Forward-curved Centrifugal Fan Research Articles

Aerodynamic design and acoustic effect study of key geometric parameters of a sirocco fan

A sirocco fan (forward-curved centrifugal fan), including impeller blades and volute, is designed, and the empirical value ranges of several significant design parameters are discussed and summarized fromthe perspective of both aerodynamics and practical structure. Unsteady-flow numerical simulation and radiated sound-field calculation by indirect boundary element method are combined to evaluate its aerodynamic and acoustic performances. Both the discrete noise source from the rotating impeller and broadband noise source from the volute are considered. Obvious flow separation occurs in the flow passage of impeller blades due to large angle of attack, and the tongue region is the major noise source area due to the small impeller-tongue gap. Therefore, parametric studies for blade installation angle and impeller-tongue gap are performed. Analyses of flow- and sound-field indicate that appropriate reduction of blade geometry incidence angle weakens the flow separation, thereby improving both the aerodynamic and acoustic performances, and reasonable increase of the impeller-tongue gap has a remarkable noise reduction effect for the major noise source area near the volute tongue. The optimized sirocco fan meets the requirement of the industrial project, i.e., the far-field A-weighted sound power level lower than 64.0 dB(A), and achieves larger volume flow rate and total pressure rise. The results also imply that fast steady-flow numerical simulation result is indicative of the acoustic performance to some extent if the acoustic evaluation is urgent. Furthermore, optimization of the key structural parameters in the stage of design is preferable in practical engineering, instead of taking follow-up noise reduction measures.

Aerodynamic noise prediction of a centrifugal fan considering the volute effect using IBEM

Customer demands for quieter centrifugal fans in the industry have brought their noise to the forefront. It is found that dipole sources on the surfaces of the rotating impeller and volute are the main acoustic noise sources. The volute effect is seen to have a significant influence on the radiation characters of the fan, although this is frequently ignored by previous studies. Hence, the indirect boundary element method (IBEM) is employed to study the noise of an industrial forward-curved centrifugal fan and to take the effect of volute reflection and scattering of the sound wave into consideration. A large eddy simulation (LES) is used to gain reliable pressure fluctuations on the surfaces of volute and rotating blades. Then the FW-H equation and Lowson equation are applied to calculate the dipole sources on the surfaces of the volute and the blades respectively. The predicted aerodynamic noise of the fan with and without the volute is compared to experiment. The results indicate that the pressure fluctuations on the volute surfaces, especially on the tongue surface, are the main dipole source. It is also found that the application of IBEM can improve the prediction accuracy greatly, especially for the blade passing frequency and its higher harmonics.

Passive control of centrifugal fan noise by employing open-cell metal foam

Experimental and numerical studies were conducted to investigate passive control of a forward-curved centrifugal fan noise by employing the open-cell metal foam (OCMF). The results indicated that a reduction of about 5dB in overall A-weighted sound pressure level (OASPL) was successfully achieved with a decline of about 200Pa in total pressure rise (TPR). For the OCMF investigated in the present paper with the pores per inch (PPI) of 20 and the porosity of 97%, the noise control mechanism was to suppress the source strength of tonal noise generated from the periodic impeller–tongue interaction rather than to absorb the broadband acoustic energy. The decline of the aerodynamic performance was mainly caused by reducing the work capacity of the impeller rather than caused by flow loss owing to the flow resistance of the OCMF. An improved design of the OCMF was suggested to achieve more reduction in noise level with less decline of aerodynamic performance.

Accretion of the Efficiency of a Forward-Curved Centrifugal Fan by Modification of the Rotor Geometry: Computational and Experimental Study

Accretion of the Efficiency of a Forward-Curved Centrifugal Fan by Modification of the Rotor Geometry: Computational and Experimental Study

Influence of Impeller Geometry on the Unsteady Flow in a Centrifugal Fan: Numerical and Experimental Analyses

The aim of this study is to evaluate the influence of design parameters on the unsteady flow in a forward-curved centrifugal fan and their impact on the aeroacoustic behavior. To do so, numerical and experimental studies have been carried out on four centrifugal impellers designed with various geometrical parameters. The same volute casing has been used to study these impellers. The effects on the unsteady flow behavior related to irregular blade spacing, blade count and radial distance between the impeller periphery and the volute tongue have been studied. The numerical simulations of the unsteady flow have been carried out using computational fluid dynamics (CFD) tools based on the unsteady Reynolds averaged Navier Stokes (URANS) approach. The study is focused on the unsteadiness induced by the aerodynamic interaction between the volute and the rotating impeller blades. In order to predict the acoustic pressure at far field, the unsteady flow variables provided by the CFD calculations have been used as inputs in the Ffowcs Williams-Hawkings equations (FW-H). The experimental part of this work concerns measurement of aerodynamic performance of the fans using a test bench built according to ISO 5801 (1997) standard. In addition to this, pressure microphones have been flush mounted on the volute tongue surface in order to measure the wall pressure fluctuations. The sound pressure level (SPL) measurements have been carried out in an anechoic room in order to remove undesired noise reflections. Finally, the numerical results have been compared with the experimental measurements and a correlation between the wall pressure fluctuations and the far field noise signals has been found.

