Measurement and prediction of broadband fan noise

Ganz, Ulrich; Glegg, Stewart; Joppa, Paul D.

doi:10.2514/6.1998-2316

Cited by 15 publications

(12 citation statements)

References 16 publications

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“…We therefore conclude that the blade wakes were not subject to any correlated unsteadiness. All spanwise profiles (1)(2)(3)(4)(5) consisted of 20 to 30 two-point measurements. A minimum probe separation of 3.8 mm (0.027c a ) was used with an increment of 1.3 mm (0.009c a ) for small probe separations.…”

Section: Two-point Profilesmentioning

confidence: 99%

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Wake of a Compressor Cascade with Tip Gap, Part 3: Two Point Statistics

et al. 2004

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Velocity spectra and space-time correlations have been measured downstream of a low-speed linear compressor cascade with tip gap. The objective of this work is an improved understanding of the coherent turbulence structures present in fan-tip wakes and of the turbulent source terms responsible for broadband stator noise. The two-point measurements show no correlation between turbulent motions in the wakes or leakage vortices shed by adjacent blades and that the leakage vortex is not subject to low-frequency wandering motions. They also show that the tip leakage vortex turbulence is highly anisotropic and characterized by elongated eddies inclined at about 30 deg to the vortex axis. The presence of such structures, which produce no clearly identifiable footprint in velocity spectra, appears consistent with the helical structures seen in direct numerical simulations of a line vortex with unstably large streamwise velocity defect. This suggests the same mechanism is behind the generation of turbulence in this vortex. Examination of the correlation data from the point of view of a hypothetical stator blade suggests that, because of the anisotropy in turbulence structure, velocity correlations seen by a stator in a real engine are likely to be a strong function of engine geometry and operating point. IntroductionT HIS paper is our third in a series dealing with the flow downstream of a linear compressor cascade. This cascade is designed to reproduce, in an idealized setting, some of the important conditions experienced in the subsonic fan of a large-bypass-ratio aircraft engine, specifically the mechanisms leading to the generation and evolution of the tip leakage vortices that dominate the casing endwall flow, which impinges on the bypass stator. Our first two papers 1,2 focused on single-point velocity measurements of the mean flow and Reynolds-stress fields produced by the blade wakes, the leakage vortices, and the associated endwall flow, as functions of streamwise position, tip gap, and relative motion between the blade tips and endwall. Such measurements provide data and understanding to aid in the development and testing of computational-fluid-dynamics (CFD) prediction tools for calculation of the unsteady aerodynamics and tone noise produced by the stator interaction. In this paper we focus on two-point turbulence measurements. This type of information not only provides insight into the scale and form of the coherent structures that populate the turbulent regions, but is also critical to understanding the generation of broadband noise by the stator row.To predict the broadband rotor/stator interaction noise, it is, in principle, necessary to have a complete description of the rotor wake turbulence in terms of its two-point space-time correlation function and a response model for the blade row. Complete two-point information is rarely available even for relatively simple flows and cannot be provided by performing Reynolds-averaged CFD calculations. Drastic assumptions about the form of the two-point cor-

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Section: Two-point Profilesmentioning

confidence: 99%

“…Drastic assumptions about the form of the two-point correlation function are therefore made. Specifically, correlation functions based on the von Kármán spectrum for isotropic homogeneous turbulence are usually assumed, 3,4 even though neither of these adjectives fits the fan wake flow.…”

Section: Introductionmentioning

confidence: 99%

Wake of a Compressor Cascade with Tip Gap, Part 3: Two Point Statistics

et al. 2004

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“…For example modifying the engine operating condition so that the structures strike the blades with different inflow angle will alter the noise, and design schemes can be developed on this basis. 5 . Fan speed 55%, wake angle 62°, low loading.…”

Section: Resultsmentioning

confidence: 95%

Rotor/stator interaction noise from blade wakes

Glegg

Devenport

2001

7th AIAA/CEAS Aeroacoustics Conference and Exhibit

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“…The phenomenon is particularly complex as it combines with the interaction between the rotor and the boundary layer developed at the casing wall. Minimising the tip clearance is an efficient solution to reduce the vortex strength and consequently mitigate rotor tip-clearance induced noise (32) . In open configurations the front-rotor tip vortex is chopped by the aft-rotor blades because its trajectory is diverted inwards, following the flow contraction.…”

Section: Shrouded Vs Un-shrouded Propellersmentioning

confidence: 99%

Performance prediction and progress towards multi-disciplinary design of contra-rotating open rotors

Guérin¹,

Schnell²,

Becker³

2014

Aeronaut. j. (1968)

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At DLR's Institute of Propulsion Technology, the prediction tools and multi-disciplinary optimisation strategies developed for turbofan engines have been extended to contra-rotating open rotors (CROR). Thereby the objective has been to appraise and improve the performance of CROR engines and thus to reduce their environmental impact. The present paper reviews the intermediate progress achieved in this scope. The prediction is based on analytical and CFD methods and covers the fields of engine performance analysis, aerodynamics and acoustics. The aerodynamic and acoustic results could be partly validated through the comparison to experimental data obtained from wind-tunnel tests. In a multi-disciplinary approach the aforementioned aspects are optimised together. First results of an aero-acoustic optimisation are presented. Furthermore this paper undertakes some comparison between high-bypass ratio turbofan engines and open-rotor concepts.

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Measurement and prediction of broadband fan noise

Cited by 15 publications

References 16 publications

Wake of a Compressor Cascade with Tip Gap, Part 3: Two Point Statistics

Wake of a Compressor Cascade with Tip Gap, Part 3: Two Point Statistics

Rotor/stator interaction noise from blade wakes

Performance prediction and progress towards multi-disciplinary design of contra-rotating open rotors

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