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Fluid Flow and Infrared Image Analyses on Endwall Fitted with Short Rectangular Plate Fin

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Journal of Thermal Science 2006年第2期15卷 145-151页

作者： Kenyu OYAKAWA Islam Md. DIDARUL minoru yaga Dept. of Mechanical Systems Engineering University of the Ryukyus Okinawa Japan. Faculty of Engineering University of the Ryukyus Okinawa Japan.

An experimental investigation is carded out to study fluid flow and heat transfer characteristics on the endwall fitted with arrays （ 7 × 7 ） of short rectangular plate fins of different pattern （co-angular and zigzag） for different pitch ratio. Experiments were conducted in a rectangular duct of 50 mm height for an air flow of Reynolds number ranged from 18750 to 62500 based on the equivalent diameter and air velocity of the duct. Infrared image analysis technique was employed to make clear the characteristics of local heat transfer coefficients on fin base, endwall and overall surface. Flow pattern around the short rectangular plates were visualized by inducing fluorescent dye in a water channel and longitudinal vortices were observed. Increasing the distance between plates in flow direction causes heat transfer enhancement for co-angular pattern, while decreasing the distance causes heat transfer enhancement for zigzag pattern. Zigzag pattern with pitch ratio 2 is found to be more effective in heat transfer enhancement than any other cases investigated.

关键词： infrared image rectangular plate convection heat transfer flow visualization

Experimental and Numerical Study of Twin Underexpanded Impinging Jets

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Journal of Thermal Science 2003年第3期12卷 255-259页

作者： minoru yaga minoru Okano Masumi Tamashiro Kenyu Oyakawa Department of Mechanical Systems Engineering Faculty of Engineering University of the RyukyusSenbaru 1 Okinawa 903-0213 JAPANDepartment of Mechanical Systems Engineering Faculty of Engineering University of the RyukyusSenbaru 1 Okinawa 903-0213 JAPANDepartment of Mechanical Systems Engineering Faculty of Engineering University of the RyukyusSenbaru 1 Okinawa 903-0213 JAPANDepartment of Mechanical Systems Engineering Faculty of Engineering University of the RyukyusSenbaru 1 Okinawa 903-0213 JAPAN

In this paper, the dual underexpanded impinging jets are experimentally and numerically studied. The experiments were performed by measuring the unsteady and averaged wall static pressures and by visnalizing density fields using schlieren method. Numerical calculations were also conducted by solving unsteady three dimensional compressible Navier-Stokes equations with Baldwin-Lomax turbulence model. The main parametm''s for the dual jets are the non-dimensional distance between the two nozzle centers H/D covering 1.5, 2.0, the nozzle to plate separation L/D 2.0, 3.0,4.0 and 5.0 and the pressure ratio defined by Po/Pb 1.0-6.0, where D is the diameter of each nozzle exit, Po the stagnation pressure and Pb the back pressure. It is found that the agreement between the experiments and the calculations is good. The fountain flow at the middle of the two jets is observed both in the experiments and the calculation. According to FFT analysis of the experiments for the twin jets,relatively low frequgncy (up to 5 kHz) is dominant for H/D =1.5, L/D =2.0 and pressure rafio po/Pb =3.0 and 5.0,which is confLrmed by the experiments.

关键词：可压缩流体力学冲击波碰撞射流 CFD 计算流体力学喷射流动实验研究数值分析

Experimental study of unsteady supersonic flow interacting with porous cavity and jets or rods

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Journal of Thermal Science 2014年第2期23卷 153-159页

作者： Nao Kuniyoshi minoru yaga Isao Teruya Masaaki Ishikawa Graduate schools of engineering and science University of the Ryukyus1 SenbaruNishiharaOkinawa903-0213Japan Department of Mechanical System Engineering University of the Ryukyus1 SenbaruNishiharaOkinawa903-0213Japan

In this study,an experiment was performed to clarify the flow field,in which the jets were normally injected into a main supersonic flow surrounded by a porous cavity,and this report figures out interaction between starting shock wave and porous *** the experiment,a porous cavity is attached to a main duct and jets and rods are inserted to the main duct on the porous *** reveal this flow field,the thermal tuft probe was adopted to experimentally investigate the flow in the *** the experiments,the effect of the porous cavity with jets or rods on the flow field is studied by means of visualization of schlieren method with a high speed camera and measurement of cavity flow with thermal tuft *** a results,frequency analysis of output of the thermal tuft probe revealed that some clear dominant frequencies were confirmed when the starting shock wave existed around the porous cavity in all cases of jets and rods ***,visualization of schlieren method with a high speed camera clarified that a starting shock wave had the same dominant frequencies as that of the flow fluctuation in the cavity only around the cavity.

