Learning Forum

[GuillaumeCRENN]

Hello,

I am working on impinging jets and to get confidence with Fluent, I am trying to get similar results from a template report. This report has been written by Xu and al. (2011), « Particle image velocimetry study of the impinging height effect on an overexpanded supersonic impinging free jet at Ma=1.754. Part I: global coherent structure and Part II : detailed velocity distribution ».

Here are the specifications :

• Ma (exit)= 1.754
• Nozzle Pressure Ratio (NPR) = 4.7625
• T = 300K

[Rahul Kumar]

Hello, nCan you please give us details of the mesh? Also, What solution methods are you using? I would suggest AUSM with Roe flux difference (Density based approach). Also reduce the courant number. In order to monitor convergence, I would also suggest to monitor a value at a particular location using report definition. You can also refer to our free courses (found on Ansys forum) where you will find simulation examples with best practices for nozzle expansion. n

[GuillaumeCRENN]

Hello,nAbout the details of the mesh : 0.71 million elements, 0.4 million nodes, Triangles except for inflationnnnnAspect Ratio : (moyenne = average)nnSkewness :nnOrthogonal Quality :nnHere are the Mesh quality given by Fluent : nnThese are the General options :nnA clarification concerning the boundary conditions, I used a 'Pressure-Inlet' condition for the 'Outlet 1' and a 'Pressure outlet' condition for 'Outlet'. To be noted, I used the identical backflow Turbulent length scale for every boundary condition. (0.006m : diameter of the nozzle exit). This might be something to be improve. Regarding the Thermal component, I used for every boundary condition 300K. nnnAbout the Solution Methods you asked :nnAbout the Solution Controls choices. I can not increase or decrease the Courant Number with this set-up (Density-based + Steady). During my simulation, I decreased them until 0.1.nnI used a hybrid-initilization. I did not use the command /solve/initialize/fmg yes. This could be helping. nnAbout the Free Courses, I found this one :n and this one : nBut you are probably talking about this one ?nnNone of them are dealing with a Supersonic Impinging jet but I will work on it!nnThank you for your help!nnGuillaumen

[GuillaumeCRENN]

Hello, nFollowing the turorials, I have made some changes :nI used a Hydraulic diameter for Pressure Inlet (Turbulence Specification Method). I also reduced the turbulent viscosity % for Pressure Inlet and Pressure Outlet. More, I used 101 325 Pa as a Supersonic/Initial Gauge Pressure. nI used /solve/initialize/fmg yesnThe result remains the same, the solution is not convergent...nnWhere can my error come from?nThank you

[Rahul Kumar]

Hello, nThank you for all the information. Did you use AUSM? Can you also give me some information on the monitors that you have setup as that would give me a better understanding of how the simulation is behaving?n

[GuillaumeCRENN]

Hello,nI used AUSM but the result is not better.nFor the monitors, I used an Area-Weighted Average of Mach number at the outlet nozzle which is constant (1.5767) and I made a monitor video to see where the flow can change and the flow change a little bit in the stagnation zone. nI have heard that given my case, the proximity between the exit and the area impinged, L/D , with a supersonic flow, the residuals could not go below 10e-2 or 10e-3.Thank you,nGuillaumen

[Rahul Kumar]

Guillaume, nLooking at residuals alone does not determine the convergence of solution. Monitoring a value and also confirming the flux balance from the reports will also be other factors to take into consideration for convergence. nAnd your observation is right too! n