AIAA JOURNAL Vol.35.No.3.March 1997 Nozzle Thrust Optimization While Reducing Jet Noise J.M.Seiner* NASA Langley Research Center,Hampton,Virginia 23681-0001 and M.M.Gilinsky' Hampton University,Hampton,Virginia 23668 A Bluebell nozzle design concept is proposed for jet noise reduction with minimal thrust loss or even thrust augmentation.A Bluebell nozzle has a sinusoidal lip-line edge(chevrons)and a sinusoidal cross-section shape with linear amplitude increasing downstream in the divergent nozzle part(corrugations).The ex perimental tests of several Bluebell nozzle designs have shown noise reduction relative to a convergent-divergent round nozzle with design exhaust Mach number M.=1.5.The best design provides an acoustic benefit near 4 dB with about 1%thrust augmentation.For subsonic flow (Me 0.6),the tests indicated that the present method of design for Bluebell nozzles produces increased levels of jet noise.The proposed designs incorporate analytical theory and two-and three-dimensional numerical simulations.Full Navier-Stokes and Euler solvers were utilized.Boundary layer effects were used.Several different designs were accounted for in the Euler applications. Nomenclature Superscripts sonic velocity 0 baseline nozzle friction coefficient 米 boundary layer thickness Cp specific heat at constant pressure =specific heat at constant volume H total enthalpy Introduction h radial direction step size UCCESSFUL design of a nozzle system for supersonic com- h azimuthal direction step size mercial aircraft involves meeting both environmental and eco- 长 specific heat ratio,c/c nomic metrics.For nozzles,the environmental metric is noise,as Lo:Ln lip-line length of baseline and Bluebell nozzles expressedin the FAR 36 Stage III regulations.Economic metrics are M Mach number usually associated with both takeoffand cruise aero-and propulsion NPR nozzle pressure ratio performance,weight,mechanical complexity,and structural relia- ne corrugation frequency bility.These very involved issues are beyond the scope of this paper, np petal frequency but there exist fundamental considerations involving implementa- p pressure tion of both metrics that are the subject of this paper. 9 velocity vector,g(u,v,w) Severalyearsago,it became apparentthat a program was required maximum and minimum radius values that placed more emphasis on scientific methods for the design of temperature nozzles for supersonic commercial applications.Current methods u,V,W velocity components in cylindricalcoordinates heavilyrely on state-of-the-artempirical methods that are supported x,r, cylindricalcoordinates by massive data sets from previous nozzle testing.The process is x,y,2 Cartesian coordinates both cumbersome and expensive.Examples of this can be found in a wedge or cone angle a review article by Seiner and Krejsa.The most successful noz- P shock-wave angle zle designs are based on nozzle geometry that controls the strength corrugation amplitude of shock waves,that can rapidly mix high-and low-speed streams 名 petal amplitude efficiently,and that produce noise spectrally outside the range of n o normalized coordinates the Noy weighting.One discovers very quickly,however,that real p density solutions can be achieved only with a nozzle concept that is still ef- fective at reducing noise at low jet-exhaust velocities,where trades Subscripts with nozzle performanceare historicallydisappointingto date.Sub- sonic jet noise reduction represents a fine example of this point, corrugation start where noise reduction is achieved primarily through an increase of e nozzle exit the engine bypass ratio,which leads to low mixed-flow velocities. n Bluebell nozzle For supersonicaircraft,it is unknown whether an economic solution 0 baseline nozzle exists for high bypass ratio engines. 米 critical cross section One simple,yet realistic,question to pose is what technology exists that can optimize both the aeroacoustic suppression charac- teristics and suppressed mode performance of any given nozzle de- Presented as Paper 95-149at the CEAS/AIAA Aeroacoustics Conference, sign.Suppressed mode performancerefersto the nozzle's efficiency Munich,Germany,June 12-15,1995;received Aug.5,1995;revision re- with acoustic suppression devices deployed in the airflow part.One ceived Dec.6,1996;accepted for publication Dec.10,1996;also published would.in particular,like to know this for nozzles targeted to oper- in AL44Journal on Disc.Volume 2.Number 2.Copyright 97 by the ate with low jet-exhaust velocities.One cannot,of course,directly American Institute of Aeronautics and Astronautics,Inc.Ne-copyright is asserted in the United States under Title 17,U.S.Code.The U.S.Govern- answer this question.We can,however,outline aspects of this tech- ment has a royalty-free license to exercise all rights under the copyright nology.For example,in the lobed mixer of Presz,counter-rotating claimed herein for Govemmental purposes.All other rights are reserved by axial vorticity generated by mixer lobes is used to mix high-speed the copyright owner. engine primary core and fan stream flow with entrained lower speed *Senior Research Scientist.Associate Fellow AlAA secondary flow from an ejector inlet.The enhanced mixing is used Research Professor.Senior Member AlAA. to both increase the level of secondary flow entrainment and mix 420
