• Journal of Mechanical Science and Technology
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• v.19 no.8
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• pp.1632-1648
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• 2005

The effects of Reynolds number on the non-nulling calibration of a typical cone-type five-hole probe have been investigated for the representative Reynolds numbers in turbomachinery. The pitch and yaw angles are changed from - 35 degrees to 35 degrees with an angle interval of 5 degrees at six probe Reynolds numbers in range between $6.60{\times}10^3\;and\;3.17{\times}10^4$. The result shows that not only each calibration coefficient itself but also its Reynolds number dependency is affected significantly by the pitch and yaw angles. The Reynolds-number effects on the pitch- and yaw-angle coefficients are noticeable when the absolute values of the pitch and yaw angles are smaller than 20 degrees. The static-pressure coefficient is sensitive to the Reynolds number nearly all over the pitch- and yaw-angle range. The Reynolds-number effect on the total-pressure coefficient is found remarkable when the absolute values of the pitch and yaw angles are larger than 20 degrees. Through a typical non-nulling reduction procedure, actual reduced values of the pitch and yaw angles, static and total pressures, and velocity magnitude at each Reynolds number are obtained by employing the calibration coefficients at the highest Reynolds number ($Re=3.17{\times}10^4$) as input reference calibration data. As a result, it is found that each reduced value has its own unique trend depending on the pitch and yaw angles. Its general tendency is related closely to the variation of the corresponding calibration coefficient with the Reynolds number. Among the reduced values, the reduced total pressure suffers the most considerable deviation from the measured one and its dependency upon the pitch and yaw angles is most noticeable. In this study, the root-mean-square data as well as the upper and lower bounds of the reduced values are reported as a function of the Reynolds number. These data would be very useful in the estimation of the Reynolds-number effects on the non-nulling calibration.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.1
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• pp.131-138
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• 1998

Conventional yaw functions are compared with actual response of a hot wire to various yaw angles, and a new function is proposed, which can be applied at large yaw angles and low velocities. To compare the accuracy of the new yaw function with those of the conventional ones, measurements are made for the jet flow at the nozzle exit and at .chi./D=15 with an X hot-wire probe. In the potential core, the flow angles reduced by the present function, ideal angle method and full velocity-angle method are shown to be more accurate than those reduced by the cosine function and Hinze's formula. No matter which yaw functions are used, the profiles of mean velocity and turbulence intensity show little discrepancy at .chi./D=15. However, there is a significant difference between the probability density functions obtained by the present function, ideal angle method and full velocity-angle method and those obtained by the cosine function and Hinze's formula.

• Wind and Structures
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• v.17 no.5
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• pp.553-564
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• 2013

By using the nonlinear aerostatic stability theory together with the method of mean wind decomposition, a method for nonlinear aerostatic stability analysis is proposed for long-span suspension bridges under yaw wind. A corresponding program is developed considering static wind load nonlinearity and structural nonlinearity. Taking a suspension bridge with three towers and double main spans as an example, the full range aerostatic instability is analyzed under wind at different attack angles and yaw angles. The results indicate that the lowest critical wind speed of aerostatic instability is gained when the initial yaw angle is greater than $0^{\circ}$, which suggests that perhaps yaw wind poses a disadvantage to the aerostatic stability of a long span suspension bridge. The results also show that the main span in upstream goes into instability first, and the reason for this phenomenon is discussed.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.189-192
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• 2002

In this paper, the submarine model, called DARPA SUBOFF model, has been numerically analyzed to investigate the aerodynamic forces variation in terms of angle of attacks and yaw angles. The SUBOFF model is consisted of the three parts : axisymmetric body, fairwater, and four symmetric stern appendages. Three dimensional unsteady incompressible Wavier-Stokes equation was used on curvilinear multi-block grid system. To validate the present code, the SUBOFF tare hull and an ellipsoid at angle of attacks of $10^{\circ}\;and\;30^{\circ}$ were simulated and a good agreement with experiments was obtained. After the code validation, the flows over SUBOFF model were simulated at three different angle of attacks and yaw angles. The variation of aerodynamic forces in terms of angle of attack and yaw angle were calculated. Also, to understand the flow features around a submarine with variation of yaw and attack angle, the pressure contours and streamlines were plotted.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.2
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• pp.287-301
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• 2013

The present paper deals with the problems of yaw angle effects on podded propulsor performance. The study aims at providing insights on characteristics of podded propulsors in azimuthing condition. In this regard, a wide numerical simulation that concerned yaw angle effect measurement on podded propeller performance was performed. The Reynolds-Averaged Navier Stokes (RANS) based solver is used in order to study the variations of hydrodynamic characteristics of podded propulsor at various angles. At first, the propeller is analyzed in open water condition in absence of pod and strut. Next flow around pod and strut are simulated without effect of propellers. Finally, the whole unit is studied in zero yaw angle and azimuthing condition. Structured and unstructured mesh techniques are used for single propeller and podded propulsor. The performance curves of the propeller obtained by numerical method are compared and verified by the experimental results. The characteristic parameters including the torque and thrust of the propeller, the axial force and side force of unit are presented as function of velocity advance ratio and yaw angle. The results shows that the propeller thrust, torque and podded unit forces in azimuthing condition depend on velocity advance ratio and yaw angle.

