Calculation Of Oscillation Flow In Cavity And Noise Suppression

Large eddy simulation (LES) is employed to calculate the compressible fluid in the three dimensional open cavity with length-to-depth (L/D) ratio of 5. Flow field characteristics and oscillation energy distribution in the cavity are studied. Three sub-grid stress models are applied to analyze the superiority-inferiority in predicting cavity oscillation frequency. Meanwhile, it also analyzes the effectiveness of noise suppression by changing the cavity shape and filling porous medium around the aft wall.In this thesis, sustained oscillation frequency in the cavity is in agreement with Rossiter formula and experimental results. The oscillation energy mainly concentrates on the low frequency region. The first three modes are the main sustained oscillation modes. The main discrepancies of sound pressure level (SPL) occur in the region around the fore and aft walls. The results calculated by Dynamic Smagorinsky-Lilly (DSM) model are more accurate to experimental data than the results calculated by Smagorinsky-Lily (SM) model. Because the Wall Adapting Local Eddy Viscosity (WALE) model can get eddy viscosity more accurate around the wall, results calculated by WALE model are the closest to the experimental data. The calculate results of sound pressure and spectrum sound pressure level at the bottom of the cavity demonstrate the WALE model is the most accurate model to predict the self-sustained oscillation of cavity, while the DSM model is fairly good, the SM model is slightly inaccurate. The sound pressure level in triangle cavity is obviously lower than that in rectangular cavity. Although the ellipse cavity can reduce noise, effect is not evident. Porous medium can obviously reduce the self-sustained energy.This thesis reveals the oscillation mechanism and accurately predicts methods of self-sustained oscillation in the three dimensional rectangular cavity. Meanwhile, this paper also studies the noise suppression methods by changing the cavity shape and using porous medium.It provides an idea of the further study in noise suppression field.