Rotor Noise Modeling Kenneth S. Brentner Penn State University

Transcription

1 Rotor Nose Modelng Kenneth S. Brentner Penn State Unversty Joby Avaton S Kenneth S. Brentner. All rghts reserved. 5 th Transformatve Vertcal Flght Workshop, January 18-19,

2 Outlne of Presentaton Summary of Rotor Nose Sources Rotor Nose Predcton Varous Approaches Key Theory Some Avalable Predcton Tools Smple Propeller Modelng Eample 2018 Kenneth S. Brentner. All rghts reserved. 5 th Transformatve Vertcal Flght Workshop, January 18-19,

3 Rotor Nose Sources Dscrete frequency nose Thckness nose caused by flud dsplacement Loadng nose caused by acceleratng force dstrbuton Includes unsteady loadng, Blade- Vorte-Interacton nose, etc. Hgh-speed mpulsve nose corresponds wth the appearance of shocks and transonc flow Quadrupole nose for propellers Broadband nose Nondetermnstc loadng nose Turbulence ngeston nose Self nose Tralng edge nose Blade-wake-nteracton nose supersonc flow shock turbulent boundary layer 2018 Kenneth S. Brentner. All rghts reserved. 5 th Transformatve Vertcal Flght Workshop, January 18-19,

4 Man Rotor Nose Drectvty Helcopter Eample - Nose also goes above rotor - Doppler amplfcaton results n forward drectvty ncreases wth flght speed - Just one type of unsteady loadng nose - Unsteady loadng nose very mportant for low tp speeds 2018 Kenneth S. Brentner. All rghts reserved. 5 th Transformatve Vertcal Flght Workshop, January 18-19,

5 Drectvty of Loadng Nose Propeller Eample θ = θ = θ = 0 Flght drecton 180 θ = 0 Flght drecton Thckness nose s stll n the plane of the propeller θ = 90 not shown Metzger, NASA CR , Kenneth S. Brentner. All rghts reserved. 5 th Transformatve Vertcal Flght Workshop, January 18-19,

6 Practcal Approaches to Nose Predcton Analyss Smple analyss requres mathematcal and physcal nsght to acheve useful results Probably to smplstc and would requre more valdaton for comple vehcles, multple rotors, etc. Sem-emprcal analyss Can be very useful and smple to use Requres some sort of bass or database Not necessarly vald for new confguratons or operatng regmes Useful eample: R. J. Pegg, A Summary and Evaluaton of Sem-Emprcal Methods for the Predcton of Helcopter Rotor Nose, NASA TM 80200, Computatonal Methods Integral methods Acoustc Analogy Krchhoff Method Drecton computatons 2018 Kenneth S. Brentner. All rghts reserved. 5 th Transformatve Vertcal Flght Workshop, January 18-19,

7 2018 Kenneth S. Brentner. All rghts reserved. 7 5 th Transformatve Vertcal Flght Workshop, January 18-19, 2018 Acoustc analogy: FW-H equaton surface & volume ntegrals requred etenson of Lghthll s acoustc analogy wth surfaces practcal appromaton only surface ntegrals Krchhoff or Permeable Surface FW-H: physcal sources represented by mathematcal sources on surface only surface ntegrals Drect computaton: lmted to relatvely near feld full doman dscretzed provdes nput to other approaches, 2 f F f Q t t p, 2 2 f H T f F f Q t t p j j ~ ~, 2 f F f Q t t p Approaches to Nose Predcton

8 Ffowcs Wllams Hawkngs Equaton Rearrangement of Naver-Stokes equatons nto an nhomogeneous wave equaton 2 p, t t 2 Q f F f T H f j j f = 0 descrbes the ntegraton surface M > 1 Thckness dsplacement of flud generates sound Loadng acceleratng force dstrbuton generates sound ncludes BVI nose Quadrupole All volume sources, non-lnear effects nonunform sound speed 2018 Kenneth S. Brentner. All rghts reserved. 5 th Transformatve Vertcal Flght Workshop, January 18-19,

9 Rotor Nose Theory Farassat s Formulaton 1A of the FW-H equaton 4πp T, t = 4πp L, t = 1 c f=0 + 1 c f=0 ρ 0 v n + v n r 1 M 2 r f=0 lr r 1 M 2 r ret ret ds + ds + l r rm r + cm r M 2 r 2 1 M 3 r f=0 f=0 ρ 0 v n rm r + cm r M 2 l r l M r 2 1 M 2 r ret 2018 Kenneth S. Brentner. All rghts reserved. 5 th Transformatve Vertcal Flght Workshop, January 18-19, ds Needed for nose predcton: Blade moton Blade loadng r 2 1 M 3 r ds ret ds thckness loadng v and M terms have to do wth blade moton velocty and Mach number r s the dstance between observer and source.e., each pont on blade l terms are the loadng on the blade and ther tme dervatves These come from: - Eternal codes - Theory - Appromatons Acoustc results depend on ther accuracy

