Angular measurement of acoustic reflection coefficient for substrate materials and layered structures by V(z) technique

1997 ◽  
Vol 30 (2) ◽  
pp. 75-83 ◽  
Author(s):  
W-J. Xü ◽  
M. Ourak
Keyword(s):  
Reflection Coefficient ◽  
Layered Structures ◽  
Angular Measurement ◽  
Acoustic Reflection

Experimental Investigation of the Acoustic Reflection Coefficient of a Modeled Gas Turbine Impingement Cooling Section

2012 ◽  
Author(s):  
Christoph Jörg ◽  
Michael Wagner ◽  
Thomas Sattelmayer
Keyword(s):  
Reflection Coefficient ◽  
Flow Velocity ◽  
Gas Turbines ◽  
Acoustic Energy ◽  
Quality Data ◽  
Mean Flow ◽  
Impingement Cooling ◽  
Acoustic Reflection ◽  
The Mean ◽  
Mean Flow Velocity

The thermoacoustic stability of gas turbines depends on a balance of acoustic energy inside the engine. While the flames produce acoustic energy, other areas like the impingement cooling system contribute to damping. In this paper, we investigate the damping potential of an annular impingement sleeve geometry embedded into a realistic environment. A cold flow test rig was designed to represent real engine conditions in terms of geometry, and flow situation. High quality data was delivered by six piezoelectric dynamic pressure sensors. Experiments were carried out for different mean flow velocities through the cooling holes. The acoustic reflection coefficient of the impingement sleeve was evaluated at a downstream reference location. Further parameters investigated were the number of cooling holes, and the geometry of the chamber surrounding the impingement sleeve. Experimental results show that the determining parameter for the reflection coefficient is the mean flow velocity through the impingement holes. An increase of the mean flow velocity leads to significantly increased damping, and to low values of the reflection coefficient.

Effects of the Wave Front on the Acoustic Reflection coefficient

2016 ◽  
Vol 102 (4) ◽  
pp. 675-687 ◽  
Author(s):  
R. Dragonetti ◽  
R. Opdam ◽  
M. Napolitano ◽  
R. Romano ◽  
M. Vorländer
Keyword(s):  
Reflection Coefficient ◽  
Wave Front ◽  
Acoustic Reflection

Passive Control of the Inlet Acoustic Boundary of a Swirled Turbulent Burner

2008 ◽  
Author(s):  
Nicolas Tran ◽  
S. Ducruix ◽  
T. Schuller
Keyword(s):  
Reflection Coefficient ◽  
Passive Control ◽  
Pressure Fluctuations ◽  
Linear Regime ◽  
Acoustic Oscillations ◽  
Small Surface ◽  
Acoustic Damping ◽  
Acoustic Reflection ◽  
Acoustic Liners ◽  
Injection Line

The efficiency of perforated panels inserted in the injection line of a swirled turbulent burner is investigated as a passive control solution for combustion instabilities. Perforated panels backed by a cavity are widely used as acoustic liners, mostly in the hot gas region of combustion chambers to reduce pure tone noise levels. This paper focuses on the implementation of this technology in the injection line of a burner. The system is used to control the inlet acoustic reflection coefficient of the burner to stabilize the combustion. This method is shown to be particularly efficient because high acoustic fluxes issued from the combustion region are concentrated on a small surface area in the injection line. Theoretical results are used to design two types of perforated plates featuring similar acoustic damping properties when submitted to low amplitude pressure fluctuations (linear regime). However it is shown that their behavior largely differs when facing large pressure fluctuations levels (non linear regime) typical of those encountered during self-sustained combustion oscillations. Design criteria are given to control the reflection coefficient of perforated panels submitted to high pressure fluctuations levels and damp thermo-acoustic oscillations. While developed on a laboratory scale swirled combustor, this method is more general and could easily be adapted to practical combustors.

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