Les Software for the Design of Low Emission Combustion Systems for Vision 21 Plants

Smith, Clifford E.

CFD Research Corporation

关键词: Nitrogen Oxides;    Heat Transfer;    Ducts;    Heat Losses;    42 Engineering;   

DOI  :  10.2172/823953
RP-ID  :  NONE
RP-ID  :  FC26-00NT40975
RP-ID  :  823953

美国|英语

来源: UNT Digital Library

【 摘 要 】

Previous LES calculations for one SIMVAL case ({phi}{sub inj} = 0.7) have repeatedly shown that the heat transfer/heat losses were not correctly captured, resulting in predicted NO{sub x} emissions being much higher than measurements. In a current Navy Phase I SBIR project, we are studying ways to improve the prediction of heat transfer/heat loss in LES calculations. To improve our understanding of heat transfer at walls, a series of thermal channel flow cases were analyzed and compared to DNS predictions. When trying to fully resolve the boundary layer, it was found that the grid size in all directions (i.e. {Delta}x, {Delta}y, and {Delta}z) must be smaller than the size of eddies formed in the boundary layer. Thus, the cell aspect ratio at the wall needs to typically be less that 25 when the boundary layer is being resolved. In previous SIMVAL LES calculations, this cell aspect ratio requirement was not followed, and thus the heat transfer was less than desired. For this quarter, the grid was adjusted, and the SIMVAL case was rerun. The LES results show that vortices are now formed in the exhaust duct near the walls, resulting in more heat loss from the exhaust duct flow and lower NO{sub x} predictions (more in line with the measurements).