• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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• pp.25-29
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• 2005

Axial fan is used for the supplement of large amount of flows. Axial blowers show relatively high efficiency of the system. The present model of axial fan is for cooling a condenser in an air-conditioning unit that exhibits tendency toward compact size. In order to realize the compact model, the width of an axial blade should be cut down in axial distance. Main interest lies on the performance of the axial blowing system with blades having shorter chord length. One of the important design parameters for axial fan is the shape of the blades of it. Design of blades includes the cross-sectional shape and its dimension, including the chord length. We consider two types of blades; one is NACA airfoil with normal chord length and the other is with shortening chord length by $10\%$ of normal airfoil. Axial blower with the modified blades is essential for the compact model of an air-conditioner. The other design parameters are same in the two cases. Using a wind tunnel follows ASHRAE standards carries out evaluation of performance of the system. Detail of flows around the blades is prepared by velocity measurements using PIV. According to performance estimation, the axial blower with short chord blade show quite close to the performance results, including flow rate and pressure rise, of the standard one. The reason of the two similar results is that the flowpatterns depend on Reynolds number based on the chord length of a blade. In this investigation, the critical chord length is found, in which the flows near the airfoil are so unstable and the performance of the system is decreased. A series of figures is for the detail information on the flow.

• The KSFM Journal of Fluid Machinery
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• v.8 no.4 s.31
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• pp.27-38
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• 2005

The present study investigated the effect of relative position of the blade on blade surface heat transfer. The experiments were conducted in a low speed wind tunnel with a stationary annular turbine cascade. The test section has a single turbine stage composed of sixteen guide vanes and blades. The chord length of the blade is 150 mm and the mean tip clearance of the blade is $2.5\%$ of the blade chord. The Reynolds number based on blade inlet velocity and chord length is $1.5{\times}105$ and mean turbulence intensity is about $3\%$. To investigate the effect of relative position of blade, the blade at six different positions in a pitch was examined. For the detailed mass transfer measurements, a naphthalene sublimation technique was used. In general, complex heat transfer characteristics are observed on the blade surface due to various flow characteristics, such as a laminar flow separation, relaminarization, flow acceleration, transition to turbulence and tip leakage vortices. The results show that the blade relative position affects those heat transfer characteristics because the distributions of incoming flow velocity and turbulence intensity are changed. Especially, the heat transfer pattern on the near-tip region is significantly affected by the relative position of the blade because the effect of tip leakage vortex is strongly dependent on the blade position. On the pressure side, the effect of blade position is not so significant as on the suction side surface although the position and the size of the separation bubble are changed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.5 s.248
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• pp.446-456
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• 2006

The effect of relative position of the stationary turbine blade for the fixed vane has been investigated on blade tip and shroud heat transfer. The local mass transfer coefficients were measured on the tip and shroud fur the blade fixed at six different positions within a pitch. A low speed stationary annular cascade with a single turbine stage was used. The chord length of the tested blade is 150 mm and the mean tip clearance of the blade having flat tip is 2.5% of the blade chord. A naphthalene sublimation technique was used for the detailed mass transfer measurements on the tip and the shroud. The inlet flow Reynolds number based on chord length and incoming flow velocity is fixed to $1.5{\times}10^5$. The results show that the incoming flow condition and heat transfer characteristics significantly change when the relative position of the blade changes. On the tip, the size of high heat/mass transfer region along the pressure side varies in the axial direction and the difference of heat transfer coefficient is up to 40% in the upstream region of the tip because the position of flow reattachment changes. On shroud, the effect of tip leakage vortex on the shroud as well as tip gap entering flow changes as the blade position changes. Thus, significantly different heat transfer patterns are observed with various blade positions and the periodic variation of heat transfer is expected with the blade rotation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.11 s.254
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• pp.1074-1083
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• 2006

