• 제목/요약/키워드: Wall jet

검색결과 361건 처리시간 0.024초

조도가 2차원 벽부착 제트유동에 미치는 영향에 관한 연구 (An Investigation of Roughness Effects on 2-Dimensional Wall Attaching Offset Jet Flow)

  • 윤순현;김대성;박승철
    • 대한기계학회논문집
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    • 제19권1호
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    • pp.219-230
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    • 1995
  • The flow characteristics of a two-dimensional offset jet issuing parallel to a rough wall is experimentally investigated by using a split film probe with the modified Stock's calibration method. The mean velocity and turbulent stresses profiles in the up and down-stream locations of the wall-attachment regions are measured and compared with those of the smooth wall attaching offset jet cases. It is found that the wall-attachment region on the rough wall is wider than on the smooth wall for the same offset height and the jet speed. The position of the maximum velocity point is farther away from the wall than that for the smooth wall case because of the thick wall boundary layer established by the surface roughness. It is concluded that the roughness of the wall accelerates the relaxation process to a redeveloped plane wall jet and produces a quite different turbulent diffusion behavior especially near the wall from comparing with the smooth plane wall jet turbulence.

천해역에 수표면 및 수중방류된 사각형제트의 흐름 거동 (Flow behaviors of square jets surface discharged and submerged discharged into shallow water)

  • 김대근;김동옥
    • 상하수도학회지
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    • 제25권5호
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    • pp.627-634
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    • 2011
  • In the present study, the flow behaviors of square jets surface discharged and submerged discharged into shallow water were each simulated using computational fluid dynamics, and the results were compared. As for the verification of the models, the results of the hydraulic experiment conducted by Sankar, et al. (2009) were used. According to the results of the verification, the present application of computational fluid dynamics to the flow analysis of square jets discharged into shallow water was valid. As for the wall jet, which is one form of submerged discharges, at the bottom wall boundary, the peak velocity of the jet rapidly moved from the center of the jet to the bottom wall boundary due to the restriction of jet entrainment and the no-slip condition of the bottom wall boundary, and, as for the surface discharge, because jet entrainment is limited on the free water surface, the peak velocity of the jet moved from the center of the jet to the free water surface. This is because jet entrainment is restricted at the bottom wall boundary and the surface so that the momentum of the central core of the jet is preserved for considerable time at the bottom wall boundary and the surface. In addition, due to the effect of the bottom wall boundary and the free water surface, the jet discharged into shallow water had a smaller velocity diminution rate near the discharge outlet than did the free jet; at a location where it was so distant from the discharge outlet that the vertical profile of the velocity was nearly equal (b/x =20~30), moreover, it had a far smaller velocity diminution rate than did the free jet due to the effect of the finite depth.

다양한 벽면 두께를 갖는 원형 노즐에서 분사되는 난류 충돌 및 벽면 제트 유동장 특성 (Characteristics of Turbulent Impinging and Wall Jet Flow for a Circular Nozzle with Various Exit Wall Thickness)

  • 양근영;윤상헌;손동기;최만수
    • 대한기계학회논문집B
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    • 제25권6호
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    • pp.751-757
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    • 2001
  • An experimental study of impinging jet-flow structure has been carried out for a fully developed single circular jet impingement cooling on a flat plate, and the effect of the wall thickness at nozzle exit edge is investigated. Impinging jet flow structures have been measured by Laser-Doppler Velocimeter to interpret the heat transfer results presented previously by Yoon et al.(sup)(10) The peaks of heat transfer rate are observed near the nozzle edge owing to the radial acceleration of jet flow when the nozzle locates close to the impingement plate. The growth of the velocity fluctuations in the wall jet flow is induced by the vortices which originate in the jet shear layer, and consequently the radial distribution of local Nusselt numbers has a secondary peak at the certain radial position. As a wall of circular pipe nozzle becomes thicker for small nozzle-to-target distance, the entrainment can be inhibited, consequently, the acceleration of wall jet flow is reduced and the heat transfer rate decreases.

