In this paper, the characteristics of a pressure wave propagating against two parallel subsonic streams in a constant-area straight duct are investigated by one-dimensional analysis, two-dimensional numerical simulati...In this paper, the characteristics of a pressure wave propagating against two parallel subsonic streams in a constant-area straight duct are investigated by one-dimensional analysis, two-dimensional numerical simulation, and experiments. Computations have been carried out by the two-dimensional Euler Equations using the Chakravarthy-Osher-type TVD scheme. Optical observations by the schlieren method as well as wall pressure measurements have been performed to clarify both the structure and the propagation velocity of pressure waves. The results show that the pressure wave propagating against the streams changes into a bifurcated pressure wave and the bifurcation occurs in the low speed streams. It is also found that the propagation velocity of the pressure wave obtained by the analysis and computation agrees well with the present experimental data.展开更多
The acoustic properties of supersonic jet noise from a convergent-divergent nozzle with a baffle have been studied experimentally over the range of nozzle pressure ratios from 2.0 to 8.0. Acoustic measurements were co...The acoustic properties of supersonic jet noise from a convergent-divergent nozzle with a baffle have been studied experimentally over the range of nozzle pressure ratios from 2.0 to 8.0. Acoustic measurements were conducted in a carefully designed anechoic room providing a free-field environment. A new approach for screech noise suppression by a cross-wire is proposed. Schlieren photographs were taken to visualize the shock wave patterns in the supersonic jet with and without the cross-wire. The effects of the baffle and the cross-wire on acoustic properties are discussed. It is shown that the baffle has little effect on the screech frequency for the underexpanded supersonic jet without the cross-wire. Also, the cross-wire introduced in supersonic jets is found to lead to a significant reduction in overall sound pressure level.展开更多
An experimental and analytical study has been carried out to obtain the clear understanding of a shock wave transition associated with a steady two-dimensional overexpanded flow. Two-dimensional inviscid theory with r...An experimental and analytical study has been carried out to obtain the clear understanding of a shock wave transition associated with a steady two-dimensional overexpanded flow. Two-dimensional inviscid theory with respect to a shock wave reflection is used in the present study on the characteristic of shock waves. The results obtained from the flow analysis are compared with those obtained from flow visualizations. It is shown that in the region of regular reflection, the angle of an incident shock wave becomes lower than that calculated by two shock theory with an increment in the ratio PJPb of the nozzle exit pressure Pc to the back pressure Pb. It is indicated that the configuration of shock waves in overexpanded jets is influenced by the divergent angle at the nozzle exit. Also it is shown from the flow visualization that a series of shock waves move into the nozzle inside with a decrease in pressure ratio Pc/Pb, even if the Pc/Pb is under overexpanded conditions.展开更多
The thermal choking phenomenon is of great importance in an inlet isolator in dual-mode ram jet/scramjet combustor. In some cases the choked flow creates a pseudo-shock wave including a shock train in it at the engine...The thermal choking phenomenon is of great importance in an inlet isolator in dual-mode ram jet/scramjet combustor. In some cases the choked flow creates a pseudo-shock wave including a shock train in it at the engine inlet and causes large amounts of drag and radically reduces the performance of the engine at high flight Mach numbers. The present paper describes a one-dimensional flow model taking account of the upstream boundary-layer as well as heat addition by using a mass-weighted av- eraging technique. The simple relationships for the flow field in a constant area duct in which the effect of the upstream boundary-layer is considered but the effect of the wall friction in the duct can be neglected are presented. The results of the calculation such as the maximum heat addition when the thermal choking occurs, the downstream Mach number and the static pressure ratio are presented and examined in detail.展开更多
文摘In this paper, the characteristics of a pressure wave propagating against two parallel subsonic streams in a constant-area straight duct are investigated by one-dimensional analysis, two-dimensional numerical simulation, and experiments. Computations have been carried out by the two-dimensional Euler Equations using the Chakravarthy-Osher-type TVD scheme. Optical observations by the schlieren method as well as wall pressure measurements have been performed to clarify both the structure and the propagation velocity of pressure waves. The results show that the pressure wave propagating against the streams changes into a bifurcated pressure wave and the bifurcation occurs in the low speed streams. It is also found that the propagation velocity of the pressure wave obtained by the analysis and computation agrees well with the present experimental data.
文摘The acoustic properties of supersonic jet noise from a convergent-divergent nozzle with a baffle have been studied experimentally over the range of nozzle pressure ratios from 2.0 to 8.0. Acoustic measurements were conducted in a carefully designed anechoic room providing a free-field environment. A new approach for screech noise suppression by a cross-wire is proposed. Schlieren photographs were taken to visualize the shock wave patterns in the supersonic jet with and without the cross-wire. The effects of the baffle and the cross-wire on acoustic properties are discussed. It is shown that the baffle has little effect on the screech frequency for the underexpanded supersonic jet without the cross-wire. Also, the cross-wire introduced in supersonic jets is found to lead to a significant reduction in overall sound pressure level.
文摘An experimental and analytical study has been carried out to obtain the clear understanding of a shock wave transition associated with a steady two-dimensional overexpanded flow. Two-dimensional inviscid theory with respect to a shock wave reflection is used in the present study on the characteristic of shock waves. The results obtained from the flow analysis are compared with those obtained from flow visualizations. It is shown that in the region of regular reflection, the angle of an incident shock wave becomes lower than that calculated by two shock theory with an increment in the ratio PJPb of the nozzle exit pressure Pc to the back pressure Pb. It is indicated that the configuration of shock waves in overexpanded jets is influenced by the divergent angle at the nozzle exit. Also it is shown from the flow visualization that a series of shock waves move into the nozzle inside with a decrease in pressure ratio Pc/Pb, even if the Pc/Pb is under overexpanded conditions.
文摘The thermal choking phenomenon is of great importance in an inlet isolator in dual-mode ram jet/scramjet combustor. In some cases the choked flow creates a pseudo-shock wave including a shock train in it at the engine inlet and causes large amounts of drag and radically reduces the performance of the engine at high flight Mach numbers. The present paper describes a one-dimensional flow model taking account of the upstream boundary-layer as well as heat addition by using a mass-weighted av- eraging technique. The simple relationships for the flow field in a constant area duct in which the effect of the upstream boundary-layer is considered but the effect of the wall friction in the duct can be neglected are presented. The results of the calculation such as the maximum heat addition when the thermal choking occurs, the downstream Mach number and the static pressure ratio are presented and examined in detail.
