The supersonic ejector-diffuser system with a second throat was simulated using CFD. A fully implicit finite volume scheme was applied to solve the axisymmetric Navier-Stokes equations and a standard k-E turbulence mo...The supersonic ejector-diffuser system with a second throat was simulated using CFD. A fully implicit finite volume scheme was applied to solve the axisymmetric Navier-Stokes equations and a standard k-E turbulence model was used to close the governing equations. The flow field in the supersonic ejectordiffuser system was investigated by changing the ejector throat area ratio and the secondary mass flow ratio at a fixed operating pressure ratio of 10. A convergent-divergent nozzle with a design Mach number of 2.11 was selected to give the supersonic operation of the ejector-diffuser system. For the constant area mixing tube the secondary mass flow seemed not to significantly change the flow field in the ejector-diffuser systems. It was, however, found that the flow in the ejector-diffuser systems having the second throat is strongly dependent on the secondary mass flow.展开更多
An optimum design of the turbine would need a clear understanding of the influence of blade geometry on a Wells turbine performance. Practically, it is difficult to suggest the optimum geometry for the Wells turbine d...An optimum design of the turbine would need a clear understanding of the influence of blade geometry on a Wells turbine performance. Practically, it is difficult to suggest the optimum geometry for the Wells turbine due to the complex interrelation among important parameters, the solidity, hub-to-tip ratio, aspect ratio, blade sweep of rotor, and so on. In the present study, the effect of blade geometry with the hub-to-tip and aspect ratios of rotor on the turbine performance was investigated with a numerical technique. As a result, the optimum blade geometry is as follows: the hub-to-tip ratio is about 0.7, and the aspect ratio about 0.5 under other constant important parameters, NACA0020 blade with blade sweep ratio of 0.35, and solidity of about 0.67. Furthermore, the detailed flow patterns for blade geometry were also shown and discussed in this paper.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
A safety valve functions to control an upper limit of pressure inside the LNG line of transportation. If the pressure inside the safety valve nozzle exceeds a predetermined value on the valve sheet which plugs the noz...A safety valve functions to control an upper limit of pressure inside the LNG line of transportation. If the pressure inside the safety valve nozzle exceeds a predetermined value on the valve sheet which plugs the nozzle, an excess of LNG discharges through the gap between the nozzle exit and valve sheet. In this situation, the forces acting on the valve sheet are gasdynamic forces generated by the discharge of LNG and mechanical forces supported by the spring behind the valve sheet. The flow through the gap is very complicated, involving vortices, flow separation, and shock waves. These affect adversely on the system accompanying with noise and vibration. The present study aims at understanding the flow physics of safety valve. A computational work using the twodimensional, axisymmetric, compressible Navier-Stokes equations is carried out to simulate the gas flow between the nozzle exit and valve sheet, and compared with the theoretical results. It has been found that there exists a distance between nozzle exit and valve sheet in which the thrust coefficient at the valve sheet increases abruptly.展开更多
When condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, a condensing flow was produced by an expansion of moist air in a supersonic circular nozzle,...When condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, a condensing flow was produced by an expansion of moist air in a supersonic circular nozzle, and, by inserting a wedge-type shock generator placed in the supersonic part of the nozzle, the experimental investigations were carried out to clarify the effect of condensation on the normal shock wave and the boundary layer. As a result, the position of the shock wave relative to the condensation zone was discussed, together with the effect of condensation on pressure fiuctuations. Furthermore, a compressible viscous two-phase flow of moist air in a supersonic half nozzle was calculated to investigate the effect of condensation on boundary layer.展开更多
When non-equilibrium condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, in order to control the transonic flow field with shock wave, a condensing f...When non-equilibrium condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, in order to control the transonic flow field with shock wave, a condensing flow was produced by an expansion of moist air on a circular bump model and shock waves were occurred in the supersonic parts of the fields. Furthermore, the additional passive technique of shock / boundary layer interaction using the porous wall with a cavity underneath was adopted in this flow field. The effects of these methods on the shock wave characteristics were investigated numerically and experimentally. The result obtained showed that the total pressure loss in the flow fields might be effectively reduced by the suitable combination between non-equilibrium condensation and the position of porous wall.展开更多
