• Title/Summary/Keyword: Blade tip vortex

Search Result 149, Processing Time 0.022 seconds

NUMERICAL ANALYSIS OF UNSTEADY FLOW FIELD AND AEROACOUSTIC NOISE OF AN AXIAL FLOW FAN (축류팬의 비정상 유동장 및 유동소음의 수치 해석)

  • Kim, Wook;Hur, Nahm-Keon;Jeon, Wan-Ho
    • Journal of computational fluids engineering
    • /
    • v.15 no.4
    • /
    • pp.60-66
    • /
    • 2010
  • Unsteady Reynolds Averaged Navier-Stokes(URANS) and Large Eddy Simulation(LES) simulation of an axial flow fan are calculated upon same conditions and computational grids in order to study aeroacoustic noise of an axial flow fan numerically. Results of computed performance and predicted noise are compared with those of measurement. Both performances show accurate results with a significant difference of less than 5%. However, noise of LES result is more close to measured noise qualitatively than URANS. Levels of tonal noises of both LES and URANS are quite similar with those of measured at BPF(Blade Passing Frequency) in sound spectrum. However, as leading edge separation and tip vortex shedding phenomena of LES are showed more clearly than those of URANS, sound level of broadband noise of LES corresponds better than that of URANS, especially.

Visualization of Unstable Vortical Structure in a Propeller Wake Affected by Simulated Hull Wake (재현된 반류의 영향을 받는 프로펠러 후류 내 불안정한 날개끝 보오텍스 구조에 대한 정량적 가시화)

  • Kim, Kyung-Youl;Paik, Bu-Geun;Ahn, Jong-Woo
    • Journal of the Society of Naval Architects of Korea
    • /
    • v.45 no.6
    • /
    • pp.620-630
    • /
    • 2008
  • The characteristics of complicated propeller wake influenced by hull wake are investigated by using a two-frame PIV (Particle Image Velocimetry) technique. As the propeller is significantly affected by the hull wake in a real marine vessel, the measurements of propeller wake under the hull wake would be certainly necessary for more reliable validation and the prediction of numerical simulation with wake modeling. Velocity field measurements have been conducted in a medium-size cavitation tunnel with a hull wake. Generally, the hull wake generated by the boundary layer of ship's hull produces the different loading distribution on the propeller blade in both upper and lower propeller planes. The difference of the propeller wake behaviors caused by the hull wake is discussed in terms of axial velocity, vorticity and turbulence kinetic energy distribution in the present study.

A Study on the Performance Variation of a Three-Dimensional Hydrofoil Using Jet Flow

  • Eom, Myeong-Jin;Paik, Kwang-Jun;Lee, Ju-Han;Kang, Shin-Min;Kim, Dong-Young
    • Journal of Ocean Engineering and Technology
    • /
    • v.35 no.1
    • /
    • pp.24-37
    • /
    • 2021
  • As one of the development directions of high-performance ships to reduce greenhouse gas emissions, there is research on high-performance propellers. However, in the case of conventional screw propellers, as they have been studied for a long time, there is a limit to improving efficiency only by depending on the conventional design and analysis methods. In this study, we tried to solve the problems using the Coanda effect by spraying a jet on the surface of the hydrofoil. The Coanda hydrofoil consists of a tunnel and jet slit to make jet flow. The computation was performed for each tunnel and slit position, and the efficiency according to the geometry of the hydrofoil was analyzed. In addition, a study on the 3D geometry change was conducted to analyze the performance according to the span direction spraying range and hydrofoil shape. As the height of the slit and the diameter of the tip were lower, when the slit is located in the center of the hydrofoil, the lift force increased and the drag force decreased. The increase rate of lift-to-drag ratio was different according to the shape of the hydrofoil, and the efficiency of the spraying condition of 0.1S-0.5S, which had the least effect on the vortex at the tip of the blade, was high for all 3D hydrofoils. When the geometry of the slit was optimized, and also the shape and spray range of the hydrofoil in 3D was considered, the efficiency of the jet sprayed hydrofoil was increased.

