Questions related to Aeroacoustics
Please see attachment, here two terms appeared in the inhomogeneous Helmholtz equation. What is the use of these two terms for a propagating wave in a particular direction.
I am now writing a bachelor thesis on the aeroacoustics of muffler. My muffler consists of one mass-flow inlet, one pressure outlet, with a few chamber in it and it is connected to a 3 cylinder 4 strokes engine running at a constant 1500rpm. I am interested in the noise level at the outlet and also the backpressure caused by the muffler. I am using the software Ansys Fluent.
So I have a few question regarding its simulation of aeroacoustics.
1. For my mass-flow inlet, do I use constant mass flow rate or fluctuating mass flow rate? How does this affect the sound pressure level-frequency graph? By fluctuating mass flow rate, I mean the almost instantaneous release of gas during exhaust phase which I will further simplify as half of a sine wave, followed by zero mass flow, for every exhaust of each cylinder.
2. As my muffler consists of a few expansion chamber, there is a big pressure difference(~2000Pa) in the narrow tube connecting them. So I am setting my air density as ideal gas, even though it doesn't exceed 0.3 Mach. In this case which method should i use to model the acoustics, direct method or using FW-H model? I will be getting the value right at the outlet boundary, as i dont feel the need to go into far-field.
3. For the transient simulation, how should I set the time step size and the frequency of data export to CFD-Post if i am interested in frequency range up to 250Hz? Here's what i think, time step size should be 0.0004s (1/10 of period), data export frequency should be every 10 step size (every period). Is that right? In CFD-post, i wil be plotting a graph of pressure gasint time and use FFT to transform it into sound pressure level againt frequency graph.
4. Which properties should i monitor to know if my transient simulation has converged? Until now, i have only been using the residual chart as monitor, so not sure if thats the only way.
Any help or further suggestion or correction is very much welcomed. Thanks in advance.
Kai Han Goh
In the simulation tutorial of the aeroacoustics around a cylinder by ANSYS, recievers are placed at a location where mesh isn't present, how does the solver predict the acoustics at that location and what material constrains does it consider? http://dl.mr-cfd.com/tutorials/ansys-fluent/FLUENT-acoustics-Tut2-FWH.pdf
I am not so clear the use of freestream velocity in FWH equation when helicopter rotor was in forward flight condition and observer position was fixed relative to the rotor.
The description of the problem is that when i use the CFD information on blade surface as the input for non-porous FWH equation, where is the freestream velocity used, is it used for the correction of surface velocity?
I want to download some papers from the following International symposium " 14th International Symposium on Unsteady Aerodynamics, Aeroacoustics & Aeroelasticity of Turbomachines (ISUAAAT14) ". I don't know how to download papers as they are not available online and no DOI number. Does anybody know how to download papers from this? thanks in Advance
I am interested in the numerical characterisation (3D-CFD) of aerodynamics and flow-induced noise (near-field) generated during the operation of a standalone horizontal axis wind turbine. Since I am attempting this activity for the first time, I was wondering if there are any publicly available CAD and performance data of any test wind turbine to validate the numerical methodology.
On a side note, if anyone could recommend me some pivotal pertinent literature, it'll be a great help.
Also, as my knowledge on the state-of-the-art is limited, I was wondering about the practices for modelling impeller rotation. I understand that specifying an angular velocity to the rotating domain should be relatively straightforward but are there any literature/methodologies available to model the motion of the blades based on air-velocity boundary conditions.
Thank you for reading and contributing.
I am looking for material which can replace aluminium in aerospace industry as i want material which will be having high melting point and must be light in weight. As i am looking at this from commercial point of view so if that material is easily available and cheap then it would be better. Especially Aluminium 7075
I want to developed an aeroacoustics lab at the second floor of the building but the blower and the 20 HP motor is causing too much noise which dominate over the airfoil noise so we like to arrest this vibration. Is any body tell me how to arrest the vibration. Is spring based damping system is helpful in such case?
