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aeroacoustics
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Linearized and non-linear acoustic/viscous splitting techniques for low Mach number flows
, Article International Journal for Numerical Methods in Fluids ; Volume 42, Issue 10 , 2003 , Pages 1059-1072 ; 02712091 (ISSN) ; Hannani, S. K ; Ebrahimi, M ; Sharif University of Technology
2003
Abstract
Computation of the acoustic disturbances generated by unsteady low-speed flow fields including vortices and shear layers is considered. The equations governing the generation and propagation of acoustic fluctuations are derived from a two-step acoustic/viscous splitting technique. An optimized high order dispersion-relation-preserving scheme is used for the solution of the acoustic field. The acoustic field generated by a corotating vortex pair is obtained using the above technique. The computed sound field is compared with the existing analytic solution. Results are in good agreement with the analytic solution except near the centre of the vortices where the acoustic pressure becomes...
Aerodynamic and Aeroacoustic performance of a wing with structured surface inspired by owl’s wings
, Article Journal of Applied Fluid Mechanics ; Volume 15, Issue 4 , 2022 , Pages 1243-1253 ; 17353572 (ISSN) ; Taeibi Rahni, M ; Zareh, M ; Ahmadi, G ; Etemadi Haghighi, S ; Sharif University of Technology
Isfahan University of Technology
2022
Abstract
With the advent of various advanced materials, the idea of flying like birds has attracted considerable attention in recent years. In addition, aeroacoustics has become an important issue and is being widely studied. In this work, based on the shape of Owls’ wings, an attempt was made to improve the aeroacoustic and aerodynamic performances of conventional aircraft wings. For this purpose, wings with different elements, namely, square, triangular, and semicircular, on their top surface were examined. In addition, three different spatial distributions of the elements according to the Owl’s wings shape were considered. For incompressible airflow, aerodynamic and aeroacoustic parameters of wing...
Reflected shock tube experiments on aeroacoustic signature of hot jets
, Article Journal of Mechanical Science and Technology ; Volume 31, Issue 8 , 2017 , Pages 3811-3820 ; 1738494X (ISSN) ; Ebrahimi, M ; Ghorbanian, K ; Sharif University of Technology
Abstract
We used a reflected shock tube to investigate the acoustic signature of a hot jet at the far-field. Experiments were performed at Mach = 1.4 and a total temperature of Tt = 950 Kelvin. Far-field acoustic signatures of the hot jet at six polar angles θ = 15˚ to θ = 90˚ from the jet axis) were measured and imaged by the means of continuous wavelet transform in scalograms. The results were compared with experiments from a steady test facility at similar test conditions. Further, the primary characteristics of noise events in jet far-field were compared with analytical models considering wavepacket as the main source of jet noise. The results indicate that higher frequency events at θ = 90˚...
Numerical Investigation of Interaction Noise Using Rod-Airfoil Model
, M.Sc. Thesis Sharif University of Technology ; Farshchi, Mohammad (Supervisor) ; Tayyebi Rahni, Mohammad (Supervisor)
Abstract
In this thesis the interaction noise created by fluid flow with low Mach number over a rod-airfoil model simulated. Some numerical and experimental benchmark data for comparison and validation of results exist in articles. The simulation done by using Fluent 6.3 which restricts the choice of turbulence models to only 2D URANS. A study was undertaken on the cylinder as case study where some experimental aerodynamic and acoustic data are available. In this case study, the best turbulence model, discretization scheme and grid sizing were investigated. The only turbulence model which has the ability to simulate the near field and far field with a relatively good degree of accuracy was K-ω SST...
An Investigation on the Effects of Porous Media on Propagation of Aero-acoustic Waves, Using LBM
,
M.Sc. Thesis
Sharif University of Technology
;
Tayyebi Rahni, Mohammad
(Supervisor)
;
Massah, Hamid Reza
(Co-Advisor)
Abstract
With advances in technology, production and propagation of sound waves in the air has become very important. One of the main goals of study of these waves is controlling them. The environment plays the most important role in sound propagation. Therefore, the properties of the environment and their effects should be studied. One such concern studied widespread previously, is porosity and porous media effects on the properties of a fluid flow and sound waves through it. An important application of this study is sound proofing systems. In this project two-dimensional numerical simulation of aeroacoustic waves passing through a porous media is carried out, using Lattice Boltzmann Method. The aim...
