 | Herr M. Trailing-edge noise - reduction concepts and scaling laws: Diss. … Dr.-Ing. / Deutsches Zentrum für Luft- und Raumfahrt, Institut für Aerodynamik und Strömungstechnik, Braunschweig. - Köln: DLR, 2013. - xxii, 192 p.: ill. - (Forschungsbericht; 2013-32). - Res. also Germ. - Bibliogr.: p.177-192. - ISSN 1434-8454
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Nomenclature ................................................. xvii
1 Introduction ................................................. 1
1.1 Motivation and Background ............................... 1
1.2 State of the Art ........................................ 4
1.3 Scope and Research Objectives ........................... 9
1.4 Outline ................................................ 11
2 Fundamentals of Trailing-Edge Noise Prediction and
Reduction ................................................... 13
2.1 Turbulent Boundary-Layer Trailing-Edge Noise ........... 13
2.1.1 Theoretical Model Approaches .................... 13
2.1.2 Semi-Empirical Model Approaches ................. 19
2.1.3 Numerical Model Approaches and their Interplay
with Experiments ................................ 23
2.2 Blunt Trailing-Edge Noise .............................. 24
2.2.1 Semi-Empirical Model Approaches ................. 25
2.3 Edge Noise Reduction Concepts .......................... 26
2.3.1 Serrated Edges .................................. 27
2.3.2 Perforated or Porous Edges ...................... 31
2.3.3 Brush/Comb-Type or Slotted Edges ................ 35
3 Experimental Setup .......................................... 39
3.1 Test Airfoils .......................................... 39
3.2 Test Parameters ........................................ 41
3.3 Measurement Techniques and Data Reduction .............. 44
3.3.1 Hot-Wire Probe Measurements ..................... 45
3.3.2 Surface Pressure Transducer Measurements ........ 51
3.3.3 Directional Microphone Measurements ............. 59
3.4 Test Conditions ........................................ 72
3.4.1 Flow Quality .................................... 72
3.4.2 Two-Dimensionality Assumption ................... 73
3.4.3 Wind-Tunnel Corrections ......................... 74
4 Results and Discussion ...................................... 77
4.1 Solid Trailing-Edge Configurations (at Zero Lift) ...... 77
4.1.1 Turbulent Boundary-Layer Characteristics ........ 77
4.1.2 Unsteady Surface Pressure Data .................. 82
4.1.3 Farfield Sound Pressure Measurement Results ..... 92
4.2 Comb-Type / Slotted Trailing-Edges (at Zero Lift) ..... 114
4.2.1 Achieved Noise Reduction Potential ............. 114
4.2.2 Effect of Incident Flow Parameters ............. 121
4.2.3 Effect of Trailing-Edge Design Parameters ...... 126
4.3 Effect of Angle of Attack on Noise Emission ........... 135
5 Conclusions and Outlook .................................... 143
5.1 General Noise Reference Characteristics ............... 144
5.2 Effect of Comb-Type / Slotted Trailing-Edges .......... 146
5.3 Suggestions for Future Work ........................... 152
A Appendix ................................................... 155
A.l Aerodynamic Sound Generation .......................... 155
A.2 Trailing-Edge Noise in the Context of Airframe Noise .. 156
A.2.1 Airframe Noise Prediction - Historical
Overview ....................................... 156
A.2.2 Airframe Noise Sources Related to Trailing-
Edge Noise ..................................... 157
A.3 Experimental Setup .................................... 162
A.3.1 Airfoil Coordinates ............................ 162
A.3.2 Manufacturing of the Flow-Permeable Trailing-
Edge Modifications ............................. 164
A.3.3 Prediction of the Surface Pressure Spectrum
at the Trailing Edge ........................... 166
A.3.4 High-Frequency Correction of Measured Power
Spectral Densities ............................. 167
A.4 Measurement Data ...................................... 169
A.4.1 Turbulent Boundary-Layer Characteristics ....... 169
A.4.2 Comparison of Measurement Data with
Predictions .................................... 170
A.4.3 Directional Microphone Source Maps ............. 171
A.4.4 Comparisons with CAA Prediction Results ........ 173
Acknowledgments ............................................... 175
Bibliography .................................................. 176
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