• Title/Summary/Keyword: Attack Angle of $45^{\circ}$

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A Study on Aerodynamic Properties of Two-Dimensional Rectangular Prism in Various Angles of Attack (다양한 영각을 갖는 2차원 장방형 각주의 공력특성에 관한 연구)

  • 송근택;김유택;이영호
    • Journal of Advanced Marine Engineering and Technology
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    • v.26 no.4
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    • pp.485-492
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    • 2002
  • The present study is aimed to reveal macroscopic aerodynamic characteristics of two-dimensional rectangular prisms with three aspect ratios(D/H=1, 2 and 3) and six angles of attack($0^{circ}, 10^{circ}, 13.5^{circ}, 20^{circ}, 30^{circ} and 45^{\circ}$). The Reynolds number is fixed as $1\times10^4$. The SOLA-based revised finite difference method for the conservation form on irregular grid was adopted as a new numerical method. Instantaneous flow patterns at $45^{\circ}$ in case of D/H=2 and D/H=3 show larger asymmetric wake development which is closely related to the sharp decrease of drag coefficients at higher angles of attack range. Vorticity propagation into enlarged wake region is conjectured to be responsible for this phenomenon. The Strouhal number is found to be sensitive to the angle of attack at higher aspect ratios(D/H=2 and 3).

Heat Transfer Enhancement by the Combined Effect of Louver Angle and Angle of Attack of Vertex Generator (와류발생기의 충돌각과 루버각의 상호작용에 의한 열전달촉진)

  • 박병규;정재동;이준식
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.6
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    • pp.477-484
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    • 2002
  • A numerical investigation of the performance of the plate heat exchanger with rectangular winglet is conducted to examine the combined effect of vortex generator and louver fins. Velocity and temperature fields and spanwise averaged Nu and friction factor are presented. Enhancement of heat transfer and flow loss penalty is evident. A Parametric study of three factors (Re, angle of attack and louver angle) with levels of 5 (Re= 300, 500, 700, 900, 1100), 4($\alpha=15^{\circ}, 30^{\circ}, 45^{\circ}, 90^{\circ},$), and 4($\beta=0^{\circ}, 15^{\circ}, 30^{\circ}, 45^{\circ}$), respectively, indicates the performance defined by the ratio of heat transfer enhancement to flow loss penalty shows monotonic behavior for each parameter alone but the interactions between parameters is found to be considerable effect on the performance of heat exchanger and should be considered in design. The effect of stamping is also examined.

Heat Transfer and Frictions in the Convergent/divergent Channel with Λ/V-shaped Ribs on Two Walls

  • Kim, Beom-soo;Lee, Myung-sung;Ahn, Soo-whan
    • International Journal of Aeronautical and Space Sciences
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    • v.18 no.3
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    • pp.395-402
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    • 2017
  • The local heat transfer and total pressure drops of developed turbulent flows in the ribbed rectangular convergent/divergent channels with ${\Lambda}/V-shaped$ ribs have been investigated experimentally. The channels have the exit hydraulic diameter ($D_{ho}$) to inlet hydraulic diameter ($D_{hi}$) ratios of 0.67 for convergence and 1.49 for divergence, respectively. The ${\Lambda}/V-shaped$ ribs with three different flow attack angles of $30^{\circ}$, $45^{\circ}$, and $60^{\circ}$ are manufactured with a fixed rib height (e) of 10 mm and the ratio of rib spacing (S) to height (e) of 10 on the walls. Thermal performances of the ribbed rectangular convergent/divergent channels are compared with the smooth straight tube under identical pumping power. The results show that the flow attack angle of $45^{\circ}$ with ${\Lambda}-shaped$ rib has the greatest thermal performance at all the Reynolds numbers studied in the convergent channel; whereas, the flow attack angle of $60^{\circ}$ with V-shaped rib has the greatest thermal performance over Reynolds number of 30,000 in the divergent channel.