Reduction of the aerodynamic tonal noise of a forward-curved centrifugal fan by modification of the volute tongue geometry

In this work, an experimental study about the influence of some geometric features on the aeroacoustic behaviour of a squirrel-cage fan, used in automotive air conditioning units, has been carried out. The study focused on the effect of both the shape and the position of the volute tongue on the noise generated by the fan. Different geometric configurations were tested in order to compare the results. First of all, the performance curves were measured in a standardized test facility. Then, the acoustic behaviour of the fan was characterized by means of acoustic pressure measurements near the fan inlet. The comparison of the test results indicated a great dependence of both the shape and the position of the volute tongue and the noise generation. In particular, some geometric configurations of the volute tongue were able to reduce the fan noise generation without reducing the fan operating range.

Three-dimensional flow analysis and improvement of slip factor model for forward-curved blades centrifugal fan

This work developed improved slip factor model and correction method to predict flow through impeller in forward-curved centrifugal fan. Both steady and unsteady three-dimensional CFD analyses were performed to validate the slip factor model and the correction method. The results show that the improved slip factor model presented in this paper could provide more accurate predictions for forward-curved centrifugal impeller than the other slip factor models since the present model takes into account the effect of blade curvature. The correction method is provided to predict mass-averaged absolute circumferential velocity at the exit of impeller by taking account of blockage effects induced by the large-scale backflow near the front plate and flow separation within blade passage. The comparison with CFD results also shows that the improved slip factor model coupled with the present correction method provides accurate predictions for mass-averaged absolute circumferential velocity at the exit of impeller near and above the flow rate of peak total pressure coefficient.

231 前向き羽根をもつ多翼送風機の吸込ダクト形態と内部流れ

231 前向き羽根をもつ多翼送風機の吸込ダクト形態と内部流れ

An integrated experimental and numerical study of forward–curved centrifugal fan

In this work, a small forward–curved (FC) centrifugal fan is successfully generated for the thermal task of cooling laptop computers by utilizing an integrated scheme, which consists of fan design, mockup manufacture, experimental verification, and numerical simulation. In the fan design, a high-performance cooling fan (45×45×7 mm 3) is designed under the space limitations of notebook computers with the emphasis on the blade shape, blade inlet angle, and the outlet geometry of the housing. At first, a NACA4412 airfoil is adopted as the basic blade shape to match the low-velocity characteristics of a small fan. Then, by adjusting the blade inlet angle, the blade can be aligned with the incoming flow. Additionally, a redesign of outlet geometry is included to enhance the volume flow rate with less noise. Thereafter, prototypes are manufactured by the CNC machine to carry out the corresponding experimental verifications. To ensure a reliable outcome, the fan's performance and noise tests are executed in the AMCA and semi-anechoic chambers following CNS-8753 code. Moreover, the flow patterns throughout the fan are visualized using numerical techniques. By comparing the experimental and numerical results, a good agreement between them indicates a great potential to reduce expensive experimental work by using CFD tools. In summary, this study presents a reliable and systematic scheme to generate a small FC centrifugal fan for the cooling management of notebook computers.

Experimental study on the mean flow characteristics of forward-curved centrifugal fans

Measurements have been made in an automotive HVAC blower for two different centrifugal fans. This work is directed at improving the performance of a conventional forward-curved centrifugal fan for a given small blower casing. Mean velocities and pressure have been measured using a miniature five-hole probe and a pressure scanning unit connected to an online data acquisition system. First, we obtained the fan performance curves versus flow rates showing a significant attenuation of unstable nature achieved with the new fan rotor in the surging operation range. Second, aerodynamic characterizations were carried out by investigating the velocity and pressure fields in the casing flow passage for different fan operating conditions. The measurements showed that performance coefficients are strongly influenced by flow characteristics at the throat region. The main flow features were common in both fans, but improved performance is achieved with the new fan rotor, particularly in lower flow rate regions. Based on the measured results, design improvements were carried out in an acceptable operation range, which gave considerable insight into what features of flow behavior were most important.

Measurements of Primary and Secondary Flows in an Industrial Forward-Curved Centrifugal Fan

An industrial-type centrifugal-flow fan was instrumented and tested in order to obtain a fully detailed relative flow pattern at impeller discharge. Testing entailed investigation of both primary flows (jet-wake pattern and presence of return flows) and secondary flows (due to streamwise vorticity either from meridional curvature or rotation effects). In addition to conventional probing, a crossed hot-wire probe was employed in the tests. Ensemble-averaging the hot-wire signals made it possible to obtain the three-dimensional phase-averaged relative flow pattern at discharge by means of double positioning of the probe. Results show secondary-flow effects of appreciable magnitude interacting with primary flows (e.g., return flow in the hub region and variations in vortex structure and wake position with variations in flowrate).