Bluff body noise control

Abstract

The present invention provides a method of and apparatus for, reducing noise caused by the interaction of airflow between two bluff bodies which are in a generally tandem arrangement, the method comprising providing flow control such that the peak turbulence is at least partially displaced from, or reduced at, the surface of the downstream body. The invention also provides an aircraft noise reduction device, and a method of using such a device, comprising a flow control apparatus ( 2 ) arranged to be positioned downstream of a flow-facing element ( 1 ), wherein the flow control apparatus is arranged, in use, to reduce noise induced by unsteady flow downstream of the flow-facing element, and wherein the flow control apparatus ( 2 ) is arranged to be moveable in relation to the flow-facing element ( 1 ) between a stowed position and a deployed position.

1 . A method of reducing noise caused by the interaction of airflow between two bluff bodies which are in a generally tandem arrangement, the method comprising providing flow control such that the peak turbulence is at least partially displaced from, or reduced at, the surface of the downstream body. 
     
     
         2 . A method of reducing noise as claimed in  claim 1 , wherein the flow control is provided by a flow control device on the upstream or downstream body. 
     
     
         3 . A method of reducing noise as claimed in  claim 1 , wherein the flow control comprises the use of blowing. 
     
     
         4 . A method of reducing noise as claimed in  claim 3 , wherein the flow control device is arranged to provide distributed blowing through the surface of one of the bodies. 
     
     
         5 . A method of reducing noise as claimed in  claim 3 , wherein the blowing is applied to both sides of the body from 60 degrees to 150 degrees as measured from the leading-edge of the body. 
     
     
         6 . A method of reducing noise as claimed in  claim 4 , wherein the flow control device comprises a series of plenum chambers distributed around one of the bluff bodies. 
     
     
         7 . A method of reducing noise as claimed in  claim 6 , wherein the plenum chambers are covered by an air-permeable plate. 
     
     
         8 . A noise reduction apparatus for use on a bluff body which, in use, is arranged in a generally tandem arrangement with a further bluff body, the apparatus comprising a flow control device arranged such that the peak turbulence is at least partially displaced from, or reduced at, the surface of the downstream body. 
     
     
         9 . An aircraft noise reduction device comprising a flow control apparatus arranged to be positioned downstream of a flow-facing element, wherein the flow control apparatus is arranged, in use, to reduce noise induced by unsteady flow downstream of the flow-facing element, and wherein the flow control apparatus is arranged to be moveable in relation to the flow-facing element between a stowed position and a deployed position. 
     
     
         10 . An aircraft noise reduction device as claimed in  claim 9 , wherein the flow control apparatus comprises a splitter plate arranged to extend downstream of the flow-facing element when in the deployed position. 
     
     
         11 . An aircraft noise reduction device as claimed in  claim 10 , wherein, when in the deployed position, the splitter plate is substantially aligned with the free stream airflow. 
     
     
         12 . An aircraft noise reduction device as claimed in  claim 10 , wherein, when in the stowed position, the splitter plate is orientated to at least partly align with the flow-facing element. 
     
     
         13 . An aircraft noise reduction device as claimed in  claim 9 , wherein the flow control apparatus is made from a flexible material such that the flow control apparatus is deformable between the stowed and deployed positions. 
     
     
         14 . An aircraft noise reduction device as claimed in  claim 13 , wherein the flow control apparatus is made from a resiliently flexible material such that the flow control apparatus naturally assumes the deployed position. 
     
     
         15 . An aircraft noise reduction device as claimed in  claim 9 , wherein the flow control apparatus is made from rubber. 
     
     
         16 . An aircraft noise reduction device as claimed in  claim 9 , wherein the flow control apparatus comprises brushes with resiliently deformable bristles. 
     
     
         17 . An aircraft noise reduction device as claimed in  claim 9 , wherein the flow control apparatus is arranged to be automatically moved between the stowed and deployed positions when the flow-facing element is moved from its stowed and deployed positions. 
     
     
         18 . An aircraft noise reduction device as claimed in  claim 9 , wherein the flow-facing element comprises an aircraft structural element. 
     
     
         19 . An aircraft noise reduction device as claimed in  claim 18  wherein the structural element comprises a component of an aircraft landing gear. 
     
     
         20 . An aircraft noise reduction device as claimed in  claim 19 , wherein the flow control apparatus is arranged to be automatically moved between the stowed and deployed positions by a force applied by an element of the landing gear when the landing gear is moved from its stowed and deployed positions. 
     
     
         21 . An aircraft landing gear comprising a noise reduction apparatus as claimed in  claim 8  or an aircraft noise reduction device. 
     
     
         22 . An aircraft comprising a noise reduction apparatus as claimed in  claim 8 . 
     
     
         23 . A method of reducing noise caused by landing gear on an aircraft including the steps of identifying a part of the landing gear that contributes to the noise generated by the landing gear when in flight, and providing a noise reduction apparatus as claimed in  claim 8 .