Northrop F-5A aircraft transonic buffet pressure data acquisition and response analysis

Hwang, Chintsun; Pi, Wang

doi:10.2514/3.44487

Cited by 7 publications

(2 citation statements)

References 2 publications

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“…Even though a number of research organisations have invested substantial resources in this topic, literature on swept-wing buffet remains limited, calling for synergistic experimental and numerical efforts. Early studies employing wind tunnel and flight tests (Hwang & Pi 1975;Riddle 1975;Roos 1985) have shown that wing buffet differs from aerofoil buffet in two main aspects. First, the shock oscillations are non-periodic with a broadband frequency signature, and second, their chordwise excursions are smaller, varying along the span.…”

Section: Introductionmentioning

confidence: 99%

Analysis of a civil aircraft wing transonic shock buffet experiment

2019

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The 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 3.6 × 10 6 . 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.

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Section: Introductionmentioning

confidence: 99%

Analysis of a civil aircraft wing transonic shock buffet experiment

2019

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“…The early studies conducted on 3D configurations were mainly experimental. Hwang and Pi [20] presented an analysis of power spectral density (PSD) distributions obtained with unsteady pressure transducers during flight tests of a Northrop F-5A aircraft. The spectra showed a Strouhal number of about 0.23 for 3D buffet at well-established buffet conditions, but globally, the study was more focused on structural response.…”

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confidence: 99%

Analysis and Comparison of Transonic Buffet Phenomenon over Several Three-Dimensional Wings

et al. 2019

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Experimental study of transonic buffet phenomenon on a 3D swept wing

Dandois

2016

Physics of Fluids

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The objective of this paper is to analyze the 3D buffet phenomenon which appears on a swept wing at a high Mach number and/or high angle of attack. This aerodynamic instability induces strong wall pressure fluctuations and as such limits aircraft envelope. Consequently, it is interesting to understand this phenomenon in order to not only improve aircraft performance but also to provide more flexibility during the design phase. Results from two wind tunnel tests on a 3D half wing-body configuration are presented for several freestream Mach numbers (0.78–0.86) and Reynolds numbers (2.83 × 106–8.49 × 106, based on the aerodynamic mean chord). The buffet phenomenon is characterized using steady and unsteady wall pressure measurements. By opposition to the 2D buffet which exhibits rather a well marked peak in the pressure spectra, the 3D buffet is characterized by a broadband bump at a much higher Strouhal number (between 4 and 7 times higher). It is also observed that two different instabilities coexist on the suction side of the wing: the 3D buffet phenomenon (with Strouhal numbers ranging between 0.2 and 0.6) and the Kelvin-Helmholtz instability (with Strouhal numbers ranging between 1 and 4). Each phenomenon has a different Strouhal number but also different convection velocities and propagation directions.

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Northrop F-5A aircraft transonic buffet pressure data acquisition and response analysis

Cited by 7 publications

References 2 publications

Analysis of a civil aircraft wing transonic shock buffet experiment

Analysis of a civil aircraft wing transonic shock buffet experiment

Analysis and Comparison of Transonic Buffet Phenomenon over Several Three-Dimensional Wings

Experimental study of transonic buffet phenomenon on a 3D swept wing

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