10 Eamples of Nose Predcton Tools ANOPP Propeller Analyss System PAS-ANOPP Arcraft NOse Predcton Program ANOPP U.S. Release Only PAS avalablty unknown, but people have been usng t lately PSU-WOPWOP Numercal mplementaton of Farassat s Formulaton 1A Not rotor specfc, very general source motons possble Multple rotors, structured and unstructured grds data accepted as nput but must be reformat nto PSU-WOPWOP s bnary nput fle formats Permeable and mpermeable sold surface formulatons Observer parallelsm mplemented n MPI Coupled wth many analyss tools requred for nput but not generally. Ths s a research code. Eecutable verson avalable for Wndows dstrbuted as I have tme Contnuum Dynamcs, Inc. can dstrbute wth CHARM we have set up couplng wth CHARM Kenneth S. Brentner. All rghts reserved. 5 th Transformatve Vertcal Flght Workshop, January 18-19,

11 Quassteady Modelng of Unsteady Loadng XROTOR only computes the loads for steady nflow steady loadng Appromate method for computng unsteady loadng Compute tp speed at each azmuth locaton Run XROTOR wth that tp speed and get the blade loadng Repeat for each azmuth V tp = ΩR + V F sn α sn ψ Blade geometry and operatng condton V F sn α V F ψ XROTOR ΩR V F sn α ψ = 270 ΩR ψ = 180 c l, c d = fr, ψ Interface Unsteady Blade Loadng = fc l,c d, ψ ψ = 0 ΩR ψ = 90 V tp = ΩR + V F snα snψ ΩR + V F sn α PSU-WOPWOP 2018 Kenneth S. Brentner. All rghts reserved. 5 th Transformatve Vertcal Flght Workshop, January 18-19,

12 Impact of Unsteady Loadng on Propeller Nose XROTOR + PSU-WOPWOP steady loadng unsteady loadng α prop = 0 X-Z plane α prop = Kenneth S. Brentner. All rghts reserved. 5 th Transformatve Vertcal Flght Workshop, January 18-19,

13 Nose Dstrbuton of Low Tp Speed Desgns OASPL The peak OASPL n the plane of rotaton ncreases sgnfcantly Thckness nose tends to change more rapdly Wth unsteady loadng, there s a dramatc ncrease n nose along the propeller as X-Z plane Kenneth S. Brentner; Bolor-Erdene Zolbayar; Thomas Jaworsk Aeromechancs Desgn for Transformatve Vertcal Flght, San Francsco, Jan 17,

14 4. Effect of Dfferent Number of Blades M tp = 0.4 Thrust, forward speed, and swept area are held constant As the number of blades ncreases, the nose tends to decrease There are some tradeoffs between 4-bladed and 6-bladed propellers Thckness does not play as bg role as loadng nose X-Z plane Kenneth S. Brentner; Bolor-Erdene Zolbayar; Thomas Jaworsk Aeromechancs Desgn for Transformatve Vertcal Flght, San Francsco, Jan 17,

15 5. Effect of Multple Propellers M tp = 0.4 X-Z plane When α prop = 2, the nose dstrbutons are nearly the same The effect of unsteady loadng s enormous, specfcally at forward and aft drectons The nose dfference gets hgher as the α prop gets hgher Kenneth S. Brentner; Bolor-Erdene Zolbayar; Thomas Jaworsk Aeromechancs Desgn for Transformatve Vertcal Flght, San Francsco, Jan 17,

16 Concludng Remarks Not as much eperence wth low tp-speed rotor nose Importance of nose sources changes: Thckness nose decreases more rapdly than loadng nose Unsteady loadng nose becomes most mportant Predcton tools not valdated as well for ths speed regme Broadband nose could be mportant Sem-emprcal tools for helcopters probably not approprate Vehcle confguratons could promote nflow turbulence Aerodynamc nteractons between rotors and rotors and the arframe could lead to ecess nose Predcton tools are avalable Sgnfcant epertse requred Determnaton of blade loadng key challenge 2018 Kenneth S. Brentner. All rghts reserved. 5 th Transformatve Vertcal Flght Workshop, January 18-19,

17 Questons? 2018 Kenneth S. Brentner. All rghts reserved. 5 th Transformatve Vertcal Flght Workshop, January 18-19,