7,176 research outputs found
Buffet photo
No full textColour photo of three men standing around a buffet table while one of them is cutting a cake
Investigation of 3D Shock Control Bumps for Transonic Buffet Alleviation
No full textView Video Presentation: https://doi-org.tudelft.idm.oclc.org/10.2514/6.2021-2558.vidThis experimental study investigates the use of shock control bumps (SCBs) for controlling transonic buffet. Three-dimensional SCBs have been applied on the suction side of an OAT15A supercritical airfoil with the experiments conducted in the transonic-supersonic wind tunnel of TU Delft for fully developed buffet conditions (Ma=0.7, α=3.5° and Re=2.6·10^6). The effectiveness of the SCBs for different spanwise spacings (ranging from 20%c to 30%c) was verified using two optical techniques: schlieren visualization and particle image velocimetry (PIV). Both techniques showed the possibility of controlling buffet using such devices, resulting in a reduction of the unsteadiness present in the flow, both in terms of shock oscillation and pulsation of the separated area. A dedicated PIV investigation in a spanwise-chordwise measurement plane was then conducted in order to understand the effect of the spatial distribution of the bumps, focusing on the interaction of the shockwave structures along the span. The configuration with a spacing of ΔxSCB=25%c demonstrated to be the most efficient in reducing the transonic buffet oscillations.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Aerodynamic
Spanwise organization of upstream traveling waves in transonic buffet
No full textThis experimental study has the objective of providing new insight into the role of upstream traveling waves (UTWs) in the transonic buffet phenomenon, using the background-oriented schlieren (BOS) technique and corroborating the results with particle image velocimetry. The experiments were carried out on the supercritical OAT15A airfoil under transonic conditions, at a Mach number of 0.7, an angle of attack of 3.5°, and a chord-based Reynolds number of x6. The specific scope of the investigation is the characterization of the spanwise organization of the buffet phenomenon; therefore, the measurements consider a streamwise-spanwise-oriented field of view on the suction side of the airfoil. A particular topic of interest is the propagation and orientation of upstream traveling pressure waves (UTWs) that occur in transonic buffet. The experimental setup used allowed to confirm the two-dimensionality of the velocity field and of the shockwave, but revealed that the UTWs propagate at a non-zero orientation. Processing of the BOS images with two different procedures (normal and differential), has furthermore allowed to extract the frequency and propagation velocity of the UTWs, which have been confirmed to behave as acoustic waves, traveling at the speed of sound relative to the flow. A further analysis has given hints that the strength of the UTWs is modulated during the buffet cycle and, therefore, in support of the feedback-mechanism description of transonic buffet.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Aerodynamic
Analysis of a civil aircraft wing transonic shock buffet experiment
No full textThe physical mechanism governing the onset of transonic shock buffet on swept wings remains elusive, with no unequivocal description forthcoming despite over half a century of research. This paper elucidates the fundamental flow physics on a civil aircraft wing using an extensive experimental database from a transonic wind tunnel facility. The analysis covers a wide range of flow conditions at a Reynolds number of around . Data at pre-buffet conditions and beyond onset are assessed for Mach numbers between 0.70 and 0.84. Critically, unsteady surface pressure data of high spatial and temporal resolution acquired by dynamic pressure-sensitive paint is analysed, in addition to conventional data from pressure transducers and a root strain gauge. We identify two distinct phenomena in shock buffet conditions. First, we highlight a low-frequency shock unsteadiness for Strouhal numbers between 0.05 and 0.15, based on mean aerodynamic chord and reference free stream velocity. This has a characteristic wavelength of approximately 0.8 semi-span lengths (equivalent to three mean aerodynamic chords). Such shock unsteadiness is already observed at low-incidence conditions, below the buffet onset defined by traditional indicators. This has the effect of propagating disturbances predominantly in the inboard direction, depending on localised separation, with a dimensionless convection speed of approximately 0.26 for a Strouhal number of 0.09. Second, we describe a broadband higher-frequency behaviour for Strouhal numbers between 0.2 and 0.5 with a wavelength of 0.2 to 0.3 semi-span lengths (0.6 to 1.2 mean aerodynamic chords). This outboard propagation is confined to the tip region, similar to previously reported buffet cells believed to constitute the shock buffet instability on conventional swept wings. Interestingly, a dimensionless outboard convection speed of approximately 0.26, coinciding with the low-frequency shock unsteadiness, is found to be nearly independent of frequency. We characterise these coexisting phenomena by use of signal processing tools and modal analysis of the dynamic pressure-sensitive paint data, specifically proper orthogonal and dynamic mode decomposition. The results are scrutinised within the context of a broader research effort, including numerical simulation, and viewed alongside other experiments. We anticipate our findings will help to clarify experimental and numerical observations in edge-of-the-envelope conditions and to ultimately inform buffet-control strategies
Just Noticeable Differences for Variations in Quasi-Steady Stall Buffet Model Parameters
