• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.439-448
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• 2009

Three inducers were designed to avoid cavitation instabilities. This was accomplished by avoiding the interaction of tip cavity with the leading edge of the next blade. The first one was designed with extremely larger leading edge sweep, the second and third ones were designed with smaller incidence angle by reducing the inlet blade angle or increasing the design flow rate, respectively. The inducer with larger design flow rate has larger outlet blade angle to obtain sufficient pressure rise. The inducer with larger sweep could suppress the cavitation instabilities in higher flow rates more than 95% of design flow coefficient, owing to weaker tip leakage vortex cavity with stronger disturbance by backflow vortices. The inducer with larger outlet blade angle could avoid the cavitation instabilities at higher flow rates, owing to the extension of the tip cavity along the suction surface of the blade. The inducer with smaller inlet blade angle could avoid the cavitation instabilities at higher flow rates, owing to the occurrence of the cavity first in the blade passage and its extension upstream. The cavity shape and suction performance were reasonably simulated by three dimensional CFD computations under the steady cavitating condition, except for the backflow vortex cavity. The difference in the growth of cavity for each inducer is explained from the difference of the pressure distribution on the suction side of the blades.

• Journal of computational fluids engineering
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• v.21 no.2
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• pp.62-69
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• 2016

It has been highly demanded to improve the accuracy of CFD(Computational Fluid Dynamics) methods for the assessment of the hydrodynamic performance of marine propellers in cavitating and non-cavitating flows. This paper presents a validation study on the numerical simulation of the tip vortex flow of a non-cavitating marine propeller SVA VP1304. The calculations are carried out by using the Reynolds averaged Navier-Stokes(RANS) approach, where the Reynolds Stress Model(RSM) is used for turbulence closure. The present paper contains a grid dependence test for the propeller open water simulations and a special emphasis is placed on conducting a local grid adaptation on the blade tip and in the tip vortex to reasonably reproduce the velocity and the pressure in the tip vortex flow field. The numerical results are compared with the experimental validation data, which are published in the second International Symposium on Marine Propulsors 2011(SMP'11). The present numerical results show a reasonable agreement with the experiments.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.161-164
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• 2006

Three-dimensional flow and aerodynamic loss in the tip-leakage flow region of a high-turning first-stage turbine rotor blade with a squealer tip have been measured with a straight miniature five-hole probe for the tip gap-to-chord ratio, h/e, of 2,0%. This squealer tip has a indent-to-chord ratio, $h_{st}/c$, of 5.5%. The results are compared with those for a plane tip ($h_{st}/c\;=\;0.0%$). The squealer tip tends to reduce the mass flow through the tip gap and to suppress the development of the tip-leakage vortex. Therefore, it delivers lower aerodynamic loss in the near-tip region than the plane tip does. At the mid-span, however, the aerodynamic loss has nearly the same value for the two different tips.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.25-28
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• 2008

An aerodynamic calculation in hover of KUH main rotor blade is performed using a three-dimensional unstructured hybrid mesh viscous flow solver. The flow solver utilizes a vertex-centered finite-volume scheme that is based on the Roe's flux-difference splitting with an implicit Jacobi/Gauss-Seidel time integration. The eddy viscosity are estimated by the Spalart-Allmaras one-equation turbulence model. A solution-adaptive mesh refinement technique is used for efficient capturing of the tip vortex. Calculations are performed at several operating conditions with varying collective pitch setting for KUH main rotor blade in hover. Good agreements are obtained between the present and other results using HOST and CAMRAD II in overall rotor performance. It is demonstrated that the present vertex-centered flow solver is an efficient and accurate tool for the assessment of rotor performance in hover.

• 유체기계공업학회:학술대회논문집
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• 1998.12a
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• pp.240-247
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• 1998

Leakage vortices formed near blade tip causes an increase of total pressure loss near casing endwall region and as a result, the efficiency of rotor decreases. The reduction of rotor efficiency is related to the size of tip clearance. In this study, the three-dimensional flowfields in an axial flow rotor were calculated with varying tip clearance under various flow rates, and the numerical results were compared with experimental ones. The effects of tip clearance and attack angle on the leakage vortex and overall performance, and the less distributions were investigated through numerical calculations. In this study, tip leakage flow rate and total pressure loss by tip clearance were evaluated using numerical results and aprroximate equations were presented to evaluate the reduction of rotor efficiency by tip leakage flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.9 s.252
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• pp.913-920
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• 2006