Development of high performance and low noise compact centrifugal fan for cooling automotive seats (자동차 시트 쿨링용 고성능·저소음 컴팩트 원심팬 개발)

  • Kim, Jaehyun;Ryu, Seo-Yoon;Cheong, Cheolung;Jang, Donghyeok;An, Mingi
    • The Journal of the Acoustical Society of Korea
    • /
    • v.37 no.6
    • /
    • pp.396-403
    • /
    • 2018
  • In this paper, a high-performance and low-noise centrifugal fan is developed for cooling automotive seats which provide a driver with pleasant driving environment. First, the flow characteristics of the existing fan unit was analyzed using a fan performance tester and CFD (Computational Fluid Dynamics) simulations. The analysis of the predicted flow field indicated vortex flow near the tip of fan hub and stagnation flow on the top of fan hub. Two design points are devised to reduce the vortex flow and the stagnation flow observed in the existing fan unit. First, the cut-off clearance which is the minimum distance between the fan blade and the fan housing is increased to reduce the vortex strength and, as a result, to reduce the overall sound pressure level. Second, the hub shape is more modified to eliminate the stagnation flow. The validity of proposed design is confirmed through the numerical analysis. Finally, a prototype is manufactured with a basis on the numerical analysis result and its improved flow and noise performances are confirmed through the P-Q curves measured by using the Fan Tester and the SPL (Sound Pressure Level) levels measured in the anechoic chamber.

Numerical Analyses and Wind Tunnel Tests of a Propeller for the MAV Propulsion (초소형 무인기 추진용 프로펠러의 전산해석 및 풍동시험)

  • Cho, Lee-Sang;Lee, Sea-Wook;Cho, Jin-Soo
    • Journal of the Korean Society for Aeronautical & Space Sciences
    • /
    • v.38 no.10
    • /
    • pp.955-965
    • /
    • 2010
  • The MH-75 propeller for the MAV propulsion is designed using a free vortex design method which considers design parameters such as the hub-tip ratio, the twist angle distribution, the maximum camber location and the chord length of the propeller blade. Aerodynamic characteristics of the MH-75 propeller are predicted by changing the flight speed using the frequency domain panel method. And, the thrust characteristics of the MH-75 propeller are measured using the balance system of the subsonic wind tunnel for the validation of numerical results. The performance characteristics of the MH-75 propeller satisfied with design requirements. Numerical results of the MH-75, which are predicted by the frequency domain panel method, are more agree with experimental results compare with XFOIL.

Effect of Heat/Mass Transfer in the turbine blade internal passage with various rib arrangement (회전하는 터빈 블레이드 이차유로내 요철 배열이 열/물질전달에 미치는 영향)

  • Lee, Sei-Young;Cho, Hyung-Hee
    • Proceedings of the KSME Conference
    • /
    • 2001.11b
    • /
    • pp.22-29
    • /
    • 2001
  • The present study investigates the effects of various rib arrangements and rotating on heat/mass transfer in the cooling passage of gas turbine blades. The cooling passage has very complex flow structure, because of the rib turbulator and rotating effect. Experiments and numerical calculation are conducted to investigate the complex flow structures and heat transfer characteristics; the numerical computation is performed using a commercial code, FLUENT ver.5, to calculate the flow structures and the experiments are conducted to measure heat/mass transfer coefficients using a naphthalene sublimation technique. For the rotating duct tests, the test duct, which is the cross section of is $20mm\times40mm$ (the hydraulic diameter, $D_h$, of 26.7 mm, has two-pass with $180^{\circ}$ turning and the rectangular ribs on the wall. The rib angle of attack is $70^{\circ}$ and the maximum radius of rotation is $21.63D_h$. The partition wall has 10 mm thickness, which is 0.5 times to the channel width, and the distance between the tip of the partition wall and the outer wall of the turning region is 26.7 mm $(1D_h)$. The turning effect of duct flow makes the very complex flow structure including Dean type vortex and high turbulence, so that the heat/mass transfer increases in the turning region and at the entrance of the second pass. The Coriolis effect deflects the flow to the trailing surface, resulting in enhancement of the heat/mass transfer on the trailing surface and reduction on the leading surface in the first pass. However, the opposite phenomena are observed in the second pass. The each rib arrangement makes different secondary flow patterns. The complex heat/mass transfer characteristics are observed by the combined effects of the rib arrangements, duct rotation and flow turning.

