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
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
In order to clarify the natures of a rotating stall cell, the experimental investigation was carried out in a high specific-speed diagonal flow fan. The pressure field on the casing wall and the velocity fields at the...In order to clarify the natures of a rotating stall cell, the experimental investigation was carried out in a high specific-speed diagonal flow fan. The pressure field on the casing wall and the velocity fields at the rotor inlet and outlet were measured under rotating stall condition with a fast response pressure transducer and a single slant hot-wire probe, respectively. The data were processed using the “Double Phase-Locked Averaging (DPLA)”technique, which enabled to obtain the unsteady flow field with a rotating stall cell in the relative co-ordinate system fixed to the rotor. As a result, the structure and behavior of the rotating stall cell in a high specific-speed diagonal flow fan were shown.展开更多
Shock wave-boundary layer interactions(SWBLI)are observed in several practical high-speed internal flows,such as compressor blades,turbine cascades,nozzles and so on.Shock induced oscillations(SIO),aerodynamic instabi...Shock wave-boundary layer interactions(SWBLI)are observed in several practical high-speed internal flows,such as compressor blades,turbine cascades,nozzles and so on.Shock induced oscillations(SIO),aerodynamic instabilities so-called buffet flows,flutter,aeroacoustic noise and vibration are the detrimental consequences of this unsteady shockboundary layer interactions.In the present study,a numerical computation has been performed to investigate the compressible flow characteristics around a 12%thick biconvex circular arc airfoil in a two dimensional channel.Reynolds averaged Navier-Stokes equations with two equation k-ωshear stress transport(SST)turbulence model have been applied for the computational analysis.The flow field characteristics has been studied from pressure ratio(ratio of back pressure,pb to inlet total pressure,p01)of 0.75 to 0.65.The present computational results have been compared and validated with the available experimental data.The results showed that the internal flow field characteristics such as shock wave structure,its behavior(steady or unsteady)and the corresponding boundary layer interaction are varied with pressure ratio.Self-excited shock oscillation was observed at certain flow conditions.Moreover,the mode of unsteady shock oscillation and its frequency are varied significantly with change of pressure ratio.展开更多
Numerical works have been conducted to investigate the effect of nozzle geometries on the discharge coefficient.Several contoured converging nozzles with finite radius of curvatures,conically converging nozzles and co...Numerical works have been conducted to investigate the effect of nozzle geometries on the discharge coefficient.Several contoured converging nozzles with finite radius of curvatures,conically converging nozzles and conical divergent orifices have been employed in this investigation.Each nozzle and orifice has a nominal exit diameter of 12.7x10^(-3)m.A 3rd order MUSCL finite volume method of ANSYS Fluent 13.0 was used to solve the Reynolds-averaged Navier-Stokes equations in simulating turbulent flows through various nozzle inlet geometries.The numerical model was validated through comparison between the numerical results and experimental data.The results obtained show that the nozzle geometry has pronounced effect on the sonic lines and discharge coefficients.The coefficient of discharge was found differ from unity due to the non-uniformity of flow parameters at the nozzle exit and the presence of boundary layer as well.展开更多
This paper describes an experimental work to investigate the effect of a reflector on supersonic jet noise radiated from a convergent-divergent nozzle with a design Mach number 2.0.In the present study,a metal reflect...This paper describes an experimental work to investigate the effect of a reflector on supersonic jet noise radiated from a convergent-divergent nozzle with a design Mach number 2.0.In the present study,a metal reflector and reflectors made of three different sound-absorbing materials(grass wool and polyurethane foam)were employed,and the reflector size was varied.Acoustic measurement is carried out to obtain the acoustic characteristics such as frequency,amplitude of screech tone and overall sound pressure level(OASPL).A high-quality schlieren optical system is used to visualize the detailed structure of supersonic jet.The results obtained show that the acoustic characteristics of supersonic jet noise are strongly dependent upon the jet pressure ratio and the reflector size.It is also found that the reflector with sound-absorbing material reduces the screech tone amplitude by about 5-13dB and the overall sound pressure levels by about 2-5dB,compared with those of the metal reflector.展开更多
