• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.263-265
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• 2003

The aerodynamic performance of a shrouded tail rotor in hover has been studied by using a compressible inviscid flow solver on unstructured meshes. The numerical method is based on a cell­centered finite-volume discretization and an implicit Gauss-Seidel time integration. The results show that the performance of an isolated rotor without shroud compares well with experiment. In the case of a shrouded rotor, correction of the collective pitch angle is made such that the overall performance matches with experiment to account for the uncertainties of the experimental model configuration. Details of the flow field compare well with the experiment confirming the validity of the present method.

• Aerospace Engineering and Technology
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• v.6 no.2
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• pp.197-204
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• 2007

Effect of rotor tip geometry on the performance of supersonic impulse turbine was investigated experimentally. Using the shrouded supersonic impulse turbine of the 30ton class liquid rocket engine turbopump as a base model, the measured performance of de-shrouded rotor was compared. The effect of nozzle-rotor overlap also has been investigated. It has been found that the magnitude of turbine efficiency is largely affected by the existence of the rotor shroud. However, measured efficiency sensitivity of the de-shrouded supersonic impulse turbine with respect to turbine tip clearance was relatively smaller than that of high performance reaction turbine. It also has been found that there exists nozzle-rotor overlap value which results optimum efficiency in supersonic impulse turbine.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.5
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• pp.9-17
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• 2005

In the early stage of helicopter design, an optimal configuration is usually determined after a numerous parametric study about the aerodynamic performance due to geometric variation. In order to improve the aerodynamic performance of a shrouded tail rotor, optimization of the tip clearance gap between blade and shroud, the blade planform shape, and the arrangement of blade spacing is required. In the present study, the aerodynamic performance characteristics of a shrouded tail rotor due to geometric variation was investigated by using an inviscid compressible unstructured mesh flow solver for rotary wings.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.5
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• pp.1-9
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• 2003

Detailed flow of a shrouded tail rotor in hover is studied by using a compressible inviscid flow solver on unstructured meshes. The numerical method is based on a cell-centered finite-volume discretization and an implicit Gauss-Seidel time integration. Numerical simulation is made for a single blade attached to the center body and guide by the duct by imposing a periodic boundary condition between adjacent rotor blades. The results show that the performance of an isolated rotor without shroud compares well with experiment. In case of a shrouded rotor, correction of the collective pitch angle is made such that the overall performance matches with experiment to account for the uncertainties of the experimental model configuration. Details of the flow field compare well with the experiment confirming the validity of the present method.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.545-548
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• 2002

Turbines have been known to be particularly susceptible to flow-induced self-excited vibration. In such vibrations, direct damping and cross stiffness effects of aerodynamic forces determine rotordynamic stability. In axial turbines with eccentric shrouded rotors, the non-uniform sealing gap causes azimuthal non-uniformities in the seal gland pressure and the turbine torque which destabilize the rotor system. Previously, research efforts focused solely on either the seal flow or the unshrouded turbine passge flow. Recently, a model for flow in a turbine with a statically offset shrouded rotor has been developed and some stiffness predictions have been obtained. The model couples the seal flow to the passage flow and uses a small perturbation approach to determine nonaxiymmetric flow conditions. The model uses basic conservation laws. Input parameters include aerodynamic parameters (e.g. flow coefficient, reaction, and work coefficient); geometric parameters (e.g. sealing gap, depth of seal gland, seal pitch, annulus height); and a prescribed rotor offset. Thus, aerodynamic stiffness predictions have been obtained. However, aerodynamic damping (i.e. unsteady aerodynamic) effects caused by a whirling turbine has not yet been examined. Therefore, this paper presents a new unsteady model to predict the unsteady flow field due to a whirling shrouded rotor in turbines. From unsteady perturbations in velocity and pressure at various whirling frequencies, not only stiffness but also damping effects of aerodynamic forces can be obtained. Furthermore, relative contributions of seal gland pressure asymmetry and turbine torque asymmetry are presented.

