Numerical Simulation And Experiment Study Of The Noise Radiated By A Cavity Flow

The aerodynamic noise around ground vehicles at high speeds has become increasingly important and in more and more cases dominates the vehicle noise. It is attributable to the facts that the noises from engine, tire and power train and other noise sources have been significantly reduced and the speeds of ground vehicles constantly increase in the past decades. It is therefore crucial to carry out the study of aerodynamic noise and explore proper countermeasures for suppressing its contribution to the vehicle noise. The reduction of such noise can give a comfortable in-car condition and reduce noise radiation to the surroundings, all which can offer social and commercial advantages.The flow mechanism and radiated noise by a low-speed turbulent flow over an open cavity has been investigated computationally. After acquired the flow field data which is obtained by using Large Eddy Simulation, hybrid method that couples numerical flow computations with an implementation of the Ffowcs Williams-Hawkings equation is used to capture the flow induced noise. At the same time, design and processing of the cavity model and the flow in the wind tunnel experimental noise. Numerical simulation and experimental research acquire the following conclusions:1. In order to investigate the influence of the cavity deeps, different cavity deeps (such as D=3mm, D=4mm, D=6mm) are used to investigate the influence of cavity configuration while the velocity of incoming flow is 50m/s. SPL of the cavity with the deepth D=6mm is 104dB while the cavity with the deepth D=3mm is 120dB. The transition of flow mode is the main cause of such reduction.2. In order to investigate the influence of the different cavity configurations, different cavity configurations (such as the rectangular cavity, the trapezoid cavity, the arcuated cavity) are used to investigate the influence of cavity configuration while the velocity of incoming flow is 50m/s. When L/D=3, the SPL of the arcuated cavity is 96dB while the rectangular cavity is 115dB. The transition from wake mode to shear layer mode is the main cause of such reduction.3. Self-sustained oscillation in cavity and the coupling between flow field and radiated noise are observed in all these computations.4. Cavity noise experiment is conducted in wind tunnel and the result is shown good agreement with numerical simulation.5. The reduction of cavity noise is also discussed in this article. With cavity deeps increase(L/D≤4), the SPL of cavity noise can be reduced; Or with cavity configurations change (L/D≤4) so that cavity walls smooth as possible, such as a transition from the rectangular cavity to arcuated cavity, and the drag due to the change of the cavity walls greatly reduced. In the wake mode, self-sustained oscillation become weak, the cavity flow becomes stable on a large scale,the SPL of cavity noise greatly reduced.