The objective of this paper is the numerical study of the flow through an axial fan and examining the effects of blade design parameters on the performance of the fan. The axial fan is extensively used for cooling of the electronic devices and servers. Simulation of the three-dimensional incompressible turbulent flow was conducted by numerical solution of the (RANS) equations for a model. The SST-k-ω and k-ε turbulence models are applied in the simulations which are done using CFX software. The comparison between available experimental data and simulation results indicates that the SST k-ω model gives more accurate results than the k-ε model. The results also show that in separation regions and vortices, the pressure will decrease. Hub area and blade root contain large vortices. The effects of changes in the blade geometry and the number of blades on the fan performance are studied in detail. For the primary fan model with the different number of blades (4, 5, and 6), the maximum mass flow rate of 800 CFM is obtained. Hence, the number of blades had negligible effects on the maximum flow rate. By 3o% decreasing in the chord of the blades, the maximum mass flow rate of the fan with the different number of blades (5, 6 and 8) will be reduced to 500 CFM. Therefore, in order to increase the maximum mass flow rate, the chord and the width of blades should be increased. On the other hand, by increasing blades from 4 to 6 in the primary model, the maximum outlet pressure has been increased by 32%. Furthermore, it was found that in high flow rates, an increment in the number of blades had no effect on the produced static pressure.

Noise is one of the key indicators to evaluate axial flow fans, and in many cases, it is also the only indicator for determining their suitability for use. In this study, a new method to reduce axial fan’s noise was proposed for changing the section chord length to transform the blades of two axial fans with the same design parameters but distinct chord lengths to wavy blades. The aerodynamic calculations and noise reduction mechanism of the wavy configuration of the two fans were studied by combining CFD of large eddy simulation with the Lighthill acoustic analogy method. The results showed that the main mechanism contributing to noise reduction through wavy configuration was the promotion of transformation of the blade surface's layered vortex structure into an uncorrelated comb vortex structure. For fan blades with smaller chord lengths, the comb structure with low spanwise correlation was still maintained after the trailing edge, while for fan blades with larger chord lengths, the comb structure of the shedding vortex rapidly dissipated downstream of the trailing edge. Under the rated design conditions, the implementation of wavy leading edge blades resulted in noise reductions of 1.9 dB and 1.5 dB for the two fans, respectively, while wavy trailing edge blades yielded reductions of 2.6 dB and 2.1 dB, respectively. Furthermore, the adoption of wavy configuration induced a phenomenon of pressure increase and efficiency decrease in both axial fans at medium and low flow rates, with minimal impact at high flow rates. These outcomes underscored the superior noise reduction efficacy of the wavy trailing edge blades, offering a promising way for the noise reduction design of axial flow fans.

Introduction: The issue of noise pollution is one of the concerns of most societies and industries because of their relationship to the environmental comfort of life or work of people are paying attention. The Aero-acoustics not only because of government regulations on the noise pollution, but also due to the increasing demand of the people's living standards and create a safe environment for farm animals is considered important. At the same time, products with high aero-acoustic performance will attract a lot of customers, which is in the interest of the global economy. Reducing current noise is often accompanied by a reduction in energy costs, resulting in durability of structures and improved product quality. Materials and Methods: Sound measurements were carried out at the wind tunnel in Tabriz Tractor Engineers Company. Using the measurements performed by the instrument, the sound levels were measured at different periods of the fan. In many practical applications that include turbulent flow, no noise has any specific tone and the sound energy is continuously distributed over a wide range of frequencies. In cases where broadband noise is present, statistical disturbance values easily calculated from the RANS equations can be used in conjunction with semi-experimental correlations and audio coordination to reveal some broadband noise sources. Based on the problem, the boundary condition is the type of "input velocity" for the input and "output pressure" for the output. It was also used to move the mesh to apply the rotary motion of the fan. The thermodynamic conditions at these boundaries should be considered. Results and Discussion: The accuracy of the simulation results data was verified with the measured data. In the laboratory results, the audio level is accompanied by an audio environment and an inverter and a belt that is about 15 db. With this in mind, the simulation results had a good agreement with experimental results. The velocity is a critical parameter in fan-related discussions. In the upper part of the fan, the speed of the air increases as the fan sucks, and this speed will increase as the fan approaches. In the second part, which includes the fan, for speeding objects, the speed will increase as the radius increases (due to the constant rotational speed), so the maximum speed will be at the tip of the blades. In the lower part of the fan, the speed will decrease as the fan impact decreases on the air molecules as well as the boundary layer behavior near the walls. As the speed and intensity of the turbulence are higher at the tip of the blades, hence the kinetic energy of these regions must also be higher. The kinetic energy of the turbulence in these areas is the highest. At the bottom of the fan, it is also observed that the kinetic energy of the turbulence has been relatively high, due to the existence of flow vortices that emerge from the fan period and the presence of positive and negative pressure (negative pressure due to suction of the fan center). The high pressure difference on both sides of the fluid particles causes a rotating flow in the particles, which affects the adjacent particles and causes vortex formation. Conclusions: The results showed that the numerical acoustic evaluation simulates the performance of the broadband band with good results and has good agreement with the effects of the current on the noise. Increasing the recognition of the factors and their effects on the fan noise level can help to reduce the noise effects of turbo-machines. Using numerical simulations in predicting and reducing noise, in addition to time saving, dramatically reduces costs by using direct methods and mechanical design physically. With regard to all aspects and calculations, it can be concluded that acoustic numerical simulation and broadband noise model have a good ability to analyze noise in fans and rotary machines.

