• 제목/요약/키워드: Plane Tip

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Three Component Velocity Field Measurements of Turbulent Wake behind a Marine Propeller Using a Stereoscopic PIV Technique (Stereoscopic PIV 기법을 이용한 선박용 프로펠러 후류의 3차원 속도장 측정)

  • Lee, Sang-Joon;Paik, Nu-Geun;Yoon, Jong-Hwan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.12
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    • pp.1716-1723
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    • 2003
  • A stereoscopic PIV(Particle Image Velocimetry) technique was employed to measure the 3 dimensional flow structure of turbulent wake behind a marine propeller with 5 blades. The out-of-plane velocity component was determined using two CCD cameras with the angular displacement configuration. Four hundred instantaneous velocity fields were measured for each of four different blade phases and ensemble averaged to investigate the spatial evolution of the propeller wake in the near-wake region from the trailing edge to one propeller diameter(D) downstream. The phase-averaged velocity fields show the potential wake and the viscous wake developed along the blade surfaces. Tip vortices were generated periodically and the slipstream contraction occurs in the near-wake region. The out-of-plane velocity component and strain rate have large values at the locations of tip and trailing vortices. As the flow goes downstream, the turbulence intensity, the strength of tip vortices and the magnitude of out-of-plane velocity component at trailing vortices are decreased due to viscous dissipation, turbulence diffusion and blade-to-blade interaction.

Comparison of Velocity Fields of Wake behind a Propeller Using 2D PIV and stereoscopic PIV (2D PIV와 stereoscopic PIV 기법으로 측정한 프로펠러 후류의 속도장 비교 연구)

  • Paik Bu-Geun;Lee Sang-Joon
    • 한국가시화정보학회:학술대회논문집
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    • 2002.11a
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    • pp.23-26
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    • 2002
  • The phase-averaged velocity fields of 3 dimensional turbulent wake behind a marine propeller measured by 2D PIV and stereoscopic PIV(SPIV) were compared directly. In-plane velocity fields obtained from the consecutive particle images captured by one camera in 2D PIV have perspective errors due to out-of-plane motion. However, the perspective errors can be removed by measuring three component velocity fields using SPIV method with two cameras. It is also necessary to measure three components velocity fields for the investigation of complicated near-wake behind the propeller for the suitable propeller design. 400 instantaneous velocity fields were measured for each of four different blade phases of $0^{\circ},\;18^{\circ},\;36^{\circ}C\;and\;54^{\circ}$. They were ensemble averaged to investigate the spatial evolution of the propeller wake in the downstream region. The phase-averaged velocity fields show the viscous wake developed along the blade surfaces and tip vortices were formed periodically. The perspective errors caused by the out-of-plane motion was estimated by the comparison of 2D PIV and SPIV results. The difference in the axial mean velocity fields measured by both techniques are nearly proportional to the mean out-of-plane velocity component which has large values in the regions of the tip and trailing vortices. The axial turbulence intensity measured by 2D PIV was overestimated since the out-of-plane velocity fluctuations influence the in-plane velocity vectors and increase the in-plane turbulence intensities.

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Effect of Tip Gap Height on Heat/Mass Transfer over a Cavity Squealer Tip (팁간극높이가 전면스퀼러팁 표면의 열전달 특성에 미치는 영향)

  • Kang, Dong Bum;Moon, Hyun Suk;Lee, Sang Woo
    • The KSFM Journal of Fluid Machinery
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    • v.16 no.6
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    • pp.19-25
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    • 2013
  • The effect of tip gap height on heat/mass transfer characteristics on the floor of cavity squealer tip has been investigated in a turbine cascade for power generation by employing the naphthalene sublimation technique. The squealer rim height is chosen to be an optimal one of $h_{st}/c$ = 5.51% for the tip gap height-to-chord ratios of h/c = 1.0, 2.0, 3.0 and 4.0%. The results show that heat transfer on the cavity floor is strongly dependent upon the behavior of the cavity flow falling down onto the floor. For lower h/c, the floor heat transfer is influenced by the tip leakage flow falling down along the inner face of the suction-side squealer, whereas the floor heat transfer for higher h/c is augmented mainly due to the impingement of leakage flow on the floor near the leading edge. Compared to the plane tip surface heat transfer, the cavity floor heat transfer is less influenced by h/c. For h/c = 1.0%, the average thermal load is as low as a half of the plane tip surface one, and the difference in the thermal load between the two cases tends to decrease with increasing h/c.

