Seung-Hee Kang

Comparison of Aerodynamic Loads for Horizontal Axis Wind Turbine (I): with and without Turbulent Inflow

ABSTRACT Thisstudyfocusedontheaerodynamicloadsofthehorizontalaxiswindturbinebladeduetothenormalturbulenceinflowcondition.Normalturbulencemodel(NTM)includesthevariationsofwindspeedanddirection,anditischaracterizedbyturbulenceintensityandstandarddeviationofflowfluctuation.IEC61400-1recommendsthefatigueanalysisfortheNTMandthenormalwindprofile(NWP)conditions.TheaerodynamicloadsareobtainedatthebladehubandthelowspeeddriveshaftforMWclasshorizontalaxiswind turbine which is designed by using aerodynamically optimized procedure. The6-componentsofaerodynamicloadsareinvestigatedbetweennumericalresultsandloadcomponentsanalysis.FromthecalculatedresultsthemaximumamplitudesofoscillatedthrustandtorqueforLSSwithturbulentinflowconditionareabout5~8timeslargerthanthosewithnoturbulentinflowcondition.Itturnsoutthattheaerodynamicloadanalysiswithnormalturbulencemodelisessentialforstructuraldesignofthewindturbineblade. 초 록 본 연구에서는 난류 유입조건을 갖는 수평축 풍력터빈 블레이드의 공력 하중에 대해 초점을 맞추어 연구하였다.난류모델은 풍속과 방향에 대한 변동을 포함하며,그 특성은 난류강도와 표준편차로 표현된다.IEC61400-1에서는 정상 난류 모델과 정상 풍속 측면도에 대해서 피로해석을 수행하도록 규정하고 있다.이를 위해 공력 최적설계 절차를 통해 얻어낸 MW급 수평축 풍력터빈 블레이드 허브와 저속 회전축에 대한 공력하중 해석을 수행한다.공력하중 성분은 수치적인 절차를 통해 얻어내며 이를 블레이드 회전 특성을 고려하여 해석적으로 검토하였다.난류 조건을 고려했을 때의 최대 추력과 토크의 변동치는 난류 조건을 고려하지 않았을 때의 값들에 비해 5~8배 더 큰 값을 보였다.따라서 난류 조건을 반영한 하중 해석은 풍력터빈 블레이드의 구조설계에 있어서 필수적임을 확인하였다.KeyWords:NormalTurbulenceModel(NTM,정상 난류 모델),HorizontalAxisWindTurbine(HAWT,수평축 풍력 발전기),AerodynamicLoad(공력하중),BladeElementMomentumTheorem(BEMT,블레이드 요소 모멘텀 이론)

Performance and Noise Characteristics of UH-1H and UH-60 Helicopter Blades in Hovering Motion

Aerodynamic characteristics and noise fields of main rotors in hovering motion for UH-1H and UH-60 operated in Korean army were analyzed numerically. Unlike UH-1H blade, UH-60 blade has a 20˚ swept tip, which can decrease the wave drag at high speed range. A density-based compressible and incompressible solver of CFD++ was used for flow analysis. The Farassat formula 1A as a way of acoustic analogy was adopted for noise fields. Rotational speed of the blade set to maximum of design value, and any local shocks or delocalization of shocks from the blade were not observed at given rotational speed. FFT analysis was performed for timewise noise data, and overall sound pressure level (OASPL) was obtained based on the A-weighted scale. It turns out that the OASPL of UH-60 rotor at the designed tip speed shows 12 dB (18 dBA) lower than that of UH-1H one.