The main goal of the present study is to determine the stable and unstable performance limits of a reversible axial flow fan by 3D numerical simulation. Reversible axial fans are a special type of axial fans that have the ability to create air flow in both directions by using a symmetrical blade profile in them. The main use of these fans is to discharge smoke and polluted air from channels and highway tunnels in emergency situations such as fire and also in normal operating conditions. In the present study, a reversible axial flow fan has been simulated three dimensionally.The qualitative results obtained from the numerical simulation indicate the presence of instability and the creation of vortices in areas such as the tip of the blade (flow leakage from the pressure surface to the suction in the gap distance of the tip of the blade) and also on the trailing edge and the suction surface of the blades (flow separation) in lower volume flows  from 26 (m3/s) and entering the fan in the stall area. The study of aerodynamic parameters and performance curves shows that the best performance range of the fan at a rotational speed of 900 rpm, is in the volume flow range of more than 26 (m3/s).

Appropriate changes to the blade tip pattern can effectively improve fan performance. In this research, the effect of two blade tip patterns and speed variation on aerodynamic performance of a ducted axial-flow fan was numerically investigated. In order to ensure the accuracy of the solving method, numerical results were compared with the experimental data from wind tunnel of the NACA Propeller-Research Center. Numerical results show that both the coefficients of pressure and torque increases with the appropriate groove at the tip of the blade. But due to the higher rate of increase in the coefficient of pressure than that of the torque, aerodynamic efficiency has also increased significantly. This increase has been observed in both patterns and in all operational speed of the fan. But, the increase in aerodynamic coefficients had rising trend up to 3000 rpm and, then, declined. The results determine the best pattern for the tip of the blade. In fact, the structure of the groove is such that it traps a rotating airflow with high kinetic energy at the tip, and this vortex, like a barrier, prevents air leakage. This causes reduction in losses due to mixing of the leakage flow and passage flow. With increasing fan rpm, the generated vortexes in tip groov are amplified, which, in addition to a further decrease in the leakage flow rate from the tip region, increases the viscosity and turbulence losses in the area.

The Counter-Rotating Fan (CRF) offers higher aerodynamic performance, in terms of pressure head and aerodynamic efficiency, compared to the single rotor fan, thus making it an attractive solution for equipment cooling and ventilation of mines and tunnels. Nevertheless, further investigations are required to understand the flow interactions between the front rotor (FR) and the rear rotor (RR), as these interactions are sources of noise emission. This numerical study used the Unsteady Reynolds Average Navier-Stokes (URANS) flow simulations and the Fast Fourier transformation (FFT) to analyse the rotor-rotor interactions and consequences on the aero-acoustic performance. The static pressure fluctuations were recorded at several locations and analysed by FFT to reveal the mechanisms of flow interactions and the effects of axial inter-distance between the two rotors. The inter-distance seems to influence the aerodynamic loading of RR more than that of FR and the total-to-static isentropic efficiency tends to drop. Over one chord distance, the noise level decreases but at the expense of isentropic efficiency. The balanced performance does not seem to improve for an inter-distance greater than 1. 5 chords, considered the optimum distance in this study. Finally, a graphical correlation which can be used to estimate the Sound Pressure Level (SPL) is developed for this category of CRF.

