Learning Forum

[Akshay1993]

Hello,

 

I am Akshay Barpute and i am doing my master project on DTU 10 MW offshore wind turbine.  I have to perform CFD operations. I have modeled the blade and i have started doing meshing. My problem arises here, without inflation my skweness and orthogonal quality is good i.e max skweness (0.79) and min ortho quality (0.21) but after creating inflation layer it is drastically decreasing. can you please help me to find a solution.

[Rob]

You need to look at where the poor cells are being created and then see why they're occurring.  Look at the graph for statistics, adjust the scales and then click (hold CTRL) on the top 2-3 bars. This should highlight where the mesh is of poor quality. 

[Akshay1993]

Thank you for the reply.

I have already seen the areas where the mesh is of poor quality. The mesh is poor on the surface of the blade(i.e) at the trailing edge. I have tried to change the design of my blade near the trailing edge(i.e) like round type, straight trailing edge and smooth finish. None have given me good results. what should i do know??????

[Rob]

There are a few options:  

      Increase the surface mesh resolution near the trailing edge as this helps the inflation. 

     Create an O-grid block around the blade (look this up) as the decomposition faces will aid the inflation layer growth

      Check the angle in the inflation advanced settings: increase it to the maximum 

     Create one fairly thick inflation layer and adapt in Fluent

 

Simply, you're trying to help the mesh build the layers: this may mean breaking the model up. 

 

[Akshay1993]

I thank you for your guidence, Sir i have increased the surface mesh resolution near the trailing edge, but there was not much improvement in the mesh and i cannot increase  the resolution more as i need to resist the no of cell to 7 million. And i have increased the inflation angle as well. 

But i havent tried creating a thick inflation layer . what does it mean can you please explain me ???

i am attaching my  ansys file as well for clear understanding.

---

 

[Rob]

I'm not allowed to open ANSYS files: as staff we operate under several restrictions. Other community members are able to open files. 

A thick layer is simply that you create inflation of only 1-2 layers but set the initial height to be much higher than normal. You then use adaption in the solver to refine the mesh as needed. It's an old approach for when thin layers give poor mesh quality. 

[Akshay1993]

Respected Sir,

Luckily I have achieved the quality with  inflation layer. Now my problem is that, my solution is not converging. I am using the turbulence model K-Epsilon model. I have used the Yplus value between 30 and 300. I have given the convergence criteria as 1e-6. I am able to get the convergence for K, X, y,, z. but for epsilon and continuity i am not getting convergence. Is there any solution for this?????. should i change the under relaxation factor  for the momentum so that there may be a chance for continuity to converge.

[Rob]

It'll depend on what the cause is. What you've probably got is some transient behaviour in the flow, put some monitor points into the domain and look for fluctuations. What you're after is flat residuals and monitors, plus low mass imbalance: typically getting two of the list to work is enough but you'll need to understand the flow field to decide. 

[Akshay1993]

Respected Sir,

 

Thank you for the reply. What do you mean by monitor points??. I have kept the report definition for lift coefficient and drag and moment coefficient. What do you mean  by mass imbalance????. Can you please explain me.