To achieve a detailed understanding of underexpanded supersonic jet structures influenced by afterburning and other flow conditions, the underexpanded turbulent supersonic jet with and without combustions are investig...To achieve a detailed understanding of underexpanded supersonic jet structures influenced by afterburning and other flow conditions, the underexpanded turbulent supersonic jet with and without combustions are investigated by computational fluid dynamics （CFD） method. A program based on a total variation diminishing （TVD） methodology capable of predicting complex shocks is created to solve the axisymmetric expanded Navie^Stokes equations containing transport equations of species. The finite-rate ratio model is employed to handle species sources in chemical reactions. CFD solutions indicate that the structure of underexpanded jet is typically influenced by the pressure ratio and afterburning. The shock reflection distance and maximum value of Mach number in the first shock cell increase with pressure ratio. Chemical reactions for the rocket exhaust mostly exist in the mixing layer of supersonic jet flows. This tends to reduce the intensity of shocks existing in the jet, responding to the variation of thermal parameters.展开更多
BACKGROUND:Stent under-expansion is a main cause of acute coronary syndrome(ACS),which can lead to serious clinical outcomes.The rotational atherectomy of underexpanded coronary stents(academically called stent ablati...BACKGROUND:Stent under-expansion is a main cause of acute coronary syndrome(ACS),which can lead to serious clinical outcomes.The rotational atherectomy of underexpanded coronary stents(academically called stent ablation,SA)by intravascular ultrasound(IVUS)may provide more visual reference in the intervention.We aim to analyze the procedural and long-term outcomes of the optimized strategy of SA in patients with ACS and to provide real-world data on this technique.METHODS:A total of 11 patients with ACS who underwent SA between April 2017 and January 2019 were analyzed.Clinical follow-ups were obtained either by telephone call or by scheduled visit.Clinical end-points included periprocedural and postprocedural myocardial infarction,stent thrombosis,target lesion revascularization,and major adverse cardiac events.RESULTS:The mean age of patients was 69.6±6.5 years,and five(45.5%)patients were males.All cases presented with unstable angina and were admitted with ACS.All patients required at least two burrs during the intervention and the size of the burr was selected based on the data of minimum lumen diameter(MLD),and the fi rst and the second burr/stent MLD ratios were 0.93(0.88-0.99)and 1.09(1.02-1.14),respectively.Nine patients were treated with drug-eluting stents and two were treated with drug-coated balloons.There were no complications including no fl ow,perforation,or burr entrapment during the intervention.No in-hospital deaths or major adverse cardiac events were documented during the follow-up period.In our study,less contrast agent and a lower dose of radiation were used during the intervention.CONCLUSIONS:SA guided by IVUS can reduce the risk of complications,assess the results of surgery,inform the selection of stent size,and decrease the required dose of radiation and contrast.展开更多
An underexpanded jet has typical shock-cell structure and strongly oscillates, its behavior being known to cause many industrial problems. An underexpanded jet radially issues from intake and exhaust valves of an inte...An underexpanded jet has typical shock-cell structure and strongly oscillates, its behavior being known to cause many industrial problems. An underexpanded jet radially issues from intake and exhaust valves of an internal combustion engine, a pressure control valve and so on. When a supersonic jet exhausted from a circular nozzle impinges on a flat plate, the wall jet formed on the plate often becomes underexpanded and spreads out radially. Such underexpanded impinging jet is one of models of supersonic jets on laser cutting process and glass tempering process. In this study, an underexpanded jet radially discharged from a circular slit nozzle, which consists of two cylinders, was experimentally examined for different nozzle pressure ratios and for different diameters of cylinder. Jet structure was analyzed by means of a visualization e.g. Schlieren method. A noise emitted from the jet was measured and the frequency of screech tone was analyzed. The experimental results were compared with those of a two dimensional jet issuing from a rectangular nozzle. Furthermore, a comparison of visualized sound waves with the screech tone frequency reveals that the sound source measured was in the vicinity of the end of the second cell and that the length of the second or third cell was one of the most important parameters to determine the frequency of the emitted screech tone.展开更多
