Management of Vortices Trailing Flapped Wings via Separation Control

Abstract

A pilot study was conducted on a flapped semi-span model to investigate the concept and viability of near-wake vortex management via separation control. Passive control was achieved by means of a simple fairing and active control was achieved via zero mass-flux blowing slots. Vortex sheet strength, estimated by integrating surface pressure ports, was used to predict vortex characteristics by means of inviscid rollup relations. Furthermore, vortices trailing the flaps were mapped using a seven-hole probe. Separation control was found to have a marked effect on vortex location, strength, tangential velocity, axial velocity and size over a wide range of angles of attack and control conditions. In general, the vortex trends were well predicted by the inviscid rollup relations. Manipulation of the separated flow near the flap edges exerted significant control over both outboard and inboard edge vortices while producing negligible lift excursions. Dynamic separation and attachment control was found to be an effective means for dynamically perturbing the vortex from arbitrarily long wavelengths down to wavelengths less than a typical wingspan. In summary, separation control has the potential for application to time-independent or time-dependent wake alleviation schemes, where the latter can be deployed to minimize adverse effects on ride-quality and dynamic structural loading. Nomenclature A= wing area, s×c AR = wing aspect ratio c = wing chord-length h = slot width= separation control excitation frequency f w = wake control frequency F + = reduced excitation frequency,

Active Management of Flap-Edge Trailing Vortices

“…Firstly, the flow approaches fully separated and attached states to a greater degree than that for sinusoidal perturbation due to the abrupt nature of both the perturbation initiation and termination. Unsteady pressure measurements on the flap revealed that there is an overshoot of the static flap pressures as a result of the modulation (Greenblatt, 2005). This accounts for the larger movement of the vortex centroid that results from burst modulation.…”

“…Furthermore, decoupling vortex management from the control surfaces and only applying it selectively, ensures relatively small wing-load excursions. The aforementioned assertions were initially made by the first author (Greenblatt, 2005(Greenblatt, , 2007) based on the method of Betz (1933) as extended by Donaldson et al (1974). The principle computation advantage of Betz's method is that it does not explicitly treat the rollup mechanism, but rather employs three conservation relations between the span-loading ) ( y and the rolling-up vortex ) (r .…”

“…The model used was a NACA 0015 profile (AR=4) and was equipped with zero mass-flux blowing slots, as well as multiple surface pressure ports (see fig. 3 and further details in Greenblatt, 2005Greenblatt, , 2007. Passive control was achieved using a simple fairing placed over a control slot and active control was achieved via zero mass-flux blowing from the slots.…”

“…All work presented is based on two experimental investigations: the first was conducted at NASA LaRC (supported by the National Research Council; Greenblatt, 2005Greenblatt, , 2006Greenblatt et al, 2005); and the second was conducted at the Berlin University of Technology in collaboration with the German Aerospace Center (DLR) (Vey et al, 2008). The approach adopted here was to build the concept from the ground up, namely: (a) hypothesis, (b) simple experiment as demonstration of concept, and (c) more complex experiment approaching an airliner configuration.…”

A position based iterative learning control applied to active flow control

“…As an important area of interest, active control of flow separation can be useful in many other applications of fluid dynamics research. For example, methods of active control have been used for jet vectoring [4], [5], engine performance improvement [6], [7], and wing tip/flap side edge vortex breakdown control [8].…”