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Characteristics of the Mach Disk in the Underexpanded Jet in which the Back Pressure Continuously Changes with time

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Journal of thermal Science 2003年第2期12卷 132-137页

作者： t.Irie t.Yasunobu H.Kashimura t.setoguchi Department of Mechanical Engineering Kitakyushu National College of TechnologyShiiKokuraminami-kuKitakyushu 802-0985JapanDepartment of Control and Information Systems EngineeringKitakyushu National College of TechnologyShiiKokuraminami-kuKitakyushu 802-0985JapanDepartment of Control and Information Systems EngineeringKitakyushu National College of TechnologyShiiKokuraminami-kuKitakyushu 802-0985JapanDepartment of Mechanical EngineeringSaga UniversityHonjoSaga 840-8502Japan

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 *** eventual purpose of this study is to clarify the unsteady phenomenon of the underexpanded free jet when the back pressure continuously changes with *** characteristic of the Mach disk has been clarified in consideration of the diameter and position of it by the numerical analysis in this *** 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 *** 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.

关键词： underexpanded jet sonic jet regular reflection Mach reflection Mach disk tVD method.

Optimization Study of a Coanda Ejector

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Journal of thermal Science 2006年第4期15卷 331-336页

作者： H.D.Kim G.Rajesh t.setoguchi S.Matsuo School of Mechanical Engineering Andong National University388Songcheon-dongAndongGyeongbuk 760-749Korea Department of Mechanical Engineering Saga University1HonjoSaga 840-8502Japan

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.

关键词： Coanda ejector compressible mixing layer flow dragging mixing length induced flow

A Study of the Weak Shock Wave Propagating over a Porous Wall/Cavity System

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Journal of thermal Science 2005年第4期14卷 329-333页

作者： H.D.KIM S.J.JUNG t.AOKI t.setoguchi School of Mechanical Engineering.Andong National University Songchun-dongAndong 760-746Korea Department of Energy and Environmental Engineering Kyushu University6-1Kasuga-kouenKasugaFukuoka 816-8580Japan Department of Mechanical Engineering Saga University1HonjoSaga 840-8502Japan

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.

关键词： compressible flow perforated wall railway tunnel shock wave.

Effect of Duct Geometry on Shock Wave Discharge

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Journal of thermal Science 2006年第4期15卷 349-354页

作者： Y.-H.Kweon Y.Miyazato t.Aoki H.-D.Kim t.setoguchi Department of Energy and Environmental Engineering Kyushu UniversityKasuga 816-8580Japan Faculty of Environmental Engineering The University of KitakyushuKitakyushu 808-0135Japan School of Mechanical Engineering Andong National UniversityAndong 760-749Korea Department of Mechanical System Engineering Saga UniversitySaga 840-8502Japan

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.

关键词： unsteady flow compressible flow shock wave shock impingement duct geometry

Performance estimation of bi-directional turbines in wave energy plants

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Journal of thermal Science 2007年第4期16卷 346-352页

作者： S.Anand V.Jayashankar S.Nagata K.toyota M.takao t.setoguchi Department of Electrical Engineering IIT MadrasIndia IOES Saga UniversityJapan Department of Mechanical Engineering Matsue National College of TechnologyJapan Department of Mechanical Engineering Saga UniversityJapan

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.

关键词： Bidirectional turbine differential pressure flow rate impulse turbine

A Study of the Critical Nozzle for Flow Rate Measurement of High-Pressure Hydrogen Gas

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Journal of thermal Science 2007年第1期16卷 28-32页

作者： H.D.Kim J.H.Lee K.A.Park t.setoguchi S.Matsuo School of Mechanical Engineering Andong National University388Songchun-dongAndong 760-749Korea Dynamics Group Korea Research Institute of Standards and SciencePO Box 102YusongTaejon 305-606Korea Department of Mechanical Enginering.Saga University 1Honjo—machiSaga-shiSaga 840—8502Japan

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.

关键词： critical nozzle compressible flow hydrogen gas ideal gas law real gas effect

Internal Flow Simulation of High-Performance Solid Rockets using a k-ω turbulence Model

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Journal of thermal Science 2005年第2期14卷 114-119页

作者： V.R.SANAL KUMAR H.D.KIM B.N.RAGHUNANDAN t.setoguchi S.RAGHUNAtHAN Andong National University Andong 760-749 KoreaAndong National University Andong 760-749KoreaIndian Institute of Science Bangalore-560 012IndiaSaga University Honjo-machiSaga 840-8502JapanThe Oueen's University of Belfast Northern IrelandUK

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.

关键词： solid rockets pressure spike instability thrust oscillation turbulent separation.

the Effect of Reflector with Sound-Absorbing Material on Supersonic Jet Noise

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Journal of thermal Science 2005年第1期14卷 22-27页

作者： Y.-H.KWEON M.tSUCHIDA Y.MIYAZAtO t.AOKI H.-D.KIM t.setoguchi Department of Energy and Environmental Engineering Kyushu University Kasuga 816-8580Japan School of Mechanical Engineering Andong National University Andong 760-749Korea Department of Mechanical Engineering Saga University Saga 840-8502Japan

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 *** 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 *** 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 *** results obtained show that the acoustic characteristics of supersonic jet noise are strongly dependent upon the jet pressure ratio and the reflector *** 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.

关键词： supersonic jet supersonic jet noise screech tone OASPL reflector sound-absorbing material.

Nozzle geometry variations on the discharge coefficient

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Propulsion and Power Research 2016年第1期5卷 22-33页

作者： M.M.A.Alam t.setoguchi S.Matsuo H.D.Kim Institute of Ocean Energy Saga University(IOES)1HonjoSaga-shiSaga 840-8502Japan Department of Advanced technology Fusion Saga UniversityJapan Department of Mechanical Engineering Andong National UniversityKorea

Numerical works have been conducted to investigate the effect of nozzle geometries on the discharge *** contoured converging nozzles with finite radius of curvatures,conically converging nozzles and conical divergent orifices have been employed in this *** 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 *** numerical model was validated through comparison between the numerical results and experimental *** results obtained show that the nozzle geometry has pronounced effect on the sonic lines and discharge *** 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.

关键词： Boundary layer Compressible flow Reynolds-averaged Navier-Stokes(RANS) Shear layer Sonic lines Supersonic core