• Wind and Structures
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• v.28 no.2
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• pp.71-87
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• 2019

The yaw and interference effects of blades affect aerodynamic performance of large wind turbine system significantly, thus influencing wind-induced response and stability performance of the tower-blade system. In this study, the 5MW wind turbine which was developed by Nanjing University of Aeronautics and Astronautics (NUAA) was chosen as the research object. Large eddy simulation on flow field and aerodynamics of its wind turbine system with different yaw angles($0^{\circ}$, $5^{\circ}$, $10^{\circ}$, $20^{\circ}$, $30^{\circ}$ and $45^{\circ}$) under the most unfavorable blade position was carried out. Results were compared with codes and measurement results at home and abroad, which verified validity of large eddy simulation. On this basis, effects of yaw angle on average wind pressure, fluctuating wind pressure, lift coefficient, resistance coefficient,streaming and wake characteristics on different interference zone of tower of wind turbine were analyzed. Next, the blade-cabin-tower-foundation integrated coupling model of the large wind turbine was constructed based on finite element method. Dynamic characteristics, wind-induced response and stability performance of the wind turbine structural system under different yaw angle were analyzed systematically. Research results demonstrate that with the increase of yaw angle, the maximum negative pressure and extreme negative pressure of the significant interference zone of the tower present a V-shaped variation trend, whereas the layer resistance coefficient increases gradually. By contrast, the maximum negative pressure, extreme negative pressure and layer resistance coefficient of the non-interference zone remain basically same. Effects of streaming and wake weaken gradually. When the yaw angle increases to $45^{\circ}$, aerodynamic force of the tower is close with that when there's no blade yaw and interference. As the height of significant interference zone increases, layer resistance coefficient decreases firstly and then increases under different yaw angles. Maximum means and mean square error (MSE) of radial displacement under different yaw angles all occur at circumferential $0^{\circ}$ and $180^{\circ}$ of the tower. The maximum bending moment at tower bottom is at circumferential $20^{\circ}$. When the yaw angle is $0^{\circ}$, the maximum downwind displacement responses of different blades are higher than 2.7 m. With the increase of yaw angle, MSEs of radial displacement at tower top, downwind displacement of blades, internal force at blade roots all decrease gradually, while the critical wind speed decreases firstly and then increases and finally decreases. The comprehensive analysis shows that the worst aerodynamic performance and wind-induced response of the wind turbine system are achieved when the yaw angle is $0^{\circ}$, whereas the worst stability performance and ultimate bearing capacity are achieved when the yaw angle is $45^{\circ}$.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.4 s.148
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• pp.460-466
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• 2006

The three-dimensional RANS equations were applied to analyze the flow field of a submarine. To validate the code, the DARPA SUBOFF bare hull and an eliipsoid at angles of attack of $10^{\circ}\;and\;30^{\circ}$ were simulated and good agreement with experiments was obtained. After the code validation, the flows over the full configuration of DARPA SUBOFF model having a fairwater and four stern appendages were simulated at four angles of attack $(0^{\circ},\;10^{\circ},\;20^{\circ},\;30^{\circ})$ and three yaw angles $(10^{\circ},\;20^{\circ},\;30^{\circ})$ Specifically, the pressure contours and streamlines of fairwater and stern appendage were compared as the angle of attack and yaw angle changed. The variations of hydrodynamic forces were also calculated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.1
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• pp.85-92
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• 2000

Easy measurement method of orthogonal triple-sensor hot-wire anemometer is developed. Advantages of the new method is that it does not require either the exact orthogonality of the installed wires which cannot be kept during the probe manufacture and repair, nor the knowledge of the wire installation angles and the yaw and pitch coefficient of the wires. The new method introduced yaw and pitch calibration coefficients which are designed to increase monotonically with yaw and pitch angles. So the resulting calibration network is simple to recognize compared with that of the previously suggested calibration method. Verification experiments showed good accuracy and independency of the directional calibration on velocity.

• Journal of computational fluids engineering
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• v.4 no.3
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• pp.1-11
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• 1999

This paper describes the flow field analysis of an automobile with crosswind effects of 15°, 30° 45° and 60° of yaw angles. The governing equations of the 3-D incompressible Navier-Stokes equations are solved by the iterative time marching scheme. The Chimera grid technique has been applied to efficiently simulate the flow around the side-view mirror. The computated surface pressure coefficients have been compared with experimental results and a good agreement has been achieved. The A- and C-pillar vortex and other flow phenomena around the ground vehicle are evidently shown. The variation of aerodynamic coefficients of drag, lift, side force and moments with respect to yaw angle is systematically studied.

• Journal of Mechanical Science and Technology
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• v.18 no.6
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• pp.1042-1051
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• 2004

The vortex flow characteristics of a sharp-edged delta wing at high angles of attack were studied using a computational technique. Three dimensional, compressible Reynolds-averaged Navier-Stokes equations were solved to understand the effects of the angle of yaw, angle of attack, and free stream velocity on the development and interaction of vortices and the relationship between suction pressure distributions and vortex flow characteristics. The present computations gave qualitatively reasonable predictions of vortical flows over a delta wing, compared with past wind tunnel measurements. With an increase in the angle of yaw, the symmetry of the pair of leading edge vortices was broken and the vortex strength was decreased on both windward and leeward sides. An increase in the free stream velocity resulted in stronger leading edge vortices with an outboard movement.