Prediction of counter-rotation propeller noise

This paper is the first part of a series of three papers dedicated to the prediction of lowspeed interaction noise of an isolated contra-rotating open rotor (CROR). The objective of this study is to assess available analytical and numerical methodologies in terms of robustness, performance and accuracy. The analytical procedure follows the classical Sears' theory, while the numerical procedure follows a two-step approach based on CFD coupled with the analogy of Ffowcs Williams-Hawkings (FWH). Concerning the numerical tools, both chorochronic (single-passage) and Chimera (full-annulus) approaches are considered. The prediction of interaction noise requires fulfilling three modelling steps: the aerodynamic perturbations, the rotor unsteady blade response and the resulting noise radiation. Comparisons with noise measurements are provided. It is shown that the results are highly sensitive to the description of the incoming wake deficit. The chorochronic approach, as a single blade passage is computed, allows the use of much finer meshes than the Chimera approach and requires a lower computational cost. This approach is therefore highly attractive for computing isolated axisymmetric configurations. Nomenclatureunsteady lift k X = chord-wise wave number M ri = relative Mach number across blade i mR = Rear rotor tones frequency, m×BPF (rear rotor) nF = Front rotor tones frequency, n×BPF (front rotor) nF+mR = Rotor-to-rotor tones frequency, n×BPF (front rotor) + m×BPF (rear rotor) RPM = Revolutions Per Minute R i = radius of rotor i S = Incompressible Sears function S c,hf = High-frequency compressible Sears function S c,lf = Low-frequency compressible Sears function SPL = Sound Pressure Level 2 U ri = relative velocity across blade i (X i , Y i ) = coordinate system attached to the blade row i α i = local stagger angle of the section i ß r = relative Mach number function Ω i = rotational speed of blade row i σ 2 = reduced frequency φ = reception angle

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“…XXIV of Schlichting 22 and chap. 5 of Parry 11 . The dependences of ' u and b on both 1 X and D c are similar in these two models.…”

Section: A Analytical Methodsmentioning

confidence: 98%

“…The wake model considered in this study consists of a model developed by Schlichting 21 (see also the detailed descriptions in chap. 5 of Parry 11 , chap XXIV of Schlichting 22 and chap. XIII of Goldstein 23 ).…”

Section: A Analytical Methodsmentioning

confidence: 99%

Computational strategy for predicting CROR noise at low-speed Part I: review of the numerical methods

Colin

Carazo

Caruelle

et al. 2012

18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)

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“…Since n and r k R are respectively the order and argument of the Bessel function which governs the radiation, the lower limit here is a statement that it is only when the argument of the Bessel function is greater than its order that the source radiates, as previously noted by Parry (1988). Within the upper limit, the quantity ∂R/∂r expresses the effect of the streamtube contraction; ∂R/∂r increases from a value of unity far upstream as we move towards the rotor.…”

Section: 2mentioning

confidence: 96%

Noise generation by turbulence–propeller interaction in asymmetric flow

Robison

Peake

2014

J. Fluid Mech.

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This paper is concerned with a particular source of both broadband and tonal aeroengine noise, termed unsteady distortion noise. This noise arises from the interaction between turbulent eddies, which occur naturally in the atmosphere or are shed from the fuselage, and the rotor. This interaction produces broadband noise across a broad frequency spectrum. In cases in which there is strong streamtube contraction, which is especially true for open rotors at low-speed conditions (such as at take-off or for static testing), tonal noise at frequencies equal to multiples of the blade passing frequency are also produced, owing to the enhanced axial coherence caused by eddy stretching. model for unsteady distortion noise was developed in axisymmetric flow. However, asymmetric situations are also of much interest, and in this paper we consider two cases of asymmetric distortion: firstly that induced by the proximity of a second rotor, and secondly that caused by non-zero inclination to the flight direction, as found at take-off. This requires significant extension of the previous axisymmetric analysis. We find that the introduction of asymmetric flow features can have a significant decibel effect on the radiated sound power. For instance, in low-speed conditions we find that the tonal level is reduced significantly by the proximity of a second rotor, compared to the axisymmetric case, while the effect on the broadband levels is rather modest.

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“…Rotor-alone tones (RATs) and interaction tones are both considered. The methods presented herein are based on those presented by Parry [4]. The models that we derive are valid in the nearfield.…”

Section: Introductionmentioning

confidence: 98%

Open Rotor Tone Acoustics: Near-field Prediction & Projection

Sureshkumar

Kingan

2012

18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)

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Recent interest in countra-rotating open rotor engines by the aeronautical industry has prompted a renewal in research methods for predicting open rotor engine noise. The following paper outlines frequency domain methods to predict open rotor tone noise. The methods are exact and are valid in the nearfield, and are used to analyse and understand cruise test data from rig scale open rotor experiments conducted by Rolls-Royce plc. Since the experimental data is only collected in the nearfield and at various observer distances, analytical methods for projecting open rotor tone noise to different observer locations are also proposed. The nearfield acoustic methods are used to visualise and provide insight into the sound field in regions near to the open rotor. The exact expressions are also compared with faster more approximate methods, to show their suitability in predicting the typical level of sound. The projection methods are based on the nearfield frequency domain acoustic expressions, where both exact and approximate methods are described. Both methods are assessed for their robustness and the approximate projection method is then used on open rotor cruise data from experiments. Approximating loading and thickness noise with rotating point forces and rotating point acoustic doublets respectively is shown to be a suitable method. The projection methods are shown to work extremely well on theoretical input data, and the approximate projection method is also used on experimental data with promising results. Nearfield acoustic data, whether theoretical or experimental, can be effectively projected from one observer distance to another, using the analytical projection methods outlined in this paper, for a range of operating conditions and open rotor geometries. Nomenclature = loading source distribution = thickness source distribution = observer position = lift coefficient = tip Mach number = axial Mach number = net normal velocity = ambient speed of sound = non-dimensional wavenumber = hub radius = Mach radius = source radius = tip radius = = axial wavenumber = modespeed = elemental blade lift = non-dimensional blade thickness = blade loading = source position = blade number = rotor diameter = point force (dipole) strength = acoustic doublet (monopole) strength = blade surface = blade chordwise coordinate = maximum blade thickness = blade chord = harmonic number = Green's function azimuthal mode number = acoustic pressure = radial coordinate = blade sweep = time = axial coordinate = = blade stagger = radial wavenumber = wavenumber = = density = retarded time = rotational velocity = azimuthal angle = acoustic velocity = time averaged acoustic intensity

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Prediction of counter-rotation propeller noise

Cited by 75 publications

References 9 publications

Computational strategy for predicting CROR noise at low-speed Part I: review of the numerical methods

Computational strategy for predicting CROR noise at low-speed Part I: review of the numerical methods

Noise generation by turbulence–propeller interaction in asymmetric flow

Open Rotor Tone Acoustics: Near-field Prediction & Projection

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