AIAA JOURNAL Vol. 35, No. 3, March 1997 Nozzle Thrust Optimization While Reducing Jet Noise J. M. Seiner¤ NASA Langley Research Center, Hampton, Virginia 23681-0001 and M. M. Gilinsky² Hampton University, Hampton, Virginia 23668 A Bluebell nozzle design concept is proposed for jet noise reduction with minimal thrust loss or even thrust augmentation. A Bluebell nozzle has a sinusoidal lip-line edge (chevrons) and a sinusoidal cross-section shape with linear amplitude increasing downstream in the divergent nozzle part (corrugations). The experimental tests of several Bluebell nozzle designs have shown noise reduction relative to a convergent±divergent round nozzle with design exhaust Mach number Me = 1.5. The best design provides an acoustic bene®t near 4 dB with about 1% thrust augmentation. For subsonic ¯ ow (Me = 0.6), the tests indicated that the present method of design for Bluebell nozzles produces increased levels of jet noise. The proposed designs incorporate analytical theory and two- and three-dimensional numerical simulations. Full Navier±Stokes and Euler solvers were utilized. Boundary layer effects were used. Several different designs were accounted for in the Euler applications. Nomenclature c = sonic velocity c f = friction coef®cient c p = speci®c heat at constant pressure cv = speci®c heat at constant volume H0 = total enthalpy hr = radial direction step size h} = azimuthal direction step size k = speci®c heat ratio, c p/ cv L0, Ln = lip-line length of baseline and Bluebell nozzles M = Mach number NPR = nozzle pressure ratio nc = corrugation frequency n p = petal frequency p = pressure q = velocity vector, q(u, v, w) r+ , r¡ = maximum and minimum radius values T = temperature u, v, w = velocity componentsin cylindrical coordinates x, r, } = cylindrical coordinates x, y, z = Cartesian coordinates a = wedge or cone angle b = shock-wave angle d = corrugation amplitude e = petal amplitude n, g, } = normalized coordinates q = density Subscripts c = corrugation start e = nozzle exit n = Bluebell nozzle 0 = baseline nozzle ¤ = critical crosssection Presented as Paper 95-149at theCEAS/AIAA AeroacousticsConference, Munich, Germany, June 12±15, 1995; received Aug. 5, 1995; revision re- ceived Dec. 6, 1996; accepted for publication Dec. 10, 1996; also published in AIAA Journal on Disc, Volume 2, Number 2. Copyright°c 1997 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes. All other rights are reserved by the copyright owner. ¤Senior Research Scientist. Associate Fellow AIAA. ²Research Professor. Senior Member AIAA. Superscripts 0 = baseline nozzle ¤ = boundary layer thickness Introduction S UCCESSFUL design of a nozzle system for supersonic com- mercial aircraft involves meeting both environmental and eco- nomic metrics. For nozzles, the environmental metric is noise, as expressedin the FAR 36 Stage IIIregulations.Economicmetrics are usually associatedwith both takeoff and cruise aero- and propulsion performance, weight, mechanical complexity, and structural reliability.These very involvedissues are beyond the scope of this paper, but there exist fundamental considerations involving implementation of both metrics that are the subject of this paper. Severalyearsago, it became apparentthat a programwasrequired that placed more emphasis on scienti®c methods for the design of nozzles for supersonic commercial applications. Current methods heavilyrely on state-of-the-artempiricalmethodsthat are supported by massive data sets from previous nozzle testing. The process is both cumbersome and expensive.Examples of this can be found in a review article by Seiner and Krejsa.1 The most successful noz- zle designs are based on nozzle geometry that controlsthe strength of shock waves, that can rapidly mix high- and low-speed streams ef®ciently, and that produce noise spectrally outside the range of the Noy weighting. One discovers very quickly, however, that real solutions can be achieved only with a nozzle concept that is still effective at reducing noise at low jet-exhaust velocities, where trades with nozzle performanceare historicallydisappointingto date. Subsonic jet noise reduction represents a ®ne example of this point, where noise reduction is achieved primarily through an increase of the engine bypass ratio, which leads to low mixed-¯ ow velocities. Forsupersonicaircraft,it is unknownwhether an economic solution exists for high bypass ratio engines. One simple, yet realistic, question to pose is what technology exists that can optimize both the aeroacoustic suppression characteristics and suppressedmode performance of any given nozzle design. Suppressedmode performancerefersto the nozzle’s ef®ciency with acoustic suppressiondevices deployed in the air¯ ow part. One would, in particular, like to know this for nozzles targeted to operate with low jet-exhaust velocities. One cannot, of course, directly answer this question.We can, however, outline aspects of this technology. For example, in the lobed mixer of Presz,2 counter-rotating axial vorticity generated by mixer lobes is used to mix high-speed engine primary core and fan stream¯ ow with entrainedlowerspeed secondary ¯ ow from an ejector inlet. The enhanced mixing is used to both increase the level of secondary ¯ ow entrainment and mix 420
