NASA Contractor Report 2954 A Method for Calculating Externally Blown Flap Noise Martin R. Fink NASA Contractor Report 2954 A Method for Calculating Externally Blown Flap Noise Martin R. Fink UnitedTechnologies Research Center EastHartford, Connecticzlt Prepared for LewisResearch Center under Contract NAS3-17863 National Aeronautics and Space Administration Scientific and Technical Information Office 1978 I CONTENTS Page DESCRIPTIONOF EBF NOISE PREDICTION METHOD Development ofAnalysis Under ThisContract ........... 3 Assumptions Within UTRC Method Basicconcepts ....................... 7 ullw Slotted Wing ...................... 50 ullw fixer Nozzle ...................... 15 Upper Surface Blowing .................... 15 UTW Slotless Wing ...................... 17 Engine inFront of Wing ................... 17 EVALUATION OF EBF NOISE PIGDICTION METHODS Other EBF Noise Prediction Methods ................. 18 Designated EBF Model Configurations ............... 21 ComparisonsWith Designated u?w Data TripleSlotted Flap. Approach ................ 22 TripleSlotted Flap. Takeoff ................ 24 SlotlessVersion of Three-Flap Wing ............. 25 Comparisons With Designated USB Data QCSEEUSB. Takeoff ..................... 27 QCSEEUSB. Approach ..................... 30 TF-34 Scale Model ...................... 31 USB Vane Deflector ..................... 32 Discussion of Error ....................... 34 Comparisons for Additional EBF Configurations Additional UTW Slotless Wings ................ 36 UTW fixer Nozzle ...................... 39 Engine inFront of Wing ................... 40 Noise Predictions for Full-scale QCSEF: Configurations ZeroForward Speed ..................... 40 Effects of Forward Flight .................. 42 43 RECOMMENDATIONSFOR FUTLTRE RESEARCH .................. 44 i ii Paae TABLE I: EXTERNALLY BLOWN FLAPMODELS FOR COMPARISON OFMEASURED AND PREDICTED NOISE. 5 TABLE 11: CAPABILITIES AND LIMITATIONSOF EBF NOISE PREDICTION METHOD 1.9 TABLE 111: OASPL AND PIG PREDICTION ERROR FOR 90° FLYOVERPOSITION. 35 APPENDIX A: LIST OF SYMBOLS. 49 APPENDIX B: LIST OF PUBLICATIONS PRODUCED. 50 APPENDIX C: COMPUTER PROGRAM FOR CALCULATING EBF NOISE GeneralDescription. 52 InputVariables. , . 54 Test Case. 56 ProgramListing. 57 TestCaseOutput.. ...................... 64 APPENDIX D: NOISE SOURCE LOCATION FOR UPPERSURFACE BLOWING Purpose of Experiment. 68 Apparatus and FYocedure Test Apparatus . 69 Procedure . 70 Presentation and Interpretation of Data Velocity and Turbulence Profiles. 71 CrosscorrelationTraces . 71 Results of Crosscorrelation . 74 iv A METHOD FOR CALCULATING EXTERNALLY BLOWN FLAP XOISE Martin R. Fink UnitedTechnologies Research Centgr SUMMARY A method is described for calculating externally blown flap noise as a sum of severalsimple basic noise components.These components are (1) com- pact lift dipoles associated with the wingand flaps, (2) trailing edge noise associated with the last trailing edge, and (3) quadrupolenoise associated with the undeflected exhaust jet, deflection by a flap surface or nozzlede- flecting surface, and the free jet located downstreamof the trailing edge. These noise components are combined to allow prediction of directivity and spectrafor under-the-wing (UTW) slottedflaps with conventional or mixer nozzles, UlW slotlessflaps, upper-surface-blowing (USB) slotlessflaps, and engine-in-front-of-the-wingslotted flaps. The development of this method as part of a four-yeareffort under this Contract is described. A digital computerprogram listing is given for this calculation method. Directivities and spectra calculated by this method, the current NASA MOP method,and a method developed by Lockheed-Georgia Co. are compared with free-field data for U'IW and USB configurations recently tested by NASA Lewis ResearchCenter. These data had not been part of the data base used in development of thesethree methods. The UTRC method bestpredicted the details of the measured noise emission, but the AXOP method best estimated the noise levels directly below these configurations. 1 INTRODUCTION Noise generated by stationary solid bodies in the presence of the turbulent airflow in fan ducts is ama,jor part of the noise of installed turbofanaircraft engines. For example, acousticallytreated splitters within the engine inlet and exhaustducts can attenuateturbomachinery noise butproduce noise at their edges.Internal struts, necessaryfor structural support of theengine and splitters, are likely to beimmersed inhigh-veloc- ityturbulent engine airflows. Turbofan statorblades are subjected to fluctuating wakes produced by thefan rotor blade. For STOL aircraft, externally blown flaps deflect engine exit airflow in order to generate additional wing lift force at low flightspeeds. In all these cases, a solid