Numerical Investigation of the Entropy Wave Generator Test Case Using Multirate Impedance Boundary Conditions

2015 ◽  
Author(s):  
Jean-Michel Lourier ◽  
Berthold Noll ◽  
Manfred Aigner
Keyword(s):  
Boundary Conditions ◽  
Numerical Investigation ◽  
Test Case ◽  
Impedance Boundary ◽  
Impedance Boundary Conditions ◽  
Wave Generator

Large Eddy Simulation of a Thermoacoustic Instability Within a Swirl-Stabilized Burner Using Impedance Boundary Conditions

2014 ◽  
Author(s):  
Jean-Michel Lourier ◽  
Berthold Noll ◽  
Manfred Aigner
Keyword(s):  
Boundary Conditions ◽  
Feedback Loop ◽  
Numerical Data ◽  
Test Case ◽  
Driving Mechanism ◽  
Impedance Boundary ◽  
Thermoacoustic Instability ◽  
Impedance Boundary Conditions ◽  
Eddy Simulation ◽  
Experimental Findings

A thermoacoustic instability observed within a lean swirl-stabilized burner is analyzed by means of numerical calculations. As extension to previously reported numerical data for the considered test case, the numerical domain is extended to include the fuel plenum and the acoustic outlet impedance is modeled by time domain impedance boundary conditions. The predicted thermoacoustic frequency is in excellent agreement with experimental findings. Furthermore, the thermoacoustic feedback loop is discussed by means of phase resolved data which show that a variation of the equivalence ratio within the swirler is the driving mechanism of the instability. Finally, the Rayleigh criterion is shown to be satisfied within the combustion chamber. Hence, a closed thermoacoustic feedback loop is observed.

scholarly journals Hearing the shape of a compact Riemannian manifold with a finite number of piecewise impedance boundary conditions

1997 ◽  
Vol 20 (2) ◽  
pp. 397-402 ◽  
Author(s):  
E. M. E. Zayed
Keyword(s):  
Riemannian Manifold ◽  
Boundary Conditions ◽  
Finite Number ◽  
Spectral Function ◽  
Compact Riemannian Manifold ◽  
Smooth Boundary ◽  
Beltrami Operator ◽  
Smooth Functions ◽  
Impedance Boundary ◽  
Impedance Boundary Conditions

The spectral functionΘ(t)=∑i=1∞exp(−tλj), where{λj}j=1∞are the eigenvalues of the negative Laplace-Beltrami operator−Δ, is studied for a compact Riemannian manifoldΩof dimension “k” with a smooth boundary∂Ω, where a finite number of piecewise impedance boundary conditions(∂∂ni+γi)u=0on the parts∂Ωi(i=1,…,m)of the boundary∂Ωcan be considered, such that∂Ω=∪i=1m∂Ωi, andγi(i=1,…,m)are assumed to be smooth functions which are not strictly positive.

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