• Title/Summary/Keyword: diffuser wall

Search Result 65, Processing Time 0.027 seconds

Pressure Loss in the Discharge Flow Path from a Diffuser to a wall (디퓨저에서 벽면으로의 방출유로에서의 압력손실)

  • Lee, J.;Kim, Y.I.;Kim, S.H.;Lee, D.J.
    • Proceedings of the KSME Conference
    • /
    • 2001.11b
    • /
    • pp.517-522
    • /
    • 2001
  • The exit edges of a diffuser are smoothly rounded, and a wall is located perpendicularly to a diffuser exit. The fluid is discharged towards the radial direction of a diffuser after impinging against a wall from a diffuser. In this flow path, pressure loss coefficients have been calculated by the variables of Reynolds number at a diffuser inlet, distance between a diffuser exit and a wall, and turbulence models. As a result, it was calculated that $h/D_0$ ratio between $0.35\sim0.4$ has the minimum pressure loss coefficient regardless of Reynolds number and turbulence models. It was also found that in case of the flow with relatively high Reynolds number at a diffuser inlet, the pressure loss coefficients by RNG $k-\varepsilon$ model have a tendency to be near to those by standard $k-\varepsilon$ model at small ratio of $h/D_0$, but to those by RSM at large ratio.

  • PDF

Large Eddy Simulation of Turbulent Flow in an Optimal Diffuser (큰에디모사법을 이용한 최적 디퓨져내의 난류유동 해석)

  • Lim Seokhyun;Caoi Haecheon
    • Proceedings of the KSME Conference
    • /
    • 2002.08a
    • /
    • pp.811-814
    • /
    • 2002
  • Using a mathematical theory, we show that the optimality condition of a turbulent diffuser with maximum pressure recovery at the exit is zero shear stress along the wall. The optimal diffuser shape is designed through iterative procedures by using the $k-{\varepsilon}-{\nu}^{2}-f$ turbulence model for flow simulation. The Reynolds number based on the bulk mean velocity and the channel height at the diffuser entrance is 18,000. We also perform large eddy simulation to validate the shape design results and investigate the flow characteristics near the zero-skin friction wall. Results from large eddy simulation show that the skin friction is slightly higher than zero but is still very small as compared to that of the flat plate boundary layer flow Although the time-averaged wall shear stress is slightly above zero along the diffuser wall, instantaneous flow reversals occur intermittently. The streamwise mein velocity shows an asymptotic behavior of the half-power-law near the wall where the skin friction is close to zero.

  • PDF

A Numerical Study on Flow and Heat Transfer Characteristics of Supersonic Second Throat Exhaust Diffuser for High Altitude Simulation (고고도 모사용 초음속 이차목 디퓨저의 유동 및 열전달 특성에 대한 수치적 연구)

  • Yim, Kyungjin;Kim, Hongjip;Kim, Seunghan
    • Journal of the Korean Society of Propulsion Engineers
    • /
    • v.18 no.5
    • /
    • pp.70-78
    • /
    • 2014
  • A numerical study has been conducted to investigate flow and heat transfer characteristics of supersonic second throat exhaust diffusers for high altitude simulation. By changing pressure and configuration, flow and cooling characteristics of the diffuser have been studied. At the normal operation of the diffuser, there were high temperature regions over 3,000 K without cooling, especially near wall and in subsonic diffuser part. If the cooling system of the diffuser is added, flow velocity is increased due to the cooled wall temperature.

The Effect of Dead Zone on Hydraulic Efficiency in Clearwell (정수지내 사류지역이 수리학적 효율에 미치는 영향 연구)

  • Lee, Seungjae;Shin, Eunher;Kim, Sunghoon;Park, Heekyung
    • Journal of Korean Society of Water and Wastewater
    • /
    • v.21 no.2
    • /
    • pp.177-185
    • /
    • 2007
  • Hydraulic efficiency($T_{10}/T$) in clearwell is often estimated by L/W ratio. However, this estimation is not accurate because other factors which give an effect on hydraulic efficiency such as shape of basin, diffuser wall and intra-basin is ignored. Therefore, in this research, hydraulic efficiency is predicted by the quantitative analysis of dead zone using CFD simulation in a pilot scale clearwell. The results show that the reason why higher L/W ratio increase the hydraulic efficiency is to decrease the dead zone of linear region which is located between baffles. Diffuser wall or intra-basin also affects on hydraulic efficiency with this process. Also, we conclude that hydraulic efficiency can not be reached to 0.8 or higher.

A Study on Performance Characteristics Planar angle diffuser with PIV (PIV를 이용한 평판형 디퓨저의 유동특성에 관한 실험적 연구)

  • Oh, Jeong Hun;Cho, Dae-Hwan;Seok, Baek Un
    • Proceedings of the Korean Society of Marine Engineers Conference
    • /
    • 2012.06a
    • /
    • pp.261-262
    • /
    • 2012
  • In planar angle diffuser, the increasement of cross-sectional area so rapidly cause possibly separate from the diffuser wall and forming areas of backflow. The flow characteristics of planar angle diffuser was investigated for three kind of inclined angle. Judging from the results, wide planar diffuser can be used as an effective means of improvement for diffuser performance and inclined angle of diffuser was through to be the best among three cases.

