• Title/Summary/Keyword: Cavitation number

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Sludge Pre-Treatment by Hydrodynamic Cavitation-I: Optimization of Pre-Treatment System (수리동력학적 캐비테이션을 이용한 하수 슬러지의 전처리-I: 전처리 시스템의 최적화)

  • Maeng, Jang-Woo;Lee, Eun-Young;Bae, Jae-Ho
    • Journal of Korean Society of Environmental Engineers
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    • v.32 no.12
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    • pp.1119-1125
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    • 2010
  • Most of the sludge pre-treatment methods to improve the anaerobic digestibility of sludge are not practied in the fields with low economical efficiency. The venturi cavitation system (VCS) adopting hydrodynamic cavitation is simple and requires low energy. This research was conducted to investigate the optimum design and operating conditions of the VCS. The experimental results indicated that the optimum number of venturi in series was three, and the suction mode operation of the pump yielded 1.6 times higher pre-treatment efficiency per unit energy consumption than the discharge mode. The combination of venturies with different throat sizes did not affect the pre-treatment efficiency. Also, the parallel installation of the three in series venture unit yielded 30% higher pre-treatment efficiency per unit energy consumption than the single unit. Under parallel conditions, the solubilization efficiency was 5.6 mg ${\Delta}SCOD/g$ TS/kWh, which is higher than the previously reported value.

A Numerical Analysis of Gravity and Free Surface Effects on a Two-Dimensional Supercavitating Flow (2차원 초공동 유동의 중력과 자유표면 효과에 대한 수치해석)

  • Kim, Hyoung-Tae;Lee, Hyun-Bae
    • Journal of the Society of Naval Architects of Korea
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    • v.51 no.5
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    • pp.435-449
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    • 2014
  • The effects of the gravity field and the free surface on the cavity shape and the drag are investigated through a numerical analysis for the steady supercavitating flow past a simple two-dimensional body underneath the free surface. The continuity and the RANS equations are numerically solved for an incompressible fluid using a $k-{\epsilon}$ turbulence model and a mixture fluid model has been applied for calculating the multiphase flow of air, water and vapor using the method of volume of fluid and the Schnerr-Sauer cavitation model. Numerical solutions have been obtained for the supercavitating flow about a two-dimensional $30^{\circ}$ wedge in wide range of depths of submergence and inflow velocities. The results are presented for the cavity shape, especially the length and the width, and the drag of the wedge in comparison with those of the case for the infinite fluid flow neglecting the gravity and the free surface. The influences of the gravity field and the free surface on the aforementioned quantities are discussed. The length and the width of the supercavity are reduced and the centerline of the cavity rises toward the free surface due to the effects of the gravity field and the free surface. The drag coefficient of the wedge, however, is about the same except for shallow depths of submergence. As the supercavitating wedge is approaching very close to the free surface, it is found the length and the width of a cavity are shorten even though the cavitation number is reduced. Also the present result suggests that, under the influence of the gravity field and the free surface, the length of the supercavity for a certain cavitation number varies and moreover is proportional to the inverse of the submergence depth Froude number.

Development of KD- Propeller Series using a New Blade Section (새로운 날개단면을 이용한 KD-프로펠러 씨리즈 개발)

  • J.T. Lee;M.C. Kim;J.W. Ahn;H.C. Kim
    • Journal of the Society of Naval Architects of Korea
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    • v.28 no.2
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    • pp.52-68
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    • 1991
  • A new propeller series is developed using the newly developed blade section(KH18 section) which behaves better cavitation characteristics and higher lift-drag ratio at wide range of angle-of-attack. The pitch and camber distributions are disigned in order to have the same radial and chordwise loading distribution with the selected circumferentially averaged wake input. Since the geometries of the series propeller, such as chord length, thickness, skew and rate distribations, are selected by regression of the recent full scale propeller geometric data, the performance prediction of a propeller at preliminary design stage can be mure realistic. Number of blades of the series propellers is 4 and the expanded blade area ratios are 0.3, 0.45, 0.6 and 0.75. Mean pitch ratios are selected as 0.5, 0.65, 0.8, 0.75 and 1.1 for each expanded area ratio. The new propeller series is composed of 20 propellers and is named as KD(KRISO-DAEWOO) propeller series. Propeller open water tests are performed at the experimental towing tank, and the cavitation observation tests and fluctuating pressure measurements are carried out at the cavitation tunnel of KRISO. $B_{P}-\delta$ curves, which can be used to select the optimum propeller diameter at the preliminary design stage, are derived from a regression analysis of the propeller often water test results. The KD-cavitation chart is derived from the cavitation observation test results by choosing the local maximum lift coefficient and the local cavitation number as parameters. The caviy extent of a propeller can be predicted more accurately by using the KD-cavitation chart at a preliminary design stage, since it is derived from the results of the cavitation observation tests in the selected ship's wake, whereas the existing cavitation charts, such as the Burrill's cavitation chart, are derived from the test results in uniform flow.

