• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2591-2596
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• 2007

The effect of incidence angle on the three-dimensional flow and aerodynamic loss in the downstream region of a high-turning turbine rotor blade has been investigated with a straight miniature five-hole probe. The incidence angle is changed to be +10, +5, 0, -10, -20, -30 and -40 degrees. The results show that the positive incidence reinforces the three-dimensional vortical flows within the turbine passage including the passage vortex, but the negative incidence weaken them significantly. A small increment in the positive incidence angle results in a remarkable aerodynamic loss increase, while increasing the incidence angle in the negative range leads to a very small change in the aerodynamic loss.

• 대한기계학회논문집B
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• 제31권4호
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• pp.357-366
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• 2007

The present study investigated local heat/mass transfer characteristics on the surface of the rotating turbine blade with various incidence angles. The experiments are conducted in a low speed annular cascade with a single stage turbine. The blade has a flat tip with the mean tip clearance of 2.5% of the blade chord. A naphthalene sublimation method is used to measure detailed mass transfer coefficient on the blade. At design condition, the inlet Reynolds number is $Re_c=1.5{\times}10^5$ which results in the blade rotation speed of 255.8 rpm. Also, the effect of off-design condition is examined with various incidence angles between $-15^{\circ}$ and $+7{\circ}$. The results indicated that the incidence angle has significant effects on the blade surface heat transfer. In mid-span region, the laminar separation region on the pressure side is reduced and the laminar flow region on the suction side shrinks with increasing incidence angle. Near the tip, the effect of tip leakage flow increases in span wise and axial directions as the incidence angle decreases because the tip leakage flow is formed near the suction side surface. However, the effect of tip leakage flow is reduced with positive incidence angle.

• 대한기계학회논문집B
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• 제26권9호
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• pp.1292-1301
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• 2002

An experimental study of turbine performance is conducted with various incidence angles on a rotating turbine rotor. 5 different incidence angles are applied from -17$^{\circ}$to 13$^{\circ}$with 7.5$^{\circ}$gaps. In order to precisely set up the incidence angles at the rotor inlet, 5 turbine discs are manufactured with the different fir tree section. Total-to-total efficiencies are obtained on the several off-design points with considering the exit total pressure, which is meas fred at 12 locations between the hub and casing using a pressure rake. The degree of reaction is 0.373 at the mean radius, and Reynolds number based on the rotor chord is 0.86$\times$10$^{5}$ at the turbine inlet on the design point experiment. The experiment on a single-stage turbine is conducted at the low-pressure and low-speed state, but it is sufficient to consider the blade loading effect due to the rotating apparatus even though the total pressure loss at the exit is increased proportionally to the turbine output power. The experimental results recommend 6$^{\circ}$as an optimum incidence angle on the turbine blade design. The total-to-total efficiency is steeply decreased when the incidence angle is over $\pm$9$^{\circ}$ from the optimum incidence angle. In the range of less than -10$^{\circ}$incidence angle, 7.5$^{\circ}$ reduction of incidence angle generates 15% decrease of total-to-total efficiency. This result is obtained on the same rotor blade by changing only the rotational speed to minimize the effect of profile and secondary flow loss in the passage. Experimental results show that the change rate of total-to-total efficiency according to the incidence angle change is unchanged although the turbine operates at the off-design condition.

• 대한기계학회논문집B
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• 제29권8호
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• pp.887-894
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• 2005

This paper describes effects of incidence angle on the wake turbulent flow of a high-turning turbine rotor blade. For three incidence angles of -5, 0 and 5 degrees, energy spectra as well as profiles of mean velocity magnitude and turbulence intensity at mid-span are reported in the wake. Vortex shedding fiequencies are obtained from the energy spectra. The result shows that as the incidence angle changes from -5 to 5 degrees, the suction-side wake tends to be widened and the deviation angle is increased. Strouhal numbers based on the shedding fiyequencies have a nearly constant value, regardless of the tested incidence angles.

