Acoustic optimization of ultra-low count bypass outlet guide vanes

An optimization process has been used to design an ultra-low count fan outlet guide vane with an unconventional leading edge profile to reduce the interaction noise. Computational fluid dynamics has been used to predict the aerodynamic and acoustic performance of the stator vane. The final stator design has been built and tested in a representative fan stage rig to determine its tone noise characteristics. The stator vane is found to give significant tone noise reduction at the fundamental blade passing frequency at cut-back in line with design expectations. Detailed comparisons of predicted circumferential and radial modes levels against measured mode detection data are also presented. A good agreement was found between numerical predictions and experimental data.

Investigating landing gear noise using fly-over data: The case of a Boeing 747-400

Modeling the noise originating from a landing gear has proven to be a challenging task, because of its complicated structure. In full-scale, landing gear noise can only be investigated experimentally by source localization techniques and fly-over measurements with microphone arrays. In the present work, measurements of a Boeing B747-400 were used to determine the contribution of the landing gear to the overall noise emitted during a fly-over and how the broadband noise from the landing gear scales with the flight velocity. A tonal source from the nose landing gear was identified at 380 Hz with a harmonic at 760 Hz and it most likely originates from a cavity. It was also found that the Power Spectral Density (PSD) of the high frequency broadband component varies linearly with frequency and there is some scaling with the ow velocity. Finally, the nose landing gear was shown to be a significant contributor to the overall airframe noise as expected.

Cabaret finite-difference schemes for the one-dimensional Euler equations

In the present paper we consider second order compact upwind schemes with a space split time derivative (CABARET) applied to one-dimensional compressible gas flows. As opposed to the conventional approach associated with incorporating adjacent space cells we use information from adjacent time layer to improve the solution accuracy. Taking the first order Roe scheme as the basis we develop a few higher (i.e. second within regions of smooth solutions) order accurate difference schemes. One of them (CABARET3) is formulated in a two-time-layer form, which makes it most simple and robust. Supersonic and subsonic shock-tube tests are used to compare the new schemes with several well-known second-order TVD schemes. In particular, it is shown that CABARET3 is notably more accurate than the standard second-order Roe scheme with MUSCL flux splitting.

Measurements of intake separation hysteresis in a model fan and nacelle RIG

A 1/20-scale, low speed model rig representing the fan and nacelle of a high bypass ratio jet engine has been tested under crosswind conditions. The flow conditions under which the intake flow separates and reattaches have been found to exhibit considerable hysteresis. This phenomenon has been examined by a careful test procedure in which the crosswind angle has been slowly increased and then decreased. Measurements of the hysteresis associated with separation and reattachment are presented for independent variations in stream-tube contraction ratio, ground clearance, fan operating point and Reynolds number. The results reveal that particular care must be taken to allow for any hysteresis when testing intakes under crosswind conditions. They also indicate that separation hysteresis is particularly sensitive to fan operating point and the position of the ground plane. These findings suggest that it is important for high Reynolds number intake tests and calculations to include a ground plane and a model of the downstream turbomachinery. © 2002 by the author(s).