Centrifugal Fan Analysis for Determination of Characteristic Curve

[01melihgazi]

Hello. I am trying to analyze a backward curved centrifugal fan. The model that I created includes stator,impeller and volute. My aim was determining the characteristic curve which is volume flowrate vs outlet pressure. As boundary condition I tried inlet and outlet as static pressure or openings. At low pressure values it converges however for outlet bc at high pressure values convergence is a bit problematic.It doesn't converge. I don't think that it is related to mesh as at low pressure values it converges and also y+ value close to the wall of the blades are lower than 30.  So what are your suggestions and trying transient solution is the only way to achieve convergence?

Will be looking forward to your answer,

Best regards.

[Petros]

Hi, do you know the mass flow at the choke line? Maybe you have approached this limit. You can also use Exit Corrected Mass Flow that is available as a boundary condition in CFX, for which you can find more information on section 1.9.3.1.11 of the Theory Guide. There is a tutorial as well, which explains how to correctly set up such simulations.

CFX Reference Guide includes convergence tips for turbomachinery components.

[01melihgazi]

 

Thank you for the documents Mr.Petros. Based on experimental results, when I close the outlet of the volute completely the static pressure in the conduit is 2350 Pa(Shut off point). In this point actually the simulation shows the volume flowrate close to 0. However, when I try to simulate it very close to shut off pressure, for example 1800 Pa and higher by giving opening bc or other pressure based bc, the solution doesn’t converge. 

In this case I know the mass flowrate as I conducted an experimental study. However I wonder how it would be if I design a prototype model and find out the characteristic curve of it. I think in this condition I would need to give pressure inlet-outlet and revolution of the impeller.