The mass flow rate measurement using a critical nozzle shows the validity of the inviscid theory, indicating that the discharge coefficient increases and approaches unity as the Reynolds number increases under the ide...The mass flow rate measurement using a critical nozzle shows the validity of the inviscid theory, indicating that the discharge coefficient increases and approaches unity as the Reynolds number increases under the ideal gas law However, when the critical nozzle measures the mass flow rate of a real gas such as hydrogen at a pressure of hundreds bar, the discharge coefficient exceeds unity, and the real gas effects should be taken into account. The present study aims at investigating the flow features of the critical nozzle using high-pressured hydrogen gas. The axisymmetric, compressible Navier-Stokes computation is employed to simulate the critical nozzle flow, and a fully implicit finite volume method is used to discretize the governing equation system. The real gas effects are simulated to consider the intermolecular forces, which account for the possibility of liquefying hydrogen gas. The computational results are compared with past experimental data. It has been found that the coefficient of discharge for real gas can be corrected properly below unity adopting the real gas assumption.展开更多
This paper describes computational work to understand the unsteady flow-field of a shock wave discharging from an exit of a duct and impinging upon a flat plate. A flat plate is located downstream, and normal to the a...This paper describes computational work to understand the unsteady flow-field of a shock wave discharging from an exit of a duct and impinging upon a flat plate. A flat plate is located downstream, and normal to the axis of the duct. The distance between the exit of the duct and flat plate is changed. In the present study, two different duct geometries （i.e., square and cross section） are simulated to investigate the effect of duct geometry on the un-steady flows of a shock wave. In computation, the total variation diminishing （TVD） scheme is employed to solve three-dimensional, unsteady, compressible, Euler equations. Computations are performed over the range of shock Mach number from 1.05 to 1.75. Computational results can predict the three-dimensional dynamic behaviour of the shock wave impinging upon the flat plate. The results obtained show that the pressure increase generated on the plate by the shock impingement depends on the duct geometry and the distance between the duct exit and plate, as well as the shock Mach number. It is also found that for the duct with cross-section, the unsteady loads acting on the flat plate are less, compared with the square duct.展开更多
For technological reasons many high-performance solid rocket motors are made from segmented propellant grains with non-uniform port geometry. In this paper parametric studies have been carried out to examine the geome...For technological reasons many high-performance solid rocket motors are made from segmented propellant grains with non-uniform port geometry. In this paper parametric studies have been carried out to examine the geometric dependence of transient flow features in solid rockets with non-uniform ports. Numerical computations have been carried out in an inert simulator of solid propellant rocket motor with the aid of a standard k-ω turbulence model. It was seen that the damping of the temperature fluctuation is faster in solid rocket with convergent port than with divergent port geometry. We inferred that the damping of the flow fluctuations using the port geometry is a meaningful objective for the suppression and control of the instability and/or pressure/thrust oscillations during the starting transient of solid rockets.展开更多
Oscillating water column （OWC） based wave energy plants have been designed with several types of bidirectional turbines for converting pneumatic power to shaft power. Impulse turbines with linked guide vanes and fix...Oscillating water column （OWC） based wave energy plants have been designed with several types of bidirectional turbines for converting pneumatic power to shaft power. Impulse turbines with linked guide vanes and fixed guide vanes have been tested at the Indian Wave Energy plant. This was after initial experimentation with Well＇s turbines. In contrast to the Well＇s turbine which has a linear damping characteristic, impulse turbines have non-linear damping. This has an important effect in the overall energy conversion from wave to wire. Optimizing the wave energy plant requires a turbine with linear damping and good efficiency over a broad range of flow coefficient. This work describes how such a design can be made using fixed guide vane impulse turbines. The Indian Wave Energy plant is used as a case study.展开更多