Performance estimation of conical picks with slim design by the linear cutting test (I): depending on attack angle variation (선형절삭시험에 의한 슬림 코니컬커터의 절삭성능 평가(I): Attack Angle 변화에 의한 결과)

  • Choi, Soon-Wook;Chang, Soo-Ho;Park, Young-Taek;Lee, Gyu-Phil
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.16 no.6
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    • pp.573-584
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    • 2014
  • In this study, the variations of cutter acting forces depending on cutting conditions were examined to obtain basic data for roadheader cutting head design. The linear cutting tests were performed in the condition of different attack angles, penetration depths, cutter spacings by using a slim conical pick for the light cutting condition. Cutter acting forces were measured by 3-directional load cell under different test conditions, and the analysis for cutting performance were carried out after calculating average values of the measured results. It is confirmed that the optimal cutting condition for the mortar specimen is the 50 degree attack angle, the cutter spacing of 12 mm, the cutting depth of 9 mm which are obtained from the analysis results. In addition, 50 degree attack angle is more effective than 45 degree attack angle to design optimal specifications of cutting head.

Flow and Heat Transfer Characteristics due to the Variations of the Angle of Attack at the Vortex Generators located behind a Circular Cylinder (원주 후미에 부착된 와동발생기의 영각 변화에 따른 유동 및 열전달 특성)

  • 하홍영;홍철현;양장식;이기백
    • Journal of Advanced Marine Engineering and Technology
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    • v.26 no.4
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    • pp.439-449
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    • 2002
  • Experimental investigations of the flow structure and heat transfer enhancement in a channel with a built-in circular cylinder and a wing-let type vortex generator are presented. Without any vortex generators, relatively low heat transfer takes place in the downstream of the circular cylinder where is a recirculation region with low velocity fluid is formed. However with a wing-let type longitudinal vortex generator in the wake region behind the cylinder, heat transfer in the region can be enhanced. In order to control the strength of longitudinal vortices, the angle of attack of the vortex generators is varied from $20^{circ} to 45^{\circ}$, but spacings between the vortex generations are fixed to be 5 mm. The 3-dimensional mean velocity field downstream of the vortex generator is measured by a five-hole pressure probe, and the hue-capturing method using thermochromatic liquid crystals has been used to provide the local distribution of the heat transfer coefficient. The vorticity field and streamwise velocity contour are obtained from the velocity field. Streamwise distributions of averaged Stanton number on the measurement planes show very similar trends for all the experimental cases($\beta=20^{circ}, 30^{circ} and 45^{\circ}$). Circulation strength and heat transfer coefficient have the maximum values when the angle of attack($\beta$) is $30^{\circ}$.

Effects of Rib Angles on Heat Transfer in a Divergent Square Channel With Ribs on One Wall (한 면에 리브가 설치된 확대 정사각 채널에서 리브 각이 열전달에 미치는 효과)

  • Lee, Myung Sung;Ahn, Soo Whan
    • Journal of Advanced Marine Engineering and Technology
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    • v.39 no.6
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    • pp.609-613
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    • 2015
  • In this study, the experiments are performed to investigate the local heat transfer and pressure drops of developed turbulent flows in the diverging square channels along the axial distance. The square divergent channels are manufactured with a fixed rib height (e) = 10 mm. Four different parallel angled ribs ($a=30^{\circ}$, $45^{\circ}$, $60^{\circ}$, and $90^{\circ}$) are placed on the channel's one-sided wall only. TThe measurement are conducted within the range of Reynolds numbers from 22,000 to 79,000. The results show that a rib angle-of-attack of $45^{\circ}$ produces the best heat-transfer performance.

Effects of Duct Aspect Ratios on Heat/Mass Transfer With Discrete V-Shaped Ribs (쐐기형 단락요철이 설치된 덕트의 종횡비가 열/물질 전달에 미치는 영향)

  • Lee, Dong-Hyun;Rhee, Dong-Ho;Cho, Hyung-Hee
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.1453-1460
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    • 2003
  • The present study investigates the effects of rib arrangements and aspect ratios of a rectangular duct simulating the cooling passage of a gas turbine blade. Two different V-shaped rib configurations are tested with the aspect ratios (W/H) of 3 to 6.82. One is the continuous V-shaped rib configuration with $60^{\circ}$ attack angle, and the other is the discrete V-shaped rib configuration with $45^{\circ}$ attack angle. The square ribs with the pitch to height ratio of 10.0 are installed on the test section in a parallel arrangement for both rib configurations. Reynolds numbers based on the hydraulic diameter are changed from 10,000 to 30,000. A naphthalene sublimation method is used to measure local heat/mass transfer coefficients. For the continuous V-shaped rib configuration, two pairs of counter-rotating vortices are generated in a duct, and high transfer region is formed at the center of the ribbed walls of the duct. However, for the discrete V-shaped rib configuration with $45^{\circ}$ attack angle, complex secondary flow patterns are generated in the duct due to its geometric feature, and more uniform heat/mass transfer distributions are obtained for all tested cases