In the present study, the effect of blade rotation on blade heat transfer is investigated by comparing with the heat transfer results for the stationary blade. The experiments are conducted in a low speed annular cascade with a single stage turbine and the turbine stage is composed of sixteen guide vanes and blades. The chord length and the height of the tested blade are 150 mm and about 125 mm, respectively. The blade has a flat tip and the mean tip clearance is 2.5% of the blade chord. A naphthalene sublimation method is used to measure detailed mass transfer coefficient on the blade. For the experiments, the inlet Reynolds number is $Re_c=1.5{\times}10^5$, which results in the blade rotation speed of 255.8 rpm. Blade rotation induces a relative motion between the blade and the shroud as well as a periodic variation of incoming flow. Therefore, different heat/mass transfer patterns are observed on the rotating blade, especially near the tip and on the tip. The relative motion reduces the tip leakage flow through the tip gap, which results in the reduction of the tip heat transfer. However, the effect of the tip leakage flow on the blade surface is increased because the tip leakage vortex is formed closer to the surface than the stationary case. The overall heat/mass transfer on the shroud is not affected much by the blade rotation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.4 s.235
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• pp.485-494
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• 2005

For the extensive investigation of local heat/mass transfer on the near-tip surface of turbine blade, experiments were conducted in a low speed stationary annular cascade. The turbine test section has a single stage composed of sixteen guide vanes and blades. The chord length and the height of the tested blade are 150 mm and about 125 mm, respectively. The blade has flat tip geometry and the mean tip clearance is about $2.5{\%}$ of the blade chord. Detailed mass transfer coefficient on the blade near-tip surface was obtained using a naphthalene sublimation technique. The inlet flow Reynolds number based on chord length and incoming flow velocity is changed from $1.0{\times}10^{5}\;to\;2.3{\times}10^{5}.$ Extremely complex heat transfer characteristics are observed on the blade surface due, to complicated flow patterns, such as flow acceleration, laminarization, transition, separation bubble and tip leakage flow. Especially, the suction side surface of the blade has higher heat/mass transfer coefficients and more complex distribution than the pressure side surface, which is related to the leakage flow. For all the tested Reynolds numbers, the heat/mass transfer characteristics on the turbine blade are the similar. The overall averaged $Sh_{c}$ values are proportional to $Re_{c}^{0.5}$ on the stagnation region and the laminar flow region such as the pressure side surface. However, since the flow is fully turbulent in the near-tip region, the heat/mass transfer coefficients are proportional to $Re_{c}^{0.8}.$

• Advances in Energy Research
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• v.6 no.1
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• pp.35-54
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• 2019

A successful blade design must satisfy some criterions which might be in conflict with maximizing annual energy yield for a specified wind speed distribution. These criterions include maximizing power output, more resistance to fatigue loads, reduction of tip deflection, avoid resonance and minimize weight and cost. These criterions can be satisfied by modifying the geometrical parameters of the blade. This study is dedicated to the aerodynamic assessment of a 20 kW horizontal axis wind turbine operating with two possible airfoils; that is $G{\ddot{o}}ttingen$ 413 and NACA 2415 airfoils (the Gottingen airfoil never been used in wind turbines). For this study parameters such as chord (constant, tapered and elliptic), twist angle (constant and linear) are varied and applied to the two airfoils independently in order to determine the most adequate blade configuration that produce the highest annual energy output. A home built numerical code based on the Blade Element Momentum (BEM) method with both Prandtl tip loss correction and Glauert correction, X-Foil and Weibull distribution is developed in Matlab and validated against available numerical and experimental data. The results of the assessment showed that the NACA 2415 airfoil section with elliptic chord and constant twist angle distributions produced the highest annual energy production.

