Showing 6 results for Acoustics
Hossein Mohammadi, Mahdi Ramezanizadeh,
Volume 17, Issue 5 (7-2017)
Abstract
The objective of this paper is to obtain acoustical behavior of air flow around 65° sweep back cropped, 66°/42° cranked arrow and 53° diamond delta wing configuration by using large eddy simulation approach with 0.17 of smagorinsky-lilli coefficient. It is worthy to mention that the root chord of the wings is 360 mm. Validation of the aerodynamics coefficient is performed using available experimental results which showed good agreements. CFD simulations were performed for 15 degree angles of attack at a Mach number of 0.147 and a Reynolds number of 1.2 million based on the root chord. Acoustic measurements such as power spectral density, acoustic pressure, sound pressure level and sound amplitude, were taken using 3 microphones in the wake region of the mentioned wings. The amount of sound pressure level of microphone which is placed at 1.835 meter from apex of above wings in the range of Strouhal 0 to 1 is, 22 to 66, 10 to 73 and 9 to 44 which indicates aeroacoustic behavior of the diamond delta wing, is more better than cropped and cranked arrow delta wing.
M. Sangbori, A. Nejat, K. Gharali,
Volume 20, Issue 3 (2-2020)
Abstract
In this article, noise generation mechanisms are studied at different Reynolds numbers and angles of attack. Tonal noise is the major part of airfoil noise at low Reynolds numbers. Studying the tonal noise and the effects of Reynolds number and angle of attack is challenging in aeroacoustics. 3D numerical simulation is conducted using the large eddy simulation method on SD7037 airfoil. Sound propagation is computed using the Ffowcs Williams-Hawkings (FW-H) analogy. The numerical results are validated using available experimental results. Some discrete peaks and a dominant peak exist in frequency spectra at low angles of attack. Increase of Reynolds number and the angle of attack decreases the number of discrete peaks and at high angles of attack and the dominant peak is diminished too. Studying the flow features shows that when a laminar boundary layer covers a vast area of the suction side, it can amplify acoustic waves that are generated in wake of the airfoil and this mechanism causes a dominant peak in the acoustic spectrum. Amplifying Tollmien-Schlichting waves by shear layer in laminar separation at suction side cause the discrete peaks and when a transition occurs in the airfoil suction side, discrete peaks are diminished. In the original semi-empirical Brooks, Pope and Marcolini (BPM) formulation, the boundary layer thickness of the pressure side is usually used as the length scale and it is replaced by the suction side boundary layer thickness. The results predict the frequency and amplitude of tonal noise successfully.
R. Mohammadi Gahrouyi , A. Maleki, M. Lashgari,
Volume 20, Issue 3 (2-2020)
Abstract
The intensity of sound in most industries and processes is a disturbing factor. Sound absorbers are a means of reducing noise. There are various types of sound absorbers with different designs and materials, but sound absorbers that can have a high absorption coefficient will be effective. The design of the manger sponge with fractal structure will be a good solution to this problem. Various factors such as composition type, step, and frequency affect this adsorbent. In this research, each of these factors was investigated and analyzed. The effects of the absorption coefficient and changes in sound level influenced by composition type, step and frequency factors were investigated and analyzed. Investigation of the step factor revealed that the amount of absorption coefficient in step 2 had better results compared to the step 1. The absorption coefficient in steps 1 and 2 were 0.3 and 0.38, respectively. Among the effective factors on the amount of absorption coefficient of manger sponge, the composition type was more effective. The results showed that the adsorbent with harder texture has a lower absorption coefficient and the adsorbent with a lighter texture has a higher absorption coefficient. Among the composition type used for this adsorbent, the sponge has a maximum absorption coefficient of 0.4 and MDF has a minimum absorption coefficient of 0.3.
Mohsen Mohammadi_sarasia, Hossein Ajam, Ahmad Moloodi,
Volume 21, Issue 7 (7-2021)
Abstract
In the present study, the effect of the porous medium in natural-gas pressure regulators, on the operation and reduce the intensity of the sound produced, is studied. First, it was studied experimentally. Experiments apply for the porous medium 20 ppi (pores per inch) and 10 ppi and non-porous system. To check the validity of the results, experiments were evaluated in four different pressure upstream 20, 10, 5, and 2.5 MPa on the critical pressure ratio. Afterward, for evaluation of the flow parameters on the performance of regulators and the sound intensity level, numerical simulation of fluid flow was performed. The results show that the use of porous media for 10 ppi and 20 ppi, flow coefficient decrease, respectively 7% and 15%, and sound intensity level decrease, respectively 25 and 30 dB. The amount of porosity does not have much effect on the sound intensity. On the other hand, the results of the fluid flow simulation show that placing the porous medium in the flow direction reducing the turbulent intensity and regulating the flow. As well, it decreases the sound intensity by decreasing the maximum velocity and the vortex power.
Hamidreza Kaviani, Ehsan Bashtalam,
Volume 23, Issue 8 (8-2023)
Abstract
| Icing is a common issue in blowers, wind turbines and flying vehicles. This phenomenon has a great impact on reducing aerodynamic performance, increasing noise pollution and imposing extra load on the structure. In this article, the effect of icing on the aerodynamic and aeroacoustic performance of the Naka-0012 airfoil has been studied. Transient and three-dimensional Navier-Stokes equations have been used for aerodynamic prediction. Sound wave is calculated using Fox-Williams and Hawkins equations. Simulation of eddies has been done using LES method and WALE subgrid scale model. First, all calculation methods have been validated using experimental data. Then the effect of icing on airfoil performance has been studied. Flow vortices have been studied and sound production mechanisms corresponding to these vortices have been identified. The results show that icing reduces the lift force by 9.7% and increases the drag force by 3.8 times. In the range of maximum human hearing sensitivity (one to five kHz), the average amount of sound increase is around 9 dB, which is a significant amount in terms of noise pollution. The increase in sound caused by icing can be used to identify and deal with this phenomenon faster and reduce its risks. |
Hamidreza Kaviani, Ehsan Bashtalem,
Volume 23, Issue 11 (11-2023)
Abstract
This study examines the accuracy of three different methods for calculating the aerodynamic noise of the NACA-0012 airfoil in a homogeneous shear flow. The strength of flow vortices is crucial in aeroacoustic calculations, and it can be modeled more cost-effectively using the k-ω SST method or directly simulated up to 90% using large eddy simulation (LES) with higher cost. Additionally, a hybrid method called IDDES, which offers moderate accuracy and cost, is also considered in this research. The primary sources of noise generation identified are vortex shedding from the laminar boundary layer and its interference with the trailing edge, as well as Tollmien-Schlichting waves. Experimental data of the sound pressure level (SPL) in 1/3 octave is used to validate the accuracy of the methods. The results indicate that LES and IDDES show the closest agreement with the experimental data, with LES showing better accuracy. Furthermore, when studying the intensity of sound attenuation with distance, it is observed that the rapid attenuation of small vortices in LES leads to similar SPLs as IDDES after a distance of 1.2 meters. Moreover, since IDDES does not require strict regulations for creating a near-wall grid, it reduces the computing mesh by approximately 41% with less than 2 dB of error. This finding suggests that in similar applications, the IDDES method can be used as a suitable approximation instead of LES to expedite calculations and conduct parametric studies
