305 research outputs found
[Buffet (Henri-François)]. Ille-et-Vilaine
No full textLabat Alexandre. [Buffet (Henri-François)]. Ille-et-Vilaine . In: La Gazette des archives, n°32, 1961. pp. 50-51
Buffet (Henri-François), La ville et la citadelle du Port-Louis. Guide historique.
No full textLabat Alexandre. Buffet (Henri-François), La ville et la citadelle du Port-Louis. Guide historique.. In: La Gazette des archives, n°39, 1962. p. 191
Buffet (Henri-François), La ville et la citadelle du Port-Louis. Guide historique.
No full textLabat Alexandre. Buffet (Henri-François), La ville et la citadelle du Port-Louis. Guide historique.. In: La Gazette des archives, n°39, 1962. p. 191
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
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.
Investigation of transonic buffet using high speed PIV
No full textTransonic buffet of a supercritical airfoil (OAT15A) is investigated by means of schlieren visualization and high speed PIV. The buffet conditions were observed to be strongest at M = 0.7 and a = 3.5o at a frequency of 160 Hz. By means of conditional averaging according to the shock location and movement, the typical buffet cycle is illustrated, confirming observations from literature. In addition, proper orthogonal decomposition is used to further characterize the unsteadiness and it was found that the first 3 modes contain the bulk (> 80%) of the fluctuating energy. Furthermore, through spectral analysis it was found that the typical frequency connected to these modes is equal to the buffet frequency. For mode 4 and higher no peak in the power spectrum is found at the buffet frequency.Aerodynamic
Stall Buffet Modeling using Swept Wing Flight Test Data
No full textAs of April 2019, upset prevention and recovery training in flight simulation training devices is a mandatory practice for commercial and civil aircraft pilots. Aircraft stalls are a well-known upset type, therefore simulation of aircraft stall behavior is required. A key characteristic of stalls is the stall buffet, which in current stall models is still insufficiently modeled. In this research, a new methodology to more accurately model stall buffet behavior derived from swept wing flight test data is presented. Buffet effects occur after exceeding the critical angle of attack, with an aircraft type-specific buffet onset duration to fully develop the maximum buffet intensity. The buffet transient behavior is modeled with a frequency response fit and a multivariate second-order polynomial to capture aircraft eigenmode-shape frequencies and state dependent buffet intensity, respectively. Aircraft recovery and thus receding buffet effects occur as the angle of attack starts increasing again after the initial recovery dip, which is used as buffet offset scheduling parameter. Generalization of the results was shown with the validation of data set of a straight-wing aircraft, which indicates a step towards a more generic stall buffet model methodology.Virtual/online event due to COVID-19Control & Simulatio
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
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
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