Flow Control and Separation Reduction on Wind Turbine Airfoil

Mohammad Moshfeghi,Nahmkeon Hur 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

An innovative passive flow control method is proposed for aerodynamic performance enhancement over the wind turbine airfoils. The new geometry is based on splitting airfoil and is investigated by numerical simulations. Three dimensional CFD simulations are carried out using the SST-k-ω turbulence model. The results show that the split airfoil can produce more lift and less drag by weakening the separation effects and breaking down the large vortex into small vortices. It is observed that level of influence of split depend on split exit location inside the separated flow. For the small AOAs the injected flow through the split triggers an early separation which consequently reduces the airfoil efficiency. However, at high AOA where the upper end of split falls deep inside the separated area, injected flow through the slot effectively increases the airfoil performance. For AOAs at which the separation point occurs near the split exit, the airfoil’s aerodynamic forces are not changed significantly.

EFFECTS OF SYNTHETIC JET ACTUATOR EXIT LOCATION ON AERODYNAMICS OF S809 AIRFOIL AT HIGH ANGLE OF ATTACK

Mohammad Moshfeghi(모하메드),Nahmkeon Hur(허남건) 한국전산유체공학회 2013 한국전산유체공학회 학술대회논문집 Vol.2013 No.10

The present research investigates the results of DES simulation of a finite span wing equipped with synthetic jet actuator (SJA), in order to study the influence of the jet exit location on the aerodynamic forces and streamlines. The wing airfoil is S809 with the chord length 400 mm, which is stretched 200 mm and rotated to create the angle of attack of 25℃. The momentum coefficient for the SJA is considered to be 4.5×10<SUP>- 3</SUP>. The results of the jet exit locations 0.25, 0.35 and 0.45 are analysed . It is observed that for all cases the SJA affects the aerodynamic behavior of wing and the flow patterns and aerodynamic forces on the wing are sensitively dependent on the jet exit location. When the jet exit location is at x/c=0.25, the SJA presents an effective role; however, for the cases in which the jet exit is located at x/c=0.35 or 0.45, the SJA effects become weaker and the range of results of are very close to each other.

AN INVESTIGATION ON HVLS FAN PERFORMANCE WITH DIFFERENT BLADE CONFIGURATIONS

Mohammad Moshfeghi,Nahmkeon Hur(허남건),Young Joo Kim(김영주),Hyun Wook Kang(강현욱) 한국전산유체공학회 2014 한국전산유체공학회지 Vol.19 No.4

High-volume low-speed (HVLS) fans are one category of ceiling fan installed in large enclosings such as warehouses, large barns and health clubs in order to generate comfortable air circulation. As a rotary blade, aerodynamic performance of a HVLS fan is predominantly related to its airfoil(s), and the pitch and twist angles. This paper first, investigates the effects of airfoil on the performances of three different HVLS fans with NACA 5414, 6413 and 7415 airfoils. The fans have six untwisted blades with the diameter of 6 m and rotate at 60 RPM. The blades pitch angels are 12°, 12° and 13°, respectively. The results are presented in the form of the aerodynamic forces and moments, volumetric flow rate and streamlines. Regarding the volumetric flow of air, the results show that the model with NACA 7415 has the best performance. Hence, two other HVLS fans with the same airfoil but, with four and five blades are studied in order to investigate the effects of number of blades. From the point of view of air circulation still the six-bladed fan is the best one; however, the five-bladed fan is more efficient in power consumption.

Numerical Simulation of the SJA Flow for Prediction of Aerodynamic Behavior of an Airfoil

Mohammad Moshfeghi,Nahmkeon Hur 한국전산유체공학회 2014 한국전산유체공학회 학술대회논문집 Vol.2014 No.10

CFD Simulations are preferably popular because of their cost and simplicity. However, one source of the differences between the CFD and experimental results in a SJA simulation is the simplifications applied to the simulation, which cause different aerodynamics loads and flow structure on the suction surface of an airfoil. This paper numerically investigates the effect of different boundary conditions for the simulation of the SJA; including simulating the SJA using inlet surface at the suction surface of an airfoil and applying the moving mesh technique for simulation of the oscillating piston. The aim is to investigate effects of different methods on the aerodynamic behavior of an airfoil.

풍차날개의 공력 성능 향상과 유동 박리 감소를 위한 수동 유동 제어에 대한 DES 해석

Mohammad Moshfeghi,Shahrokh Shams,Morteza Ramezani,허남건 한국전산유체공학회 2018 한국전산유체공학회지 Vol.23 No.4

Power generation of a horizontal axis wind turbine is severely dependent upon aerodynamic phenomena over the blade, especially the flow separation. Since, usually the local AoA (Angle of Attack) in the inner and middle parts of a blade is much greater than the separation onset, the blade section encounters a highly separated flow or even stall condition. Hence, flow control methods can be employed in order to reduce or weaken the negative effects of the separation. This paper investigates the effects of a recently verified passive flow control method for HAWTs via a validated three dimensional DES(Detached Eddy Simulation) of split versions of the S809 airfoil. In this research, two different airfoil families with four various split width values of 0.5, 1, 2 and 4 percent of chord length are simulated at a range of angle of attack from 0 to 25 degrees. As a result of existence of the split, flow from the high-pressure zone at the lower surfaces gets injected into the separated area over the suction surfaces. The positive or negative effect of this method is mainly dependent upon split end location on the suction surface. Direction of the jet flow with respect to the free stream and also the width of split are the other important parameters. Also, the findings reveal that in each family there exists one optimal split width for which the airfoil aerodynamic performance is enhanced remarkably.