In many engineering practices, frequently an impulsive wave is a consequence of discharge of a shockwave from the exit of a tube, leading to an annoying noise like a sonic boom. The impulsive noisehas often been a maj...In many engineering practices, frequently an impulsive wave is a consequence of discharge of a shockwave from the exit of a tube, leading to an annoying noise like a sonic boom. The impulsive noisehas often been a major factor to limit the performance of flow devices as well as to affect hazardousinfluences on human being. The current paper describes a new control method for the reduction ofimpulsive wave. An experiment using a simple shock tube was carried out to examine the effect of acavity/helical vane system on the impulsive wave strength. The resulting impulsive wave was influencedby the detailed configuration of the belieal vane inside the cavity which is located at the vicinity ofthe exit of a tube. The effect of the belieal vane was compared with no belieal vane tests to ensurevalidation of this kind of control strategy. The results showed that the strength of the impulsive wavecould be significantly reduced by the current passive control using the cavity/helical vane system.展开更多
A Wells turbine for wave power conversion has hysteretic characteristics in a reciprocating flow. The hysteretic loop is opposite to the well-known dynamic stall of an airfoil. In this paper, the mechanism of the hyst...A Wells turbine for wave power conversion has hysteretic characteristics in a reciprocating flow. The hysteretic loop is opposite to the well-known dynamic stall of an airfoil. In this paper, the mechanism of the hysteretic behavior was elucidated by an unsteady 3-dimensional Navier-Stokes numerical simulation. It was found that the hysteretic behavior was associated with a streamwise vortical flow appearing near the blade suction surface. The effects of hub-to-tip ratio and tip clearance on the hysteretic characteristics of the Wells turbine have also been discussed in this paper.展开更多
When the high-pressure gas is exhausted to the vacuum chamber from the supersonic nozzle, the overexpanded supersonic jet is formed at specific condition. In two-dimensional supersonic jet, furthermore, it is known th...When the high-pressure gas is exhausted to the vacuum chamber from the supersonic nozzle, the overexpanded supersonic jet is formed at specific condition. In two-dimensional supersonic jet, furthermore, it is known that the hysteresis phenomena for the reflection type of shock wave in the flow field is occurred under the quasi-steady flow and for instance, the transitional pressure ratio between the regular reflection （RR） and Mach reflection （MR） is affected by this phenomenon. Many papers have described the hysteresis phenomena for underexpanded supersonic jet, but this phenomenon under the overexpanded axisymmetric jet has not been detailed in the past papers. The purpose of this study is to clear the hysteresis phenomena for the reflection type of shock wave at the overexpanded axisymmetric jet using the TVD method and to discuss the characteristic of hysteresis phenomena.展开更多
The objective of this paper is to compare the performances of the themes, which could be used for wave energy conversion in the near future, under various irregular wave conditions. The turbines included in the paper ...The objective of this paper is to compare the performances of the themes, which could be used for wave energy conversion in the near future, under various irregular wave conditions. The turbines included in the paper are as follows: (a) Wells turbine with guide vanes; (b) impulse turbine with self-pitch-controlled guide vanes; (c) impulse turbine with fixed guide vanes. In this study, experimental investigations were carried out to clarify the performances of the turbines under steady flow conditions, and then a numerical simulation was used for predicting the performances under irregular wave conditions with various significant wave heights. As a result it was found that the running and starting characteristics of the impulse turbines could be superior to those of the Wells turbine.展开更多
The total efficiency of power plants depends on the energy conversion in a combustor and a turbine .Considerably higher energy transfer rates can be obtained from a pulsed combustion.but unsteady flow of a single jet ...The total efficiency of power plants depends on the energy conversion in a combustor and a turbine .Considerably higher energy transfer rates can be obtained from a pulsed combustion.but unsteady flow of a single jet combustor reduces the turbine efficiency.Therefore.two pulse combustors were set in parallel and connected to a settling chamber that supplies a flow with constant pressure to the turbine.The aim of investigations presented here is a demonstration of technical feasibility for industrial applications and to show the benefits obtained from the pulse combustors.展开更多