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Estimation of Cavitation Bubble Distribution Using Multi-Frequency Acoustic Signals (다중 주파수를 이용한 캐비테이션 기포의 분포량 추정)

  • Kim, Dae-Uk;La, Hyoung-Sul;Choi, Jee-Woong;Na, Jung-Yul;Kang, Don-Hyug
    • The Journal of the Acoustical Society of Korea
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    • v.28 no.3
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    • pp.198-207
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    • 2009
  • Distribution of cavitation bubbles relative to change of the sound speed and attenuation in the water was estimated using acoustic signal from 20 to 300 kHz in two cases that cavitation bubbles exist and do not exist. To study generation and extinction property of cavitation bubble, bubble distribution was estimated in three cases: change of rotation speed (3000-4000 rpm), surface area of blade ($32-98\;mm^2$) and elapsed time (30-120 sec). As a result, the radii of the generated bubbles ranged from 10 to $60{\mu}m$, and bubble radius of $10-20{\mu}m$ and $20-30{\mu}m$ was accounted for 45 and 25% of the total number of cavitation bubbles, respectively. And generation bubble population correlated closely with the rotating speed of the blades but did not correlate with the surface area of blade. It was observed that 80% of total bubble population disappeared within 2 minutes. Finally, acoustic data of bubble distribution was compared with optical data.

An Experimental Study on the Internal Flow Characteristics of a Jet Pump for the Smart UAV Fuel System (스마트무인기 연료계통 제트펌프의 내부 유동 특성에 관한 실험적 연구)

  • Lee, Yoon-Kwon;Lee, Chang-Ho;Choi, Hee-Joo;Lee, Jee-Keun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.32 no.2
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    • pp.107-116
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    • 2008
  • The jet pumps are widely used to transfer the fuel between the tanks in an aircraft fuel supply system. However detailed design procedures for determining the size of components of the jet pumps are not known so well. In this paper, the flow characteristics of the jet pump, which is applied in the fuel transfer system for the smart UAV (Unmanned Aerial Vehicle), were experimentally investigated using the acrylic jet pump model for the visualization of the internal flow. The pressure distributions within the jet pump were measured, and then the loss coefficients of each part were calculated. The effects of Reynolds number and the distances (S) between the exit of the primary nozzle and the mixing chamber entrance were investigated. In addition, cavitation phenomena were considered through the flow visualization inside the jet pump. As a conclusion from the experiment, the contraction shape of the primary nozzle has a strong effect on the loss coefficient of the nozzle and the cavitation occurrence. Cavitation starts around the nozzle exit, and then it propagates to the full flow fields of the jet pump.

Hydraulic Performance Test of a Turbopump (터보펌프의 수력 성능시험)

  • Hong Soon-Sam;Kim Dae-Jin;Kim Jin-Sun;Choi Chang-Ho;Kim Jinhan
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • v.y2005m4
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    • pp.243-247
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    • 2005
  • Hydraulic performance test was conducted for a fuel pump of a liquid rocket engine turbopump. The pump driven by an electric motor was tested in water environment. It is experimentally shown that the inducer had very small effect on the pimp's head and efficiency but great effect on the pump's cavitation performance. Additionally, inducer test was carried out to investigate the effect of the inducer on the pump in detail, and it was found that the pump had a critical cavitation number when the inducer head dropped by $55\%$.

