Surface-mounted half cylinder acoustics



	Acoustics Simulation of the Flow-Induced Noise in the Wake of a Surface-Mounted Half-Cylinder:
	This example considers a 200km/hour air flow over a surface-mounted half-cylinder. Mean data and statistics are computed initially using an anisotropic RANS model. The figure on the right illustrates that the bulk of the unsteady kinetic energy is contained in the boundary layer and in a narrow wake downstream of the cylinder.	RANS solution showing 0.1%k(max) isosurfaces.
	The CAA++ suite contains analytic methods to extract noise directly from an initial set of RANS data. The figure on the right illustrates predictions from the waveprop1 tool at two points in the near wake (point 1 on the cylinder rear face and point 2 downstream on the ground plane). Even with simple wave solutions, agreement with data is often good enough to provide useful information on trends.	Sound-pressure levels computed directly from the RANS data using the waveprop1 tool.
	Analysis of the waveprop1 sound-source terms can be used to rapidly indicate regions of significant sound generation. The figure on the right illustrates these regions in the wake and on a cut-plane raised slightly above the ground.	Visualization of noise source strength in symmetry plane and a near-ground plane.
	More accurate solutions can be obtained using the Non-Linear Acoustics Solver (NLAS), which is based on the solution of perturbation equations. This simulation can be carried out on a separate acoustics mesh and does not involve the cost of additional transport equations (as with LES or hybrid RANS/LES). Results on the right compare SPL predictions with a traditional hybrid RANS/LES method against the NLAS acoustics solver. These spectra, and the vorticity isosurface plots below, show the improved high-frequency detail obtained with the non-linear acoustics solver, even on relatively coarse meshes. (Note that both methods used the same mesh and time-step.) NLAS simulation. Hybrid RANS/LES.	Sound pressure levels computed using NLAS. Sound pressure levels computed using traditional hybrid RANS/LES. (Note the early tail-off in power at higher frequencies because of the coarse mesh resolution.)