!!!FLUENT在气动噪声问题上的处理方法

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利用Fluent直接方法CAA对Helmholtz共振器进行气动噪声计算 cavity-计算过程

利用Fluent直接方法CAA对Helmholtz共振器进行气动噪声计算Modeling Aeroacoustics for a Helmholtz Resonator Using the Direct Method (CAA)1.网格Check mesh, reorder, 总网格量为3万Re = 2e6, 空腔外近壁面第一层1e-4,2.模型采用可压缩二维大涡模拟LES二维命令：(rpsetvar ’les-2d? #t)亚格子模型：W ALE动量方程求解格式自动改为：bounded central-deferencing （BCD）可压缩：打开理想气体3.边界条件速度进：velocity inlet, 30m/s, spectral synthesizer, 湍流度1%，水力直径0.2 m, 101325Pa 压力出：pressure-outlet, 0Pa上：滑移壁面，速度与入口速度一致，30m/s操作压力101325，表压为0速度定常解为了考虑流动的随机成分，FLUENT提供了两种算法。

这些算法模拟了速度入口的脉动速度。

利用频谱合成器从傅里叶谐波的总和中合成一个无散度的速度矢量场来计算波动速度分量4.准稳定求解在提取声源数据进行声学分析之前，需要建立准平稳流。

通过监测近壁面和远场观测点的压力扰动来识别。

可压缩求解器求解：Fractional Step/PISO瞬态控制：非迭代时间步进Non-Iterative Time Advancement时间推进：2nd-Order Implicit梯度控制：Node-Based压力离散插值：PRESTO!PRESTO! 适用于所有类型的网格，是FLUENT一种更精确的从单元压力内插面压力值的格式。

动量离散：Bounded Central Differencing由于每个时间步都要执行大量的外部迭代，标准的瞬态格式(iterative time advancement，迭代时间推进)需要大量的计算工作。

CGNS导入VL进行气动噪声步骤

注意：需要在fluent12版本以上才能得到CGNS文件，在此用fluent12为例
1、打开fluent声模块
2、双击上面红色框，就能进入下图界面，把红色框√上就行了，这样计算就能得到CGNS格式的文件
3、在计算结束之后，在fluent12中，File-Export-Solution Data，把导入的文件类型改成NASTRAN，在Surface 中选择你要导出的网格，在点击Write就可以保存为bdf格式的文件了
4、在VL中就能导入你要的CGNS和bdf格式文件了，启动b，Start-Acoustics-Acoustic Harmonic BEM，在此以进入声学边界元为例，再File-Import，选择CGNS文件类型，在计算结果文件夹中选择，你要导入的CGNS文件，一般从fluent残差曲线图中选取计算过程中曲线较稳定的迭代步数，你就选择步数相应的CGNS文件即可，CNGS是每一步都对应一个相应的文件。

你在选中一个之后，在此之后的CGNS 都能自动导入
导入bdf文件：同上，只是把文件类型选成NASTRAN Bulk File，再选中你要导入的相应文件，即可导入边界元网格。

基于FLUENT计算的某燃气热水器噪声消除的模型选择分析

基于FLUENT计算的某燃气热水器噪声消除的模型选择分析*赵维1，王超2，苗楠2，杨晓东2，毛艳辉3（1.天津中德应用技术大学，天津 300350；2.威能（无锡）供热设备有限公司，江苏无锡 214028；3.宁波工程学院，浙江宁波 315000）摘要：所有设备在有介质流动时就会有噪声。

以某种燃气热水器为例，该热水器在以G31（丙烷）为燃料时，在高负荷状态工作下，设备会产生啸叫声。

为了解决该燃气热水器实际燃烧过程中的啸叫现象，文章通过CFD方法，对燃气热水器噪声问题求解时，涉及到的相关模型进行对比分析，在研究模型的合理性的基础上确定最终的模型选择方案。

关键词：FLUENT模拟；燃气热水器；噪声消除中图分类号：TS914.25 文献标志码：A文章编号：1672-3872（2017）10-0017-031 研究背景在燃气热水器中，当仅有空气燃烧室内流动时，空气会与热水器壁面，以及空气流剪切层之间漩涡碰撞、破碎，都会产生噪声，噪声的产生必然有一部分能量转化为声能，造成能量损失，这些属于气动噪声。

如果发生燃烧过程，燃烧产生的热量与压力耦合会进一步激化气动噪声的强度，当燃烧引发的波动与气体波动频率一致，会形成热声震荡，使燃烧室热应力不均，引发燃烧设备结构的热疲劳，影响设备使用寿命。

计算流体力学方法计算噪声主要应用于风力电站的大型叶片噪声、汽车车身各部件如车厢底板、车灯、天窗、尾翼、整车等产生的气动噪声，以及余热锅炉内蒸汽流动对换热器产生的噪声，轴流风机噪声、空调室内机噪声等。

2 计算模型分析燃气热水器噪声问题求解时，涉及到气流的流动，要选择合理的流动模型；考虑燃烧时的化学反应，则需要选择合理的燃烧模型；对于噪声，要分析热水器噪声产生根源与频率范围，就需要选择相应的噪声模型。

2.1 流动模型流动模型是采用计算流体力学解决问题时，面临的最基本问题，因为工程中几乎所有问题都是在湍流情况下发生的。

对于该热水器在t=20℃时，空气的运动粘度v=15.06×10m2/s，风机进入火排流经的空气孔直径为2.8mm，当湍流临界雷诺数为2300时，得到对应的临界湍流速度为12.3m/s，当燃烧后，热燃气密度减小，速度更大，因此热水器内气流运动作为湍流问题考虑。

