The article [10] has presented the necessity of the classification into two types: Isolated wakes and coupled wakes. In this report, different types of momentum defect diffusion at the begining of wake are analysed for the two types of coupled wake and isolated wake. According to ·numerical results obtained, we analyse the - long or short - of the wake establislrment zone before the wake established zone, and this zone is very different between isolated wake and coupled wake. | Vietnam Journal of Mechanics, NCNST of Vietnam T. XX, 1998, No 3 (37- 45) TYPES OF MOMENTUM DEFECT DIFFUSION AT THE BEGINING OF THE WAKE AND WAKE ESTABLISHMENT ZONE FOR THE COUPLED WAKE AND COMPARISON WITH THE ISOLATED WAKE HOANG THI BICH NGOC Department of Mecchanics, Hanoi University of Technology ABSTRACT. The article [10] has presented the necessity of the classification into two types: Isolated wakes and coupled wakes. In this report, different types of momentum defect diffusion at the begining of wake are analysed for the two types of coupled wake and isolated wake. According to ·numerical results obtained, we analyse the long or short - of the wake establislrment zone before the wake established zone, and this zone is very different between isolated wake and coupled wake. 1. Introduction From the established equation about the wake width, we will analyse types of momentum defect diffusion at the beginning of the wake for coupled wake and isolated wake. The difference about the type of momentum deffect diffusion of the two sorts of wakes decides different properties of these two sorts of wakes. According to obtained numerical results, we analyse the existence of the wake establishment zone before the wake established zone. For coupled wake, the wake establishment zone can be long, short, or negligible - which depends on the boundary layers before the coupled wake and Reynolds number Rex in wake. But, for isolated wake, the wake establishment zone is considerable, and before the wake establishment zone, according to each case, it exists a zone of form vortexes, in which, the numerical calculation is not converged. 2. General equation about wake width and type of momentum defect gradual diffusion at the beginning of coupled wake & comparison with the type of momentum defect sudden diffusion at the beginning of isolated wake Existing theories of wake report that the bidimensional wake width is propor- 37 tiona! to the square root of the .
