• International Journal of Fluid Machinery and Systems
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• v.6 no.2
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• pp.94-104
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• 2013

This paper describes the design to increase the blade loading factor of a low speed axial flow fan from normal 0.42 to highly loaded 0.55. A three-dimensional viscous solver is used to model the flows in the highly-loaded and normal loaded stages over its operation range. At the design point operation the static pressure rise can be increased by 20 percent with a deficit of efficiency by 0.3 percent. In the highly loaded fan stage, the rotor hub flow stalls, and separation vortex extends over the rotor hub region. The backflow, which occurs along the stator hub-suction surface, changes the exit flow from the prescribed axial direction. Results in this paper confirm that the limitation of the two dimensional diffusion does not affect primarily on the fan's performance. Highly loaded fan may have actually better performance than its two dimensional design. Three dimensional designing approaches may lead to better highly loaded fan with controlled rotor hub stall.

• The KSFM Journal of Fluid Machinery
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• v.3 no.2 s.7
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• pp.15-23
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• 2000

The present work describes the prediction method for the unsteady flow field and the acoustic pressure field of a ducted axial fan. The prediction method is comprised of time-marching free-wake method, acoustic analogy, and the Kirchhoff-Helmholtz BEM. The predicted sound signal of a rotor is similar to the experiment one. We assume that the rotor rotates with a constant angular velocity and the flow field around the rotor is incompressible and inviscid. Then, a time-marching free-wake method is used to model the fan and to calculate the flow field. The force of each element on the blade is calculated by the unsteady Bernoulli equation. Lowson's method is used to predict the acoustic source. The newly developed Helmholtz-Kirchhoff BEM lot thin body is used to calculate tile sound field of the ducted fan. The ducted fan with 6 blades is analysed and the sound field around the duct is calculated.

• The KSFM Journal of Fluid Machinery
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• v.12 no.1
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• pp.22-27
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• 2009

The important problems that arise in the design and performance of the axial flow turbine are the prediction and control of secondary flows. Some progresses have been made on understanding flow conditions that occur when the inlet endwall boundary layer separates at the point in the endwall and rolls up into the horseshoe vortex. And the flows though an axial turbine tend to be extremely complex due to its inherent unsteady and viscous phenomena. The passing wakes generated from the trailing edge of the stator make an interaction with the rotor. Unsteady flow should be considered rotor/stator interactions. The main purpose of this research is control of secondary flow and improvement efficiency in turbine by leading edge modification in unsteady state. When the wake from the stator ran into the modified leading edge of the rotor, the leading edge generated the weak pressure fluctuation by complex passage flows. In conclusion, leading edge modification(bulb2) results in the reduced total pressure loss in the flow field.

• The KSFM Journal of Fluid Machinery
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• v.14 no.1
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• pp.48-54
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• 2011

The effect of channel cutback on three-dimensional flow fields and aerodynamic losses downstream of a cavity squealer tip has been investigated in a turbine rotor cascade for the squealer rim height-to-chord ratio and tip gap height-to-chord ratio of $h_{st}/c$ = 5.51% and h/c = 2.0% respectively. The cutback length-to-camber ratio is changed to be $CB/c_c$ = 0.0, 0.1, 0.2 and 0.3. The results show that longer cutback delivers not only stronger secondary flow but also higher aerodynamic loss in the tip leakage vortex region, meanwhile it leads to lower aerodynamic loss in the passage vortex region. The discharge of cavity fluid through the cutback opening provides a beneficial effect in the reduction of aerodynamic loss, whereas there also exists a side effect of aerodynamic loss increase due to local wider tip gap near the trailing edge. With increasing $CB/c_c$ from 0.0 to 0.3, the aerodynamic loss coefficient mass-averaged all over the measurement plane tends to increase slightly.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.11
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• pp.1427-1432
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• 2012

As the size of a wind turbine increases, the rotor diameter increases. Rotor blades experience mechanical loads caused by the wind shear and the tower shadow effect. These mechanical loads reduce the life of the wind turbine. Therefore, with increasing size of the wind turbine, wind turbine control system design for the mitigation of mechanical loads is important. In this study, Individual Pitch Control in introduced for reducing the mechanical loads of rotor blades, and a simulation for IPC performance verification is discussed.

