1 Introduction
1.1 Problem set up
2 Model for mitigation pitch profile
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The flow is considered to be inviscid and incompressible.
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The vorticity elements shed from the wing trailing edge are confined to the horizontal plane.
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Vorticity is not shed from the leading edge.
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The disturbances affecting the wing are small, and thus, small-angle approximations are valid.
2.1 Circulatory Wagner component—wing motion
2.2 ‘Added Mass’ component—wing motion
2.3 Küssner component—gust interaction
2.4 Unsteady mitigation model
3 Experimental methodology
3.1 Pitch motion
3.2 Force measurements
3.3 Particle image velocimetry
4 Gust only case—no mitigation
4.1 Upwards gust
4.2 Downwards gusts
4.3 Lift response
5 Mitigation results
5.1 Upwards gust
5.2 Downwards gust
5.3 Force mitigation
\(\alpha _o = 0^{\circ }\) (%) | \(\alpha _o = 10^{\circ }\) (%) | \(\alpha _o = 20^{\circ }\) (%) | |
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Upwards | 90 | 87 | 79 |
Downwards | 89 | 88 | 84 |
5.4 Streamlines
5.5 Main limitations of the mitigation approach
6 Conclusions
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For an upwards gust encounter without mitigation, increasing the initial wing angle of attack promotes separation and results in a lower maximum lift.
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Downwards gusts suppress vorticity shedding for the wing leading edge due to the reduction in the wing \(\alpha _{eff}\). Therefore, the LEV evolution differs greatly from an upwards gust, but the relative lift peak magnitude is only slightly smaller.
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Wings at \(\alpha _o\) that produces highly separated flows (\(\alpha _o > 10^{\circ }\)) experience a secondary lift peak after exiting the gust. This peak is due to the flow around the wing being attached right after gust exit. Subsequently, a LEV emerges and shed before the wing returns to the separated steady state.
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The mitigation approach is successful in most of the cases presented. Lift mitigation of approximately 85\(\%\) is observed when the wing does not exceed an effective angle of attack of \(\pm 60^{\circ }\) in the gust-only case.
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The largest mitigation error typically occurs at the secondary peak after the wing has exited the gust. The model requires improvements to be capable of mitigating this specific condition.
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Generally, downwards gusts are more easily mitigated than upwards gusts. This is associated with the smaller effective angle of attack due to the mitigation action.