A hybrid central-upwind scheme is proposed. Two sub-schemes, the central difference scheme and the Roets flux difference splitting scheme, are hybridized by means of a binary sensor function. In order to examine the c...A hybrid central-upwind scheme is proposed. Two sub-schemes, the central difference scheme and the Roets flux difference splitting scheme, are hybridized by means of a binary sensor function. In order to examine the capability of the proposed hybrid scheme in computing compressible turbulent flow around a curved surface body, especially the flow involving shock wave, three typical eases are investigated by using detached-eddy simulation technique. Numerical results show good agreements with the experimental measurements. The present hybrid scheme can be applied to simulating the compressible flow around a curved surface body involving shock wave and turbulence.展开更多
The supersonic ejector-diffuser system with a second throat was simulated using CFD. An explicit finite volumescheme was aPPlied to solve tWo-dimensional Navier-Stokes equations with standard k - E tulbulence model. T...The supersonic ejector-diffuser system with a second throat was simulated using CFD. An explicit finite volumescheme was aPPlied to solve tWo-dimensional Navier-Stokes equations with standard k - E tulbulence model. Thevacuum Performance of the supersonic ejector-diffuser system was investigated by changing the ejector throat arearatio and the operating Pressure ratio. Two convergent-divergent nozzles with design Mach nUmber of 2. 11 and 3.41were selected to give the supersonic operahon of the ejector-diffoser system. The presence of a second throat stronglyaffected the shock wave sir’UctUI’e inside the "dxing tube as well as the spreading of the under-expanded jetdischarging from the Primary nozzle. There were optimum values of the operating pressure ratio and ejector throatarea ratio for the vacuum performance of the system to maximize.展开更多
Air jet loom, as one of the shuttleless looms, transports a yam into warps using viscosity and kinetic energy of an air jet. Performance of this picking system depends on the ability of instantaneous inhalation/exhaus...Air jet loom, as one of the shuttleless looms, transports a yam into warps using viscosity and kinetic energy of an air jet. Performance of this picking system depends on the ability of instantaneous inhalation/exhaust, configuration of nozzle, operation characteristics of a check valve, etc. In the recent past, many studies have been reported on the air jet discharged from a nozzle exit, but studies for understanding the flow field characteristics associated with shear layer and shock wave/boundary layer interaction in the nozzle were not conducted enough. In this paper, a computational study was performed to explain the flow field in the air jet nozzle with an acceleration tube and validated with previous experimental data available. The results obtained from the computational study show that, in the supersonic flow regime, the flow field depends significantly on the length of acceleration tube. As nozzle pressure ratio increases, drag force acting on the string also increases. For a longer acceleration tube, the total pressure loss is large, owing to the frictional loss.展开更多
In the present study, the flow visualizations were performed around the NACA 0012 models which differ in aspect ratios. We discussed the effects of the aspect ratio in the test models. Additionally the unsteady, two-d...In the present study, the flow visualizations were performed around the NACA 0012 models which differ in aspect ratios. We discussed the effects of the aspect ratio in the test models. Additionally the unsteady, two-dimensional, compressible Euler equations were solved for the NACA 0012 airfoil. Experiments were performed utilizing the conventional gas driven shock tube as the intermittent transonic wind tunnel. The aspect ratios of the models are about 0.86 and 1.5, respectively. The Mach numbers M 2 are about 0.84. The Reynolds numbers of the present experimental conditions were constant that Re based on chord length is about 4.0×10 5 . The results are as follows: in different aspect ratios, the difference of the shock wave location is confirmed though the Mach number and Reynolds number are same. It indicates the different correction Mach number by the effects of the side wall boundary layer though the nominal Mach number measured the same value. Also, on the difference of shock wave location for the effects of the aspect ratio, the tend of CFD shows the qualitative agreement with the result of an experiment.展开更多
We propose and demonstrate a reconfigurable and single-shot incoherent optical signal processing system for chirped microwave signal compression, using a programmable optical filter and a multiwavelength laser(MWL). T...We propose and demonstrate a reconfigurable and single-shot incoherent optical signal processing system for chirped microwave signal compression, using a programmable optical filter and a multiwavelength laser(MWL). The system is implemented by temporally modulating a specially shaped MWL followed by a suitable linear dispersive medium. A microwave dispersion value up to 1.33 ns/GHz over several GHz bandwidth is achieved based on this approach. Here we demonstrate a singleshot compression for different linearly chirped microwave signals over several GHz bandwidth. In addition, the robustness of the proposed system when input RF signals are largely distorted is also discussed.展开更多
基金Supported by the National Science Foundation for Post-doctoral Scientists of China(20100481141,201104567)the Natural Science Foundation of Jiangsu Province(BK2011723)the Planned Projects for Postdoctoral Research Foundation of Jiangsu Province(0902001C)~~
文摘A hybrid central-upwind scheme is proposed. Two sub-schemes, the central difference scheme and the Roets flux difference splitting scheme, are hybridized by means of a binary sensor function. In order to examine the capability of the proposed hybrid scheme in computing compressible turbulent flow around a curved surface body, especially the flow involving shock wave, three typical eases are investigated by using detached-eddy simulation technique. Numerical results show good agreements with the experimental measurements. The present hybrid scheme can be applied to simulating the compressible flow around a curved surface body involving shock wave and turbulence.
