The Coanda effect has long been employed in the aerospace applications to improve the performances of various devices. This effect is the ability of a flow to follow a curved contour without separation and has well be...The Coanda effect has long been employed in the aerospace applications to improve the performances of various devices. This effect is the ability of a flow to follow a curved contour without separation and has well been utilized in ejectors where a high speed jet of fluid emerges from a nozzle in the ejector body, follows a curved surface and drags the secondary flow into the ejector. In Coanda ejectors, the secondary flow is dragged in the ejector due to the primary flow momentum. The transfer of momentum from the primary flow to the secondary flow takes place through turbulent mixing and viscous effects. The secondary flow is then dragged by turbulent shear force of the ejector while being mixed with the primary flow by the persistence of a large turbulent intensity throughout the ejector. The performance of a Coanda ejector is studied mainly based on how well it drags the secondary flow and the amount of mixing between the two flows at the ejector exit. The aim of the present study is to investigate the influence of various geometric parameters and pressure ratios on the Coanda ejector performance. The effect of various factors, such as, the pressure ratio, primary nozzle and ejector configurations on the system performance has been evaluated based on a performance parameter defined elsewhere. The performance of the Coanda ejector strongly depends on the primary nozzle configuration and the pressure ratio. The mixing layer growth plays a major role in optimizing the performance of the Coanda ejector as it decides the ratio of secondary mass flow rate to primary mass flow rate and the mixing length.展开更多
Improvement of aerodynamic performance and reduction of interaction tone noise of a centrifugal compressor with vaned diffusers are discussed by experiments and visualization techniques using a colored off-film method...Improvement of aerodynamic performance and reduction of interaction tone noise of a centrifugal compressor with vaned diffusers are discussed by experiments and visualization techniques using a colored off-film method. The focus of the research is concentrated on the leading edge shape of diffuser vanes that are deeply related to the generation mechanism of the interaction tone noise. The compressor-radiated noise can be reduced by more than ten decibels by using modified diffuser vanes which have 3-D tapered shapes on both pressure and suction sur- faces of the leading edge. Furthermore, by adopting the proposed modified diffuser vanes, the secondary flow which is considered to be an obstruction of diffuser pressure recovery can be suppressed, and also the pressure decrease observed in the throat part of the diffuser flow passage is reducible. Thus, the proposed diffuser vanes show a favorable result for both noise and the aerodynamic performance of the centrifugal compressor, and offer a few basic guidelines for the diffuser vane design.展开更多
The purpose of this study is to investigate the characteristics of aerodynamic sound generated from wake interference of circular cylinder and airfoil vane located in tandem and to clarify the generation mechanism of ...The purpose of this study is to investigate the characteristics of aerodynamic sound generated from wake interference of circular cylinder and airfoil vane located in tandem and to clarify the generation mechanism of the sound source with discrete frequency. The effects of the interval between the cylinder and the airfoil on the characteristics of aerodynamic sound are investigated by acoustic measurement, flow visualization and exploration test of sound source. The relation between the flow field and the sound field with discrete frequency noise（DFN） is shown, and then it is found that the downstream airfoil works as the sound source of DFN, which has the frequency of vortex shedding from the upstream cylinder, when the interval of two bodies is longer than a critical distance.展开更多
文摘The Coanda effect has long been employed in the aerospace applications to improve the performances of various devices. This effect is the ability of a flow to follow a curved contour without separation and has well been utilized in ejectors where a high speed jet of fluid emerges from a nozzle in the ejector body, follows a curved surface and drags the secondary flow into the ejector. In Coanda ejectors, the secondary flow is dragged in the ejector due to the primary flow momentum. The transfer of momentum from the primary flow to the secondary flow takes place through turbulent mixing and viscous effects. The secondary flow is then dragged by turbulent shear force of the ejector while being mixed with the primary flow by the persistence of a large turbulent intensity throughout the ejector. The performance of a Coanda ejector is studied mainly based on how well it drags the secondary flow and the amount of mixing between the two flows at the ejector exit. The aim of the present study is to investigate the influence of various geometric parameters and pressure ratios on the Coanda ejector performance. The effect of various factors, such as, the pressure ratio, primary nozzle and ejector configurations on the system performance has been evaluated based on a performance parameter defined elsewhere. The performance of the Coanda ejector strongly depends on the primary nozzle configuration and the pressure ratio. The mixing layer growth plays a major role in optimizing the performance of the Coanda ejector as it decides the ratio of secondary mass flow rate to primary mass flow rate and the mixing length.
文摘Improvement of aerodynamic performance and reduction of interaction tone noise of a centrifugal compressor with vaned diffusers are discussed by experiments and visualization techniques using a colored off-film method. The focus of the research is concentrated on the leading edge shape of diffuser vanes that are deeply related to the generation mechanism of the interaction tone noise. The compressor-radiated noise can be reduced by more than ten decibels by using modified diffuser vanes which have 3-D tapered shapes on both pressure and suction sur- faces of the leading edge. Furthermore, by adopting the proposed modified diffuser vanes, the secondary flow which is considered to be an obstruction of diffuser pressure recovery can be suppressed, and also the pressure decrease observed in the throat part of the diffuser flow passage is reducible. Thus, the proposed diffuser vanes show a favorable result for both noise and the aerodynamic performance of the centrifugal compressor, and offer a few basic guidelines for the diffuser vane design.
文摘The purpose of this study is to investigate the characteristics of aerodynamic sound generated from wake interference of circular cylinder and airfoil vane located in tandem and to clarify the generation mechanism of the sound source with discrete frequency. The effects of the interval between the cylinder and the airfoil on the characteristics of aerodynamic sound are investigated by acoustic measurement, flow visualization and exploration test of sound source. The relation between the flow field and the sound field with discrete frequency noise（DFN） is shown, and then it is found that the downstream airfoil works as the sound source of DFN, which has the frequency of vortex shedding from the upstream cylinder, when the interval of two bodies is longer than a critical distance.
