of inlet cone and volute cutoff on a centrifugal fan performance is presented in this work. Using the flow-visualization simulating analysis of the flow-flied characteristic of air across the inner of centrifugal fan, the performance curve with different inlet cone shape, inlet clearance gap, cone position, extending angle and curvature radius of cutoff arc were obtained and explored. The Reynolds-Averaged Navier- Stokes equations with the Standard k-£` turbulence model is used to simulate the three-dimensional, steady, incompressible, turbulent flow field inside a double-suction backward-curved centrifugal fan and is solved by control volume method. The numerical model is validated by experimental data. The results showed that (i) the inlet cone can induce the air to enter into the impeller smoothly and uniformly, which reduces the flow-separation occurrence along the blade surface. However, the inlet cone with larger friction loss will also slightly lessen the fan performance; (ii) recirculation zones appear inside the volute channel due to the existence of inlet clearance gap between inlet cone and volute, which results in part of fluid leaving from the impeller outlet re-entering into the impeller inlet and reducing the fan performance. This recirculation leakage ratio of fluid through inlet clearance gap increases with increasing inlet clearance gap, which is also depends on the shape of inlet cone; (ii) the distance of inlet cone extending into the impeller will interfere the uniformity of inlet airflow distribution along each blade height. The longer the extending distance, the larger the vortex zone occupying the inter-blade space which makes less fan performance; (iv) it makes only little improvement in the fan performance to change the shape of volute cutoff. ¡@ It is found that (1) decreasing the inlet clearance from 11mm to 5mm, the outlet average total pressure increases about 3.26%; (2) increasing the distance of inlet cone extending into the impeller from 0mm from 20mm, the outlet average total pressure decreases about 6.32%; (3)changing the shape of inlet cone, the outlet average total pressure increases up to 5.4%, and (4) reducing the tongue radius of volute cutoff from 25mm to 15mm, the performance efficiency of fan promotes slightly about 1%.

In this study a centrifugal fan is studied for noise characteristics and measurements in a semi- anechoic room. A semi-anechoic room is constructed inside Fluid Mechanics Laboratory of Mechanical Engineering Department has been qualified with respect to ISO 3745 standard. The fan characteristic is obtained as proposed in AMCA standards 210-75, by simply measuring the voltage and current of the motor during operation and calculating the power consumption of the assembly. Noise measurements are taken using two microphones attached to a multi-channel data acquisition and processing system in the semi anechoic room. Several different configurations of the vacuum cleaner with some parts removed or replaced systematically are considered during the noise measurements. Some of the results showed that the damping material placed inside the motor cover is proved to be very effective in noise reduction. Two different damping materials are examined for comparative evaluation.

L'amélioration de la performance des turbomachines fonctionnant loin de leur point d'adaptation passe par la maîtrise des phénomènes instationnaires qui se produisent dans ces différents organes. L'étude présentée ici se concentre sur les interactions entre une roue de ventilateur centrifuge et son diffuseur. Elle vise, par des mesures de pression sur les différentes parois du diffuseur, ainsi que par des sondages dans les canaux inter-aubages à analyser finement ces phénomènes instationnaires et notamment les décollements fluctuants apparaissant sur les aubes à sur débit, et à mesurer leur influence sur la performance du diffuseur. Dans un second temps, un dispositif de contrôle passif de ces décollements utilisant des générateurs de vortex est proposé. Plusieurs configurations sont testés et leurs résultats sont comparés / The performance improvement of turbomachinery operating at off-design conditions can be achieved by the understanding of unsteady phenomena which are occuring in its components. The present study is focussing on the interaction between a centrifugal impeller fan and its vaned diffuser. It aims at analysing precisely these unsteady phenomena (and especially the fluctuating separated region identified on the vanes wall) and their consequences on the diffuser performance by three holes probe and unsteady pressure measurements. In a second step, devices for a passive control of the separation are introduced. Several configurations are tested and their results are compared

