ICAA++ Technology in Summary
Extensive use of modeling inevitably leads, at some point, to situations that deviate too far from the model calibration range to provide meaningful solutions. Consequently, the usefulness of simplified wave-equation solvers are typically limited to a restricted class of problem. The ICAA++ Non-Linear Acoustics Solver (NLAS) allows for much greater generality, by numerically modeling both acoustic disturbances and some of the larger scale fluctuations.The method is based on the solution of disturbance equations, which describe perturbations around a mean set of data, which is provided (along with relevant statistics) by ICFD++. The ICAA++ solvers, including NLAS, can be used with the same arbitrary geometries and meshes as ICFD++.
NLAS allows important large-scale generation effects to be captured directly on the mesh and provides a means of modeling reflection, refraction and blocking effects caused by the presence of complex surface geometries. NLAS offers a number of interesting capabilities. Calculations can be performed on separate acoustics meshes, which can require less near-wall resolution and a reduced far-field extent, due to specialized boundary-condition treatments. The benefits of this are that the acoustics solver can operate on more isotropic cells (particularly in the near-wall region, where a grid converged RANS solution is already available), resulting in a reduction in the overall number of mesh points from the relaxed near-wall requirements and a suitably truncated outer domain. Truncated outer boundaries in NLAS are assigned self-tuning absorbing layer boundary conditions, with far-field (and damping layer) data provided by the (a priori) RANS solution. This provides a good description of the outer boundaries and minimizes spurious wave reflections back into the simulation domain, even for boundaries located close to the source region of interest.
Compared with direct numerical simulation (DNS), the reduced grid requirements of a traditional LES are rather minimal, particularly in the near-wall region. Hybrid RANS/LES methods can achieve a reduction in mesh size by eliminating the mesh requirements in planes parallel to the wall (the normal-to-wall resolution is still required for the near-wall RANS modeling). NLAS further relaxes these meshing requirements, since a priori RANS statistics are always available, even on coarser regions of the NLAS mesh.