Experimental Aeroacoustic Investigation of Transient Impinging Jet Using Shock Tube
, Ph.D. Dissertation Sharif University of Technology ; Ebrahimi, Mohammad (Supervisor) ; Ghorbanian, Kaveh (Supervisor)
Abstract
Supersonic impinging jets, similar to the jet flows exhausted from a nozzle, generate high unsteady pressure and acoustic loads on the rocket payload or the VTOL aircraft structure with possible mission failure during the launch/starting phase. In the past, experimental studies were concentrated on characterizing the steady impingement flow and not the initial transient process. It was shown that one of the main characteristics of supersonic impinging jets is the dominance of the feedback loop mechanism. The present investigation is an attempt to examine the flow characteristics of a high temperature supersonic impinging jet through a convergent-divergent nozzle during the transient starting...
Vortex Shedding Control behind Helicopter Rotor Blades, using Thin Oscillating Plates- Application to Helicopter Noise Reduction
, M.Sc. Thesis Sharif University of Technology ; Javadi, Khodayar (Supervisor)
Abstract
The interaction of the vortices and helicopter’s blades is the most significant source of generating the main rotor’s noise, especially in landing and rising. The kind of this noise is broadband and it is produced because of establishing the vortices behind the forward blade, their interaction with backward blade, changing their structures and creating turbulency loading. The known method for modeling of the interaction of the vortices structures and solid surfaces is the simple compounding the rod and airfoil. In this project, by using this method, the noise of the interaction of vortex and blade is modeled in the Reynolds number of 48000 with LES and FW-H Analogy as a hibrid method in...
Aeroacoustic Simulation of Rod-Airfoil Noise
, M.Sc. Thesis Sharif University of Technology ; Farshchi, Mohammad (Supervisor)
Abstract
Wall systems are an essential part of the buildings and their capacity should be properly considered in their design. However, the seismic behavior of building systems with in-filled walls and their interaction is a very complex issue, yet to be understood. Using the in-filled walls in the buildings without including them in the design process changes the whole behavior of the structural system as well as their failure mechanism under earthquake excitations. On the other hand, there have been extensive researches on rehabilitation of the structures with in-filled walls or designing them as the main or one of the lateral load carrying systems against seismic input. In this research, first the...
Numerical study of aero- acoustic characteristics in an automotive air-intake system
, Article 42nd International Congress and Exposition on Noise Control Engineering 2013, INTER-NOISE 2013: Noise Control for Quality of Life ; Volume 7 , 2013 , Pages 5990-5999 ; 9781632662675 (ISBN) ; Beigmoradi, S ; Sharif University of Technology
OAL-Osterreichischer Arbeitsring fur Larmbekampfung
2013
Abstract
Compartment noise has gained significant importance to meet customer expectation. One of the dominant sources of noise from whole engine as a system is the one which is induced from fresh air intake. Geometrical features in air induction systems (AIS) airflow path are often responsible for unusual noise due to the complex air flow structure and its interaction with the internal acoustic field. To reduce air intake noise basically resonator and expansion chamber are used on automotive vehicles. Resonators are widely used for noise reduction of air induction systems. Although, airflow bench tests are faster to evaluate various alternate design geometries, understanding the mechanism of such...
Prediction of fluid flow and acoustic field of a supersonic jet using vorticity confinement
, Article Journal of the Acoustical Society of America ; Volume 144, Issue 3 , 2018 , Pages 1521-1527 ; 00014966 (ISSN) ; Hejranfar, K ; Ebrahimi, M ; Sharif University of Technology
Acoustical Society of America
2018
Abstract
In this study, the numerical simulation of the fluid flow and acoustic field of a supersonic jet is performed by using high-order discretization and the vorticity confinement (VC) method on coarse grids. The three-dimensional Navier-Stokes equations are considered in the generalized curvilinear coordinate system and the high-order compact finite-difference scheme is applied for the space discretization, and the time integration is performed by the fourth-order Runge-Kutta scheme. A low-pass high-order filter is applied to stabilize the numerical solution. The non-reflecting boundary conditions are adopted for all the free boundaries, and the Kirchhoff surface integration is utilized to...