Effects of inflow pulsation on a turbulent coaxial jet = 난류동축제트에 대한 입구유동 가진의 영향

The effects of inflow pulsation on the flow characteristics and mixing properties of turbulent confined coaxial jet flows have been studied. Large eddy simulations were performed at Re = 9000 and the mean velocity ratio of the central to annular jet was 0.6. Pulsation was generated in the inflow jet by varying the flow rates. First, inflow pulsation was applied at frequencies in the range 0.1 < St < 0.9 while other parameters were fixed. The pulsation frequency responses were scrutinized by examining the phase- and time-averaged turbulence statistics. The pulsation frequencies St = 0.180 and 0.327 were found to produce the largest enhancement in mixing and the largest reduction in the reattachment length respectively. The effects of the phase difference between the two inflow jets at these two optimal frequencies were then investigated. The optimal phase difference conditions for mixing enhancement and the reduction in the reattachment length were obtained when the strength of the outer vortices was high. Further, we found that the strength of the inner vortices was reduced by varying the phase difference, and the reattachment length was minimized, and that if the strength of the inner vortices was increased, mixing was enhanced. The flow in an axisymmetric contraction fitted to a fully developed pipe flow is numerically studied. The reduction in turbulence intensity in the core region of the flow is discussed on the basis of the budgets for the various turbulent stresses as they develop downstream. The contraction generates a corresponding increase in energy in the near-wall region where the sources for energy production are quite different and of opposite sign compared to the core region, where these effects are caused primarily by vortex stretching. The vortices in the pipe become aligned with the flow as the stretching develops through the contraction. Vortices which originally have a spanwise component in the pipe are stretched into pairs of counter-rotati...
Advisors
Sung, Hyung-Jinresearcher성형진researcher
Publisher
한국과학기술원
Issue Date
2011
Identifier
466299/325007  / 020047508
Language
eng
Description

학위논문(박사) - 한국과학기술원 : 기계공학전공, 2011.2, [ vii, 91 p. ]

Keywords

turbulent pulsating flow; mixing enhancement; coaxial jet; axisymmetric contraction; 축대칭 수축관; 난류맥동유동; 혼합; 동축제트

URI
http://hdl.handle.net/10203/43454
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=466299&flag=t
Appears in Collection
ME-Theses_Ph.D.(박사논문)
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