fluent气动噪声算例-Flow-Induced (Aeroacoustic) Noise

Tutorial:Modeling Flow-Induced(Aeroacoustic)Noise Problems Using FLUENTIntroductionThis tutorial demonstrates how to model2D turbulentﬂow across a circular cylinder using large eddy simulation(LES)and computeﬂow-induced(aeroacoustic)noise using FLUENT’s acoustics model.You will learn how to:•Perform a2D large eddy simulation.•Set parameters for an aeroacoustic calculation.•Save acoustic source data for an acoustic calculation.•Calculate acoustic pressure signals.•Postprocess aeroacoustic results.PrerequisitesThis tutorial assumes that you are familiar with the FLUENT interface and that you have a good understanding of basic setup and solution procedures.Some steps will not be shown explicitly.In this tutorial you will use the acoustics model.If you have not used this feature before,ﬁrst read Chapter21,Predicting Aerodynamically Generated Noise,of the FLUENT6.2 User’s GuideModeling Flow-Induced(Aeroacoustic)Noise Problems Using FLUENTProblem DescriptionThe problem considers turbulent airﬂow over a2D circular cylinder at a free stream ve-locity(U)of69.2m/s.The cylinder diameter(D)is1.9cm.The Reynolds number based on the diameter is90,000.The computational domain(Figure1)extends5D upstream and 20D downstream of the cylinder.U = 69.2 m/s D = 1.9 cmFigure1:Computational DomainPreparation1.Copy theﬁle cylinder2d.msh to your working directory.2.Start the2D version of FLUENT.Approximately2.5hours of CPU time is required to complete this tutorial.If you are interested exclusively in learning how to set up the acoustics model,you can reduce the computing time requirements considerably by starting at Step7and using the provided case and dataﬁles.Modeling Flow-Induced(Aeroacoustic)Noise Problems Using FLUENT Step1:Grid1.Read the gridﬁle cylinder2d.msh.File−→Read−→Case...As FLUENT reads the gridﬁle,it will report its progress in the console window.Since the grid for this tutorial was created in meters,there is no need to rescale the grid.Check that the domain extends in the x-direction from-0.095m to0.38m.2.Check the grid.Grid−→CheckFLUENT will perform various checks on the mesh and will report the progress in the console window.Pay particular attention to the reported minimum volume.Make sure this is a positive number.3.Reorder the grid.Grid−→Reorder−→DomainTo speed up the solution procedure,the mesh should be reordered,which will substan-tially reduce the bandwidth and make the code run faster.FLUENT will report its progress in the console window:>>Reordering domain using Reverse Cuthill-McKee method:zones,cells,faces,done.Bandwidth reduction=32634/253=128.99Done.Modeling Flow-Induced(Aeroacoustic)Noise Problems Using FLUENT4.Display the grid.Display−→Grid...(a)Display the grid with the default settings(Figure2).Use the middle mouse button to zoom in on the image so you can see the meshnear the cylinder(Figure3).Figure2:Grid DisplayModeling Flow-Induced(Aeroacoustic)Noise Problems Using FLUENTFigure3:The Grid Around the CylinderQuadrilateral cells are used for this LES simulation because they generate less numerical diﬀusion than triangular cells.The cell size should be small enough to capture the relevant turbulence length scales,and to make the numerical diﬀusion smaller than the subgrid-scale turbulence viscosity.The mesh for this tutorial has been kept coarse in order to speed up the calculations.A high quality LES simulation will require aﬁner mesh near the cylinder wall.Modeling Flow-Induced(Aeroacoustic)Noise Problems Using FLUENT Step2:Models1.Select the segregated solver with second-order implicit unsteady formulation.Deﬁne−→Models−→Solver...(a)Retain the default selection of Segregated under Solver.(b)Under Time,select Unsteady.(c)Under Transient Controls,select Non-Iterative Time Advancement.(d)Under Unsteady Formulation,select2nd-Order Implicit.(e)Under Gradient Option,select Node-Based.(f)Click OK.Modeling Flow-Induced(Aeroacoustic)Noise Problems Using FLUENT2.Select the LES turbulence model.The LES turbulence model is not available by default for2D calculations.You can make it available in the GUI by typing the following command in the FLUENT console window:(rpsetvar’les-2d?#t)Deﬁne−→Models−→Viscous...(a)Under Model,select Large Eddy Simulation.(b)Retain the default option of Smagorinsky-Lilly under Subgrid-Scale Model.(c)Retain the default value of0.1for the model constant Cs.(d)Click OK.You will see a Warning dialog box,stating that Bounded Central-Diﬀerencing is default for momentum with LES/DES.Click OK.The LES turbulence model is recommended for aeroacoustic simulations because LES resolves all eddies with scales larger than the grid scale.Therefore,wide band aeroa-coustic noise can be predicted using LES simulations.Modeling Flow-Induced(Aeroacoustic)Noise Problems Using FLUENTStep3:MaterialsYou will use the default material,air,which is the workingﬂuid in this problem.The default properties will be used for this simulation.Deﬁne−→Materials...1.Retain the default value of1.225for Density.2.Retain the default value of1.7894e-05for Viscosity.You can modify theﬂuid properties for air or copy another material from the database if needed.For details,refer the chapter Physical Poperties in the FLUENT User’s Guide.Step4:Operating ConditionsDeﬁne−→Operating Conditions...1.Retain the default value of101325Pa for the Operating Pressure.Step5:Boundary Conditions1.Retain the default conditions for theﬂuid.Deﬁne−→Boundary Conditions...(a)Under Zone,selectﬂuid.The Type will be reported asﬂuid.(b)Click Set...to open the Fluid panel.i.Retain the default selection of air as theﬂuid material in the Material Namedrop-down list.ii.Click OK.2.Set the boundary conditions at the inlet.