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A formula for the Decision of the Riprap Size for the Local Scour Protection around Bridge Piers (교각주위 국부세굴 방지를 위한 사석크기 결정 공식)

  • Choe, Gye-Un;Kim, Hyeon-Tae;An, Gyeong-Su
    • Journal of Korea Water Resources Association
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    • v.34 no.6
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    • pp.753-761
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    • 2001
  • In this paper, the experiments to decide the riprap size for the local scour protection at bridge piers and the coefficients of attack angle were conducted. A formula for the decision of the riprap size and a figure for the coefficients of attack angle were suggested based upon the experimental results. The coefficients of attack angle indicate different values based on the variation of the length-width ratio of bridge pier and the coefficients are increased by the increment of the attack angle. In this paper, the experiments using the piers having the opening ratios of 90%, 92.86% and 95% were conducted. Also, the attack angles 0$^{\circ}$, 15$^{\circ}$, 30$^{\circ}$, 45$^{\circ}$ and 60$^{\circ}$ as well as four different length-width ratios of the bridge pier were utilized. The suggested formula were compared with 6 different formulas and the riprap sizes calculated using the equation suggested in this paper indicate the similar patterns with the formula suggested by Richardson. The suggested formula in this paper can be widely applied in the riprap design for the local scour protection around the bridge pier with the consideration of the attack angle to the flow.

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Experimental Investigations of Flow Characteristics by Wing Type Vortex Generators Set up Behind a Circular Cylinder in a Rectangular Channel (사각채널내 와동발생기가 부착된 원형실린더 하류 유동 특성에 대한 실험적 연구)

  • 이상민;하홍영;양장식;이기백
    • Journal of Advanced Marine Engineering and Technology
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    • v.25 no.5
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    • pp.1076-1085
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    • 2001
  • Experimental investigations of the longitudinal vortices, which are produced by wing type vortex generators set up behind a circular cylinder in a rectangular channel, are presented. When the circular cylinder is set up in the rectangular channel, a horseshoe vortex is formed just upsteam of the circular cylinder. It generates a turbulent wake region behind the circular cylinder. Therefore, the region of the pressure loss behind the circular cylinder in increased and the size of the wake is small. These problems can be achieved by longitudinal vortices which are generated by wing-type vortex generator. In order to control the strength of longitudinal vortices, the angle of attack of the vortex generators is varied from 20 degree to 45, but the spacing between the vortex generators is fixed 6cm. The 3-dimensional mean velocity measurements are made using a five-hole probe. The vorticity field and streamwise velocity contour are obtained from the velocity field. The following results are obtained. Circulation strength is the maximum value when the angle of attack($\beta$) is $30^{\circ}$, and the vorticity field and streamwise velocity contour in case of $\beta$=$20^{\circ}$ show the trend similar to these in case of $\beta$=$30^{\circ}$, but do not in case of $\beta$=$45^{\circ}$.

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Enhanced heat transfer in the convergent rectangular channels with ∧/∨-shaped ribs on one wall (한 면에 ∧/∨형 리브가 있는 2벽면 수축 사각채널의 열전달 증가)

  • Lee, Myung-Sung;Yu, Ji-Ui;Jeong, Hee-Jae;Choi, Dong-Geun;Ha, Dong-Jun;Go, Jin-Su;Ahn, Soo-Whan
    • Journal of Advanced Marine Engineering and Technology
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    • v.40 no.4
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    • pp.270-274
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    • 2016
  • The effect of the rib angle-of-attack on heat transfer in the convergent channel with ${\vee}/{\wedge}$-shaped ribs was examined experimentally. Four differently angled ribs (a = $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, and $90^{\circ}$) were placed to only the one sided wall. The ribbed wall was manufactured with a fixed rib height (e) of 10 mm and rib spacing (p)-to-height (e) ratio of 10. The convergent channel had a length of 1,000 mm and a cross-sectional areas of $100mm{\times}100mm$ at inlet and $50mm{\times}100mm$ at exit. The measurement was conducted for the Reynolds numbers ranging from 22,000 to 75,000. The results show that the Nusselt number is generally higher at higher Reynolds number and that an angle-of-attack of $45^{\circ}$ at the ${\wedge}$-shaped rib produces the greatest Nusselt number.