文摘The supersonic ejector-diffuser system with a second throat was simulated using CFD. An explicit finite volumescheme was aPPlied to solve tWo-dimensional Navier-Stokes equations with standard k - E tulbulence model. Thevacuum Performance of the supersonic ejector-diffuser system was investigated by changing the ejector throat arearatio and the operating Pressure ratio. Two convergent-divergent nozzles with design Mach nUmber of 2. 11 and 3.41were selected to give the supersonic operahon of the ejector-diffoser system. The presence of a second throat stronglyaffected the shock wave sir’UctUI’e inside the "dxing tube as well as the spreading of the under-expanded jetdischarging from the Primary nozzle. There were optimum values of the operating pressure ratio and ejector throatarea ratio for the vacuum performance of the system to maximize.
文摘Air jet loom, as one of the shuttleless looms, transports a yam into warps using viscosity and kinetic energy of an air jet. Performance of this picking system depends on the ability of instantaneous inhalation/exhaust, configuration of nozzle, operation characteristics of a check valve, etc. In the recent past, many studies have been reported on the air jet discharged from a nozzle exit, but studies for understanding the flow field characteristics associated with shear layer and shock wave/boundary layer interaction in the nozzle were not conducted enough. In this paper, a computational study was performed to explain the flow field in the air jet nozzle with an acceleration tube and validated with previous experimental data available. The results obtained from the computational study show that, in the supersonic flow regime, the flow field depends significantly on the length of acceleration tube. As nozzle pressure ratio increases, drag force acting on the string also increases. For a longer acceleration tube, the total pressure loss is large, owing to the frictional loss.
文摘In the present study, the flow visualizations were performed around the NACA 0012 models which differ in aspect ratios. We discussed the effects of the aspect ratio in the test models. Additionally the unsteady, two-dimensional, compressible Euler equations were solved for the NACA 0012 airfoil. Experiments were performed utilizing the conventional gas driven shock tube as the intermittent transonic wind tunnel. The aspect ratios of the models are about 0.86 and 1.5, respectively. The Mach numbers M 2 are about 0.84. The Reynolds numbers of the present experimental conditions were constant that Re based on chord length is about 4.0×10 5 . The results are as follows: in different aspect ratios, the difference of the shock wave location is confirmed though the Mach number and Reynolds number are same. It indicates the different correction Mach number by the effects of the side wall boundary layer though the nominal Mach number measured the same value. Also, on the difference of shock wave location for the effects of the aspect ratio, the tend of CFD shows the qualitative agreement with the result of an experiment.
基金supported by research grants from NSERC(Canada)agenciesalso partly supported by the National Natural Science Foundation of China(61522509,61377002 and 61090391)+2 种基金Beijing Natural Science Foundation(4152052)the National High-Tech Research and Development Program of China(2015AA017102)M.L.was supported partly by the Thousand Young Talent Program
文摘We propose and demonstrate a reconfigurable and single-shot incoherent optical signal processing system for chirped microwave signal compression, using a programmable optical filter and a multiwavelength laser(MWL). The system is implemented by temporally modulating a specially shaped MWL followed by a suitable linear dispersive medium. A microwave dispersion value up to 1.33 ns/GHz over several GHz bandwidth is achieved based on this approach. Here we demonstrate a singleshot compression for different linearly chirped microwave signals over several GHz bandwidth. In addition, the robustness of the proposed system when input RF signals are largely distorted is also discussed.
