Acoustic liner use of such a liner and method for manufacturing an acoustic liner

Abstract

The present invention relates to an acoustic liner ( 1 ) arranged to attenuate sound. The acoustic liner ( 1 ) comprises a top sheet ( 5 ) having substantially linear characteristics and a liner core ( 2 ) or cavity. The top sheet ( 5 ) comprises a layer ( 3 ) of a metallic foam. The invention also relates to the use of said acoustic liner in a hot stream environment such as the outlet of an aircraft engine, and to the manufacture of an acoustic liner.

1 . An acoustic liner arranged to attenuate sound, comprising a top sheet having substantially linear characteristics and a liner core or cavity, wherein the top sheet comprises a layer of a metallic foam.  
   
   
       2 . An acoustic liner according to  claim 1 , wherein the top sheet has a non-linearity factor within a range between 1.0 and 3.0.  
   
   
       3 . An acoustic liner according to  claim 2 , wherein the nonlinearity factor is within a range between 1 and 2.5.  
   
   
       4 . An acoustic liner according to  claim 3 , wherein the nonlinearity factor is within a range between 1.5 and 2.0.  
   
   
       5 . An acoustic liner according to  claim 1 , wherein a first surface of said metallic foam layer is attached to one side of said liner core.  
   
   
       6 . An acoustic liner according to  claim 1 , wherein the liner core is a honeycomb core.  
   
   
       7 . A metallic liner according to  claim 1 , wherein the liner core is a core of metallic foam.  
   
   
       8 . An acoustic liner according to  claim 1 , wherein the top sheet further comprises a perforated sheet attached to the metallic foam layer.  
   
   
       9 . An acoustic liner according to  claim 1 , wherein the metallic foam layer is arranged to withstand temperatures above about 400° C.  
   
   
       10 . An acoustic liner according to  claim 9 , wherein the metallic foam layer is arranged to withstand temperatures around 700° C.  
   
   
       11 . An acoustic liner according to  claim 10 , wherein the metallic foam layer comprises a metal or metal alloy including Nickel, Titanium and/or Chromium.  
   
   
       12 . An acoustic liner according to  claim 1 , wherein the metallic foam is at least partly open-porous.  
   
   
       13 . An acoustic liner according to  claim 1 , wherein the top sheet is compressed.  
   
   
       14 . An acoustic liner according to  claim 13 , wherein the top sheet is compressed to a different degree in different areas of the sheet.  
   
   
       15 . An acoustic liner according to  claim 14 , wherein the degree of compression is stepwise increased/decreased over the top sheet.  
   
   
       16 . An acoustic liner according to  claim 14 , wherein the degree of compression is continuously changed over the top sheet.  
   
   
       17 . An acoustic liner according to  claim 1 , wherein the top sheet is designed for attenuating various acoustic environments such as different flight conditions for aircraft engines.  
   
   
       18 . Use of an acoustic liner according to  claim 1  in a hot stream environment.  
   
   
       19 . Use of an acoustic liner according to  claim 18  in a hot area of an aircraft engine.  
   
   
       20 . Method for manufacturing an acoustic liner, comprising the following steps: 
 forming a top sheet including a metallic foam layer and having substantially linear characteristics and brazing said top sheet onto one side of a liner core.    
   
   
       21 . Method according to  claim 20 , wherein a perforated sheet is brazed onto the foam layer in forming the top sheet.  
   
   
       22 . Method according to  claim 20 , wherein the top sheet is formed through applying pressure to selected areas of the top sheet surface.  
   
   
       23 . Method according to  claim 22 , wherein the pressure is applied to a different degree in different areas of the top sheet.  
   
   
       24 . Method according to  claim 23 , wherein the pressure applied over the different areas is stepwise increased/decreased.  
   
   
       25 . Method according to  claim 23 , wherein the pressure applied over the different areas is increased/decreased in a continuous manner.