The oscillatory motions of shocks in highly underexpanded jets with nozzle pressure ratios of 5.60, 7.47, 9.34, and11.21 are quantitatively studied by using large eddy simulation. Two types of shock oscillations are o...The oscillatory motions of shocks in highly underexpanded jets with nozzle pressure ratios of 5.60, 7.47, 9.34, and11.21 are quantitatively studied by using large eddy simulation. Two types of shock oscillations are observed： one is the Mach disk oscillation in the streamwise direction and the other is the shock oscillation in the radial direction. It is found that the Mach disk moves quickly in the middle of the oscillatory region but slowly at the top or bottom boundaries. The oscillation cycles of Mach disk are the same for different cases, and are all dominated by an axisymmetric mode of 5.298 k Hz. For the oscillation in the radial direction, the shocks oscillate more toward the jet centerline but less in the jet shear layer, and the oscillation magnitude is an increasing function of screech amplitude. The cycles of the radial shock oscillation switch randomly between the two screech frequencies for the first two cases. However, the oscillation periodicity is more complex for the jets with high nozzle pressure ratios of 9.34 and 11.21 than for the jets with the low nozzle pressure ratios of 5.6 and 7.47. In addition, the shock oscillation characteristics are also captured by coarse mesh and Smagorinsky model,but the coarse mesh tends to predict a slower and weaker shock oscillation.展开更多
In this study, flow characteristics are experimentally and numerically discussed, especially concerning shock-cell structure and oscillatory phenomena of supersonic jet. The jet becomes underexpanded when the nozzle p...In this study, flow characteristics are experimentally and numerically discussed, especially concerning shock-cell structure and oscillatory phenomena of supersonic jet. The jet becomes underexpanded when the nozzle pressure ratio of convergent nozzle exceeds the critical value. The underexpanded jet is not uniform because of the presence of the expansion wave, the compression wave and the shock wave formed in it. Many vortices are induced in jet boundary region by shearing stress generated between supersonic jet flow and atmospheric air. They interact with shock waves composing cell node of jet, which is closely related to a noise radiating from the jet. In experiment, flow field is visualized and the shape of cell structure is examined. Furthermore, frequency of vortex generation is measured. The jet is simulated using TVD scheme and the results are compared with the experimental ones. Distortion of cell structure caused by three dimensional oscillation of jet and behavior of vortices are discussed.展开更多
This study focuses on a noise emitted from a radial underexpanded jet. The underexpanded jet is well known as one of supersonic jets and it is formed when the pressure ratio across a convergent nozzle is more than the...This study focuses on a noise emitted from a radial underexpanded jet. The underexpanded jet is well known as one of supersonic jets and it is formed when the pressure ratio across a convergent nozzle is more than the critical value. The underexpanded jet has been used in many fields, such a propulsion of rocket, laser cutting and a glass tempering process. Such jet is exhausted from a circular nozzle. The expansion wave, the compression wave and the shock wave are periodically formed in the jet, which leads to quasi-periodical shock-cell structure. On the other hand, an underexpanded jet radially issues from intake and exhaust valves of an internal combustion engine and a pressure control valve. The radial underexpanded jet does not have the quasi- periodical shock-cell structure such as the jet from the circular nozzle, its cell length decreasing along jet axis. In this study, an underexpanded jet radially discharged from a circular slit nozzle, which consists of two circular tubes, is experimentally examined for different nozzle pressure ratios. The jet structure is visualized using Schlieren method and a noise emitted from the jet is measured. Typically, the shock associated broadband noise is analyzed and a relation between the jet structure and the radiation noise frequency is discussed. As a result, it is found that the broadband noise lies on lower frequency than a screech tone and that the 1st cell length plays an important role in broadband noise radiation.展开更多
