Aero-acoustical Study of Axial Fan using Computational Fluid Dynamics

ماشین های کشاورزی

Article 11, Volume 10, Issue 2 - Serial Number 20, 2020, Pages 255-264   

Document Type: Research Article

DOI: 10.22067/jam.v10i2.74963

Authors

B. Sabralilou¹; A. Mohebbi^{* 1}; E. Akbarian²; A. Rezvanivand fanaei¹

¹Biosystems Engineering Department, Faculty of Agriculture, Urmia University, Urmia, Iran

²Biosystems Engineering Department, Faculty of Agriculture, University of Mohaghegh Ardabili, Ardabil, Iran

Abstract

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.
Conclusion
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.

Keywords

Noise; Radiator fan; computational fluid dynamics; broadband noise

References

1. ANSYS Fluent Theory Guide, ANSYS, Inc., 275 Technology Drive Canonsburg, PA 15317, November 2013

2. de Jong, A., and J., Golliard. 2013. Towards a universal scaling for broadband turbulent noise in internal flow devices. In ASME 2013 International Mechanical Engineering Congress and Exposition (pp.V014T15A019-V014T15A019). American Society of Mechanical Engineers.

3. De Villiers, E. 2007. The potential of large eddy simulation for the modelling of wall bounded flows (Doctoral dissertation, University of London).

4. Fedala, D., S. Kouidri, F. Bakir, and R. Rey. 2007. Modelling of broadband noise radiated by an airfoil-application to an axial fan. International Journal of Vehicle Noise and Vibration 3: 106-117.

5. Horvath, C., and J. Vad. 2009. Broadband noise source model acoustical investigation on unskewed and skewed axial flow fan rotor cascades. In Proc. Conference on Modelling Fluid Flow (CMFF’09), Budapest, Hungary, 682-689.

6. Hubbard, H. H. 1991. Aeroacoustics of flight vehicles: Theory and practice. volume 1. noise sources (No. NASA-L-16926-VOL-1). National Aeronautics And Space Admin Langley Research Center Hampton Va.

7. Majander, P., and T. Siikonen. 2002. Evaluation of Smagorinsky‐based subgrid‐scale models in a finite‐volume computation. International Journal for Numerical Methods in Fluids 40: 735-774.

8. Nadi, F., S. A. Mehdizadeh, and U. N. Zonuz. 2017. Comparing between predicted output temperature of flat-plate solar collector and experimental results: computational fluid dynamics and artificial neural network. Journal of Agricultural Machinery 7 (1): 298-311. (In Farsi).

9. Rezvanivandefanayi, A., and A. Nikbakht. 2015. A CFD Study of the Effects of Feed Diameter on the Pressure Drop in Acyclone Separator, International Journal of Food Engineering 11: 71-77.

10. Roshko, A. 1961. Experiments on the flow past a circular cylinder at very high Reynolds number. Journal of Fluid Mechanics 10: 345-356.

11. Smagorinsky, J. 1963. General circulation experiments with the primitive equations: I. The basic experiment. Monthly Weather Review 91: 99-164.

12. Wang, Y. P., J. Chen, H. C. Lee, and K. M. Li. 2012. Accurate simulations of surface pressure fluctuations and flow-induced noise near bluff body at low mach numbers. In The Seventh International Colloquium on Bluff Body Aerodynamics and Applications (BBAA7).