(a)Under Zone,select inlet.The Type will be reported as velocity-inlet(b)Click Set...to open the Velocity Inlet panel.i.Set the Velocity Magnitude to69.2m/s.ii.Retain the default No Perturbations in the Fluctuating Velocity Algorithm drop-down list,and click OK..This tutorial does not make use of FLUENT’s ability to impose inlet pertur-bations at velocity inlets when using LES.It is assumed that all unsteadinessis due to the presence of the cylinder in theﬂow.Modeling Flow-Induced(Aeroacoustic)Noise Problems Using FLUENT3.Set the boundary conditions at the outlet.(a)Under Zone,select outlet.The Type will be reported as pressure-outlet(b)Click Set...to open the Pressure Outlet panel.i.Conﬁrm that the Gauge Pressure is set to0.ii.Retain the default option of Normal to Boundary in the Backﬂow Direction Speciﬁcation Method drop-down list,and click OK.The top and bottom boundaries are set to symmetry boundaries.No user input is required for this boundary type.Step6:Quasi-Stationary Flow Field SolutionBefore extracting the source data for the acoustic analysis,a quasi-stationaryﬂow needs to be established.The quasi-stationary state will be judged by monitoring the lift and drag forces.1.Set the solution controls.Solve−→Controls−→Solution...(a)Retain the default PISO scheme for Pressure-Velocity Coupling.(b)Under Discretization,select PRESTO!in the Pressure drop-down list.PRESTO!is a more accurate scheme for interpolating face pressure values fromcell pressures.Modeling Flow-Induced(Aeroacoustic)Noise Problems Using FLUENT(c)Retain the default Bounded Central Diﬀerencing for Momentum.For LES calculations on unstructured meshes,the Bounded Central Diﬀerencingscheme is recommended for Momentum.(d)Set the Relaxation Factor for Pressure to0.75.(e)Retain the default Relaxation Factor for Momentum.The pressureﬁeld is relaxed only during the initial transient phase.The Relax-ation Factor for Pressure will be increased to1at a later stage.(f)Click OK.2.Initialize the solution.Solve−→Initialize−→Initialize...(a)Initialize theﬂow from the inlet conditions by selecting inlet in the Compute Fromdrop-down list.(b)Click Init to initialize the solution and click Close.3.Enable the plotting of residuals.Solve−→Monitors−→Residual...(a)Select Plot under Options.(b)Under Storage,enter10000Iterations.(c)Under Plotting,enter20Iterations.(d)Retain the default values for the other parameters and click OK.4.Set the time step parameters.Solve−→Iterate...(a)Set the Time Step Size(s)to5e-6.The time step size required in LES calculations is governed by the time scaleof the smallest resolved eddies.That requires the local Courant-Friedrichs-Lewy(CFL)number to be of an order of1.It is generally diﬃcult to know the propertime step size at the beginning of a simulation.Therefore,an adjustment aftertheﬂow is established,is often necessary.For a given time step∆t,the highestfrequency that the acoustic analysis can produce is f=12∆t .For the time step sizeselected here,the maximum frequency is100kHz.Typically in most aeroacoustic calculations,the maximum frequency obtained from the analysis is higher than the audible range of interest.(b)Click Apply.5.Save the case and dataﬁles(cylinder2d t0.00.cas.gz and cylinder2d t0.00.dat.gz).File−→Write−→Case&Data...Save the case and dataﬁles before theﬁrst iteration.This will save you time in the event of user error or code divergence,where the caseﬁle would have to be set up all over again.6.Run the case for a few time steps before activating the force monitors.Solve−→Iterate...(a)Set the Number of Time Steps to20.(b)Click Iterate.The residual history will be displayed as the calculation proceeds.When the non-iterative time advancement scheme is used,by default,two residuals are plotted per time step.7.Enable the monitoring of the lift and drag forces.Setting the force monitors after some initial transient state limits the range of the drag coeﬃcient when starting from an impulse initial condition.Solve−→Monitors−→Force...(a)In the Coeﬃcient drop-down list,select Drag.(b)In the Wall Zones list,select wall cylinder.(c)Verify that the X and Y values under Force Vector are1and0,respectively.(d)Under Options,select Plot to enable plotting of the drag coeﬃcient.(e)Under Options,select Write to save the monitor history to aﬁle,cd-history willbe the defaultﬁle name.If you do not select the Write option,the history information will be lost when you exit FLUENT.(f)Click Apply.(g)In the Coeﬃcient drop-down list,select Lift.(h)Under Force Vector,specify X and Y to be0and1,respectively.(i)Under Options,select Plot to enable plotting of the lift coeﬃcient.(j)Under Options,select Write to save the monitor history to aﬁle.This time, cl-history will be the defaultﬁle name.(k)Close the panel.8.Set the reference values to be used in the lift and drag coeﬃcient calculation.Report−→Reference Values...(a)Set the values as shown in the table:Parameter ValueArea0.019Velocity69.2Length0.019(b)Retain the default values for the other parameters and click OK.The reference area is calculated using the cylinder diameter,D,and the default depth of1m for2D problems.Adjust the reference area if a diﬀerent depth (Depth)value is used.For the actual force coeﬃcient calculation,only the reference area,density and velocity are needed.The reference length(Length)will be needed later for the Strouhal number calculation.9.Overwrite the previously saved initial conditions(cylinder2d t0.00.cas.gz andcylinder2d t0.00.dat.gz).File−→Write−→Case&Data...10.Advance theﬂow in time until a quasi-stationary state is reached.Solve−→Iterate...(a)Set the Number of Time Steps to4000.(b)Click Iterate.The4000time steps will advance theﬂow up to t=0.02s.At that time the bulkﬂow will have crossed the computational domain about three times.The residual history,lift and drag force histories will be displayed as the calculation proceeds.The lift and drag histories should be similar to Figure4and Figure5, respectively.Diﬀerences in the long-termﬂow evolution can occur due to operating system dependent round-oﬀerrors.Once the lift and drag histories are suﬃciently oscillatory and periodic in nature,you are ready to set up the acoustics model and perform the acoustic calculations.Figure4:Lift Coeﬃcient History11.Verify that the selected time step size is reasonable for the given mesh andﬂowcondition.Plot−→Histogram...Figure5:Drag Coeﬃcient History(a)Under Histogram of,select Velocity....