The present computational study addresses the attenuation of the shock wave propagating in a duct, using a porous wall/cavity system. In the present study, a weak shock wave propagating over the porous wall/cavity sys...The present computational study addresses the attenuation of the shock wave propagating in a duct, using a porous wall/cavity system. In the present study, a weak shock wave propagating over the porous wall/cavity system is investigated with computational fluid dynamics. A total variation diminishing scheme is employed to solve the unsteady, two-dimensional, compressible, Navier-Stokes equations. The Mach number of an initial shock wave is changed in the range from 1.02 to 1.12. Several different types of porous wall/cavity systems are tested to investigate the passive control effects. The results show that wall pressure strongly fluctuates due to diffraction and reflection processes of the shock waves behind the incident shock wave. From the results, it is understood that for effective alleviation of tunnel impulse waves, the length of the perforated region should be sufficiently long.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In order to clarify the natures of a rotating stall cell, the experimental investigation was carried out in a high specific-speed diagonal flow fan. The pressure field on the casing wall and the velocity fields at the rotor inlet and outlet were measured under rotating stall condition with a fast response pressure transducer and a single slant hot-wire probe, respectively. The data were processed using the “Double Phase-Locked Averaging (DPLA)”technique, which enabled to obtain the unsteady flow field with a rotating stall cell in the relative co-ordinate system fixed to the rotor. As a result, the structure and behavior of the rotating stall cell in a high specific-speed diagonal flow fan were shown.
基金The present work has been carried out with computa-tional resource support from Higher Education Quality Enhancement Project(HEQEP)AIF(2nd Round)-Sub-Project CP 2099UGC,MoE,Government of Bangladesh(Contract no.28/2012).
文摘Shock wave-boundary layer interactions(SWBLI)are observed in several practical high-speed internal flows,such as compressor blades,turbine cascades,nozzles and so on.Shock induced oscillations(SIO),aerodynamic instabilities so-called buffet flows,flutter,aeroacoustic noise and vibration are the detrimental consequences of this unsteady shockboundary layer interactions.In the present study,a numerical computation has been performed to investigate the compressible flow characteristics around a 12%thick biconvex circular arc airfoil in a two dimensional channel.Reynolds averaged Navier-Stokes equations with two equation k-ωshear stress transport(SST)turbulence model have been applied for the computational analysis.The flow field characteristics has been studied from pressure ratio(ratio of back pressure,pb to inlet total pressure,p01)of 0.75 to 0.65.The present computational results have been compared and validated with the available experimental data.The results showed that the internal flow field characteristics such as shock wave structure,its behavior(steady or unsteady)and the corresponding boundary layer interaction are varied with pressure ratio.Self-excited shock oscillation was observed at certain flow conditions.Moreover,the mode of unsteady shock oscillation and its frequency are varied significantly with change of pressure ratio.
文摘Numerical works have been conducted to investigate the effect of nozzle geometries on the discharge coefficient.Several contoured converging nozzles with finite radius of curvatures,conically converging nozzles and conical divergent orifices have been employed in this investigation.Each nozzle and orifice has a nominal exit diameter of 12.7x10^(-3)m.A 3rd order MUSCL finite volume method of ANSYS Fluent 13.0 was used to solve the Reynolds-averaged Navier-Stokes equations in simulating turbulent flows through various nozzle inlet geometries.The numerical model was validated through comparison between the numerical results and experimental data.The results obtained show that the nozzle geometry has pronounced effect on the sonic lines and discharge coefficients.The coefficient of discharge was found differ from unity due to the non-uniformity of flow parameters at the nozzle exit and the presence of boundary layer as well.
文摘This paper describes an experimental work to investigate the effect of a reflector on supersonic jet noise radiated from a convergent-divergent nozzle with a design Mach number 2.0.In the present study,a metal reflector and reflectors made of three different sound-absorbing materials(grass wool and polyurethane foam)were employed,and the reflector size was varied.Acoustic measurement is carried out to obtain the acoustic characteristics such as frequency,amplitude of screech tone and overall sound pressure level(OASPL).A high-quality schlieren optical system is used to visualize the detailed structure of supersonic jet.The results obtained show that the acoustic characteristics of supersonic jet noise are strongly dependent upon the jet pressure ratio and the reflector size.It is also found that the reflector with sound-absorbing material reduces the screech tone amplitude by about 5-13dB and the overall sound pressure levels by about 2-5dB,compared with those of the metal reflector.
