THE STRUCTURE OF INSTANTANEOUS REVERSALS IN HIGHLY TURBULENT FLOWS

被引:5
作者
SINGH, RK
AZAD, RS
机构
[1] Department of Mechanical and Industrial Engineering, University of Manitoba, Winnipeg, R3T 2N2, Manitoba
关键词
D O I
10.1007/BF00208463
中图分类号
TH [机械、仪表工业];
学科分类号
0802 ;
摘要
Structure of instantaneous flow reversals has been measured in a highly turbulent axisymmetric diffuser flow using pulsed-wire anemometry. In this 8 degrees nominal included angle conical diffuser, the adverse pressure gradient (APG) is strong enough to cause appreciable instantaneous flow reversals (instantaneous backflow up to 30% of the time), but the time-averaged flow is non-separated. The results are compared with the other severe APG separating flows reported in literature. An increase in entry Reynolds number indicated a decrease in the size of near-wall instantaneous reversals region as well as a decrease in the magnitude of instantaneous backflow. Also, the region of instantaneous reversals moves slightly downstream at appreciably higher Reynolds numbers. The initiation and growth of instantaneous reversals in a conical diffuser was found to strongly influence the wall-layer and the central region. Present results also suggest that the instantaneous backflow should be considered for modelling of instantaneously-separating diffuser flows. In the final stages of a conical diffuser, the magnitudes of cross-stream pressure gradient were found to be appreciably larger than that of the longitudinal pressure gradient, indicating that accurate representation of a conical diffuser flow can not be achieved without considering V-momentum equation. A comparison of various separating flows revealed remarkable similarity of instantaneous reversals regions and distributions even in different flow configurations.
引用
收藏
页码:409 / 420
页数:12
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