1 Introduction ................................................ 21
1.1 Objectives ............................................. 21
1.2 Challenges ............................................. 22
1.3 The analytical approach ................................ 22
1.4 State of the art on prediction models .................. 23
1.5 New prediction tool: PropNoise ......................... 25
2 Steady aerodynamics ......................................... 27
2.1 Motivation and approach ................................ 27
2.2 Definition of parameters and assumptions ............... 27
2.3 Relation between pressure rise, flow turning and lift .. 31
2.4 Definition of design and off-design conditions ......... 32
2.5 Distribution of flow velocities around the blades ...... 33
2.6 Losses ................................................. 33
2.6.1 Relation between loss, drag and entropy
production ...................................... 33
2.6.2 Blade loading, diffusion factor and stall ....... 34
2.6.3 Loss caused by boundary layers .................. 35
2.6.4 Loss caused by shocks ........................... 37
2.6.5 Endwall loss .................................... 37
2.7 Fan performance ........................................ 38
2.8 Application of the models .............................. 40
2.8.1 Cascade performance ............................. 42
2.8.2 Fan performance at off-design conditions ........ 43
2.9 Conclusion ............................................. 45
3 Engine and fan aerodynamic design ........................... 47
3.1 Motivation and approach ................................ 47
3.2 Design constraints ..................................... 47
3.3 Preliminary engine design .............................. 50
3.3.1 Methodology ..................................... 50
3.3.2 Engine thrust ................................... 50
3.3.3 Engine airflow and fan diameter ................. 51
3.3.4 Engine length and nacelle dimensions ............ 52
3.3.5 Engine weight ................................... 53
3.3.6 Engine drag ..................................... 53
3.4 Fan design ............................................. 54
3.4.1 Principles ...................................... 54
3.4.2 Exemplary results ............................... 56
3.5 Engine performance ..................................... 59
3.6 Off-design operating points ............................ 61
3.7 Validation at design conditions ........................ 62
3.8 Conclusion ............................................. 64
4 Unsteady aerodynamics ....................................... 65
4.1 Introduction ........................................... 65
4.2 Potential field ........................................ 65
4.2.1 Initial strength of the potential field ......... 65
4.2.2 Circumferential distribution and modes .......... 66
4.2.3 Decay of the potential field .................... 67
4.3 Mean-flow wakes ........................................ 67
4.3.1 Wake model ...................................... 68
4.3.2 Spectral content ................................ 69
4.3.3 Wake decay ...................................... 69
4.4 Turbulence ............................................. 73
4.4.1 Inflow turbulence ingested by the fan ........... 73
4.4.2 Wall-pressure fluctuations ...................... 74
4.5 Change of reference frame .............................. 75
4.6 Airfoil response function .............................. 76
5 Extrapolation of meanline data .............................. 79
5.1 Need for a radial extrapolation ........................ 79
5.2 Steady flow velocities ................................. 79
5.3 Blade geometry ......................................... 79
5.4 Lift, drag and unsteady flow velocities ................ 80
6 Acoustics ................................................... 81
6.1 Modelling approach ..................................... 81
6.2 Assumptions ............................................ 83
6.3 Noise propagation ...................................... 84
6.3.1 The convective and flyover problems ............. 84
6.3.2 Dispersion relation ............................. 85
6.3.3 Sound propagation ............................... 86
6.3.4 Overall sound power ............................. 88
6.4 Extension to propagation with rotating flow ............ 90
6.5 Noise generated by rotating blades ..................... 92
6.5.1 Derivation of the modal pressure ................ 92
6.5.2 Application to the free-field and in-duct
problems ........................................ 98
6.5.3 Tonal noise .................................... 100
6.5.4 Broadband noise ................................ 101
6.5.5 Summary ........................................ 105
6.6 Interpretation of the results ......................... 106
6.6.1 Classification of sources ...................... 106
6.6.2 Modelling of the sources ....................... 107
6.6.3 Generalized cut-on criterion for efficient
radiation ...................................... 112
6.6.4 Effect of source non-compactness ............... 114
6.6.5 Application to a single propeller: effect of
rotation speed and blade count ................. 117
6.7 Validation of the acoustic models ..................... 120
6.8 Jet noise ............................................. 122
6.9 Concluding remarks .................................... 122
7 Application of the models .................................. 125
7.1 Introduction .......................................... 125
7.2 Assumptions done for the parametric studies ........... 125
7.2.1 Aerodynamic and design assumptions ............. 125
7.2.2 Noise-relevant design assumptions .............. 126
7.3 First parametric study: acoustic impact of the fan
pressure ratio ........................................ 128
7.4 Second parametric study: acoustic impact of the
design rotor speed at constant fan pressure ratio ..... 134
7.5 Conclusions about the parameter studies ............... 139
8 Conclusions and outlook .................................... 141
8.1 Feasibility of acoustic pre-design by analytical
methods ............................................... 141
8.2 Main conclusions on the model predictions ............. 141
8.2.1 Comparison of the fan concepts ................. 142
8.2.2 Choice of the design fan pressure ratio and
fan loading .................................... 143
8.3 Prediction capability of the models ................... 145
8.4 Further extensions of the method and outlook .......... 148
8.5 Afterwords ............................................ 148
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