Stability analysis and design of time-domain acoustic impedance boundary conditions for lined duct with mean flow

2014 ◽  
Vol 136 (5) ◽  
pp. 2441-2452 ◽  
Author(s):  
Xin Liu ◽  
Xun Huang ◽  
Xin Zhang
Keyword(s):  
Stability Analysis ◽  
Boundary Conditions ◽  
Time Domain ◽  
Acoustic Impedance ◽  
Mean Flow ◽  
Impedance Boundary ◽  
Analysis And Design ◽  
Impedance Boundary Conditions

Filter-Based Time-Domain Impedance Boundary Conditions for CFD Applications

2008 ◽  
Author(s):  
Andreas Huber ◽  
Philipp Romann ◽  
Wolfgang Polifke
Keyword(s):  
Boundary Conditions ◽  
Time Domain ◽  
Problem Formulation ◽  
Mean Flow ◽  
Acoustic Boundary Conditions ◽  
Impedance Boundary ◽  
Filter Model ◽  
Impedance Boundary Conditions ◽  
Computational Fluid Dynamics Cfd ◽  
New Formulation

For flow simulations, proper boundary conditions are essential for realizing a well-posed, physically meaningful and numerically stable problem formulation. This is particularly difficult for compressible flow, where in general boundary conditions have to be imposed both for mean flow and acoustic quantities. For the acoustic variables, boundary conditions can be formulated in terms of the acoustic impedance or alternatively the reflection coefficient, which are general a complex-valued, frequency dependent quantity. The present work presents a novel, efficient and flexible approach to impose time-domain impedance boundary conditions (TDIBC) for computational fluid dynamics (CFD): The acoustic boundary conditions are represented as a discrete filter model with appropriately optimized filter coefficients. Using the z-transformation the filter model is transferred to a time-domain formulation and applied to the CFD environment in form of advanced filter realizations. Validation studies using various acoustic boundary conditions have been carried out with the new formulation. The results demonstrate that the method works in an accurate and robust manner.

Control-Oriented Methods for Turbomachinery Noise Simulation

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Alex Siu Hong Lau ◽  
Siyang Zhong ◽  
Xun Huang
Keyword(s):  
Stability Analysis ◽  
Time Domain ◽  
Sound Propagation ◽  
Impedance Boundary Condition ◽  
Generalized Function ◽  
Mean Flow ◽  
Impedance Boundary ◽  
Analysis And Design ◽  
Hopf Method ◽  
The Stability

This paper presents an innovative stability analysis and design approach for time-domain impedance boundary conditions to simulate noise propagation and radiation from a lined turbomachinery duct in the presence of a mean flow. A control-oriented model is developed for the stability analysis of the impedance boundary condition by using generalized function at the lining surface. The mean flow effect and sound propagation are considered in the model as well. Then, the numerical stability issue is analyzed by using the Bode plots before stabilized accordingly by employing the phase lead compensator method, which results in a rational transfer function. Finally, the corresponding time-domain implementation is achieved by using the so-called controllable canonical form rather than an inconvenient convolution operation. The performance of the current proposed approach is first validated in an in-duct propagation case by comparing to analytical solutions obtained by employing the Wiener–Hopf method and then demonstrated in a couple of duct acoustic problems with representative turbomachinery setups. The innovative cross-disciplinary nature of the current proposed approach can shed light on impedance problems and is very useful to time-domain acoustic simulations for turbomachinery applications.

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