(b)From the Velocity...category,select Cell Courant Number.(c)Set the value for Divisions to100.(d)Click Plot and verify that the peak CFL value is less than3.5.The histogram(Figure6)shows that most cells have a Cell Courant Number of less than1.12.Save the case and dataﬁles(cylinder2d t0.02.cas.gz and cylinder2d t0.02.dat.gz).File−→Write−→Case&Data...Figure6:A Histogram Displaying the Range of the CFL Number Step7:Aeroacoustics Calculation1.Deﬁne the acoustics model settings.Deﬁne−→Models−→Acoustics...(a)Under Model,select Ffowcs-Williams&Hawkings.(b)Under Options,select Export Acoustic Source Data.(c)Click the Sources...button.This will open the Acoustic Sources panel.i.Under Source Zones,select wall cylinder.All relevant acoustic source data(i.e.pressure in this case)will be extracted from the wall cylinder surface.ii.In the text-entry box for Source Data Root Filename,enter cylinder2d.This is theﬁlename root of the indexﬁle which will be created.The index ﬁle contains information about the source dataﬁles that are created when you run the case.The indexﬁle is automatically created with a.indexﬁle extension.iii.Under Write Frequency,enter2.Depending on the physical time step size and the important time scales in theﬂow,it is not necessary to write the acoustic source data at every time step.In this tutorial,the source data is coarsened(in time)by a factor of two.Thus,the highest possible frequency the acoustic analysis can generate is reduced to f=1=50kHz.2(2∆t)iv.Set the No.of Time Steps Per File to200.The source data can be conveniently segmented into multiple source data ﬁles.This makes it easier to process partial sequences when calculating the receiver signals.A value of200for No.of Time Steps Per File means that each source dataﬁle covers a time span of200time steps.With a Write Frequency of2,there are100data sets written into each source dataﬁle.v.Click Apply and Close.(d)Click OK to close the Acoustics Model panel.2.Modify the solution controls.Solve−→Controls−→Solution...(a)Increase the Relaxation Factor for Pressure to1.(b)Click OK.3.Resume the calculation.Solve−→Iterate...(a)Retain the Number of Time Steps at4000.(b)Click Iterate.The additional4000time steps will advance theﬂow up to t=0.04s.At every second time step,a message will be displayed in the FLUENT console window informing you that data is written to a source dataﬁle(.asdﬁle extension).4.Save the case and dataﬁles(cylinder2d t0.04.cas.gz and cylinder2d t0.04.dat.gz).File−→Write−→Case&Data...5.Set the acoustics model constants.Deﬁne−→Models−→Acoustics...(a)Retain the Far-Field Density at1.225kg/m3.The far-ﬁeld density is the density of theﬂuid outside the computational domain,i.e.the density of theﬂuid near the receivers.In most calculations it is the sameas the density within the computational domain.(b)Use the default value of340m/s for the Far-Field Sound Speed.(c)Leave the Reference Acoustic Pressure at2e-05Pa.The reference acoustic pressure is used to calculate decibel values during postpro-cessing.(d)Set the Source Correlation Length to0.095m.That is equal toﬁve cylinderdiameters.The source correlation length is very important when performing aeroacoustic cal-culations in2D.FLUENT assumes that the sound sources are perfectly correlatedover the speciﬁed correlation length,and zero outside.That is,FLUENT internallybuilds a source volume with a depth equal to the speciﬁed correlation length andneglects sources outside.In your practical2D application,you will have to esti-mate the source correlation length;your obtained sound pressure levels will de-pend on your input.That makes it diﬃcult to rely on2D calculations to obtainabsolute sound pressure levels.Therefore,you should use aeroacoustic2D simu-lations primarily to observe trends.The source correlation length is not neededfor3D calculations.(e)Click OK to close the panel.6.Calculate the acoustic signals.Solve−→Acoustic Signals...(a)Click the Receivers...button.This will open the Acoustic Receivers panel.Note that you can open the Acoustic Receivers panel also from the Acoustics Model and Acoustic Sources panels.i.Increase the No.of Receivers to2.ii.For the receiver-1coordinates,enter0m for X-Coord.,-0.665m(35D)for Y-Coord.,and0for Z-Coord.iii.For the receiver-2coordinates,enter0m for X-Coord.,-2.432m(128D)for Y-Coord.,and0for Z-Coord.iv.Retain the defaults for Signal File Name(receiver-1.ard and receiver-2.ard).v.Click OK to close the Acoustic Receivers panel.(b)Under Active Source Zones,select wall cylinder.All source zones which were selected in the Acoustic Sources panel are now avail-able under the Active Source Zones.In this tutorial,the sound sources are ex-tracted from only one zone.It is important to select the source zones consistentlyif redundant source zones were selected in the Acoustic Sources panel.(c)Under Source Dataﬁles,select allﬁles available.Selecting a subset of the available sourceﬁles is a convenient way to analyzeshorter sequences.It is important to select a contiguous set of source dataﬁles.(d)Under Receivers,select the two available receivers.As soon as the source zones,source dataﬁles,and receivers are selected,theCompute/Write function becomes available.(e)Click Compute/Write.The FLUENT console window will conﬁrm that the source dataﬁles are beingread and that the receiver signals are computed and written into receiverﬁles.(f)Click Close to close the Acoustic Signals panel.Step8:Aeroacoustic Postprocessing1.Display the acoustic pressure signals at the two receiver locations.Plot−→File...(a)Click Add...in the File XY Plot panel.This will open the Select File panel where you can now select receiver-1.ardand receiver-2.ard from the Files list.(b)Click OK to close the Select File panel.