NASA’s Commercial Supersonic Technology (CST) project has formulated a technical challenge to design a quiet propulsion system for a low boom supersonic aircraft that meets Federal AviationAuthority’s airport noise regulations with sufficientmargin. Several proposed configurations take advantage of shielding from the wing or other air-frame components. Development of carefully validated computational tools are necessary for critically evaluating installation concepts that are currently being proposed to meet the technical challenge. Semiempirical models that predict the noise reduction potential of arbitrary shielding surfaces are yet to mature. Another key challenge is the systematic assessment of additional noise from the interaction between high speed jet turbulence and a surface in it’s vicinity. As a first step towards predicting noise reduction due to radical installation concepts from first principles, we simulate the noise generated by a high speed turbulent round jet near a simple planar surface. Detailed comparisons are made with a dedicated experiment conducted at NASA’s Glenn Research Center. Sensitivity of far-field noise predictions to grid resolution is systematically documented. A permeable FfowcsWilliams Hawkings (FWH) surface enclosing both the jet and the shielding surface is used to predict far-field noise from the simulated flowfield. Details of the structured overset grids, numerical discretization, and turbulence model are provided. Near-field comparisons to PIV data and far-field comparisons to microphone array measurements are discussed. Excellent agreement for an initial validation study on an isolated free round jet was obtained and the findings were utilized in the jet surface interaction study. The split between shielded and reflected side of the microphone array was captured with good agreement, as well as the peak in the noise spectra due to scattering of turbulent energy into sound by the trailing edge of the surface.
In flames, extinctions and subsequent re-ignitions occur continuously, with such small lifetime that they are difficult to perceive. Here, the light emitted by a vortex in reactive conditions is sampled in time and projected on a wavelet base. The result of the analysis is a statistical description of these shutdown and re-ignition phenomena in terms of the event duration, occurrence, amplitude, and shape. The proposed data analysis technique is applied for the first time in the field of combustion, but has had a widespread application in nonreactive fluid dynamics and aeroacoustics.
Landing gears are recognized as one of the most significant contributors to airframe noise for commercial aircraft in the approach configuration. 1 Wheels are the major contributors to the landing gear noise. 2,3 everal experimental and numerical tests have been performed to study the flow features and far-field acoustics of landing gear wheels.Casalino et al. 4 numerically investigated the noise from two facing wheels with rim cavities on the LAGOON (LAnding Gear nOise database for CAA validatiON) 5 landing gear geometry.Two tonal peaks were found in the sideline direction due to the wheel cavity resonances.Zhang et al. 6 performed aerodynamic and aeroacoustic experiments of an isolated high-fidelity landing gear wheel.They found that the wheel noise is characterized by broadband middle frequency noise centred around 630 Hz and 1250 Hz.Wang et al. 7,8 conducted numerical simulations with the same geometry used by Zhang et al. 6 and found that the noise at 630 Hz and 1250 Hz is generated by the first and second depth modes of the hub cavity.However, these previous works have not considered the interaction noise from wheels in tandem, which is significant for four-wheel and six-wheel landing gear noise.Flow interactions can occur for wheels in a tandem configuration.A benchmark case of tandem cylinders, with a separation distance of L = 3.7D (where D is the diameter of the wheel), was proposed to represent tandem landing gear wheels. 9In the experiment of this benchmark case, a co-shedding state was found with both cylinders shedding vortices. 9The downstream cylinder was demonstrated to be the dominant noise source, which is characterised with tonal noise at the shedding frequency.For a typical landing gear, the separation distance of the tandem wheels is between 1.1D and 1.5D, 10 and in such a range, the shear layer from the upstream cylinder is expected to reattach on the downstream cylinder, 11,12,13,14 and no regular shedding can be observed.Additionally, wheels can be considered as circular cylinders of short aspect ratios, the flow field surrounding which is more complex compared to the large aspect ratio circular cylinders.Thus, the tandem landing gear wheels noise is expected to be more broadband.Spagnolo et al. experimentally 10 and numerically 15 studied the aerodynamic loads of a tandem wheel case, with three separation distances, i.e. 1.1D, 1.3D and 1.5D.The wheels are simplified by short circular cylinders.They found a general trend of higher mean drag coefficient and a lower RMS of force coefficients with increasing separation distance.Despite the previous investigations of aerodynamic and aeroacoustic behaviour of tandem cylinders flow and aerodynamic loads of tandem wheels flow, the noise from tandem landing gear wheels, especially with realistic wheel geometries, has not been studied separately.In this paper, the interaction noise between two wheels in tandem at L = 1.5D will be investigated.The wheels have a detailed geometry including a hub and rim cavities, which is the same as the one used in the experiment by Zhang et al. 6 This paper is structured in the following manner.The wheel geometry and the grid generation are provided in Section II.Section III describes the numerical method and the computational setup in the simulations.The aerodynamic and acoustic simulation results are provided in Section IV, together with comparisons to the experimental data by Spagnolo et al. 16 The results are compared to the isolated wheel and the effect of covering the hub and rim cavities on the downstream wheel is also investigated.The summary of this paper is given in Section V.
Measurements of the noise emitted by the V2500 engines of the Airbus A320 research aircraft ATRA of DLR have been performed under static conditions in a ground test and in a flight test. The ground test measurements were performed with a linear microphone array laid out on the ground in parallel with the engine axis. The fly-over measurements were performed using a large multi-arm spiral array. Frequency spectra from different directions calculated from the ground test data and Doppler corrected frequency spectra from the flight test data show good agreement in the broadband levels and even in the levels of the engine tones.