关键词： Shock wave Compressible flow Porous cavity Unsteady flow direction

Flow Characteristics of Rectangular Underexpanded Impinging Jets

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Journal of Thermal Science 2006年第1期15卷 59-64,30页

作者： minoru yaga Yoshio KINJO Masumi TAMASHIRO Kenyu OYAKAWA Dept. of Mechanical System Engineering University of the Ryukyus Okinawa 903-0213 Japan Mazda Motor Corporation Hiroshima 730-8670 Japan

In this paper, the flow fields of underexpanded impinging jet issued from rectangular nozzles of aspect ratio 1, 3 and 5 are numerically and experimentally studied. Two dimensional temperature and pressure distributions are measured by using infrared camera and the combination of a pressure scanning device and a stepping motor, respectively. The variation of the stagnation pressure on the impinging plate reveals that a hysteretic phenomenon exists during the increasing and decreasing of the pressure ratio for the aspect ratio of 3.0 and 5.0. It is also found that the nozzle of aspect ratio 1.0 caused the largest total pressure loss Pc /p0= 0.27 at the pressure ratio of Po /p0 = 6.5, where Pc is the stagnation center pressure on the wall, P0 the upstream stagnation pressure, Pb the ambient pressure. The other two nozzles showed that the pressure loss Pc / P0 =0.52 and 0.55 were achieved by the nozzles of the aspect ratio 3,0 and 5.0, respectively. The comparison between the calculations and experiments is fairly good, showing the three dimensional streamlines and structures of the shock waves in the jets. However, the hysteresis of the pressure variations observed in the experiments between the pressure ratio of 3.5 and 4.5 cannot be confirmed in the calculations.

关键词： compressible flow shock wave under-expanded rectangular impinging jet CFD.

Study of Interaction between Supersonic Flow and Rods Surrounded by Porous Cavity

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Journal of Thermal Science 2006年第4期15卷 324-330页

作者： minoru yaga Kenji YAMAMOTO Piotr DOERFFER Kenyu OYAKAWA Dept.of Mech.Systems Eng. Univ.of the RyukyusSenbaru 1NishiharaOkinawa903-0213 Graduate student Faculty of Eng.Univ.of the RyukyusSenbaru 1NishiharaOkinawa903-0213 Institute of Fluid Flow Machinery Polish Academy of ScienceFiszera 14PL-80 952 GdanskPoland

In this paper, some preliminary calculations and the experiments were performed to figure out the flow field, in which some rods were normally inserted into the main flow surrounded by a porous cavity. As a result, it is found that the starting shock wave severely interacts with the rods, the bow shock wave, its reflections, and the porous wall, which are numerically well predicted at some conditions. Moreover, inserting the rods makes the pressure on the upper wall in the porous region increase when the main flow in the porous region is completely supersonic. The calculations also suggest that three rods cause the widest suction area.

关键词： shock wave compressible flow porous cavity bow shock wave rod

Unsteady Correlation between Pressure and Temperature Field on Impinging Plate for Dual Underexpanded Jets

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Journal of Thermal Science 2009年第3期18卷 215-219页

作者： minoru yaga Hiroyuki HIGA Shoichi MATSUDA Izuru SENAHA Depts. Mech. Systems Eng. Univ. of the Ryukyus Graduate student Faculty of Eng. Univ. of the Ryukyus Okinawa National College of Technology

In this paper, dual underexpanded impinging jets are experimentally studied by measuring unsteady wall staticpressure and temperature fields using high response semiconductor pressure sensors and infrared imaging cam-era(100 captures per sec) with dual converging sonic nozzles. The flow field is also visualized by means of highspeed schlieren system( up to 70000 frame per second) to clarify the unsteady behavior of the jet structures suchas barrel shock wave, and Mach disk. Experiments were performed with a blow down tunnel changing the parameterssuch as the nozzle to plate distance, the distance between the two nozzles, and wind tunnel pressure *** nozzle to plate distance L and the distance between the two nozzles H are non-dimensionalized by the nozzlediameter D covering H/D=1.5, 2.0, and 3, L/D= 2, 3,and 4, and po/pb=1.0 - 5.0, where po and pb are stagnationpressure and back pressure respectively. Although the response of the infrared camera is quite different fromthat of the high speed camera, the unsteady correlation between the pressure and temperature fields is confirmedunder some conditions. Also the high speed schlieren pictures and the wall static pressure fluctuations suggestthat the generation of the Mach disk promote the unsteady behavior of the jets. After the confirmation of the correlation,a simple way to find the severe fluctuating region can be provided according to the two dimensional unsteadytemperature images without a lot of unsteady pressure measurements.