(c)Click Plot to display the receiver signals(Figure7).Modify the line and markerstyles as necessary,using the Curves panel.You will notice a shift in time of approximately5e-3s for the signal at the second receiver.Receiver-2is farther away from the source surface and the sound will therefore arrive later.Also notice that the signal at receiver-2is weaker due to the increased distance and geometrical attenuation.Figure7:Acoustic Pressure Signals2.Perform a spectral analysis of the receiver signals.Plot−→FFT...(a)Under Process Options,select Process Receiver.This will activate the Receiverlist.If the Ffowcs Williams and Hawkings(FW-H)acoustics model is used and the receiver signals have been calculated,then the signals are directly available for postprocessing.As an alternative,the receiver data can be loaded manually from ﬁles by using the Process File Data option under Process Options.(b)Select receiver-1from the Receiver list.(c)Select Sound Pressure Level(dB)from the Y Axis Function drop-down list.(d)Select Frequency(Hz)from the X Axis Function drop-down list.(e)Click Plot FFT to plot the sound pressure spectrum for receiver-1(Figure8).The overall sound pressure level(OASPL)is printed to the FLUENT console window:>>Overall Sound Pressure Levelin dB(reference pressure=2.000000e-05)=1.156790e+02=50kHz,as expected.Note that the maximum frequency plotted is f=12(2∆t)Figure8:Spectral Analysis of Pressure Signal for receiver-1(f)Click Axes....This will open the Axes-Fourier Transform panel.i.Deselect Auto Range for the X Axis.ii.Manually set the Maximum for Range to5000.iii.Click Apply and Close the panel.(g)Replot the sound pressure spectrum for receiver-1.The spectrum peaks at about900Hz(Figure9).Note that the spectral resolution is only about50Hz,since the receiver signal was calculated for a short period only(approximately0.02s).For a sampled signal oflength T,the spectral resolution is1T .You may increase the spectral resolutionby running the simulation longer in time before recalculating the receiver signals.(h)Select the Strouhal Number from the X Axis Function drop-down list.i.Reset the Maximum for the x-axis Range to1,in the Axes-Fourier Transformpanel.(i)Replot the sound pressure spectrum as a function of the Strouhal Number.Thespectrum peaks at a Strouhal Number of about0.25(Figure10).If the Strouhal number calculation does not seem correct,verify that the correct values are speciﬁed in the Reference Values panel.(j)Repeat the spectral analysis for receiver-2by selecting receiver-2from the Receiver list.You should expect an OASPL of about104dB for receiver-2.3.Plot the power spectral density of the lift force history to see that the observed peaksin the receiver spectra match the dominant frequency in the lift force history.(a)Under Process Options,select Process File Data.(b)Click Load Input File...and select the lift monitorﬁle(cl-history).(c)Select Power Spectral Density from the Y Axis Function drop-down list.Figure9:Spectral Analysis of Pressure Signal for receiver-1at a Reduced Frequency RangeFigure10:Spectral Analysis of Pressure Signal for receiver-1as a Function of Strouhal Numbers(d)Under X Axis Function,select Strouhal Number.(e)Verify that the Maximum for the x-axis Range in the Axes-Fourier Transformpanel is1.(f)Click Plot/Modify Input Signal...to open the Plot/Modify Input Signal panel.Thispanel lets you modify and plot the signal before the Fourier Transform is applied.i.Select Clip to Range and set the Min value for X Axis Range to0.02.Without clipping the temporal range,the complete lift monitor history wouldbe analyzed including the initial transient state leading up to the quasi-stationary state.ii.Click Apply/Plot and Close to return to the Fourier Transform panel.Since the x-axis range was manually set for the spectral plot,you will not see the proper range when plotting the modiﬁed signal.You will need to temporarily reset the range if you want to plot the input signal.(g)Click Plot FFT to plot the power spectral density for the lift monitor history(Figure11).The spectrum peaks at a Strouhal number of about0.25.As indicated in Step7,2D aeroacoustic predictions depend strongly on the selected source correlation length.As a consequence,the results can beﬁne-tuned to be in better agreement with experimental data.4.You can repeat the calculation of the acoustic signals for the additional source corre-lation lengths of2.5D and10D,using Step7as a starting point.Table1compares the obtained OASPL values with experimental values reported by Revell et al.[1].Reasonable agreement is found for correlation lengths2.5D and5D.Figure11:Spectral Analysis of Lift Force HistoryTable1:Dependence of the Predicted OASPL on the Speciﬁed Source Correlation Lengths (L=2.5D,5D,10D)2.5D5D10D Experimental Resultsreceiver-1109.7115.7121.6117receiver-298.4104.4110.4100SummaryThis tutorial demonstrated the use of FLUENT’s acoustics model to calculate the far-ﬁeld sound signals generated by theﬂow over a2D cylinder.You have learned how to set up the relevant parameters,save the acoustic source data,calculate,and postprocess the acoustic pressure signals.The main computational eﬀorts are spent calculating the time dependent turbulentﬂow. It is therefore advisable to export the sound sources during theﬂow calculation.This allows you to recalculate the acoustic signals for diﬀerent receivers or model parameters with minimal computational costs.The tutorial demonstrated the use of the Ffowcs Williams and Hawkings acoustics tool on a2D case.You have seen that it is diﬃcult to obtain absolute SPL predictions in2D due to the need to estimate the correlation length of the turbulentﬂow structures in the spanwise direction.This diﬃculty does not exist when solving3D acoustics problems. References1.Revell,J.D.,Prydz,R.A.,and Hays,A.P.,“Experimental Study of Airframe Noise vs.Drag Relationship for Circular Cylinders,”Lockheed Report28074,Feb.1977.Final Report for NASA Contract NAS1-14403.。