Study on the Three Dimensional Flow Characteristics of the Propeller Wake Using PIV Techniques (PIV 기법을 이용한 프로펠러 후류의 3차원 유동 특성 연구)

  • Paik, Bu-Geun;Kim, Jin;Kim, Kyung-Youl;Kim, Ki-Sup
    • Journal of the Society of Naval Architects of Korea
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    • v.44 no.3 s.153
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    • pp.219-227
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    • 2007
  • A stereo-PIV (particle image velocimetry) technique is used to investigate the vortical structure of the wake behind a rotating propeller in the present study. A four bladed propeller is tested in a cavitaion tunnel without any wake screen. Hundreds of instantaneous velocity fields are phase-averaged to reveal the three dimensional spatial evolution of the flow behind the propeller. The results of conventional 2-D PIV are also compared with those of the stereo-PIV to understand the vortical structure of propeller wake deeply. The variations of radial and axial velocities in the 2-D PIV results seem to be affected by the out-of-plane motion. generating a little perspective error in the in-plane velocity components of the slipstream. The strong out-of-plane motion around the hub vortex also causes the perspective error to vary the axial velocity component a little at the near wake region. The out-of-plane velocity component had the maximum value of about 0.3U0 in the tip vortices and continued its magnitude in the wake region.

THE STUDY BY USING THE COMPUTERIZED TOMOGRAPHY IMAGING IN ORDER TO ACCESS TO MANDIBULAR FORAMEN WHILE INFERIOR ALVEOLAR NERVE ANESTHESIA (하치조신경 마취시 하악공으로의 접근을 위한 전산화단층촬영을 통한 방사선적 연구)

  • Kim, Ji-Kwang;Gu, Hong;An, Jin-Suk;Kook, Min-Suk;Park, Hong-Ju;Oh, Hee-Kyun;Cho, Jin-Hyoung
    • Journal of the Korean Association of Oral and Maxillofacial Surgeons
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    • v.32 no.6
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    • pp.566-574
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    • 2006
  • Purpose : This study was performed to provide an anatomical information of the mandibular ramus for the successful inferior alveolar nerve block. Three dimensional images were reconstructed from the computerized tomography (CT) and the anatomical evaluation of the mandibular ramus was done. Materials and methods : Sixty-four patients who had been taken the facial CT scans from 2000, Jan to 2003, June was selected. The patients who had the anterior or posterior teeth misssing, edentulous ridge, and jaw fracture were excepted. In the occulusal plane, the lingual surface angle (LSA) between the mid-sagittal plane and the mandibular molar lingual surface from the 2nd premolar to the 2nd molar, the inner ramal surface angle (IRSA), the maximum inner ramal surface angle (MxIRSA), and the outer ramal surface angle (ORSA) to the-mid sagittal plane were measured. The inner ramal surface angle in the ligular tip level (IRSA-L) and the outer ramal surface angle in the ligular tip level (ORSA-L), the ramal length (RL), and the anterior ramal length (ARL) were also measured in the lingular tip level. Results : In the lingular tip level, the mean IRSA-L and ORSA-L were $28.6{\pm}6.3^{\circ}$ and $17.9{\pm}4.9^{\circ}$ respectively. The larger was the IRSA, the larger was the ORSA. In the lingular tip level, the mean ramal length was 35.8${\pm}$3.4 mm. The larger was the IRSA-L, the shorter was the ramal length. On the lingular tip level, the mean anterior ramal length from anterior ramus to lingular tip was 19.6${\pm}$3.3 mm. when the ramal length was longer, the anterior ramal length was also longer. On the lingular tip level, there was positive correlation vetween the IRSA and the ORSA, negative correlation between the IRSA and the ramal length, and positive correlation between the ramal length and the lingular tip level to the anterior ramus. There was no statistical meaning of data between sex and age. Conclusion : In the clinical view of the results so far achieved, if the direction of needle is closer to posterior it is able to contact bone on lingular tip when the internal surface of ramus is wided outer.