In recent years trends towards designing axial fan with low aspect ratio have been increased. Application of this kind of blades leads to higher rotor efficiency relative to blade with high aspect ratios. In contrast, applying this kind of blade causes to intensify 3D flows, increasing secondary losses and creating losses due to shock occurrence. In the current study, designing of a two stage axial fan with low aspect ratio is carried out. To obtain losses in the axial fan, appropriate models have been employed for profile loss, secondary loss shock loss and tip clearance loss. For extracting blade’ s profile, polynomial camber and naca 65 thickness distribution have been used. Comparing the obtained results including loss estimation, meridional velocity, pressure and diffusion factor distribution and blade geometrical parameters such as stagger angle, chord length, solidity and camber angle show good agreement. The 3D shape of the blade have been extracted by calculating the stagger angle and thickness distribution in each section.

Background: Ventilation systems in buildings are one of the most important sources of noise, which are spread into the surrounding environment through fans and channels or distributors. Since axial fans are used in industry very much and silencers are among ways to voice control. The purpose of this study is investigation on use of Absorptive silencer in reduction Low-frequency noise Iranian axial fan.Methods: In this study, we used galvanized channel 0.6 mm with 30*30 cm2 dimension and axial fan. Absorptive silencer as channel was designed to cross section of channel and silencers after embedded the absorber be identical together. Length of absorptive silencer was 50cm and there used mineral wool absorbent (density 80, 100 Kg/m3 and thickness 5, 10 cm). To determine the sound pressure level in a channel, two microphones are embedded that be accomplished by using MATLAB software in the one third of octave broadband and variable speeds 600-2500 rpm. we investigate amount of the reduction in absorption silencer sound filled with Iranian absorbing materials and influence of thickness and density of adsorbent material in silence.Findings: The maximum 2 dB reduction is in pressure sound at low frequencies of designed absorptive silencer that design in the channel surface. In this study, an increase in the thickness of the absorbent material of absorption silencer, there was a little change in the volume decreasing but with increasing density from 80 to 100 Kg/m3 better results were seen to reduce noise levels and it caused to increase NR rate.Conclusion: According to data from the present study we can used silencer with 5cm thick and 100 Kg/ m3 density in the reduction of sound pressure level at frequencies lower than 250 Hz in the ventilation system as an effective device.

Design models of multi-stage, axial flow compressor are developed for gas turbine engines. Axial flow compressor is one of the most important parts of gas turbine units.Therefore, its design and performance prediction are very important. One-dimensional modeling is a simple, fast and accurate method for performance prediction of any type of compressors with different geometries. In this approach, inlet flow conditions and compressor geometry are identified and by considering various compressor losses, velocity triangles at rotor, and stator inlets and outlets are determined, and then compressor performance characteristics are predicted.Numerous models have been developed theoretically and experimentally for estimating various types of compressor losses. In the present work, performance characteristics of the axial-flow compressor are predicted based on one-dimensional modeling approach. Firstly, the proposed algorithm for modeling and then the losses model for calculation of pressure loss coefficient in the blades cascade have been represented. In this study, models of Lieblein, Koch-Smith, Aungier, Hawell are implemented to consider the compressor losses. Finally, the model results are compared with experimental data to validate the model.

We investigate the effect of an axial Poiseuille annular flow on the stability of Taylor vortices via numerical simulation using CFD Ansys Fluent software. The working conditions are identical to those of the Taylor-Couette experimental device of the LaSIE laboratory, where the inner cylinder is rotated. An incompressible fluid of density ρ= 998 kg/m3, with a kinematic viscosity m2/s at a temperature T= 19. 5 °C is considered. The geometrical parameters of the flow system are characterized by a height H=275 mm, a radius ratio η=0. 804, and an axial aspect factor Γ=45. 45. The axial Reynolds number and Taylor number are respectively in the ranges of, and. Flow control is carried out according to two distinct protocols to bring out the effect of axial flow on the evolution of the Taylor vortex Flow (TVF). The first consists of superimposing an azimuthal flow around the critical TVF threshold with increasing axial flow until the Taylor vortices disappear. In the second, an axial field is set and the Taylor number is varied until onset of the TVF mode. It is predicted that in the presence of an axial flow, the critical threshold for first instability triggering (TVF) is delayed. In addition, the ratio of the axial phase velocity to the mean axial velocity of the axial base flow is 1. 16. This value agrees well with previous results reported in literature.