• The KSFM Journal of Fluid Machinery
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• v.3 no.2 s.7
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• pp.7-14
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• 2000

For a given axial turbine blade, reverse design method is developed to improve blade efficiency, optimize blade profile, or repair parts etc. In this process, design parameters for designing axial turbine blade are induced. The induced design parameters are as follows; ellipse at leading edge, radios of trailing edge, axial chord, tangential chord, wedge angle at the inlet, and unguided turning angle. Suction and pressure surfaces of turbine blade are described by cubic polynomials. Two sample blades we chosen and their blade profiles are measured at the mean radius. Values of design parameters for sample blades are obtained by the reverse design method. Re-designed blade profiles using calculated design parameters are compared with the measured data, and they show good agreement. So, the developed design method could be applied to design general turbine blades. Various blade shapes are designed, and they show that designed blade profiles can be adjusted by controlling design parameters.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.4 s.235
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• pp.495-503
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• 2005

Experiments were conducted in a low speed stationary annular cascade to investigate local heat transfer characteristics on the tip and shroud and the effect of inlet Reynolds number on the tip and shroud heat transfer. Detailed mass transfer coefficients on the blade tip and the shroud were obtained using a naphthalene sublimation technique. The turbine test section has a single stage composed of sixteen guide vanes and blades. The chord length and the height of the tested blade are 150 mm and about 125 mm, respectively. The blade has flat tip geometry and the mean tip clearance is about $2.5{\%}$of the blade chord. The inlet flow Reynolds number based on chord length and incoming flow velocity is changed from $1.0{\times}10^{5}\;to\;2.3{\times}10^{5}.$ to investigate the effect of Reynolds number. Flow reattachment after the recirculation near the pressure side edge dominates the heat transfer on the tip surface. Shroud surface has very intricate heat/mass transfer distributions due to complex flow patterns such as acceleration, relaminarization, transition to turbulent flow and tip leakage vortex. Heat/mass transfer coefficient on the blade tip is about 1.7 times as high as that on the shroud or blade surface. Overall averaged heat/mass transfer coefficients on the tip and shroud are proportional to $Re_{c}^{0.65}\;and\;Re_{c}^{0.71},$ respectively.

• Journal of Power System Engineering
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• v.21 no.1
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• pp.70-79
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• 2017

The output power of turbine is greatly affected by the losses generated within the passage. In order to develop a better turbine or loss models, an experimental study was conducted using a linear cascade experimental apparatus. The total pressure loss and flow structures were measured at two cross-sectional planes located downstream of blade row. Measurement was conducted in a steady state for the several different locations of the blade row along the rotational direction. The blade row moved by 20 % of the pitch, and tip clearance was varied from 2% to 8%. Axial-type blades were used and its blade chord was 200mm. A square nozzle was applied and its size was $200mm{\times}200mm$. The experiment was conducted at a Reynolds number of $3{\times}10^5$ based on the chord. Nozzle flow angle sets to $65^{\circ}$ based on the axial direction and the solidity of blade row was 1.38. From the experimental results, the total pressure loss was greatly varied in the receding region than in the entering region. The flow properties within the blade passage were strongly changed according to the location of blade row.

• Journal of KSNVE
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• v.6 no.5
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• pp.661-669
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• 1996

Proposed is an aero-acoustic performance prediction method of axial fan. The fan aerodynamic performance is predicted by combining pitch-averaged quasi 3-D flow analysis with pressure loss models for blade boundary layer and wake, secondary flow, endwall boundary layer and tip leakage flows. Fan noise is assumed to be radiated as dipole distribution type, and its generation is assumed to be mainly due to the vortex street shed from blade trailing edge. The fluctuating pressure and lift on the blade surface are analyzed by incorporating the wake vortex stree shed from blade trailing edge. The fluctuating pressure and lift on the blade surface are analyzed by incorporating the wake vortex street model with thin airfoil theory. The aero-acoustic performance prediction results by the present method are in good agreement with the measured results of several axial fans. With the present prediction method, parametric studies are carried out to investigate the effects of blade chord length and spacing on the efficiency and the noise level of fan. In the case of lightly loaded fan, both efficiency improvement and noise reduction can be achieved by decreasing chord length or by increasing blade specing. However, when fan is designed at highly loaded condition, the noise reduction by increasing blade spacing penalizes the attaninable efficiency of fan.