### Abstract

Two groups of unsteady flows over a stationary SD7003 airfoil are studied with the large eddy simulation method. In the first group, the angle of attack (AoA) is fixed, while the freestream velocity magnitude varies harmonically with various frequencies and amplitudes. In the second group, the freestream velocity magnitude is fixed but its direction, therefore the AoA varies harmonically. Over the range of parameters considered in this study the mean lift and drag coefficients of the unsteady flows with oscillating freestream velocity magnitude are found to be nearly the same as those calculated for steady flows. However, there are significant phase shifts between the aerodynamic forces and the unsteady freestream velocity. The phase shift for drag force is larger than that for lift force, even though both increase as the frequency of freestream velocity oscillations increases. Furthermore, the computed lift amplitudes are found to be noticeably higher than those predicted by Greenberg's inviscid theory, while the lift phase shifts are in better agreement with the theory. For flows with oscillating freestream AoA, there is little change in the mean lift, while the mean drag is reduced by oscillations in AoA due to Katzmayr effect. As the frequency of oscillations in AoA increases, the phase shift for lift increases while that for drag decreases. Our results also indicate that the mean separation point moves downstream and the mean reattachment point moves upstream when the freestream velocity magnitude or the freestream flow direction oscillates with respect to the airfoil.

Language | English (US) |
---|---|

Pages | 155-170 |

Number of pages | 16 |

Journal | Computers and Fluids |

Volume | 161 |

DOIs | |

State | Published - Jan 15 2018 |

### Profile

### Keywords

- Airfoils with oscillatory freestream flow
- LES
- Unsteady aerodynamics

### ASJC Scopus subject areas

- Computer Science(all)
- Engineering(all)

### Cite this

*Computers and Fluids*,

*161*, 155-170. DOI: 10.1016/j.compfluid.2017.11.014

**Large eddy simulations of unsteady flows over a stationary airfoil.** / Qin, Shiwei; Koochesfahani, Manoochehr; Jaberi, Farhad.

Research output: Contribution to journal › Article

*Computers and Fluids*, vol 161, pp. 155-170. DOI: 10.1016/j.compfluid.2017.11.014

}

TY - JOUR

T1 - Large eddy simulations of unsteady flows over a stationary airfoil

AU - Qin,Shiwei

AU - Koochesfahani,Manoochehr

AU - Jaberi,Farhad

PY - 2018/1/15

Y1 - 2018/1/15

N2 - Two groups of unsteady flows over a stationary SD7003 airfoil are studied with the large eddy simulation method. In the first group, the angle of attack (AoA) is fixed, while the freestream velocity magnitude varies harmonically with various frequencies and amplitudes. In the second group, the freestream velocity magnitude is fixed but its direction, therefore the AoA varies harmonically. Over the range of parameters considered in this study the mean lift and drag coefficients of the unsteady flows with oscillating freestream velocity magnitude are found to be nearly the same as those calculated for steady flows. However, there are significant phase shifts between the aerodynamic forces and the unsteady freestream velocity. The phase shift for drag force is larger than that for lift force, even though both increase as the frequency of freestream velocity oscillations increases. Furthermore, the computed lift amplitudes are found to be noticeably higher than those predicted by Greenberg's inviscid theory, while the lift phase shifts are in better agreement with the theory. For flows with oscillating freestream AoA, there is little change in the mean lift, while the mean drag is reduced by oscillations in AoA due to Katzmayr effect. As the frequency of oscillations in AoA increases, the phase shift for lift increases while that for drag decreases. Our results also indicate that the mean separation point moves downstream and the mean reattachment point moves upstream when the freestream velocity magnitude or the freestream flow direction oscillates with respect to the airfoil.

AB - Two groups of unsteady flows over a stationary SD7003 airfoil are studied with the large eddy simulation method. In the first group, the angle of attack (AoA) is fixed, while the freestream velocity magnitude varies harmonically with various frequencies and amplitudes. In the second group, the freestream velocity magnitude is fixed but its direction, therefore the AoA varies harmonically. Over the range of parameters considered in this study the mean lift and drag coefficients of the unsteady flows with oscillating freestream velocity magnitude are found to be nearly the same as those calculated for steady flows. However, there are significant phase shifts between the aerodynamic forces and the unsteady freestream velocity. The phase shift for drag force is larger than that for lift force, even though both increase as the frequency of freestream velocity oscillations increases. Furthermore, the computed lift amplitudes are found to be noticeably higher than those predicted by Greenberg's inviscid theory, while the lift phase shifts are in better agreement with the theory. For flows with oscillating freestream AoA, there is little change in the mean lift, while the mean drag is reduced by oscillations in AoA due to Katzmayr effect. As the frequency of oscillations in AoA increases, the phase shift for lift increases while that for drag decreases. Our results also indicate that the mean separation point moves downstream and the mean reattachment point moves upstream when the freestream velocity magnitude or the freestream flow direction oscillates with respect to the airfoil.

KW - Airfoils with oscillatory freestream flow

KW - LES

KW - Unsteady aerodynamics

UR - http://www.scopus.com/inward/record.url?scp=85036452354&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85036452354&partnerID=8YFLogxK

U2 - 10.1016/j.compfluid.2017.11.014

DO - 10.1016/j.compfluid.2017.11.014

M3 - Article

VL - 161

SP - 155

EP - 170

JO - Computers and Fluids

T2 - Computers and Fluids

JF - Computers and Fluids

SN - 0045-7930

ER -