In this study, an underexpanded radial jet issuing from a small gap between two circular tubes facing each other is investigated numerically. Radial jet is formed, for example, downstream of high-pressure valves in pi...In this study, an underexpanded radial jet issuing from a small gap between two circular tubes facing each other is investigated numerically. Radial jet is formed, for example, downstream of high-pressure valves in piping system and of poppet valves in engines, and causes many industrial problems such as the noise generation and the fatigue failure of structure. In this study, the jet issuing from a small gap between two tubes with same diameter is numerically simulated. The flow field is assumed to be axisymmetric against the central axis of tubes and to be symmetric against the intermediate plane between the exits of two tubes. The axisymmetric Euler equations are solved using symmetric TVD (Total Variation Diminishing) scheme. The effects of nozzle pressure ratio and of diameter of circular tubes on the structure and the behavior of jets are examined. Typical cell structure of underexpanded jet appears in radial jet and the length of cell becomes smaller in downstream region because the jet spreads radially like a disc. The length and width of first cell are larger with higher nozzle pressure ratio. Many vortices are generated one after another near the jet boundary and move downstream, which cause the oscillation of jet. Outside of jet, two types of density waves are observed. One of them propagates toward the nozzle (toward the upstream region) and the other propagates in opposite direction. Focusing on the pressure change caused by the former waves, which is related to well-known screech, dominant frequency obtained by FFT analysis was found to become lower with higher pressure ratio and smaller diameter of tube.展开更多
The three-dimensional visualization of flow and screech-tone emission from an underexpanded circular jet is first investigated experimentally using high-speed cross-schlieren imaging and microphone measurements in the...The three-dimensional visualization of flow and screech-tone emission from an underexpanded circular jet is first investigated experimentally using high-speed cross-schlieren imaging and microphone measurements in the cross-sectional planes along the jet axis. This experimental technique allows the visualization of the shock-cell structure, directivity of sound intensity, and frequency spectrum in the cross-sectional planes of the screeching jet. The high-speed cross-schlieren observation of the screeching jet shows the occurrence of an asymmetrical shock-cell structure that is generated by the flapping mode in the screeching jet. This contributes to the generation of a screech tone propagating upstream along the jet axis and non-uniform sound intensities around the jet in circumferential direction. These observations by high-speed cross</span><span style="white-space:normal;font-size:10pt;font-family:"">-</span><span style="white-space:normal;font-size:10pt;font-family:"">schlieren imaging were validated by the microphone measurements.展开更多
Highly undcrexpanded axisymmctric jet was simulated using the Runge-Kutta Discontinuous Galerkin （RKDG） finite element method, which, based on two-dimensional conservation laws, was used to solve the axisymmetric Eu...Highly undcrexpanded axisymmctric jet was simulated using the Runge-Kutta Discontinuous Galerkin （RKDG） finite element method, which, based on two-dimensional conservation laws, was used to solve the axisymmetric Euler equations. The computed results show that the complicated flow field structures of interest, including shock waves, slipstreams and the triple point observed in experiments could be well captured using the RKDG finite element method. Moreover, comparisons of the Mach disk location exhibit excellent agreements between the computed results and experimental measurements, indicating that this method has high capability of capturing shocks without numerical oscillation and artificial viscosity occurring near the discontinuous point.展开更多