• 대한기계학회논문집B
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• 제29권6호
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• pp.696-702
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• 2005

The effect of incidence angle on the endwall heat (mass) transfer characteristics within a turbine rotor cascade passage has been investigated by employing the naphthalene sublimation technique. The experiments are carried out at the Reynolds number of $2.78{\times}10^5$ for two incidence angles of -5 and 5 dog. The result shows that the incidence angle has a considerable influence on the transport phenomena over the endwall. The positive incidence angle tends to promote development of the pressure-side leg of a leading-edge horseshoe vortex. The endwall thermal load is augmented by 7.5 percents at i = -5 deg but is reduced by 2.5 percents at i = 5 deg, in comparison with that at the design condition.

• Earthquakes and Structures
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• 제27권3호
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• pp.227-237
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• 2024

The incidence angle of seismic excitation relative to the two orthogonal major axes of structures has been a subject of considerable research interest. Previous studies have primarily focused on single-storey symmetric and asymmetric structures, suggesting a minimal effect of incidence angle on structural behavior. This research extends the investigation to multi-storey structures, including vertically irregular configurations, using a comprehensive set of 20 near fault and 20 far field seismic excitation. The study employs nonlinear time-history analysis with a bidirectional hysteresis model to capture inelastic deformations accurately. Various structural models, including one-storey and two- storey regular structures (R1, R2) and vertically irregular structures with setbacks in one direction (IR1) and both directions (IR2), are analysed. The analysis reveals that the incidence angle has no discernible impact over the response of regular multi-storey structures. However, vertically irregular structures exhibit notable responses at corner columns, which decrease towards central columns, irrespective of the incidence angle. This response is attributed to the inherent mass distribution and stiffness irregularities rather than the angle of seismic excitation. The findings indicate that for both near fault and far field seismic excitation, the incidence angle's impact remains marginal even for complex structural configurations. Consequently, the study suggests that the angle of incidence of seismic excitation need not be a primary consideration in the seismic design of both regular and vertically irregular structures. These conclusions are robust across various structural models and seismic excitation characteristics, providing a comprehensive understanding the impact of incidence angle on seismic response.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.55-62
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• 2003

This paper describes the effect of the incidence angle on the turbulence structure in the wake of a turbine rotor blade at the low inlet free-stream turbulence level. For three incidence angles of -5, 0 and 5 degrees, mid-span energy spectrum as well as mid-span profiles of mean velocity magnitude and turbulence intensity are reported at three downstream locations in the wake. Vortex shedding frequencies are obtained from the energy spectrum. The result shows that as the incidence angle changes from-5 to 5 degrees, the boundary layer on the suction surface tends to be thickened, which results in widening of the wake. Strouhal numbers based on the shedding frequencies have a nearly constant value of 0.3, independent of tested incidence angles.

• 대한방사선기술학회지:방사선기술과학
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• 제35권2호
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• pp.83-92
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• 2012