Prediction of Aerodynamic Loads for NREL Phase VI Wind Turbine Blade in Yawed Condition

Aerodynamic loads for a horizontal axis wind turbine of the National Renewable Energy Laboratory (NREL) Phase VI rotor in yawed condition were predicted by using the blade element momentum theorem. The classical blade element momentum theorem was complemented by several aerodynamic corrections and models including the Pitt and Peters’ yaw correction, Buhl’s wake correction, Prandtl’s tip loss model, Du and Selig’s three-dimensional (3-D) stall delay model, etc. Changes of the aerodynamic loads according to the azimuth angle acting on the span-wise location of the NREL Phase VI blade were compared with the experimental data with various yaw angles and inflow speeds. The computational flow chart for the classical blade element momentum theorem was adequately modified to accurately calculate the combined functions of additional corrections and models stated above. A successive under-relaxation technique was developed and applied to prevent possible failure during the iteration process. Changes of the angle of attack according to the azimuth angle at the specified radial location of the blade were also obtained. The proposed numerical procedure was verified, and the predicted data of aerodynamic loads for the NREL Phase VI rotor bears an extremely close resemblance to those of the experimental data.

A Study on Wall Interference Effect Around the Wind Turbine Airfoil

The wall interference effects around the wind-turbine airfoil are experimentally investigated at low Reynolds numbers in a closed test-section wind tunnel. The test is performed at free-stream velocities from 10 to 31 m/s, which correspond to Reynolds numbers ranging from to based on chord of the airfoil. The blockage-area ratios, which is the ratio of the chord to the test-section width, are 27.8%, 38.5%, 41.7%, 45.5%, and 55.6%. The test results for the airfoil show that the transition point on the airfoil surface tends to move backward due to wall interference. The wall pressures for an adequate interference correction by a measured-boundary-condition method are desirable more than three times region of the chord before and after around the reference center.

Flow Control on Wind Turbine Airfoil with a Vortex Cell

A flow control on airfoil installed a vortex cell for high efficiency wind turbine blade in stationary and dynamic stall conditions have been numerically investigated by solving the compressible Navier-Stokes equations. The numerical scheme is based on a node-based finite-volume method with Roe`s flux-difference splitting and an implicit time-integration method coupled with dual time step sub-iteration. The computed result for the airfoil in the stationary showed that lift-drag ratio increases due to low pressure by the vortex cell. The oscillating airfoil with the vortex cell showed that the magnitude of hysteresis loop is reduced due to the enhanced vortex in the cell.

Unsteady Wall Interference Effect on Flows around a Circular Cylinder in Closed Test-Section Wind Tunnels

For study on the unsteady wall interference effect, flows around a circular cylinder in closed test-section wind tunnels have been numerically investigated by solving compressible Navier-Stokes equations. The numerical scheme is based on a node-based finite-volume method with the Roe`s flux-difference splitting and an implicit time-integration method coupled with dual time-step sub-iteration. The computed results showed that the unsteady pressure gradient over the cylinder is enhanced by the wall interference, and as a result the fluctuations of lift and drag are augmented. The drag is further increased because of the lower base pressure. The vortex shedding frequency is also increased by the wall interference. The pressure on the test section wall shows the harmonics having the shedding frequency contained in the wall effect.

Blockage Correction Method for Separated Flows over an Aircraft in a Closed Test-Section Wind Tunnel

A new blockage correction method has been developed for the wall interference correction of closed test-section subsonic wind tunnels based on the nonlinear relationship between separation blockage and separation drag. This method can be applied continuously from the linear lift-slope region to the highly nonlinear post-stall region by on-line processing. The present method was validated by comparing the results with a classical method based on the test results of a bluff body and a measured-boundary-condition method. It was shown that the present method is in good agreement with the measured-boundary-condition method, enabling better wall corrections than the bluff body method in both near-stall and post-stall regions.

A Study on the Measurement of Aerodynamic Load of Aircraft Wing

A study on the test, design and fabrication of wind tunnel model for measurement of air load distribution on wing surfaces is presented. 447 pressure taps are installed normal to the wing surfaces, and measured by PSI-8400 system using total 8 ESPs modules installed in the model. The test was performed at 50 m/sec constant speed in the low speed wind tunnel of Agency for Defense Development. Tests were carried out to determine effects of angle of attack, angle of sideslip and flap and stores for the load distribution of wing. The test results in this paper can be applied to the design optimization of structure and validation of computational fluid dynamics.