• Journal of Hydrogen and New Energy
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• v.23 no.6
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• pp.688-695
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• 2012

The present study represents the effects of boundary condition on the performance of a centrifugal blower at the interference plane between rotational and stationary domains using three dimensional compressible Navier-Stocks equations. Two boundary conditions, frozen-rotor and stage, are compared to analyze the blower performance. Installation angle between the cutoff of a volute casing and a impeller blade is also introduced to evaluate the blower performance and to understand the internal flow inside the blower. Throughout numerical simulation, it is found that the frozen rotor interface method at the interference plane represents well the variations of flow field inside the blower compared to stage interface method. However, pressure has maximum two percent error according to the installation angles while pressure is almost constant for the stage interface method. And stage interface method can relatively well predict the blower performance. Detailed internal flows of the centrifugal blower are compared and analyzed by numerical simulation.

• Journal of Ocean Engineering and Technology
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• v.24 no.4
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• pp.8-12
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• 2010

The use of a tidal-current power system is one source of renewable energy that can minimize the environmental impact of power production and offer many other advantages compared to conventional energy sources. Unlike other energy production approaches, rate of energy production can be precisely predicted and the operational rate is very high. The performance of the rotor, which has a vital role in energy production using tidal currents, is determined by various design factors, and it should be optimized for the specific ocean environment in the field. The horizontal-axis turbine is very sensitive to the direction of flow, and flow direction changes due to rise and fall of the tides. To investigate the performance of the rotor considering the interaction problems with incidence angle of flow, a series of experiments were conducted, and a 3D CFD model was designed and analyzed by ANSYS CFX. The results and findings are summarized in the paper.

• The KSFM Journal of Fluid Machinery
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• v.13 no.2
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• pp.41-47
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• 2010

The effect of incidence angle on the three-dimensional flow and aerodynamic loss in the tip leakage flow region downstream of a turbine rotor cascade has been investigated for two tip gap-to-chord ratios of h/c=0.0% (no tip gap) and 2.0%. The incidence angle is changed to be $i=-10^{\circ}$, $0^{\circ}$, and $5^{\circ}$. The results show that for $i=5^{\circ}$, secondary flows including the passage vortex are intensified noticeably, and there is a strong interaction between the passage and tip leakage vortices. For $i=-10^{\circ}$, however, the passage vortex is weakened significantly, so that there exists only a strong leakage-jet-like secondary flows near the casing wall. For h/c=0.0% and 2.0%, aerodynamic loss tends to increase with increasing i from $-10^{\circ}$ to $5^{\circ}$. A small increment of i in its positive incidence range results in a remarkable aerodynamic loss increase, while increasing i in the negative incidence range leads to a small change in the aerodynamic loss generation.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.2192-2197
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• 2003

The purpose of this 3-D numerical simulation is evaluate the application of a commercial CFD code to predict 3-D flow and power characteristics of wind turbines. The experimental approach, which has been main method of investigation, appears to be its limits, the cost increasing with the size of the wind turbines, hence mostly limited to observing the phenomena on rotor blades. Therefore, the use of Computational Fluid Dynamics (CFD) techniques and Navier-Stokes solvers are considered a very serious contender. The flow solver CFX-TASCflow is employed in all computations in this paper. The 3-D flow separation and the wake distribution of 2 and 3 bladed Horizontal Axis Wind Turbines (HAWTs) are compared to Heuristic model and smoke-visualized experimental result by NREL(National Renewable Energy Laboratory). Simulated 3-D flow separation structure on the rotor blade is very similar to Heuristic model and the wake structure of the wind turbine is good consistent with smoke-visualized result. The calculated power of the 3 bladed rotor by CFD is compared with BEM results by TV-Delft. The CFD results of which is somewhat consist with BEM results, under an error less than 10%.

• Journal of Mechanical Science and Technology
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• v.15 no.12
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• pp.1860-1868
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• 2001

An experimental investigation was carried out to clarify unsteady flow fields with rotating stall cell, especially behavior of stall cell, in a high specific-speed diagonal flow fan. As its specific-speed is vary high for a diagonal flow fan, its pressure-flow rate curve tends to indicate unstable characteristics caused by rotating stall similar to axial flow fan. Although for an axial flow fan many researchers have investigated such the flow field, for a diagonal flow fan tittle study has been done. In this study, velocity fields at rotor Inlet in a high specific-speed diagonal flow fan were measured by use of a single slant hot-wire probe. These data were processed by using the "Double Phase-Locked Averaging"(DPLA) technique, i. e. phases of both the rotor blade and the stall cell were taken into account. The behaviors of stall cell at rotor inlet were visualized for the meridional, tangential and radial velocity.