surface of finite extent is scrubbed by airflow containing velocity and pressurefluctuations. Thesame basicaeroacoustic mechanisms should be pre- sent for all of these examples. The subject of this report is prediction of noise caused by externally blown flaps.This comprised the major portionof the investigation conducted under thisfour-year contract. Experiments with simple configurations were utilized to develop simple analytical models of several noninteracting noise components. Some components could, in concept, be calculated by rigorous methods. Such a theory would be extremely complex and is notpresently availablefor externally blown flaps.Therefore a semi-empiricalnoise componentmethod for externally blown flap (EBF) noise was developedinstead. This UTRC method canbe applied to under-the-wing slotless or slotted flaps and conventional or mixer nozzles , upper -surface-blowing configurations with uniform exhaust' flow , and engine-in-front-of -the-wing installations. Other prediction methods also exist for some of these types of EBF configurations. All of these methods are described and are evaluated herein bycomparing their predictions with NASA-designated free field data for a rangeof EBF configu- rations. These recentdata had not beenused in developmentof these methods, so thatthe comparison-wouldnot be biased. Crosscorrelation measurements to identify noise source locations are reported in Appendix D herein. A companion final report describes the remainder of the contract effort, devotedtoward the development of a method for predicting and reducing noise radiation fromgas turbine engine struts and. splitters. Editorial review of this Contractor Report was performed at NASA Lewis ResearchCenter and by colleagues within UTRC in order to assure clarity of ideasexpressed. Drafts of this report were also reviewed by persons at NASA Lewis ResearchCenter and at Lockheed-Georgia Co.who havedeveloped competingmethods, in order to assure correct evaluation of their ZBF noise prediction methods. DESCRIPTIOlV OF' Tm UTRC EBF NOISE mDICTfON MET€IOD Development of Analysis Under This Contract Thework conductedunder this Contract was based on an earlier noise componentmethod developed at UTRC and first presentedin reference 1. That method had regardedunder-the-wing (UTW) externaly flown flap (EBF) noise as a sum of threetypes of noise components.Scrubbing noise as described therein was taken to be a lift dipole noise acting on the wingand flap panelsscrubbed by the exhaust jet. The noisegenerating process was taken as that described by Sharland (reference 2) for noise produced by a turbulent boundary layer on an airfoil surface. Such noise was assumed proportional to velocity raised to the sixth power , surface area scrubbed by the jet, and surfacepressure fluctuation squared. Pressure fluctuations on theflap surfaces wereassumed equal to those for the free-jet mixing region, an order of magnitude largerthan those for an attached boundary layer. It was shown that equation (10) of reference 2 predicted lobes of flap-generated lift dipole noise that generally matched the available EBF noise data at low ex- haustvelocities for directions aboveand below theflaps. Another noise component was quadrupole noise generated by deflection of the exhaust jet. This noise contribution was evaluated from the data of reference 3 for a jet deflected by a largeflat surface. Slotted and slotless U'IW configurations were noted to have approximately equal peaks of quadrupole-like noise at shallowangles above and below the deflected jet. Measured deflected jet noise radiation was therefore assumed to apply at both these directions de- spitelack of an explanation for the upward-radiated noise. The sum of these quadrupoie and lift dipole components generally matched the available data except for underprediction of noise measured in the upper forwardquadrant. The onlynoise generating process that is strongest at directions opposite to the deflected flap trailing edge would be trailing edgenoise. This addi- tional noise component therefore had been assumed in order to matchmeasured U'IW directivity shapes in all quadrants. The first fiscal year's workunder this Contract, reported in references 4, 5, and 6, consistedof experiments directed toward evaluating the several available theories for incidence fluctuation noise, trailing edge noise, and scrubbingnoise. Results for incidence fluctuation noise were presented in reference 5. Thatportion of the Contract effort, and additionalContract effort directed to predicting noise generated by struts and splitter rings withinturbofan exit ducts, is summarized in reference 7. The study of trailing edge noise was also presented in reference 5. Those data, and 2/3 of the summary data given byHayden in reference