Flow in a High Speed Compressor Due to Axisymmetric Tip (대칭 팁 간극에 기인한 고속으로 회전하는 압축기에서의 유동)

  • Joo, Hyun Suh;Song, Seung Jin
    • 유체기계공업학회:학술대회논문집
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    • 2002.12a
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    • pp.279-283
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    • 2002
  • The effects of finite gap at the tip of turbomachinery blades have long been topics of both theoretical and experimental research because tip clearance degrades turbomachinery performance. This paper presents an analytical study of radial flow redistribution in a high speed compressor stage with axisymmetric tip clearance. The flow is assumed to be inviscid and compressible. The stage is modeled as an actuator disc and the analysis is carried out in the meridional plane. Upon going through the stage, the radially uniform upstream flow splits into the tip clearance and passage flows. The tip clearance flow is modeled as a jet driven by blade loading, or pressure difference between the pressure and suction sides. The model takes into consideration the detached shocks which occur in the rotor passage at the design point. This shock model is used to calculate the density ratio across the stage. Thus, the model is capable of predicting the kinematic effects of tip clearance in the high speed compressor flow field.

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A Study on the 5-Axis Machining of End Mill Body with Insert Tip (Insert Tip용 End Mill Body의 5-축 가공에 관한 연구.)

  • 조현덕;박영원
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 2001.10a
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    • pp.399-406
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    • 2001
  • This study describes the geometric characteristic and the 5-axis machining method of end mill body with insert tip. The geometry of end mill body is consisted of the flute part and the insert tip part. Thus, this study defines the flute part as ruled surface with constant helix angle and the insert tip part as rectangular plane on general direction. The geometric algorithm and the 5-axis NC part program were calculated by our programmed software and a sampled end mill body was machined on 5-axis machining center equipped with two index tables. The machined end mill body with insert tip was very agreeable to the designed end mill body with insert tip. Thus, the method proposed in this study may be very useful for the machining of end mill body with insert tip.

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Near-tip grid refinement for the effective and reliable natural element crack analysis

  • Cho, J.R.
    • Structural Engineering and Mechanics
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    • v.70 no.3
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    • pp.279-287
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    • 2019
  • This paper intends to introduce a near-tip grid refinement and to explore its usefulness in the crack analysis by the natural element method (NEM). As a sort of local h-refinement in FEM, a NEM grid is locally refined around the crack tip showing the high stress singularity. This local grid refinement is completed in two steps in which grid points are added and Delaunay triangles sharing the crack tip node are divided. A plane-state plate with symmetric edge cracks is simulated to validate the proposed local grid refinement and to examine its usefulness in the crack analysis. The crack analysis is also simulated using a uniform NEM grid for the sake of comparison. The near-tip stress distributions and SIFs that are obtained using a near-tip refined NEM grid are compared with the exact values and those obtained using uniform NEM grid. The convergence rates of global relative error to the total number of grid points between the refined and non-refined NEM grids are also compared.

Finite Element Analysis on the Small Scale Yielding of a Crack Tip in Plane Stress (平面應力狀態 에서 균열先端 의 小規模降伏 에 관한 有限要素解析)

  • 임장근;맹주성;김병용
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.7 no.3
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    • pp.270-277
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    • 1983
  • Plastic plane stress solutions are given for a center cracked strip, characterized by the Ramberg-Osgood plastic index, under bi-axial tension. Using a power law hardening stress-strain relation, an incremental plasticity finite element formulation is developed, and simple formulation is given for computing J-integral with nodal displacements. The near tip angular distribution of von Mises effective stress doesn't differ significantly in magnitude according to the change of loading stress and bi-axial load combination factor. But, for smaller plastic index, the location of its maximum value moves vertically at a head of crack. J-integral value, in the plastic zone near crack tip, decreases with load combination factor for large and small plastic index.

Work Function Change of W(123) Plane Due to Hydrogen and Deuterium Adsorption at 78K (78K에서 수소 혹은 중수소 흡착으로 인한 W(123)면의 일함수 변화)

  • 박노길;김기석;김성수;정광호;황정남;최대선
    • Journal of the Korean Vacuum Society
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    • v.1 no.1
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    • pp.78-82
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    • 1992
  • The changes in work function due to hydrogen and deuterium adsorption on W(123) plane are measured by means of Field Emission Method. In the case of hydrogen or deuterium adsorption, work function of W(123) plane at 78 K increase and after a maxium value, it decrease and saturated as increasing coverage. After annealing the tungsten emission tip at 200 K, the coverage corresponding to maximum change in work function was shifted toward low coverage and the effect of work function by terraces or steps of which orientation is [ O l l ] was observed.

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