Atomization Improvement of a Liquid Jet with Wall Impingement and its Application to a Jet Engine Atomizer

  • Shiga, Seiichi
    • 한국분무공학회지
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    • 제11권3호
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    • pp.176-189
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    • 2006
  • In the present study, capability of improving the liquid atomization of a high-speed liquid jet by using wall impingement is explored, and its application to a jet engine atomize. is demonstrated. Water is injected from a thin nozzle. The liquid jet impinges on a wall positioned close to the nozzle exit, forming a liquid film. The liquid film velocity and the SMD were measured with PDA and LDSA, respectively. It was shown that the SMD of the droplets was determined by the liquid film velocity and impingement angle, regardless of the injection pressure or impingement wall diameter. When the liquid film velocity was smaller than 300m/s, a smaller SMD was obtained, compared with a simple free jet. This wall impingement technique was applied to a conventional air-blasting nozzle for jet engines. A real-size air-blasting burner was installed in a test rig in which three thin holes were made to accommodate liquid injection toward the intermediate ring, as an impingement wall. The air velocity was varied from 41 to 92m/s, and the liquid injection pressure was varied from 0.5 to 7.5 MPa. Combining wall impinging pressure atomization with gas-blasting produces remarkable improvement in atomization, which is contributed by the droplets produced in the pressure atomization mode. Comparison with the previous formulation for conventional gas-blasting atomization is also made, and the effectiveness of utilizing pressure atomization with wall impingement is shown.

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A numerical study of a confined turbulent wall jet with an external stream

  • Yan, Zhitao;Zhong, Yongli;Cheng, Xu;McIntyre, Rory P.;Savory, Eric
    • Wind and Structures
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    • 제27권2호
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    • pp.101-109
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    • 2018
  • Wall jet flow exists widely in engineering applications, including the simulation of thunderstorm downburst outflows, and has been investigated extensively by both experimental and numerical methods. Most previous studies focused on the scaling laws and self-similarity, while the effect of lip thickness and external stream height on mean velocity has not been examined in detail. The present work is a numerical study, using steady Reynolds-Averaged Navier Stokes (RANS) simulations at a Reynolds number of $3.5{\times}10^4$, of a turbulent plane wall jet with an external stream to investigate the influence of the wall jet domain on downstream development of the flow. The comparisons of flow characteristics simulated by the Reynolds stress turbulence model closure (Stress-omega, SWRSM) and experimental results indicate that this model may be considered reasonable for simulating the wall jet. The confined wall jet is further analyzed in a parametric study, with the results compared to the experimental data. The results indicate that the height and the width of the wind tunnel and the lip thickness of the jet nozzle have a great effect on the wall jet development. The top plate of the tunnel does not confine the development of the wall jet within 200b of the nozzle when the height of the tunnel is more than 40b (b is the height of jet nozzle). The features of the centerline flow in the mid plane of the 3D numerical model are close to those of the 2D simulated plane wall jet when the width of the tunnel is more than 20b.

초기조건의 변형에 따른 축대칭 충돌분사류의 난류특성에 대한 연구 (Experimental Study on Turbulent Characteristics of Axisymmetric Impinging Jet with a Modified Initial Condition)

  • 한용운;이근상
    • 대한기계학회논문집
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    • 제17권12호
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    • pp.3166-3178
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    • 1993
  • The turbulent flow characteristics of impinging jet have been investigated by the hot wire anemometry with a movable impinging wall. Turbulences were generated by the meshed jet as well as the typical round jet and their characteristics were compared, of mean velocity profiles, turbulent intensities. Reynolds stresses, similarities and their centerline flow behaviors. The meshed jet tends to make shear layer wider than the normal one in the initial region and the velocity profiles of the normal jet is rather contractive being compared with those of the meshed one near the wall. The effect of meshed exit appears only within 4D at the begining of jets and the cascading process of the meshed one marches more rapidly than that of the normal jet. The wall effects appear in the downstream of about 0.85 H to the impinging wall for every case of wall positions in both nozzles.