关键词： Shock wave CFD supersonic flow unsteady jet fluctuation

Synchronal Measurement of Flow Structure and Heat Transfer of Impingement Jet

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Journal of Thermal Science 2010年第3期19卷 228-233页

作者： Shoichi MATSUDA Naomichi SAJI minoru yaga Masaaki ISHIKAWA Kenyu OYAKAWA Dept.Mech.Systems Eng. Univ.of the RyukyusSenbaru 1NishiharaOkinawaJapan903-0213 Graduate student Faculty of Eng.Univ.of the RyukyusSenbaru 1NishiharaOkinawaJapan903-0213

This paper will present the characteristics of flow behavior and thermal field of both free and impingement jet issued from a circular orifice nozzle at Re=*** flow behavior of a single round jet and impingement jet was observed by smoke flow visualization recorded by a high speed camera using 5000 frame per *** transfer coefficient on the impingement surface was measured by means of infrared camera (TVS-8500,Avio) with a two-dimensional array of Indeum-Antimony (In Sb) sensors varying in the separation distance between the nozzle and the target *** heat transfer coefficient changes in time and ***,the root mean square distribution of the heat transfer was obtained from the *** a result,it was confirmed that the longitudinal vortex was observed outside of the ring vortex,and then the longitudinal vortex was penetrated in the jet ***,the high value of root mean square of the heat transfer coefficient has spread radially in stripy manner,which is caused as the results of the longitudinal vortexes flowing in the radial direction on the impingement plate.

关键词： Impingement jet Forced convection Heat transfer Ring vortex Longitudinal vortex

Special Column for the 9th Asian Joint Workshop on Thermophysics and Fluid Science 2022(AJWTF 2022)

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Journal of Thermal Science 2024年第3期33卷 793-793页

作者： SURYAN Abhilash yaga minoru SUN Dakun College of Engineering Trivandrum TrivandrumIndia University of the Ryukyus OkinawaNishiharaJapan Beihang University BeijingChina

This Special Column of Journal of Thermal Science(JTS)contains a selection of peer-reviewed papers from AJWTF 2022,held in Utsunomiya,Japan during 27 to 30November,*** Asian Joint Workshop and Thermophysics is a biennial international conference facilitating cooperation between scientists of Asian *** conference was founded by three renowned academicians *** Dong Kim,from South Korea,*** YU from China and *** Setoguchi from *** inaugural edition of the conference was held at Qufu,China in *** was followed by Luoyang,China(2008),Matsue,Japan(2010),Busan,Korea(2012),Nagasaki,Japan(2014),Guilin,China(2016),Trivandrum,India(2018),Daegu,Korea(2020).The ninth edition of the conference,held at Utsunomiya,Japan in November,2022 was chaired by *** Yamamoto of the Department of Mechanical Engineering,Tokyo University of Science,*** conference involved keynote lectures and talks from distinguished academicians and professionals from the *** made and future directions on research involving fluid and thermal sciences and engineering were part of the *** conference also provided an opportunity for cultural exchanges and promotion of soft power of participating nations.

关键词： promotion Korea edition

Numerical Simulation of Interaction between Supersonic Flow and Backward Inclined Jets Surrounded by Porous Cavity

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Open Journal of Fluid Dynamics 2017年第3期7卷 276-287页

作者： Nao Kuniyoshi minoru yaga Department of Marine Electronics and Mechanical Engineering Tokyo University of Marine Science and Technology Koto-ku Japan Department of Mechanical Systems Engineering University of the Ryukyus Nishihara Japan

As one of supersonic mixing techniques, a supersonic mixing technique using a cavity and a porous wall has been proposed. The cavity and the porous wall generate the low speed region in the cavity, which enhances mixing the main flow with the jets. In this study, numerical simulations were conducted to clarify the effects of backward inclined jets on the mixing technique using a porous wall and a cavity. In the numerical simulations, three patterns of jet injections which combined normal jets with backward inclined jets were studied. As a result, the combination of a backward inclined jet and a normal jet generates the suction flow behind the backward inclined jet, which is useful for making the injected jets flow into the cavity. In addition, the introduction of backward inclined jets reduces the total pressure loss. On the other hand, the mass flow rate through the porous holes decreases with increase in the number of the backward inclined jets.

关键词： Supersonic Mixing Cavity Porous Wall Backward Inclined Jet