Abstract
Bluff body is a simple but a central shape for many engineering applications. The geometry shape of the bluff body characterises the behaviour of the flow over the bluff body, where a more complex flow structure is found near downstream. Shear layer separation is mainly responsible for the periodic global phenomena, that includes the generation of sound. The magnitude of the aerodynamically generated sound is dominated by the fluctuations of aerodynamics forces, i.e., drag and lift. The study also shows that the sound pressure field is shaped by the aeolian tones that is related strongly to the lift fluctuations of the bluff body. Amplitude and frequency of the fluctuating lift change naturally with the shape of a particular bluff body. Triangular cylinder exhibits the largest sound pressure level (41.9 dB) followed by ellipse and circular shapes. Square cylinder emits the lowest sound pressure level (36.7 dB). This corresponds to the longest downstream vortex formation length at which for a square cylinder the long vortex formation length provides space for more vortex to dissipate.
Highlights
OF THE STUDYFlow over a bluff body is a fundamental and important subject of fluid mechanics
There is no available study, at least to the author's knowledge, to investigate the possibility of a downstream flat plate to be made as an anti noise source signal, i.e. lift fluctuations, except for a square cylinder case
The flow is modelled in two-dimensional governing equations to reduce the computational cost. This assumption is valid by the fact that the Reynolds number of the current study is lower than the critical Reynolds number for the onset of three-dimensional instability, which is Re = 161 according to the Floquet stability analysis of Robichaux et al [13]
Summary
In the engineering pratical applications, their behaviour in the various flow conditions needs to be well understood and if it is not, the annoying flow-induced-problems may exist and degrade the performance of the design This can be clearly observed from the noise emitted from a side view mirror of passenger car when moving at high speed, i.e., 80 km/h [1], a landing gear system of aircraft when about to land [2,3] and a pantograph system of high speed train when moving at transition speed 225 km/h [4]. This study provides the necessary physical flow and noise features for flow over an isolated bluff body in four different geometrical shapes This information is vital in designing a downstream flat plate for a sound cancellation in the later stage
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