적외선 카메라를 이용한 초음속 충돌 동축제트의 벽면 온도 측정 (An Experimental Study of the Wall Temperature of the Supersonic Impinging Coaxial Jet Using an FLIR)

  • 곽종호;;김희동
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2004년도 춘계학술대회
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    • pp.1631-1636
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    • 2004
  • The supersonic impinging jet has been extensively applied to rocket launching system, gas jet cutting control, gas turbine blade cooling, etc. In such applications, wall temperature of an object on which supersonic jet impinges is a very important factor to determine the performance and life of the device. However, wall temperature data of supersonic impinging jets are not enough to data. The present study describes an experimental work to measure the wall temperatures of a vertical flat plate on which supersonic, dual, coaxial jet impinges. An Infrared camera is employed to measure the wall temperature distribution on the impinging plate. The pressure ratio of the jet is varied to obtain the supersonic jets in the range of over-expanded to moderately under-expanded conditions at the exit of coaxial nozzle. The distance between the coaxial nozzle and the flat plate was also varied. The coaxial jet flows are visualized using a Shadow optical method. The results show that the wall temperature distribution of the impinging plate is strongly dependent on the jet pressure ratio and the distance between the nozzle and plate.

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천해역에 방류되는 원형 다공바닥젵의 유속구조 (Velocity Structure of Wall Jet Originating from Circular Orifices in Shallow Water)

  • 김대근;서일원
    • 한국환경과학회지
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    • 제11권10호
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    • pp.1039-1044
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    • 2002
  • In this study, breakwater model which has several outlet pipes to discharge water is settled in the experimental open channel and mean velocity distributions of multi wall jet are measured. The length of zone of flow establishment of wall jet is shorter than that of free jet and decay rate of jet centerline longitudinal velocity along x is linear in $0.3{leq}x/I_p{leq}17$. The rate of vertical width and lateral width spreading of multi wall jet is respectively 0.0753, 0.157.

충돌수분류에 의한 벽면분류 영역에서의 전열특성 (Heat Transfer Characteristics in Wall Jet Region with Impinging Water Jet)

  • 엄기찬;서정윤
    • 대한설비공학회지:설비저널
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    • 제13권1호
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    • pp.14-21
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    • 1984
  • The purpose of this investigation is to study heat transfer characteristics in wall jet region on a flat plate caused by upward impinging water jet. In the wall jet region, heat transfer results by impinging water jet are being compared with the ones with supplementary water. As the radius increases, the heat transfer coefficient in the wall jet region consquently decreases, but decreasing nozzle-heat plate distance, the reduction rate increases. The experimental equation is expressed as follows : $$\frac{N_{ur}}{P_r^{0.4}}{\cdot}\overline{\xi}=m(\overline{\eta}{\codt}Re{\delta})^n,\;m=0.034\~0.056,\;n=1.74\~2.007$$ The optimum height of supplementary water is obtained to improve heat transfer effect of wall jet region.

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2次元 亂流 Stepped Wall Jet 의 流動特性 (Flow Characteristics of Two-Dimensional Turbulent Stepped Wall Jet)

  • 부정숙;김경천;박진호;강창수
    • 대한기계학회논문집
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    • 제9권6호
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    • pp.732-742
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    • 1985
  • 본 논문에서는 이 2차원 재부착분류(본문에서는 stepped wall jet라 명명함) 유동장을 재부착상류 부분, 재부착점 근방, 재부착 이후의 재발전 벽면분류 지역의 세 영역으로 구분하여 재부착 길이, 평균속도, 벽면정압을 측정하고 on-line에 의한 디지 틀 데이터 처리기법을 이용하여 난류강도, 레이놀즈 전단응력, 속도의 3승적(triple velocity product), integral length scale, Taylor's microscale 등을 실험적으로 구 하여 재부착 상류 부분에서는 자유분류와 비교하고, 재부착 이후에서는 2차원 벽면분 류와 비교하기로 한다.그리하여 초기 교란을 받는 분류가 벽면에 재부착하여 2차원 벽면분류로 재발전되어 가는 과정에 있어서의 평균 유동장과 급격한 변화를 갖는 난류 특성을 상세히 조사하여, 보다 일반적으로 적용될 수 있는 난류모델을 개발함에 있어 서 실험적인 자료를 제공하고자 한다. Fig. 1은 본 실험의 유동장에 대한 개약도를 보여주고 있다.