The surface pressure fluctuations due to the flow separation in the A-pillar region on the front side windows of a passenger car is a dominant source of aerodynamic noise. Aerodynamically generated noise adversely affects vehicle occupant's comfort and safety (due to fatigue caused by long time noise exposure). The size and magnitude of the A-pillar flow separation mainly depend on the local A-pillar and windshield geometry and yaw angles. The primary objective of this was to develop a computational fluid dynamic (CFD) and computational aero-acoustics (CAA) model to simulate aerodynamic flow and noise generation in the A-pillar region of a simplified 40% scale vehicle with elliptical windshield radius at ±15° yaw angles. Observations made from the CFD and CAA results showed trailing edge and boundary layer noise were generated, caused by turbulent airflow separation behind the A-pillar region. The trailing edge noise was dominant in the leeward region while boundary layer noise was seemed to dominate in the windward region. High sound pressure levels were observed on the vehicle body, close to the noise source, which gradually decreased as the aerodynamic noise propagated further from the vehicle body. The following conclusions were obtained from the work presented here: (1) Mechanism of turbulent generation was due to trailing edge separation originating from the front and side corner of the hood, A-pillar vortex separation and turbulent boundary layer separation originating from the apex of the A-pillar. (2) The trailing edge separation generated from the front and side corner of the hood resulted in an elongated quasi two-dimensional physical form. This vortex separation in the leeward region formed an elongated helical vortex as the flow travelled downstream. Turbulence flow generated due to the presence of turbulent boundary layer in the windward region of the flow remains attached as the flow travels downstream. (3) Trailing edge separation and A-pillar vortex separation translate to trailing edge noise and A-pillar vortex noise observed as source for aerodynamic noise in the leeward region. Turbulent boundary layer noise was observed as source for aerodynamic noise in the windward region. (4) The model surface revealed a 1 dB to 2 dB increment during transient propagation in the leeward and windward region. A loss of around 4.5 dB was obtained between the model surface and the surrounding CAA domain during transient propagation. Acoustical propagation investigation conducted at the surrounding CAA domain revealed a mean OSPL increase of 2.5 dB. (5) CFD model predictions were obtained with a mean deviation of 20.3% from the experimental results. (6) CAA model showed an overall PSD mean discrepancy of 5 dB and 13 dB at the windward and leeward region respectively, which was below the benchmark value of 15 dB obtained from literatures.


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    Titel :

    A computational fluid dynamics study of crosswind effects on vehicle A-pillar aero-acoustics


    Weitere Titelangaben:

    Eine CFD-Studie der Seitenwindeinflüsse auf die Aeroakustik von Fahrzeug-A-Säulen


    Beteiligte:
    Murad, Nurul M. (Autor:in) / Naser, Jamal (Autor:in) / Alam, Firoz (Autor:in) / Watkins, Simon (Autor:in)


    Erscheinungsdatum :

    2013


    Format / Umfang :

    24 Seiten, 21 Bilder, 30 Quellen




    Medientyp :

    Aufsatz (Zeitschrift)


    Format :

    Print


    Sprache :

    Englisch