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NUMERICAL ANALYSIS OF CAVITATION WITH COMPRESSIBILITY EFFECTS AROUND HEMISPHERICAL HEAD-FORM BODY (반구형 전두부 실린더에서 발생하는 캐비테이션 유동의 압축성 효과에 대한 수치해석 연구)

  • Park, S.;Rhee, S.H.;Shin, B.R.
    • Journal of computational fluids engineering
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    • v.18 no.4
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    • pp.9-16
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    • 2013
  • Cavitation on an axi-symmetric hemispherical head-form body was studied using an Reynolds-averaged Navier-Stokes equations solver based on a cell-centered finite volume method. To consider compressibility effects on the vapor phase and cavity interface, a pressure-based compressible flow CFD code was developed. To validate the developed CFD code, cavitating flow around the hemispherical head-form body was simulated using pressure-based incompressible and compressible CFD codes and validated against existing experimental data in the three-way comparison. The cavity shedding behavior, length of re-entrant jet, drag history, and Strouhal number of the hemispherical head-form body were compared between two CFD codes. The results, in this paper, suggested that the computations of cavitating flow with compressibility effects improve the description of cavity dynamics.

The Improvement of Surface Roughness of Marine Propeller by Continuous Control of Cutter Posture in 5-Axis Machining (공구자세의 연속제어를 통한 선박용 프로펠러의 5축 가공 표면조도의 개선)

  • Son, Hwang-Jin;Lim, Eun-Seong;Jung, Yoon-Gyo
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.11 no.2
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    • pp.27-33
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    • 2012
  • A marine propeller is designed for preventing cavitation priority. Cavitation is a phenomenon which is defined as the vibration or noise by dropping the pressure on the high-speed rotation of the propeller. There has to be a enough thrust on the low-speed rotation for preventing cavitation. Thus, it has to be considered in the increasing of the number of blade and the angle of wing to design the propeller. In addition, flow resistance will be increasing by narrowing the width between blades. So high quality surface roughness of the hub to minimize flow resistance is required. Interference problems with tool and neighboring surfaces often take place from this kind of characteristics of the propeller. During 5-Axis machining of these propellers, the excessive local interference avoidance, necessary to avoid interference, leads to inconsistency of cutter posture, low quality of machined surface. Therefore, in order to increase the surface quality, it is necessary to minimize the cutter posture changes and create a continuous tool path while avoiding interference. This study, by using a MC-space algorithm for interference avoidance and a MB-spline algorithm for continuous control, is intended to create a 5-Axis machining tool path with excellent surface quality. Also, an effectiveness is confirmed through a verification manufacturing.

Hydrodynamic Performance Test of a Turbopump (터보펌프의 수력 성능시험)

  • Hong Soon-Sam;Kim Dae-Jin;Kim Jin-Sun;Choi Chang-Ho;Kim Jin-Han
    • Journal of the Korean Society of Propulsion Engineers
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    • v.10 no.1
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    • pp.18-22
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    • 2006
  • Hydrodynamic performance test was conducted for a fuel pump of a liquid rocket engine turbopump. The pump driven by an electric motor was tested using water. It is experimentally shown that the inducer had very small effect on the pump's head and efficiency but great effect on the pump's cavitation performance. Additionally, inducer test was carried out to investigate the effect of the inducer on the pump in detail, and it was found that the pump reached a critical cavitation number when the inducer head dropped by 55%.

Numerical and experimental investigation on the performance of three newly designed 100 kW-class tidal current turbines

  • Song, Mu-Seok;Kim, Moon-Chan;Do, In-Rok;Rhee, Shin-Hyung;Lee, Ju-Hyun;Hyun, Beom-Soo
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.4 no.3
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    • pp.241-255
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    • 2012
  • Three types of 100 kW-class tidal stream turbines are proposed and their performance is studied both numerically and experimentally. Following a wind turbine design procedure, a base blade is derived and two additional blades are newly designed focusing more on efficiency and cavitation. For the three designed turbines, a CFD is performed by using FLUENT. The calculations predict that the newly designed turbines perform better than the base turbine and the tip vortex can be reduced with additional efficiency increase by adopting a tip rake. The performance of the turbines is tested in a towing tank with 700 mm models. The scale problem is carefully investigated and the measurements are compared with the CFD results. All the prediction from the CFD is supported by the model experiment with some quantitative discrepancy. The maximum efficiencies are 0.49 (CFD) and 0.45 (experiment) at TSR 5.17 for the turbine with a tip rake.