Kindly suggest some way to arrest the vibration produce by the Motor and blower which are connected using pulley arrangement and sound generated in the duct.
I have a 76/40 degree double delta wing. I want to find the bevel angle for the leading edge of the wing configuration. The root chord of the wing is 191 mm and wing span is 195 mm. Is there any literature available on this? If yes Please advise.
Thanks in advance.
I am going to simulate a 2D aeroacoustics simulation in Fluent using a DES model on a stator. Actually, the simulation should be performed on a complete 3D rotor-stator setup but due to some limitations, I don’t have access to the rotor geometry and computing power. A simplified model of my setup is shown in the attached picture.
I have been searching for parameters that I can extract from the DES simulations. These are the following parameters that I can think of:
1)A common parameter is the FFT of pressure data recorded in the wake region of the blade. Using FFT, I want to see if I can see tonal noise peaks or broadband peaks. Based on these observations I can characterize the sound sources such as vortex shedding or just random turbulence.
2) Another parameter that I have come across is the sound pressure which can be calculated by subtracting the instantaneous pressure from the average pressure. How this can be done in Fluent, I am not sure.
3) The other is " divergence of velocity" or dilatation contours. I found it in this article
I am not able to understand what's the significance of this parameter.
4) Another quantity that can be visualized is the normalized Q-criterion, but this will be good to see the turbulence sources and not aeroacoustics as such.
5) Also, I was wondering if one can actually extract the noise from a pressure signal at a point so that you can hear it. I came across this in the STAR-CCM+‘s user guide some time ago and they say that it can be done. The guide mentioned that that one needs to perform inverse FFT of the signal.
Perhaps, people with experience in aeroacoustics can suggest me any additional parameters that can be used. Although the near-field region sound is of interest and not far-field, I am open to using the FW-H model if it provides additional insights.
I wanna use the mentioned formulation for computing noise radiation from a fluid solid interaction system. I faced with some difficulty in my mind due to lack of enough knowledge, so I would like to have your support; Furthermore, any collaboration would be so pleasant.
I have artificial reflections at the freestream boundary and contaminating results at certain frequency range. Specially at corners of a spherical domain. I use a commercial CFD software.
If anyone can provide me some damping functions it would be helpful...
I am working on computing noise due to HVAC system. Noise is generated due to aerodynamics, turbulence (aeroacoustic) and structural vibration (vibroacoustic).
So I am having a problem with solving aeroacoustics and vibroacoustics simultaneously in ANSYS. Aeroacoustics and vibroacoustics can be solved individually but how to do both together is a problem.
I use an in-house CFD code to simulate the flow over Idealized Side Mirror. The reference paper is Caraeni2011. To compare with the reference paper, I obtain the pressure history at the monitor points. By subtracting the mean of the pressure history, the fluctuation pressure is obtained.
Sound Pressure Level is defined as follows,
Now, my question is: is the fluctuation pressure the same as the sound pressure? Can I directly use my fluctuation pressure to calculate the SPL?
I know SPL is a single value and it requires Root Mean Square of the pressure history. What I want to calculate is actually the spectra of SPL. Just like the following pic. The unit of frequency is dB, and I guess it's typo.
In order to get the spectra of SPL, I apply FFT on the fluctuation pressure history and then feed the absolute value of the FFT result as input into the SPL formula to get the spectra of SPL.
Conference Paper Tandem Cylinder and Idealized Side Mirror Far-Field Noise Pr...
I am trying to model a Doppler shift induced in a microwave signal by a flowing liquid in order to measure the flow speeds. I currently have 2 problems. The first is getting the plane wave to be incident on my flowing liquid at an angle. The plane wave seems to behave when modeled separately but not when combined with the flow block (even when the interaction isn't accounted for in the study).
The second problem is how model the Doppler interaction within the flowing medium. (I can't see how to adapt the acoustic Comsol Doppler example. Similarly, I can't see how to adapt the radar Comsol example).
