• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.92-98
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• 2003

Turbine blades experience significant surface degradation with service. This paper presents experimental evidence of blade surface roughness reducing turbine efficiency. Performance tests were conducted in a low speed, single-stage axial flow turbine rig with roughened blade surfaces. Sheets of sandpaper with equivalent sandgrain roughnesses of 106 and $400{\mu}m$ were used to roughen the blades. In these tests, effects of roughened stator vanes and rotor blades were separately evaluated. In the fully rough regime ($k_{s}=400{\mu}m$), the experimental results show an 11 percent decrease in normalized efficiency with roughness only on stator vanes ; an 8 percent decrease with roughness only on rotor blades ; and a 19 percent decrease with roughness on both the stator and rotor blades. In the transitionally rough regime ($k_{s}=106{\mu}m$), the trends are similar approximately 4 percent decrease with either roughened stator or roughened rotor and an 8 percent decrease with roughness on both stator and rotor blades. Thus, roughened stator vanes incur more performance penalty than roughened rotor blades.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.173-179
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• 2012

Steady and unsteady three-dimensional RANS simulations have been performed on partial admission supersonic axial turbine having backward/forward sweep angles(${\pm}15^{\circ}$) and the results are compared with each other. The objective of this paper is to study the effect of unsteadiness on turbine flow characteristics and performances. The all results indicated that the losses of unsteady simulations were greater than those of steady cases. It was also shown that BSW model give the effect on the reducing of mass flow rates of tip leakage. In unsteady simulation, the increase of t-to-s efficiency at Rotor Out plane was observed more clearly.

• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.449-455
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• 2009

A reversible axial flow fan called jet fan has been widely used for longitudinal ventilation in road tunnels to secure a safe and comfortable environment cost-effectively. As shifting the flow direction is usually made by only switching the rotational direction of an electric motor due to heavy duty, rotor blades having identical aerodynamic performance for bidirectional flow should be necessary. However, such aerodynamically desirable blades haven't been developed sufficiently, since most of the related studies have been done from the viewpoint of unidirectional flow. In the present paper, we demonstrate a method to profile the blade section suitable for bidirectional flow, which is validated by studying the aerodynamic performances of rotor blades of a two-stage jet fan experimentally and numerically.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.273-276
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• 2006

To generate electricity from wind energy, wind turbine generally has a rotor blade. Since this rotor blade is a kind of the rotating machinery, the wake from the rotor is very Important role in the side of the aerodynamic performances. Thus the study about wake is essential to analyze wind turbine aerodynamics. In this study wake characteristics are analyzed by hot-wire probe in the K.A.F.A(Korea Air Force Academy) wind tunnel. It is possible to analyze the wake characteristics by hot-wire probe from acquiring the velocity fluctuations at given positions in the flow. This velocity data are arranged by trigger signal at same azimuth of the blade in periodic manner of the rotor blade. From this various wake characteristics are found : radial and axial position of the tip vortex, vortex core characteristics in the flow etc.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2518-2523
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• 2007

In this paper, thermo-flow characteristics of an outer-rotor type of a BLDC motor are numerically analyzed using three-dimensional turbulence modeling. In an advance design of BLDC motor, cooling blades and holes are preferred for the enhanced cooling performances. Rotating the blades and holes generates axial air flow passing through stator slots, which cools down stator by forced convection. For the present study, a new design of the BLDC motor has been developed and major design parameters such as the arrangement of cooling holes, the area of cooling holes, and cooling blades and the cooling blade angle, are analyzed for the enhanced convective heat transfer rate. It is found that the convective heat transfer rate of the new BLDC motor model is increased by about 8.1%, compared to that of the reference model.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.264-270
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• 2002

This paper presents roughness effects on flow characteristics and efficiency of multi-stage axial compressor using numerical simulation. which is carried out with a commercially available software, CFX-TASCflow. In this paper, the third of four stages of GE low pressure compressor is considered including me stator and rue rotor. Mixing-plane approach is adopted to model the interface between the stator and the rotor: it is appropriate for steady state simulation. First, a flat plate simulation was performed to validate how exact the numerical simulation predicts the roughness effect for smooth and rough walls. Then GE compressor model was calculated about at each roughness height. Concluding, very small roughness height largely affects the performance of compressor and the increasing rate of loss decrease as roughness height increase.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.209-214
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• 2002

The present study is to compare the performance of turbulence models in the analysis of the complex flowfield of an axial flow compressor. Baldwin-Lomax turbulence model and k-$\omega$ turbulence model were selected for the comparison. The thin-layer Wavier-Stokes equation was calculated by explicit, finite-difference numerical scheme. A spatially-varying time-step and an implicit residual smoothing were used to improve convergence. Experimental measurements for NASA rotor 37 were cited fer the comparison with numerical data. The compared two turbulence models gave similar performance over all except for total pressure.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.42-48
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• 2004

Numerical simulation of viscous compressible flow in turbomachinery cascade involves many problems due to the complex geometry of blade but also flow phenomena. In the present study, numerical investigations have been performed to examine the three-dimensional flow characteristics inside the transonic linear turbine cascades using a commercial code, FLUENT. Multi-block H-type grids are applied to the high-turning turbine rotor blades and comparisons with the experimental data and the numerical results have been done. In addition, the effects of turbulence models on the prediction of the endwall flows are analyzed in the sense of the flow compressibility.

• Journal of computational fluids engineering
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• v.11 no.4 s.35
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• pp.1-8
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• 2006

Clocking effects of a stator on the performance and internal flow in an UTRC 1.5 stage axial turbine are investigated using a three-dimensional unsteady flow simulation. Six relative positions of two rows of stator are investigated by positioning the second stator being clocked in a step of 1/6 pitch. The relative efficiency benefit of about 1% is obtained depending on the clocking positions. However, internal flows have some different characteristics from that in the previous study at the best and worst efficiency positions, since the first stator wake is mixed out with the rotor wake before arriving at the leading edge of the second stator. Instead of the first stator wake, it is found that the wake interaction of the first stator and rotor has a important role on a relative efficiency variation at each clocking position. The time-averaged local efficiency along the span at the maximum efficiency is more uniform than that at the minimum efficiency. That is, the spanwise efficiency distribution at the minimum efficiency has larger values in mid-span but smaller values near the hub and casing in comparison to those at the maximum efficiency. Moreover, the difference between maximum and minimum instantaneous efficiencies during one period is found to be smaller at the maximum efficiency than at the minimum efficiency.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.473-480
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• 2005

Clocking effects of a stator on the performance and internal flow in an UTRC 1.5 stage axial turbine are investigated using a three-dimensional unsteady flow simulation. Six relative positions of two rows of stator are investigated by positioning the second stator being clocked in a step of 1/6 pitch. The relative efficiency benefit of about 1% is obtained depending on the clocking positions. However, internal flows have some different characteristics from that in the previous study at the best and worst efficiency positions, since be first stator wake is mixed out with the rotor wake before arriving at the leading edge of the second stator. Instead of the first stator wake, it is found that the wake interaction of the first stator and rotor has a important role on a relative efficiency variation at each clocking position. The time-averaged local efficiency along the span at the maximum efficiency is more uniform than that at the minimum efficiency. That is, the spanwise efficiency distribution at the minimum efficiency has larger values in mid-span but smaller values near the hub and casing in comparison to those at the maximum efficiency. Moreover, the difference between maximum and minimum instantaneous efficiencies during one period is found to be smaller at the maximum efficiency than at the minimum efficiency.