Influence of Large-Scale Freestream Turbulence on the Performance of a Thin Airfoil

Ravi, Sridhar; Watkins, Simon; Watmuff, Jonathan H.; Massey, Kevin; Peterson, P.; Marino, Matthew

doi:10.2514/1.j051640

Cited by 22 publications

(20 citation statements)

References 18 publications

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“…Effects of unsteady wakes and vortices are similar to those of freestream turbulence with large amplitude and length scale (Hoffmann 1991; Ravi et al. 2012; Kay, Richards & Sharma 2020; Li & Hearst 2021). For example, the decreased lift slope observed at zero offset in the wakes (Durgesh et al.…”

Section: Introductionmentioning

confidence: 89%

Aerodynamics of a wing in turbulent bluff body wakes

2022

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The aerodynamics of a stationary wing in a turbulent wake are investigated. Force and velocity measurements are used to describe the unsteady flow. Various wakes are studied with different dominant frequencies and length scales. In contrast to the pre-stall angles of attack, the time-averaged lift increases substantially at post-stall angles of attack as the wing interacts with the von Kármán vortex street and experiences temporal variations of the effective angle of attack. At an optimal offset distance from the wake centreline, the time-averaged lift becomes maximum despite of small amplitude oscillations in the effective angle of attack. The stall angle of attack can reach 20° and the maximum lift coefficient can reach 64 % higher than that in the freestream. Whereas large velocity fluctuations at the wake centreline cause excursions into the fully attached and separated flows during the cycle, small-amplitude oscillations at the optimal location result in periodic shedding of leading edge vortices. These vortices may produce large separation bubbles with reattachment near the trailing-edge. Vorticity roll-up, strength and size of the vortices increase with increasing wavelength and period of the von Kármán vortex street, which also coincides with an increase in the spanwise length scale of the incident wake, and all contribute to the remarkable increase in lift.

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Section: Introductionmentioning

confidence: 89%

Aerodynamics of a wing in turbulent bluff body wakes

2022

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“…(2011), Ravi et al. (2012) found that increasing the integral length scales causes an increase in the time-averaged peak lift coefficient. Using pressure taps, Ravi et al.…”

Section: Introductionmentioning

confidence: 99%

“…(2011), Ravi et al. (2012) and Vita et al. (2020) set out to determine the effect of the integral length scale of incoming turbulence on a wing.…”

Section: Introductionmentioning

confidence: 99%

“…Ravi et al. (2012) investigated how variations in integral length scale affect a thin airfoil. Similar to work by Cao et al.…”

Section: Introductionmentioning

confidence: 99%

“…Using pressure taps, Ravi et al. (2012) observed that at integral length scales greater than the chord, the magnitude of the standard deviations is larger than when the integral length scale is equal to the chord. The discrepancies in the findings of Ravi et al.…”

Section: Introductionmentioning

confidence: 99%

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Effects of integral length scale variations on the stall characteristics of a wing at high free-stream turbulence conditions

Thompson,

Biler,

Symon

et al. 2023

J. Fluid Mech.

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The effect of variations in the integral length scale of incoming free-stream turbulence on a NACA0012 wing is investigated with the use of force, moment and particle image velocimetry measurements. At a chord-based Reynolds number ( $Re = U_\infty c/\nu$ where c is the chord length, $U_\infty$ is the free-stream velocity and $\nu$ is the kinematic viscosity) of $2\times 10^5$ , an active grid generates turbulence intensities of 15 % at normalised integral length scales ranging from 0.5 $c$ to 1 $c$ . The introduction of turbulence improves the time-averaged performance characteristics of the wing by delaying stall and increasing the peak lift coefficient. It is found that for half-chord integral length scales, the magnitude of the fluctuations in forces and moments is larger than that of full-chord integral length scales, as the former amplifies the naturally occurring unsteadiness in the flow (when there is no free-stream turbulence). The increase in magnitude is ascribed to a larger density of smaller-scale vortices within the separated flow and wake region of the wing.

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