Experimental and theoretical aero-acoustics

Acoustic noise problems are encountered in many fields and are very often undesirable. The localisation of sound sources is the first step 10 reducing noise problems. In this thesis, the ability and feasibility of an acoustic camera in this regard is demonstrated The acoustic camera deals with the problem of sound sources coming from different directions by estimating the sound contributions incident to the acoustic camera. One example of an aero-acoustic noise problem is an air plane with its air foil. These cause unwanted noise due 10 the flowed air. Or another example is the current collector on trains which causes unwanted noise as well as affecting driving. Another problem, dealt with later in this thesis, is a cylinder flowed by air in a wind tunnel. A practical case 0/ this problem is a car antenna in the form of a cylinder; this causes noise due to the driving wind Fans can be optimised for aero-acoustics as well - an example is a cooling fan in a computer, or larger fans for air conditioners that can transport the noise over the whole tunnel in which they are built. Some processing techniques are used and implemented in the acoustic camera. The first technique is the "classical" Delay-and-Sum Beam/arming technique and the improved orthogonal beamforming, with the ability to separate non-correlated sound sources in a Single measurement. The second technique is based on the decomposition of the Eigenvalues of the cross spectral matrix. In addition to the experimental section of this thesis, the results are compared to a simulation, where a flowed object measured with the acoustic camera is compared to a suitable simulation with the same parameters like dimensions and velocity. Here f/owed means that a suitable object, a cylinder for example, is placed in the wind tunnel and flowed by air. The outcome of this thesis is the analysing of a flow induced problem, a fan for example. First steps were done with 2D flow simulations of a cylinder to become familiar with the topic program and implementing MATLAB® code to process the points of interest. This analysing could be done with a simulation or with the acoustic camera. The aim of this work is concerned with sound sources and the mechanism behind it. Suitable aero-acoustic experiments were chosen that can be analysed with the acoustic camera and with numerical simulation as well. With the acoustic camera, these sound sources can be visualised using the beamforming method A similar procedure should be done to the numerical simulations. These simulations are done and the sound sources are visualised there as well by rebuilt an array of microphones, which acts as acoustic camera, in the numerical simulations.EThOS - Electronic Theses Online ServiceGBUnited Kingdo