A compression wave discharged from an open end of a tube causes positive impulsive noise. Active noise cancellation which is the canceling of the noise by the addition of an inverse wave is a useful technique for redu...A compression wave discharged from an open end of a tube causes positive impulsive noise. Active noise cancellation which is the canceling of the noise by the addition of an inverse wave is a useful technique for reducing impulsive noise. The main objective of this study is to present the design for a negative impulsive wave generator utilizing unsteady mass influx. In this paper, in order to clarify the relationship between the unsteady mass influx and the negative impulsive wave! numerical and aeroacoustic analyses have been carried out using an unsteady expansion wave discharged from an open end of a shock tube. As a result, the effect of an unsteady expansion wave on a negative impulsive wave was clarified.展开更多
In order to investigate the effectiveness of an orifice system in producing pressure drops and the effect of compressibility on the pressure drop, computations using the mass-averaged implicit Navier-Stokes equations ...In order to investigate the effectiveness of an orifice system in producing pressure drops and the effect of compressibility on the pressure drop, computations using the mass-averaged implicit Navier-Stokes equations were applied to the axisymmetric pipe flows with the operating pressure ratio from 1.5 to 20.0. The standard k- ε turbulence model was employed to close the governing equations. Numerical calculations were carried out for some combinations of the multiple orifice configurations. The present CFD data showed that the orifice systems, which have been applied to incompressible flow regime to date, could not be used for the high operating pressure ratio flows. The orifice interval did not strongly affect the total pressure drop, but the orifice area ratio more than 2.5 led to relatively high pressure drops. The total pressure drop rapidly increased in the range of the operating pressure ratio from 1.5 to 4.0, but it nearly did not increase when the operating pressure ratio was over 4.0. In the compressible pipe flows through double and triple orifice systems, the total pressure drop was largely due to shock losses.展开更多
In this paper,the effect of geometries of tube open end on the shock,compression and expansion wavespropagating in the tube was investigated numerically and experimentally.One of them is a conventional straightshock t...In this paper,the effect of geometries of tube open end on the shock,compression and expansion wavespropagating in the tube was investigated numerically and experimentally.One of them is a conventional straightshock tube with an open end.The other has a divergent tail tube at the exit.Applying a divergent tail tube(flaretube)to an open end shock tube,the period of one-cycle process could be shortened and the pressure behind theexpansion wave produced at the exit of the shock tube could be lowered much more below the atmosphericpressure than that produced in the straight tube.The results suggested that the intake air into the engine wassignificantly increased by applying a flare tube instead of a straight tube.展开更多
The Phenomena of the interaction between a supersonic jet and an obstacle is a very interesting and important problem relating to the industrial engineering. This paper aims to investigate the characteristics of the t...The Phenomena of the interaction between a supersonic jet and an obstacle is a very interesting and important problem relating to the industrial engineering. This paper aims to investigate the characteristics of the two-dimensional temperature distribution on an inclined plate surface and the relation between the temperature distribution and some shock waves formed in the flow field. In this study, the measurement of temperature distribution on an inclined plate surface and the now visualization has carried out for various conditions using the thermo-sensitive liquid crystal sheet and the schlieren method. The two dimensional temperature distribution on the plate surface is clearly obtained by the thermo-sensitive liquid crystal sheet. The relation between the temperature distribution on an inclined plate surface and some shock waves reached at a plate surface is discussed. In this paper, the characteristics of the temperature distribution and the maximum temperature, and some other experimental evidences are presented.展开更多