When the high-pressure gas is exhausted to the vacuum chamber from the nozzle,the underexpanded supersonic jet contained with the Mach disk is generally formed.The eventual purpose of this study is to clarify the unst...When the high-pressure gas is exhausted to the vacuum chamber from the nozzle,the underexpanded supersonic jet contained with the Mach disk is generally formed.The eventual purpose of this study is to clarify the unsteady phenomenon of the underexpanded free jet when the back pressure continuously changes with time.The characteristic of the Mach disk has been clarified in consideration of the diameter and position of it by the numerical analysis in this paper.The sonic jet of the exit Mach number Me=1 is assumed and the axisymmetric conservational equation is solved by the TVD method in the numerical calculation.The diameter and position of the Mach disk differs with the results of a steady jet and the influence on the continuously changing of the back pressure is evidenced from the comparison with the case of steady supersonic jet.展开更多
The numerical analysis of a turbulent sonic jet from a two-dimensional convergent nozzle has been carried out using the compressible k-? turbulence model and TVD finite difference scheme. Numerical conditions have bee...The numerical analysis of a turbulent sonic jet from a two-dimensional convergent nozzle has been carried out using the compressible k-? turbulence model and TVD finite difference scheme. Numerical conditions have been varied over a range of operating pressure ratios from 1.893 to 6.0 which cover the jet flow conditions from correctly expanded to underexpanded. Numerical flow visualization of sonic jet structure using the computer schlieren, a relation between shock cell length in the jet with the operating pressure ratio and the pressure distribution along jet centerline are obtained. Also, a transition process of a two-dimensional sonic jet from correctly expanded to underexpanded conditions is shown in detail and a flow model of jet structure is proposed.展开更多
基金supported by the National Natural Science Foundation of China (No. 51306019)
文摘To achieve a detailed understanding of underexpanded supersonic jet structures influenced by afterburning and other flow conditions, the underexpanded turbulent supersonic jet with and without combustions are investigated by computational fluid dynamics （CFD） method. A program based on a total variation diminishing （TVD） methodology capable of predicting complex shocks is created to solve the axisymmetric expanded Navie^Stokes equations containing transport equations of species. The finite-rate ratio model is employed to handle species sources in chemical reactions. CFD solutions indicate that the structure of underexpanded jet is typically influenced by the pressure ratio and afterburning. The shock reflection distance and maximum value of Mach number in the first shock cell increase with pressure ratio. Chemical reactions for the rocket exhaust mostly exist in the mixing layer of supersonic jet flows. This tends to reduce the intensity of shocks existing in the jet, responding to the variation of thermal parameters.
基金the Chongqing Health Commission(2016ZDXM024)the Zhejiang Provincial Public Welfare Technology Research Project(LGF20H020012)the Scientifi c Research Project of the Department of Education in Zhejiang(Y21330290).
文摘BACKGROUND:Stent under-expansion is a main cause of acute coronary syndrome(ACS),which can lead to serious clinical outcomes.The rotational atherectomy of underexpanded coronary stents(academically called stent ablation,SA)by intravascular ultrasound(IVUS)may provide more visual reference in the intervention.We aim to analyze the procedural and long-term outcomes of the optimized strategy of SA in patients with ACS and to provide real-world data on this technique.METHODS:A total of 11 patients with ACS who underwent SA between April 2017 and January 2019 were analyzed.Clinical follow-ups were obtained either by telephone call or by scheduled visit.Clinical end-points included periprocedural and postprocedural myocardial infarction,stent thrombosis,target lesion revascularization,and major adverse cardiac events.RESULTS:The mean age of patients was 69.6±6.5 years,and five(45.5%)patients were males.All cases presented with unstable angina and were admitted with ACS.All patients required at least two burrs during the intervention and the size of the burr was selected based on the data of minimum lumen diameter(MLD),and the fi rst and the second burr/stent MLD ratios were 0.93(0.88-0.99)and 1.09(1.02-1.14),respectively.Nine patients were treated with drug-eluting stents and two were treated with drug-coated balloons.There were no complications including no fl ow,perforation,or burr entrapment during the intervention.No in-hospital deaths or major adverse cardiac events were documented during the follow-up period.In our study,less contrast agent and a lower dose of radiation were used during the intervention.CONCLUSIONS:SA guided by IVUS can reduce the risk of complications,assess the results of surgery,inform the selection of stent size,and decrease the required dose of radiation and contrast.