Three-dimensional flow and aerodynamic loss in the tip-leakage flow region of a high-turning first-stage turbine rotor blade with a squealer tip have been measured with a straight miniature five-hole probe for the tip gap-to-chord ratio, h/c, of 2.0%. This squealer tip has a indent-to-chord ratio, $h/{st}/c$, of 5.5%. The results are compared with those for a plane tip $(h_{st}/c=0.0%)$. The squealer tip tends to reduce the mass flow through the tip gap and to suppress the development of the tip-leakage vortex. Therefore, it delivers lower aerodynamic loss in the near-tip region than the plane tip does. At the mid-span, however, the aerodynamic loss has nearly the same value for the two different tips.

• International Journal of Aeronautical and Space Sciences
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• v.10 no.2
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• pp.95-105
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• 2009

The flow fields around the HARTII rotor were numerically investigated using a viscous flow solver on adaptive unstructured meshes. An overset mesh and a deforming mesh technique were used to handle the blade motion including blade deflection, which was obtain from the HARTII experimental data. A solution-adaptive mesh refinement technique was also used to capture the rotor wake effectively. Comparison of the sectional normal force and pitching moment at 87% radial station between the two cases, with and without the blade deflection, showed that the blade loading is significantly affected by blade torsion. It was found that as the mesh was refined, the strength of tip vortex is better preserved, and the magnitude of high frequency blade loading, caused by blade-vortex interaction (BVI), is further magnified. It was also found that a proper time step size, which corresponds to the cell size, should be used to predict unsteady solutions accurately. In general, the numerical results in terms of the unsteady blade loading and the rotor wake show good agreement with the experimental data.

• Journal of the Korean Society of Visualization
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• v.15 no.1
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• pp.19-24
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• 2017

In this study, we conduct a numerical experiment of the single 5MW NREL wind turbine and compare the performance of various vortex core identification for the wake behind the wind turbine. In the kinetic analysis of wind turbine, 20% velocity deficit at 200 s is observed, showing wake which contains tip vortex near blade tip and rotor vortex at the center of the wind turbine. Time series of velocity and turbulent intensity show numerical simulation converge to a quasi-steady state near 200 s. In the comparison between methods for vortex identification, ${\lambda}_2$-method has good performance in terms of tip vortex, rotor vortex, vortex during its cascade process compared to vorticity magnitude criteria, ${\Delta}$-method. We conclude that ${\lambda}_2$-method is suitable for vortex identification method for wake visualization.

• The KSFM Journal of Fluid Machinery
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• v.2 no.1 s.2
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• pp.73-80
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• 1999

Leakage vortices formed new blade tip causes an increase of total pressure loss near the casing endwall region and as a result, the efficiency of rotor decreases. The reduction of rotor efficiency is related to the size of the tip clearance. In this study, the three-dimensional flowfields in an axial flow rotor were calculated by varying the tip clearance under various flow rates, and the numerical results were compared with experimental ones. The effects of tip clearance and attack angle on the leakage vortex and overall performance, and the loss distributions were investigated through numerical calculations. In this study, tip leakage flow rate and total pressure loss by tip clearance were evaluated using numerical results and approximate equations were presented to evaluate the reduction of rotor efficiency by tip leakage flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.12
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• pp.1750-1757
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• 2003

This paper describes the flow measurements inside the blade passage of an axial flow fan by using a rotating hot-wire probe sensor from a relative flame of reference fixed to the rotor blades. The validity of fan rotor designed by a streamline curvature equation was performed by the measurement of the three-dimensional flow upstream and downstream of the fan rotor using a 5-hole pitot tube. The vortical flow structure near the rotor tip can be clearly observed by the measurements of a relative velocity and its fluctuation on quasi-orthogonal planes to a tip leakage vortex. Larger vortical flow, which results in higher blockage in the main flow, is formed according to decrease a flow rate. The vortical flow spreads out to the 30 percent span from the rotor tip at near stall condition. In the design operating condition, the tip leakage vortex is moved downstream while the center of the vortex keeps constant in the spanwise direction. Detailed characteristics of a velocity fluctuation with relation to the vortex were also analyzed.