A computational investigation has been conducted to determine the effectiveness of a passive control technique of attenuating cavity-induced pressure oscillations in a confined two-dimensional supersonic flow. The pas...A computational investigation has been conducted to determine the effectiveness of a passive control technique of attenuating cavity-induced pressure oscillations in a confined two-dimensional supersonic flow. The passive control technique is achieved by fitting two flat plates near the front wall of a square cavity at Mach number 1.83 at the cavity entrance. The results showed that the flat plates attached near the front wall of the cavity, discouraged the formation of feedback loop which is widely believed to be the reason of cavity resonance. The resultant amount of attenuation of pressure oscillations was also dependent on the length of the flat plate used as an oscillation suppressor.展开更多
A rapid expansion of moist air or steam in a supersonic nozzle gives rise to nonequilibrium condensation phenomena. Thereby, if the heat released by condensation of water vapour exceeds a certain quantity, the flow wi...A rapid expansion of moist air or steam in a supersonic nozzle gives rise to nonequilibrium condensation phenomena. Thereby, if the heat released by condensation of water vapour exceeds a certain quantity, the flow will become unstable and periodic flow oscillations of the unsteady condensation shock wave will occur. For the passive control of shock-boundary layer interaction using the porous wall with a plenum underneath, many papers have been presented on the application of the technique to transonic airfoil flows. In this paper, the passive technique is applied to three types of oscillations of the unsteady condensation shock wave generated in a supersonic nozzle in order to suppress the unsteady behavior As a result, the effects of number of slits and length of cavity on the aspect of flow field have been clarified numerically using a 3rd-order MUSCL type TVD finite-difference scheme with a second-order fractional-step for time integration.展开更多
When an expansion wave propagated along a constant area straight tube reaches at the open end, the negative impulsive wave and the compression wave are formed by the emission and reflection of expansion wave. The nega...When an expansion wave propagated along a constant area straight tube reaches at the open end, the negative impulsive wave and the compression wave are formed by the emission and reflection of expansion wave. The negative impulsive wave is emitted toward the surrounding area and causes an impulsive noise like the sonic boom. The compression wave propagates in the tube toward the upstream and may cause the impulsive noise at the surrounding area of tube portal. With the advance of industrial engineering, it seems that the discharging of the expansion wave will become important problems. In this study, the experimental and numerical investigations are carried out using the shock tube and the TVD numerical method. The formation process of compression wave near the open end, the relationship with the compression wave and the expansion wave and the characteristics of compression wave are discussed.展开更多
The time-dependent behavior of non-equilibrium condensation of moist air through a Ludwieg tube with a diaphragm downstream is investigated by using a computational fluid dynamics work. The two-dimensional, compressib...The time-dependent behavior of non-equilibrium condensation of moist air through a Ludwieg tube with a diaphragm downstream is investigated by using a computational fluid dynamics work. The two-dimensional, compressible, Navier-Stokes equations, fully coupled with the condensate droplet growth equations, are numerically solved by a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. Baldwin-Lomax turbulence model is employed to close the governing equations. The present computations represent the experimental flows well. The results obtained show that for an initial relative humidity over 40 %, the periodic excursions of the condensation shock occurs in the Ludwieg tube, and the frequency increases with the initial relative humidity. It is also found that total pressure loss due to non-equilibrium condensation in the Ludwieg tube should not be ignored even for a very low initial relative humidity. Furthermore, the variations of condensation properties are also展开更多
文摘The supersonic ejector-diffuser system with a second throat was simulated using CFD. A fully implicit finite volume scheme was applied to solve the axisymmetric Navier-Stokes equations and a standard k-E turbulence model was used to close the governing equations. The flow field in the supersonic ejectordiffuser system was investigated by changing the ejector throat area ratio and the secondary mass flow ratio at a fixed operating pressure ratio of 10. A convergent-divergent nozzle with a design Mach number of 2.11 was selected to give the supersonic operation of the ejector-diffuser system. For the constant area mixing tube the secondary mass flow seemed not to significantly change the flow field in the ejector-diffuser systems. It was, however, found that the flow in the ejector-diffuser systems having the second throat is strongly dependent on the secondary mass flow.
