Abstracts Submitted: 510
Number of Users: 708
View Abstracts Submitted
Back to home Page
Turbulent Boundary Layer (TBL) is one of the major sources of vibration and noise in any aircraft or automobile structure. TBL induced vibration of the structure perturbs the adjacent acoustic domain and the perturbation in terms of noise propagates into an enclosure or radiates in the free field. Prolonged exposure to high sound pressure level (SPL) is detrimental for human beings as well as for structures. To deal with this adverse noise effect it is necessary to understand the TBL induced vibro-acoustic phenomenon. As the wall-pressure fluctuation beneath a TBL is random, stochastic approach needs to be adopted and cross-spectral density of fluctuating pressure terms has to be estimated at different pre-defined points. Langtry-Menter 4-equations transitional shear stress transport (SST) model is used to estimate the wall-pressure fluctuations beneath TBL, and subsequent cross-correlation is done. Sufficient spatial and temporal resolution is used to capture the near-wall eddies which are primarily responsible for the pressure fluctuation. In the present research work, a numerical simulation is conducted to estimate TBL induced vibration and resulting noise level radiated into the free field when a turbulent flow occurs over a flat panel. A rectangular steel panel of dimension 47cm×37cm, clamped at its four sides and placed in an infinite baffle is considered for the present simulation. Air is assumed to flow over the plate with an initial velocity of 44.7 m⁄s. The primary objective is to obtain the wall-pressure fluctuation over the plate. This pressure fluctuation acts as the random disturbance on the flexible plate which results in the vibration of the plate. Subsequently, by modeling the coupling effect of the structural response and the free field acoustic domain, estimation of sound transmission can be done. Fluent and APDL modules of ANSYS Workbench (ver. 14.5) are employed to calculate the wall-pressure fluctuation under TBL and frequency-mode shape data of the plate respectively. The fluid flow is modelled with 1500 time steps and time step size of 0.001 sec. For free vibration analysis of the plate, involving Finite Element (FE) approach, 60×20 element meshing is used. To capture the plate bending wave accurately, 60 elements have been provided in the stream wise direction. To couple pressure data in cross-correlated form and frequency-mode shape data of the plate, an in-house Matlab (ver. 11.0) code is developed. Another Matlab based in-house program is developed to account the coupling effect of the TBL induced structural velocity and the semi-infinite acoustic domain (free field) using Boundary Element (BE) approach. Finally, the radiated sound pressure level (SPL) in the free field is estimated in the low frequency region.
© Copyright 2017 All Rights Reserved