CAA Code Research Articles

Study of the refraction of sound by shear and boundary layers

Performing accurate acoustic measurements in aerodynamic wind tunnel is a challenge of great interest for the aeroacoustics community. Hence aeroacoustic measurements could be obtained in the same facility under the same aerodynamic conditions. This paper shows the refraction effects to be taken into account during aeroacoustics measurements in a closed test section, including flows up to high subsonic Mach numbers. In closed wind tunnel, the wall-mounted microphones are either flush-mounted or recessed in a cavity to avoid perturbations from the boundary layer. Besides, due to the wall, interference pattern generated by reflections occur. Thus, the acoustical wave front is strongly modified compared to the open test section configuration. Numerical computations, using the ONERA’s sAbrinA-v0 CAA code solving the Euler’s equations, allow us to accurately characterize the influence of a shear layer (recessed microphones) and of a boundary layer (flush-mounted microphones) and measurement setups, on the radiation from a monopolar source in the presence of a rigid wall. The CAA computations are made in the range 1 kHz to 10 kHz and for different boundary/shear layers thicknesses. The paper details a comparison between the Amiet’s model and the CAA computations. The comparisons are in a good agreement despite the absence of a wall in the Amiet’s model.

Aeroacoustic Simulation of a Complete H145 Helicopter in Descent Flight

In the past years, the aeroacoustic noise emission of a helicopter became one of the most important, but also challenging issues in helicopter development. The blade vortex interaction phenomenon is one of the dominant phenomena characterizing the helicopter's aeroacoustic footprint, which is insufficiently predicted by low fidelity computational methods. For a high fidelity noise prediction of a helicopter configuration, a multidisciplinary CFDCSD-CAA tool chain has been established at the Institute of Aerodynamics and Gas Dynamics of the University of Stuttgart. With higher order CFD computed noise generation at the near field and the noise convection using a Ffowcs-Williams Hawkings based CAA code, very good agreement to measured aeroacoustic noise in wind tunnel as well as free flight experiments of helicopters is achieved. However, the simulations had been limited to the main rotor's geometry up to now, where some residual deviations to the experiment still exist. In this paper, we present a high fidelity aeroacoustic simulation of a complete helicopter configuration and the benefit compared to an isolated rotor simulation in predicting its aeroacoustic noise emission. Shading and reflection effects are clearly resolved, influencing the behaviour of the helicopter's noise radiation. The simulated aeroacoustic noise emission of the helicopter lies within the experimental variation and shows therefore highly promising results for the next generation of aeroacoustic noise prediction.

CFD Prediction with LES for Psycho Acoustic Relevance in Ventilation

The classical adage: “Less Noise __ More Sound” challenged our interest -whether if it is or not possible to model by numerical simulation a suitable prediction in terms of sound quality to discriminate between Consonant _ Dissonant _Neutral sound patterns. Ansys_Fluent CFD_CAA code was used (with a 1e -6 time-step for 12milon of hexahedral cells grid) in order to perform related gas-dynamic numerical prediction – in ventilation. We have started our investigations with a simplest designed flat plated blades (for a revers spinning centrifugal fan) –prescribing three different incremented blade disposal. We have set some monitoring points (at certain transversal sections). The LES model with FW-H mode predicted results, were first Fast Fourier Transformation converted, than we have processed them with Matlab –in order find the most relevant group (octaves)/musical notes, and finally to decide by the use of an dedicated Wolfram code –whether the predicted sound should experience psycho acoustic supportability (i.e.-perception).

Numerical Modelling of Aerodynamic Noise in Compressible Flows

The solution of the AeroAcoustics (CAA) problems by means of the Direct Numerical Simulation (DNS) or even the Large Eddy Simulation (LES) for a large computational domain is very time consuming and cannot be applied widely for engineering applications. In this paper the in-house CFD and CAA codes are presented. The in-house CFD code is based on the LES approach whereas the CAA code is an acoustic postprocessor solving the non-linearized Euler equations for fluctuating (acoustic) variables. These codes are used to solve the aerodynamically generated sound field by a flow over a rectangular cavity with inlet Mach number 0.53.

Aeroacoustics research in Europe: The CEAS-ASC report on 2009 highlights

The Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC) supports and promotes the interests of the scientific and industrial aeroacoustics community on an European scale and European aeronautics activities internationally. In this context, “aeroacoustics” encompasses all aerospace acoustics and related areas. Each year the committee highlights some of the research and development projects in Europe. This paper is a report on highlights of aeroacoustics research in Europe in 2009, compiled from information provided to the ASC of the CEAS. In April 2009, the Level-2 project OPENAIR of the Seventh Framework Programme of the European Commission has been launched with the goal of delivering a step change in noise reduction, beyond the successful achievements of the predecessor SILENCE(R). Some contributions submitted to the editor summarizes findings from programmes launched before 2009, while other contributions report on activities supported by national associations and industries. Furthermore, a concise summary of the workshop on “Resolving Uncertainties in Airframe Noise Testing and CAA Code Validation” held in Bucharest is included in this report. Enquiries concerning all contributions should be addressed to the authors who are given at the end of each subsection.

Some parameters required for producing small fruit preserves

Traditional homemade methods are followed to produce small fruit preserves in the Andean–Patagonic region crossed by the 42° parallel. Fruits like sweet and sour cherry, raspberry, boysenberry, etc., are placed in glass containers together with sugar liquor as covering liquid. Among the various technological and legal requirements set for these preparations, the final drained weight of the finished product must be indicated, since the Código Alimentario Argentino (CAA or Argentine Food Code) requires both net and drained weights to be labeled. The same legislation also stipulates a minimum for the drained weight. Our aim in this work is to determine: The minimum amount of fruit in the containers to comply with the minimum drained weight limits set by the CAA as well as to avoid “floating” fruits. The maximum amount of fruit that can be placed in the containers without causing fruit deformation or squash. The fruit drained weight in the finished product in connection with the variables that affect it. Easy-to-use correlation based on the experimental results to be obtained, to facilitate producers' work.