Abstract:a b s t r a c tWall pressure data acquired during flight tests at several flight conditions are analysed and the correlation and coherence lengths of the data reported. It is found that the correlation and coherence lengths are influenced by the origin of the structure producing the pressure and the frequency bandwidth over which the analyses are performed. It is shown how the frequency bandwidth biases the correlation length and how the convection of the pressure field might reduce the coherence measured betw… Show more
“…It was based on the displacement thickness of the boundary layer * . One can also mention a similar attempt made by Palumbo 40 that adjusted the model proposed by Efimsov 41 to experimental data measured on a Gulfstream aircraft fuselage, but here the data is applicable to very high Reynolds number of 2-4.10 7 i.e. about 50 times greater than that of the present study, and the application to the CROR case may be questionable.…”
Broadband noise is a significant part of the noise emitted by contra-rotating open rotors. Several noise sources can contribute to the total broadband sound field, with the most dominant ones probably being trailing edge noise, rotor-wake interaction noise and pylon-wake interaction noise. This paper addresses the prediction of these noise sources using analytical models based on Amiet's flat plate airfoil theory and also to empirical turbulence models, fed by input data extracted from steady and unsteady CFD RANS simulations. The models are assessed against wind tunnel tests of Rolls-Royce's rig 145 (build 1) conducted at the DNW anechoic open jet test facility using Rolls-Royce blades and Airbus pylons. The study showed promising results in terms of the ability of the models to predict acoustic power spectrum shapes, peak frequencies and absolute levels. The effects of changes in thrust on broadband wake-interaction noise are well reproduced. However, the models significantly underestimate the effect of thrust on trailing edge noise and the effect of rotational velocity on pylon interaction noise.
Nomenclature
“…It was based on the displacement thickness of the boundary layer * . One can also mention a similar attempt made by Palumbo 40 that adjusted the model proposed by Efimsov 41 to experimental data measured on a Gulfstream aircraft fuselage, but here the data is applicable to very high Reynolds number of 2-4.10 7 i.e. about 50 times greater than that of the present study, and the application to the CROR case may be questionable.…”
Broadband noise is a significant part of the noise emitted by contra-rotating open rotors. Several noise sources can contribute to the total broadband sound field, with the most dominant ones probably being trailing edge noise, rotor-wake interaction noise and pylon-wake interaction noise. This paper addresses the prediction of these noise sources using analytical models based on Amiet's flat plate airfoil theory and also to empirical turbulence models, fed by input data extracted from steady and unsteady CFD RANS simulations. The models are assessed against wind tunnel tests of Rolls-Royce's rig 145 (build 1) conducted at the DNW anechoic open jet test facility using Rolls-Royce blades and Airbus pylons. The study showed promising results in terms of the ability of the models to predict acoustic power spectrum shapes, peak frequencies and absolute levels. The effects of changes in thrust on broadband wake-interaction noise are well reproduced. However, the models significantly underestimate the effect of thrust on trailing edge noise and the effect of rotational velocity on pylon interaction noise.
Nomenclature
“…Additional sensors spaced at 6 mm, 12 mm and 36 mm were added to increase the length of the arrays beyond the point of expected significant correlation. Detailed information about the flight test data, test bed instrumentation, data consistency and analysis are described in [10,29]. Flight tests measurements were acquired at three different flight conditions, as shown in Table 1, which will be referred to as Cases 1, 2 and 3 throughout this paper.…”
Section: Flight Tests Data Versus Predicted Datamentioning
confidence: 99%
“…The objective is to compare the experimental data with the empirical results in order to establish a quantitative analysis on the produced plate radiated sound power (RSP). The experimental data for the present study were acquired in a flight test that was a cooperative work between the Gulfstream Aerospace Corporation, Boeing Commercial Airplanes and the National Aeronautics and Space Administration (NASA) [10].…”
“…The reference power spectrum and coherence length are predicted using Efimtsov's models which, in turn, depend on flight conditions. The results of a recent flight test 10 indicated that the measured wall pressure varied over short distances, at some locations agreeing with predictions, at others substantially deviating from predictions. This kind of spatial variability has been observed before 11 and had been attributed to differences in the flushness of the sensors 12 .…”
Section: Introductionmentioning
confidence: 65%
“…Gulfstream, Boeing and NASA conducted a cooperative flight test to acquire wall pressure data in an effort to validate and/or advance the models in use by the respective organizations 10 . The data were acquired from sensors mounted in a window blank installed in the forward window area of a G550 aircraft, Fig.…”
Predictions of the wall pressure in the turbulent boundary of an aerospace vehicle can differ substantially from measurement due to phenomena that are not well understood. Characterizing the phenomena will require additional testing at considerable cost. Before expending scarce resources, it is desired to quantify the effect of the uncertainty in wall pressure predictions and measurements on structural response and acoustic radiation. A sensitivity analysis is performed on four parameters of the Corcos cross spectrum model: power spectrum, streamwise and cross stream coherence lengths and Mach number. It is found that at lower frequencies where high power levels and long coherence lengths exist, the radiated sound power prediction has up to 7 dB of uncertainty in power spectrum levels with streamwise and cross stream coherence lengths contributing equally to the total.
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