In CFD of reacting flows, the low-Mach number formulation is often used in LES or DNS as the time-step requirement is much more relaxed compared to the full compressible formulation. In turn, this allows for the consideration of more complex kinetics, which can lead to better prediction of the flame itself and turbulence-flame interactions. However in return, the acoustics are neglected.
Are the benefits of such simulations purely fundamental (i.e. better description of physical phenomena for various reasons?) For most of applications I can think off, either the incompressible assumption breaks down (i.e. piston engines, high speed flows) or the acoustic term is essential to ensure flame stability (jet combustion engine).
I am trying to build several cases for solver and CAA-library code validation. There are breathing, trembling sphere, baffled piston.
In all cases we can see phase difference between pressure signals. I'm explaining it by inertia like in the mass-spring system. Is it correct?
How can i modify wave equation results or my CFD solution to clear it from such kind of discrepancy? I need to clear it because i'm trying to validate very different solvers (for example with mesh motion) and already observe reflections from boundaries (so then i will need to test some types of non-reflecting) and i suppose that this phase difference could make further analysis harder.
Thank you for any help ("to read" recommendations are also appreciated).
Last figure just for reference (baffled piston, 2d-axissymmetric case).
How to set Mach number in FLUENT using species transport method for shock waves phenomena, in Pulse Detonation Engine
I am doing a 1D fintie element anlysis of a simple expansion chamber in matlab, i want to apply a anechoic termination at the inlet and outlet of muffler so that no reflection occurs. But i am stuck on how to incorporate that into my code.
I mean if we would want to modify a muffler based on parametric design, which parameters should be evaluated in the study, for example the cross section of the tube, the number of mufflers (inline or parallel), etc.
What kind of engine specifications should be evaluated in the study?
I am a Young researcher in aeroacoustics and I work with Kirchhoff integral in supersonic flow, due to Mach cone I face with a singular integral, in simple form of these integrals are in attached figure form and i like to solve this problem,
who can help me?
With Best Regards for your time
- How one can measure/distinguish between different sources of sound?
- In general combustion has mono pole source induced from mass and heat release, how can we differentiate between the same (monopole) source of sound, whether it is induced from mass or heat source?
- Further it would be helpful if you can refer some reference about measuring them ?
Any references on this topic. I think it will resemble a dipole radiation.
I did a quick calculation assume it is dipole of a sphere with radius been the length of the beam. For a moderate frequency of 1KHz (about the resonance of the cantilever), I found that the damping mostly come from the acoustic radiation rather than from the cantilever's internal loss. Is it true ? Want to confirm...
While modeling aeroacoustics of the fan using DDES, I have to use the transient formulation. Fluent is recommending to use Bounded second order implicit. After using this, I have observed lot of fluctuation in acoustic signal. Can anybody elaborate why it is so?
Plinian and subplinian style explosive eruptions are aeroacoustic emittors. They radiate infrasounds. The aeroacoustic emission and spectral content is related to the physical parameters of the impulsively starting jet as well.
Aeroacoustic experimental studies suggest that turbulent jets can change their dominant aeroacoustic noise emission in response to a forcing vibration such as ground vibration or excitation by wind or as a result of changing vent geometry. This is also the basis for aeroacoustic noise reduction from the jet engines of jumbo jets.
In turn, these studies suggest that a lock-on effect, a sort of resonance may set in.
When it does entrainment is increased by up to 30% according to experimental studies on aeroacoustic forcing and turbulent jets and this, in the case of particle-laden turbulent jet flows, can influence mass distribution and particle ejection and reduce the mass loading in the turbulent and increasingly dilute jet flow.
Conversely, if aeroacoustic excitation is not at the resonance dominant frequency mode, entrainment may be reduced by up to 30% and in the case of an explosive eruption jet one may anticipate that this may result in a sudden change of style into fountain collapse. Particularly in the case where the mass flow rate is such that the eruption column is in the transitional regime, that between the stable plume and the collapsing fountain regimes.
