Auxiliary power unit intake duct with aero-acoustic guide vanes

1. An auxiliary power unit intake duct with aero-acoustic guide vanes for an aircraft, the intake duct comprising

an internal straight portion, an internal first bend portion and an internal second bend portion, said internal portions extending between a duct air inlet and a plenum entry of the auxiliary power unit, the second bend having a first side wall having a first side wall curvature and a second side wall having a second side wall curvature, the second side wall being shorter than the first side wall, the first bend portion extending between the straight portion and the second bend portion, said second bend portion having a bend curvature; and

wherein the intake duct further comprises

a plurality of acoustic guides vanes located in said straight portion of the intake duct, said acoustic guide vanes extending horizontally between opposite side portions of said straight portion; and

a plurality of curved aerodynamic guide vanes located in said second bend portion proximate to said plenum inlet, said curved aerodynamic guide vanes extending vertically between a top portion and a bottom portion of said second bend portion; each of said curved aerodynamic guide vanes being concentric with said bend curvature of said second bend portion.

2. An auxiliary power unit intake duct according to claim 1 , wherein said plurality of acoustic guide vanes comprise an upper acoustic guide vane and a lower acoustic guide vane being positioned such that the straight portion is horizontally divided into flow paths.

3. An auxiliary power unit intake duct according to claim 2 , wherein the first bend portion of the intake duct bends downwards, and the upper acoustic guide vane is longer than the lower acoustic guide vane and extends into the first bend portion.

4. An auxiliary power unit intake duct according to claim 2 , wherein the intake duct has a substantially quadrangular horizontal cross section.

5. An auxiliary power unit intake duct according to claim 3 , wherein the intake duct has a substantially quadrangular horizontal cross section.

6. An auxiliary power unit intake duct according to claim 1 , wherein the first bend portion of the intake duet bends downwards and the lower acoustic guide vane is shorter than the upper guide vane and extends into the first bend portion.

7. An auxiliary power unit intake duct according to claim 6 , wherein the intake duct has a substantially quadrangular horizontal cross section.

8. An auxiliary power unit intake duct according to claim 1 , wherein the plurality of curved aerodynamic guide vanes comprise

a curved first aerodynamic guide vane located in a radial position R 1 in the middle between at least a first external radius (Rext) given by the first side wall curvature of said second bend portion and at least a first internal radius (Rint) given by the second side wall curvature of said second bend portion, and

a curved second aerodynamic guide vane located in a radial position R 2 in the middle between said first aerodynamic guide vane and said second sidewall.

9. An auxiliary power unit intake duct according to claim 8 , wherein

the first side wall curvature is comprised of a plurality of differing first arched sections (a 1 a ; a 1 b );

the first aerodynamic guide vane is comprised of a plurality of curved sections being equal in number to said first arched sections;

said curved sections are located in radial positions in the middle between a plurality of external radius' (Rext,Rext′) given each by one of said first arched sections of the first side wall curvature of said second bend portion and at least said first internal radius (Rint) given by said second side wall curvature of said second bend portion.

10. An auxiliary power unit intake duct according to claim 9 , wherein the second aerodynamic guide vane is shorter than the first aerodynamic guide vane.

11. An auxiliary power unit intake duct according to claim 9 , wherein the intake duct has a substantially quadrangular horizontal cross section.

12. An auxiliary power unit intake duct according to claim 8 , wherein

a first curved section of the first aerodynamic guide vane is located in a radial position R 1 in the middle between the first external radius (Rext) given by a first arched section of the first side wall curvature, and a first internal radius (Rint) given by a first arched section of the second side wall curvature of said second bend portion, and

a second curved section of the curved first aerodynamic guide vane is located in a radial position R 1 ′ in the middle between a second external radius (Rext′) given by a second arched section of the first side wall curvature and a second internal radius (Rint′) given by a second arched section of the second side wall curvature.

13. An auxiliary power unit intake duct according to claim 12 , wherein the second aerodynamic guide vane is shorter than the first aerodynamic guide vane.

14. An auxiliary power unit intake duct according to claim 12 , wherein the intake duct has a substantially quadrangular horizontal cross section.

15. An auxiliary power unit intake duct according to claim 8 , wherein

a first curved section of the second aerodynamic guide vane is located in a radial position R 2 in the middle between the first guide vane radius (R 1 ) given by a first arched section of the first side wall curvature, and a first internal radius (Rint) given by a first arched section of the second side wall curvature of said second bend portion, and

a second curved section of the curved second aerodynamic guide vane is located in a radial position R 2 ′ in the middle between the first guide vane radius (R 1 ′)given by a second arched section of the first side wall curvature and a second internal radius (Rint′) given by a second arched section of the second side wall curvature.

16. An auxiliary power unit intake duct according to claim 15 , wherein the in take duct has a substantially quadrangular horizontal cross section.

17. An auxiliary power unit intake duct according to claim 8 , wherein the second aerodynamic guide vane is shorter than the first aerodynamic guide vane.

18. An auxiliary power unit intake duct according to claim 17 , wherein the intake duct has a substantially quadrangular horizontal cross section.

19. An auxiliary power unit intake duct according to claim 8 , wherein the intake duct has a substantially quadrangular horizontal cross section.

20. An auxiliary power unit intake duct according to claim 1 , wherein the intake duct has a substantially quadrangular horizontal cross section.