High-speed flows in cavities such as grooves,wheel wells,and weapon bays,are often encountered in aerospace and aeronautical *** most cases the flow field is complex and unsteady,featured by shear-layer instability,fl...
详细信息
High-speed flows in cavities such as grooves,wheel wells,and weapon bays,are often encountered in aerospace and aeronautical *** most cases the flow field is complex and unsteady,featured by shear-layer instability,flow separation and formation of vortex structures,shock wave/boundary-layer interactions at transonic and supersonic *** unsteady flow characteristics occur therein,such as fluctuating pressure and *** aerodynamic noise inside the cavity can reach 170 dB,which can damage some installed apparatus inside the cavity and structural components of the ***-stream boundary layer has significant influence on aero-acoustic characteristics inside *** paper presents that sound pressure level(SPL) distributions and sound pressure frequency spectrum(SPFS) characteristics at different measurement positions on cavity floor centerline utilizing two terms of experimental results under experimental *** of different free-stream boundary-layer thickness to cavity depth ratios on shallow cavities(transitional and closed cavity flow) were *** data presented herein was obtained about the cavities with length to depth ratios of 12 and 15 over a Mach number of 0.6 at a Reynolds number of 1.23×10～7 per *** results show that decrease in the boundary-layer thickness to the cavity depth ratios(δ/D)causes SPL amplification and noise enhancement at different measurement positions inside the cavities,especially the front and ***,decrease in δ/D)has a significant influence on SPFS characteristics and leads to increase in SPL in the frequency range of 0Hz
In analogy to photonic crystals, phononic crystals may exhibit complete band gaps in their transmission spectra where the propagation of acoustic or elastic waves is strictly forbidden in all directions. The complete ...
详细信息
In analogy to photonic crystals, phononic crystals may exhibit complete band gaps in their transmission spectra where the propagation of acoustic or elastic waves is strictly forbidden in all directions. The complete band gaps could be engineered to provide a vibrationless environment for high precision mechanical systems in given frequency ranges. Understanding the full band structures is expected to lead to the design of new generations of sound shields, filters, transducers, refractive devices such as acoustic lenses and acoustic interferometers, etc. By breaking the periodicity of the systems, it is possible to create highly localized defect or guided modes within the acoustic band gaps, which are analogous to localized modes in a photonic crystal and to localized impurity states in a semiconductor. This makes the phononic crystals potential candidates for the design of elastic or acoustic wave guides. In the case of solid/solid systems, the existence of full band gaps and localized defect modes and the possibility of guiding waves have been investigated theoretically using the different methods. In the present paper, this boundary element method is extended to the calculation of the defect states in two-dimensional phononic crystals. We consider a 2D phononic crystal consisting of a square array. Both scatterers and matrix are homogeneous, isotropic and linear elastic solids. Due to the periodicity of the system, we can restrict our attention to a supercell. For the solid/solid system, when the binary components perfectly contact, the boundary conditions along the interface are that the displacements and the stresses are *** addition, the periodicity of the structures implies that any field quantity(e.g. the displacement, stress, pressure and their derivatives) should obey the following Bloch theorem. The Bloch theorem allows us to solve the problem in a supercell. We bulid the boundary integral equations of the matrix and every scatter. Then the boun
暂无评论