Because an external excitation (noise intensity) of 1 in a million of the characteristic jet noise intensity may result in lock-on or the opposite, this may lead to the possibility of artificially modulating the entrainment and eruption style of some explosive éruptions.
That is to a partial external control, potentially, on the evolution of some explosive eruptions, given the means to do so (eg. 3 "jumbo jet" or "anchored missiles" arranged in a triangle around the erupting volcano, as aeroacoustic external sources of forcing).
To my knowledge this has not been studied either by doing any field tests, which is understandable or by studying this possibility using analogue particle laden jet systems in the lab with the view of applications to volcanic eruptions.
I am wondering if anyone has carried out integrated time-dependent studies of subplinian style explosive eruption jets (eg. at Sakurajima or Etna ?) with the view of assessing potential correlations between aeroacoustic emissions by the jet itself, time-dependent jet video images, radar/sodar imagery, continous volcanic gas flux monitoring (eg. DOAS), ground tremor characteristics, time-dependent wind intensity and/or obvious changes in vent shape over time ?
Looking forward to any info that may relate to this.
With best wishes and kindest regards,
In general, gasoline engines are inherently smoother and quieter than diesel engines due to the difference in combustion characteristics. Going by this principle, exhaust system of gasoline engines should need lesser muffler volumes as compared to the exhaust system of diesel engines to achieve similar noise reduction However, the muffler volumes of production gasoline engines are about 5 liters more than that of the corresponding diesel engines. What could be the technical explanation for this in terms of acoustics and vehicle level noise control?
I want to calculate noise shielding from monopole source in semi-infinite barrier shielding, but some previous work done are suggest to combine the resultant shielding at a given field point from all four sides of the quadrilateral . But I cant see a picture how noise traveling through each quadrilateral edge and diffracted to observer.
In normal mode analysis, for example in instability problem in axisymmetric jet, what is the physical significance of the real and imaginary parts?
in orr-sommerfeld solution there is a normal mode present which is the combination of amplitude and phase, in the phase what is the physical meaning of exponential power?
I am in need to validate the codes for aeroacoutics computational simulation.
I am in need to validate the codes for aeroacoutics computational simulation. What are the standard test cases in computational simulation of Aeroacoustics, whose experimental data will be available?
I am working on an Aeroacoustics Competency Development Program.
As I don't have much solid experience on Aeroacoustics and its allied processes, I would like to know which will be the best way to start with.
I'm making a Jet Noise Analysis, I need to know how to simulate an aeroacoustic simulation in openFOAM for a conventional nozzle. Thanks.
Using compressible CFD methods such as the lattice Boltzmann method, it is easy to set up initial conditions that result in sound waves.
One example is a Gaussian density distribution in an otherwise quiescent fluid, which results in an outgoing sound pulse. Another example is Poiseuille flow initialisation of the flow field in a simple 2D channel with an obstacle; sound waves will propagate until the flow is stabilised.
My intuition suggests that if Ma << 1 then it should be possible to decompose a given initial condition into an incompressible flow part and a sound wave part. For instance, we know for an initial condition with ∇2p ≠ 0 that it must contain a sound wave component. This must be true because ∇2p = 0 is a defining characteristic of incompressible flow, and because the wave equation tells us that ∇2p ≠ 0 means that a wave will be propagating.
Understanding this decomposition would be essential for setting up pure sound simulations or pure flow simulations in compressible CFD methods. However, I have not been able to find anything about this in the literature. Would anyone here have any relevant references for me?
Our present aeroacoustic model for rotating blade aeroacoustics does not include thickness noise. What are the options? Wind turbine application.
Of course these flying objects must not just floating in air like fine solid particles or liquid droplets. Their motion must be controllable. What is limitation of the scale? Can anyone give some micro-scale or nano-scale existing examples and talk about how they are flying?
I want solve by shooing method but I am not getting it. We can also use F''(-infinty) =0;
and F''(+infinity) =0; can anyone help?