  • PDF

Internal Short-circuiting Estimation in Clearwell : Part B. Improving T10/T Using Intra Basin and Diffuser Wall by Applying ISEM to Field (정수지 내부 단락류 발생 평가 : Part B. 내부 단락류 평가 방법의 현장 적용을 통한 내부 도류벽과 정류벽을 이용한 T10/T 증가분석)

  • Shin, Eunher;Lee, Seungjae;Kim, Sunghoon;Park, Heekyung
    • Journal of Korean Society of Water and Wastewater
    • /
    • v.22 no.1
    • /
    • pp.113-120
    • /
    • 2008
  • A large majority of clearwell must be modified with maintaining the present baffles since they were underground built with the material like concrete. Therefore it is unreasonable to apply the previous research in clearwell modification which is studied with the assumption that distance between baffles is constant. In this study, internal short-circuiting estimation method (ISEM), which has the advantage of being applied at any condition, is applied to evaluate modification of A clearwell and modify B and C clerwell which have unusual characteristics. After analyzing the hydraulic efficiency at current state, modifications, where baffles, intra basins and diffuser walls are additionally installed, are considered and evaluate using ISEM. And the effect of intra basin and diffuser wall on $T_{10}/T$ is estimated and application feasibility of ISEM is evaluated. The improvement of intra basins is almost same with that of baffles. Also, short-circuiting in effluent zone can be reduced with the same level of channel zone if intra basin is added in effluent zone. However, effect range is restricted to the next channel zone. Diffuser wall can obtain the lower ISI than minimum ISI of cases where baffles and intra basins are installed. Therefore, additional improvement of $T_{10}/T$ value can be expected after $T_{10}/T$ value converges maximum only using baffles

A passive control on shock oscillations in a supersonic diffuser (초음속 디퓨져에서 발생하는 충격파 진도의 피동제어)

  • Kim, Heuy-Dong;Matsuo, Kazuyasu
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.20 no.3
    • /
    • pp.1083-1095
    • /
    • 1996
  • Shock wave/boundary layer interaction frequently causes the shock wave to oscillate violently and thus the global flow field to unstabilize. In order to stabilize the shock wave system in the diffuser of a supersonic wind tunnel, the present study attempted to control the shock oscillations by using a passive control. A porous wall with the porosity of 19.6% was mounted on a shallow cavity. Experiment was made by means of schlieren optical observation and wall pressure measurements. The flow Mach number just upstream the shock system and Reynolds number based on the turbulent boundary layer thickness were 2.1 and 1.8 * 10$\^$6/, respectively. The results show that the present passive control method on the shock wave/boundary layer interaction in the supersonic diffuser can significantly suppress the oscillations of shock system, especially when the shock system locates at the porous wall.

Numerical simulations of convergent-divergent nozzle and straight cylindrical supersonic diffuser

  • Mehta, R.C.;Natarajan, G.
    • Advances in aircraft and spacecraft science
    • /
    • v.1 no.4
    • /
    • pp.399-408
    • /
    • 2014
  • The flowfields inside a contour and a conical nozzle exhausting into a straight cylindrical supersonic diffuser are computed by solving numerically axisymmetric turbulent compressible Navier-Stokes equations for stagnation to ambient pressure ratios in the range 20 to 34. The diffuser inlet-to-nozzle throat area ratio and exit-to-throat area ratio are 21.77, and length-to-diameter ratio of the diffuser is 5. The flow characteristics of the conical and contour nozzle are compared with the help of velocity vector and Mach contour plots. The variations of Mach number along the centre line and wall of the conical nozzle, contour nozzle and the straight supersonic diffuser indicate the location of the shock and flow characteristics. The main aim of the present analysis is to delineate the flowfields of conical and contour nozzles operating under identical conditions and exhausting into a straight cylindrical supersonic diffuser.

A New Experiment on Interaction of Normal Shock Wave and Turbulent Boundary Layer in a Supersonic Diffuser (초음속디퓨져에서 발생하는 수직충격파의 난류경계층의 간섭에 관한 실험)

  • 김희동;홍종우
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.19 no.9
    • /
    • pp.2283-2296
    • /
    • 1995
  • Experiments of normal shock wave/turbulent boundary layer interaction were conducted in a supersonic diffuser. The flow Mach number just upstream of the normal shock wave was in the range of 1.10 to 1.70 and Reynolds number based upon the turbulent boundary layer thickness was varied in the range of 2.2*10$^{[-994]}$ -4.4*10$^{[-994]}$ . The wall pressures in streamwise and spanwise directions were measured for two test cases, in which the turbulent boundary layer thickness incoming into the supersonic diffuser was changed. The results show that the interactions of normal shock wave with turbulent boundary layer in the supersonic diffuser can be divided into three patterns, i.e., transonic interaction, weak interaction and strong interaction, depending on Mach number. The weak interactions generate the post-shock expansion which its strength is strong as the Mach number increases and the strong interactions form the pseudo-shock waves. From the spanwise measurements of wall pressure, it is known that if the flow Mach number is low, the interacting flow fields essentially appear two-dimensional, but they have an apparent 3-dimensionality for the higher Mach numbers.

Compressor Performance with Variation of Diffuser Vane Angle (디퓨저 베인각의 변화에 따른 압축기 성능 특성)

  • Shin, Y. H.;Kim, K. H.;Bae, M. H,;Kim, J. H.
    • The KSFM Journal of Fluid Machinery
    • /
    • v.3 no.2 s.7
    • /
    • pp.36-43
    • /
    • 2000
  • This study presents the centrifugal compressor performance for three different vane stagger angles and wall pressure distribution within vaned diffuser channels, and is also discussed about the stability with respect to the compressor components. As the vane stagger angle decreases, the flow rate for the stall onset decreases, and higher pressure can be obtained at the low flow rate region, however, the effective operation range of the compressor decreases because of the blockage effect of the diffuser vane. Low pressure pocket within the vaned diffuser channel moves from the pressure side of leading edge to the suction side as the flow rate decreases. The compressor system stability mainly depends on that of the diffuser.

  • PDF