• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.59.2-59.2
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• 2011

Although there are many activities on the construction of wind farm to produce amount of power from the wind, in practice power productions are not as much as its expected capabilities. This is because a lack of both the prediction of wind resources and the aerodynamic analysis on turbines with far wake effects. In far wake region, there are velocity deficits and increases of the turbulence intensity which lead to the power losses of the next turbine and the increases of dynamic loadings which could reduce system's life. The analysis on power losses and the increases of fatigue loadings in the wind farm is needed to prevent these unwanted consequences. Therefore, in this study velocity deficits have been predicted and aerodynamic analysis on turbines in the far wake is carried out from these velocity profiles. Ainslie's eddy viscosity wake model is adopted to determine a wake velocity and aerodynamic analysis on wind turbines is predicted by the numerical methods such as blade element momentum theory(BEMT) and vortex lattice method(VLM). The results show that velocity recovery is more rapid in the wake region with higher turbulence intensity. Since the velocity deficit is larger when the turbine has higher thrust coefficient, there is a huge aerodynamic power loss at the downstream turbine.

• Journal of Mechanical Science and Technology
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• v.17 no.8
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• pp.1234-1245
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• 2003

An experimental study was carried out to investigate the reduced frequency effect on the near-wake of an elliptic airfoil oscillating in pitch. The airfoil was sinusoidally pitched around the center of the chord between -5$^{\circ}$and ＋25$^{\circ}$angles of attack at an airspeed of 3.4 m/s. The chord Reynolds number and reduced frequencies were 3.3 ${\times}$10$^4$, and 0.1, 0.7, respectively Phase-averaged axial velocity and turbulent intensity profiles are presented to show the reduced frequency effects on the near-wake behind the airfoil oscillating In pitch. Axial velocity defects in the near-wake region have a tendency to increase in response to a reduced frequency during pitch up motion, whereas it tends to decrease during pitch down motion at a positive angle of attack. Turbulent intensity at positive angles of attack during the pitch up motion decreased in response to a reduced frequency, whereas turbulent intensity during the pitch down motion varies considerably with downstream stations. Although the true instantaneous angle of attack compensated for a phase-lag is large, the wake thickness of an oscillating airfoil is not always large because of laminar or turbulent separation.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.2
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• pp.198-204
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• 2011

This paper presents the experimental result to investigate the characteristics of turbulent wake generated by submarine. A SUBOFF nude model which was assumed as an axial -symmetric body was used to create wake, and a thin strut was mounted on the top of the model. The experiments were conducted in a circulating water channel(CWC), and a hot-film was used to measure the turbulence in wake cross-section at the distance range of 0.0~2.0L from the model. The hot film anemometer measured turbulent velocity fluctuations, and the timeaveraged mean velocity and turbulent intensity are obtained from the acquired time-series data. Measured results show well the general characteristics of turbulent intensity, kinetic energy and mean velocity distribution. Also, experimental equations are derived. These experimental equations show well the general characteristics of the turbulent wake behind the submerged body with simple configuration.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.3
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• pp.364-371
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• 2011

This paper presents experimental results and derived experimental equations to investigate the turbulent wake characteristics generated by the self-propelled SUBOFF submarine model. A self-propelled SUBOFF model which was assumed as an axial-symmetric body was used to create wake, and a thin strut was mounted on the topside of the model. The experiments were conducted in a circulating water channel(CWC), and the hot-film was used to measure the turbulence in wake cross-section at the distance range of 0.0~2.0L from the model. The hot film anemometer measured turbulent velocity fluctuations, and the time-averaged mean velocity and turbulent intensity are obtained from the acquired time-series data. Measured results show well the general characteristics of turbulent intensity, kinetic energy and mean velocity distribution. Also, this paper presents derived experimental equations, which is extended result to the reference [1]. These experimental equations show well the general characteristics of the turbulent wake behind the self-propelled submerged body.

