The effect of grazing flow on the steady state resistance of square-edged orifices

Effect of Grazing–bias Flow Interaction on Acoustic Impedance of Perforated Plates

“…The quasi-steady assumption has been employed in this model, and also a hypothesis is made that the #uctuating velocity due to the sound excitation is far smaller than the mean #ow velocity. The previous #ow visualization experiments [22,24] demonstrated that, in the out#ow case the ori"ce #ow was de#ected downstream while grazing #ow was de#ected upward, and in the in#ow case the #ow was drawn into the ori"ce at a downstream slope; in both cases the ori"ce jet was characterized by the minimum e!ective #ow area as shown in Figure 14. At this neck of the ori"ce jet, the #ow velocity is almost uniformly distributed and the #ow pressure is equal to that of the ambient air.…”

“…Note that equation (6) di!ers from that for the steady state ori"ce resistance in reference [22] by a factor of 2. Next, we will try to "nd the relation between the e!ective discharge coe$cient and the mean #ow speeds.…”

“…E!ective discharge coe$cient as a function of the ratio of bias #ow Mach number to grazing #ow Mach number, the ** curves are calculated from equations (8) and (9) from Figure 15 that, generally a good correlation of the data is obtained for out#ow whereas there is much scattering in the data for in#ow. According to Rogers and Hersh [22], for the steady-state ori"ce resistance the plate thickness has a far greater e!ect on the data correlation in the in#ow case than in the out#ow case. Taking advantage of the close connection between the steady state and acoustic resistance, we think that the in#uence of plate thickness may account for the data scattering in Figure 15(b).…”

“…Among all the tests carried out, in the case of perforated plate 4 with out#ow being present, grazing #ow has the least in#uence on the way that bias #ow changes the ori"ce impedance. Rogers and Hersh [22] have presented an investigation of the interaction between grazing and ori"ce #ow with emphasis on the steady state resistance. The present measured ori"ce acoustic resistance is compared with the steady state ori"ce resistance of reference [22], and we "nd that both kinds of resistance show similar characteristics, such as the di!erence between grazing-in#ow and grazing-out#ow interactions, and the so-called &&negative grazing #ow e!ect'' in the out#ow case.…”

“…To the authors' knowledge, so far few e!orts have been made on this problem. Rogers and Hersh [22] presented an investigation of the interaction between grazing and ori"ce #ow, but only steady state ori"ce resistance is considered in their work. It is believed that there is some connection between steady state and acoustic resistance of an ori"ce.…”