  • PDF

Aerodynamic Shape Optimization of Helicopter Rotor Blades in Hover Using a Continuous Adjoint Method on Unstructured Meshes (비정렬 격자계에서 연속 Adjoint 방법을 이용한 헬리콥터 로터 블레이드의 제자리 비행 공력 형상 최적설계)

  • Lee, S.-W.;Kwon, O.-J.
    • Journal of the Korean Society for Aeronautical & Space Sciences
    • /
    • v.33 no.1
    • /
    • pp.1-10
    • /
    • 2005
  • An aerodynamic shape optimization technique has been developed for helicopter rotor blades in hover based on a continuous adjoint method on unstructured meshes. The Euler flow solver and the continuous adjoint sensitivity analysis were formulated on the rotating frame of reference for hovering rotor blades. In order to handle the repeated evaluation of the design cycle efficiently, the flow and adjoint solvers were parallelized using a domain decomposition strategy. A solution-adaptive mesh refinement technique was adopted for the accurate capturing of the tip vortex. Applications were made for the aerodynamic shape optimization of Caradonna-Tung rotor blades and UH60 rotor blades in hover. The results showed that the present method is an effective tool to determine optimum aerodynamic shapes of rotor blades requiring less torque while maintaining the desired thrust level.

Numerical and experimental investigation of conventional and un-conventional preswirl duct for VLCC

  • Shin, Hyun-Joon;Lee, Jong-Seung;Lee, Kang-Hoon;Han, Myung-Ryun;Hur, Eui-Beom;Shin, Sung-Chul
    • International Journal of Naval Architecture and Ocean Engineering
    • /
    • v.5 no.3
    • /
    • pp.414-430
    • /
    • 2013
  • This paper shows the study of preswirl duct as an effective energy saving devices that have been devised and reviewed to support the propeller performance, especially for the ship of VLCC with large block coefficients. From the bare hull wake measurements, typical upper/lower asymmetry of hull wake at the propeller disk was found. The 2 kinds of pre-swirl duct, Unconventional half circular duct and Conventional circular pre-swirl duct have been designed and reviewed to recover the loss of propeller running in that condition. The general function of the pre-swirl duct was set to work against this asymmetry of wake and generate pre-swirled flow into the propeller against the propeller rotating direction. The optimum self propulsion tests with various angle configurations were carried out and the best configuration was decided. Accordingly, cavitation test was carried out with best configuration of unconventional half circular duct. The blade surface and tip vortex cavitation behaved smoother when the duct was mounted. The hull pressure amplitudes reflected this difference, so the hull pressure amplitude with duct was smaller than that of without duct.

Investigation on relative contribution of flow noise sources of ship propulsion system (선박 추진시스템 유동 소음원 상대적 기여도 분석)

  • Ha, Junbeom;Ku, Garam;Cheong, Cheolung;Seol, Hanshin;Jeong, Hongseok;Jung, Minseok
    • The Journal of the Acoustical Society of Korea
    • /
    • v.41 no.3
    • /
    • pp.268-277
    • /
    • 2022
  • In this study, each component of flow noise source of underwater propeller installed to the scale model of the KVLCC2 is investigated and the effect of each noise source on underwater-radiated noise is quantitatively analyzed. The computation domain is set to be the same as the test section of the large cavitation tunnel in the Korea Research Institute of Ship and Ocean Engineering. First, for the high-resolution computation of flow field which is noise source region, the incompressible multiphase Delayed Detached Eddy Simulation is performed. Based on flow simulation results, the Ffowcs Williams and Hawkings integral equation is used to predict underwater-radiated noise and its validity is confirmed through the comparison with the tunnel experiment result. For the quantitative comparison on the contribution of each noise source, the spectral levels of sound pressure and power levels predicted using propeller tip-vortex cavitation, blade surface and rudder surface as the integral region of noise sources are investigated. It is confirmed that the cavitation which is monopole noise source significantly contributed to the underwater-radiated noise than propeller blades and rudder which is dipole noise source, and the rudder have more contribution than propeller blades due to the influence of the propeller wake.