hi all.... due to the complications in analyzing flow field in a centrifugal pump , for a start, i would like to investigate the 2D blade to blade relative flow field of a closed -shroud centrifugal pump......using FLUENT v4.3 the grids have extensions area before and after the blade section and it is axissymmetric about its axis ....i understand that rotating frame of reference and Reynolds Stress model is more suitable in solving the relative flow field ... i would like to find out what is the suitable value to input for the turbulence intensity to analze the flow????2% or 5% or 10%??? what is characteristic length ?In FLUENT it is referred to as hydraulic radius.....what does it mean????is it referring to the chord length of the blade or the inner radius of the extensions area before the blade or what????

thanks bernard

(1). You have picked one of the most difficult problem to start. (2). At this stage, you can set the intensity to 5% and the length scale to the inlet radius. It is easier to remember this way. (3). The reason why I said that it is one of the most difficult problem is: it is always 3-D and likely with flow separations all the time.

the hydraulic diameter is: 4A/U=pi*r*r/(2*pi*r)=2*r (in the case of a tube).

Yes, the question was about the hydraulic diameter not the hydraulic radius, thanks. Regardless of what number you use in the study, try to keep it consistent. (Unless you are studying the inlet turbulence effect.) Actually, you should plot the contour plot of TKE(turbulence kinetic energy) to see how it develops from the inlet. You will get a better feeling when you look at the plots for different TKE values at the inlet.

Dear contributors,

I fully agree with what all you said, which I appreciate.

By the way, to our client, I wonder if you want to upgrade the software ? FLUENT 4.3 is at least 5 years old, and 5 yrs is a long time in CFD world.