文摘An optimum design of the turbine would need a clear understanding of the influence of blade geometry on a Wells turbine performance. Practically, it is difficult to suggest the optimum geometry for the Wells turbine due to the complex interrelation among important parameters, the solidity, hub-to-tip ratio, aspect ratio, blade sweep of rotor, and so on. In the present study, the effect of blade geometry with the hub-to-tip and aspect ratios of rotor on the turbine performance was investigated with a numerical technique. As a result, the optimum blade geometry is as follows: the hub-to-tip ratio is about 0.7, and the aspect ratio about 0.5 under other constant important parameters, NACA0020 blade with blade sweep ratio of 0.35, and solidity of about 0.67. Furthermore, the detailed flow patterns for blade geometry were also shown and discussed in this paper.
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A safety valve functions to control an upper limit of pressure inside the LNG line of transportation. If the pressure inside the safety valve nozzle exceeds a predetermined value on the valve sheet which plugs the nozzle, an excess of LNG discharges through the gap between the nozzle exit and valve sheet. In this situation, the forces acting on the valve sheet are gasdynamic forces generated by the discharge of LNG and mechanical forces supported by the spring behind the valve sheet. The flow through the gap is very complicated, involving vortices, flow separation, and shock waves. These affect adversely on the system accompanying with noise and vibration. The present study aims at understanding the flow physics of safety valve. A computational work using the twodimensional, axisymmetric, compressible Navier-Stokes equations is carried out to simulate the gas flow between the nozzle exit and valve sheet, and compared with the theoretical results. It has been found that there exists a distance between nozzle exit and valve sheet in which the thrust coefficient at the valve sheet increases abruptly.
文摘When condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, a condensing flow was produced by an expansion of moist air in a supersonic circular nozzle, and, by inserting a wedge-type shock generator placed in the supersonic part of the nozzle, the experimental investigations were carried out to clarify the effect of condensation on the normal shock wave and the boundary layer. As a result, the position of the shock wave relative to the condensation zone was discussed, together with the effect of condensation on pressure fiuctuations. Furthermore, a compressible viscous two-phase flow of moist air in a supersonic half nozzle was calculated to investigate the effect of condensation on boundary layer.
文摘When non-equilibrium condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, in order to control the transonic flow field with shock wave, a condensing flow was produced by an expansion of moist air on a circular bump model and shock waves were occurred in the supersonic parts of the fields. Furthermore, the additional passive technique of shock / boundary layer interaction using the porous wall with a cavity underneath was adopted in this flow field. The effects of these methods on the shock wave characteristics were investigated numerically and experimentally. The result obtained showed that the total pressure loss in the flow fields might be effectively reduced by the suitable combination between non-equilibrium condensation and the position of porous wall.
文摘In many engineering practices, frequently an impulsive wave is a consequence of discharge of a shockwave from the exit of a tube, leading to an annoying noise like a sonic boom. The impulsive noisehas often been a major factor to limit the performance of flow devices as well as to affect hazardousinfluences on human being. The current paper describes a new control method for the reduction ofimpulsive wave. An experiment using a simple shock tube was carried out to examine the effect of acavity/helical vane system on the impulsive wave strength. The resulting impulsive wave was influencedby the detailed configuration of the belieal vane inside the cavity which is located at the vicinity ofthe exit of a tube. The effect of the belieal vane was compared with no belieal vane tests to ensurevalidation of this kind of control strategy. The results showed that the strength of the impulsive wavecould be significantly reduced by the current passive control using the cavity/helical vane system.