• Wind and Structures
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• v.19 no.2
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• pp.199-217
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• 2014

Reported experimental and computational fluid dynamic (CFD) studies have demonstrated significant power augmentation of diffuser shrouded horizontal axis micro wind turbine compared to bare turbine. These studies also found the degree of augmentation is strongly dependent on the shape and geometry of the diffuser such as length and expansion angle. However study flow field over the rotor blades in shrouded turbine has not received much attention. In this paper, CFD simulations of an experimental diffuser shrouded micro wind turbine have been carried out with the aim to understand the mechanisms underpinning the power augmentation phenomenon. The simulations provide insight of the flow field over the blades of bare wind turbine and of shrouded one elucidating the augmentation mechanisms. From the analysis, sub-atmospheric back pressure leading to velocity augmentation at the inlet of diffuser and lowering the static pressure on blade suction sides have been identified as th dominant mechanisms driving the power augmentation. And effective augmentation was achieved for ${\lambda}$ above certain value. For the case turbine it is ${\lambda}$ greater than ${\approx}2$.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.563-568
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• 2015

풍력터변의 성능을 높이기 위한 방법으로 최근 해외에서는 쉬라우드를 장착하여 유입 유량을 증진시키는 형상에 대한 새로운 아이디어가 제안되고 시범적으로 적용되고 있다. 본 연구에서는 쉬라우드가 장착된 수평축 풍력터빈에 대해서 EDISON CFD를 이용하여 쉬라우드 내부로 유입되는 질량 유량의 변동을 몇 가지 형상에 대해 수치적으로 비교 분석하였다. 유동장은 비압축성 난류유동으로 가정하였으며, 수치 해석 결과로부터 쉬라우드 주변의 순환의 세기를 형상 변동에 따라 도출하였다. 쉬라우드 형상으로는 캠버를 갖는 goe 417 에어포일을 두 개의 받음각(5도, 10도)에 대해서 수치해석을 수행하였으며, 브림을 갖는 디퓨저 형상(Wind-lens)에 대해서도 유입 유량 변동과 순환 세기에 대해 수치해석을 수행하고 결과를 상호 비교하였다. 본 연구를 통해 쉬라우드가 발생시키는 순환에 의한 유입 유량 증가 현상을 파악할 수 있었으며, 이로써 풍력터빈의 출력을 증대시킬 수 있음을 확인하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.1
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• pp.102-110
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• 1998

The analysis of lateral hydrodynamic forces in the leakage path between a shrouded pump impeller through wear-ring seal and its housing is presented. Governing equations are derived based on Bulk-flow and Hirs' turbulent lubrication model. By using a perturbation analysis and a numerical integration method, governing equations are solved to yield leakage and rotordynamic coefficients of force developed by the impeller shroud and wear-ring seal. The variation of rotordynamic coefficients of pump impeller shroud and wear-ring seal is analyzed as parameters of rotor speed, pressure difference, shroud clearance, wear-ring seal clearance, and circumferential velocity at the entrance of impeller shroud for a typical multi-stage centrifugal pump.

• Wind and Structures
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• v.35 no.3
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• pp.147-155
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• 2022

This research proposes a wind-lens turbine design that can startup and operate at a low wind speed (< 5m/s). The performance of the wind-lens turbine was investigated using CFD and wind tunnel testing. The wind-lens turbine consists of a 3-bladed horizontal axis wind turbine with a diameter of 0.6m and a diffuser-shaped shroud that uses the suction side of the thin airfoil SD2030 as a cross-section profile. The performance of the 3-bladed wind-lens turbine was then compared to the two-bladed rotor configuration while keeping the blade geometry the same. The 3-bladed wind-lens turbine successfully startup at 1m/s and produced a torque of 66% higher than the bare turbine, while the two-bladed wind-lens turbine startup at less than 4m/s and produced a torque of 186 % higher than the two-bladed bare turbine at the design point. Findings testify that adding the wind-lens could improve the bare turbine's performance at low wind speed.