• Journal of the Korean Society of Visualization
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• v.15 no.3
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• pp.47-51
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• 2017

In this study, we investigate the wake characteristics in laminar inflow and two different turbulent inflow cases. To solve the flow with wind turbines and its wake, we use large eddy simulation (LES) technique with actuator line method (ALM) and turbulent inflow of Turbsim. We perform the quantitative analysis of velocity deficit and turbulent intensity in laminar inflow case and turbulent inflow case with different turbulent intensity. In turbulent inflow, unsteady strong wake recovery which is highly fluctuated in time. Normalized power in turbulent inflow case is also highly fluctuated with unsteady wake recovery, while that in laminar inflow has quasi steady characteristic in power generation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.1
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• pp.21-29
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• 2016

The wake effects behind wind turbines were investigated by using data from a Met Mast tower and the SCADA (Supervisory Control and Data Acquisition) system for a wind turbine. The results of the wake investigations and predicted values for the velocity deficit based on the eddy viscosity model were compared with the turbulence intensity from the Lange model. As a result, the velocity deficit and turbulence intensity of the wake increased as the free stream wind speed decreased. In addition, the magnitude of the velocity deficit for the center of the wake using the eddy viscosity model was overestimated while the turbulence intensity from the Lange model showed similarities with measured values.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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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.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1795-1800
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• 2003

An experimental study was carried out to investigate near-wake characteristics of an elliptic airfoil oscillating in pitch. The airfoil was sinusoidally pitched about the half chord point between $-5^{\circ}C$ and $+25^{\circ}C$ angles of attack at the freestream velocities of 3.4 and 23.1 m/s The corresponding Reynolds numbers based on the chord length were $3.3{\times}10^4$ and $2.2{\times}10^5$, respectively. A hot-wire anemometer was used to measure the near-wake flow variable at the reduced frequency of 0.1. Ensemble-averaged velocity and turbulence intensity profile were presented to examine the near-wake characteristics depending on the Reynolds number. The axial velocity deficit in the near-wake region tend to decrease with the increase in the Reynolds number a found in many stationary airfoil test . Turbulence intensity in the near-wake region have a tendency to decrease with the increase in the Reynolds number during the pitch-up motion, whereas it shows different feature during the pitch-down motion either the laminar boundary layer or turbulent boundary layer separation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.3
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• pp.334-346
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• 2003

An experimental study was carried out to investigate near-wake characteristics of an elliptic airfoil oscillating in pitch. The airfoil was sinusoidally pitched about the half chord point between -5$^{\circ}$and +25$^{\circ}$angles of attack at the freestream velocities of 3.4 and 23.1 m/s. The corresponding Reynolds numbers based on the chord length were 3.3$\times$10$_{4}$ and 2.2$\times$10$^{5}$ , respectively. A hot-wire anemometer was used to measure the near-wake flow variables at the reduced frequency of 0.1. Ensemble-averaged velocity and turbulence intensity profiles were presented to examine the near-wake characteristics depending on the Reynolds number. The axial velocity deficit in the near-wake region tends to decrease with the increase in the Reynolds number as found in many stationary airfoil tests. Turbulence intensity in the near-wake region have a tendency to decrease with the -increase in the Reynolds number during the pitch-up motion, whereas it shows different feature during the pitch-down motion according to the separation characteristics.

• 한국가시화정보학회:학술대회논문집
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• 2004.12a
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• pp.169-175
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• 2004

The characteristics of flow around a rotating propeller were investigated using PIV technique. For each of four different blade phases of $0^{\circ},\;18^{\circ},\;36^{\circ}\;and\;54^{\circ}$four hundred instantaneous velocity fields were ensemble averaged to investigate the spatial evolution of the flow around a propeller. The phase-averaged mean velocity fields show that the viscous wake formed by the boundary layers developed on the blade surfaces and the slipstream contraction in the near-wake region. The out-of-plane velocity component and strain rate had large values at the locations of the tip and trailing vortices. The boundary layer developed along the ship hull bottom surface of the ship stern provides a strong turbulent shear layer, affecting the vortex structure in the propeller near-wake. As the flow develops in the downstream direction, the trailing vortices formed behind the propeller hub move upward slightly due to the presence of the hull wake and free surface. The turbulence intensity has large values around the tip and trailing vortices. As the wake moves downstream, the strength of the vorticity diminishes and the turbulence intensity increases due to turbulent diffusion and active mixing between the tip vortices and adjacent wake flow.