경추 정면 방사선검사시 하악골, 후두골의 겹침방지, 경추 추체의 배열 및 관절의 형태 등을 관찰하기 위하여 X선 입사각을 머리 방향으로 $15{\sim}20^{\circ}$를 주고 있는 것이 보편적이다. 하지만 한국인의 체형에 맞는 입사각에 대한 연구는 거의 이루어지지 않고 있다. 이에 본 연구에서는 한국인에 적합한 입사각을 찾고, 방법을 제시하는데 목적이 있다. 입사각을 측정하기 위하여 서산에 위치한 S병원을 내원한 환자 1,044명을 대상으로 하였으며, 제 2번~제 5번 경추의 길이, 피사체-영상판 거리(OID), 제2번경추(axis)의경사도, 초점-영상판 간거리(FID)를 측정하였으며, 연령대 성별에 대한 평균값을 측정하여 적용공식에 의하여 입사각을 산출하였다. 경추 제2번~제5번의 평균길이는 6cm 이였으며, 10대부터 20대까지는 경추의 길이가 커지고 30대 이후로는 경추의 길이가 작아졌으며, 남성과 여성의 차이는 약 1cm 차이가 나타났다(p<.001). OFD는 연령대, 성별과 상관없이 거의 같은 값이 측정이 되었다. 제2번 경추(axis)의 경사도는 10대와 20대는 경사도가 증가하였지만, 30대 이후로는 작게 나타났다. 또한 남성과 여성은 약 $2^{\circ}$차이가 났다(p<.001). FID의 측정 결과, 연령대, 성별과 상관없이 거의 같은 값이 측정되었으며, 이 값으로 입사각을 측정한 결과, 10대는 $15.9^{\circ}$, 20대 $16.9^{\circ}$, 30대 $16.6^{\circ}$, 40대 $16.2^{\circ}$, 50대 $15.9^{\circ}$, 60대 $14.5^{\circ}$로 측정되었다. 10대와 20대까지 입사각이 증가하였지만, 30대 부터는 입사각이 작게 나타났다. 또한 10대는 남성과 여성이 같은 값으로 측정이 되었고, 20대부터는 남성과 여성이 $2^{\circ}$ 차이가 나타났다. 입사각과 제 2번~제 5번 경추의 길이측정, OID, 제 2번 경추의 경사도, FID와의 상관관계를 실시하였고, 입사각과 모두 유의한 상관관계가 나타났다(p<.001). 본 연구에서 경추의 평균 길이, OID, FID, 제2번 경추(axis)의 경사도에 따라서 입사각이 다르게 나타났고, 성별과 연령에 따라 입사각이 다른 것을 알 수 있었다. 그러므로 경추 정면검사 시 연령, 성별을 고려하여 입사각을 설정하면서 검사를 시행하여야 함이 사료되며, 향후 경추검사의 입사각을 설정할 때 참고 자료로 이용될 것으로 기대된다.

• 대한기계학회논문집B
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• 제31권4호
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• pp.349-356
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• 2007

The present study investigated local heat/mass transfer characteristics on the tip of the rotating turbine blade with various incoming flow incidence angles. The experiments are conducted in a low speed annular cascade with a single stage turbine. The blade has a flat tip with a mean tip clearance of 2.5% of the blade chord. The incoming flow Reynolds number is $1.5{\times}10^5$ at design condition. To examine the effect of off-design condition, the experiments with various incidence angles ranging between $-15^{\circ}$ and $+7{\circ}$ were conducted. A naphthalene sublimation method is used to measure detailed mass transfer coefficient on the blade. The results indicated that the incidence angle strongly affects the behavior of tip leakage flow around the blade tip and consequently plays an important role in determining heat transfer characteristics on the tip. For negative incidence angles, the heat/mass transfer in the upstream region on the tip decreases by up to 20%. On the contrary, for positive incidence angles, much higher heat transfer coefficients are observed even with small increase of incidence angle.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.55.2-55.2
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• 2011

This research aims to study the effects of the incidence angle and surface temperature on the power generation performance of a thin-film CIGS solar cell for solar powered unmanned aerial vehicles (UAVs). The test rig consists of a unit CIGS solar cell is installed on a table whose angle is controlled manually. A K-type thermocouple is attached to the solar cell surface for temperature measurements. A solar module analyzer measures the voltage and current generated from the test solar cell. The solar module analyzer also calculates the maximum solar power and efficiency of the solar cell. All test data are acquired in a PC. Test results show that the solar cell efficiency decreases significantly with increasing incidence angle and increasing surface temperature in general. As the incidence angle increases from 0 degree to 90 degree, the solar cell efficiency decreases by 60%. The solar cell efficiency decreases by 10% with increasing solar cell surface temperature from $20^{\circ}C$ to $30^{\circ}C$, for exmaple. The direct cooling method of the solar cell using dry ice decreases dramatically the solar cell surface temperature, thus increasing the solar cell efficiency by 15%.