CFD ANALYSIS OF A NEW ACTIVE FLOW CONTROL METHOD FOR WIND TURBINE AIRFOILS USING A PADDLE WHEEL INSIDE THE SPLIT OF AIRFOIL

Mohammad Moshfeghi,Amir Maleki,Morteza Ramezani,Nahmkeon Hur(허남건) 한국전산유체공학회 2021 한국전산유체공학회지 Vol.26 No.2

In the following years, the wind energy industry will maintain its surge during the last few decades. Meanwhile, horizontal axis wind turbines (HAWT) are the most prominent one among other wind turbines. Accordingly, enhancing blade aerodynamic performance should be the main part of study over this type of turbines. For this purpose, various active and passive flow control methods are being extensively investigated. Investigating new hybrid method is the main aim of this paper. Therefore, in this present study a novel idea, that uses a paddle wheel which is located inside the split, is investigated. This new configuration is based on the split method and the rotation of a paddle wheel that provides pulsatile flow inside the split. The flow then gets injected into the bulk flow over the airfoil, causing hybrid flow control effects. Optimized split geometry of S809 airfoil has been selected and then a paddle wheel is placed inside the split. First, the effect of split width on passing flow and separation zone was investigated. Second, the effect of rotational speed of the paddle is discussed. To this end, 2D CFD simulations using SST-k-ω turbulence model have been performed. The simulations have been conducted for a wide range of angles of attack (AOA). The results are discussed in the form of aerodynamics force coefficients as well as streamlines to compare the size of the separation area at higher angles of attack.

Effects of pitching frequency on the dynamic stall behavior of an airfoil at relatively low Reynolds number

Mohammad Moshfeghi,Nahmkeon Hur 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.5-2

Aerodynamic behavior of a finite span blade with different combination of synthetic jet actuators at a high angle of attack

Mohammad Moshfeghi,Nahmkeon Hur 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12

During the past decade, flow control, especially the synthetic jet actuator (SJA) technique, has become one of the most interesting issues for aerodynamists, particularly in the wind turbine industry. This paper investigates the aerodynamic behavior of a finite span blade with a wind turbine airfoil under three different combinations of SJAs. The S809 airfoil is modeled with the chord of c=400 mm, which is spanned b=200 mm and is simulated with Reynolds’ number of 10<SUP>6</SUP>, at an angle of attack (AOA) of 25˚. The SJAs are assumed to be at x/c=0.25 (model M1) and x/c=0.35 (model M2) with the maximum jet exit velocity of 42.3 m/s. The third model (model M12) is the simultaneous operation of M1 and M2, each working with maximum exit velocity of 29.91 m/s. The results show that the vortex breakdown is the main impact of the SJA on the flow. Also, combinations of SJAs create different vortex patterns and result in dissimilar velocity and pressure distributions. It is observed that the SJA stretches the separated area towards downstream behind the trailing edge and effectively weakens the separated area over the suction surface. As a result, the SJAs severely change the aerodynamic forces. Despite the harmonic injection of the SJA, the lift and drag in all models fluctuate irregularly, which is due to the high AOA and the sever separation over the blade.

Effects of SJA boundary conditions on predicting the aerodynamic behavior of NACA 0015 airfoil in separated condition

Mohammad Moshfeghi,허남건 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.5

Synthetic jet actuators (SJAs) are popular active-flow control devices. Hence, they have been widely investigated through computationalfluid dynamics (CFD) simulations and experiments. Although such simulations are faster, cheaper, and more popular than experiments,the simulation results of similar geometries often differ from one another. A reason for the differences between CFD results is thesimplification of CFD models. To determine the influence level of SJA simplifications on the aerodynamics of an airfoil under a separatedcondition, this study compares the most complicated assumption for SJA simulation with the simplest one. A NACA 0015 airfoil issimulated at an angle of attack of 16.6° and a Reynolds number of 896000. Two different methods are applied to simulate SJA, namely,morphing mesh (MM) technique for piston movement and oscillatory inlet velocity (OIV) at the jet-exit location. Results reveal that themean lift value of the MM case is only 3% less than that of the OIV case. However, the drag forces of MM case are approximately 15%higher than those of the OIV case. In addition, the vortex structures in the OIV case are smaller than those in the MM case. Finally, thecycle-averaged streamlines of the two models are similar near the trailing edge, but they differ in the vicinity of the SJA exit location.

Aerodynamic and acoustic behavior of a finite span wing equipped with synthetic jet actuator

Mohammad Moshfeghi,Hanru Liu,Yonghui Xie,Jinjia Wei,Nahmkeon Hur 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12

In the current paper, aerodynamic and acoustic behaviors of a finite span wing with a synthetic jet actuator (SJA) are investigated using the DES turbulence model at three different angles of attack (AOA=14°, 18° and 25°). Aerodynamically, the main role of the SJA actuator is causing the vortex breakdown, weakening the separation effects and generating aerodynamic forces which fluctuate in time. As the AOA increases, the separated area becomes larger and stronger and, hence, the lift and drag values turns from the harmonic shapes to irregular fluctuation. From the acoustic point of view, for the AOAs of 14° and 18° the sound source occurs near the trailing edge. However, at AOA=25°, the dominant frequency of sound spectrum tends to move to a low frequency and the overall sound pressure level becomes the highest. Also, for this AOA the sound emits from both trailing edge and leading edge. Moreover, it is observed that the sound directivity changes to a no-dipole shape at a frequency lower than that of AOA=14° and 18°.