文摘A Wells turbine for wave power conversion has hysteretic characteristics in a reciprocating flow. The hysteretic loop is opposite to the well-known dynamic stall of an airfoil. In this paper, the mechanism of the hysteretic behavior was elucidated by an unsteady 3-dimensional Navier-Stokes numerical simulation. It was found that the hysteretic behavior was associated with a streamwise vortical flow appearing near the blade suction surface. The effects of hub-to-tip ratio and tip clearance on the hysteretic characteristics of the Wells turbine have also been discussed in this paper.
文摘When the high-pressure gas is exhausted to the vacuum chamber from the supersonic nozzle, the overexpanded supersonic jet is formed at specific condition. In two-dimensional supersonic jet, furthermore, it is known that the hysteresis phenomena for the reflection type of shock wave in the flow field is occurred under the quasi-steady flow and for instance, the transitional pressure ratio between the regular reflection （RR） and Mach reflection （MR） is affected by this phenomenon. Many papers have described the hysteresis phenomena for underexpanded supersonic jet, but this phenomenon under the overexpanded axisymmetric jet has not been detailed in the past papers. The purpose of this study is to clear the hysteresis phenomena for the reflection type of shock wave at the overexpanded axisymmetric jet using the TVD method and to discuss the characteristic of hysteresis phenomena.
文摘The objective of this paper is to compare the performances of the themes, which could be used for wave energy conversion in the near future, under various irregular wave conditions. The turbines included in the paper are as follows: (a) Wells turbine with guide vanes; (b) impulse turbine with self-pitch-controlled guide vanes; (c) impulse turbine with fixed guide vanes. In this study, experimental investigations were carried out to clarify the performances of the turbines under steady flow conditions, and then a numerical simulation was used for predicting the performances under irregular wave conditions with various significant wave heights. As a result it was found that the running and starting characteristics of the impulse turbines could be superior to those of the Wells turbine.
文摘The total efficiency of power plants depends on the energy conversion in a combustor and a turbine .Considerably higher energy transfer rates can be obtained from a pulsed combustion.but unsteady flow of a single jet combustor reduces the turbine efficiency.Therefore.two pulse combustors were set in parallel and connected to a settling chamber that supplies a flow with constant pressure to the turbine.The aim of investigations presented here is a demonstration of technical feasibility for industrial applications and to show the benefits obtained from the pulse combustors.
文摘A compression wave discharged from an open end of a tube causes positive impulsive noise. Active noise cancellation which is the canceling of the noise by the addition of an inverse wave is a useful technique for reducing impulsive noise. The main objective of this study is to present the design for a negative impulsive wave generator utilizing unsteady mass influx. In this paper, in order to clarify the relationship between the unsteady mass influx and the negative impulsive wave! numerical and aeroacoustic analyses have been carried out using an unsteady expansion wave discharged from an open end of a shock tube. As a result, the effect of an unsteady expansion wave on a negative impulsive wave was clarified.
文摘In order to investigate the effectiveness of an orifice system in producing pressure drops and the effect of compressibility on the pressure drop, computations using the mass-averaged implicit Navier-Stokes equations were applied to the axisymmetric pipe flows with the operating pressure ratio from 1.5 to 20.0. The standard k- ε turbulence model was employed to close the governing equations. Numerical calculations were carried out for some combinations of the multiple orifice configurations. The present CFD data showed that the orifice systems, which have been applied to incompressible flow regime to date, could not be used for the high operating pressure ratio flows. The orifice interval did not strongly affect the total pressure drop, but the orifice area ratio more than 2.5 led to relatively high pressure drops. The total pressure drop rapidly increased in the range of the operating pressure ratio from 1.5 to 4.0, but it nearly did not increase when the operating pressure ratio was over 4.0. In the compressible pipe flows through double and triple orifice systems, the total pressure drop was largely due to shock losses.
