Dear evrybody,

Is there anybody who knows well about SMD(Sauter Mean Diameter)? How can I get the number of droplets which were placed at a point on a plane after injected? I don't have any idea and tired to think about it. Is there a variable to calcuate it in STAR-CD? Thank you...

Hi,

the SMD describes the ratio of the volume to the surface of the injection jet and is defined as the sum of all droplet diameters^3 divided by the sum of all droplet diameters^2. This is a very important parameter to describe the physical behaviour of your droplets (e.g. evaporation).

I have no idea what to do with your 2nd question. Perhaps you could try to select all droplets that are stuck to the plane with the coordinates you want.

Regards,

Thomas Lauer Institute for Internal Combustion Engines TU Vienna, Austria

Dear, Sir:

Thank you very much for your kind comment. As you said, SMD is directly proportional to the ratio of the volume to the surface of the injected droplet. However, Don¡¯t we need dn(delta n) to calculate SMD? dn(delta n) means the ration of the total no. of droplet to no. of droplet in each section (d ~ d+deta d). So I thought the total no. of droplet should be needed to calculate SMD. If I¡¯m thinking in a wrong way, Please give me an advice. And one more question, if I like to decide whether injected droplets are distributed well in any area or not, can I regard SMD to the index or do I have to calculate any other such as an uniformity index? Thank you again, thank you...

Regards

Wally

Dear Wally:

Your assumption is correct. You will have to sum up the d^3 and d^2 for all parcels. I think it will be necessary to create a macro with the following structure:

loop,index,1 to [number of parcels]; N = Number of droplets in parcel(index); d = Diameter of droplets in parcel(index); sumd3=sumd3+N*d**3; sumd2=sumd2+N*d**2; end; smd=sumd3/sumd2;

Please check the manuals for the STAR command language. The SMD only describes the physical behaviour of your droplets not the spatial distribution. I am not sure how to achieve that in general. It depends on your problem. The inquiry and evaluation of the parcels' coordinates would probably be a good starting point. Please notice that the correct distribution of your droplets is also influenced by the number of parcels you introduce. Try to get yourself a good textbook.

Regards, Thomas

Dear, Sir;

I'm almost come to the solution I asked with your detail explanation. So much thank you, sir! When I finish this research, I'd like to send a thanks mail to you individually again ^^. Be happy! Thank you!