What is ICAA++?

The ICAA++ suite contains algorithms that allow acoustic simulations to focus on component parts. Acoustic-damping boundary conditions, automatic turbulent eddy-seeding at inlets, specialized acoustic solvers and a unique sub-domain capability allow computational efforts to be focused on the design feature of interest.  ICFD++, like many other commercial CFD solvers, allows for direct prediction of aeroacoustic phenomena using LES or hybrid RANS/LES.  However, such methods are often prohibitively expensive, particularly for near-wall flows, far-field propagation or scattering of high-frequency acoustic waves.  ICAA++ allows you to go beyond these traditional methods with a variety of analytic tools for far field propagation and more efficient, specialized numerical solvers for modeling sound generation.

Accurate simulation of flow-driven acoustics requires detailed resolution of the small, noise-generating turbulent eddies and the full spectrum of transmitted acoustic waves.  ICAA++ provides a suite of tools that simplifies these tasks, greatly reducing the cost in comparison to traditional CFD methods.

ICAA++ enhances ICFD++ noise-prediction capabilities:

• Waveprop tools - fast, analytic wave propagation
• Hybrid RANS/LES – 2nd gen methods with LEST
• NLAS – Non-Linear Acoustics Solver for coarse meshes and/or flows with weak shear instabilities
• Sub-domain and re-interpolation tools to reduce cost
• State of the art far-field propagation/directivity tools
• Advanced signal processing tools

Many CFD Codes Offer Unsteady-Modeling Capabilities, So What Sets ICAA++ Apart?

A Comprehensive Suite of Tools

CAA++ is a comprehensive suite of tools for simulating aeroacoustics problems. Designed to synergistically complement CFD++, CAA++ provides the user with an extended set of analytical and numerical methods to simulate the generation and transmission of sound waves through fluids. Many of the CAA++ methods are designed to operate on a reduced set of data. For example, by exploiting established mean and statistical data on modest meshes covering small sub-domains, NLAS offers a cost-effective noise prediction approach for boundary-layer or weak-shear problems in which hybrid RANS/LES would only give rise to quasi-steady solutions. The CAA++ suite also includes sub-domain extraction, mapping and re-interpolation tools as well as a wide variety of post processing tools.

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.

Tools include

• Acoustic Surface Creation Tools
• Acoustic Re-Interpolator Tools
• Time Domain Volume Source Integration
• Frequency Domain Volume Source Integration
• Surface Source Integration Tool
• Wavepath Integration Tool
• Far Field Directivity Tool
• Surface Data Maps

Publications

• Batten, P., Ribaldone, E., Casella, M., and Chakravarthy, S.R., Towards a Generalized Non-Linear Acoustics Solver, AIAA-2004-3001, 10th AIAA/CEAS Aeroacoustics Conference, Manchester, UK, 10-12 May, 2004.
• Batten, P., Goldberg, U.C., and Chakravarthy, S.R., Interfacing Statistical Turbulence Closures with Large Eddy Simulation, AIAA Journal, 42, 3, March, 2004.
• Batten, P. Goldberg, U.C. and Chakravarthy, S.R., Reconstructed Sub-Grid Methods for Acoustics Predictions at all Reynolds Numbers, AIAA-2002-2511, 8th AIAA/CEAS Aeroacoustics Conference, Breckenridge, CO, 17-19 June", 2002.
• Batten, P. Goldberg, U.C. and Chakravarthy, S.R., Sub-Grid Turbulence Modeling for Unsteady Flow with Acoustic Resonance, AIAA-00-0473, 38th Aerospace Sciences Meeting, Reno, NV, 2000

ICAA++ Verificaion Cases