![]() An inexpensive and traditional alternative is to use a length of plastic tubing, to place one end in your ear and to pass the other end around the glasswork and door seals. These include the use of an intensity probe inside the vehicle to check for aspiration noise. (1999) detail objective methods of assessment. Publications by Anderson (2002) and by Coney et al. The resulting recordings can be played to juries, or Zwicker loudness or Articulation Index are frequently used as a measure of improvement (see Section 1.6.3.2). Windows and doors are taped up, lead sheeting is added to wheel arches and to the underfloor, bodywork protrusions are removed and, at every stage, binaural recordings are made in the car using a dummy head system. Frequently, aerodynamic noise development is undertaken on a subjective basis. The use of a windtunnel allows the car to be stationary thus removing noise contributions from the powertrain and from the tyres. Ĭavity flows through partially open windows and sunroofs causing intense low-frequency (below 25 Hz commonly) noise and buffeting.Īerodynamic noise is best investigated at full scale in a windtunnel although some promising results have been obtained at model scale ( Kim, 2003).Vortex shedding over protrusions in the bodywork (such as aerials, roof bars, etc.) causing tonal airborne noise. Noise transmission through door and glass seals due to aspiration (leakage) or due to aerodynamic excitation of doors and glass caused by disturbed airflow over the seals. Īirflow over the underside of the vehicle causing transmission of airborne sound to the interior, particularly in the wheel-arch areas.Īerodynamic excitation of the so-called ‘greenhouse surfaces’ on the car (the glass-work and the roof panel) causing structure-radiated noise in the interior.The chapter concludes with some recent developments aimed at reducing aerodynamic noise.Īerodynamic noise is caused through a variety of mechanisms: It also discusses various sources of aerodynamic noise present on a train. ![]() ![]() The chapter also describes the basic principles of aerodynamic noise, and presents some experimental and theoretical tools commonly used to investigate the phenomena. Moreover, the proportion of the flow energy that is actually converted into sound is very small. The fact that the sound is generated within the acoustic medium, through which it then propagates, increases the complexity of both measurement and analysis. Aerodynamic sources of noise differ from the others, which are due to vibrating solid surfaces. This chapter focuses mainly on the exterior noise. Thus, for a high speed train, aerodynamic sources are important for both interior and exterior noise. As speed increases, noise inevitably also increases. This means that when the construction of new high speed lines is proposed, it often leads to opposition on the grounds of noise, even more than for conventional lines. David Thompson, in Railway Noise and Vibration, 2009 Publisher SummaryĪerodynamic noise is a phenomenon associated with high speed operation.
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