气动噪音特性的研究与降噪技术

气动噪音特性的研究与降噪技术气动噪音是指由气体流过物体表面，或是气体在管道运输过程中产生的噪声。

这种噪声会对人们的身心健康产生负面影响，从而引发诸如疲劳、头痛、失眠等问题。

因此，气动噪音的研究与降噪技术变得越来越重要。

气动噪音特性研究是气动噪音降噪技术的基础。

首先，气动噪音与气体流动特性有着密切的关系。

气体的流动是指气体在管道或空气中的流动过程。

这个流动过程中，气体会产生压缩、膨胀等行为，从而产生噪音。

因此，对于不同的气体流动状态，其产生的气动噪音特性也会有所不同。

其次，噪音发生的位置和分布也会影响气动噪音的特性。

例如，噪音在较狭窄的流道中发生时，噪音的频率会更高，并且会有尖锐的尖峰噪音。

而在较宽阔的管道中，噪音的频率会更低，而且会变得更加平滑。

为了降低气动噪音，需要采用不同的降噪技术。

以下是几种常见的气动噪音降噪技术：（一）管道内障碍物降噪技术管道内障碍物降噪技术是通过在管道内部安装障碍物来降低噪音。

这种方法的原理是，障碍物的存在可以减少气体流动的速度，从而减缓气体流动的速度和压力，降低气动噪音的产生。

但是，如果安装的障碍物过多或过大，会对管道流量和压力造成很大的影响，从而影响管道的运行效率。

（二）反射式吸声器降噪技术反射式吸声器降噪技术是通过反射式吸声器来实现的。

反射式吸声器是由多个板块组成的，板块之间留有一定的空隙。

空隙中充满了一种能吸收气体噪音的吸声材料。

当气体通过板块之间的空隙时，气体的噪音能量被吸声材料吸收，从而达到降噪的效果。

这种方法的优点是吸声材料可以进行更换，而且安装简单。

缺点是，随着时间的推移，吸声材料表面会污染或损坏，从而降低吸声效果。

（三）消声器降噪技术消声器降噪技术是通过消声器来实现的。

消声器是由多个膜片组成的，膜片间留有一定的空隙。

空隙中充满了一种能吸收气体噪音的吸声材料。

当气体通过膜片之间的空隙时，空气的振荡会被吸声材料吸收，从而达到降噪的效果。

这种方法的优点是吸声效果好，而且可以适应不同的气流情况。

基于Fluent软件的发动机冷却风扇气动性能优化

柴油机设计与制造Design and Manufacture of Diesel Engine 2020 年第4 期第26 卷（总第173 期）doi：10. 3969/j. issn. 1671-0614. 2020. 04. 006基于Fluent软件的发动机冷却风扇气动性能优化栗明，刘伦伦，高建红，曾超，张鲁滨(内燃机可靠性国家重点实验室/潍柴动力股份有限公司，潍坊261061)摘要采用C型风管式台架对某发动机冷却风扇气动性能进行试验，得到了该风扇的流量、静压及静压效率的试验数据；利用Fluent软件，对风扇流场进行仿真，得到相应的仿真结果。

将仿真结果与测试数据进行对比，结果显示两者差异基本在10%以内，满足工程分析要求：根据风扇内部流场及叶片静压分布的仿真结果，提出了风扇结构优化方案优化后的风扇静压和静压效率均有明显提升。

关键词：发动机冷却风扇Fluent软件流场Optimization of Engine Cooling Fan Air Dynamic PerformanceBased on Fluent SoftwareLI Ming,LIU Lunlun,GAO Jianhong,ZENG Chao,ZHANG Lubin(State Key Laboratory of Engine Reliability/Weichai Power Co.,Ltd.,Weifang261061 ,China)Abstract：The air dynamic performance of mass flow rate,static pressure and static efficiency of an engine fan were obtained by testing with the C-type air duct system and by the simulation of fan flow field w ith the Fluent software.The difference between the simulation and test results was less than10% , which meets the engineering accuracy requirements.According to the simulation results of inner flows and pressure distributions on the fan blades,the fan structural 〇])tim ization was proposed,and the results showed that the optimized fan had higher static pressure and static efficiency.Key words：engine,cooling fan,Fluent software,flow field0 引言风扇是水冷式内燃机的重要组成部件，其消耗的功率占发动机总输出功率的5%〜8%m。

FLUENT 声学模型

目录1.ANSYS Fluent流噪声计算方法 (1)putational Aeroacoustics(CAA直接模拟) (1)1.2.Acoustic Analogy Modeling（声比拟模型） (1)1.3.Broadband（宽频噪声模型） (2)1.4.将CFD和指定的噪声计算代码耦合 (2)2.Fluent的声比拟模型（FW-H）的使用步骤 (3)1.ANSYS Fluent流噪声计算方法对于气动噪声学科的挑战，许多气动噪声计算的方法已经被呈现出来，他们的适用性和所消耗的资源都不一样。

Ansys Fluent提供了四种方式来计算气动噪声：直接模拟方法、基于声比拟的积分方法、使用宽频噪声源模型的方法以及将CFD和指定的噪声计算代码耦合。

1.1. Computational Aeroacoustics(CAA直接模拟)在这种方法中声音的产生和传播直接通过求解合适的流体动力学方程获得。

声波的预测要求控制方程的时间精确解。

进一步讲，在大多数直接模型的实际应用中，必须借助于能够模拟粘滞效应和湍流效应的控制方程，例如非稳态N-S方程，雷诺时均方程以及过DES和LES使用的过滤方程。

直接模型需要高精度的求解方法，非常细密的计算网格以及声音无反射边界条件，所以计算代价大。

当预测远场噪声（几百倍的机翼弦长处得噪声）计算代价更大。

当计算近场噪声，直接方法就变的可行，如舱室噪音。

对于许多近场噪声的计算中，由于局部压力波动导致的噪声是可以通过fluent准确计算的。

1.2. Acoustic Analogy Modeling（声比拟模型）对于中场和近场噪声，fluent采用基于Ligthill的声比拟方法，它是直接模拟的一个很好的补充。

在该方法中，近场流场从控制方程中获得，如非稳态的雷诺平均方程，过滤的DES和LES方程，然后把求解结果作为噪声源，通过求解波动方程得到解析解，这样就把流动求解过程从声学分析中分离出来。