文摘The mass flow rate measurement using a critical nozzle shows the validity of the inviscid theory, indicating that the discharge coefficient increases and approaches unity as the Reynolds number increases under the ideal gas law However, when the critical nozzle measures the mass flow rate of a real gas such as hydrogen at a pressure of hundreds bar, the discharge coefficient exceeds unity, and the real gas effects should be taken into account. The present study aims at investigating the flow features of the critical nozzle using high-pressured hydrogen gas. The axisymmetric, compressible Navier-Stokes computation is employed to simulate the critical nozzle flow, and a fully implicit finite volume method is used to discretize the governing equation system. The real gas effects are simulated to consider the intermolecular forces, which account for the possibility of liquefying hydrogen gas. The computational results are compared with past experimental data. It has been found that the coefficient of discharge for real gas can be corrected properly below unity adopting the real gas assumption.
文摘This paper describes computational work to understand the unsteady flow-field of a shock wave discharging from an exit of a duct and impinging upon a flat plate. A flat plate is located downstream, and normal to the axis of the duct. The distance between the exit of the duct and flat plate is changed. In the present study, two different duct geometries （i.e., square and cross section） are simulated to investigate the effect of duct geometry on the un-steady flows of a shock wave. In computation, the total variation diminishing （TVD） scheme is employed to solve three-dimensional, unsteady, compressible, Euler equations. Computations are performed over the range of shock Mach number from 1.05 to 1.75. Computational results can predict the three-dimensional dynamic behaviour of the shock wave impinging upon the flat plate. The results obtained show that the pressure increase generated on the plate by the shock impingement depends on the duct geometry and the distance between the duct exit and plate, as well as the shock Mach number. It is also found that for the duct with cross-section, the unsteady loads acting on the flat plate are less, compared with the square duct.
文摘For technological reasons many high-performance solid rocket motors are made from segmented propellant grains with non-uniform port geometry. In this paper parametric studies have been carried out to examine the geometric dependence of transient flow features in solid rockets with non-uniform ports. Numerical computations have been carried out in an inert simulator of solid propellant rocket motor with the aid of a standard k-ω turbulence model. It was seen that the damping of the temperature fluctuation is faster in solid rocket with convergent port than with divergent port geometry. We inferred that the damping of the flow fluctuations using the port geometry is a meaningful objective for the suppression and control of the instability and/or pressure/thrust oscillations during the starting transient of solid rockets.
文摘Oscillating water column （OWC） based wave energy plants have been designed with several types of bidirectional turbines for converting pneumatic power to shaft power. Impulse turbines with linked guide vanes and fixed guide vanes have been tested at the Indian Wave Energy plant. This was after initial experimentation with Well＇s turbines. In contrast to the Well＇s turbine which has a linear damping characteristic, impulse turbines have non-linear damping. This has an important effect in the overall energy conversion from wave to wire. Optimizing the wave energy plant requires a turbine with linear damping and good efficiency over a broad range of flow coefficient. This work describes how such a design can be made using fixed guide vane impulse turbines. The Indian Wave Energy plant is used as a case study.
文摘The present computational study addresses the attenuation of the shock wave propagating in a duct, using a porous wall/cavity system. In the present study, a weak shock wave propagating over the porous wall/cavity system is investigated with computational fluid dynamics. A total variation diminishing scheme is employed to solve the unsteady, two-dimensional, compressible, Navier-Stokes equations. The Mach number of an initial shock wave is changed in the range from 1.02 to 1.12. Several different types of porous wall/cavity systems are tested to investigate the passive control effects. The results show that wall pressure strongly fluctuates due to diffraction and reflection processes of the shock waves behind the incident shock wave. From the results, it is understood that for effective alleviation of tunnel impulse waves, the length of the perforated region should be sufficiently long.
