Experimental Investigation on the Mechanism of Flow-Type Changes in Supersonic Cavity Flows.

Abstract

Compressible flows over cavities with a series value of length-to-depth ratio (L/D) were investigated experimentally, with the objective being to elucidate the mechanism of the transition of types of cavity flows as their L/D increases or decreases. For open-type cavity flows, the freedom of backflow inside the cavity is found to be crucial in smoothing out adverse pressure gradient. The spreading of the shear layer and its gradual approach toward the cavity floor as L/D increases tend to suppress the freedom of backflow, causing the cavity flow to change from the open-type to the transitional-type. For closed-type cavity flows, the finite thickness of the upstream boundary layer leads to the presence of three kinds of characteristic lengths that correspond to the recirculation region, the deflection of the main flow and the recovery or the abrupt rise of the pressure, respectively. The compression fans at the foot of the impingement and the exit shock waves will approach each other well in advance of the possible merge of the vertices of the conventionally defined separation and recompression wakes. As the L/D of a closed cavity decreases, the reattached boundary layer on the mid-portion of the cavity floor will have less developing distance, thus it will be more susceptible to adverse pressure gradient and prone to separation. For the present two-dimensional cavity models, the critical values of L/D were found to be about 10 and 14 for the transition of cavity flows from the open-to the transitional-type and from the transitionalto the closed-type, respectively. The sum of the pressure lengths at the front and rear wakes agrees remarkably well with the second critical L/D.

Experimental Investigation of the Supersonic Flow over an Axisymmetric Ring Cavity

“…While the upper boundary λ C weakly depends on β, the lower boundary λ O and, accordingly, the length of the transition region differ markedly for the considered values of β. The upper boundary of the transition region is thereby in good agreement with the known data [1][2][3][4][5][6][7][8][9][10][11][12], and the lower boundary turned out to be much lower than the value of λ O = 10 predicted in the literature.…”

“…The supersonic fl ow over rectangular cavities was investigated experimentally and numerically in [1][2][3][4][5][6][7][8][9][10][11][12]. Depending on the ratio of the length of the cavity L to its depth h, two different fl ow schemes are possible [1,2]…”

“…In the external supersonic fl ow fi eld, shock waves arise thereby: a compensation shock 5 ahead of the front separation region and a shock 6 ahead of the rear separation region. The range λ O < λ < λ C corresponds to the so-called transition region for which there is an additional classifi cation of fl ow schemes [1][2][3][4].…”

“…In the external supersonic fl ow fi eld, shock waves arise thereby: a compensation shock 5 ahead of the front separation region and a shock 6 ahead of the rear separation region. The range λ O < λ < λ C corresponds to the so-called transition region for which there is an additional classifi cation of fl ow schemes [1][2][3][4].The character of the supersonic cavity fl ow depends also on the state of the boundary layer at the cavity inlet and the Mach M and Reynolds Re numbers. For plane cavities of rectangular cross-section in supersonic turbulent fl ow in the range of moderate Mach numbers M = 2-4, there are empirical estimates of the boundaries of regions in which a particular fl ow scheme is realized: λ O = 10, λ C = 13.…”

On Supersonic flow over an circular cavities at angle of attack

“…Сверхзвуковое обтекание каверн изучалось экспериментально [1][2][3][4][5][6][7][8][9][10][11] и численно [4,[11][12][13][14][15]. Рассматривались особенности сверхзвукового обтекания последовательно установленных каверн [16,17], а также гиперзвуковое обтекание каверн [18].…”