文摘An underexpanded jet has typical shock-cell structure and strongly oscillates, its behavior being known to cause many industrial problems. An underexpanded jet radially issues from intake and exhaust valves of an internal combustion engine, a pressure control valve and so on. When a supersonic jet exhausted from a circular nozzle impinges on a flat plate, the wall jet formed on the plate often becomes underexpanded and spreads out radially. Such underexpanded impinging jet is one of models of supersonic jets on laser cutting process and glass tempering process. In this study, an underexpanded jet radially discharged from a circular slit nozzle, which consists of two cylinders, was experimentally examined for different nozzle pressure ratios and for different diameters of cylinder. Jet structure was analyzed by means of a visualization e.g. Schlieren method. A noise emitted from the jet was measured and the frequency of screech tone was analyzed. The experimental results were compared with those of a two dimensional jet issuing from a rectangular nozzle. Furthermore, a comparison of visualized sound waves with the screech tone frequency reveals that the sound source measured was in the vicinity of the end of the second cell and that the length of the second or third cell was one of the most important parameters to determine the frequency of the emitted screech tone.
基金Project supported by the National Natural Science Foundation of China(Grant No.11602028)the Science and Technology Project of General Administration of Quality Supervision Inspection and Quarantine of China(Grant Nos.2017QK119 and 2017QK188)
文摘The oscillatory motions of shocks in highly underexpanded jets with nozzle pressure ratios of 5.60, 7.47, 9.34, and11.21 are quantitatively studied by using large eddy simulation. Two types of shock oscillations are observed： one is the Mach disk oscillation in the streamwise direction and the other is the shock oscillation in the radial direction. It is found that the Mach disk moves quickly in the middle of the oscillatory region but slowly at the top or bottom boundaries. The oscillation cycles of Mach disk are the same for different cases, and are all dominated by an axisymmetric mode of 5.298 k Hz. For the oscillation in the radial direction, the shocks oscillate more toward the jet centerline but less in the jet shear layer, and the oscillation magnitude is an increasing function of screech amplitude. The cycles of the radial shock oscillation switch randomly between the two screech frequencies for the first two cases. However, the oscillation periodicity is more complex for the jets with high nozzle pressure ratios of 9.34 and 11.21 than for the jets with the low nozzle pressure ratios of 5.6 and 7.47. In addition, the shock oscillation characteristics are also captured by coarse mesh and Smagorinsky model,but the coarse mesh tends to predict a slower and weaker shock oscillation.
文摘In this study, flow characteristics are experimentally and numerically discussed, especially concerning shock-cell structure and oscillatory phenomena of supersonic jet. The jet becomes underexpanded when the nozzle pressure ratio of convergent nozzle exceeds the critical value. The underexpanded jet is not uniform because of the presence of the expansion wave, the compression wave and the shock wave formed in it. Many vortices are induced in jet boundary region by shearing stress generated between supersonic jet flow and atmospheric air. They interact with shock waves composing cell node of jet, which is closely related to a noise radiating from the jet. In experiment, flow field is visualized and the shape of cell structure is examined. Furthermore, frequency of vortex generation is measured. The jet is simulated using TVD scheme and the results are compared with the experimental ones. Distortion of cell structure caused by three dimensional oscillation of jet and behavior of vortices are discussed.
文摘This study focuses on a noise emitted from a radial underexpanded jet. The underexpanded jet is well known as one of supersonic jets and it is formed when the pressure ratio across a convergent nozzle is more than the critical value. The underexpanded jet has been used in many fields, such a propulsion of rocket, laser cutting and a glass tempering process. Such jet is exhausted from a circular nozzle. The expansion wave, the compression wave and the shock wave are periodically formed in the jet, which leads to quasi-periodical shock-cell structure. On the other hand, an underexpanded jet radially issues from intake and exhaust valves of an internal combustion engine and a pressure control valve. The radial underexpanded jet does not have the quasi- periodical shock-cell structure such as the jet from the circular nozzle, its cell length decreasing along jet axis. In this study, an underexpanded jet radially discharged from a circular slit nozzle, which consists of two circular tubes, is experimentally examined for different nozzle pressure ratios. The jet structure is visualized using Schlieren method and a noise emitted from the jet is measured. Typically, the shock associated broadband noise is analyzed and a relation between the jet structure and the radiation noise frequency is discussed. As a result, it is found that the broadband noise lies on lower frequency than a screech tone and that the 1st cell length plays an important role in broadband noise radiation.