fluent 噪声计算

fluent 噪声计算Fluent噪声计算是一种用于模拟和预测噪声传播的工程软件。

本文将介绍Fluent噪声计算的原理、应用场景以及其在工程设计中的重要性。

我们来了解一下Fluent噪声计算的原理。

Fluent噪声计算基于有限元法和声学理论，通过对流体流动的数值模拟来计算噪声的产生、传播和衰减过程。

它可以模拟各种流动噪声，包括气体流动噪声、水流噪声以及机械振动噪声等。

Fluent噪声计算的应用场景非常广泛。

在航空航天领域，它可以用于预测飞机发动机的噪声辐射和传播，帮助设计更安静的发动机。

在汽车工程中，它可以用于优化汽车外壳的设计，降低车内的噪声水平。

在工业设备设计中，它可以用于减少机器运行时的噪声，提高工作环境的舒适度。

Fluent噪声计算在工程设计中的重要性不言而喻。

首先，它可以帮助工程师在设计初期就对噪声进行预测和评估，避免在后期需要进行昂贵的修改和改进。

其次，它可以帮助工程师找到噪声产生的主要源头，从而有针对性地采取措施来降低噪声水平。

此外，Fluent 噪声计算还可以帮助工程师进行优化设计，找到噪声与其他设计参数之间的最佳平衡点。

除了以上应用场景，Fluent噪声计算还可以在城市规划和环境保护领域发挥重要作用。

通过对城市交通流动和建筑物布局进行噪声计算，可以帮助规划者合理规划道路和建筑物的位置，减少城市噪声对居民生活的影响。

此外，Fluent噪声计算还可以用于评估工厂、发电厂等工业设施对周围环境的噪声影响，保护自然生态和居民生活环境。

Fluent噪声计算是一种强大的工程软件，具有广泛的应用价值。

它可以帮助工程师预测和评估噪声，找到噪声源头，并进行优化设计，从而降低噪声水平。

在航空航天、汽车工程、工业设备设计以及城市规划等领域，Fluent噪声计算都发挥着重要的作用，为工程师提供了可靠的噪声控制解决方案。

通过合理利用Fluent噪声计算，我们可以创造更安静、更舒适的工作和生活环境。

Fluent案例｜螺旋桨气动噪声

Fluent案例｜螺旋桨气动噪声本案例利用ANSYS Fluent计算NACA 4-(3)(08)-03螺旋桨气动噪声。

注：本案例来自Fluent案例集。

1 问题描述案例要计算的模型如图所示。

螺旋桨转速3770 rpm，采用SRF模型考虑其旋转。

螺旋桨部件的主要噪声来源包括：•厚度噪声（由于叶片的体积位移）•稳定负载噪音（由于叶片上的稳定力）•不稳定负载噪声（由于循环的不均匀负载）•四极子（非线性）噪声•宽带噪声本案例模拟螺旋桨仅旋转时的噪声，其主要的贡献来自于稳定负载。

所以可以通过使用在FLUENT中提供的GUTIN Ffwcs Williams和Hawkings（FWH）模型来考虑。

该模型为声比拟模型的稳态版本，可以利用RANS模拟的湍流。

2 Fluent设置•以3D、Double Precision模式启动Fluent•读入计算网格2pale_16.5deg-3770rpm.msh.gz读入四面体及棱柱层网格约220万。

2.1 Models设置•设置采用SST k-omega湍流模型2.2 计算区域设置•设置区域沿x轴旋转速度为3770 rpm，如下图所示•设置将区域信息拷贝到另外的区域•将区域fluid数据拷贝到fluid-vol1，如下图所示2.3 边界条件设置1、壁面边界设置•如下图所示，同时选中三个壁面，点击鼠标右键，选择Multi Edit…•如下图所示设置3个壁面相对旋转速度为02、入口设置•设置2个入口速度•如下图所示设置入口速度为2 m/s，设置方向为x方向3、outlet设置•设置出口条件，如下图所示4、修改边界类型•修改边界vol1-shadow的边界类型为interior注：其实完全没必要这么建模。

2.4 创建周期边界•如下图所示利用命令mesh/modify-zones/make-periodic创建周期边界•同样方式创建另一个周期边界2.5 转化多面体网格•利用工具按钮Make Polyhedra将四面体网格转化为多面体网格2.6 Methods设置•如下图所示设置计算方法2.7 Controls设置•设置控制参数•设置高级控制参数注：这个只影响收敛快慢，其实作用并不明显。

FLUENT 声学模型

Ansys Fluent提供了四种方式来计算气动噪声：直接模拟方法、基于声比拟的积分方法、使用宽频噪声源模型的方法以及将CFD和指定的噪声计算代码耦合。

1.1. Computational Aeroacoustics(CAA直接模拟)在这种方法中声音的产生和传播直接通过求解合适的流体动力学方程获得。

声波的预测要求控制方程的时间精确解。

直接模型需要高精度的求解方法，非常细密的计算网格以及声音无反射边界条件，所以计算代价大。

当预测远场噪声（几百倍的机翼弦长处得噪声）计算代价更大。

当计算近场噪声，直接方法就变的可行，如舱室噪音。

对于许多近场噪声的计算中，由于局部压力波动导致的噪声是可以通过fluent准确计算的。

1.2. Acoustic Analogy Modeling（声比拟模型）对于中场和近场噪声，fluent采用基于Ligthill的声比拟方法，它是直接模拟的一个很好的补充。

Fluent计算远场噪声设置

Fluent计算远场噪声设置XXX远场噪声FW-H声比计算设置Fluent可以准确地计算偶极子壁面积分的远场噪声，并且可以计算其他类型的声源积分面。

1）设置求解器首先打开Fluent。

在计算之前，需要设置并行核数与电脑相同，以及当前文件路径和是2D还是3D。

等到计算基本稳定后，开始打开声学模块采样计算。

可以通过观察升阻力系数曲线或流动出口质量流量等指标来判断流动周期是否稳定，当曲线上下波动时可以开始计算，例如在0.2时。

打开声学求解器，空气参数默认不需改动，勾选输出ASD和CGNS格式。

打开define sources，选择需要积分计算的壁面边界条件，给文件名、写入频率和多少个时间步一个文件保存。

如果需要积分超声速的空间四极子噪声，需要设置interface自由空间边界条件或导出数据到其他声学软件，速度不是特别大的情况下可以忽略。

define receivers观测点位置可以在任何时候设置。

2）FFT后处理时域数据计算完噪声后，打开run n里面的Acoustic signals，点击Compute开始计算。

观测点计算完之后，点击XY Plot，选择所有类型，在最后打开观测点的.ard文件的格式读取、计算和显示观测点随着时间变化的曲线，处于上下波动的状态用FFT 转化到频域。

点击Load Input Files读入观测点时间的数据，点击Acoustics Analysis，选择SPL声压级，将横坐标改为log分布，并关闭Auto自动，手动给横坐标范围分块加汉宁窗对曲线进行改进，勾选Subdivide into Segments分块，窗口选择hanning或其他类型，分块可以用sample或Frequencty，分块采样数看着给，分成4~10块，看具体实验数据的横坐标频率分辨率是多少对应，每块overlap重叠在到1之间。