No full textTo gain more insight into human sensitivity to variations in simulated stall buffets, Just Noticeable Difference (JND) thresholds were estimated using a passive human-in-the-loop flight simulator experiment. Using an in-house developed flow separation-based stall and buffet model of the Cessna Citation II, JND thresholds were determined for the model's buffet characteristic frequency parameter omega0 and the buffet onset threshold parameter Xthres for the vertical stall buffet only. With a subjective yes/no 1-up/1-down staircase procedure that uses repeated pairwise comparisons of quasi-steady symmetric stall simulations (where one is a stall with the baseline buffet model and the other one has an offset buffet parameter), upper and lower JND thresholds were measured from 21 pilots. The experiment results show that the pilots noticed the differences in simulated buffet dynamics at comparably similar percentage-wise offsets for Xthres and omega0 with respect to the baseline parameter values. The maximum observed JND thresholds did not exceed 30-35% across all experiment conditions, indicating that pilots are fairly sensitive to even small offsets in the key stall buffet model parameters. Moreover, the estimated JND thresholds for omega0 are in agreement with the +/-2 Hz tolerance currently used in stall buffet simulation qualification standards. However, for Xthres, the results show that human pilots already notice differences in stall buffet onset characteristics well before the maximum allowed tolerance (+/- 2.0 deg angle of attack) is reached, which suggests that stricter tolerances on simulated buffet onsets for quasi-steady symmetric stalls may help to further enhance stall training in simulators.Control & Simulatio
Transonic buffet control by means of upper Gurney flaps
No full textThis study investigates the possibility of controlling transonic buffet by means of a Gurney Flap with an upward deflection at the trailing edge of the airfoil (UGF). Different geometries and dimensions of UGFs have been studied for their impact on the buffet behaviour. The effectiveness of the UGFs has been tested experimentally with Schlieren and PIV in the transonic-supersonic wind tunnel of TU Delft at Ma=0.7, a=3.5. It is found that the best performing UGF is a straight UGF with a height of 1.5% or 2% of the chord. These UGFs allow the reduction of the energy associated with buffet. This result has been corroborated by a flow description of the phases of buffet, a spectral analysis and a POD approach. In addition, the straight UGFs resulted to be effective in a less developed buffet condition too.Aerodynamic
Experimental study of the effect of wing sweep on transonic buffet
No full textIn this study the effect of wing sweep on transonic buffet is studied experimentally to reveal the differences between two-dimensional (2D) and three-dimensional (3D) wing configurations. Background oriented schlieren (BOS) and stereographic particle image velocimetry (PIV) have been used as measurement techniques, performing experiments on: an airfoil, an unswept wing and two swept wings with a sweep angle of 15° and 30° respectively (all wings are based on the OAT15A airfoil). All wings have been tested at a constant normal Mach number (Ma∞n=0.7) with respect to the leading edge. The results show that the buffet oscillations are much stronger for the airfoil than for the three finite-span wings. A large difference in the buffet behavior can be noticed between the airfoil and the unswept wing, particularly in correspondence of the more outboard spanwise locations, suggesting that in the latter an important role could be played by finite-wing effects, notably the tip vortex. A spectral analysis has shown that for the swept wings the classical 2D buffet peak (occurring at f=160 Hz for the present conditions) is substantially attenuated, while additional contributions in the range of 450-850 Hz appear. The PIV results showed, for the 30° sweep angle wing, a periodical occurrence of a secondary supersonic area downstream of the main shockwave structure, which is absent for the other wing models. The stereographic PIV configuration allowed the reconstruction of the spanwise oriented velocity component, obtaining in the trailing edge area, spanwise outboard velocities (80-100 m/s) which are in agreement with the spanwise convection of buffet cells observed in literature in this region.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Aerodynamic
Physics and Control of Transonic Buffet
No full textThe flight envelope of an aircraft operating at high subsonic velocities is bounded by several limitations, one of these consists in thewing experiencing oscillations of a shockwave on its suction side for a certain range ofMach number (Ma), angle of attack (®) and Reynolds number (Re). This phenomenon is referred to as transonic buffet and it may ultimately result in violent structural oscillations of the wing (the so-called buffeting), in addition to the oscillations of the aerodynamics loads. Notwithstanding the relevance of this topic, there is not yet an only explanation regarding its mechanism, therefore, the first aim of this experimental project is to obtain further insight on the physics of transonic buffet (Part I). As a second objective, in Part II different strategies for the control of buffet have been investigated. The experiments of this study have been carried out in the transonic-supersonic wind tunnel of TUDelft on supercritical airfoil and wings based on theOAT15A airfoil. The behavior of this phenomenon has been scrutinized using optical experimental techniques, such as particle image velocimetry (PIV), schlieren, and, background oriented schlieren (BOS)..
Buffet Pricing.
No full textThis article analyzes a commonly used pricing practice, which the author calls 'buffet pricing,' in which for a fixed entry fee consumers can consume an unlimited quantity during a specified period of time. When consumers are homogeneous in preferences, this form of pricing can be more profitable than a two-part tariff if the total cost under a two-part tariff is greater than the 'net' total cost under buffet pricing. For heterogeneous consumers, depending on the distribution of consumer types and the relative magnitudes of transaction and production costs, buffet pricing can also be more profitable than two-part tariffs. Copyright 1999 by University of Chicago Press.
Prière de guerre dédiée aux veuves de la Revanche, créée par Eugénie Buffet [couverture de la partition grand format, portrait Eugénie Buffet]
No full textPrière de guerre dédiée aux veuves de la Revanche, créée par Eugénie Buffet ; (dédicace) “Hommage à Madame Waldeck Rousseau” ; cadre ornemental et photo anonymes ; musique de René de Buxeuil ; poésie de Jean Natu [Jean Natu (1888-1938), identification Daphy sous réserves] ; propriété de Eugénie Buffet, 83 rue Blanche, Paris, en dépôt chez Bloch & Valsien éditions musicales ; © by Eugénie Buffet 1915 ; imprimerie Ghidone. Titre inconnu du catalogue Opale BNF ; titre non présent dans la collection Leblanc
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