文摘In this paper,the effect of geometries of tube open end on the shock,compression and expansion wavespropagating in the tube was investigated numerically and experimentally.One of them is a conventional straightshock tube with an open end.The other has a divergent tail tube at the exit.Applying a divergent tail tube(flaretube)to an open end shock tube,the period of one-cycle process could be shortened and the pressure behind theexpansion wave produced at the exit of the shock tube could be lowered much more below the atmosphericpressure than that produced in the straight tube.The results suggested that the intake air into the engine wassignificantly increased by applying a flare tube instead of a straight tube.
文摘The Phenomena of the interaction between a supersonic jet and an obstacle is a very interesting and important problem relating to the industrial engineering. This paper aims to investigate the characteristics of the two-dimensional temperature distribution on an inclined plate surface and the relation between the temperature distribution and some shock waves formed in the flow field. In this study, the measurement of temperature distribution on an inclined plate surface and the now visualization has carried out for various conditions using the thermo-sensitive liquid crystal sheet and the schlieren method. The two dimensional temperature distribution on the plate surface is clearly obtained by the thermo-sensitive liquid crystal sheet. The relation between the temperature distribution on an inclined plate surface and some shock waves reached at a plate surface is discussed. In this paper, the characteristics of the temperature distribution and the maximum temperature, and some other experimental evidences are presented.
文摘A computational investigation has been conducted to determine the effectiveness of a passive control technique of attenuating cavity-induced pressure oscillations in a confined two-dimensional supersonic flow. The passive control technique is achieved by fitting two flat plates near the front wall of a square cavity at Mach number 1.83 at the cavity entrance. The results showed that the flat plates attached near the front wall of the cavity, discouraged the formation of feedback loop which is widely believed to be the reason of cavity resonance. The resultant amount of attenuation of pressure oscillations was also dependent on the length of the flat plate used as an oscillation suppressor.
文摘A rapid expansion of moist air or steam in a supersonic nozzle gives rise to nonequilibrium condensation phenomena. Thereby, if the heat released by condensation of water vapour exceeds a certain quantity, the flow will become unstable and periodic flow oscillations of the unsteady condensation shock wave will occur. For the passive control of shock-boundary layer interaction using the porous wall with a plenum underneath, many papers have been presented on the application of the technique to transonic airfoil flows. In this paper, the passive technique is applied to three types of oscillations of the unsteady condensation shock wave generated in a supersonic nozzle in order to suppress the unsteady behavior As a result, the effects of number of slits and length of cavity on the aspect of flow field have been clarified numerically using a 3rd-order MUSCL type TVD finite-difference scheme with a second-order fractional-step for time integration.
文摘When an expansion wave propagated along a constant area straight tube reaches at the open end, the negative impulsive wave and the compression wave are formed by the emission and reflection of expansion wave. The negative impulsive wave is emitted toward the surrounding area and causes an impulsive noise like the sonic boom. The compression wave propagates in the tube toward the upstream and may cause the impulsive noise at the surrounding area of tube portal. With the advance of industrial engineering, it seems that the discharging of the expansion wave will become important problems. In this study, the experimental and numerical investigations are carried out using the shock tube and the TVD numerical method. The formation process of compression wave near the open end, the relationship with the compression wave and the expansion wave and the characteristics of compression wave are discussed.
文摘The time-dependent behavior of non-equilibrium condensation of moist air through a Ludwieg tube with a diaphragm downstream is investigated by using a computational fluid dynamics work. The two-dimensional, compressible, Navier-Stokes equations, fully coupled with the condensate droplet growth equations, are numerically solved by a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. Baldwin-Lomax turbulence model is employed to close the governing equations. The present computations represent the experimental flows well. The results obtained show that for an initial relative humidity over 40 %, the periodic excursions of the condensation shock occurs in the Ludwieg tube, and the frequency increases with the initial relative humidity. It is also found that total pressure loss due to non-equilibrium condensation in the Ludwieg tube should not be ignored even for a very low initial relative humidity. Furthermore, the variations of condensation properties are also