文摘In this study, an underexpanded radial jet issuing from a small gap between two circular tubes facing each other is investigated numerically. Radial jet is formed, for example, downstream of high-pressure valves in piping system and of poppet valves in engines, and causes many industrial problems such as the noise generation and the fatigue failure of structure. In this study, the jet issuing from a small gap between two tubes with same diameter is numerically simulated. The flow field is assumed to be axisymmetric against the central axis of tubes and to be symmetric against the intermediate plane between the exits of two tubes. The axisymmetric Euler equations are solved using symmetric TVD (Total Variation Diminishing) scheme. The effects of nozzle pressure ratio and of diameter of circular tubes on the structure and the behavior of jets are examined. Typical cell structure of underexpanded jet appears in radial jet and the length of cell becomes smaller in downstream region because the jet spreads radially like a disc. The length and width of first cell are larger with higher nozzle pressure ratio. Many vortices are generated one after another near the jet boundary and move downstream, which cause the oscillation of jet. Outside of jet, two types of density waves are observed. One of them propagates toward the nozzle (toward the upstream region) and the other propagates in opposite direction. Focusing on the pressure change caused by the former waves, which is related to well-known screech, dominant frequency obtained by FFT analysis was found to become lower with higher pressure ratio and smaller diameter of tube.
文摘The three-dimensional visualization of flow and screech-tone emission from an underexpanded circular jet is first investigated experimentally using high-speed cross-schlieren imaging and microphone measurements in the cross-sectional planes along the jet axis. This experimental technique allows the visualization of the shock-cell structure, directivity of sound intensity, and frequency spectrum in the cross-sectional planes of the screeching jet. The high-speed cross-schlieren observation of the screeching jet shows the occurrence of an asymmetrical shock-cell structure that is generated by the flapping mode in the screeching jet. This contributes to the generation of a screech tone propagating upstream along the jet axis and non-uniform sound intensities around the jet in circumferential direction. These observations by high-speed cross</span><span style="white-space:normal;font-size:10pt;font-family:"">-</span><span style="white-space:normal;font-size:10pt;font-family:"">schlieren imaging were validated by the microphone measurements.
文摘Highly undcrexpanded axisymmctric jet was simulated using the Runge-Kutta Discontinuous Galerkin （RKDG） finite element method, which, based on two-dimensional conservation laws, was used to solve the axisymmetric Euler equations. The computed results show that the complicated flow field structures of interest, including shock waves, slipstreams and the triple point observed in experiments could be well captured using the RKDG finite element method. Moreover, comparisons of the Mach disk location exhibit excellent agreements between the computed results and experimental measurements, indicating that this method has high capability of capturing shocks without numerical oscillation and artificial viscosity occurring near the discontinuous point.
文摘When the high-pressure gas is exhausted to the vacuum chamber from the nozzle,the underexpanded supersonic jet contained with the Mach disk is generally formed.The eventual purpose of this study is to clarify the unsteady phenomenon of the underexpanded free jet when the back pressure continuously changes with time.The characteristic of the Mach disk has been clarified in consideration of the diameter and position of it by the numerical analysis in this paper.The sonic jet of the exit Mach number Me=1 is assumed and the axisymmetric conservational equation is solved by the TVD method in the numerical calculation.The diameter and position of the Mach disk differs with the results of a steady jet and the influence on the continuously changing of the back pressure is evidenced from the comparison with the case of steady supersonic jet.
文摘The numerical analysis of a turbulent sonic jet from a two-dimensional convergent nozzle has been carried out using the compressible k-? turbulence model and TVD finite difference scheme. Numerical conditions have been varied over a range of operating pressure ratios from 1.893 to 6.0 which cover the jet flow conditions from correctly expanded to underexpanded. Numerical flow visualization of sonic jet structure using the computer schlieren, a relation between shock cell length in the jet with the operating pressure ratio and the pressure distribution along jet centerline are obtained. Also, a transition process of a two-dimensional sonic jet from correctly expanded to underexpanded conditions is shown in detail and a flow model of jet structure is proposed.