点击apply。

close，点击Plot FFT就得到频谱曲线。

基于Fluent的高速列车气流噪声数值模拟

基于Fluent的高速列车气流噪声数值模拟刘悦卫;陆森林;左言言【摘要】The airflow noise on the surface of vehicle mainly depends on the fluctuating pressure on its body surface, so it is of great significance to control the airflow noise of high-speed trains in order to research the fluctuating pressure on the surface of vehicle. The fluctuating pressure on the surface of the high-speed train is calculated using large eddy simulation and Fluent noise module. lts fluc-tuating pressure is made change from the time domain into the frequency domain through the fast Fourier transform, then the aerody-namic noise characteristics for the high-speed train is got. By the analysis of the noise spectrum, some aerodynamic noise character-istics for high-speed train are obtained. This provides the reference for reducing the aerodynamic noise.%研究表明车辆气流噪声主要取决于车辆表面的脉动压力，因此研究车辆表面的脉动压力对控制车辆气流噪声具有十分重要的意义。

气动噪声模型使用指南

ANSYS Fluent气动噪声模型使用指南ANSYS Fluent气动噪声模型使用指南 (1)1 ANSYS Fluent的气动噪声模型特点介绍 (1)1.1C A A（直接模拟模型） (1)1.2A c o u s t i c A n a l o g y M o d e l i n g（声比拟模型） (2)1.3B r o a d b a n d（宽频噪声模型） (2)2 ANSYS Fluent的气动噪声模型设置 (4)2.1B r o a d b a n d（宽频噪声模型） (4)2.2F-W-H（声比拟模型） (7)2.3C A A（直接模拟模型） (16)3 ANSYS Fluent气动噪声测试案例 (22)3.1圆柱绕流 (22)3.2跨音速空腔流动 (26)3.3跨音速翼型绕流 (31)1 ANSYS Fluent的气动噪声模型特点介绍1.1C A A（直接模拟模型）ANSYS Fluent中的CAA方法可以通过求解流体动力学方程直接得到声波的产生和繁殖现象。

声波的预测需要控制方程时间精度的解，而且，CAA方法需要ANSYS Fluent通过求解非稳态N-S方程（如DNS）、非稳态雷诺平均RANS方程以及在分离涡DES和大涡LES 模拟中用到的滤波方程，精确模拟粘性效应和湍流效应。

CAA方法需要高精度的数值求解方法、非常精细的网格以及声波非反射边界条件，因此计算代价较高。

如果要计算远场噪声（比如几百倍的机翼弦长远处的噪声传播），CAA方法则需要超大规模并行计算支持；但是如果计算近场噪声（比如，机身表面的APU、空穴、微小部件扰动噪声），CAA方法是容易可行的。

在大多包含近场噪声的计算中，由于局部压力波动导致的噪声是可以通过ANSYS Fluent准确模拟的。

既然CAA方法直接求解声波传播，那么需要求解可压缩的控制方程（如雷诺平均方程、可压缩的LES大涡模拟的滤波方程）。

当流动速度较低或亚音速流动时，而且近场中的噪声源主要由局部压力波动构成，则可以使用不可压缩流动。

fluent meshing气动噪声计算

fluent meshing气动噪声计算
Fluent Meshing是一种计算机辅助设计(CAD)工具，可用于分析和计算复杂的几何模型，其中包括气动噪声的计算。

其计算步骤包括：1. 导入几何模型：将需要进行分析的几何模型导入到Fluent Meshing中。

2. 进行网格划分：使用Fluent Meshing的网格划分工具进行复杂的几何模型的网格划分。

3. 设置边界条件：设定物理模型的边界条件，例如流速、温度、压力等。

4. 求解计算：使用Fluent Meshing的求解器进行计算，求解模型中的物理方程，计算出气动噪声的大小。

5. 分析结果：使用Fluent Meshing的结果分析工具对计算结果进行分析，可以查看噪声的大小、频率分布以及噪声的来源等信息。

在气动噪声计算中，可以使用Fluent Meshing提供的几种计算方法，例如Fluent提供的FfowcsWilliams-Hawkings积分方法以及基于波动方程的方法，这些方法适用于近场接收器、中场到远场噪声的预测，也可以用于预测管道或墙壁封闭空间内的噪声传播。

fluent 计算圆柱扰流气动噪声

fluent 计算圆柱扰流气动噪声
计算圆柱扰流气动噪声通常涉及以下步骤：
1. 通过数值模拟或实验测量等手段确定圆柱体的流场特性，包括流速、压力分布等。

2. 在流场中选择一个合适的观测点进行声场计算。

3. 根据观测点的流场特性，利用相关理论和模型计算出圆柱体表面的不规则脉动压力分布。

4. 利用声学理论和模型，将不规则脉动压力分布转换为声场信息，计算各个频率下的声压级。

5. 根据特定的指标和限制条件，对得到的声压级结果进行优化和分析。

需要注意的是，由于圆柱扰流气动噪声计算涉及多个复杂的物理过程，计算结果可能会受到各种因素的影响，例如流场模型、声学模型、边界条件等。

因此，进行准确的圆柱扰流气动噪声计算需要有一定的专业知识和经验，并且可能需要进行多次的迭代和调整。

ANSYS Fluent航空气动噪声解决方案

ANSYS Fluent航空气动噪声解决方案
安世亚太流体产品业务部
【期刊名称】《航空制造技术》
【年(卷),期】2012(000)009
【总页数】2页(P103-104)
【作者】安世亚太流体产品业务部
【作者单位】
【正文语种】中文
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FLUENT

ANSYS Fluent 对于气动降噪设计，Fluent中的三种噪声模型完全可以满足设计分析需求。

但是对于一些复杂的噪声模拟，比如带有声反射、噪声在固体结构中的传播、声振耦合计算等问题中，单纯的流体动力学分析和波动方程是无法满足需要的，必须要采用一些专用的噪声分析软件，如ACTRAN等。

耦合分析首先要在Fluent中用瞬态计算获得噪声源数据，如单极子、偶极子、四极子噪声源，为了获得准确的噪声源数据，对于低雷诺数流动通常要采用大涡，而高雷诺数通常采用分离涡杂交湍流模型.。