Unsteady flow past an airfoil pitching at a constant rate

Shih, Chiang; Lourenco, L.; Dommelen, Leon van; Krothapalli, Anjaneyulu

doi:10.2514/3.11045

Cited by 112 publications

(52 citation statements)

References 17 publications

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“…Shih et al [37] observed that the leading edge boundary layer separation leads to the formation of a vortical structure which dominates the aerodynamic performance. Ghia et al [15] and Yang et al [58] analyzed the effect of modulated suction or injection in delaying the onset of dynamic stall over pitching NACA airfoils and also successfully compared their computational results with the previous computations of Mehta [26] and the experimental results for Re, = 10' and Re, = 4.5 X 104 .…”

Section: Literature Surveymentioning

confidence: 99%

Effects of compressibility, pitch rate, and Reynolds number on unsteady incipient leading-edge boundary layer separation over a pitching airfoil

Choudhuri

Knight

1996

J. Fluid Mech.

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Public reporting burden for this collection of information is estimated to average 1 hour per respoinse. including the time for reviewing instructions. searching existing data sources. gathering and maintaining the data needed, and comoleting anrd ryaevwing the collection of information. Send comments re< arding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden. SUPPLEMENTARY NOTESThe view, opinions and/or findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy,--or decision, -unless so designated by other documentation. 12a. DISTRIBUTION /AVAILABILITY STATEMENT 12b. DISTRIBUTION CODEApproved for public release; distribution unlimited. ABSTRACT (M-xiMum200words)The effects of compressibility, pitch rate and Reynolds number on the initial stages of 2-D unsteady separation of laminar subsonic flow over a pitching NACA-0012 airfoil have been studied numerically. Computations have been performed using two separate algorithms (structured grid algorithm of Beam and Warming, and unstructured grid algorithm employing fluxdifference splitting method of Roe) for the compressible laminar NavierStokes equations. The simulations show the appearance of a primary recirculating region near the leading edge, followed by a secondary and tertiary recirculating regions. The primary and secondary recirculating regions interact with each other to give rise to the unsteady separation of the boundary layer. Increasing the Mach number from 0.2 to 0,5 causes a delay in the formation of the primary recirculating region. Increasing the pitch rate also delays the formation. Increasing the Reynolds number hastens the appearance of the primary recirculating region and leads to the appearance of a shock on the top surface alon g with the formation of multiple recirculating regions near the leading edge. A linear stability anal ,sis has shown that the appearance of the primary recirculating region is related

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Section: Literature Surveymentioning

confidence: 99%

Effects of compressibility, pitch rate, and Reynolds number on unsteady incipient leading-edge boundary layer separation over a pitching airfoil

Choudhuri

Knight

1996

J. Fluid Mech.

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“…For instance, Graham and Yeow 8 visualized the linear pitch-ramp LEV structure in water, at higher angle of attack excursions but lower rates than those presently considered. Shih et al 22 and Crisler et al 23 applied particle image velocimetry to the airfoil pitch-ramp problem. Computational examples include Ghosh Choudhuri and Knight 24 , Okongo'o and Knight 25 , and Visbal et al 26,27,28 .…”

Section: Introductionmentioning

confidence: 99%

High-Amplitude Pitch of a Flat Plate: An Abstraction of Perching and Flapping

Eldredge

Wang

2009

International Journal of Micro Air Vehicles

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We compare water tunnel experiment and 2D vortex-particle computation for a generalization of the classical problem of flat-plate constant-rate pitch and related motions, at frequencies and Reynolds numbers relevant to Micro Air Vehicle applications. The motivation is problems of maneuvering, perching and gust response. All of the examined flows evince a strong leading edge vortex. Increasing pitch rate tends to tighten the leading edge vortex and to produce a trailing-edge vortex system dominated by a counter-rotating pair. Pitch pivot point location is crucial to the leading edge vortex size and formation history, and to its subsequent behavior in convecting over the airfoil suction-side. Despite the respective limitations of the experiment and computations, agreement in vorticity fields between the two at an overlapping case at Re = 10,000 is good, whence it is possible to use the computation to obtain integrated force data unavailable in the experiment. These were studied for Re= 100 and 1000. Lift prediction from the computation shows a direct proportionality of lift to the pitch rate on the pitch upstroke. Finally, we compare pitch vs. plunge, and find that quasi-steady prediction is reasonably successful in predicting a combined pitch-plunge that effectively cancels the leading edge vortex, but not in canceling the trailing vortex system. NOMENCLATURE

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“…Shortly before this, and not immediately obvious, there is an increase in suction an obvious localized peak (P3) with an associated pressure wave that travels a short distance towards the leading edge. This is a consequence of the formation of a vortical system of opposite circulation, known as the trailing-edge vortex (TEV) and is a result of the mass influx from the high-pressure region, on the airfoil lower surface, to the upper surface 25,26 . As mentioned earlier, the peak nose-down moment (C Mmax ) observed in Fig.…”

Section: Resultsmentioning

confidence: 99%