Noise from information technology (IT) equipment is a significant problem in today's modern society. Active Noise Control (ANC) has shown promise in reducing the effect of IT fan noise on users. Though ANC has been applied to axial fans (such as those found in desktop computers), it has not been applied to centrifugal fans, such as those found in laptop computers. This work applies an ANC method to a centrifugal fan mounted in a mock laptop enclosure. This method is applied in four steps. First, secondary sources are placed in the vicinity of the fan. Second, an accurate model of the radiation from the fan and secondary sources is constructed. Third, the total power radiated from this system is minimized. This creates nodal lines in the vicinity of the fan. Fourth, ANC error sensors are placed on the nodal lines predicted by the model. This creates these nodal lines experimentally, thus creating the minimum power condition. The noise from the exhaust and inlets of the fan will first be controlled individually. Then the method will be applied to the combined system. Global sound power radiation will be measured in all cases.

In this study, the effects of design parameters on the fan noise level are investigated both theoretically and experimentally. For the theoretical study, a computational aero- acoustic method is used to predict the flow induced noise of a fan. This method involves the coupling of a flow solver and a wave equation solver. Unsteady flow analysis is performed with URANS using FLUENT. Then the time dependent data are processed with LMS Sysnoise to compute the acoustic radiation. Experimental studies are performed to verify the theoretical results and additionally to investigate the effects of different design alternatives on noise level of the fan. The sound pressure and intensity level measurements are performed in the full anechoic room of Ar&ccedil / elik A.S. Research and Development Laboratories. The validation experiments indicate that there is a good agreement between numerical and experimental results. The experimental study with different fan designs gives information about the noise reduction possibilities.

Le développement de turbomachines à faible vitesse spécifique suscite actuellement une forte demande dans de nombreux domaines industriels. De nos jours, les ventilateurs centrifuges constituées d'une roue, d'un diffuseur et d'un canal de retour sont largement utilisés dans de nombreuses applications telles que l'automobile, l'aéronautique, appareils domestiques, etc. En raison de leur grande adaptabilité, ils peuvent fonctionner sur une large plage de débit en particulier avec une vitesse de rotation importante. Cependant, leur utilisation nécessite une meilleure compréhension de leur fonctionnement et notamment de l'interaction rotor-stator pour mieux les concevoir. L'objectif de cette étude est d'analyser et de quantifier l'influence de la solidité des aubes du diffuseur (ou serrage des profils) sur les performances aérauliques du ventilateur centrifuge. Une étude numérique et expérimentale a été menée pour analyser les performances d'un ventilateur centrifuge avec différents niveaux d'interaction rotor-stator. Différentes géométries de diffuseur ont été proposées dans le but de réduire les dissipations énergétiques liées aux phénomènes de recirculation et aux forces de viscosité. L'étude approfondie de la norme ISO 5801 et ISO 5167 a permis de dimensionner et réaliser le banc d'essai et les organes de mesures. Ces normes proposent des calculs et des spécifications qui nous ont permis de fixer des critères quant au choix des éléments du banc d’essai AERO2VACCUM. / Nowadays, centrifugal fans are widely used in many industrial applications such as automotive, aeronautic, vacuum cleaner, etc. Due to their high adaptability, they can operate over a wide flow range especially with high speed rotation. In order to reduce the impact on environment, centrifugal fan as other energy conversion system has to display a high efficiency. However, a better understanding of their working and of the rotor-stator interaction is required to enhance their design and to make them widely integrated in current applications. The purpose of this study is to analyze and to quantify the influence of the solidity vaned diffusers on the performance of a centrifugal fan. A computational study has been conducted to analyze the performance of a centrifugal fan under various levels of impeller-diffuser interactions. The objective was to understand the pressure recovery phenomena in each diffuser. Different geometries were proposed to reduce both separation flow phenomenon and viscous losses. The geometries are all composed with the same impeller and return channel, only the vaned diffusers differ; the trailing edges are maintained at the same position while the leading edges have different radial positions. The characterization of the fan has been realized by an experimental setup designed and built in agreement to the standards ISO 5801 and 516